Increasing moisture was very evident Sunday in the form of an overcast sky of low clouds that kept daytime temperatures cooler than they’ve been in months. Roanoke’s high of 66 was the coolest since May 14, and Blacksburg’s 65 the coolest since June 2, each 10-12 degrees below normal. Lows of 61 and 56 were each 3-5 degrees above normal, also owing to the gathering humidity, but that left the day as a whole still 2-4 degrees below normal. Excluding only Saturday, each day since Sept. 8 has averaged at least a degree below normal in temperature, and it appears likely the majority of days from here to the end of the month will also.
Over the next 2 days, Southwest Virginia will experience its first cool-season type storm system of the fall, with influences from disturbances in both the southern and northern branches of the jet stream. Sunday evening’s infrared satellite photograph, inset at left, captures the upper-level low in Texas very well, pulling a plume of Gulf of Mexico moisture into eastern Texas, Oklahoma and Arkansas, streaming eastward throughout the Southeast and even into southern Virginia. This is a big piece of what is to come, as it will lift buckets of moisture from the Gulf northward over the next 48 hours or so, leading to widespread and locally heavy rainfall over many southern states. The wider view of the same satellite picture, linked here, also captures the second piece of the storm system over the Dakotas. These two systems will join forces near or just north of us by Tuesday to create a strong early season low that will move inland through the East. It appears the heaviest rain in Southwest Virginia is likely to occur late Monday night and during the day Tuesday, with widespread amounts near 2 inches and some higher amounts expected in western Virginia. Strong winds aloft, changing direction and speed with height, also carry some threat of severe storms with damaging winds developing Tuesday, though it appears the greatest threat will be east of the Blue Ridge where warmth and therefore atmospheric instability are likely to be greater. I would not be surprised if there end up being a handful of tornado reports in central and eastern Virginia come Tuesday afternoon.
Late Tuesday or early Wednesday, a cold front will push the rain out, and bring a day of breezy cool behind it in which temperatures probably will not make the 70s most places in Southwest Virginia. Thursday morning looks to be chilly, lots of 40s, maybe a few of the typically coldest spots reaching the mid-upper 30s. Another push of cold, likely stronger than this week’s, arrives around Sunday or Monday. The long-term pattern favors continued reinforcements of cooler-than-normal Canadian air through most of the next couple of weeks.