SWODY1
SPC AC 142000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT TUE JUL 14 2009
VALID 142000Z - 151200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CNTRL PLAINS THROUGH
THE MIDDLE AND UPPER MS VALLEY AREAS...
...ERN SD THROUGH UPPER MS VALLEY REGION...
STORMS ARE IN THE PROCESS OF DEVELOPING OVER ERN SD WITHIN ZONE OF
FRONTAL CONVERGENCE ON SRN PERIPHERY OF DEEPER ASCENT ASSOCIATED
WITH EWD ADVANCING SHORTWAVE TROUGH. DESTABILIZATION OF THE BOUNDARY
LAYER HAS BEEN MITIGATED BY PERSISTENT LOW CLOUDS...BUT TEMPERATURES
WARMING TO NEAR 80 HAVE RESULTED AN AXIS OF 1000-1500 J/KG MLCAPE
EAST OF DEVELOPING STORMS. UPPER JET ROTATING THROUGH BASE OF UPPER
TROUGH WILL CONTINUE TO SUPPORT BULK SHEAR OF 40-50 KT OVER WARM
SECTOR DESPITE VEERING LOW LEVEL WIND PROFILES CLOSER TO THE FRONT.
ORGANIZED STORM STRUCTURES INCLUDING BOWING LINE SEGMENTS AND
SUPERCELLS WILL BE POSSIBLE WITH THE STRONGER STORMS.
LARGEST 0-1 KM HODOGRAPHS REMAIN ACROSS SRN MN WHERE SLY LOW LEVEL
JET INTERSECTS SELY NEAR SURFACE WINDS ALONG AND NORTH OF WARM
FRONT. THE BOUNDARY LAYER HAS BEEN SLOW TO DESTABILIZE OVER SRN MN
WHERE THE STRONGER LOW LEVEL SHEAR EXISTS...AND THIS MAKES THE
TORNADO THREAT CONDITIONAL. HOWEVER...A WINDOW OF OPPORTUNITY MAY
EXIST FOR ISOLATED TORNADOES LATER THIS AFTERNOON OR EARLY EVENING
AS TEMPERATURES WARM INTO THE LOW 80S AND BEFORE THE LOW LEVEL JET
AXIS SHIFTS EAST OF THE DESTABILIZING WARM SECTOR.
...KS THROUGH MID MS VALLEY...
REF SWOMCD 1559 FOR LATEST INFORMATION ON THIS THREAT AREA.
..DIAL.. 07/14/2009
.PREV DISCUSSION... /ISSUED 1127 AM CDT TUE JUL 14 2009/
...SYNOPSIS...
THE EXPECTED SYNOPTIC PATTERN EVOLUTION THROUGH EARLY WEDNESDAY
REMAINS LARGELY UNCHANGED SINCE YESTERDAY...AS A STRONG SHORTWAVE
TROUGH MOVES EWD OVER THE NRN PLAINS ALONG WITH AN ASSOCIATED COLD
FRONT. HOWEVER...THE SCENARIO IS COMPLICATED BY THE INFLUENCES OF
OVERNIGHT AND ONGOING CONVECTION FROM THE ERN DAKOTAS TO MO.
...ERN ND/NE SD INTO CENTRAL AND NRN MN THIS AFTERNOON/EVENING...
ONGOING CONVECTION FROM NE SD INTO ERN ND IS IMMEDIATELY DOWNSTREAM
FROM THE PRIMARY MID LEVEL WAVE MOVING EWD OVER THE DAKOTAS...AND IT
APPEARS LIKELY THAT THIS CONVECTION WILL PERSIST THROUGH THE DAY
WHILE OVERSPREADING THE REMAINDER OF ERN ND AND NW MN. WIDESPREAD
CLOUDS/RAINFALL WILL TEND TO LIMIT DESTABILIZATION NEAR AND N OF
I-94 ACROSS MN...WITH THE GREATER THREAT FOR LARGE HAIL/DAMAGING
WINDS AND AN ISOLATED TORNADO CONFINED TO THE SRN FLANK OF THE
ONGOING CONVECTIVE CLUSTER AS IT PROGRESSES FROM NE SD INTO
WRN/CENTRAL MN ALONG THE SYNOPTIC WARM FRONT.
...SE SD/SW MN/NE NEB/NW IA THIS AFTERNOON/EVENING...
THE STRONGER MID LEVEL HEIGHT FALLS WILL BRUSH THIS AREA...AND THE
LOW-LEVEL FLOW IS EXPECTED TO WEAKEN AND VEER AS THE PRIMARY NRN
STREAM LLJ SEGMENT DEVELOPS NEWD TO THE UPPER MS VALLEY THIS
AFTERNOON/EVENING. THUS...EXPECT MAINLY SHALLOW ASCENT ALONG THE
COLD FRONT TO PROVIDE THE PRIMARY FOCUS FOR WIDELY SCATTERED
THUNDERSTORM DEVELOPMENT LATER THIS AFTERNOON. SURFACE HEATING AND
GRADUAL EROSION OF LOW CLOUDS...ALONG WITH UPPER 60S BOUNDARY LAYER
DEWPOINTS...WILL CONTRIBUTE TO MLCAPE OF 1500-2000 J/KG BY MID-LATE
AFTERNOON. THIS MODERATE INSTABILITY AND DEEP LAYER SPEED
SHEAR/STRAIGHT HODOGRAPHS WILL FAVOR SUPERCELLS OR SHORT LINE
SEGMENTS CAPABLE OF PRODUCING DAMAGING WINDS AND LARGE HAIL. A
TORNADO OR TWO WILL BE POSSIBLE...BUT THE STRONGER LOW-LEVEL SHEAR
IS EXPECTED TO REMAIN GENERALLY E OF THE CORRIDOR OF INSTABILITY
ALONG THE COLD FRONT.
...NE KS/NW MO AND EXTREME SE NEB/SW IA THIS AFTERNOON/TONIGHT...
THE NRN STREAM SHORTWAVE TROUGH WILL PASS WELL TO THE N...LEAVING
THIS AREA ON THE SRN FRINGE OF THE 30-40 KT WLY MID LEVEL FLOW. THE
RICHER LOW-LEVEL MOISTURE /BOUNDARY LAYER DEWPOINTS IN THE 70S/ HAS
BEEN CONFINED TO ERN KS AS OF MID MORNING BY CONVECTIVE OUTFLOW IN
THE WAKE OF THE MCV/WEAKENING MCS ACROSS CENTRAL/NE MO. THIS
MOISTURE WILL BE AUGMENTED BY EVAPOTRANSPIRATION DURING THE
AFTERNOON AND WILL SPREAD NWD INTO NE KS/NW MO AS THE MORNING
OUTFLOW RETREATS...AND A SECONDARY WARM FRONTAL SEGMENT LIFTS NEWD
ACROSS KS IN ADVANCE OF A SECONDARY CYCLONE DEVELOPING ENEWD FROM SW
TOWARD CENTRAL/NE KS. THIS WILL RESULT IN A TRIPLE POINT SETUP BY
21-00Z NEAR OR A LITTLE W OF CNK...WITH AN EFFECTIVE WARM FRONT TO
THE E INTO NW MO.
STRONG SURFACE HEATING/MIXING ACROSS KS AND LOW-LEVEL CONVERGENCE
NEAR THE TRIPLE POINT SHOULD SUPPORT THUNDERSTORM DEVELOPMENT BY
THIS EVENING. STRONG INSTABILITY /MLCAPE OF 3000-4000 J/KG/ AND
EFFECTIVE BULK SHEAR OF 35-45 KT WILL BE SUFFICIENT FOR SUPERCELLS
CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS. A TORNADO OR
TWO MAY ALSO OCCUR WITH THE INITIAL/MORE DISCRETE STORMS GIVEN THE
LOWER LCL HEIGHTS AND SOMEWHAT ENHANCED LOW-LEVEL SHEAR E OF THE
TRIPLE POINT AND ALONG THE EFFECTIVE WARM FRONT.
HOWEVER...CONVECTION MAY GROW RATHER QUICKLY INTO AN MCS BY LATE
EVENING/EARLY TONIGHT FROM NE KS/EXTREME SE NEB EWD ACROSS NRN MO
AND SRN IA.
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