ACUS01 KWNS 281259
SWODY1
SPC AC 281256
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT THU AUG 28 2008
VALID 281300Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CNTRL PLNS/LWR MO VLY
TO UPR GRT LKS...
...SYNOPSIS...
UPR TROUGH NOW OVER THE DAKS WILL CONTINUE E ACROSS THE UPR MS VLY
AND UPR GRT LKS THIS PERIOD AS ELONGATED E PACIFIC/SW U.S. RIDGE
BUILDS FARTHER E ACROSS THE SRN RCKYS AND SRN PLNS. REMNANTS OF
T.D. FAY AND EXISTING UPR LOW OVER OH HAVE EVOLVED INTO AN ILL-
DEFINED TROUGH OVER THE OH/TN VLYS AND APPALACHIANS. WHILE THE
TROUGH SHOULD FURTHER WEAKEN THROUGH FRIDAY...SMALLER SCALE
DISTURBANCES WITHIN IT WILL CONTINUE TO MODULATE DIURNALLY-ENHANCED
TSTMS OVER THE ERN STATES. ELSEWHERE...LITTLE OVERALL MOVEMENT...OR
PERHAPS A SLIGHT WSW DRIFT...EXPECTED WITH UPR CIRCULATIONS OVER NRN
CHIHUAHUA AND NRN BAJA CA.
...CNTRL PLNS/LWR MO VLY TO UPR GRT LKS...
COLD FRONT ASSOCIATED WITH DAKS UPR TROUGH WILL SERVE AS MAIN FOCUS
FOR AFTN/EVE TSTM DEVELOPMENT OVER PARTS OF THE CNTRL AND N CNTRL
STATES TODAY. ELEVATED PREFRONTAL MCS NOW OVER IA/IL/MO SHOULD
FURTHER WEAKEN LATER THIS MORNING WHILE CONTINUING SLOWLY SSEWD.
REGENERATIVE CELLS WILL...HOWEVER...LIKELY PERSIST ON THE SYSTEM'S
WRN FLANK.
WITH HEATING LATER TODAY...EXPECT STORMS TO ONCE AGAIN STRENGTHEN ON
WRN SIDE OF WHATEVER IS LEFT OF THE IA/IL/MO SYSTEM...WHILE NEW
STORMS FORM ALONG COLD FRONT FROM NRN MO AND PERHAPS SE IA/WRN IL
WSW INTO KS. COMBINATION OF FAIRLY STEEP MID LVL LAPSE RATES WITH
FAIRLY RICH MOISTURE /SFC DEWPOINTS IN THE UPR 60S TO AROUND 70F/
SHOULD YIELD SBCAPE AOA 2500 J/KG FROM ERN KS INTO NRN MO. MUCH
WEAKER SFC-BASED INSTABILITY EXPECTED OVER MOST OF NRN IL AND SRN
WI...WHERE DEBRIS FROM OVERNIGHT MCS WILL LIMIT HEATING.
AS HAS BEEN THE CASE OVER THE PAST TWO DAYS OVER THE N CNTRL
STATES...ENVIRONMENT ALONG COLD FRONT WILL BE ON SRN EDGE OF
STRONGER UPR FLOW AND HEIGHT FALLS ASSOCIATED WITH PASSING TROUGH IN
THE UPR MS VLY. NEVERTHELESS...GIVEN THE DEGREE OF INSTABILITY AND
LOW LVL SOURCE FOR UPDRAFT DEVELOPMENT...30+ KT SLIGHTLY DIFFLUENT
MID/UPR LVL FLOW SHOULD BE SUFFICIENT FOR SCTD TO NUMEROUS SUSTAINED
STORMS ALONG FRONT. THE STORMS COULD PRODUCE SVR HAIL AND
WIND...ESPECIALLY DURING THEIR EARLIER STAGES OF DEVELOPMENT WHEN
BRIEF SUPERCELL STRUCTURES MAY BE ATTAINED. THE STORMS LIKELY WILL
MERGE INTO A MORE OR LESS SOLID BAND THAT MOVES SSE WITH THE FRONT
THROUGH MID EVE. PARTS OF THE BAND MAY LINGER INTO EARLY
FRIDAY...WITH WEAK/VEERING LLJ JET SUPPORTING
REGENERATIVE/BACKBUILDING SEGMENTS.
FARTHER NE...N OF CLOUDS/LOW LVL OUTFLOW ASSOCIATED WITH OVERNIGHT
IA/IL/MO MCS...A SEPARATE AREA OF STORMS MAY FORM THIS AFTN AND EVE
ALONG MORE PROGRESSIVE PART OF COLD FRONT FROM NRN/ERN WI INTO
WRN/NRN MI. BUOYANCY WILL BE WEAK IN THIS REGION RELATIVE TO THAT
IN KS/MO...BUT LIKELY SUFFICIENT TO SUPPORT STORMS GIVEN MUCH
STRONGER FORCING FOR ASCENT /DPVA/. COUPLED WITH 40-50 KT
DEEP...LARGELY UNIDIRECTIONAL WSWLY SHEAR...STORMS COULD CONTAIN
BOWING SEGMENTS WITH HIGH WIND.
...NRN/ERN NC INTO SE VA...
REMNANT CIRCULATION WITH T.D. FAY HAS JUST ABOUT BECOME COMPLETELY
ABSORBED WITHIN LARGER SCALE TROUGH OVER THE ERN STATES...AND THE
ASSOCIATED WIND FIELD IS NOTABLY WEAKER THAN IN RECENT DAYS.
NEVERTHELESS...CURRENT SFC OBSERVATIONS SHOW A WEAK WARM FRONT
CONTINUING TO PROGRESS SLOWLY NE ACROSS ERN NC...WHILE BACK-DOOR
BOUNDARY FARTHER N IN VA REMAINS MORE OR LESS STNRY FROM E OF DAN
TOWARD NHK. HEATING OF VERY MOIST AREA S AND E OF THESE
BOUNDARIES...AND LINGERING SELY SFC FLOW...MAY POSE A RISK FOR VERY
ISOLD TORNADOES UNTIL LATE IN THE DAY...ESPECIALLY IN SE VA/FAR NE
NC.
...AZ...
VERY MOIST AIR REMAINS OVER THE SRN THIRD OF AZ...WITH PW AROUND
1.50 IN. ONCE CLOUDS FROM OVERNIGHT STORMS DISSIPATE/DRIFT
SWWD...EXPECT HEATING TO TRIGGER A NEW ROUND OF STORMS...MAINLY OVER
SRN AND CNTRL PARTS OF THE STATE. ANOMALOUSLY STRONG /30 KT/ E TO
ENE FLOW ON SRN FRINGE OF ELONGATED UPR RIDGE WILL PROVIDE AMPLE
SHEAR TO FOSTER STORM PROPAGATION TOWARD THE WSW FROM BOTH THE RIM
AND THE WHITE MOUNTAINS. PARTICULARLY ON THE NWRN FRINGE OF CLOUD
DEBRIS/PW AXIS IN S CNTRL/SW AZ...WHERE SFC TEMPERATURES COULD REACH
THE UPR 90S OR 100F...COMBINATION OF DEEP SEASONABLY STRONG ENE FLOW
WITH FAIRLY MOIST BUT DEEPLY-MIXED BOUNDARY LAYER MAY SUPPORT
OUTFLOW MERGERS AND SWATHS OF DMGG SFC WINDS. HOWEVER...PRESENCE OF
WEAK UPR CIRCULATIONS IN NRN MEXICO CASTS UNCERTAINTY REGARDING
LOCATION AND COVERAGE OF DIURNAL STORMS IN AZ. THUS...WILL MAINTAIN
LOW PROBABILITY RISK ATTM. BUT AN UPGRADE TO CATEGORICAL SLIGHT
RISK MAY BE REQUIRED LATER IN THE DAY IF IT APPEARS THAT A
SIGNIFICANT CLUSTER OF STORMS WILL INDEED EVOLVE OVER S CNTRL AZ.
..CORFIDI/BRIGHT.. 08/28/2008
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