Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 221713
SPC MCD 221712

Mesoscale Discussion 1394
NWS Storm Prediction Center Norman OK
1212 PM CDT Sat Jul 22 2017

Areas affected...Portions of MD...DE...northern VA...southern
PA...Washington DC

Concerning...Severe potential...Watch unlikely

Valid 221712Z - 221945Z

Probability of Watch Issuance...20 percent

SUMMARY...A small, remnant convective system will spread across
parts of the Mid-Atlantic through the afternoon, posing a risk for
at least isolated wind damage. While present indications are that
Watch issuance is unlikely, convective and environmental trends will
continue to be monitored across the area.

DISCUSSION...The leading convective line of a persistent MCS is
crossing the Appalachians, and should continue along its eastward
track across portions of the Mid-Atlantic region through the
afternoon hours. This activity lies well in advance of a mid-level
speed maximum crossing the lower Great Lakes region, and principally
south of a broader belt of enhanced westerly flow aloft.

The LWX VAD wind profile is indicating only around 10-20 kt of flow
in the 1-2-km layer, suggesting that convective momentum transport
will be quite limited, as the remnant system maintains some
semblance of pseudo-organization amid modest 25-30 kt of effective
shear. Regardless, diurnally strengthening baroclinicity along the
gust front owing to surface heating ahead of the convective line has
resulted in a slight uptick of convective cores, as convective
inflow destabilizes. With surface temperatures breaching 90F amid
dewpoints in the lower 70s, adequate buoyancy may exist for
sufficiently robust convective cores to produce sporadic wind damage
eastward toward the Atlantic Coast.

Modest deep shear, the lack of a more substantial convectively
driven cold pool, weak low-level flow, and weak mid-level lapse
rates should all limit the severe risk. Regardless, if a stronger,
convectively-driven cold pool were to eventually evolve from
convection as it spreads east of the Appalachians and encounters
steeper low-level lapse rates, prospects for Watch issuance could

..Cohen/Grams.. 07/22/2017

...Please see for graphic product...


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