SPC AC 270221
DAY 1 CONVECTIVE OUTLOOK AMEND 1
NWS STORM PREDICTION CENTER NORMAN OK
0921 PM CDT SAT JUL 26 2008
VALID 270215Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN PLAINS AREA...
...THERE IS A SLGT RISK OF SVR TSTMS OVER A LARGE PART OF NY...
AMENDED TO EXTEND SLIGHT RISK INTO NW NEB
...NRN PLAINS AREA...
A BAROCLINIC ZONE EXTENDS FROM SE MT SEWD THROUGH SD AND ERN NEB. IN
VICINITY OF AND JUST SOUTH OF THE BOUNDARY THE ATMOSPHERE HAS BECOME
QUITE UNSTABLE WITH MLCAPE FROM 1500 J/KG OVER ERN MT TO NEAR 3000
J/KG OVER CNTRL AND ERN SD AND NEB WHERE DEWPOINTS IN THE UPPER 60S
EXIST. A VERY WARM EML WITH 700 MB TEMPERATURES AROUND 15C HAS
OVERSPREAD WRN PORTION OF THE INSTABILITY AXIS RESULTING IN A
CAP...AND THIS WAS CONFIRMED ON THE 00Z RAOB FROM RAPID CITY. WARM
EML IN CONJUNCTION WITH SHORTWAVE RIDGING OVER THE NRN PLAINS HAS
PRECLUDED THUNDERSTORM DEVELOPMENT SO FAR OVER MOST OF UNSTABLE WARM
SECTOR. STORMS THAT DEVELOPED OVER THE HIGHER TERRAIN OF WY CONTINUE
TO STRUGGLE AS THEY SPREAD EWD TOWARD WRN SD WHERE CONVECTIVE
INHIBITION IS STRONGER.
A SHORTWAVE TROUGH IS CURRENTLY CRESTING UPPER RIDGE OVER NERN MT
AND THIS FEATURE WILL TURN SEWD INTO THE DAKOTAS TONIGHT. STORMS
HAVE DEVELOPED OVER NERN MT WITHIN ZONE OF ASCENT ASSOCIATED WITH
THIS FEATURE. ELY LOW LEVEL FLOW BENEATH A 50 KT MID LEVEL JET
ATTENDING THE IMPULSE MOVING THROUGH NERN MT IS RESULTING IN 50+ KT
BULK SHEAR FAVORABLE FOR SUPERCELLS AND BOWING SEGMENTS WITH LARGE
HAIL AND DAMAGING WIND THE MAIN THREATS. THIS ACTIVITY MAY SPREAD
SEWD THROUGH ERN MT ALONG NRN FRINGE OF EML AND ALONG INSTABILITY
GRADIENT INTO THE WRN ND AND NWRN SD LATER THIS EVENING.
OTHER STORMS MAY DEVELOP AS SLY LOW LEVEL JET STRENGTHENS THIS
EVENING OVER PARTS OF CNTRL OR ERN SD IN VICINITY OF INSTABILITY
GRADIENT WHERE 00Z RAOB FROM ABERDEEN SHOWS COOLER MID LEVEL
TEMPERATURES ON ERN PERIPHERY OF THE WARMER EML. BULK SHEAR OF 50+
KT WILL BE SUPPORTIVE OF SUPERCELLS. LOWER LCLS AND INCREASING
HODOGRAPH SIZE ASSOCIATED WITH THE STRENGTHENING LOW LEVEL JET WILL
PROVIDE A SMALL WINDOW OF OPPORTUNITY FOR AN ISOLATED TORNADO OR TWO
IF STORMS MANAGE TO DEVELOP BEFORE THE BOUNDARY LAYER DECOUPLES.
OTHERWISE STORMS MAY EVENTUALLY EVOLVE INTO AN MCS AND SPREAD EWD
TOWARD THE UPPER MS VALLEY LATER TONIGHT.
...UPPER OH VALLEY THROUGH NY...
SCATTERED STORMS THAT DEVELOPED IN PRE-FRONTAL WARM SECTOR WITHIN
ZONE OF ASCENT ASSOCIATED WITH EWD MIGRATING SHORTWAVE TROUGH WILL
REMAIN CAPABLE OF PRODUCING ISOLATED DAMAGING WIND AND HAIL. THE 00Z
BUFFALO RAOB SHOWS MLCAPE NEAR 2000 J/KG AND WLY UNIDIRECTIONAL BULK
SHEAR AROUND 35 KT SUFFICIENT FOR SOME STORMS TO DEVELOP MID LEVEL
ROTATION. INTENSITIES SHOULD GRADUALLY DECREASE THIS EVENING WITH
THE ONSET OF NOCTURNAL COOLING.
...SRN KS THROUGH SRN MO...
CLUSTER OF STORMS FROM S CNTRL THROUGH ERN KS AND SWRN MO MAY
CONTINUE TO PROPAGATE SLOWLY SWD NEXT HOUR OR TWO. THE STORMS ARE
MOVING SOUTH OF THE STRONGER FLOW ALOFT AND ORGANIZATION APPEARS
LIMITED. THE 00Z RAOB DATA SHOW MODERATE TO STRONG MLCAPE...BUT WARM
MID LEVEL TEMPERATURES WHICH SHOULD LIMIT ANY REMAINING THREAT FOR
LARGE HAIL. PRIMARY THREAT WILL BE ISOLATED DAMAGING WIND NEXT
COUPLE HOURS...AFTER WHICH THE THREAT SHOULD BEGIN TO DIMINISH AS
THE BOUNDARY LAYER COOLS. REFERENCE SWOMCD 1926 FOR ADDITIONAL
INFORMATION.
..DIAL.. 07/27/2008
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0600Z
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