Look at that rain/snow line.
Keeps bouncing back and forth in the District, all snow to the west, all (or mostly) rain to the east.
Wednesday, March 6, 2013
Radar Shows the Problem
This radar I "borrowed" from the CWG page shows the issues:
Look at that rain/snow line.
Keeps bouncing back and forth in the District, all snow to the west, all (or mostly) rain to the east.
Look at that rain/snow line.
Keeps bouncing back and forth in the District, all snow to the west, all (or mostly) rain to the east.
In the City and East - A Different Story
In the city and points east, the dreaded temperature issues are having an effect. Rain is falling throughout most of southern Maryland and the eastern Shore. Very wet and non-accumulating snow is falling in parts of the District itself. I think these areas don't do well in this storm although a changeover should occur as the storm moves to our north.
Expect the NWS to lower snow total forecasts for these areas and, really, anywhere east of central Fairfax County.
Still, a snowy day to "end" the winter isn't all that bad.
Expect the NWS to lower snow total forecasts for these areas and, really, anywhere east of central Fairfax County.
Still, a snowy day to "end" the winter isn't all that bad.
Things are On Track - West of the City
For most of the area west of DC, things are on track. Snow has been falling overnight and mixing with (even changing to) rain as expected for areas in the city and eastward. It's been all snow to the west - even in Annandale just outside of the Beltway.
Snow was light to moderate overnight and had the expected difficult time sticking due to the warm temperatures yesterday.
Today snow will be heavy at times and the bulk of our accumulations will fall during the daytime hours. I think.
The snow will have a harder-than-usual time accumulating because of the temperatures and its consistency - especially on the roads and sidewalks and we have to watch that rain/snow line.
I think the city and points east will have a hard time getting to the forecast snow amounts. Westward, things should be better.
Here's the NAM clown map which is more realistic than previous NAM versions.
Enjoy whatever snow does fall and be safe!
Snow was light to moderate overnight and had the expected difficult time sticking due to the warm temperatures yesterday.
Today snow will be heavy at times and the bulk of our accumulations will fall during the daytime hours. I think.
The snow will have a harder-than-usual time accumulating because of the temperatures and its consistency - especially on the roads and sidewalks and we have to watch that rain/snow line.
I think the city and points east will have a hard time getting to the forecast snow amounts. Westward, things should be better.
Here's the NAM clown map which is more realistic than previous NAM versions.
Enjoy whatever snow does fall and be safe!
Tuesday, March 5, 2013
Winter Storm Warning
A Winter Storm Warning has been issued for most of the DC metro. This is the latest forecast from the NWS. Note that the snowfall totals are shifted west somewhat indicating less snow around the city but still a significant snowstorm. NWS is expecting some problems with mixing during the first half of Wednesday.
Forecast Mostly On Track
As it has looked from the beginning, this is going to be an issue of temperatures and whether the intensity of the storm and the dynamic cooling processes in the atmosphere can overcome the marginal cold air and the complete lack of a strong cold air source.
This storm and the forecasts around it have high bust potential.
Still - climatology and atmospheric analysis suggests that the DC metro area and especially points west and north have a good chance to end a 2-year snow drought in spectacular fashion.
The NAM model run from this morning is one of the more bullish solutions for this storm. Here is the clown map it rendered from the morning run:
Now the NAM does have a precipitation bias - it can overdo the precipitation forecast. Still, if this were to verify, it suggests widespread totals of a foot or more in DC and especially westward where totals could exceed 15 inches.
The GFS is slightly less excited but still shows our region in the bullseye of the storm:
Although as you can see, the gradient of precipitation is quite tight on the eastern side and the snowfall amounts drop off rapidly as you go east.
Track is often the most important thing with winter storms but in this case, the track is almost the entire story. There's not much question about precipitation falling tonight, tomorrow and tomorrow night. The question is, "what type?"
A small shift - and we're talking maybe 50 miles - southward and this becomes a snowstorm with 10-15 inches of snow even inside the Beltway. The same shift northward dramatically decreases the snowfall totals in the region and pushes everything west.
My sense is that snow will fall and accumulate and that we'll end the 2-year snow drought tonight and tomorrow. But I do worry about the rain/snow line and how far westward it will move. I also worry about how much precipitation will fall before it changes to snow.
Like I said: high bust potential.
Right now, it seems reasonable to go with this forecast:
Tonight: Precipitation begins as rain, probably in the evening, 5-6 PM is a good guess for the immediate DC metro. Earlier to the west, of course. The rain should fairly quickly start to mix with snow. Overnight, closer to midnight, the rain/snow mix will changeover to all snow and the precipitation rates really get going. If everything works out, we could see 2 or 3 inches on the ground by the time we wake up in the morning.
Tomorrow: Snow for most of us but more mixing issues will be in store the further east you go in the region. Out in Loudoun I expect they stay all snow but there probably be mixing issues east of the city. The precipitation will be heavy both in the "intensity" sense and the "weight" sense. This will be a wet snow which, combined with the expected winds, could cause power outages.
Tomorrow Night: Snow continues but starts to end from west to east overnight. Only the far northeast suburbs should see any lingering light snow Thursday morning.
This NWS map seems reasonable at this time:
I'll update if anything changes!
This storm and the forecasts around it have high bust potential.
Still - climatology and atmospheric analysis suggests that the DC metro area and especially points west and north have a good chance to end a 2-year snow drought in spectacular fashion.
The NAM model run from this morning is one of the more bullish solutions for this storm. Here is the clown map it rendered from the morning run:
Now the NAM does have a precipitation bias - it can overdo the precipitation forecast. Still, if this were to verify, it suggests widespread totals of a foot or more in DC and especially westward where totals could exceed 15 inches.
The GFS is slightly less excited but still shows our region in the bullseye of the storm:
Although as you can see, the gradient of precipitation is quite tight on the eastern side and the snowfall amounts drop off rapidly as you go east.
Track is often the most important thing with winter storms but in this case, the track is almost the entire story. There's not much question about precipitation falling tonight, tomorrow and tomorrow night. The question is, "what type?"
A small shift - and we're talking maybe 50 miles - southward and this becomes a snowstorm with 10-15 inches of snow even inside the Beltway. The same shift northward dramatically decreases the snowfall totals in the region and pushes everything west.
My sense is that snow will fall and accumulate and that we'll end the 2-year snow drought tonight and tomorrow. But I do worry about the rain/snow line and how far westward it will move. I also worry about how much precipitation will fall before it changes to snow.
Like I said: high bust potential.
Right now, it seems reasonable to go with this forecast:
Tonight: Precipitation begins as rain, probably in the evening, 5-6 PM is a good guess for the immediate DC metro. Earlier to the west, of course. The rain should fairly quickly start to mix with snow. Overnight, closer to midnight, the rain/snow mix will changeover to all snow and the precipitation rates really get going. If everything works out, we could see 2 or 3 inches on the ground by the time we wake up in the morning.
Tomorrow: Snow for most of us but more mixing issues will be in store the further east you go in the region. Out in Loudoun I expect they stay all snow but there probably be mixing issues east of the city. The precipitation will be heavy both in the "intensity" sense and the "weight" sense. This will be a wet snow which, combined with the expected winds, could cause power outages.
Tomorrow Night: Snow continues but starts to end from west to east overnight. Only the far northeast suburbs should see any lingering light snow Thursday morning.
This NWS map seems reasonable at this time:
I'll update if anything changes!
Monday, March 4, 2013
Worrisome Trend?
The GFS has been trending further and further northwest with each run. This was an "ok" trend at first because it brought the heaviest core of precipitation northward towards us. However, it's starting to become a touch uncomfortable because a northern track is also a warmer track which we don't want.
Temperatures for this event were going to be marginal anyway.
The official NWS call for the DC area is 2-4 inches east of I-95 and then a fairly tight gradient of about 6-8 inches just west of DC to over a foot for the western suburbs.
We need to keep a southern component to the track or we'll definitely have precipitation type issues.
Most March storms are like this but the snowfall forecasts are too close for comfort:
I should note that the GFS has the furthest northward track of any model and has been leading the northward charge for the last few cycles. In fact, the Euro - which is considered a better model - insists on a more southerly track. The disparity between the models - especially after the storm gets off the coast - is quite remarkable at this timeframe and highlights the complexity of the atmosphere and the interactions between pressure systems.
All I can say is "stay tuned". Snow still seems likely but we're getting close - too close - to having rain mixing problems, especially near the city itself.
Temperatures for this event were going to be marginal anyway.
The official NWS call for the DC area is 2-4 inches east of I-95 and then a fairly tight gradient of about 6-8 inches just west of DC to over a foot for the western suburbs.
We need to keep a southern component to the track or we'll definitely have precipitation type issues.
Most March storms are like this but the snowfall forecasts are too close for comfort:
I should note that the GFS has the furthest northward track of any model and has been leading the northward charge for the last few cycles. In fact, the Euro - which is considered a better model - insists on a more southerly track. The disparity between the models - especially after the storm gets off the coast - is quite remarkable at this timeframe and highlights the complexity of the atmosphere and the interactions between pressure systems.
All I can say is "stay tuned". Snow still seems likely but we're getting close - too close - to having rain mixing problems, especially near the city itself.
NAM Total Precipitation Forecast
You can see we're in the "bullseye" for the NAM which shows 1.5-2+ inches of liquid precipitation from this storm. Even losing some of that to rain/slop and assuming low snow-liquid ratios, that suggests at least 6 inches of snowfall.
Snow Seems Likely
It's down to a question of "how much?" which will be strongly driven by the ultimate storm track and the intensity of the storm as it passes through. We could "lose" some precipitation to rain at the beginning (Tuesday afternoon/evening) but the changeover to snow should start from west to east overnight Tuesday.
The closest analog to this storm and the pattern seems to be February 5-6, 2010 which dumped 18-32 inches of snow in the DC area. This will not perform as well for two reasons:
1 - Lack of abundant cold air at the surface. This storm will depend on dynamic processes to cool the air and change initial precipitation to snow. The forecast high for DCA on Tuesday is 47 so there will be some distance to go - even at night - before the atmosphere is fully conducive to supporting snowfall.
2 - Lower liquid-snow ratios. The rule-of-thumb is 1 inch of liquid = 10 inches of snow. Because of the marginal temperatures, the ratios are likely to be more like 8:1.
Still, most of the models produce significant QPF (precipitation forecast amounts) for our area - well over an inch in many cases. Those of you along and east of I-95 stand the best chance of having precipitation problems with rain mixing in even on Wednesday which may keep totals down. To the west, the precipitation is more likely to remain snow.
The timing for this is:
Tuesday afternoon/evening: rain starts and changes to snow overnight.
Tuesday night: rain/snow changing to all snow by morning
Wednesday: snow (possibly mixed with rain to the east)
Wednesday night: snow ending from west to east
Here is the NAM clown map from this morning's run:
Looks like 6-12 inches from DC westward, over a foot in the mountains. Less as you go east. The gradient is pretty tight along I-95 so this will be a tough call. I can see scenarios where only rain falls in the I-95 corridor and I can see others where all snow falls.
It's a tough forecast as almost all March snowstorms tend to be.
I'll say a general 6-inch snowstorm is likely now for the DC metro with greater amounts to the north and west and lesser amounts to the east.
We'll see what the models have to say this afternoon.
The closest analog to this storm and the pattern seems to be February 5-6, 2010 which dumped 18-32 inches of snow in the DC area. This will not perform as well for two reasons:
1 - Lack of abundant cold air at the surface. This storm will depend on dynamic processes to cool the air and change initial precipitation to snow. The forecast high for DCA on Tuesday is 47 so there will be some distance to go - even at night - before the atmosphere is fully conducive to supporting snowfall.
2 - Lower liquid-snow ratios. The rule-of-thumb is 1 inch of liquid = 10 inches of snow. Because of the marginal temperatures, the ratios are likely to be more like 8:1.
Still, most of the models produce significant QPF (precipitation forecast amounts) for our area - well over an inch in many cases. Those of you along and east of I-95 stand the best chance of having precipitation problems with rain mixing in even on Wednesday which may keep totals down. To the west, the precipitation is more likely to remain snow.
The timing for this is:
Tuesday afternoon/evening: rain starts and changes to snow overnight.
Tuesday night: rain/snow changing to all snow by morning
Wednesday: snow (possibly mixed with rain to the east)
Wednesday night: snow ending from west to east
Here is the NAM clown map from this morning's run:
Looks like 6-12 inches from DC westward, over a foot in the mountains. Less as you go east. The gradient is pretty tight along I-95 so this will be a tough call. I can see scenarios where only rain falls in the I-95 corridor and I can see others where all snow falls.
It's a tough forecast as almost all March snowstorms tend to be.
I'll say a general 6-inch snowstorm is likely now for the DC metro with greater amounts to the north and west and lesser amounts to the east.
We'll see what the models have to say this afternoon.
Sunday, March 3, 2013
Keep an Eye on Tuesday-Wednesday
As you've probably heard by now, the potential for significant snow exists for Tuesday night through Wednesday night in our area. This is a potentially serious situation because the precipitation, if it indeed falls as all snow, would be wet and heavy and according to some models I'm looking at now - there could be a lot of it.
Here's the GFS "clown map" for example:
showing our area "bullseyed" with 12-16 inch snows. The GFS does some strange things in this run so we'll have to watch to see if it's repeated in tomorrow's run and if the other models agree.
There's a ton of data to look over and most importantly, the track is going to be a big big deal. In March, the sun angle is higher and it's going to be hard to get temperatures down to the level where everything sticks (or even falls as snow). But if the track is just right, this could happen.
I'm still checking things but let's just say that the chance of significant accumulating snowfall starting Tuesday night and continuing through Wednesday night is better than 50%.
The rain/snow line is more of a question now rather than the question of whether or not anything will fall.
Here's the GFS "clown map" for example:
showing our area "bullseyed" with 12-16 inch snows. The GFS does some strange things in this run so we'll have to watch to see if it's repeated in tomorrow's run and if the other models agree.
There's a ton of data to look over and most importantly, the track is going to be a big big deal. In March, the sun angle is higher and it's going to be hard to get temperatures down to the level where everything sticks (or even falls as snow). But if the track is just right, this could happen.
I'm still checking things but let's just say that the chance of significant accumulating snowfall starting Tuesday night and continuing through Wednesday night is better than 50%.
The rain/snow line is more of a question now rather than the question of whether or not anything will fall.
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