UPDATE 12 NOON: Severe storm risk increases for today; Roanoke may hit 100 by Saturday, as it gets hotter before it gets cooler
UPDATE 12 NOON: Severe thunderstorm watch until 7 p.m. Roanoke and westward/southwestward. Clusters of storms continue to move southward through West Virginia and the I-77 corridor of Southwest Virginia. They may expand and/or intensify in peak afternoon heating. Click on Radar / Future Cast in right margin for latest location of storms. END UPDATE
UPDATE 8:45 AM: Western half of Virginia just upgraded to a slight risk of severe weather today by the Storm Prediction Center. Concern is upper-air cold pool associated with overnight storm cluster in Great Lakes drifting southward into the Appalachians today, which could lead to clusters of strong to severe storm with afternoon heating. Also note the link added above for the National Weather Service-Blacksburg’s review of the June 29 derecho. END UPDATE
UPDATE 8:30 AM: A small storm cluster just east of Beckley, W.Va., and a larger storm cluster in northern Ohio are drifting southward and may affect some or all of Southwest Virginia today, with some clouds and outflow breezes if not directly. Forecast models favor locations west of I-77 for more organized storms today, with pop-up afternoon/evening storms possible anywhere. This may hold afternoon temperatures a few degrees cooler than they otherwise would have been today. Some storms may become strong to severe with locally strong winds and hail possible. Latest radar linked here. END UPDATE
The core of the “heat dome” has relocated from the Southeast U.S. to the Midwest — St. Louis/Chicago area. You can see its location fairly well from the excessive heat warnings/heat advisories on the map linked here. It is expanding eastward again into the Ohio Valley and Great Lakes, and toward us. The result will be another push of very hot temperatures — not that they’ve cooled down a whole lot — aided once more by those northwesterly downsloping winds that aid in heating locally. Those breezes coming down the mountain slopes compress, adding a few degrees to the afternoon temperatures — Roanoke is often a major bullseye for this effect, lying on flatter terrain east of the slope of Catawba and Fort Lewis mountains. As a result, 100-degree temperatures are again possible any of the next three days in Roanoke, always depending on how much and where any afternoon showers and storms may form. A small storm this evening dropped some hail on the east side of Roanoke, and kicked out enough cooling outflow breezes to drop the official Roanoke Regional Airport weather station from a high of 97 degrees to 83 by 8 p.m. It probably didn’t deliver enough rain over most of the Roanoke Valley to affect Thursday’s temperatures all that much. Roanoke has hit 97 on four of the last seven days, going higher on two days (Friday’s 104 and Saturday’s 102) and cooler once (Monday’s 94). 97 may well be the floor of what to expect Thursday through Saturday in Roanoke, with widespread 90s across Southwest Virginia below 3,000 feet (including Blacksburg) and some 100-105 readings in lower elevations to Roanoke’s south and east.
The weather pattern is changing, though. The location of the heat dome has moved the main steering winds for major thunderstorm complexes to the north. The convection that develops and moves around a strong summertime high pressure system is sometimes called the “Ring of Fire.” We were in the middle of the “Ring of Fire” last Friday when the derecho roared through, but now it appears that large storm complexes rocketing toward us from the northwest will be less likely (though not entirely zero chance, with some northwesterly component to the upper winds continuing) through at least Saturday. (There is one storm cluster in Ohio tonight that may have some chance of working southward, perhaps into West Virginia later tonight, close enough for Southwest Virginia to keep an eye on.) A larger change appears to be in the works for next week, as the core of the heat dome is expected to shift all the way to near the West Coast by the middle of next week. Follow the shift of the yellow-green colors, depicting above-normal temperatures from Friday to Sunday to Wednesday on the European forecast model. The Wednesday map linked again here leaves a little dab of blue “below-normal” coloring on western Virginia amid a sea of white, signaling near-normal temperatures. I don’t think we’re headed for a major cool spell next week, but some days of 80s highs and 50s-60s lows appear likely. A cold front arriving Sunday will introduce the change — but also could trigger some strong thunderstorms, continuing into Monday.