[BNAWX] Severe Storm Outlook Narrative

[EMWIN Server]

ACUS11 KWNS 072140
SWOMCD
SPC MCD 072140
MIZ000-INZ000-KYZ000-ILZ000-TNZ000-MOZ000-080015-

Mesoscale Discussion 1701
NWS Storm Prediction Center Norman OK
0440 PM CDT Sat Oct 07 2017

Areas affected...Portions of far southern lower MI...IN...
eastern/southern IL...western KY/TN...and far southeastern MO

Concerning...Severe potential...Watch unlikely

Valid 072140Z - 080015Z

Probability of Watch Issuance...20 percent

SUMMARY...Some threat for a tornado or two and isolated strong to
locally damaging winds may increase through this evening. Due to the
overall marginal nature of the severe threat, watch issuance appears
unlikely at this time.

DISCUSSION...A well-defined upper trough will continue moving
northeastward across the Upper Midwest into the Great Lakes region
this evening. A related surface cold front will develop eastward
across parts of the lower Great Lakes and OH/TN Valleys. Recent
radar and visible satellite imagery indicate convection is beginning
to strengthen along the front in eastern/southern IL. Even with
ample diurnal heating downstream of the front this afternoon, poor
mid-level lapse rates (generally 5.0-5.5 C/km in the 700-500 mb
layer) have greatly limited the degree of buoyancy. 21Z RAP
Mesoanalysis estimates MLCAPE generally ranges from 100-500 J/kg,
weaker with northward extent, and additional increases in
instability are not expected this evening with the loss of daytime
heating.

Even with the limited buoyancy, strong mid-level winds and a veering
wind profile in the lower/mid troposphere are contributing to 45-50
kt of effective bulk shear, which will allow for thunderstorm
organization. A linear mode is expected with thunderstorms
developing along the front, and isolated strong to locally damaging
winds and perhaps a QLCS tornado should be the main threats with
this activity. A few discrete cells could form ahead of the front in
western KY/TN and southern IN over the next several hours within a
low-level tropical moisture plume emanating from the Gulf of Mexico.
Given the degree of low-level shear present across this region,
updraft rotation within low-topped supercells could occur, and a
tornado or two cannot be ruled out. At this time, the weak buoyancy
suggests the overall severe threat will probably remain too
marginal/isolated to warrant watch issuance. However, radar trends
will be monitored closely through the evening, especially across
western KY/TN and southern IN where the best overlap of weak
instability and strong shear resides.

..Gleason/Hart.. 10/07/2017

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

ATTN...WFO...LMK...IWX...GRR...OHX...IND...PAH...LOT...ILX...
MEG...LSX...

LAT...LON   37338977 38648881 39368820 41628714 42118656 42358596
            42308497 41758482 40858487 38538609 37408718 36018856
            35998928 36388944 37338977
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