I hadn't posted because, really, there's not much to get excited about when Snow Chance #1 pretty much slopped for 3 hours and went away.
Friday night's chance looks like that's still a possibility but a few models have a different, more significant idea for Friday night into Saturday.
It's a mess of temperature issues and whether or not the storm can get going off the coast before it moves too far away. If it can do this - and it's still a big "if" - we could have a better chance at accumulating snow here in the DC area.
I'll post again if there's anything to it...
Thursday, February 14, 2013
Monday, February 11, 2013
Review of Big Storm, Three Upcoming Chances for DC
Hopefully all of our friends and family in the northeast - especially Connecticut and Massachusetts - are doing well after the historic storm last week. Truly amazing amounts of snow fell in parts of northern New England.
If you haven't seen this video yet, give it a look. This is a time-lapse video of the snowfall near Hartford, CT.
When you consider NYC even got in on the action at 8-12 inches, why didn't we see any snow here? It sleeted/snowed for about an hour on Thursday night and then rained a bit into Friday morning.
Boring!
Let's have a look at what happened because this has bearing on the upcoming possibilities. To save you from sensationalistic plugs that make you read an entire post before you get what you're looking for, I present a digest:
3 chances in the next 7-10 days:
- Wednesday 2/13
- This coming weekend
- Next Monday-Tuesday or so
Those of you with short attention spans can now go merrily on your - LOOK! SOMETHING SHINY!
Onward...
It's all about storm type and phasing. There were two systems moving eastward in the two main branches of the jet stream. The Northern Stream storm would head on a path across the Upper Midwest and to the north of our area.
Since winds move counterclockwise around a low pressure system, this created a southerly flow around our area that quickly changed frozen precipitation to liquid overnight on Thursday.
This was a Miller B type storm (as they all have been this year) and as the Northern Stream system moved eastward it transferred its energy and phased with the Southern Stream system which had moved out of the southeastern US and up the Atlantic Coast.
Now, storms moving along the coast from the south in the winter is usually a good thing for us. However, with that Northern Branch system moving north of us and the phase happening just to our northeast, we were caught in the middle - in an area between two phasing low pressure systems. This is almost always a zone of minimum precipitation and it's a big problem with Miller B storms that don't phase to our south.
The Southern Stream storm would move from the southeast and then up the coast, phasing with the Northern Stream late in the afternoon on Friday - well to our northeast. The precipitation gradient was extreme with parts of the Eastern Shore seeing heavy rain all day Friday while we in DC saw some sunshine in the afternoon.
Here are the two storms last Thursday morning as they began to phase.
Watch the following animation and see the phase as the southern system absorbs the northern system.
And then off the coast by hour 96 (Thursday morning)
The GFS is in favor of a more northward track:
If you haven't seen this video yet, give it a look. This is a time-lapse video of the snowfall near Hartford, CT.
When you consider NYC even got in on the action at 8-12 inches, why didn't we see any snow here? It sleeted/snowed for about an hour on Thursday night and then rained a bit into Friday morning.
Boring!
Let's have a look at what happened because this has bearing on the upcoming possibilities. To save you from sensationalistic plugs that make you read an entire post before you get what you're looking for, I present a digest:
3 chances in the next 7-10 days:
- Wednesday 2/13
- This coming weekend
- Next Monday-Tuesday or so
Those of you with short attention spans can now go merrily on your - LOOK! SOMETHING SHINY!
Onward...
It's all about storm type and phasing. There were two systems moving eastward in the two main branches of the jet stream. The Northern Stream storm would head on a path across the Upper Midwest and to the north of our area.
Since winds move counterclockwise around a low pressure system, this created a southerly flow around our area that quickly changed frozen precipitation to liquid overnight on Thursday.
This was a Miller B type storm (as they all have been this year) and as the Northern Stream system moved eastward it transferred its energy and phased with the Southern Stream system which had moved out of the southeastern US and up the Atlantic Coast.
Now, storms moving along the coast from the south in the winter is usually a good thing for us. However, with that Northern Branch system moving north of us and the phase happening just to our northeast, we were caught in the middle - in an area between two phasing low pressure systems. This is almost always a zone of minimum precipitation and it's a big problem with Miller B storms that don't phase to our south.
The Southern Stream storm would move from the southeast and then up the coast, phasing with the Northern Stream late in the afternoon on Friday - well to our northeast. The precipitation gradient was extreme with parts of the Eastern Shore seeing heavy rain all day Friday while we in DC saw some sunshine in the afternoon.
Here are the two storms last Thursday morning as they began to phase.
Watch the following animation and see the phase as the southern system absorbs the northern system.
Notice a couple of things here. First, the northern storm starts to weaken (the 1008 mb contour disappears from the center of that storm towards the end) and the storm on the coast significantly intensifies as it moves up the coast (the last few frames show a center contour of 996 mb). Where are we?
Right in the middle.
Ok - congratulations to our friends up north. What about our snow? Let's talk about the first chance.
WEDNESDAY 2/13 - THURSDAY 2/14
The models have been showing a "Valentine's Day Storm" for a while now and it's encouraging that this close to the event, they still have it.
What's discouraging is that they seem to have little consensus about what path its going to take and whether temperatures in our area will be suitable for frozen precipitation.
At the moment, I would classify the event as marginal as we're in one of those situations where a more northern track would produce heavier precipitation but also warmer temperatures (rain) and a southern track would produce lighter precipitation but colder temperatures (snow). In this case (ironically), the best place for us to be would be in the middle of those track solutions.
Here's the Euro at hour 72 (Wednesday night) showing the storm center in the southeastern US:
And then off the coast by hour 96 (Thursday morning)
which, as you can see, would move the higher axis of snow accumulations northward.
This bears watching and until there's a track consensus, anything is possible from warning-criteria snow to a rain event here.
We'll see what the evening model runs hold.
I'll post later about snow chances on the weekend and then a bigger chance early next week.
Thursday, January 24, 2013
Forecast On Track
Not much change in the thinking. A quick-moving storm will produce about 6 hours of snow tomorrow starting in the early afternoon most likely. I expect 1-2 inches but depending on where small-scale bands set up, more is possible in some areas, less as you go north.
The "storm" should be out of here by nightfall.
The weekend will be cold again but temperatures begin to moderate by Monday and we could be near 60 again by Wednesday before the next cold air arrives.
Rain probable next week with an outside chance of snow as the cold air arrives Wednesday night. But the next real chance for snow shows up on the models for the February 2-4 timeframe. Plenty of time to watch that one.
Enjoy whatever snow falls tomorrow. I'll post an update if there's any change.
The "storm" should be out of here by nightfall.
The weekend will be cold again but temperatures begin to moderate by Monday and we could be near 60 again by Wednesday before the next cold air arrives.
Rain probable next week with an outside chance of snow as the cold air arrives Wednesday night. But the next real chance for snow shows up on the models for the February 2-4 timeframe. Plenty of time to watch that one.
Enjoy whatever snow falls tomorrow. I'll post an update if there's any change.
Wednesday, January 23, 2013
NAM "Clown Map" For Friday
Hot off the presses, the "Clown Map" for Friday which shows forecast snowfall amounts. You can see that the forecast from this model is between 1 and 2 inches for the DC metro. The interesting (and somewhat sad, given the last two winters) is that this is actually an improvement over previous NAM runs.
Maybe we're headed in the right direction...
Maybe we're headed in the right direction...
One Shot at Light Snow Tonight, Another on Friday
At the moment, it doesn't look like any major storms are in our near future. The best chance we had of a moderate storm was Friday but at this point, the storm looks like it will be weaker and will not produce all that much precipitation.
Let's look at where we are - first with tonight's event.
A weak "clipper" system is poised to move over our area overnight - probably after midnight and into the hours around dawn. The GFS and the NAM both show this clipper and show a decent amount of energy (for a storm like this) passing over our region. We can expect a dusting to perhaps an inch and the enjoyment of watching snow fall if you're up late enough (or early enough). The track is far enough south that areas around Fredericksburg could see the most snow - but even there, an inch or so is about as good as it will probably get.
Because of the very cold airmass that is currently locked in our region, the snow ratios should be higher than the standard rule-of-thumb 10-1. So even though the amount of available moisture is small, the chances of snow accumulation are pretty good. I'd say in the DC metro area we stand a 60-70% chance of seeing around an inch of snow tonight.
If the snow should continue into the morning rush hour, expect the NWS to put out Winter Weather Advisories.
This is a fairly narrow band of energy (as you can see from the model output above) so if we don't see much of anything on the ground and just a few flurries flying, I wouldn't be that surprised.
On to Friday:
The models are slowly coming into agreement and the news for snow-lovers isn't that good. The phasing I discussed in my previous post seems unlikely to happen as the southern stream energy gets shunted south and sheared apart. That means the northern stream energy has to work with whatever moisture it has and since it's continental in origin, that's not much.
Also, the storm will be a Miller B type scenario. Miller B storms are characterized by a primary low moving over land that weakens and transfers energy to a secondary low - usually off the coast. Sometimes this is a really good thing. For example, the Snowmageddon storm was a Miller B.
But.
In that case the energy transfer happened earlier and the southern stream low pressure system was much stronger (and had its origins in the Gulf Coast). As the storm moved up the coast, it actually almost stopped to our east before proceeding up the coast because of blocking patterns.
In this case, however, the southern stream energy is weak and the energy transfer may happen right over our area. These are bad things. If the energy transfer happens directly over us, we could be caught in the middle - what meteorologists call a "snow hole". That would result in us seeing very little snow at all.
The models are still in a bit of disagreement as to the path and the amount of moisture available to the system. At this point, it's unlikely that the storm will be anything to get excited about but we'll see how the models look this afternoon.
For now, there's a pretty good chance of light snow on Friday that could maybe result in 1-3 inches of snow if we're lucky.
Let's look at where we are - first with tonight's event.
A weak "clipper" system is poised to move over our area overnight - probably after midnight and into the hours around dawn. The GFS and the NAM both show this clipper and show a decent amount of energy (for a storm like this) passing over our region. We can expect a dusting to perhaps an inch and the enjoyment of watching snow fall if you're up late enough (or early enough). The track is far enough south that areas around Fredericksburg could see the most snow - but even there, an inch or so is about as good as it will probably get.
 |
| GFS model output showing light band of snow across the region overnight. Liquid equivalent precipitation forecasts are around 0.05 - 0.1 inches which translate to around an inch of snow. |
Because of the very cold airmass that is currently locked in our region, the snow ratios should be higher than the standard rule-of-thumb 10-1. So even though the amount of available moisture is small, the chances of snow accumulation are pretty good. I'd say in the DC metro area we stand a 60-70% chance of seeing around an inch of snow tonight.
If the snow should continue into the morning rush hour, expect the NWS to put out Winter Weather Advisories.
This is a fairly narrow band of energy (as you can see from the model output above) so if we don't see much of anything on the ground and just a few flurries flying, I wouldn't be that surprised.
On to Friday:
The models are slowly coming into agreement and the news for snow-lovers isn't that good. The phasing I discussed in my previous post seems unlikely to happen as the southern stream energy gets shunted south and sheared apart. That means the northern stream energy has to work with whatever moisture it has and since it's continental in origin, that's not much.
Also, the storm will be a Miller B type scenario. Miller B storms are characterized by a primary low moving over land that weakens and transfers energy to a secondary low - usually off the coast. Sometimes this is a really good thing. For example, the Snowmageddon storm was a Miller B.
But.
In that case the energy transfer happened earlier and the southern stream low pressure system was much stronger (and had its origins in the Gulf Coast). As the storm moved up the coast, it actually almost stopped to our east before proceeding up the coast because of blocking patterns.
 |
| Radar composite image from February 5-6, 2010 showing strong southern stream low receiving energy from a weaker low over the Tennessee Valley before moving up the coast. |
In this case, however, the southern stream energy is weak and the energy transfer may happen right over our area. These are bad things. If the energy transfer happens directly over us, we could be caught in the middle - what meteorologists call a "snow hole". That would result in us seeing very little snow at all.
The models are still in a bit of disagreement as to the path and the amount of moisture available to the system. At this point, it's unlikely that the storm will be anything to get excited about but we'll see how the models look this afternoon.
For now, there's a pretty good chance of light snow on Friday that could maybe result in 1-3 inches of snow if we're lucky.
Tuesday, January 22, 2013
Cold! Then Another Chance of Wintry Precipitation Friday
Cold is easier to forecast than snow, so let's start there.
It's cold. It's going to be cold - until Sunday, at least. The worst of the cold weather will be today through Friday. Highs in the 20's, lows in the teens and a noticeable wind which will make it feel even colder. Bundle up!
Now - let's have a look at Friday...
Most of the forecast models show a fast-moving low pressure system moving out of the southeast on Thursday night and making it here on Friday morning. That's about all they agree on however.
A few (GFS, Euro) show the storm tracking just to our south before reforming off the coast and moving out to sea. This would give us a relatively quick shot of precipitation but would keep it all snow.
Others (UKMET, NOGAPS) show the storm tracking just over us or just to our north. This would create an "overrunning" situation where warm air on the southeast side of the low slides over the cold air at the surface. Depending on the depth of the cold air, this can create the "mixed bag" of precipitation which starts and snow then changes to sleet or possibly freezing rain. I'd consider this the least likely scenario at this point.
The big questions as usual are:
An extra component to this situation is the cold air mass over our area. This cold will produce higher-than-normal snow ratios which means we can squeeze a bit more snow out of the same amount of precipitation.
Here is the GFS model showing precipitation overspreading the area on Friday:
You can see that the freezing line (blue) is quite a bit south of here which indicates a mostly snow event.
The storm remains a quick-mover and doesn't really get going until it's well off the coast. An event like this could produce 2-4 inches but what we want is a phase. In this scenario, the southern energy is sheared away which produces a weaker low.
The energy that will be producing this precipitation isn't even on the West Coast yet so there's plenty of time for things to change.
This is more of a "heads-up" that some snow is likely on Friday and it looks like there will be multiple parameters to consider before a solid forecast can be made. We'll see if there is any consensus from the models and what the energy looks like when it finally arrives.
Stay tuned.
It's cold. It's going to be cold - until Sunday, at least. The worst of the cold weather will be today through Friday. Highs in the 20's, lows in the teens and a noticeable wind which will make it feel even colder. Bundle up!
Now - let's have a look at Friday...
Most of the forecast models show a fast-moving low pressure system moving out of the southeast on Thursday night and making it here on Friday morning. That's about all they agree on however.
A few (GFS, Euro) show the storm tracking just to our south before reforming off the coast and moving out to sea. This would give us a relatively quick shot of precipitation but would keep it all snow.
Others (UKMET, NOGAPS) show the storm tracking just over us or just to our north. This would create an "overrunning" situation where warm air on the southeast side of the low slides over the cold air at the surface. Depending on the depth of the cold air, this can create the "mixed bag" of precipitation which starts and snow then changes to sleet or possibly freezing rain. I'd consider this the least likely scenario at this point.
The big questions as usual are:
- Storm track. Half the models are still forecasting a northward track.
- Phasing. There is a scenario where energy from the Pacific phases with the southern stream jet which then moves across our area. This scenario, by far, would produce more precipitation.
An extra component to this situation is the cold air mass over our area. This cold will produce higher-than-normal snow ratios which means we can squeeze a bit more snow out of the same amount of precipitation.
Here is the GFS model showing precipitation overspreading the area on Friday:
You can see that the freezing line (blue) is quite a bit south of here which indicates a mostly snow event.
The storm remains a quick-mover and doesn't really get going until it's well off the coast. An event like this could produce 2-4 inches but what we want is a phase. In this scenario, the southern energy is sheared away which produces a weaker low.
The energy that will be producing this precipitation isn't even on the West Coast yet so there's plenty of time for things to change.
This is more of a "heads-up" that some snow is likely on Friday and it looks like there will be multiple parameters to consider before a solid forecast can be made. We'll see if there is any consensus from the models and what the energy looks like when it finally arrives.
Stay tuned.
Thursday, January 17, 2013
Southward Track - No Significant Snow Expected
The southward track of the storm seems to be verifying and radar trends (and, frankly, the sky appearance) are not favorable for significant snowfall here in the DC area. I think some snow will fall, maybe a coating here and there on grassy surfaces - but nothing memorable.
This is another case of a storm which looked like nothing a few days ago, looked like something significant for two model runs yesterday and then beginning yesterday evening, started to look like nothing again. Inconsistencies in model runs like that within 24-36 hours of the start of the storm can cause forecasting havoc. This one sure did. When I stopped looking last night, the NWS was still forecasting 3-5 inches for the Fairfax area.
We're now 2 years into our snow drought. Cold air returns for the beginning to middle of next week but very little moisture will be passing by. I think there's a chance of snow showers on Inauguration Day but apart from that, looks like we'll have to wait a little longer for significant snow.
This is another case of a storm which looked like nothing a few days ago, looked like something significant for two model runs yesterday and then beginning yesterday evening, started to look like nothing again. Inconsistencies in model runs like that within 24-36 hours of the start of the storm can cause forecasting havoc. This one sure did. When I stopped looking last night, the NWS was still forecasting 3-5 inches for the Fairfax area.
We're now 2 years into our snow drought. Cold air returns for the beginning to middle of next week but very little moisture will be passing by. I think there's a chance of snow showers on Inauguration Day but apart from that, looks like we'll have to wait a little longer for significant snow.
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