Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 181625
SWOMCD
SPC MCD 181624
INZ000-KYZ000-ILZ000-TNZ000-MOZ000-ARZ000-181830-

Mesoscale Discussion 1769
NWS Storm Prediction Center Norman OK
1024 AM CST Sat Nov 18 2017

Areas affected...Northeast AR to Central IN

Concerning...Severe potential...Watch likely

Valid 181624Z - 181830Z

Probability of Watch Issuance...80 percent

SUMMARY...Severe threat will increase into the early afternoon hours
ahead of progressive cold front. Severe thunderstorm watch will be
issued by 18z to account for this potential.

DISCUSSION...Strong 12hr mid-level height falls will overspread the
OH Valley and mid-south region this afternoon ahead of a progressive
cold front. Large-scale forcing for ascent will be focused across
this region but environmental capping is expected to restrict
appreciable pre-frontal convection, except for the warm advection
corridor across the OH Valley. Latest visible satellite imagery
suggests strongest boundary-layer heating is noted just ahead of the
front from central AR into southwest IL. This is supported in OA
fields where surface-3km lapse rates are now on the order of 6.5
C/km where partial sunshine is observed. Given the strong capping
observed, thunderstorms are expected to initiate along the surging
cold front. Latest radar data supports this scenario with convection
gradually increasing along the wind shift from east-central IL into
southeast MO where lightning is currently observed. Damaging wind
threat will increase with frontal convection as it matures,
potentially encouraging strong environmental winds to mix to the
surface with stronger downdrafts.

..Darrow/Hart.. 11/18/2017

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

ATTN...WFO...ILN...LMK...IND...PAH...ILX...MEG...LSX...LZK...
SGF...

LAT...LON   35909142 37759080 40398674 40148496 38308630 35718927
            35909142




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