Thunderstorms, unseasonably cool temperatures and very hot temperatures appear to be a major part of our week ahead. What doesn’t appear likely for Southwest Virginia is a direct impact from Tropical Storm Debby … but even that has at least a slight chance to change.
First, Sunday and Monday. After Saturday’s sunny, warm day with low dew points, moisture will be rebuilding as winds turn southerly Sunday. Daytime heating, terrain effects, an weak upper-level impulse and, by Monday, and approaching cold front will ramp up the chance of showers and thunderstorms each of those days. Some localized severe weather — high winds, mainly — and heavy rain are possible, but as is typically the case in summer, areawide coverage of such impacts is not expected.
That cold front moving through on Monday will bring a subsantial punch of cool, dry air — possibly so much that Tuesday has highs in the 70s across much of Southwest Virginia, with widespread lows in the 50s and perhaps even a few 40s in outlying areas. (Map at left is Tuesday’s projected highs from Hydrometeorological Prediction Center). The jet stream trough, or southerly dip, pushing the front through will temporarily push back the heat dome building to our southwest. Perhaps an even more important issue is whether the jet stream will dip far enough south to nudge Debby eastward. So far, the National Hurricane Center is siding with a large number of foreign forecast models (and against several runs of the American GFS model) in expecting the trough to slip north of Debby, allowing it to slide westward toward the western Gulf later in the week. If the trough can affect Debby’s path and push it more toward Florida and the Southeast U.S., that’s where our slight chance of having a direct impact in Southwest Virginia would lie. Slight, and getting slimmer, I would say.
Compare the colors and numbers of Tuesday’s high temperature map above to the map for Friday’s projected high temperatures at left. Warmth is expected to slowly rebuild in our region Wednesday and Thursday as the influence of Canadian air behind the front weakens and the hot high pressure sytem begins building overhead from the southwest. That high is an important player for Debby, too, as its clockwise circulation is expected to slowly push Debby westward, and also provide calm air aloft that would allow Debby’s eyewall to strengthen rather than get sheared off as would happen with strong jet stream flow or the influence of an upper-level low pressure system. In turn, while hurricanes tend to be guided more by high-pressure systems than the other way around, Debby’s presence in the Gulf may nudge the core of the hot high a little more north and east toward us. So in a sense, we may pay for missing a direct impact of Debby with temperatures well into the 90s by Friday and Saturday.
Linked here is a satellite image from newly dubbed Tropical Storm Debby early this evening. The circulation is visible on the image, but as you can see, the heavy clouds where most of the rain is falling is well east of the circulation (some of it already affecting Florida). In time, we’ll probably see more storminess develop aroudn the circulation center, and a gradual intensification as it drifts north, then west. Debby — the earliest “D” storm in the Atlantic on record, a full 2 months ahead of when a “D’” storm would emerge in a “normal” hurricane season — has a chance to be a significant to major troublemaker somewhere along the Gulf Coast. If you travel plans in that direction later this week, be ready to change them.