DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 302000
SWODY1
SPC AC 301958

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0258 PM CDT FRI AUG 30 2013

VALID 302000Z - 311200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE GREAT
LAKES/MIDWEST...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS WESTERN DAKOTAS/WESTERN
NEB...

...GREAT LAKES/MIDWEST...
STRONG TO SEVERE TSTMS WILL CONTINUE TO DEVELOP THIS AFTERNOON
WITHIN A MODERATE TO STRONGLY UNSTABLE AIRMASS /1500-3000 J PER KG
MLCAPE/ NEAR AND AHEAD OF A COLD FRONT. BASED ON SHORT-TERM
TRENDS/NUMERICAL GUIDANCE...PRIMARY ADJUSTMENT WAS TO EXPAND THE
SLIGHT RISK A BIT FARTHER SOUTH-SOUTHEASTWARD TO ACCOUNT FOR THE
POSSIBILITY OF PERSISTENT STRONG/SEVERE TSTM CLUSTERS THIS EVENING.

...NORTHERN/CENTRAL HIGH PLAINS...
RELATIVELY LITTLE CHANGE IN PRIOR FORECAST REASONING...ALTHOUGH THE
CATEGORICAL SLIGHT RISK WAS EXTENDED SOUTHWARD TO INCLUDE PORTIONS
OF WESTERN NEB IN ACCORDANCE WITH SEVERE TSTM WATCH 505.
FOR ADDITIONAL SHORT-TERM DISCUSSION...SEE MESOSCALE DISCUSSION
1804.

..GUYER.. 08/30/2013

.PREV DISCUSSION... /ISSUED 1130 AM CDT FRI AUG 30 2013/

...SYNOPSIS...
A LARGE MID- AND UPPER-LEVEL RIDGE WHICH HAS PREVAILED ACROSS A
LARGE PORTION OF THE U.S. FOR SEVERAL DAYS WILL PERSIST...THOUGH
SOME FLATTENING OF THE RIDGE ON ITS NRN PERIPHERY AND SOME EROSION
ON ITS ERN FRINGE IS EXPECTED THIS PERIOD -- RESULTING IN A
MODEST/SLOW SWWD SUPPRESSION OF THE FEATURE. THE FLATTENING ON THE
NRN PERIPHERY OF THE RIDGE IS OCCURRING AS A SERIES OF SHORT-WAVE
TROUGHS EMBEDDED WITHIN AN ENHANCED BELT OF WLY FLOW PROGRESS
REPETITIVELY EWD ACROSS THE NRN U.S. AND ADJACENT SRN CANADA.
MEANWHILE...AS THESE FEATURES CREST THE RIDGE AND DROP SEWD...SOME
WWD EXPANSION OF A WEAK MEAN TROUGH OVER THE WRN ATLANTIC WILL AID
IN THE AFOREMENTIONED EROSION ON THE ERN EDGE OF THE LARGE-SCALE
RIDGE. MORE IMPORTANTLY...THE REPETITIVE PASSAGE OF THESE
SHORT-WAVE FEATURES IN AN ANTICYCLONIC ARC AROUND THE PERIPHERY OF
THE RIDGE WILL CONTRIBUTE TO ONGOING CONVECTIVE/SEVERE POTENTIAL
ACROSS N CENTRAL PORTIONS OF THE COUNTRY THROUGH THE PERIOD.

...WRN DAKOTAS VICINITY...
A PAIR OF WEAK UPPER FEATURES CROSSING THE NRN INTERMOUNTAIN REGION
ATTM -- THE STRONGEST OF WHICH NOW ENTERING NWRN MT -- WILL MAINTAIN
WEAK LARGE-SCALE ASCENT ACROSS MT AND INTO THE NRN HIGH PLAINS AREA
THIS AFTERNOON. WHILE MODEST CAPE IS FORECAST ACROSS MT GIVEN
LIMITED LOW-LEVEL MOISTURE...GREATER DESTABILIZATION IS PROGGED TO
CONTINUE ACROSS THE HIGH PLAINS VICINITY AND INTO NEB...ALONG
TRAILING PORTIONS OF A WEAK COLD FRONT WHICH HAS BACKED WWD INTO
THIS AREA. WITH WEAK SLY FLOW MAINTAINING LOW 60S
DEWPOINTS...CONTINUED HEATING WILL YIELD 1000 TO 2000 J/KG
MIXED-LAYER CAPE. THOUGH ISOLATED STORMS ARE FORECAST TO DEVELOP
ACROSS MT -- WHICH MAY POSE ISOLATED WIND POTENTIAL...MORE
WIDESPREAD DEVELOPMENT IS EXPECTED WITHIN THE MORE FAVORABLE AIRMASS
ACROSS THE HIGH PLAINS. AS STORMS DEVELOP IN THIS AREA...35 TO 45
KT MID-LEVEL WLYS WILL CONTRIBUTE TO SHEAR SUPPORTIVE OF ORGANIZED
STORMS/ISOLATED SUPERCELLS. THE STRONGEST CONVECTION WILL BE
CAPABLE OF PRODUCING LARGE HAIL AND LOCALLY DAMAGING WINDS INTO THE
EVENING HOURS -- SUPPORTING A CONTINUATION OF THE SLIGHT RISK
FORECAST OVER THIS REGION.

...SRN UPPER GREAT LAKES/UPPER MIDWEST REGION...
A WEAK COLD FRONT EXTENDING FROM THE UPPER GREAT LAKES REGION WSWWD
INTO THE MID MO VALLEY WILL CONTINUE TO MOVE SLOWLY SEWD THIS
PERIOD...AS UPPER DISTURBANCES CREST THE DOMINANT RIDGE. WITH A
MOIST/HEATING BOUNDARY LAYER ALONG AND AHEAD OF THE FRONT BECOMING
INCREASINGLY FAVORABLE FOR CONVECTIVE DEVELOPMENT...EXPECT ONGOING
STORMS ACROSS NRN LOWER MI TO INCREASE...EXPANDING SWWD ALONG THE
FRONT ACROSS LOWER WI AND INTO IA BY AFTERNOON -- ALONG WITH AN
ASSOCIATED INCREASE IN STORM INTENSITY WITH TIME.

THOUGH DEEP-LAYER FLOW WILL REMAIN SOMEWHAT MODEST -- WITH ONLY 25
KT LOWER AND MID-TROPOSPHERIC WNWLYS ACROSS THE REGION...SHEAR WILL
BE SUFFICIENT IN CONJUNCTION WITH ANTICIPATED MODERATE
DESTABILIZATION TO SUPPORT SOME SEVERE RISK WITHIN STRONGER
CELLS/CONVECTIVE CLUSTERS. GIVEN EXPECTED DESTABILIZATION AND
HI-RES CONVECTION-ALLOWING MODELS ALL SUPPORTING THE AFOREMENTIONED
SCENARIO...UPGRADE TO 15% HAIL AND WIND PROBABILITY/SLIGHT RISK
FORECAST APPEARS WARRANTED FOR THE EXPECTED AFTERNOON/EVENING
MAXIMUM IN CONVECTIVE INTENSITY.

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