Monday, February 12, 2007
Nasty Storm on the Way with Wintry Mix
Ice the biggest threat
Team Forecast @ 8:31 AM
*Winter Storm Watch in Effect from Monday evening through Wednesday afternoon*
What once appeared like it could be a heavy snowstorm for the DC area now looks to be a sloppy mess of snow, ice and rain. Some areas, particularly north and west of DC could experience a serious ice storm with the worst of the storm likely Tuesday night. Details are still evolving with this complex storm and this forecast is subject to change.
When/where will the heaviest frozen precipitation fall? Most likely Tuesday night in the north and west suburbs. Significant and even dangerous ice accumulations are possible.
When will the precipitation start? Intermittent light snow could begin as early as dawn Tuesday morning although significant accumulations that would affect schools may not begin until the late morning or early afternoon. Be on the lookout for early dismissal possibilities.
Will the snow stick? Yes -- the ground is relatively cold so it should not take that long for snow to begin sticking on the grass and untreated, lightly traveled surfaces.
When will travel be most difficult? From Tuesday's evening rush hour through Wednesday morning. Freezing rain could make for dangerous conditions after dark on Tuesday.
Could there be power outages due to ice? Yes. Especially north and west of DC where temperatures will be colder and the heaviest precipitation could fall as ice.
What about precipitation type? This is the most difficult aspect of this storm to forecast. Some precipitation will fall initially as snow, but amounts will be light. By the time the heaviest precipitation moves in, mid layers of the atmosphere will have warmed enough so that the precipitation will have changed to sleet or freezing rain (late afternoon Tuesday and overnight). Precipitation may even change to plain rain in DC and points south and east which would reduce the storm's impact early Wednesday morning in those areas. There is a slight chance the precipitation could turn back to snow early Wednesday, particularly to the west, but this is not a sure thing.
When will conditions improve? Most likely midday Wednesday.
Could it fizzle out? Yes -- especially from the perspective of those who want snow. Models have been trending warmer and warmer in the layer of the atmosphere where it's required to be cold for it to snow. So snow amounts could be quite modest. While the threat of ice is real, if the storm track takes a more northerly track, an east or southeast wind could warm temperatures enough for plain old rain. We also need to watch out for a dry slot that could form when the initial storm transfers its energy to the coast. If we get "dry slotted," the amount of precipitation we get could be significantly reduced.
Could the storm bring more snow or ice than expected? Perhaps. The key for the storm to outperform expectations from the perspective of snow lovers would be if it takes a more southerly track. There isn't a lot of hope for this, however. Also, if the coastal low rapidly intensifies and shifts the winds to the northerly direction more rapidly than forecast (this scenario isn't shown by the models, however), this could help produce more snow. The storm could be even more of an ice threat if the low-level cold air holds strong and does not erode. This is a possibility.
What are other forecasters saying? Most forecasters are mentioning light snow accumulations before the threat of serious icing, especially north and west. WUSA (Tony Pann) predicted a general 1-3" snowfall for the area before a changeover, and FOX5 and NBC4 are calling for 2-4" before icing.
What's the bottom line? Big-time snow amounts are no longer likely. In fact, just a couple inches of snow seem like the best estimate at this point. But the impact of the storm may still be significant due to icing issues, particularly north and west of DC.
What once appeared like it could be a heavy snowstorm for the DC area now looks to be a sloppy mess of snow, ice and rain. Some areas, particularly north and west of DC could experience a serious ice storm with the worst of the storm likely Tuesday night. Details are still evolving with this complex storm and this forecast is subject to change.
 | 
4am to 8am TUE: Light snow or flurries. Little accumulation. Temps 28-32. |
 Travelcast: Schoolcast (Wed.): | |
Frequently Asked Questions
When/where will the heaviest frozen precipitation fall? Most likely Tuesday night in the north and west suburbs. Significant and even dangerous ice accumulations are possible.
When will the precipitation start? Intermittent light snow could begin as early as dawn Tuesday morning although significant accumulations that would affect schools may not begin until the late morning or early afternoon. Be on the lookout for early dismissal possibilities.
Will the snow stick? Yes -- the ground is relatively cold so it should not take that long for snow to begin sticking on the grass and untreated, lightly traveled surfaces.When will travel be most difficult? From Tuesday's evening rush hour through Wednesday morning. Freezing rain could make for dangerous conditions after dark on Tuesday.
Could there be power outages due to ice? Yes. Especially north and west of DC where temperatures will be colder and the heaviest precipitation could fall as ice.
What about precipitation type? This is the most difficult aspect of this storm to forecast. Some precipitation will fall initially as snow, but amounts will be light. By the time the heaviest precipitation moves in, mid layers of the atmosphere will have warmed enough so that the precipitation will have changed to sleet or freezing rain (late afternoon Tuesday and overnight). Precipitation may even change to plain rain in DC and points south and east which would reduce the storm's impact early Wednesday morning in those areas. There is a slight chance the precipitation could turn back to snow early Wednesday, particularly to the west, but this is not a sure thing.
When will conditions improve? Most likely midday Wednesday.
Could it fizzle out? Yes -- especially from the perspective of those who want snow. Models have been trending warmer and warmer in the layer of the atmosphere where it's required to be cold for it to snow. So snow amounts could be quite modest. While the threat of ice is real, if the storm track takes a more northerly track, an east or southeast wind could warm temperatures enough for plain old rain. We also need to watch out for a dry slot that could form when the initial storm transfers its energy to the coast. If we get "dry slotted," the amount of precipitation we get could be significantly reduced.
Could the storm bring more snow or ice than expected? Perhaps. The key for the storm to outperform expectations from the perspective of snow lovers would be if it takes a more southerly track. There isn't a lot of hope for this, however. Also, if the coastal low rapidly intensifies and shifts the winds to the northerly direction more rapidly than forecast (this scenario isn't shown by the models, however), this could help produce more snow. The storm could be even more of an ice threat if the low-level cold air holds strong and does not erode. This is a possibility.
What are other forecasters saying? Most forecasters are mentioning light snow accumulations before the threat of serious icing, especially north and west. WUSA (Tony Pann) predicted a general 1-3" snowfall for the area before a changeover, and FOX5 and NBC4 are calling for 2-4" before icing.
What's the bottom line? Big-time snow amounts are no longer likely. In fact, just a couple inches of snow seem like the best estimate at this point. But the impact of the storm may still be significant due to icing issues, particularly north and west of DC.
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