SPC MD 1544

MD 1544 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF THE MID MISSISSIPPI VALLEY

Mesoscale Discussion 1544
NWS Storm Prediction Center Norman OK
0329 PM CDT Mon Aug 21 2017

Areas affected...Portions of the mid Mississippi Valley

Concerning...Severe potential...Watch unlikely 

Valid 212029Z - 212200Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated damaging gusts and large hail may occur with the
strongest storms through this evening. However, watch issuance is
not currently expected.

DISCUSSION...Scattered thunderstorms continue to develop along an
outflow boundary stretching eastward from the St. Louis metro area
this afternoon. Along and south of this boundary, ample heating has
combined with very moist low levels (e.g., surface dew points in the
upper 70s) to promote MLCAPE values upwards of 3500 J/kg, despite
unimpressive mid-level lapse rates. Modest mid-level westerlies are
offering around 30 kt of effective shear, sufficient for
multicell/transient supercell modes capable of isolated damaging
downbursts and severe hail. However, deep-layer flow oriented
parallel to the boundary will likely promote continued cell
mergers/destructive interference, limiting the overall threat some.
Additionally, the continued southward advance of the outflow
boundary may favor persistent undercutting of updrafts. These
factors should preclude a more organized threat, such that watch
issuance is not presently expected.

..Picca/Grams.. 08/21/2017

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

ATTN...WFO...IND...PAH...ILX...LSX...

LAT...LON   39119142 39389116 39478944 39398778 39098718 38348730
            38058797 38098955 38359080 38829128 39119142 

Read more

from SPC Forecast Products http://ift.tt/12TIBZb