SPC AC 271630
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CDT MON AUG 27 2007
VALID 271630Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL PLAINS ACROSS
THE UPPER MS RIVER VALLEY...
...CENTRAL PLAINS INTO THE UPPER MS RIVER VALLEY...
SEASONABLY STRONG FRONT IS NOW WELL ENTRENCHED ACROSS THE NRN PLAINS
EXTENDING FROM N-CENTRAL MN SWWD TO S-CENTRAL SD AND THEN WNWWD INTO
CENTRAL WY THIS MORNING. SURFACE LOW INVOF TRIPLE POINT OVER SRN SD
IS EXPECTED TO PROGRESS NEWD ALONG THIS BOUNDARY THROUGH THE
AFTERNOON AHEAD OF SUBTLE SHORTWAVE TROUGH NOW EJECTING NEWD ACROSS
THE CENTRAL ROCKIES. SURFACE WARM FRONT/OUTFLOW BOUNDARY NOW
EXTENDING FROM THE LOW CENTER INTO NERN IA. THIS BOUNDARY SHOULD
PUSH NWD WITH STRONG HEATING TO ITS SOUTH OVER ERN SD/SWRN MN THIS
AFTERNOON...WITH ERN PORTION BEING SLOWER TO RETREAT OVER THE UPPER
MS RIVER VALLEY. EXTENSIVE CLOUDS REMAIN IN PLACE BETWEEN THE WARM
FRONT AND STATIONARY FRONT OVER CENTRAL/NRN MN AND ERN ND THIS
MORNING. THIS MAY LIMIT NWD PUSH TO THE WARM FRONT FOR MUCH OF THE
DAY...AND BE PROBLEMATIC FOR SURFACE BASED STORMS NEAR THE FRONT
OVER MN LATER TODAY.
EXPECT A VERY UNSTABLE AIR MASS WILL DEVELOP WHERE HEATING WILL BE
ROBUST OVER THE CENTRAL PLAINS INTO MUCH OF IA/SWRN MN/ERN SD THIS
AFTERNOON. SURFACE DEW POINTS IN THE 70S WILL SUPPORT MLCAPES IN
EXCESS OF 3000 J/KG BY THE LATE AFTERNOON. THIS WILL WEAKEN
CAP...WITH THUNDERSTORMS LIKELY DEVELOPING AND QUICKLY BECOMING
SEVERE AS WEAK IMPULSE AND RESULTANT FOCUSED LLJ ACTS ON THIS STRONG
INSTABILITY. INITIAL DEVELOPMENT IS MORE LIKELY WITH INCREASING
CONVERGENCE INVOF SURFACE LOW/FRONT OVER PORTIONS OF NERN SD/SERN ND
INTO WRN MN...POSSIBLY AS EARLY AS 21Z. HOWEVER...DELAYED HEATING
FROM MORNING CLOUDS AND SUBSEQUENT SLOWER EROSION OF CAP MAY RESULT
IN SURFACE BASED DEVELOPMENT OCCURRING CLOSER TO 00Z. AS WAS THE
CASE YESTERDAY IN ERN ND...APPEARS INITIAL DEVELOPMENT WILL OCCUR AS
SUPERCELLS WITH STRONG LOW AND DEEP LAYER SHEAR AND VERY STEEP LAPSE
RATES SUPPORTING BOTH THREATS OF LARGE HAIL /SOME OF WHICH COULD BE
QUITE LARGE/ AND A FEW TORNADOES. ACTIVITY SHOULD EVOLVE/BUILD INTO
ONE OR MORE MCSS AFTER DARK ALONG NOSE OF STRONG SWLY LLJ WITH
DAMAGING WIND POTENTIAL INCREASING PRIOR TO NOCTURNAL INCREASE IN
SBCIN LATER THIS EVENING.
FARTHER SW ALONG THE FRONT... DEVELOPMENT WILL BE STRONGLY DRIVEN BY
HEATING AND BE MORE WEAKLY ORGANIZED DUE TO MARGINAL SHEAR.
HOWEVER...EXTREME INSTABILITY AND SUFFICIENT SHEAR WILL BE IN PLACE
FOR WEAKLY ORGANIZED CLUSTERS WITH ATTENDANT LARGE HAIL AND DAMAGING
WIND THREATS. THIS ACTIVITY SHOULD WEAKEN DURING THE MID EVENING
WITH LOSS OF HEATING.
...GREAT BASIN...
PLUME OF RICH MOISTURE WILL CONTINUE TO FEED NEWD AS SRN STREAM
IMPULSE EJECTS ACROSS THE GREAT BASIN TODAY. THIS SYSTEM SHOULD
PROVIDE SUFFICIENT FOCUS FOR A FEW STRONGER TO BRIEFLY SEVERE STORMS
WITHIN MARGINAL TO MODERATE INSTABILITY EXPECTED OVER THE REGION.
...SOUTHEAST...
ONCE AGAIN A VERY MOIST AIR MASS AND STRONG HEATING WILL PRODUCE
AREAS OF STRONGER STORMS TODAY. ACTIVITY WILL FOCUS ALONG RESIDUAL
OUTFLOW BOUNDARIES AND STALLED SURFACE FRONT...ALTHOUGH WEAK SHEAR
AND SMALL LAPSE RATES SHOULD LIMIT COVERAGE/INTENSITY OF ANY SEVERE
THREAT.
..EVANS/LEVIT.. 08/27/2007
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z
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