If you thought the last couple of days were cool for mid-August in Southwest Virginia with 70s highs, just wait til the weekend likely brings 60s highs. The cooler weekend temperatures, however, will not come with sunshine, but with cloud cover, patchy fog, drizzle and intermittent periods of rain. What we have setting up is the common “wedge” effect with high pressure to our northeast turning surface winds to the northeast, east and eventually southeast, pulling in moisture off the Atlantic Ocean and banking against the higher terrain of western Virginia (labeled map linked here represents Sunday morning on Friday’s 12Z GFS model) We began seeing a touch of this today with some persistent cloud cover in the higher terrain south of Roanoke. For the Roanoke and New River valleys, Friday will be the transition day between the sunny, dry, summer-defying cool weather of the past two days and the cloudy, showery, dank, cool weather of the weekend, with clouds and moisture increasing from south to north. Some showers may sneak into the counties closer to the Virginia-North Carolina border during the day Friday, and perhaps as far north as Roanoke by Friday evening. Weekend rain chances will be augmented by upper-level flow from the southwest, curving around a low-pressure trough over the lower Mississippi River Valley. That will carry warm, moist air from the Gulf of Mexico up and over the trapped cool, damp air at the surface, and also carry impulses northward to squeeze out some heavier periods of rain amid the drizzly, showery stuff. A widespread flooding situation is not expected, and rain totals generally aren’t expected to be all that heavy in much of our region, but some locations on the eastern slopes of the mountains particularly south of Roanoke may need to watch for some locally flooding downpours by the latter part of the weekend, especially considering how wet it’s been this summer.
Tropical Storm Erin formed in the far eastern Atlantic late Wednesday, but of more concern for the United States in the next several days is the system near the Yucatan Peninsula that will likely eventually drift into the Gulf of Mexico. Much remains uncertain about this system’s path and evolution, so all interests in the southern and eastern U.S. need to at least keep an eye on it. Long-term over the next couple of weeks, there are signals of growing high pressure over much of the northern U.S. that could lead to an expansion of more summerlike heat over much of the lower 48. Could it be that late August/early September hot spell I guessed might happen earlier in this soaking summer? Time will tell.