SPC AC 061329
DAY 1 CONVECTIVE OUTLOOK RESENT 1
NWS STORM PREDICTION CENTER NORMAN OK
0829 AM CDT THU AUG 06 2009
VALID 061300Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS THROUGH TONIGHT ACROSS A BROAD
AREA OF THE NRN ROCKIES TO THE CENTRAL AND NRN PLAINS...
...SYNOPSIS...
THE TRANSITION TO A MORE PROGRESSIVE LARGE SCALE REGIME IS UNDERWAY
AS THE CLOSED LOW OVER NRN CA BEGINS TO EJECT NEWD TOWARD ID...THE
MID LEVEL RIDGE DEVELOPS EWD OVER THE SRN PLAINS...AND THE
DOWNSTREAM TROUGH MOVES EWD FROM THE GREAT LAKES TO NEW ENGLAND. AT
THE SURFACE...A COLD FRONT WILL CONTINUE TO MOVE SLOWLY SEWD OFF THE
SE NEW ENGLAND AND MID ATLANTIC COASTS TODAY...REACHING THE SE
ATLANTIC COAST THIS EVENING. THE FRONT WILL EXTEND WWD FROM THE
CAROLINAS ACROSS THE NRN GULF STATES...AND THEN NWWD ACROSS THE
SRN/CENTRAL PLAINS TO A DEVELOPING LEE CYCLONE INVOF ERN WY.
FARTHER W...A COLD FRONT AND SURFACE LOW WILL TRANSLATE ACROSS THE
ERN GREAT BASIN IN ADVANCE OF THE EJECTING CA MID LEVEL TROUGH...AND
WITH THE GREAT BASIN AND HIGH PLAINS LEE CYCLONES CONSOLIDATING AS A
SINGLE LOW INVOF WRN SD BY LATE TONIGHT.
...NRN ROCKIES AREA TODAY...
HEIGHT FALLS AND INCREASING LARGE SCALE ASCENT DOWNSTREAM FROM THE
EJECTING CA TROUGH /IN THE LEFT EXIT REGION OF THE UPPER JET/ WILL
COMBINE WITH DAYTIME HEATING TO SUPPORT INCREASING COVERAGE THROUGH
THE DAY OF CLUSTERS/SHORT LINES OF THUNDERSTORMS FROM NRN NV NEWD
ACROSS ID INTO SW MT. STEEP LOW-LEVEL LAPSE RATES AND A MODEST
INCREASE IN L0W-MID LEVEL MOISTURE /PW VALUES NEAR 1 INCH/ WILL
RESULT IN SUFFICIENT INSTABILITY FOR SEVERE STORMS WITH DAMAGING
WINDS AND SOME HAIL. INCREASING MID-UPPER SSWLY FLOW WILL
SIMULTANEOUSLY CONTRIBUTE TO EFFECTIVE BULK SHEAR OF 30-40 KT WHICH
WILL BE SUFFICIENT FOR ORGANIZED BOWING SEGMENTS AND SUPERCELLS
TODAY ACROSS NRN NV/ID AND CONTINUING INTO EARLY TONIGHT ACROSS SRN
MT.
...CENTRAL AND NRN HIGH PLAINS THROUGH TONIGHT...
LEE CYCLOGENESIS INVOF ERN WY WILL PROMOTE NWD/NWWD TRANSPORT OF
LOW-LEVEL MOISTURE FROM THE CENTRAL PLAINS /BOUNDARY LAYER DEWPOINTS
IN THE MID 60S ACROSS NEB AND UPPER 60S ACROSS KS/ TO ERN MT BY THIS
AFTERNOON/EVENING. THIS MOISTENING WILL OCCUR BENEATH A PLUME OF
STEEP MID LEVEL LAPSE RATES SPREADING NEWD FROM THE CENTRAL
ROCKIES...AND IN AN ENVIRONMENT OF INCREASING DEEP LAYER WLY SHEAR
AND A 30-40 KT SLY LLJ. THE NET RESULT WILL BE SUFFICIENT
INSTABILITY AND BULK SHEAR FOR SUPERCELLS AND ORGANIZED STORM
CLUSTERS TODAY INTO TONIGHT.
THE CONVECTIVE EVOLUTION ACROSS THE PLAINS IS SOMEWHAT UNCERTAIN
GIVEN THE PRESENCE OF ONGOING THUNDERSTORM CLUSTERS THIS MORNING
FROM CENTRAL OK INTO CENTRAL KS...AND FROM NE NEB INTO WRN SD AND SE
MT. REGIONAL 12Z SOUNDINGS SHOW SUFFICIENT ELEVATED INSTABILITY
/3000+ J/KG MUCAPE AT UNR/ TO MAINTAIN THE STORMS AND AN ATTENDANT
THREAT FOR LARGE HAIL THROUGH THE MORNING AND INTO AT LEAST EARLY
AFTERNOON IN ASSOCIATION WITH LOW-LEVEL WAA AND THE SLY LLJ. THE
CONVECTION COULD ALSO BE AIDED BY SUBTLE SPEED MAXIMA EJECTING
EWD/NEWD FROM THE CENTRAL ROCKIES. ADDITIONAL STORMS MAY FORM THIS
AFTERNOON ALONG THE RESULTANT OUTFLOW BOUNDARIES IN KS/NEB/SD AS THE
LOW LEVELS WARM AWAY FROM THE CLOUD SHIELDS WITH THESE STORMS...AS
WELL AS ALONG THE RETREATING FRONT AND STRENGTHENING LEE TROUGH
ACROSS THE CENTRAL/NRN HIGH PLAINS THIS AFTERNOON/EVENING. THESE
STORMS WILL BE CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING
WINDS...AND POTENTIALLY AN ISOLATED TORNADO OR TWO ALONG ONE OF THE
REMNANT SURFACE BOUNDARIES WHERE LOW-LEVEL SHEAR AND MOISTURE WILL
BE MAXIMIZED.
NOCTURNAL STRENGTHENING OF THE CENTRAL PLAINS LLJ TO AOA 50 KT WILL
HELP MAINTAIN SUBSTANTIAL LOW-LEVEL WAA ON THE ERN EDGE OF THE WARM
SECTOR...AND A CONTINUING THREAT FOR ELEVATED STORMS WITH LARGE HAIL
INTO THE OVERNIGHT HOURS.
..THOMPSON/GARNER.. 08/06/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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