UPDATE 9AM, 5/13: As expected, a flash flood watch has been issued for part of our region, generally from Roanoke southwestward along Interstate 81 and southward along the Blue Ridge into northwestern North Carolina. It is effective from 9 p.m. tonight to 9 p.m. Tuesday night. So far we’ve started Mother’s Day with a little bit of sunshine in the Roanoke Valley and nearby areas. Moisture will gradually build today with showers encroaching from the south and west later in the day into this evening. END UPDATE
UPDATE 1 AM, 5/13: Saturday night’s rainfall projection fls through Tuesday evening from the Hydrometeorological Prediction Center show rainfall may top 3 inches in some locations from the slow-moving upper-level low that will begin spreading showers into Southwest Virginia during the day Sunday, with heavy rain possible overnight Sunday into Monday. Don’t be surprised to see the National Weather Service in Blacksburg issue flood watches during the day Sunday for some or all of our region. You can follow the advance of rainfall and its potential for the region on the Radar /Future Cast link at right. (Just ran the Future Cast for rain accumulation, and it concurs with HPC, with about 3 inches of rain for Roanoke by 1 a.m. Tuesday). END UPDATE
It would have been hard to create a prettier day for Virginia Tech’s commencement Friday than the one that occurred (well, OK, I know some folks would have liked it warmer, especially after a morning low of 36 in Blacksburg and kind of a nip in the breeze even as it pushed into the 60s). Saturday will be similar, though a bit warmer, over most of Southwest Virginia (far southwest areas west of I-77 may get a few showers). But Mother’s Day — and especially the day after — are likely to be a different story. A slow-moving upper-low bringing rain and storms to Texas is going to dawdle east and northeast over the next few days. That will supply a lot of Gulf of Mexico moisture, squeezed out by upper-level impulses and our region’s higher terrain. The result will a period of significant to downright heavy rain, possibly exceeding 2 inches in many places by Tuesday. Mother’s Day is a bit of a question mark — the best chance of showers will be west of Interstate 81, as moisture slowly builds ahead of the storm system. By sometime in the afternoon or evening, rain will become widespread, and periods of rain are expected to continue into Monday and at least some of Tuesday.
Having a slow-moving Southeast U.S. upper-level low deliver a period of significant rain has become a tradition connected to the departure of the Virginia Tech storm chase team for the Plains states. We’ve seen this happen with amazing regularity the day we leave or a few days thereafter, and the circulation patterns leading to rain here often dry out the central U.S. for a few days. We’re planning to leave Tuesday, likely headed for the Northern Plains as moisture and jet energy slowly recharge in that region by next weekend.