Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 231536
SPC MCD 231536

Mesoscale Discussion 1407
NWS Storm Prediction Center Norman OK
1036 AM CDT Sun Jul 23 2017

Areas affected...Portions of the Carolinas...southern VA...north
GA...and east TN

Concerning...Severe potential...Watch unlikely

Valid 231536Z - 231800Z

Probability of Watch Issuance...5 percent

SUMMARY...Thunderstorm coverage and intensity will gradually
increase through the afternoon, with isolated strong wind gusts
capable of producing tree and power-line damage. Watch issuance will
not be necessary.

DISCUSSION...Low-level lapse rates are steepening in the vicinity of
the southern Appalachians to the Piedmont. This is in response to
insolation to the south of persistent, convectively-generated,
multi-layered cloud decks and surface outflow. Convection will
likely continue to blossom along the periphery of this outflow and
nearby differential-heating zones, and along preceding gravity waves
across middle and eastern TN. Additional convection will develop and
intensify in response to strengthening orographic circulations over
the Appalachians, and perhaps a weak lee trough across the adjacent
Piedmont. Cumulus agitation and isolated thunderstorm development
are already ongoing across portions of the region -- owing to
initial diabatic heating of a moist, uncapped boundary layer, with
surface dewpoints in the lower/middle 70s.

All of the aforementioned convection will gradually spread eastward
to southward through the afternoon, while intensifying as it
encounters around 2000-3000 J/kg of MLCAPE -- aided by moderately
steep lapse rates around the 700-600-mb layer based on the
Greensboro NC and Nashville TN 12Z soundings. A few vigorous
updrafts may ensue, with around 15 kt of mid-level westerlies
supporting a few small-scale, loosely-organized multicell clusters.
Collapsing convection and related enhancements to downdrafts, and
enhanced storm-scale vertical circulations with merging cold pools,
may support isolated strong wind gusts capable of producing damage
to trees and power lines. DCAPE increasing to around 1100-1400 J/kg
will facilitate such potential. The strong buoyancy may also support
small hail during incipient updraft phases. However, weak deep shear
and ascent should prevent a more substantial severe risk from

..Cohen/Grams.. 07/23/2017

...Please see for graphic product...


LAT...LON   35318514 36488146 36717775 35547782 34317944 33588275
            34078474 35318514 is the U.S. government's official web portal to all federal, state and local government web resources and services.