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DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0102 AM CDT WED MAY 19 2004
VALID 191200Z - 201200Z
THERE IS A MDT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 50 WSW
YKN 45 N ATY 20 NW AXN 30 NW RWF 25 NNW FRM 10 SSE MCW 15 SW ALO 35
SW OTM 40 NNE FNB 20 SW LNK 20 NNE GRI 50 WSW YKN.
THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 40 NE
ORF 15 W BLF 25 NE BWG 10 ESE MDH JEF 25 ENE MKC 20 NNE MHK 40 SSW
EAR 10 SW LBF 20 ENE PHP 40 NE Y22 50 NNW MOT ...CONT... 35 NNW TVC
GRR 45 NNE FWA 35 SSE FDY 20 SSE AOO 25 S JFK.
GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 15 SE BPT 15 NNE ESF
35 S GWO 40 N TUP 15 NNE MKL 20 ESE POF 20 NE JLN 40 SSW EMP 20 WNW
HUT 35 WNW GAG 50 SE LBB 20 ESE P07 ...CONT... 40 S DMN 45 SE GNT 20
E RTN 35 SSE LIC 35 WSW AKO 10 WNW FCL 15 NNE SLC 60 NW ELY 45 SSE
NFL 30 WSW TVL 30 NW SAC 50 SW MHS 35 NE MFR 35 N SEA 20 NE BLI.
GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 40 NNW SYR 10 NNE ELM
15 S AVP 15 S BDR.
...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS PORTIONS OF ERN NEB/ERN SD/SWRN MN AND MUCH OF CENTRAL/WRN
IA...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN/CENTRAL PLAINS
EWD TO THE WRN GREAT LAKES REGION...AND MID MS/OH VALLEYS TO MID
ATLANTIC REGION...
...ACTIVE SEVERE WEATHER DAY IS EXPECTED ACROSS PORTIONS OF THE ERN
PLAINS INTO THE UPPER MS VALLEY...
...SYNOPSIS...
NERN PACIFIC UPPER RIDGE WILL CONTINUE TO BUILD NWD TODAY ACROSS
ALASKA...RESULTING IN DOWNSTREAM PACIFIC NW TROUGH TO RETROGRADE
SWWD ALONG THE U.S. WEST COAST AS HEIGHTS RISE ACROSS THE CENTRAL/
SRN PLAINS. SHORT WAVE TROUGH...NOW OVER CENTRAL MT...WILL MOVE
ENEWD ACROSS ND/FAR SRN CANADA AS AN OPEN...POSITIVELY TILTED
TROUGH...REACHING CENTRAL ONTARIO/UPPER GREAT LAKES BY 12Z THURSDAY.
AN INCREASE IN WLY MID-LEVEL FLOW IS EXPECTED ACROSS THE NORTH
CENTRAL STATES THIS FORECAST PERIOD AS THE HEIGHT GRADIENT TIGHTENS
BETWEEN THE BUILDING RIDGE OVER THE CENTRAL/SRN PLAINS AND A TROUGH
MOVING SWD ACROSS THE CENTRAL CANADIAN PROVINCES. AT THE SURFACE...
A LEE LOW OVER THE WRN DAKOTAS WILL DEEPEN AS IT MOVES ENEWD ACROSS
NRN MN...AND THEN ACCELERATE TOWARD JAMES BAY BY 12Z THURSDAY.
SURFACE BOUNDARY INITIALLY OVER THE LOWER MO VALLEY WILL MOVE NEWD
AS A WARM FRONT ACROSS THE UPPER MS VALLEY REACHING MI/OH BY THE END
OF THE PERIOD. THIS BOUNDARY COMBINED WITH A COLD FRONT MOVING EWD
ACROSS THE NRN PLAINS TO THE UPPER MS VALLEY BY THE END OF THE
PERIOD WILL BE THE FOCI FOR AN ACTIVE SEVERE WEATHER DAY...
PARTICULARLY IN THE PLAINS/UPPER MS VALLEY.
IN THE EAST...UPPER TROUGH INITIALLY OVER THE NERN STATES TO UPPER
OH VALLEY WILL MOVE EWD AND BE REPLACED BY SHORT WAVE RIDGING.
...LOWER MO/UPPER MS VALLEYS EWD TO THE GREAT LAKES REGION...
THUNDERSTORMS...SOME SEVERE...MAY BE ONGOING AT THE START OF THE
PERIOD ACROSS NRN SD INTO ND WITHIN MOIST/WAA REGIME TO THE EAST OF
THE SURFACE LOW...SUPPORTING ISOLATED HAIL. NOCTURNAL SLY LLJ OVER
THE DAKOTAS...AND SECOND SLY LLJ OVER THE SRN PLAINS WILL MAINTAIN
THEIR INTENSITY AS THEY TRANSLATE EWD THROUGH THE DAY. THIS SLY
LOW-LEVEL FLOW WILL ADVECT MOISTURE NWD AS THE WARM FRONT RETREATS
NNEWD. AXIS OF SURFACE DEWPOINTS IN THE 60S WILL EXTEND ACROSS THE
ERN DAKOTAS/WRN MN BY MID-LATE AFTERNOON WITH VALUES IN THE LOWER
70S ACROSS ERN NEB/WRN IA. SUFFICIENT MOISTURE /850 MB DEWPOINTS
16-18C BY 00Z ACROSS ERN NEB/...SURFACE HEATING AND STEEP LAPSE
RATES WILL RESULT IN A VERY UNSTABLE AIR MASS FROM ERN SD/ERN NEB
INTO IA WITH EXTREME INSTABILITY /MLCAPE AOA 4000 J/KG/ OVER ERN
NEB/FAR WRN IA. NNELY RETURN OF MOISTURE WILL ALSO SUPPORT A
MODERATELY UNSTABLE AIR MASS NWD ACROSS NWRN MN AND EWD INTO WI THIS
EVENING AND NRN IL OVERNIGHT.
INCREASING MID-LEVEL FLOW WITH THE SHORT WAVE TROUGH MOVING ACROSS
THE DAKOTAS/NRN MN WILL RESULT IN STRONG WLY ORIENTED DEEP LAYER
SHEAR VECTORS OF 45-60 KT TO SUPPORT WIDESPREAD SEVERE STORMS...
ESPECIALLY WITHIN THE MODERATE RISK AREA BY LATE AFTERNOON.
MODELS SUGGEST ONGOING STORMS OVER THE DAKOTAS THIS MORNING WILL
REDEVELOP AND/OR INTENSIFY AS THEY MOVE EWD ACROSS NRN/CENTRAL MN
THIS AFTERNOON. ADDITIONAL STORMS WILL LIKELY DEVELOP SWD ALONG THE
WARM FRONT FROM ERN SD/NERN NEB/WRN IA...WHERE THE AIR MASS WILL BE
EXTREMELY UNSTABLE AND SUPPORT POTENTIALLY LONG-LIVED
SUPERCELLS/SUPERCELL CLUSTERS WITH TORNADOES...LARGE HAIL AND
DAMAGING WINDS. THE GREATEST POTENTIAL FOR SIGNIFICANT TORNADOES
SHOULD BE ACROSS ERN NEB/FAR SERN SD/FAR SWRN MN AND WRN/SRN IA
WHERE SHEAR VECTORS FAVOR STORMS REMAINING ALONG THE WARM FRONT.
THIS ACTIVITY WILL MOVE EWD ACROSS SRN MN/IA THIS EVENING/ OVERNIGHT
IN THE FORM OF ONE OR TWO SEVERE MCS/S WITH THE THREAT TRANSITIONING
INTO PRIMARILY A WIND THREAT AS THESE COMPLEXES MOVE INTO WI/ERN
IA/NRN IL. ACTIVITY MAY REACH FAR WRN LOWER MI BY 12Z THURSDAY.
ADDITIONAL SEVERE STORMS WILL ALSO LIKELY DEVELOP ALONG THE COLD
FRONT AS IT MOVES EWD ACROSS THE ERN DAKOTAS/ERN NEB AND UPPER MS
VALLEY AFTER 00Z.
...MID ATLANTIC REGION WWD TO THE MIDWEST/MID MS VALLEY...
SURFACE BAROCLINIC ZONE WILL SAG SWD ACROSS THE DELMARVA REGION WWD
TO THE OH/MID MS VALLEYS...WITH ABUNDANT MOISTURE REMAINING ALONG
AND SOUTH OF THIS BOUNDARY. ADDITIONAL MOISTURE SHOULD ADVECT NEWD
ALONG TROUGH IN LEE OF THE SRN/CENTRAL APPALACHIANS INTO THE
DELMARVA REGION. LONG-LIVED MCV/SHORT WAVE TROUGH...CURRENTLY
LOCATED ACROSS ERN IND/WRN OH...WILL MOVE ESEWD ACROSS THE MID
ATLANTIC REGION TODAY ENHANCING WIND FIELDS/DEEP LAYER SHEAR AND
LARGE SCALE ASCENT FOR THUNDERSTORMS ALONG THE SURFACE BOUNDARY
WITHIN MARGINALLY TO MODERATELY UNSTABLE AIR MASS. DEEP WLY FLOW
WITH 30-35 KT OF DEEP LAYER SHEAR WILL SUPPORT LINES/BOW SEGMENTS
WITH THIS ACTIVITY ALONG WITH HAIL.
FARTHER WEST ALONG THE QUASI-STATIONARY BOUNDARY...SCATTERED STORMS
SHOULD DEVELOP FROM SRN OH WWD TO THE MID MS VALLEY...WITH A CLUSTER
OF STORMS POTENTIALLY ONGOING AT THE START OF THE PERIOD OVER THE
NRN HALF OF MO INTO WRN IL. DESPITE WEAK LAPSE RATES...A MOIST AIR
MASS WITH SURFACE DEWPOINTS IN THE MID-UPPER 60S WILL CONTRIBUTE TO
MLCAPE VALUES RANGING FROM 500-1000 J/KG ALONG THE BAROCLINIC ZONE.
THIS COMBINED WITH WEAK DEEP LAYER SHEAR VALUES WILL RESULT IN
PULSE-TYPE MULTI-CELL STORMS WITH STRONG WIND GUSTS AND HAIL THE
MAIN THREATS THROUGH THE DAY. SEVERE ACTIVITY IS EXPECTED TO WEAKEN
DURING THE EVENING WITH THE LOSS OF DAY TIME HEATING.
..PETERS/TAYLOR.. 05/19/2004
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