Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 231536
SWOMCD
SPC MCD 231536
NCZ000-VAZ000-SCZ000-TNZ000-GAZ000-231800-

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
evolving.

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

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...AKQ...MHX...RAH...ILM...RNK...CAE...GSP...MRX...
FFC...

LAT...LON   35318514 36488146 36717775 35547782 34317944 33588275
            34078474 35318514




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