Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 201825
SWOMCD
SPC MCD 201825
MIZ000-INZ000-ILZ000-IAZ000-202000-

MESOSCALE DISCUSSION 1738
NWS STORM PREDICTION CENTER NORMAN OK
0125 PM CDT SAT SEP 20 2014

AREAS AFFECTED...NRN/CENTRAL IL...SRN LAKE MI...NRN INDIANA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 201825Z - 202000Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...STORMS ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSIFY
THIS AFTERNOON ACROSS NRN/CENTRAL IL INTO NRN INDIANA.  AREA WILL BE
MONITORED FOR POSSIBLE SEVERE THUNDERSTORM WATCH BY 20Z.

DISCUSSION...A FEW STORMS ARE DEVELOPING FROM ERN IA INTO NRN IL
WITHIN A PRE-FRONTAL AIR MASS EARLY THIS AFTERNOON.  THIS REGION IS
AHEAD OF A WELL-DEFINED EWD MOVING SHORT WAVE TROUGH/ZONE OF
MID-UPPER LEVEL DRYING EVIDENT IN WV IMAGERY MOVING ACROSS IA.
VISIBLE IMAGERY SHOWS THE SRN EDGE OF A REGION OF THICKER CLOUD
COVER EXTENDING FROM ERN IA ACROSS FAR NRN IL AND SRN LAKE MI...WITH
THIN CLOUDS TO THE SOUTH.  STRONGER DIABATIC HEATING IS OCCURRING TO
THE SOUTH OF THE CLOUD EDGE WITH RESULTANT MESOSCALE DIFFERENTIAL
HEATING CIRCULATIONS OCCURRING ALONG THIS AXIS.  THIS IS EXPECTED TO
PROMOTE ADDITIONAL CONVECTIVE DEVELOPMENT THIS AFTERNOON WITHIN THE
DISCUSSION AREA.

MOISTURE CONTINUES TO SPREAD NEWD FROM THE MIDDLE MS VALLEY WITH
SURFACE DEW POINTS IN THE MID/UPPER 60S ACROSS MUCH OF IL INTO  NWRN
INDIANA...CONTRIBUTING TO AIR MASS DESTABILIZATION WITH SBCAPE OF
1000-2000 J/KG.  LARGELY UNIDIRECTIONAL WESTERLY WINDS OF 35-45 KT
ABOVE 1-2 KM AGL INDICATED ON LATEST DVN AND LOT VAD PROFILES AND
ASSOCIATED VERTICAL SHEAR OF 35-40 KT IN THE LOWEST 4-6 KM WILL
ENHANCE STORM ORGANIZATION...WITH SHORT LINE SEGMENTS AND ISOLATED
SUPERCELLS POSSIBLE.  AS ACTIVITY STRENGTHENS THIS AFTERNOON...MORE
INTENSE CELLS WILL HAVE POTENTIAL TO PRODUCE DAMAGING WIND GUSTS AND
HAIL...WHILE AN ISOLATED TORNADO CANNOT BE RULED OUT.  AREA IS BEING
MONITORED FOR THE POSSIBLE ISSUANCE OF A SEVERE THUNDERSTORM WATCH
BY 20Z.

..WEISS/CARBIN.. 09/20/2014

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...IWX...IND...LOT...ILX...DVN...

LAT...LON   41829016 42398950 42478764 42108632 41748571 40778592
            40508708 40178887 39959036 40439116 41419064 41829016



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