As expected, the Arctic front is making its push into western Virginia late on this Friday afternoon/early on this Friday evening. The clouds it is causing show up well on the afternoon satellite, at left — just enough clouds that some sites west of Roanoke didn’t quite make 60 today. When exactly the front passes is an academic matter — there have been some prefrontal westerly breezes stirring the leaves around, and the Hydrometeorological Prediction Center was still placing the front to our west just before 5 p.m. on Friday. But in any event, it will be passing very soon with chilly breezes from the Arctic beginning. Dominated by those chilly northwest winds, Saturday, even with some peekaboo sunshine, will have a hard time reaching 40 in most locations west of Roanoke, and probably won’t get above 45 even in the Roanoke Valley and many points south and east. As we’ve noted before, it’ll be blustery for the Virginia Tech-Virginia midday game in Blacksburg. A few snow showers may develop as the northwest winds lift over the Appalachians in West Virginia, and a few of those flakes may drift into western Virginia overnight and early Saturday, but this does not appear likely to be a long-duration or particularly intense upslope snow event, even in the west-facing slopes areas that sometimes get hammered by them. Lows in the 20s are likely by Sunday and Monday mornings, perhaps some teens in sheltered valleys.
This shot of Arctic air will be just that, a quick shot, not the start of a long-term pattern. We’ll get another shot of Arctic air behind a midweek storm system — maybe not quite as intense as this one. But the upper-air pattern remains unfavorable for these cold shots to stick around long. That’s largely because of the persistent Pacific-North American negative (PNA-) pattern that continues to redevelop as strong low-pressure systems continually re-form off the coast of the Pacific Northwest. This European model forecast map (small version inset at left), courtesy of Allen Huffman’s forecast model page, shows yet another strong low off the northwest coast in a week. That low will maintain a a dominant wind flow from west-southwest to east-northeast in the mid to upper levels across the nation during much of the foreseeable future, and this wind flow will bounce these shots of cold quickly out to sea. The mid-term Climate Prediction Center outlooks now favor warmer than normal temperatures over much of the country in both the 6-10-day and 8-14-day slots, as well as continued mostly dry weather in our part of the world as well (6-10-day and 8-14-day precipitation maps linked here). Until this PNA- pattern flips, we will not experience prolonged cold or have much threat of wintry storm systems, though short shots of cold may continue to hit us from time to time. There are some signs on long-range models it may flip about 2 weeks out, but even for some of the world’s most sophisticated computer programs, anything that far out is at least a bit speculative.