Friday’s weather will continue to be breezy with highs a little warmer than Thursday, upper 40s and low 50s. Low 60s still look to be a pretty good bet one or both days weekend, at least from Roanoke south and east, with rain likely early in the coming week, and cooler temperatures again beyond that. More on the next week’s weather this weekend.
There’s a lot of buzz in the D.C. area about how the snowstorm forecast was a huge bust there — minimal amounts in the central city when various forecasts by experienced meteorologists ranged from 3-6 inches on the low end to 8-14 inches on the upper end. Of course, snow accumulation picked up a bit in D.C.’s western suburbs, and the overall forecast for a major winter storm affecting the Mid-Atlantic region was generally accurate, as the area expected to be most heavily affected — the Shenandoah Valley and Blue Ridge region generally along and north of I-64 — was indeed hammered by 6-24 inches of heavy, wet snow.
Southwest Virginia area forecasts from various sources generally settled toward the correct idea that the heaviest snow would be to the north near I-64 with lighter snow amounts south to near the U.S. 460 corridor and little or nothing to the south. But ahead of the game on that shift in thinking on the winter storm as early as the previous weekend (as shown on the map he posted at left) was Zach Robinson, a Virginia Tech geography student from Fancy Gap who puts some of his thoughts on his “Blue Ridge Weather Blog,” and often posts comments and links on Weather Journal. (And I will get the link to his blog added to regional weather blogs on the right margin of this page).
Zach had an interesting online discussion with famous meteorologist Larry Cosgrove, who pointed out that the “blocking” pattern in place was far from perfect. Cosgrove pointed out to Zach that blocking high pressure over Greenland had shifted somewhat eastward and been replaced by a low-pressure shortwave, and that high pressure was not showing signs of recovering over Greenland and eastern Canada behind the shortwave. The result was that it was not a true Greenland block that we expect to see during the more persistent cold outbreaks and large winter storm threats for our latitude. The “50-50″ low near Newfoundland, a common feature in many Southwest Virginia winter storms acting as a “traffic cop” to guide a storm system farther south, also drifted somewhat eastward as a result. The butterfly’s wings were flapping, and it fluttered a couple of factors just a little out of place for the potential large scale winter storm hammering all of our region.
Zach said his conversation with Cosgrove took place after he had already started to back off the big snow threat, but it expanded his knowledge and confirmed some of his thinking, which is summarized by Zach himself below:
“Why was I so adamant on this being a relatively minor event for most of our region, and what did I see early on that others didn’t? Very early on, a few weeks ago I was very skeptical on my blog and Facebook page (Blue Ridge Weather), that a cold pattern would actually setup. My argument was the pattern over the Pacific was simply too strong and too fast to allow any major blocking to setup. … So going into last week, I had my doubts that a true cold pattern would take shape and hold. …. Using this belief, I had a sneaking suspicion of two things. One: The energy diving south out of Canada would enter further EAST than originally forecast. Consequently, the energy would have to take a steeper angle to get to our latitude, and given the lack of significant blocking I didn’t see that happening. I thought the models would adjust North some. The amount of amplification in the Jet Stream to get the energy to dive into Georgia/South Carolina was just simply not there. 2) From this, I believed that the initial surface low would also ride a bit further west into the Ohio Valley, because I believed (again due to the lack of a real block) that the 50/50 low would escape to the East, allowing the initial energy to ride into the Ohio Valley. Using basically these two criteria, I thought that the energy would not develop far enough South to hit our area with a widespread crippling storm.
Backing me was my knowledge and history of storms of these types. To get to the point to have the storm re-develop far enough to the South, we would have to be in a very high amplitude pattern, and we simply were not. A bit of it too, was my gut. I’m not going to lie it was a very difficult call to make, because the models we’re screaming something different, but I just had this feeling that they would adjust. The driving reason behind that I would attribute more to my knowledge and history of patterns in this area, rather than to my understanding of the blocking pattern of the Northern Hemisphere. I had seen storms growing up do this exact same thing. The pattern to me screamed Shenandoah Snowstorm, and not Southwest Virginia Snowstorm. 9/10 snowstorms for us seem to not involve some sort of energy transfer. “
So there you have it from a young weather forecaster who ended up looking pretty good in how it all played out.