UPDATE 11:30 PM, 3/23: Weekend rain, front won’t end warmth, but may stop daily challenges to record books
UPDATE 11:30 PM, 3/23: Intermittent showers are expected to continue overnight across Southwest Virginia. There is potential for strong to severe storms on a Saturday once the sun pops out when a dry slot moves in during the day, destabilizing the atmosphere with surface warming that could lead to strong updrafts into colder air aloft with the approaching upper-level low. Exactly where the biggest severe weather threat will be in the Carolinas or Virginia remains a bit in question. I’ll plan to put up a new blog post sometime Saturday morning taking a closer look at any severe threat. END UPDATAE
UPDATE 5:20 PM: Roanoke has its first record high of the March hot spell: 84 degrees, breaking the previous March 23 record of 82 set in 2007. Today’s high is 24 degrees above normal and equivalent to normal nigh for June 15. Blacksburg reached 78 for the second day in a row, again 2 degrees short of a record. Showers and thunderstorms are building in from the southwest. Some heavy rain and gusty winds are possible with the stronger storms this evening. Latest National Weather Service-Blacksburg radar linked here. END UPDATE
High temperatures on Thursday of 80 in Roanoke and 78 in Blacksburg missed daily records for March 22 by 4 and 2 degrees, respectively. Friday provides one more opportunity, with forecast highs expected to be near Roanoke’s March 23 record of 82 degrees set in 2007 and Blacksburg’s record of 80 set in 1968. It may come as a little surprise that, as warm as it’s been on a consistent basis, Roanoke has yet to set a single daily record high temperature this month (unlike Blacksburg, that has set 3). Friday may be the final chance for several days.
We finally have something significant weatherwise to talk about other than potential record highs and scattered afternoon summerlike pop-up storms. The massive, slow-moving upper-low in the central U.S. — the big pinwheel on the satellite photograph at left — will begin to affect our weather by Friday evening. Its broad circulation will pull Gulf of Mexico moisture in several bands, and that will lead to intermittent periods of rain and some thunderstorms Friday night and Saturday, lingering into Sunday as the cold upper-air pool at the center of the upper-low drifts overhead. It’s always difficult to forecast the timing and amounts of rainfall in a broad upper low like this, but national forecasters are projecting widespread amounts near an inch through Sunday evening as slow-moving bands of thick moisture are pulled through the region, with southeasterly upslope flow perhaps enhancing lift and squeezing out a little more. The upper level low may also pull through some dry slots. It is possible one of these dry slots arrives Saturday afternoon, allowing sunshine to destabilize the atmosphere a little. Warmth, plus moisture, plus strong winds aloft created by the upper-level low may lead to a risk of severe storms with hail, strong winds and possibly even isolated tornadoes on Saturday, especially east of the Blue Ridge. At this time, a major outbreak of severe weather is NOT expected, but anytime it’s been as warm as it has been, there tends to be a heightened risk of stronger storms.
The air following a front this low will pull through by Sunday is greatly modified, with no real Arctic connection, so temperatures will only retreat slightly behind the front. We may have a day or two — Sunday/Monday, perhaps — with highs in the 60s (low 70s if there is lots of sun) and lows in the 40s. The overall warm pattern rebounds next week, at least back to widespread 70s for highs (maybe not as many low 80s), but there continues to be signs the core of it shifts westward and weakens somewhat, as shown in the 8 to 14-day temperature map from the Climate Prediction Center, with much of Virginia out of the red colors in the white “equal chances” of warm, cold and normal area. A westward shift in the mean position of the upper-level high-pressure ridge that has caused the prolonged March warmth may also allow its clockwise circulation to pull down a few more cold fronts into the East in the long-range — the Northeast U.S. may be at particular risk for a post-warmth freeze, with no clear indication yet that level of cold air would extend as far south as Southwest Virginia. For now, there is no signal of a major pattern change, just some indications that summer-in-March will undergo some gradual erosion and won’t hold on at full strength throughout April.