Mesoscale Discussion 0695
NWS Storm Prediction Center Norman OK
1258 PM CDT Thu May 11 2017
Areas affected...Portions of KY...extreme southern IL...extreme
southern IN...southern WV...western VA
Concerning...Severe potential...Watch unlikely
Valid 111758Z - 112030Z
Probability of Watch Issuance...20 percent
SUMMARY...Strong to locally severe thunderstorms may move across
southern parts of the Ohio Valley region spreading toward the
Appalachians through the afternoon. Isolated damaging wind gusts
should be the primary concern, and present indications are that
Watch issuance is unlikely.
DISCUSSION...Convection is deepening from southern IN into adjacent
KY, ahead of an MCV emanating from earlier convective activity over
the southern Plains, and along a cold front moving southeastward.
The pre-frontal air mass is characterized by modest instability amid
lower/middle 60s dewpoints, with MLCAPE around 750-1000 J/kg and
little capping. As such, with pre-frontal insolation yielding
steepening low-level lapse rates, convection will likely gradually
increase while spreading across the region during the next several
hours.
Mid-level lapse rates are not particularly steep, and related upward
convective accelerations should be modest, yielding only a gradual
intensification of convection. Nevertheless, 40-55 kt of effective
shear is present across the area, with unidirectional/westerly flow
sampled by area VAD wind profiles in the lower/middle troposphere.
As a result, small, semi-organized convective clusters will spread
eastward with isolated damaging wind gusts possible, and perhaps
very sporadic marginally severe hail. However, flow in the lowest
couple of kilometers is rather modest (20 kt or less), which could
limit the propensity for convective momentum transport to bolster
surface wind gusts. Furthermore, the lack of stronger buoyancy will
limit updraft/downdraft strength. These factors cast considerable
doubt regarding a greater-coverage severe risk, and lacking
low-level/deep ascent should also limit severe coverage. Regardless,
convective and environmental trends will continue to be monitored.
..Cohen/Guyer.. 05/11/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...RNK...RLX...MRX...JKL...LMK...PAH...
LAT...LON 36778555 36858735 37038889 37488925 38118866 38218689
38108414 37548132 36868088 36658162 36778555
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