Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 021258
SWODY1
SPC AC 021256

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT SUN AUG 02 2015

VALID 021300Z - 031200Z

...THERE IS AN ENH RISK OF SVR TSTMS CENTRAL/ERN WI...NERN
IL...CENTRAL/SRN LM...LOWER MI...NRN INDIANA...EXTREME NWRN OH...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING ENH RISK...

...THERE IS A MRGL RISK OF SVR TSTMS ELSEWHERE FROM PORTIONS CENTRAL
PLAINS TO GREAT LAKES...

...SUMMARY...
SEVERE STORMS ARE EXPECTED ACROSS THE GREAT LAKES REGION
TODAY...POTENTIALLY AS FAR WEST AS NEBRASKA.  THIS MAY INCLUDE ONE
OR TWO ORGANIZED STORM CLUSTERS CAPABLE OF GENERATING SWATHS OF
POTENTIALLY DAMAGING WIND GUSTS...IN ADDITION TO SEVERE HAIL...AND
PERHAPS A COUPLE OF TORNADOES FROM THE UPPER MISSISSIPPI VALLEY AREA
TO LOWER MICHIGAN.

...SYNOPSIS...
IN MIDDLE-UPPER LEVELS...HIGH-AMPLITUDE SYNOPTIC PATTERN WILL
PERSIST ACROSS CONUS...CHARACTERIZED BY WRN RIDGING AND ERN
TROUGHING...DOWNSTREAM FROM BROAD/QUASISTATIONARY CYCLONE OVER NERN
PAC.  STRONGEST PART OF CYCLONIC-FLOW FIELD ASSOCIATED WITH BIG
HUDSON BAY GYRE WILL CONTINUE TO TRAVERSE UPPER GREAT LAKES BUT WILL
BACK DIRECTIONALLY AS SHORTWAVE TROUGH -- NOW OVER SRN MB --
AMPLIFIES AND MOVES SEWD.  THAT PERTURBATION IS EXPECTED TO REACH LS
AND NRN MN BY 00Z...MOVING TO LH...LOWER MI AND SRN WI BY 12Z.  AS
THAT OCCURS...BOTH CURVATURE AND GRADIENT OF HEIGHT FIELD ALOFT WILL
TIGHTEN OVER THIS REGION...WHILE HEIGHT FALLS WILL OVERSPREAD MUCH
OF CONUS N OF ABOUT 37N AND FROM MID/UPPER MS VALLEY EWD.

AT SFC...11Z ANALYSIS SHOWED SFC LOW OVER ND/SD/MN BORDER
CONFLUENCE...WITH COLD FRONT ARCHING WSWWD THEN WNWWD OVER
CENTRAL/WRN SD AND SERN MT.  WAVY WARM FRONT WAS DRAWN ESEWD THROUGH
SECONDARY LOW OVER NWRN WI THEN ACROSS CENTRAL/SRN LM TO SRN LOWER
MI.  WARM FRONT SHOULD MOVE NEWD ACROSS SLGT/ENH-RISK AREAS TODAY
PRIOR TO COLD FROPA.  BY 00Z COLD FRONT SHOULD REACH CENTRAL/NRN
LOWER MI...SRN WI...WRN IA...CENTRAL NEB AND SERN WY. BY 12Z COLD
FRONT SHOULD REACH FROM SRN ONT ACROSS NRN INDIANA TO NRN KS AND ERN
CO...DECELERATING OVER CENTRAL PLAINS.

...UPPER MIDWEST GREAT LAKES REGION...
ISOLATED TO WIDELY SCATTERED STG-SVR TSTMS ARE EVIDENT ATTM FROM
UPPER MI AND LM WNWWD ACROSS NRN MN IN ZONE OF LOW-LEVEL WAA AND
FAVORABLE MOISTURE JUST ABOVE SFC.  ACTIVITY IS MOVING SEWD NEAR NRN
FRINGES OF OUTLOOK AND MAY CONTRIBUTE TO LATER DEVELOPMENT/UPSCALE
SHIFT IN SVR POTENTIAL.  REF SPC MESOSCALE DISCUSSIONS 1582 AND 1583
FOR NEAR-TERM GUIDANCE ON SVR SCENARIO FOR PARTS OF THIS REGION.

SVR THREAT IS EXPECTED TO INCREASE LATE THIS MORNING AND ESPECIALLY
INTO AFTN WITH SEWD EXTENT.  THIS WILL OCCUR AS MID/UPPER-LEVEL
HEIGHT FALLS...STRONGER FLOW ALOFT AND DCVA AHEAD OF AMPLIFYING
SHORTWAVE TROUGH BECOME BETTER JUXTAPOSED WITH DIABATICALLY
DESTABILIZING PARTS OF SFC WARM SECTOR NEAR SFC COLD FRONT.  ASIDE
FROM FRONTAL FORCING...INTENSIFICATION OF ANY PERSISTENT ANTECEDENT
CONVECTION ALSO MAY OCCUR WHILE MOVING INTO THIS REGIME.
DIFFERENTIAL-HEATING/OUTFLOW BOUNDARIES ALSO MAY SERVE AS FOCI FOR
SUPPORTIVE PREFRONTAL LIFT.  MORNING MPX/ABR RAOBS SHOW
RESIDUAL/ELEVATED MIXED LAYER AND RELATED PLUME OF STEEP
LOW/MIDDLE-LEVEL LAPSE RATES.  MODIFIED RAOBS AND FCST SOUNDINGS
SUGGEST THAT FACTOR...IN TANDEM WITH SFC DEW POINTS COMMONLY 60S F
AND LOCALLY NEAR 70...WILL LEAD TO PEAK AFTN MLCAPE RANGING FROM
AROUND 2000 J/KG OVER ERN LOWER MI TO 3500 J/KG NEAR MS RIVER PART
OF OUTLOOK.

AS FOR KINEMATIC SUPPORT...DEEP SHEAR SHOULD BE STRONGEST IN THAT
PART OF WARM SECTOR IMMEDIATELY ADJACENT TO COLD FRONT...WITH 40-50
KT EFFECTIVE-SHEAR MAGNITUDES POSSIBLE...DIMINISHING WITH SWWD AND
SEWD EXTENT.  DESPITE SWLY-WLY SFC FLOW...VEERING/STRENGTHENING OF
WINDS WITH HEIGHT WILL IMPART SUFFICIENT HODOGRAPH CURVATURE FOR
RISK OF SUPERCELLS AS LONG AS CONVECTION REMAINS RELATIVELY
DISCRETE.  GIVEN THERMODYNAMIC ENVIRONMENT...ANY SUSTAINED
SUPERCELLS MAY PRODUCE LARGE/DAMAGING HAIL AND OFFER AT LEAST
TRANSIENT TORNADO RISK.  EVOLUTION OF ONE OR MORE
ELONGATED/QUASI-LINEAR TSTM COMPLEXES IS EXPECTED INVOF FRONT...WITH
HAIL SIZE DIMINISHING AND WIND POTENTIAL INCREASING INTO THIS
EVENING.  SVR POTENTIAL SHOULD RAMP DOWNWARD LATE THIS EVENING INTO
OVERNIGHT HOURS AS MUCH OF WARM SECTOR COOLS/STABILIZES...THOUGH AT
LEAST ISOLD HAIL/WIND THREAT MAY PERSIST INTO CENTRAL PORTIONS OF
OH/INDIANA/IL.

...CENTRAL PLAINS TO CENTRAL/WRN IA...
ISOLATED TO WIDELY SCATTERED TSTMS ARE POSSIBLE INVOF FRONT MAINLY
THIS AFTN INTO EARLY EVENING.  SPORADIC LARGE HAIL AND SVR GUSTS ARE
POSSIBLE...THOUGH INCREASING MLCINH WITH WWD EXTENT FROM MS RIVER
INTO WARMER EML AIR WILL DELAY INITIATION AND RESTRICT COVERAGE
COMPARED TO AREAS OF GREATER UNCONDITIONAL SVR PROBABILITIES FARTHER
NE.

..EDWARDS/DEAN.. 08/02/2015



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