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Posted at 01:27 PM ET, 03/01/2013

Significant winter storm potential around March 6, but major questions remain

There is a possibility of a snowstorm around March 6 and it could be significant. This is the best looking snow threat in two years but there is way too much uncertainty in the forecast for this to be “in the bag.”

The models have been displaying tremendous differences in their solutions ranging from a significant wet snowstorm to a non-event over the past several runs.

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Next chance of accumulating snow: March 5-7

Chance of at least 1 inch: 30 percent (note: this percentage would be higher if the storm was happening tomorrow; but with the storm still 5+ days away, we are necessarily being conservative. We will provide more detailed accumulation information - as warranted - as this possible storm draws closer)

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[As an aside: AccuWeather is already comparing this storm to the Ash Wednesday storm of 1962, which - in our view - is over the top. The Ash Wednesday storm was one of the most severe East Coast storms of the last 150 years. While this *possible* storm may have significant impacts for the Mid-Atlantic, it is premature to be elevating the hype to this level. - Wes and Jason]


GFS model shows an impressive, wound-up low pressure center off the Mid-Atlantic coast - which if it is correct - would produce significant snows from Washington D.C. to New York City next Tuesday-Thursday. (NOAA)
This time of year, forecasting a snowstorm is even tougher than normal because the sun’s intensity is growing and the climate is warming. To get accumulating snow, unless it is unseasonably cold, you need heavy precipitation to overcome temperatures just barely freezing or a little above. For the snow to really pile up, it helps for it to fall at night.

Even if we end up getting precipitation, there is no guarantee that it will be all snow. The precipitation could mix with and/or change to rain and sleet if warm air gets wrapped into the storm.

To get meaningful snow accumulation, we need an almost perfect storm track to keep the cold air in place along with a wound-up storm tapping copious amounts of moisture. This morning’s GFS and European model runs simulated such a scenario and would give the area a snowstorm.

Technical discussion

Yesterday Jason noted that the European model had generally trended away from a potential snowstorm with the storm developing far enough south to keep the precipitation away. The GFS also showed the storm squashed too far south to impact us.

Last night’s European run shifted the storm track back north again raising snow prospects, while the GFS nudged the storm slightly north but still kept meaningful precipitation to our southeast.


European model simulates a heavy area of snow from Richmond to Baltimore between 1 p.m. and 7 p.m. Wednesday. (StormVistaWxModels.com)
Today’s GFS run made a big northward move and now would even threaten New York City with a major snowstorm. The latest European run has the axis of heavy snow a bit farther south, simulating a snowstorm from roughly Richmond to Philadelphia, including Washington and Baltimore.

Lots of uncertainty persists concerning the storm and much of it still is dependent on the block (trough of low pressure) to the northeast that yesterday forced the approaching low south of us, and far enough off the coast to keep us out of significant precipitation. However, today’s European and GFS models move this trough out allowing the storm to make that north move.

A plume diagram of the precipitation forecasts of the various GEFS ensemble members give a feel for the wide range of solutions that remain possible with this storm. Remember that the only differences between the various members are slight differences in the initial analyses (starting conditions). These small differences grow with time. How fast they grow is a pretty good measure of the uncertainty in a forecast.


The members of the GEFS ensemble (from last night) vary from an almost total non-event to one in which 1.64 inches of precipitation falls as snow (that’s over a foot, assuming it’s cold enough). More of the members predict less than 0.25 inches of liquid equivalent than predict amounts above that threshold. Despite the seeming consensus between today’s GFS and last night’s European model, the ensembles suggest that getting a snowstorm is not assured and there is still time for things to go wrong.

The bulk of ensemble members forecasts for Sterling, Va. also display how marginal that the temperatures are likely to be for accumulating snow unless we get intense snowfall. Compare the plume diagrams showing the timing of precipitation above with the temperature forecast below (pay attention to the area outlined in red).


You can see that most of the members have the temperatures falling from in the 40s to the mid-to-low 30s once the precipitation commences. The ensemble mean (in black) settles to right around freezing on March 6. Change the temperatures a couple degrees colder and you could get accumulating snow, while a few degrees warmer might result in rain or non-accumulating snow provided the precipitation materializes.

Conclusion

The March 6 storm should be monitored closely. The pattern favors the development of a significant storm off the Southeast coast. Such storms are typically our biggest snow producers. Whether we get snow will depend on the track of this low and whether it tracks up the coast.

This storm could produce rain or snow but has the potential to produce significant snow in the area if a scenario like today’s GFS and Euro models play out. That is one possibility but the storm still could skirt us to the south or be just warm enough to produce rain or very wet snow with no accumulation.

By  |  01:27 PM ET, 03/01/2013

Categories:  Latest, Winter Storms

 
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