Severe Storm Outlook Narrative (AC)
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309
ACUS11 KWNS 231804
SWOMCD
SPC MCD 231803
OHZ000-MIZ000-INZ000-ILZ000-WIZ000-232030-

Mesoscale Discussion 1408
NWS Storm Prediction Center Norman OK
0103 PM CDT Sun Jul 23 2017

Areas affected...Portions of IL...IN...OH...southern Lower
MI...southern WI

Concerning...Severe potential...Watch unlikely

Valid 231803Z - 232030Z

Probability of Watch Issuance...5 percent

SUMMARY...Thunderstorms will increase in number and intensity
through the afternoon and continue into the evening, posing some
isolated severe risk. Watch issuance will be unlikely.

DISCUSSION...Air-mass modification continues in the wake of an MCS
that crossed the Ohio Valley vicinity, owing to diabatic heating of
residual moist air characterized by surface dewpoints in the lower
70s. The more convectively unperturbed air -- farther north toward
the lower Great Lakes region -- is similarly moist and is also
experiencing diabatic surface-layer heating. The net result of these
factors is moderate destabilization, with MLCAPE increasing to
1500-2500 J/kg. This buoyancy will support an uptick in convective
coverage and intensity amid an assortment of residual outflow
boundaries deposited by the aforementioned MCS, differential-heating
zones peripheral to MCS-related cloud debris, and subtle/weakly
convergent surface baroclinic troughs from southern WI to southern
Lower MI.

Effective shear around 25-35 kt may support a few organized,
sustained convective elements capable of marginally severe wind/hail
moving eastward to southeastward through the early evening. However,
water vapor imagery implies that air with a history of subsidence --
reflected by a notable dry intrusion within the base of an
approaching mid-level cyclonic perturbation -- will tend to suppress
convective-scale upward accelerations owing to statically stable
layers aloft. This will limit convective intensity. Furthermore, the
lack of stronger deep shear and surface convergence suggest that
severe coverage will be limited.

..Cohen/Grams.. 07/23/2017

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

ATTN...WFO...CLE...ILN...DTX...IWX...IND...LOT...ILX...MKX...
DVN...

LAT...LON   41328243 40918226 40208342 39798443 39408603 39578818
            40718940 41678987 42498969 42728859 42118668 41568300
            41328243




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