You may have noticed on radar, or watching the sky, that storms over Southwest Virginia on this Friday afternoon were actually moving west to east, or southwest to northeast, the way they normally do, instead of the atypical north to south and east to west angles we’ve seen in recent days. That shows that we’re starting to see the end of the “retrograde pattern” that brought a hot dome of high pressure westward across much of the central and eastern U.S., bumping a rainy low all the way from West Virginia to northern Mexico. A trough of low-pressure is starting to dig into the Great Lakes and will eventually dip much farther south, bringing relatively strong winds aloft from the west and northwest. The Global Forecast System model from this morning illustrates the changes going on at 34,000 feet. The first map, linked here, shows three lines pointed in different directions over Virginia with either one or no barb on the back of them — this shows weak, diffuse winds aloft that existed overhead this morning. The second map, linked here, shows the same map on Tuesday morning, with the wind markers all pointing west-southwest to east-northeast over us and about three barbs (30 knots) on most of them. This shows organized wind flow aloft from a direction we usually expect, and while 30 knots (34.5 mph) is not terribly fast for upper-level winds speed compared to what we see in other seasons, it’s pretty darn fast for mid to late July over our part of the country. The blue colors in both of these maps mark the super-fast jet-stream winds, which as they usually do this time of year, are staying mostly over Canada.
What does this mean of terms of weather? We’re going to get a cold front to push in this weekend, and that will create lift with the heat and humidity present, leading to an increase in thunderstorms. Some storms with gusty winds are possible, and locally heavy rain will be a threat. The front, as is typical this time of year, likely won’t be able to push all the way through, but will stall just south of us and maybe flip and flop back and forth before washing out. So it will provide a focus of showers and storms for several days, aided by additional disturbances moving through the strengthened upper-level wind flow. As Sunday evening’s projected weather map from the Weather Predictions shows at left, a few different waves of low-pressure, the L’s, may ripple along the front, each one lifting moisture northward and upward, stirring up some more showers and storms. Don’t expect constant pouring rain this weekend, but many will see showers and storms sometime on Saturday, and almost everywhere in Southwest Virginia will probably get at least a little wet by late Sunday. Daytime temperatures will back down from the upper 80s-low 90s that have been common (and will likely occur again Saturday)– subtract 7-10 degrees off those by early next week. Nighttime lows, however, may not drop much beyond the upper 60s-low 70s we’ve been seeing, because high dew points will hold temperatures up at night.
FloydFest interests: Late next week’s weather will depend on the fate of another cold front. Some forecast models push it all the way through to the Gulf Coast, bringing a shot of cooler, drier air for next weekend. Count me skeptical on that, as the Carolinas tend to be the graveyard for cold fronts this time of year in general and this summer in particular, which would lead to a very different showery, humid forecast for us. But there is at least some hope of a relatively dry weekend for FloydFest (and any other outdoor activities) IF this front can push through. If that occurs, you may buy 2 or 3 days of nice weather with 1 day of potentially strong storms. Too far out for details. For now, plan on taking rain gear if you go.