Wednesday, January 11, 2012

arctic front 1/12-1/13

After being spoiled the past few years, there has yet to be very many big snowstorms for Virginia this winter.  Instead, much of the northern half of the state has been blasted with smaller, surprise storms.  These have often caught people by surprise, due to the fact that lake effect, shortwaves out of the midwest, and arctic front snows are all very difficult to predict.  The problem with forecasting for much of the state is the Appalachian mountains.  These events often dry up precipitation on the western facing ridges in West Virginia.  For these 3 different types of events that I mentioned, it takes pretty strong dynamics to get snow anywhere east of the mountains.  So far this year, there have been a couple events that have done just that, dumping anywhere from a dusting to an inch across the northern half of the state.  We will very likely see out third such event as we head into tomorrow night.
The current storm affecting the east coast has been warm.  Too warm for snow all the way up the eastern seaboard,even as far north as areas such as New York.  An artic front is being dragged behind the system, showed by the dotted line in the map above.  This is what will bring the significant change in weather as we head into tomorrow night.  Notice how much colder the air is behind it. 

As the arctic front nears the area, expect for snow to really get cranking across much of the midwest.  Above is the 18z nam simulated area for late tomorrow night.  The nam has been consistently showing this rather impressive looking band the past several runs, since yesterday in fact.  So where is the trouble in making this forecast?  Of course, the Appalachian mountains.  How well will this line hold together?  That is the question.  A few of the other short range models I like to look at, the NMM and the ARW, are showing the same scenario.  I'm not going to post them on here because I think they overdo just how much of the line will make it over the mountains.  Regardless, this will bring in the coldest air of the season thus far, and last through the weekend.  Below I'm posting my thoughts on just how much snow I believe will occur.  Keep in mind that this system is coming overnight, so the sun will not be a factor.  This is also a high risk forecast.  Many things can go wrong.  I'll be tracking the intensity of the line and just how much it holds together over the mountains, for that will make all the difference in the world.  One last problem could be the temperatures, especially the farther you go south.  The arctic air will be trying to catch up with the precipitation.  How fast the arctic air moves in and how slow the precipitation moves out will be big

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