|Mesoscale Discussion 1258|
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Mesoscale Discussion 1258
NWS Storm Prediction Center Norman OK
0235 PM CDT Fri Jul 07 2017
Areas affected...southeast OH...southwest PA...much of WV...western
and northern VA
Concerning...Severe Thunderstorm Watch 402...
Valid 071935Z - 072100Z
The severe weather threat for Severe Thunderstorm Watch 402
SUMMARY...Swaths of wind damage from isolated 50-65 mph gusts are
likely west of the spine of the Appalachians. It is unclear how
much of a severe risk will develop east of severe thunderstorm watch
402. An additional watch is possible (50%).
DISCUSSION...Radar mosaic shows a forward propagating squall line
with a bowing segment moving southeast at 40 kt over far
southeastern OH with a MCV probably beginning to develop in
east-central OH. Surface observations from central OH have measured
gusts in the 35-50 kt range during the past 1.5 hours. Subjective
surface analysis indicates a low-level moist axis extending
northeast from northern Ky along the OH River Valley into southwest
PA with 68-73 degree F surface dewpoints. A slightly drier airmass
(less buoyant) is located over the Shenandoah Valley with lower 60s
dewpoints but 0-3 km lapse rates have steepened.
Current thinking is the squall line will move into the eastern
portions of severe thunderstorm watch 402 over the next few hours.
An EXtension-in-Area (EXA) to the watch will likely be needed given
the airmass recovery from Cumberland county, MD southward into
Pocahontas county, WV. Although short-term model guidance suggests
an overall weakening in the convective line from the Cumberland
county to Pocahontas county corridor, the airmass has destabilized
east of the higher terrain. The convective line will probably be
maintained and may yield a localized to isolated risk for wind
damage during the early evening across western and northern portions
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 40238094 39537855 38557753 37357875 37208012 37668138
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