Severe Storm Outlook Narrative (AC)
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288
ACUS11 KWNS 200645
SWOMCD
SPC MCD 200645
ILZ000-KYZ000-TNZ000-MOZ000-ARZ000-200815-

Mesoscale Discussion 0797
NWS Storm Prediction Center Norman OK
0145 AM CDT Sat May 20 2017

Areas affected...Southeast Missouri...northeast Arkansas...southern
Illinois

Concerning...Severe potential...Watch likely

Valid 200645Z - 200815Z

Probability of Watch Issuance...80 percent

SUMMARY...A threat of damaging wind, a brief tornado and marginal
hail is expected to develop eastward toward the Mississippi and
lower Ohio Valleys tonight.

DISCUSSION...The leading edge of a line of storms driven by outflow
continues to move eastward across southern MO and northwest AR, and
extending into southeast OK. Meanwhile, other cells were
periodically developing ahead of the line, with the strongest
activity containing hail over southeast MO currently. Additional
cells also extend eastward along the OH river along and north of a
stationary front.

The air mass remains very moist and unstable, with sufficient
effective shear and mean flow to sustain long lived storms. While
the current linear MCS is not optimal for tornadoes, a brief tornado
cannot be ruled out across the warm sector as the upper trough
continues to emerge and the low-level jet increases further. The
best low-level shear should remain near the stationary/warm front,
from southeast MO into southern IL. Also in this area, deep-layer
shear vector orientation appears more favorable for individual cells
even within the approaching line.

..Jewell/Guyer.. 05/20/2017

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

ATTN...WFO...PAH...MEG...LSX...LZK...SGF...

LAT...LON   38468798 37738836 36878906 35948974 35519056 35329142
            35449197 35749232 36199224 37219128 37919034 38338958
            38538903 38588829 38468798




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