Tracking the Cold & Chances for Snow

I awoke this morning to the rumbling of an idling oil truck in the alley behind my home, perhaps a sign that the word has spread that colder days are ahead and it's time to fill up. The deep trough that will dig into the eastern U.S early next week will bring an air mass with a real bite into the region. It's likely that much of central and northern Virginia will see highs remaining in the upper 30s, which isn't at all unusual for the first week of January, but an abrupt change from the relatively mild fall and winter we have seen to this point. The overnight lows during this period will fall into the upper teens and low 20s. As I mentioned in my post from yesterday, the chance for snow with this pattern change appears slim to none, with only a slight chance of seeing a quick burst of light snow early Monday. If you're scheduled to be at work that day, you'll be working. We'll have another possibility for snow later in the week that looks pretty interesting. Both the GFS and Euro operational models are indicating the presence of an upper-level wave that will dive south out of the upper Midwest and move just south of Virginia on Thursday. This isn't an ideal setup by any stretch for snow, but it's the type of scenario that can become more favorable with time. You'll note my confidence in seeing anything isn't very high by the 20% chance I have in my 7-day forecast. I'll peruse the model suites again this evening and track the movements of birds and small rodents in the morning. Check back for another update tomorrow, and if you haven't already done so, click here to drop by my facebook page and click the "like" button. Have a great Friday. -Zach

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

Our Potential for Snow: Part 2

The possibilities for what happens next week still range from sunny and mild to a heavy snow, with one medium range model staying bullish on developing a Nor'easter for the Mid-Atlantic and Northeast. I'm big on consistency when it comes to longer term forecasting, but each model seems consistent in its own way. The GFS continues to show nothing, while the Euro is going gangbusters. The Euro is many times the big winner in medium range solutions, but I've seen it be consistently wrong on a system before. So with a good measure of cautiousness, and a heck of a lot of optimism, I'll put forth my expectations for next week based only on what the Euro is showing. After all, what's the fun of blogging about a non-event? Yesterday I mentioned the possibility of a big snow, citing the pattern change the Euro was depicting. There has been a change between yesterday's model run, and the runs from last night and this morning. That change?...colder and snowier to put it succinctly. The 500 mb low is slower and farther south and the surface low develops a little farther offshore. The overall amount (QPF) of moisture has increased, and more of that moisture falls into an air mass supportive of snow. So for you snow lovers, it continues to look better and better for a decent snow in the Jan 3-4 time frame. The next run of the Euro will begin a little after midnight. Check back here for my analysis. -Zach