Friday, March 16, 2007
Storm Lashes Region: Winter Wakes, If Only Briefly
Heavy rain changing to snow and sleet from NW to SE
Team Forecast @ 7:30 PM
*Flood Warning in Effect Until 11 PM*
*Winter Weather Advisory in Effect (N&W) Until Midnight*
*Winter Storm Warning in Effect (Far N&W) Until Midnight*
7:30 PM Nowcast: Sleet in DC and points south and east will change to snow over the next hour or so. A slushy accumulation of less than 1" is possible. Snow will continue over the north and west suburbs with amounts around an inch -- except up to a couple inches in NW Montgomery Co and extreme western Fairfax Co. Precipitation will end from southwest to northeast between 8 and 11pm.
When/where will the heaviest snow fall? Far north & west of the beltway (e.g., places like Frederick, Leesburg and points north and west), snow will accumulate during the afternoon and evening with a general 3-5" (5-10" in the mountains). The latest data indicates that accumulations in the 1-3" band on the map above may be toward the higher end of that range, or more like 2-4".
Will the snow accumulate in the immediate metro area? The District and especially points north and west may see a light accumulation of a slushy snow/sleet mix toward evening, especially on grassy surfaces, sidewalks and untreated roads -- and especially during heavy bursts. Accumulation on treated roads will depend on the intensity of the precipitation, with heavier bands or bursts of snow accumulating more easily.
Where is the precipitation now? Click here for the latest radar loop.
When will travel be most difficult? Well north and west, travel conditions will continue to deteriorate into the evening. In the metro area, wintry conditions just north and west of town could cause problems during the evening commute, for example, on I-270. In the District, heavy rain and mixed precipitation could have a significant impact on traffic, but slipperiness due to snow and ice won't be as much of a concern as to the north and west. In general, treated roads should fare pretty well in the metro area except during periods of heavier precipitation, especially after dark.
What about precipitation type? Areas to the north and west have been transitioning from rain to sleet to snow first. The timing of this transition is tough to call. Places like Leesburg and Frederick have alredy seen that transition. Dulles, VA and Gaithersburg, MD are seeing the transition now with areas inside the beltway changing over toward evening.
Could the storm bring more snow than expected? As the storm intensifies off the coast, it could siphon down more cold air aloft than expected, changing the rain over to snow more quickly -- particularly if the storm takes more of an easterly track. As usual, small deviations in storm track as well as in temperatures at the surface and aloft could cause major differences between the "most likely" forecast and reality. That's why it's important to understand what the range of possibilities is and their odds (see bar chart of snow probabilities).
When will conditions improve? Where snow accumulates (most likely north and west of DC), precipitation will end and the road crews will have a chance to clear the streets by midnight tonight.
What are TV weathercasters saying? As of last night, Doug Hill said it will be "nasty" all day and the areas north and west could get significant snow. Bob Ryan was calling for 3-5" near Hagerstown and western Maryland with some wet snow upper Montgomery and Loudoun counties and the higher elevations. Sue Palka was predicting 1-3" in Loudoun county, north Montgomery county, northern Fauquier, and points north and west. 3-6" for Frederick, Md. Topper thought 6-12" would fall in the mountains with some wet snow overnight Friday in the District. Did not specify amounts in between the District and mountains.
What about the weekend? Cloudy and cold conditions will prevail during Saturday with highs in the upper 30s, at best. A batch of heavier snow showers/squalls could head through the region during the mid-afternoon hours as instability in the atmosphere, aloft, moves over us. Sunday will warm a little and have a great deal more sun, with high temperatures of 46-49 degrees.
*Winter Weather Advisory in Effect (N&W) Until Midnight*
*Winter Storm Warning in Effect (Far N&W) Until Midnight*
7:30 PM Nowcast: Sleet in DC and points south and east will change to snow over the next hour or so. A slushy accumulation of less than 1" is possible. Snow will continue over the north and west suburbs with amounts around an inch -- except up to a couple inches in NW Montgomery Co and extreme western Fairfax Co. Precipitation will end from southwest to northeast between 8 and 11pm.
 Note: The latest data indicates that accumulations in the 1-3" band may be toward the higher end of that range, or more like 2-4". | 
Pre-dawn to 1pm: Heavy rain and breezy across the entire region. Far N&W areas may begin to see a changeover to frozen precip late morning. Temps 34-40 (far NW suburbs-city). |
  Travelcast: Schoolcast(Fri PM): | |
Frequently Asked Questions
When/where will the heaviest snow fall? Far north & west of the beltway (e.g., places like Frederick, Leesburg and points north and west), snow will accumulate during the afternoon and evening with a general 3-5" (5-10" in the mountains). The latest data indicates that accumulations in the 1-3" band on the map above may be toward the higher end of that range, or more like 2-4".
Will the snow accumulate in the immediate metro area? The District and especially points north and west may see a light accumulation of a slushy snow/sleet mix toward evening, especially on grassy surfaces, sidewalks and untreated roads -- and especially during heavy bursts. Accumulation on treated roads will depend on the intensity of the precipitation, with heavier bands or bursts of snow accumulating more easily.
Where is the precipitation now? Click here for the latest radar loop.
When will travel be most difficult? Well north and west, travel conditions will continue to deteriorate into the evening. In the metro area, wintry conditions just north and west of town could cause problems during the evening commute, for example, on I-270. In the District, heavy rain and mixed precipitation could have a significant impact on traffic, but slipperiness due to snow and ice won't be as much of a concern as to the north and west. In general, treated roads should fare pretty well in the metro area except during periods of heavier precipitation, especially after dark.
What about precipitation type? Areas to the north and west have been transitioning from rain to sleet to snow first. The timing of this transition is tough to call. Places like Leesburg and Frederick have alredy seen that transition. Dulles, VA and Gaithersburg, MD are seeing the transition now with areas inside the beltway changing over toward evening.
Could the storm bring more snow than expected? As the storm intensifies off the coast, it could siphon down more cold air aloft than expected, changing the rain over to snow more quickly -- particularly if the storm takes more of an easterly track. As usual, small deviations in storm track as well as in temperatures at the surface and aloft could cause major differences between the "most likely" forecast and reality. That's why it's important to understand what the range of possibilities is and their odds (see bar chart of snow probabilities).When will conditions improve? Where snow accumulates (most likely north and west of DC), precipitation will end and the road crews will have a chance to clear the streets by midnight tonight.
What are TV weathercasters saying? As of last night, Doug Hill said it will be "nasty" all day and the areas north and west could get significant snow. Bob Ryan was calling for 3-5" near Hagerstown and western Maryland with some wet snow upper Montgomery and Loudoun counties and the higher elevations. Sue Palka was predicting 1-3" in Loudoun county, north Montgomery county, northern Fauquier, and points north and west. 3-6" for Frederick, Md. Topper thought 6-12" would fall in the mountains with some wet snow overnight Friday in the District. Did not specify amounts in between the District and mountains.
What about the weekend? Cloudy and cold conditions will prevail during Saturday with highs in the upper 30s, at best. A batch of heavier snow showers/squalls could head through the region during the mid-afternoon hours as instability in the atmosphere, aloft, moves over us. Sunday will warm a little and have a great deal more sun, with high temperatures of 46-49 degrees.
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