Mesoscale Discussion 1009
NWS Storm Prediction Center Norman OK
1118 AM CDT Tue Jun 13 2017
Areas affected...Portions of OH/IN/KY/WV/VA/MD/PA
Concerning...Severe potential...Watch unlikely
Valid 131618Z - 131845Z
Probability of Watch Issuance...5 percent
SUMMARY...An isolated damaging wind risk could accompany the
strongest storms across portions of the lower Great Lakes and
middle/upper Ohio Valley region through the afternoon. Watch
issuance will not be needed.
DISCUSSION...Subtle low-level confluence per surface observations
and plan-view depictions of 1-km-above-ground flow per VAD wind
profiles, amid a very weakly capped and moist boundary layer, are
already supporting isolated to scattered thunderstorm development.
The Wilmington and Pittsburgh 12Z soundings sampled around 13.0-14.5
g/kg mean mixing ratios, highlighting the ample moisture
contributing to appreciable buoyancy, with diurnal heating
supporting MLCAPE upwards of 2000 J/kg. Where convective overturning
has not already been abundant, insolation continues to contribute to
steepening low-level lapse rates, allowing MLCAPE, as well as DCAPE,
to increase. As such, convection should experience an overall
increase in coverage/intensity into the afternoon, with the
potential for isolated damaging wind gusts.
Given around 1000 J/kg of DCAPE indicated by the aforementioned
soundings suggesting the potential for strong convective outflow
(with further diurnal gains in DCAPE ongoing), and given moderate
midlevel lapse rates implying some enhancement to convective-scale
upward accelerations, isolated strong to damaging wind gusts will be
possible through the afternoon -- especially with cell mergers and
local outflow amalgamation and as cells collapse. However, deep
shear is very weak -- with midlevel wind speeds generally 15 kt or
less. As such, convective organization will be greatly lacking,
which should limit severe coverage.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 37408365 38078552 38988710 40668725 41378573 41178203
40247969 37917909 36798027 36948228 37408365