UPDATE 4:30 PM: Take a look at a visible satellite photo from this afternoon, linked here, to see why Roanoke and points east are staying in the low 60s with drizzle and fog under dense low cloud cover, while locations to the west are in sunshine and rising into the 70s and low 80s — enough to cook up at least one thunderstorm that has led to a severe thunderstorm warning in parts of Wythe and Grayson counties (current radar linked here). END UPDATE
Kind of a weird day Sunday, though a beautiful one, with Blacksburg having a high temperature (78) that was 7 degrees warmer than Roanoke (71). It wouldn’t be odd to see something like that when Roanoke is socked into fog that clears farther west, or some kind of rain band or storms moving in a way to affect Roanoke but not Blacksburg, but it is quite unusual to see a +7 temperature differential in Blacksburg’s favor when both sites are in sunshine. The trick was that a high pressure system pressing in cooler air held in just a little longer to the east, so Roanoke’s temperature was more stubborn to rise.
Through the next two days, we’re still near a back-and-forth front that has been sliding north and south for several days, and there will be continued upper-air disturbances zipping by. This will keep a chance of showers and storms around that will be hard to time on days that may just as easily be mostly sunny and warm, like Sunday (perhaps very warm on Tuesday, well into the 80s possible). By Wednesday and Thursday, the front finally gets a good shove northward as a warm front and, a very warm, mostly dry air mass takes hold for several days. Expect widespread 80s for the latter half of the week, with a 90-degree reading or two not impossible somewhere in our general region on a day or two. Don’t get used to it though, as there are signs that the pattern may collapse rapidly at some point next week, and turn around to an unseasonably cool scenario for several days after the hot spell. The North Atlantic and Arctic oscillations are projected to dip into a negative phase for early to mid May, meaning more blocking high pressure in the far north forcing cooler air south, and several forecast models show a southward-dipping jet stream developing. Sunday’s computer-generated temperature forecast maps from the Climate Prediction Center (inset at left: 6 to 10 day map at top, 8 to 14 day map at bottom) show the potential temperature contrast vividly. So our short-term flip-flopping may stop for a few days with a warmup later this week, but a big flip-flop back to cooler weather may well occur in the longer term next week.