2009.07.20
Moisture returns in a torrent, not a trickle
Instead of a gradual transition from the weekend's mild, dry air mass to more of a showery situation, it happened quite suddenly with heavy thunderstorms moving northward along the Blue Ridge this morning. A flash flood warning is in effect until 1:30 p.m. for the Roanoke Valley and points southward along the Blue Ridge (western and central Franklin County, eastern Floyd County southwest Botetourt County in addition to Roanoke, Roanoke County and Salem). Reports of water over roads were received earlier by the National Weather Service in Blacksburg from Mudlick Road in Southwest Roanoke and from Virginia Route 116 near the Franklin-Roanoke County line southeast of the city. There was also a report of up to quarter-sized hail at Hollins earlier this morning. Rainfall amounts of 1-3 inches have been reported in Roanoke and central and eastern Roanoke County.
A flash flood watch has recently been issued for most of Southwest Virginia. There will be a threat of continued showers and storms today as moisture continues to converge along the Blue Ridge, thanks to a slow-moving upper-level disturbance to the west and east winds being drawn off the Atlantic up the slope of the Piedmont and Appalachians.
Latest National Weather Service radar
Rainfall totals at remote sensors in the Roanoke area
Rainfall totals at remote sensors throughout western Virginia
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That was some heavy stuff.
The water level in the Roanoke River jumped nearly three feet in an hour.
Comment by Brandon R. — July 20, 2009 @ 10:47 am
Something to keep an eye on with any redeveloping storms today is severe potential. The Storm Prediction Center has outlined a severe risk area just to our south:
http://www.spc.noaa.gov/products/outlook/day1otlk.html
Wind dynamics are unusually strong, according to SPC forecast tools ... 40-50 knots of deep-layer shear, for instance, with 40 knots often considered to be supercell caliber. Instability is limited because the sun isn't out cooking the lower levels of the atmosphere, but if any big storms develop this afternoon, there's a chance a couple of them could start rotating, especially south and east of Roanoke.
Comment by Kevin Myatt — July 20, 2009 @ 12:30 pm
Storms, some severe, are developing south, east and west of Southwest Virginia's I-81 corridor this afternoon ... but it would appear morning storms and a day of sun-blocking cloudiness has limited instability to the point that no storms are firing in our immediate neck of the woods.
Comment by Kevin Myatt — July 20, 2009 @ 6:32 pm