Wednesday, December 28, 2011

To Snow or Not to Snow...

That is the question, and it appears as though we'll be left high and dry. The Euro model must have finally awakened from its post-holiday leaded-eggnog stupor, because as quickly as one can say La Nina, the computerized pundit reversed its thinking on next week's nor'easter. Even more disappointing to snow lovers, is the strong agreement of all the medium range models of a deep and cold trough digging into the eastern half of the nation January 2nd-4th. Cold is good, yes, but not cold AND dry, and it appears as though that is what we will likely be dealing with. It was fun while it lasted, but big swings like this are very common, as I touched on in my blog entries from the past couple of days. The image below indicates the Euro model from yesterday morning (12z) and just below that image is the GFS model from the same time. The solutions are completely different, with a nor'easter indicated by the Euro, and a dry and cool setup shown by the GFS.The next two images show the same two models 24 hours later (12z this morning), and while both have shifted considerably, they now are in very good agreement. The big u-shaped area over the eastern U.S. is the deep trough, which this time of year translates to a very cold and dry air mass. The shades of yellow, orange, and red within the trough highlight areas of vorticity, and the vorticity pattern is relatively smooth throughout the trough, with very little concentrated maxima. A strong and isolated vorticity maximum, also called a short wave, upper-level disturbance, or vort max, is often necessary to bring our region snow. A strong vort max can create snow through lift directly attributed to the disturbance, and can also result in surface cyclogenesis that strengthens into a nor'easter. The latter was the solution the Euro was teasing us with over the past couple of days, but now neither scenario appears possible without a concentrated upper disturbance.We could certainly see a return to more of a pattern conducive for snow, but the current consistency of the most reliable suite of models makes any big change very unlikely. 'Tis the season for model flip-flopping and looking ahead for our first snow with great anticipation. I'll continue to track this situation closely and will have updates on any potential for another one headed this way. Check back again tomorrow for another update. -Zach

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