Monday, March 4, 2013

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This. Is. Not. A. Drill.

HIGH-IMPACT SNOW EVENT FOR MID-ATLANTIC
Region faces most widespread storm since Jan 26, 2011

3:30 PM EST 3/4/13 | LATEST FROM OUR WINTER STORMCAST TEAM 
Forecasters Greg J., Michael N., Zachary F., Connor M., Jason M., Foot, Davies


As part of our team's pre-storm process to establish the basis for a snowfall forecast, we first introduce the data origins, that of "QPF" or "Quantitative Precipitation Forecast" The enclosed chart is based on NOAA data as rendered by the weather website coolwx.com.

THE GENERAL GIST? 
Several computer models have projected a general 1.5 to 2.0 inches of liquid for much of Virginia and Maryland, with up to 1.0 inches for southern Pennsylvania. With snow ratios expected to start "lower" due to marginal temperatures, we are anticipating much of the snow will fall at an 8:1 ratio, ending near 10:1 in western areas of the Mid-Atlantic.



RATIOS VS. SNOWFALL: 

The chart show indicates what is possible were this storm to "overperform" regarding both liquid amounts (closer to 2.0") and ratios. We expect snow to begin late Tuesday night, with the bulk of the heavy snow Wednesday morning to midday. This may cause ratios to decrease in areas near the coast, along I-95, with normally colder areas west of the major cities, along I-81 corridor staying with higher ratios.

BOTTOM LINE? We want readers in the Mid-Atlantic to be prepared for a heavy wet snow event that may produce 5-8 inches in the major mid- Atlantic cities by Wednesday noon. Much higher amounts of up to 12 inches are possible just west of those areas-- from southern PA to northern Baltimore County through Carroll, western Howard and down to west of DC and along I-81.

If liquid equivalent trends continue rising, and the storm begins Tuesday night as mostly snow, much of the region may face a significantly higher impact storm than is currently being forecasted by our team and other outlets.


(Forecasters Foot, Connor, Jason, Greg, Zach; Meteorologist Davies)



10:30 AM EST 3/4 : Previous update from the Winter Stormcast Team 

NOAA/NWS WINTER STORM STATEMENTS:
  • Eastern US NWS Regional HQ:  Winter Storm Watches in effect for all of central & western Maryland, northern & central Virginia, the Baltimore-Washington metro areas and southern Pennsylvania.

WINTER STORM MODE Due to the likelihood of significant winter weather within the next 48 hours,  "Winter Storm Mode" is activated for the following zones. This is to notify our readers of increased coverage and postings in affected local zones:
  • ALL MARYLAND ZONES, ALL VIRGINIA ZONES, POTOMAC RIVER VALLEY
  • THREE RIVERS, SOUTHEAST PENNSYLVANIA, CENTRAL PENNSYLVANIA

SYNOPSIS: After anxiously waiting for months on end for a big snowfall, it appears as though many readers in the mid-Atlantic will finally receive THE snowstorm of the year in a powder-filled last hurrah. The latest computer projections of liquid equivalents in this storm are showing a possible 1.0" or greater for the Baltimore-Washington area into southern Pennsylvania. Some models, such as the short-range NAM (North American Mesoscale) show up to 0.79" of liquid falling as snow, whereas the GFS (Global Forecast System) reduces snow liquid equivalent to just 0.49" as snow, with a disruptive 1.12" of sleet as another possibility! 

If the storm starts as all snow, then snow-to-liquid ratios may start lower, but end higher, at a point in time when the storm is at its peak in the overnight hours into Wednesday.  If so, the resulting snowfall could become a significant event for the region.
  • Bulk of the snowstorm should move through from Tuesday night to Wednesday night providing a period of heavy snow to many areas of central mid-Atlantic. The exact track of heaviest snow is still an uncertainty, but at the moment much of central and western Maryland look to be the center point.
  • This storm is likely to be a high impact event for much of the region, causing difficult travel, widespread school closures, and flight cancellations Tuesday night through Thursday morning. Below we outline the current scenarios that we see for this significant snowstorm with the first being most likely. 

SNOWFALL SCENARIOS: The map shown below displays shows our two scenarios for the heaviest snowfall amounts. If you are not in the areas, it does not mean you will not see snow, it just means that you will likely not be in the heaviest snow area. We will have additional updates and preliminary snowfall totals posted later today.



SCENARIO A (Slower storm with a northerly component, heavy snow in MD)

TIMING: In this scenario, the storm is a bit slower and is able to push further north before moving offshore. Expect precipitation to push into portions of the mid-Atlantic Tuesday evening. Snow would be heaviest through the day Wednesday before coming to an end from west to east Wednesday night.  

ACCUMULATIONS: Central and western Maryland, along with and south central Pennsylvania could see significant to high snowfall accumulations. Other areas across southern Pennsylvania could see a moderate to significant snowfall, especially across Franklin and Adams counties. Further east across southern New Jersey and Delaware, precipitation should start as rain and might change to snow for a few hours before pushing offshore leading to slushy accumulations of a few inches.  

IMPACTS:  Portions of central and southern Maryland could start as rain before changing to heavy snow. An extended period of heavy snow is likely across Maryland and extreme south central Pennsylvania (southern Adams, Franklin, Fulton, and Bedford counties) which could last for up to 12 hours. 

The snow would be heavy wet snow and given the heavy accumulations, damage would be expected for weak structures than cannot handle the weight of the snow. This would cause travel problems Tuesday night through Thursday morning across Maryland and southern Pennsylvania. Many flights would likely be cancelled on Wednesday at Dulles and BWI.

SCENARIO B (Storm departs more quickly. heavy snow stays in Virginia)

TIMING: Precipitation would begin across the mid-Atlantic Tuesday afternoon. Heaviest snow would fall across Virginia Tuesday night and taper off around midday Wednesday. 
IMPACTS/ACCUMULATIONS: The storm could push offshore before developing and not provide much precipitation to the central mid-Atlantic. This could lead to a mix of rain and snow changing to heavy snow with significant accumulations across Central Virginia. 
Further north some light to moderate snow is possible, but rain may mix in and lower accumulations. The snow would be heavy wet snow, so damage is possible if enough of it piles up on a weak structure. Travel would be affected Tuesday afternoon through Wednesday afternoon across portions of central and northern Virginia.

Sunday, March 3, 2013

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END TO THE SNOW DROUGHT?


8:25 PM 3/3/13 - TEAM STATEMENT - As you can see in the graphic above, the lack of snow for the past two years has been very significant. Many Mid-Atlantic cities have not had notable accumulation since January 26th, 2011! After holding back all year, the pattern looks like it will all come together to end winter 2012-13 with a bang. 

After anxiously waiting for months on end for a big snowfall, it looks like many of us in the mid-Atlantic will finally receive our snowstorm of ’13. The snowstorm should move through Tuesday night through Wednesday night providing a period of heavy snow to someone in the mid-Atlantic. The exact track of heaviest snow is still an uncertainty, but at the moment looks to be somewhere over Maryland. Nevertheless, this storm will be a high impact event for the mid-Atlantic causing difficult travel, school closures, and flight cancellations Tuesday night through Wednesday. Below we outline the current scenarios that we see for this significant snowstorm with the first being most likely. 

Winter Stormcast Team Projections


SCENARIO A: (70% Chance, Storm similar to current models)


TIMING: Expect precipitation to push into portions of the mid-Atlantic Tuesday evening. Snow would be heaviest through the day Wednesday before coming to an end from west to east Wednesday night.


IMPACTS:
In this scenario, the storm is a bit slower and is able to push further north before moving offshore. Portions of central and southern Maryland could start as rain before changing to heavy snow. An elongated period of heavy snow is likely across Maryland and extreme south central Pennsylvania (southern Adams, Franklin, Fulton, and Bedford counties) which could last for up to 12 hours. The snow would be heavy wet snow and given the heavy accumulations, damage would be expected for weak structures than cannot handle the weight of the snow. This would cause travel problems Tuesday night through Thursday morning across Maryland and southern Pennsylvania. Many flights would likely be cancelled on Wednesday at Dulles and BWI.


ACCUMULATIONS: Maryland and extreme south central Pennsylvania could see significant to high snowfall accumulations. Other areas across southern Pennsylvania could see a moderate to significant snowfall, especially across Franklin and Adams counties. Further east across southern New Jersey and Delaware, precipitation should start as rain and might change to snow for a few hours before pushing offshore leading to slushy accumulations of a few inches.


SCENARIO B:
(30% Chance, Faster Storm, Snow Further South)


TIMING: Precipitation would begin across the mid-Atlantic Tuesday afternoon. Heaviest snow would fall across Virginia Tuesday night and taper off around midday Wednesday.


IMPACTS/ACCUMULATIONS: The storm could push offshore before developing and not provide much precipitation to the central mid-Atlantic. This could lead to a mix of rain and snow changing to heavy snow with significant accumulations across Central Virginia. Further north some light to moderate snow is possible, but rain may mix in and lower accumulations. The snow would be heavy wet snow, so damage is possible if enough of it piles up on a weak structure. Travel would be affected Tuesday afternoon through Wednesday afternoon across portions of central and northern Virginia.

The map here shows our two scenarios for the heaviest snowfall amounts. If you are not in the areas, it does not mean you will not see snow, it just means that you will likely not be in the heaviest snow area.

Winter Stormcast Team - (Greg J., Michael N., Zachary F., Connor M., Jason M.)

Saturday, March 2, 2013

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"We have a situation..." 
- Actor John Amos in Die Hard 2

11:55 AM EST 3/3/12 (Mid-Atlantic & Southeast Winter Stormcast Teams


  • UPDATE: A major winter weather event is possible for the upper Midwest to the Mid-Atlantic region by mid-week. The storm is currently onshore east of Canada's Coast Range as shown left in the Surface Low Tracks map.
  • Black Ice event overnight as reported by our North Georgia Team indicates overnight low temperatures in other regions are conducive to winter weather.
SNOWFALL PROBABILITY OF 4" OR GREATER WITHIN 72 HOURS

SITUATION: Although the Mid-Atlantic region has been rather tranquil lately, regarding winter weather, that may change drastically into the first full week of March. Indications continue to suggest a possible snowstorm for the region from Wednesday into Thursday. At this point there is high uncertainty with the track of this system, with one scenario going south of the region, and another delivering the mid-Atlantic with a late season snowstorm. 

ANALYSIS: We do expect better consensus later this weekend as the storm is still offshore from the Pacific Northwest and should move inland this weekend. This will allow NOAA ground-based data collection systems to provide more inputs to computer models, and in turn this data  should help projections gain more clarity on potential outcomes. 



Another reason for uncertainty is that this storm would be one part of multiple storms that will have to come together to deliver a major event. Computer models at times, have difficulty  modeling these types of complex systems. Below we outline the two scenarios for this system that we see at the moment. At this time, given the current available projections, we will way each of these scenarios has a 50% chance of occurring as stated.