Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 211853
SPC MCD 211853

Mesoscale Discussion 0302
NWS Storm Prediction Center Norman OK
0153 PM CDT Tue Mar 21 2017

Areas affected...Parts of middle into southern Tennessee...northern
Alabama and Georgia...far western Carolinas

Concerning...Severe potential...Watch likely

Valid 211853Z - 212130Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms are expected to evolve rapidly this
afternoon across multiple regimes from TN across northern AL, GA,
and the western Carolinas. Large hail and damaging winds will be

DISCUSSION...Surface analysis shows a trough extending westward from
NC into southern TN, and across northern AL and GA. Strong heating
continues in this axis, where moisture and instability are also
maximized. Pressure falls also persist at a rate of up to 2mb/hr.
Visible satellite imagery shows substantial CU developing, and
scattered cells are expected to form over the next few hours. In
addition, an outflow surge is currently exiting southeastern MO and
moving into western TN, with substantial pressure rises behind. This
feature will also initiate new storm development as it enters a
warmer and more unstable environment to the east.

Although shear profiles are not particularly strong, mean winds are
sufficient for forward-propagating severe clusters. Further,
thermodynamics should compensate for the lack of shear. The 18Z BNA
and FFC soundings both show impressive midlevel lapse rates in
excess of 8 C/km with MUCAPE on the order of 1500-2000 J/kg.
Downdraft/DCAPE values are also relatively large owing to the steep
lapse rates and dry air in the EML.

The ample instability and lapse rates should support hail into the
1.50 to 2.00" range, with increasing damaging wind threat as storms
increase in coverage and outflow production is maximized.

..Jewell/Hart.. 03/21/2017

...Please see for graphic product...


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