Severe Storm Outlook Narrative (AC)
Issued by NWS
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.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 33248481 34018640 34368744 35178848 35628860 35968831
36018817 35978724 35898638 35398417 35168321 34908279
34618271 34158281 33668313 33338382 33248481