DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 091951
SWODY1
SPC AC 091949

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0249 PM CDT MON SEP 09 2013

VALID 092000Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF MN...WI...AND
UPPER MI...

...UPPER GREAT LAKES...
NO CHANGES HAVE BEEN MADE TO THE PREVIOUS OUTLOOK. DESPITE
FAVORABLE SHEAR AND CAPE COMBINATIONS...CONVECTIVE INITIATION
REMAINS A BIG QUESTION FOR THIS AFTERNOON AND EVENING OVER PARTS OF
MN/WI AND UPPER MI. MODEL SOLUTIONS VARY SIGNIFICANTLY REGARDING
LOCATION...TIMING...AND EXTENT OF THUNDERSTORM DEVELOPMENT.
HOWEVER...FAVORABLE INSTABILITY AND WIND FIELDS WILL PROMOTE A RISK
OF LARGE HAIL...DAMAGING WINDS...AND EVEN AN ISOLATED TORNADO IN ANY
SUSTAINED CONVECTION THIS EVENING OVER THE SLIGHT RISK AREA.

ELSEWHERE PREVIOUS FORECAST APPEARS ON TRACK.

..HART.. 09/09/2013

.PREV DISCUSSION... /ISSUED 1120 AM CDT MON SEP 09 2013/

...SYNOPSIS...

AN UPPER HIGH CENTERED OVER THE MID MS VALLEY WILL FLATTEN/ELONGATE
WHILE EDGING EWD INTO THE OH/TN VALLEYS. THIS IS IN RESPONSE TO THE
EWD PROGRESSION OF A DE-AMPLIFYING SHORT-WAVE TROUGH WHICH WILL
SHIFT FROM THE NRN HIGH PLAINS AND SRN CANADA PRAIRIE PROVINCES
TOWARD THE UPPER GREAT LAKES. ELSEWHERE...AN UPPER LOW WILL REMAIN
QUASI-STATIONARY OVER THE LOWER CO VALLEY.

IN THE LOW LEVELS...A SURFACE CYCLONE ASSOCIATED WITH THE NRN HIGH
PLAINS TROUGH WILL DEVELOP EWD ALONG A POLEWARD-MOVING WARM FRONT
FROM ERN ND TO THE ERN U.P. OF MI/NRN LAKE HURON BY TUESDAY MORNING.
MEANWHILE...A TRAILING COLD FRONT WILL PROGRESS SEWD THROUGH THE NRN
PLAINS AND UPPER MS VALLEY INTO THE UPPER GREAT LAKES...MID MO
VALLEY...AND CNTRL HIGH PLAINS BY 10/12Z.

...UPPER MIDWEST/UPPER GREAT LAKES THIS AFTERNOON INTO TONIGHT...

CONSIDERABLE CLOUDINESS IS PRESENT ACROSS THE REGION THIS MORNING
OWING TO A BROAD ZONE OF WAA/ISENTROPIC ASCENT TO THE NORTH OF THE
WARM FRONT...AND IN ASSOCIATION WITH A RECENTLY DECAYED NOCTURNAL
MCS WHICH FORMED LAST NIGHT OVER THE DAKOTAS. MOREOVER...THE 12Z
ABR AND OMA SOUNDINGS SHOWED THE PRESENCE OF A PRONOUNCED EML AND
ASSOCIATED CAP WHICH WILL BE ADVECTED NEWD TODAY IN ADVANCE OF THE
MIDLEVEL TROUGH. THESE FACTORS WILL LIKELY DELAY ANY POTENTIAL FOR
STORM DEVELOPMENT UNTIL CLOSER TO 10/00Z. AT THIS TIME...
SURFACE-BASED OR NEAR-SURFACE-BASED TSTM INITIATION APPEARS MOST
PROBABLE INVOF THE SURFACE TRIPLE POINT OVER E-CNTRL/NERN MN INTO
NRN WI AS FORCING FOR ASCENT IS POSSIBLY ENHANCED BY A WEAK IMPULSE
PRECEDING THE PRIMARY UPPER SYSTEM.

SHOULD STORMS BECOME ROOTED WITHIN THE BOUNDARY LAYER...THE LOCAL
ENVIRONMENT WILL BE QUITE FAVORABLE FOR SUPERCELLS OWING TO THE
PRESENCE OF MODERATE TO STRONG INSTABILITY /MLCAPE OF 2000-3000 J
PER KG/ WHICH WILL ALIGN WITH ENHANCED LOW-LEVEL AND DEEP-LAYER
SHEAR ALONG THE WARM FRONT. AN ATTENDANT RISK FOR A COUPLE
TORNADOES...LARGE HAIL...AND DAMAGING WINDS WOULD EXIST WITHIN THE
FIRST FEW HOURS OF INITIATION. THEREAFTER...COALESCING STORM-SCALE
COLD POOLS AND THE DEVELOPMENT OF A 40-50 KT NOCTURNALLY ENHANCED
LLJ WILL BE SUPPORTIVE OF UPSCALE GROWTH INTO A FORWARD-PROPAGATING
MCS WITH A CONTINUED RISK FOR MAINLY DAMAGING WINDS.

...CNTRL HIGH PLAINS THIS AFTERNOON AND EVENING...

WHILE LARGE-SCALE FORCING FOR ASCENT WILL REMAIN NEGLIGIBLE THROUGH
THE PEAK OF THE DIURNAL HEATING CYCLE...STRONG BOUNDARY LAYER
HEATING AND CONVERGENCE ALONG THE COLD FRONT --AS WELL AS
POST-FRONTAL UPSLOPE OVER SERN WY/NERN CO-- MAY BE SUFFICIENT TO
INITIATE ISOLATED TO WIDELY SCATTERED STORMS. GIVEN THE PRESENCE OF
A DEEP...WELL-MIXED BOUNDARY LAYER AND MODEST AMOUNTS OF INSTABILITY
AND VERTICAL SHEAR...A FEW SEVERE STORMS ARE POSSIBLE WITH A RISK
FOR LOCALLY DAMAGING WIND GUSTS AND PERHAPS SOME HAIL.

...ND THIS AFTERNOON...

RESIDUAL BOUNDARY LAYER MOISTURE AND COOLING TEMPERATURES ALOFT WILL
CONTRIBUTE TO MODEST AIR MASS DESTABILIZATION TODAY ALONG
AN INVERTED TROUGH OR WEAK OCCLUDED FRONT. DEEP-LAYER FORCING FOR
ASCENT AHEAD OF THE MIDLEVEL TROUGH ALONG WITH LOW-LEVEL UPLIFT
ALONG THE SURFACE BOUNDARY MAY BE SUFFICIENT TO SUPPORT A FEW
INTENSE STORMS CAPABLE OF ISOLATED OCCURRENCES OF WIND AND HAIL.

...LOWER CO VALLEY THIS AFTERNOON AND EVENING...

DEEP-LAYER FORCING FOR ASCENT ASSOCIATED WITH THE MIDLEVEL VORTICITY
MAXIMUM WILL COMBINE WITH A VERY MOIST AIR MASS /I.E. PW VALUES
APPROACHING TWO INCHES/ TO FOSTER SCATTERED TO NUMEROUS STORMS
TODAY. SOME ENHANCEMENT OF MID TO UPPER-LEVEL FLOW WAS NOTED BY THE
12Z TUCSON AND PHOENIX SOUNDINGS WITHIN THE ERN SEMI-CIRCLE OF THE
UPPER LOW. WHEN COUPLED WITH THE MODERATELY UNSTABLE/HIGH PW
ENVIRONMENT...THE SETUP MAY FAVOR A FEW INTENSE STORMS CAPABLE OF
LOCALLY STRONG WET MICROBURSTS.

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