This has been one of the most difficult storms to forecast that I can remember. As meteorologists, I think this serves as a reminder that even in this age of advanced technology: powerful computers, advanced radar - the atmospheric system is incredibly complex. Sometimes these kinds of weather patterns are going to occur and there isn't a hell of a lot we can do but make a good guess.
Forecasts are still all over the place but just as I was typing this, the National Weather Service dropped the Winter Storm Warning for the immediate DC area and reduced our snow forecast to around an inch. Further east there's still a chance for more significant snow but the real show will be from Philadelphia northward along I-95 to Boston and beyond. Up in New England they will have the chance for more than a foot.
Here - some light snow I think. Short-term models haven't given up on the idea of some snow falling but it doesn't look like it will amount to much.
What a crazy ride it's been with this storm.
Sunday, December 26, 2010
Saturday, December 25, 2010
Keep an Eye on This One
We're under a Winter Storm Watch and it's likely to be upgraded to a warning once the 12Z guidance comes in. Models still in remarkable disagreement given how close we are to the event. 5 inches seem possible here in DC - maybe more if the storm continues to trend westward - maybe much more if a serious track change happens.
I won't be able to check the modes as regularly today but I'd say it's likely that it will snow tomorrow - at least 4 inches maybe more. Have to keep an eye on that track.
Merry Christmas!
I won't be able to check the modes as regularly today but I'd say it's likely that it will snow tomorrow - at least 4 inches maybe more. Have to keep an eye on that track.
Merry Christmas!
Friday, December 24, 2010
GFS Won't Give Up
I've been reduced to a spectator. I can't remember a case where the models had so much flip-flopping and disagreement this close to an event. There have been plenty of times when the models have all agreed and turned out to have been smoking the same hallucinogenic drug. But this is insane.
Several afternoon models (including some of the near-term models like the RUC - usually disregarded except inside of 40 hours to the event) are leaning towards the GFS solution.
Which looks like this:
That's many things (crazy is one of them) but what it's not is "no snow".
The 0Z runs tonight (which don't come out until like 1:30 AM) are going to be crucial. In any case, I still think this is a Sunday-Monday issue so it shouldn't create any serious disruptions on Christmas Day except for in the South.
Will try and check the models later tonight. Merry Christmas everyone.
Several afternoon models (including some of the near-term models like the RUC - usually disregarded except inside of 40 hours to the event) are leaning towards the GFS solution.
Which looks like this:
That's many things (crazy is one of them) but what it's not is "no snow".
The 0Z runs tonight (which don't come out until like 1:30 AM) are going to be crucial. In any case, I still think this is a Sunday-Monday issue so it shouldn't create any serious disruptions on Christmas Day except for in the South.
Will try and check the models later tonight. Merry Christmas everyone.
12Z Euro Still Out to Sea
So the Euro didn't come around to the GFS solution. With so many models agreeing on an out-to-sea scenario and the GFS now the only true outlier, have to go with consensus right now and stick to the no-major-storm scenario for the mid-Atlantic.
Still watching other models and available information.
Still watching other models and available information.
...right up Until the 12Z GFS. I need an Excedrin.
Yeah, remember that out-to-sea thing I posted about like, what, an hour and a half ago?
The GFS comes out west of its last track making the miss out to sea more of a "brush" and keeping the game alive. This is akin to watching your favorite team down 21 with 7 minutes left in the fourth quarter, turning off the TV because you figure it's over and then having them tie it up with seconds left in the game.
Will the GFS win (i.e. - will the other models also shift towards us?)...I'll see what the afternoon models show.
Here's the 12Z GFS run:
The GFS comes out west of its last track making the miss out to sea more of a "brush" and keeping the game alive. This is akin to watching your favorite team down 21 with 7 minutes left in the fourth quarter, turning off the TV because you figure it's over and then having them tie it up with seconds left in the game.
Will the GFS win (i.e. - will the other models also shift towards us?)...I'll see what the afternoon models show.
Here's the 12Z GFS run:
Models Agree: Out to Sea
Will be watching this closely. The miss is about 100 miles - not more than that. But for now, the threat of a major winter storm for the mid-Atlantic has subsided. There will be snow in the south - maybe from Atlanta through eastern North Carolina which is fun for Christmas. And there's the chance for a major storm for eastern New England. But, it looks like this will miss us in the mid-Atlantic out to sea.
The morning model runs have the suggestion of a change again...but I'm not sure it will be close enough to matter a lot for us.
As the first wave passes, the phase happens too late. Even so, the first wave could give us a bit of light snow Christmas Day afternoon and evening.
I'll be watching the afternoon runs to make sure there are no surprises.
Thursday, December 23, 2010
Models Flip Flopping Again
Quick update this morning: if you like snow, the morning models are not for you. It's still basically the Euro vs. the GFS but the GFS has gone back to its WAY out-to-sea forecast in which only eastern Maine is really affected. The Euro still has the storm but even it is a little further east than in previous runs.
It's not a good idea to latch onto any one of the model runs - good or bad. I'll be looking for some run-to-run consistency before making a call. Hopefully that comes before Saturday.
Right now - some snow is still probable but the megastorm that was in the Euro yesterday seems less likely.
Waiting for the evening runs of the models to see if this eastward shift continues.
It's not a good idea to latch onto any one of the model runs - good or bad. I'll be looking for some run-to-run consistency before making a call. Hopefully that comes before Saturday.
Right now - some snow is still probable but the megastorm that was in the Euro yesterday seems less likely.
Waiting for the evening runs of the models to see if this eastward shift continues.
Wednesday, December 22, 2010
DC, Philly, NYC Would Disappear Beneath the Snow
The 12Z ECMWF forecast model for Monday morning. If this verifies - and that's still a big IF - we're all going to be hoping we received tunneling equipment for Christmas. QPF totals around 1.6 inches with ratios of about 15:1. Ladies and gentlemen, that would be 2 feet of snow - more for Philly and NYC. Hold off the excitement because there's still a LOT of time (4-5 days) for the models to change but if this continues for another 3-4 model runs, we're going to be talking about something fairly serious.
Christmas Storm Update and Teleconnections
Quick update on the Christmas storm (which is really now a Christmas night through Sunday storm) possibility: it's basically the GFS vs the Euro in terms of models. The GFS says "no phase, out to sea, little to no impact". The Euro model says "early phase, storm rides up the coast, stalls and buries the East Coast from northern Georgia to the Northeast in heavy snow totals". Remember that consensus we had earlier this week? Yeah, it's gone.
This is a good time to talk about the other things meteorologists look at to determine the likelihood of major winter storms. First, we'll look at something meteorologists and climatologists call "teleconnections".
The concept of teleconnections is based on the idea that the atmosphere is one large system. Air is essentially a fluid and it's modeled that way in terms of equations and concepts. Since it's a fluid, atmospheric anomalies like low pressure areas and high pressure areas, fronts, storms, etc can be thought of as blocks of styrofoam floating in a pool. If we throw a rock into the pool to create waves, these blocks will move. The movement of the blocks can be measured whether we threw the rock in the middle of all the blocks or somewhere at the other end of the pool. Further, the blocks will interact with each other - some of them will move in opposite directions essentially blocking the movement of others.
The atmosphere is a similar system. Simply put, the study of teleconnections is the study of linkages between weather patterns that occur in widely separated regions of the globe. Let's take a look at two of the teleconnections that most profoundly affect the type of weather we have here in the Mid-Atlantic during the winter.
NAO
NAO stands for "North Atlantic Oscillation" and it refers to the position and strength of two pressure centers in the North Atlantic. One is a low pressure area typically located near Iceland (the "Icelandic Low"). The other is an area of high pressure often located over the Azores in the eastern Atlantic (the "Azores High").
The strength and positioning of these pressure centers affects the alignment of the jet stream - a fast moving current of air - two branches of which control the nature of our weather. It's these branches, by the way, that we look to have phase when we're talking about strong winter storms.
Over time, climatologists and meteorologists have found that specific conditions of NAO cause specific patterns of weather over the globe. We'll concentrate on the eastern U.S. for obvious reasons.
POSITIVE NAO (+NAO)
The positive condition of NAO (shorthand: +NAO) occurs when the Icelandic Low and the Azores High are both stronger-than-normal. The stronger pressure centers cause a stronger pressure gradient (pressure changes more rapidly with distance from either center towards the other center). Pressure gradients cause stronger winds - in this case because the flow around the Icelandic Low (and all low pressure centers in the Northern Hemisphere for that matter) is counterclockwise and the flow around the Azores High (and all high pressure centers in the Northern Hemisphere) is clockwise, the increase in gradient causes an increased westerly wind.
This increase in wind essentially "drains" the cold air from the eastern U.S. into the Atlantic. Therefore, generally, the following is true during +NAO:
NEGATIVE NAO (-NAO)
The negative condition of NAO (shorthand: -NAO) is, sensibly, the opposite of +NAO. A weaker-than-normal Icelandic Low and Azores High results in a weaker pressure gradient which, in turn, induces weaker winds that then allows cold air to build in the eastern U.S. and expand southward. The general trends during -NAO:
We are currently in a rather strong -NAO condition. This is believable given the temperatures around here the last couple of weeks and the increase in snow chances recently. This coming storm will be the third chance for snow in that time period. So we have NAO going for us in this.
Next!
PNA
The Pacific/North American teleconnection pattern is a complicated series of pressure centers over the Pacific Ocean and North America. The positive condition of this teleconnection (+PNA) is characterized by high pressure over Hawaii and the intermountain region of North America and low pressure over the Aleutian Islands and the southeastern United States. One effect of +PNA is to cause low temperatures in the southeastern U.S. Interestingly, +PNA is mostly associated with El Niño and -PNA with La Niña. We're in a pretty significant La Niña right now but the PNA is currently positive. This also works in our favor.
So. These two teleconnections are working in our favor to suggest that the cold air will stick around and cause snow to be most of what falls.
Right now, the big questions are:
The only thing to do right now is to keep watching. Too many parameters have yet to come together for a high-confidence forecast. It's worth noting, though, that the Hydrometeorological Prediction Center - a group whose job is to monitor and forecast these types of storms - totally believes in the European model forecast. I leave you with an excerpt from this morning's discussion (Euro = ECMWF):
...EUROPEAN CENTRE GUIDANCE STAYS THE COURSE ON POWERFUL EAST
COAST STORM DECEMBER 26-27...
WILL STICK WITH THE CONSISTENT ECMWF FOR THE PRELIMINARY FRONTS
AND PRESSURES FOR DAYS 3-7. FOR THREE CONSECUTIVE MODEL
CYCLES...THE DETERMINISTIC ECMWF HAS INDICATED A
MASSIVE...DEEP...SLOW-MOVING CYCLONE HUGGING THE CAROLINA AND MID
ATLANTIC COASTS THE TWO DAYS FOLLOWING CHRISTMAS...
...THE EUROPEAN CENTRE GUIDANCE HAS THE ADVANTAGE IN DEVELOPMENTAL
SYSTEMS WITH ITS HIGH RESOLUTION...AND WITH DYNAMIC...DEVELOPMENTAL
SYSTEMS...THE EUROPEAN GUIDANCE SHOULD HAVE THE EDGE.
THE MOST UNUSUAL...AND THREATENING...ASPECT OF THE ECMWF FORECAST
IS THE RELATIVELY LOW LATITUDE AT WHICH THE STORM MATURES AND
STALLS/LOOPS. MORE TYPICALLY...SYSTEMS WILL CLOSE OFF AND HOVER
OVER THE WATERS SOUTH OF NOVA SCOTIA...AS WITH THE MOST RECENT
CYCLONE STILL AFFECTING DOWNEAST MAINE. THE ECMWF SHOWS THE
UPCOMING CIRCULATION COMING TO A HALT JUST EAST OF THE DELMARVA
PENINSULA...WHICH PUTS THE VERY POPULATED AREAS OF THE EASTERN MID
ATLANTIC...LONG ISLAND...AND SOUTHERN NEW ENGLAND IN A PROLONGED
PERIOD OF HIGH WINDS AND HEAVY PRECIPITATION...MOSTLY SNOW. THE
EXTRAORDINARY NEGATIVE NAO THIS MONTH COULD CERTAINLY SUPPORT SUCH
AN ANOMALY. EVEN BEFORE THE RAPID DEEPENING PHASE OF THE
SYSTEM...AREAS OF THE DEEP SOUTH FROM THE INTERIOR GULF COAST
STATES TO GEORGIA AND THE MOUNTAINS AND PIEDMONT OF THE CAROLINAS
MAY SEE A VERY RARE WHITE CHRISTMAS...AGAIN...CONSISTENT WITH THE
REMARKABLE DISRUPTION AT HIGH LATITUDES.
This is a good time to talk about the other things meteorologists look at to determine the likelihood of major winter storms. First, we'll look at something meteorologists and climatologists call "teleconnections".
The concept of teleconnections is based on the idea that the atmosphere is one large system. Air is essentially a fluid and it's modeled that way in terms of equations and concepts. Since it's a fluid, atmospheric anomalies like low pressure areas and high pressure areas, fronts, storms, etc can be thought of as blocks of styrofoam floating in a pool. If we throw a rock into the pool to create waves, these blocks will move. The movement of the blocks can be measured whether we threw the rock in the middle of all the blocks or somewhere at the other end of the pool. Further, the blocks will interact with each other - some of them will move in opposite directions essentially blocking the movement of others.
The atmosphere is a similar system. Simply put, the study of teleconnections is the study of linkages between weather patterns that occur in widely separated regions of the globe. Let's take a look at two of the teleconnections that most profoundly affect the type of weather we have here in the Mid-Atlantic during the winter.
NAO
NAO stands for "North Atlantic Oscillation" and it refers to the position and strength of two pressure centers in the North Atlantic. One is a low pressure area typically located near Iceland (the "Icelandic Low"). The other is an area of high pressure often located over the Azores in the eastern Atlantic (the "Azores High").
The strength and positioning of these pressure centers affects the alignment of the jet stream - a fast moving current of air - two branches of which control the nature of our weather. It's these branches, by the way, that we look to have phase when we're talking about strong winter storms.
Over time, climatologists and meteorologists have found that specific conditions of NAO cause specific patterns of weather over the globe. We'll concentrate on the eastern U.S. for obvious reasons.
POSITIVE NAO (+NAO)
The positive condition of NAO (shorthand: +NAO) occurs when the Icelandic Low and the Azores High are both stronger-than-normal. The stronger pressure centers cause a stronger pressure gradient (pressure changes more rapidly with distance from either center towards the other center). Pressure gradients cause stronger winds - in this case because the flow around the Icelandic Low (and all low pressure centers in the Northern Hemisphere for that matter) is counterclockwise and the flow around the Azores High (and all high pressure centers in the Northern Hemisphere) is clockwise, the increase in gradient causes an increased westerly wind.
This increase in wind essentially "drains" the cold air from the eastern U.S. into the Atlantic. Therefore, generally, the following is true during +NAO:
- Above-average temperatures in the eastern U.S.
- Higher precipitation (more likely to be rain because of the temperatures)
- Lower likelihood of snowstorms
NEGATIVE NAO (-NAO)
The negative condition of NAO (shorthand: -NAO) is, sensibly, the opposite of +NAO. A weaker-than-normal Icelandic Low and Azores High results in a weaker pressure gradient which, in turn, induces weaker winds that then allows cold air to build in the eastern U.S. and expand southward. The general trends during -NAO:
- Below-average temperatures in the eastern U.S.
- Lower precipitation
- Increased likelihood of snowstorms (essentially: lower precipitation but when it happens, significant winter weather).
We are currently in a rather strong -NAO condition. This is believable given the temperatures around here the last couple of weeks and the increase in snow chances recently. This coming storm will be the third chance for snow in that time period. So we have NAO going for us in this.
Next!
PNA
The Pacific/North American teleconnection pattern is a complicated series of pressure centers over the Pacific Ocean and North America. The positive condition of this teleconnection (+PNA) is characterized by high pressure over Hawaii and the intermountain region of North America and low pressure over the Aleutian Islands and the southeastern United States. One effect of +PNA is to cause low temperatures in the southeastern U.S. Interestingly, +PNA is mostly associated with El Niño and -PNA with La Niña. We're in a pretty significant La Niña right now but the PNA is currently positive. This also works in our favor.
So. These two teleconnections are working in our favor to suggest that the cold air will stick around and cause snow to be most of what falls.
Right now, the big questions are:
- When (or if) phasing will occur. Too early and the storm rides inland up the coast which would pull warmer air off the Atlantic and give us serious mixing issues thereby cutting down snow totals. No model that I've seen is forecasting an early phase. Too late and the storm doesn't intensify and "hook" up the coast until it's either past us to the north or out-to-sea. Some models do have this solution and predict a big snowstorm for the Northeast with lesser impact in the mid-Atlantic. A near-perfect phase happens in the Euro model forecast which shows a storm coming from the northern Gulf of Mexico, across the Southeast and hooking up the coast, quite slowly, dumping serious amounts of snow here and even south of here. The GFS model doesn't think phasing happens at all - the storm remains weak and goes out to sea.
- Once the phasing happens, what is the storm track and speed? Again, the Euro model has predicted a dream storm track and speed for us. Other models have variations on the theme with the GFS being the worst of them: an out-to-sea solution that takes most, if not all, of the snow with it.
The only thing to do right now is to keep watching. Too many parameters have yet to come together for a high-confidence forecast. It's worth noting, though, that the Hydrometeorological Prediction Center - a group whose job is to monitor and forecast these types of storms - totally believes in the European model forecast. I leave you with an excerpt from this morning's discussion (Euro = ECMWF):
...EUROPEAN CENTRE GUIDANCE STAYS THE COURSE ON POWERFUL EAST
COAST STORM DECEMBER 26-27...
WILL STICK WITH THE CONSISTENT ECMWF FOR THE PRELIMINARY FRONTS
AND PRESSURES FOR DAYS 3-7. FOR THREE CONSECUTIVE MODEL
CYCLES...THE DETERMINISTIC ECMWF HAS INDICATED A
MASSIVE...DEEP...SLOW-MOVING CYCLONE HUGGING THE CAROLINA AND MID
ATLANTIC COASTS THE TWO DAYS FOLLOWING CHRISTMAS...
...THE EUROPEAN CENTRE GUIDANCE HAS THE ADVANTAGE IN DEVELOPMENTAL
SYSTEMS WITH ITS HIGH RESOLUTION...AND WITH DYNAMIC...DEVELOPMENTAL
SYSTEMS...THE EUROPEAN GUIDANCE SHOULD HAVE THE EDGE.
THE MOST UNUSUAL...AND THREATENING...ASPECT OF THE ECMWF FORECAST
IS THE RELATIVELY LOW LATITUDE AT WHICH THE STORM MATURES AND
STALLS/LOOPS. MORE TYPICALLY...SYSTEMS WILL CLOSE OFF AND HOVER
OVER THE WATERS SOUTH OF NOVA SCOTIA...AS WITH THE MOST RECENT
CYCLONE STILL AFFECTING DOWNEAST MAINE. THE ECMWF SHOWS THE
UPCOMING CIRCULATION COMING TO A HALT JUST EAST OF THE DELMARVA
PENINSULA...WHICH PUTS THE VERY POPULATED AREAS OF THE EASTERN MID
ATLANTIC...LONG ISLAND...AND SOUTHERN NEW ENGLAND IN A PROLONGED
PERIOD OF HIGH WINDS AND HEAVY PRECIPITATION...MOSTLY SNOW. THE
EXTRAORDINARY NEGATIVE NAO THIS MONTH COULD CERTAINLY SUPPORT SUCH
AN ANOMALY. EVEN BEFORE THE RAPID DEEPENING PHASE OF THE
SYSTEM...AREAS OF THE DEEP SOUTH FROM THE INTERIOR GULF COAST
STATES TO GEORGIA AND THE MOUNTAINS AND PIEDMONT OF THE CAROLINAS
MAY SEE A VERY RARE WHITE CHRISTMAS...AGAIN...CONSISTENT WITH THE
REMARKABLE DISRUPTION AT HIGH LATITUDES.
Tuesday, December 21, 2010
Christmas Storm Still on Track
All of that lovely model agreement that was present a few days ago is gone. The models are back to their bickering with one camp (the GFS and its ensembles) preferring a no-phase, out-to-sea solution for the storm this weekend and the other camp (GGEM, Euro) pointing to a big coastal storm. In fact, the QPF (forecast precipitation amounts) in the Euro model have increased significantly for our area.
Overall, the models are slowing the storm both in onset and duration. This is significant for two reasons: the first is that it's likely any snow wouldn't begin until Christmas evening/night and the second is that a longer duration means greater moisture conveyance from the Atlantic Ocean which means more snow.
With the models divided between two storm track possibilities and even within the factions some in-fighting in regards to intensity and timing - it's far too early to pinpoint things precisely. I don't think I'll feel comfortable making a first call until Thursday.
The National Weather Service has no such luxury and they're sticking to their relatively-high probabilities of snow but they're also taking heed of the timing and have moved everything up about 12-16 hours.
So "stay tuned" is still the rule of this game.
I hope to make a longer post later tonight explaining the things I'm looking at as I try and interpret all of this model data and the potential for a major winter storm on Christmas Day into Sunday.
Overall, the models are slowing the storm both in onset and duration. This is significant for two reasons: the first is that it's likely any snow wouldn't begin until Christmas evening/night and the second is that a longer duration means greater moisture conveyance from the Atlantic Ocean which means more snow.
With the models divided between two storm track possibilities and even within the factions some in-fighting in regards to intensity and timing - it's far too early to pinpoint things precisely. I don't think I'll feel comfortable making a first call until Thursday.
The National Weather Service has no such luxury and they're sticking to their relatively-high probabilities of snow but they're also taking heed of the timing and have moved everything up about 12-16 hours.
So "stay tuned" is still the rule of this game.
I hope to make a longer post later tonight explaining the things I'm looking at as I try and interpret all of this model data and the potential for a major winter storm on Christmas Day into Sunday.
Sunday, December 19, 2010
Some Snow Showers Tuesday, All Eyes on Christmas Eve/Christmas Day
So...the weekend storm formed as forecast but moved out to sea before we could see much more than a few clouds. Not entirely surprising - a few models did call the storm properly back on Thursday but remember that we look for consensus from the models before making a forecast. The consensus just wasn't there until Friday.
Right now, the meteorology world is buzzing about Christmas Eve and Christmas Day. This is the best chance for a true White Christmas (which I'd define as "significant snow" actually falling on Christmas Day) in quite some time. The amazing thing is, in fact, the model consensus this far out. We're some 120 hours away from the forecast start of the storm and this time many of the models are fairly close in their forecast of storm track. It's actually a little unsettling to have this much agreement this far out - each successive run of the models simultaneously increases confidence and leaves you wondering if it can possibly last until the 24th.
But, we'll take it after the craziness of this past week.
For now, here's the GFS forecast total precipitation for Sunday, December 26. This means all precipitation that falls from storms up to and including 12/25.
This shows our area pretty well within the 0.50-1.00 inch zone of liquid precipitation which, when you use the 10-to-1 rule of thumb leads to a forecast of 5-10 inches. Based on the storm track and strength forecasts I've seen, this may be a bit conservative.
BUT.
It's 120 hours before any snow is going to fall. A whole LOT of stuff could happen between now and then. So I'll try to post a daily update as we go through the week. For many of us, it's an exciting event on a major Holiday. For some of us, it's a possible impediment to travel.
Stay tuned. Right now, for reference, the National Weather Service has a 40% chance of snow Friday night and a 50% chance on Christmas Day. Those are pretty high percentages for an event this far away.
Right now, the meteorology world is buzzing about Christmas Eve and Christmas Day. This is the best chance for a true White Christmas (which I'd define as "significant snow" actually falling on Christmas Day) in quite some time. The amazing thing is, in fact, the model consensus this far out. We're some 120 hours away from the forecast start of the storm and this time many of the models are fairly close in their forecast of storm track. It's actually a little unsettling to have this much agreement this far out - each successive run of the models simultaneously increases confidence and leaves you wondering if it can possibly last until the 24th.
But, we'll take it after the craziness of this past week.
For now, here's the GFS forecast total precipitation for Sunday, December 26. This means all precipitation that falls from storms up to and including 12/25.
This shows our area pretty well within the 0.50-1.00 inch zone of liquid precipitation which, when you use the 10-to-1 rule of thumb leads to a forecast of 5-10 inches. Based on the storm track and strength forecasts I've seen, this may be a bit conservative.
BUT.
It's 120 hours before any snow is going to fall. A whole LOT of stuff could happen between now and then. So I'll try to post a daily update as we go through the week. For many of us, it's an exciting event on a major Holiday. For some of us, it's a possible impediment to travel.
Stay tuned. Right now, for reference, the National Weather Service has a 40% chance of snow Friday night and a 50% chance on Christmas Day. Those are pretty high percentages for an event this far away.
Thursday, December 16, 2010
Evening Models Trending Snowier for the Weekend
You can't use the evening model runs alone to make a forecast but they can support a trend. And the trend is snow for the weekend.
Apparently, the National Weather Service is coming around to the idea as well. At 6 PM, they revised the forecast for our area to include a 50% chance of snow for Saturday night and Sunday.
So...game on. I'll be checking out the late-night runs tonight. Still 48 hours or so from the event - plenty of time for things to change for better or worse.
Early call would be: a decent chance of a "significant" winter storm Saturday night into Sunday. Storm track makes all the difference, as usual. Temperatures should easily support snow.
Apparently, the National Weather Service is coming around to the idea as well. At 6 PM, they revised the forecast for our area to include a 50% chance of snow for Saturday night and Sunday.
So...game on. I'll be checking out the late-night runs tonight. Still 48 hours or so from the event - plenty of time for things to change for better or worse.
Early call would be: a decent chance of a "significant" winter storm Saturday night into Sunday. Storm track makes all the difference, as usual. Temperatures should easily support snow.
This is What I Mean
Forecast for the weekend from the National Weather Service:
According to them, there's not enough model agreement to start worrying people about snow. I tend to agree.
But...
From the SAME National Weather Service, the precipitation forecast for Sunday:
Forget the models, even the humans aren't agreeing.
So we wait and watch. The evening models are running now but they're hardly ever used operationally (i.e. in service of an official forecast). Next big model runs late tonight - we'll see how they go.
Just a thought: the above map, if the forecast verifies, would put us well into the 5-inch range for snowfall on Sunday. Not the biblical snow of last year - but respectable all the same.
.SATURDAY...MOSTLY CLOUDY. HIGHS IN THE MID 30S. WEST WINDS AROUND 5 MPH...BECOMING SOUTHWEST AROUND 5 MPH IN THE AFTERNOON. .SATURDAY NIGHT...CLOUDY. LOWS IN THE LOWER 20S. .SUNDAY...PARTLY SUNNY. HIGHS IN THE MID 30S. .SUNDAY NIGHT...PARTLY CLOUDY. LOWS IN THE LOWER 20S.
According to them, there's not enough model agreement to start worrying people about snow. I tend to agree.
But...
From the SAME National Weather Service, the precipitation forecast for Sunday:
Forget the models, even the humans aren't agreeing.
So we wait and watch. The evening models are running now but they're hardly ever used operationally (i.e. in service of an official forecast). Next big model runs late tonight - we'll see how they go.
Just a thought: the above map, if the forecast verifies, would put us well into the 5-inch range for snowfall on Sunday. Not the biblical snow of last year - but respectable all the same.
Snow Falling Now, 1-3 inches, Models All Over the Place for the Weekend
Quick update. Snow has started falling in the DC Metro. If you're not seeing it, it's because you're in an office with no windows. Go outside!
Mostly light snow with occasional moderate bursts has been falling for a couple of hours now. Expect it to continue throughout the afternoon before winding up in the evening - maybe around 6 or 7.
The models still don't know what to do with the weekend storm. I've seen the local National Weather Service forecast add and remove snow chances for Saturday night about 5 times in the last 4 days. Almost all of the models show a low forming near the Gulf, almost all of them show it moving to the Carolinas and then some kind of model kegger breaks out and they all lose their minds. At least two show measurable snow for DC and the trend in the last two model runs is for a storm that is closer to us.
All we can do is watch. More to come when I know it.
Mostly light snow with occasional moderate bursts has been falling for a couple of hours now. Expect it to continue throughout the afternoon before winding up in the evening - maybe around 6 or 7.
The models still don't know what to do with the weekend storm. I've seen the local National Weather Service forecast add and remove snow chances for Saturday night about 5 times in the last 4 days. Almost all of the models show a low forming near the Gulf, almost all of them show it moving to the Carolinas and then some kind of model kegger breaks out and they all lose their minds. At least two show measurable snow for DC and the trend in the last two model runs is for a storm that is closer to us.
All we can do is watch. More to come when I know it.
Wednesday, December 15, 2010
Thursday Snow More Likely, Weekend Snow Less Likely
Quick post just to update the situation. Storm tomorrow (Thursday) looks to track far enough north so that we get some snow from it. 1-2 inches at the most.
The storm this weekend refuses to phase on 2 of the 4 model sets that I usually use. This leads to a solution where the developing low moves off the North Carolina coast and directly out to sea. Little or nothing for us.
Two other models - including the GFS - still have a coastal storm with somewhat more phasing present. Still need more model runs to determine the final story for the weekend.
Stay tuned.
The storm this weekend refuses to phase on 2 of the 4 model sets that I usually use. This leads to a solution where the developing low moves off the North Carolina coast and directly out to sea. Little or nothing for us.
Two other models - including the GFS - still have a coastal storm with somewhat more phasing present. Still need more model runs to determine the final story for the weekend.
Stay tuned.
Monday, December 13, 2010
Two Shots at Snow: Thursday and Late Weekend
Well, it's certainly cold enough to snow but we'll have to wait a bit for any moisture or possible storms to line themselves up. Still, the atmosphere is getting busy and there's plenty of energy to fuel storms that do form. Right now, in addition to some flurries and snow showers on Tuesday that shouldn't amount to much, we have two shots at significant snow in the next 7 days. The first is Thursday the second one is late in the weekend. That second storm is the one to watch closely.
But the storm Thursday could make a difference in the track of that second potential storm this weekend.
So let's talk about Thursday first.
A weak storm is on the models for Thursday moving northeastward from the southern U.S. and sliding just to the south of our area. The models have been fairly consistent with the track of the storm being to our south but a little inconsistent in how they describe the associated precipitation field.
Then the GFS and NAM runs late this afternoon showed a slightly more northern track which placed us in the precipitation area. According to these model, the atmospheric temperatures would be cold enough to support snow and indications are for about 1-2 inches of snowfall.
Still, the other models don't agree. They show accumulating snow for southern Virginia and North Carolina only.
I'm wary of trusting one model run - but here's the GFS:
As you can see, the track of the center is predicted by this run of the GFS to be more like along the VA/NC border instead of through central NC where it had been forecast earlier in the week. It bears watching but will almost certainly be a low-impact storm even if it does take a more northern track. You can see in the map above that over land, the maximum precipitation is between 0.10 and 0.25 inches which if we assume a 10:1 ratio (the rule of thumb) means about 1-2 inches.
Here's the crazy thing though: if you love snow (like I do), you should probably hope this doesn't happen.
I can see all of you snow lovers out there now:
Bear with me. Let's talk about the weekend storm potential first and then we'll come back to this crazy "if you love snow, you may not want it to snow Thursday" idea.
Long-range models have had a fairly large coastal storm for December 18-20 in our area for some time now. Ironic since, if it does happen, it will be right around one year to the day of the first huge snow in 2009. A big storm on the anniversary of the largest one-day December snowfall in Washington, DC history.
Anyway, when you're watching long-range models a few weeks out, here's the most important thing to look for until about a week before the predicted event: is the storm still there with each consecutive model run?
As far as that goes: so far so good.
Now that we're inside of a week away, we also start to look at storm track. Here's where the models are, to use technical terms, all over the damn place.
For now, we'll take the GFS as a fairly reliable long-range model. Here's what is shows for Saturday evening:
A developing storm moving from the northern Gulf of Mexico and across the southeastern US, emerging just off the coast of South Carolina. To the northwest, a solid push of cold air that shows the freezing line to our south. According to the GFS, still some 120 hours away from this forecast time, whatever is falling Saturday night will be snow.
6 hours later the GFS has the storm intensifying rapidly. Snow really gets going especially in central VA which looks to be the "bullseye" for this run of the GFS. Up here in the DC area we have less snow as the storm slides along the North Carolina coast - more eastward than northward.
6 hours more and the low is moving off the coast throwing some precipitation back into our area but the motion of the storm suggests lighter amounts than anything we saw on the 19th of December last year:
The east-northeast motion combined with the absence of any "bombing" or rapid intensification indicates that the GFS is predicting that the jet streams will not phase. I think I wrote about phasing last year but if not: here's a quick description:
Flow patterns in the upper atmosphere occur in sequences of waves. These waves can and do interact with one another sometimes in a way that is destructive, sometimes in a way that amplifies the original wave. When waves combine to form a larger wave, it is called "phasing". In meteorology, especially in the winter, we look for phasing of the northern and southern branches of the jet stream which tends to amplify existing storms. It's a tricky thing with respect to timing and it doesn't happen all that often, relatively speaking.
If the phase doesn't happen, you get a weak storm like the one predicted for Thursday. If it happens too early, a storm like the one above goes too close to the coast and we end up with rain. If it happens too late (like in the model runs above), it goes out to sea before it can get really wound up.
All that said: it's a good model run for us (remember "snow = good"). This far out, details like storm track and phasing are several runs away from being decided. We have the storm on the models still - that's one victory. The storm moves up the coast - that's another.
Now. What's bad about the Thursday storm?
Because of a complicated series of atmospheric interactions that have to do with something called the "Polar Vortex", the probability of an out-to sea solution for the December 19th storm (like the models show above) probably increases the further north the Thursday storm tracks. So if you want the potential for a big storm on Sunday, you want that Thursday storm to be as far to our south as possible.
Lots still to be worked out. We'll be closer to a solution for the Thursday storm tomorrow. I'll be keeping an eye on things!
Wouldn't a monster storm on the anniversary of a monster storm be cool?
Just to jog your memory: 12/19/2009:
But the storm Thursday could make a difference in the track of that second potential storm this weekend.
So let's talk about Thursday first.
A weak storm is on the models for Thursday moving northeastward from the southern U.S. and sliding just to the south of our area. The models have been fairly consistent with the track of the storm being to our south but a little inconsistent in how they describe the associated precipitation field.
Then the GFS and NAM runs late this afternoon showed a slightly more northern track which placed us in the precipitation area. According to these model, the atmospheric temperatures would be cold enough to support snow and indications are for about 1-2 inches of snowfall.
Still, the other models don't agree. They show accumulating snow for southern Virginia and North Carolina only.
I'm wary of trusting one model run - but here's the GFS:
As you can see, the track of the center is predicted by this run of the GFS to be more like along the VA/NC border instead of through central NC where it had been forecast earlier in the week. It bears watching but will almost certainly be a low-impact storm even if it does take a more northern track. You can see in the map above that over land, the maximum precipitation is between 0.10 and 0.25 inches which if we assume a 10:1 ratio (the rule of thumb) means about 1-2 inches.
Here's the crazy thing though: if you love snow (like I do), you should probably hope this doesn't happen.
I can see all of you snow lovers out there now:
 |
| "Crazy fool's done lost his freakin' mind!" |
Bear with me. Let's talk about the weekend storm potential first and then we'll come back to this crazy "if you love snow, you may not want it to snow Thursday" idea.
Long-range models have had a fairly large coastal storm for December 18-20 in our area for some time now. Ironic since, if it does happen, it will be right around one year to the day of the first huge snow in 2009. A big storm on the anniversary of the largest one-day December snowfall in Washington, DC history.
Anyway, when you're watching long-range models a few weeks out, here's the most important thing to look for until about a week before the predicted event: is the storm still there with each consecutive model run?
As far as that goes: so far so good.
Now that we're inside of a week away, we also start to look at storm track. Here's where the models are, to use technical terms, all over the damn place.
For now, we'll take the GFS as a fairly reliable long-range model. Here's what is shows for Saturday evening:
A developing storm moving from the northern Gulf of Mexico and across the southeastern US, emerging just off the coast of South Carolina. To the northwest, a solid push of cold air that shows the freezing line to our south. According to the GFS, still some 120 hours away from this forecast time, whatever is falling Saturday night will be snow.
6 hours later the GFS has the storm intensifying rapidly. Snow really gets going especially in central VA which looks to be the "bullseye" for this run of the GFS. Up here in the DC area we have less snow as the storm slides along the North Carolina coast - more eastward than northward.
6 hours more and the low is moving off the coast throwing some precipitation back into our area but the motion of the storm suggests lighter amounts than anything we saw on the 19th of December last year:
The east-northeast motion combined with the absence of any "bombing" or rapid intensification indicates that the GFS is predicting that the jet streams will not phase. I think I wrote about phasing last year but if not: here's a quick description:
Flow patterns in the upper atmosphere occur in sequences of waves. These waves can and do interact with one another sometimes in a way that is destructive, sometimes in a way that amplifies the original wave. When waves combine to form a larger wave, it is called "phasing". In meteorology, especially in the winter, we look for phasing of the northern and southern branches of the jet stream which tends to amplify existing storms. It's a tricky thing with respect to timing and it doesn't happen all that often, relatively speaking.
If the phase doesn't happen, you get a weak storm like the one predicted for Thursday. If it happens too early, a storm like the one above goes too close to the coast and we end up with rain. If it happens too late (like in the model runs above), it goes out to sea before it can get really wound up.
All that said: it's a good model run for us (remember "snow = good"). This far out, details like storm track and phasing are several runs away from being decided. We have the storm on the models still - that's one victory. The storm moves up the coast - that's another.
Now. What's bad about the Thursday storm?
Because of a complicated series of atmospheric interactions that have to do with something called the "Polar Vortex", the probability of an out-to sea solution for the December 19th storm (like the models show above) probably increases the further north the Thursday storm tracks. So if you want the potential for a big storm on Sunday, you want that Thursday storm to be as far to our south as possible.
Lots still to be worked out. We'll be closer to a solution for the Thursday storm tomorrow. I'll be keeping an eye on things!
Wouldn't a monster storm on the anniversary of a monster storm be cool?
Just to jog your memory: 12/19/2009:
Friday, December 10, 2010
Weekend Storm Likely to be Rain (Primarily) Then VERY Cold Next Week
After some model wavering, it seems a pretty good bet that except for relatively short periods at the beginning and the end, the Saturday-Sunday storm will be primarily rain.
Most of the models show a pretty strong low pressure system moving north from the south central US on Saturday. Clouds will increase rapidly Saturday afternoon but I think the precipitation holds off until evening. The temperatures will be warmer than we've seen, mid-40's, but they'll drop off in the evening - especially when the precipitation starts.
Because of that, I wouldn't be surprised if the precipitation started off as a bit of sleet which would change to rain as the night progressed and the low pressure center to our west draws warm air from the south over us as it moves northward. Temperatures overnight Saturday should stay in the mid-30's because of this storm track which means the second-worst thing winter can bring: cold rain.
Rain continues most of the day Sunday and because of the strength of the cold air behind the storm, I think it probably gets in here quickly enough to change our precipitation over to snow before it ends Sunday evening/night. It will be close but this is some serious cold air and it's going to be rushing in - so any precipitation that's left will change over.
Temperatures on Monday and Tuesday will spend the majority of the day in the 20's with Tuesday being the coldest day of the week, I think. Maybe not out of the 20's at all. By Wednesday we "warm" into the mid-30's.
Next chance for precipitation looks like late next week. Too soon to tell how much cold air is still around and how much moisture that system has.
Updates as I see 'em but for now, count on more rain than anything else from Saturday night through Sunday.
Most of the models show a pretty strong low pressure system moving north from the south central US on Saturday. Clouds will increase rapidly Saturday afternoon but I think the precipitation holds off until evening. The temperatures will be warmer than we've seen, mid-40's, but they'll drop off in the evening - especially when the precipitation starts.
Because of that, I wouldn't be surprised if the precipitation started off as a bit of sleet which would change to rain as the night progressed and the low pressure center to our west draws warm air from the south over us as it moves northward. Temperatures overnight Saturday should stay in the mid-30's because of this storm track which means the second-worst thing winter can bring: cold rain.
Rain continues most of the day Sunday and because of the strength of the cold air behind the storm, I think it probably gets in here quickly enough to change our precipitation over to snow before it ends Sunday evening/night. It will be close but this is some serious cold air and it's going to be rushing in - so any precipitation that's left will change over.
Temperatures on Monday and Tuesday will spend the majority of the day in the 20's with Tuesday being the coldest day of the week, I think. Maybe not out of the 20's at all. By Wednesday we "warm" into the mid-30's.
Next chance for precipitation looks like late next week. Too soon to tell how much cold air is still around and how much moisture that system has.
Updates as I see 'em but for now, count on more rain than anything else from Saturday night through Sunday.
Monday, December 6, 2010
Outlook for Winter 2010 and a Storm (probably rain) on Sunday
Welcome back to the blog! As crazy as it is during the Holidays, I'll try to start posting regularly again. Hopefully there will be something to post about!
Everybody wants to know the same thing: will this be a winter like 2009? Will it even snow? How much?
Those things are difficult to predict and long-range forecasting is really only slightly more accurate than throwing darts at index cards on the wall with snowfall totals and dates. But it is possible to make an educated guess and large-scale climate conditions make it a bit easier.
Almost everyone has heard of El Niño and has heard it blamed for everything from huge storms in the western United States to a string of car thefts in Kansas City. In reality, El Niño is defined as "warmer-than-normal sea surface temperatures in the western Pacific Ocean". This warm water causes a succession of atmospheric responses that affect the weather in the United States.
The exact opposite condition is known as La Niña. The cooler-than-normal sea surface temperatures in the western Pacific Ocean induce a low pressure zone there. Since everything in the atmosphere is interconnected, this unusually low pressure has side effects throughout North and South America.
Currently, there is a moderate La Niña occurring and it's forecast to strengthen a bit (which is an odd turn of phrase since it actually means that sea surface temperatures in the western Pacific will get a little colder) during the months of November-January.
So, what is the typical winter experience for the United States during a La Niña of the strength we're expecting?
In terms of precipitation:
First precipitation:
Green regions labeled "A" indicate above-average precipitation. The gradient lines are percentage probability of occurrence. Orange regions labeled "B" indicate below-average precipitation.
Again, keeping in mind this is an average, this forecast map suggests that more storms will pass to our west than to our east. If you like snow, you want coastal storms that pass offshore or move up the coast. Storms that pass to our west do two things in the winter: they bring rain or they bring ice. Both of those suck.
Now temperature:
Again, look at the trends. Washington isn't quite in the "above normal" 30% area but it's close. Generally, the forecast is for normal to slightly-above normal temperatures. That, in combination with the first map, suggests a winter where snow events are less frequent than last year and where many storms are deflected to the west of us.
This all adds up to the likelihood of a winter with normal to slightly below-normal snowfall in the DC area and temperatures that are normal to just above-normal.
About Sunday. A fairly large storm is expected to develop but most models are following the large-scale trends and suggest that the storm will pass to our west. This will probably lead to a very rainy and cold Sunday. It bears watching. If the track is further to the east, it could get much more interesting.
If this were 2009, I'd be excited about the possibility but, for now, it seems like this one is going to be wet and not frozen.
We'll see how the models trend as the week goes on.
Everybody wants to know the same thing: will this be a winter like 2009? Will it even snow? How much?
Those things are difficult to predict and long-range forecasting is really only slightly more accurate than throwing darts at index cards on the wall with snowfall totals and dates. But it is possible to make an educated guess and large-scale climate conditions make it a bit easier.
Almost everyone has heard of El Niño and has heard it blamed for everything from huge storms in the western United States to a string of car thefts in Kansas City. In reality, El Niño is defined as "warmer-than-normal sea surface temperatures in the western Pacific Ocean". This warm water causes a succession of atmospheric responses that affect the weather in the United States.
The exact opposite condition is known as La Niña. The cooler-than-normal sea surface temperatures in the western Pacific Ocean induce a low pressure zone there. Since everything in the atmosphere is interconnected, this unusually low pressure has side effects throughout North and South America.
Currently, there is a moderate La Niña occurring and it's forecast to strengthen a bit (which is an odd turn of phrase since it actually means that sea surface temperatures in the western Pacific will get a little colder) during the months of November-January.
So, what is the typical winter experience for the United States during a La Niña of the strength we're expecting?
In terms of precipitation:
- Above-average precipitation in the Pacific Northwest and Northern Rockies
- Above-average precipitation in the Ohio Valley
- Below-average precipitation in the south-central and southeastern U.S.
- "Normal" everywhere else
- Below-average temperatures in the coastal sections of the western states
- Above-average temperatures in the central and southern states
- "Normal" everywhere else
First precipitation:
Green regions labeled "A" indicate above-average precipitation. The gradient lines are percentage probability of occurrence. Orange regions labeled "B" indicate below-average precipitation.
Again, keeping in mind this is an average, this forecast map suggests that more storms will pass to our west than to our east. If you like snow, you want coastal storms that pass offshore or move up the coast. Storms that pass to our west do two things in the winter: they bring rain or they bring ice. Both of those suck.
Now temperature:
Again, look at the trends. Washington isn't quite in the "above normal" 30% area but it's close. Generally, the forecast is for normal to slightly-above normal temperatures. That, in combination with the first map, suggests a winter where snow events are less frequent than last year and where many storms are deflected to the west of us.
This all adds up to the likelihood of a winter with normal to slightly below-normal snowfall in the DC area and temperatures that are normal to just above-normal.
About Sunday. A fairly large storm is expected to develop but most models are following the large-scale trends and suggest that the storm will pass to our west. This will probably lead to a very rainy and cold Sunday. It bears watching. If the track is further to the east, it could get much more interesting.
If this were 2009, I'd be excited about the possibility but, for now, it seems like this one is going to be wet and not frozen.
We'll see how the models trend as the week goes on.
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