Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 121542
SPC MCD 121542

Mesoscale Discussion 0036
NWS Storm Prediction Center Norman OK
0942 AM CST Thu Jan 12 2017

Areas affected...Portions of OH...southeastern IN...northern
KY...western PA...western WV

Concerning...Severe potential...Watch unlikely

Valid 121542Z - 121815Z

Probability of Watch Issuance...5 percent

SUMMARY...Showers and thunderstorms crossing the middle Ohio Valley
region and vicinity may produce locally strong wind gusts through
the afternoon hours. A few marginally severe wind gusts cannot be
ruled out, and the addition of a Marginal Risk area is planned
across portions of the area and vicinity for the 1630Z Day-1
Convective Outlook. However, Watch issuance is not anticipated.

DISCUSSION...The 12Z soundings at Wilmington OH and Pittsburgh PA
sampled strong 850-mb southwesterly flow -- on the order of around
60 kt -- accompanying a LLJ overlying the local area. The related
return of marginal boundary-layer moisture -- e.g. surface dewpoints
around the middle 50s -- continues ahead of a sharp cold front
analyzed from northwest OH to southern IL. As the cold front
continues to advance into the modestly moist/marginally unstable air
across the middle OH Valley region and vicinity, and weak
pre-frontal isentropic ascent continues, bands of showers and widely
scattered thunderstorms will spread eastward/northeastward through
the afternoon hours. Convective sustenance has already been noted
across parts of IN. This activity will likely grow in areal coverage
and intensity as weak boundary-layer destabilization occurs eastward
amidst pockets of weak diurnal surface-layer heating. Convective
momentum transport -- augmented by the frontal circulation -- may
support locally strong wind gusts. A few marginally severe wind
gusts cannot be ruled out. Widespread cloud coverage ahead of the
front will limit boundary-layer destabilization, mitigating a more
substantial severe risk.

..Cohen/Kerr.. 01/12/2017

...Please see for graphic product...


LAT...LON   39518578 40368438 41278121 41028013 40348045 39218201
            38368505 38538613 39518578 is the U.S. government's official web portal to all federal, state and local government web resources and services.