SWODY1
SPC AC 211922
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0222 PM CDT SUN JUN 21 2009
VALID 212000Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE CORN
BELT/MID-MS VLY REGION...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN GRT BASIN AND
NRN INTERMOUNTAIN W...
20Z OTLK CHANGES: 1/ EXPAND SLGT RISK SEWD ACROSS CNTRL/SRN IL AND
2/ EXPAND SLGT RISK INTO NERN UT.
...CORN BELT...
PREV FCST REASONING LOOKS GOOD. WRMFNT CONTINUES TO DEVELOP NWD
TOWARD THE IA/MN BORDER WITH WARM SECTOR CINH WEAKENING. WATER
VAPOR IMAGERY SHOWS EVIDENCE OF MOISTENING ALONG TRAILING PORTION OF
UPR TROUGH MIGRATING INTO MN. THIS MAY CAUSE ACCAS FIELD OVER NWRN
IA TO GROW INTO SFC-BASED TSTMS MID-LATE AFTN...ALA LATEST
HIGH-RESOLUTION RAPID REFRESH MODEL. SLATER PROFILER SHOWS 0-6KM
SHEAR IN EXCESS OF 40 KTS AND GIVEN 2000+ MLCAPES...SUPERCELLS WILL
BE POSSIBLE. WARM TEMPERATURES ALOFT WILL MAKE LARGE HAIL
PRODUCTION DIFFICULT...BUT STRONGER CELLS MAY PRODUCE SVR HAIL ALONG
WITH DMGG WIND GUSTS. TORNADO THREAT WILL INCREASE WITH THOSE CELLS
THAT CROSS/DEVELOP INVOF WRMFNT WHERE 0-1KM SRH IS PROGGED TO BE AOA
25 KTS IN NRN IA. ACTIVITY WILL MOVE INTO THE UPR MS VLY REGION
OVERNIGHT WITH DECREASING SVR THREATS.
FARTHER E...TSTMS HAVE INCREASED/BECOME SFC-BASED ALONG BACK EDGE OF
RETREATING WRMFNT OVER CNTRL IL AND INVOF OF AN APPARENT MCV.
OBJECTIVE ANALYSIS SUGGESTS A NW-SE ORIENTED INSTABILITY AXIS SEWD
TOWARD SWRN IND AND EXPECTATION IS FOR ANY SVR THREAT TO DEVELOP
SLOWLY SEWD DURING THE EVENING. WNC PROFILER EXHIBITS STRAIGHT
HODOGRAPH...AND MARGINALLY SHEARED ENVIRONMENT...SUGGESTIVE OF
SPLITTING AND BRIEF SUPERCELL ENVIRONMENT. SOME HAIL WILL BE
LIKELY...BUT DMGG WIND GUSTS AND PERHAPS AN ISOLD TORNADO WILL BE
MORE LIKELY.
...NRN INTERMOUNTAIN REGION...
PREV FCST ON TRACK. JUXTAPOSITION OF STRONGEST SHEAR /BENEATH 45 KT
SWLY H5 JET/ AND INSTABILITY /MLCAPE 1000 J PER KG/ HAVE DEVELOPED
OVER UT AND WRN WY WHERE SLGT RISK HAS BEEN ADJUSTED EWD. EXPECT
COMBO OF LINE SEGMENTS AND BRIEF ROTATING DISCRETE CELLS TO PRODUCE
SVR HAIL/WIND THROUGH THIS EVENING. FARTHER W...WEAKER SHEAR
EXISTS...BUT COLDER TEMPERATURES ALOFT AND AT LEAST MODEST FORCING
WILL LIKELY BOOST UPDRAFT STRENGTH FOR AT LEAST A HAIL THREAT.
..RACY.. 06/21/2009
.PREV DISCUSSION... /ISSUED 1144 AM CDT SUN JUN 21 2009/
CORRECTED GRAPHIC
...IA/IL/NRN MO/SRN MN/SWRN WI...
WEAKENING MOIST CONVECTION IS EXPECTED TO CONTINUE LIFTING NNEWD
ACROSS THE UPPER MS RIVER VALLEY TODAY ASSOCIATED WITH EJECTING
SHORTWAVE TROUGH. IN THE WAKE OF THIS ACTIVITY...SURFACE WARM FRONT
WILL REMAIN WELL DEFINED FROM PORTIONS OF CENTRAL IL INTO
CENTRAL/NRN IA AND SHOULD PROVIDE FOCUS FOR INCREASING SEVERE THREAT
LATER TODAY. STRONG HEATING ALONG THE MO RIVER VALLEY SHOULD ALLOW
AXIS OF NEAR 90F SURFACE TEMPERATURES TO NOSE INTO NWRN IA WHERE
CONVECTIVE INHIBITION WILL BECOME QUITE WEAK BY 21Z...ALTHOUGH WEAK
LAPSE RATES ARE EXPECTED TO LIMIT AVAILABLE MLCAPE. REGARDLESS...
AIRMASS WILL STILL BECOME MODERATELY UNSTABLE AND SEVERE
THUNDERSTORM DEVELOPMENT IS EXPECTED NEAR THE WARM FRONT OVER NWRN
IA DURING THE LATE AFTERNOON. ACTIVITY WILL LIKELY INCREASE IN
COVERAGE AND INTENSITY ESEWD THROUGH THE EVENING. MODERATE TO
STRONG SWLY H85 FLOW WILL SUPPORT FAIRLY LARGE LOW LEVEL HODOGRAPHS
NEAR THE SURFACE WARM FRONT WITHIN DEEP LAYER SHEAR AROUND 35
KT...BOTH SUPPORTIVE OF A RISK OF TORNADIC SUPERCELLS AND SMALL
SCALE BOW ECHOES INTO THE EARLY TO MID EVENING.
...NRN INTERMOUNTAIN REGION INTO THE NRN/CENTRAL HIGH PLAINS...
COOL CYCLONIC FLOW WILL PREVAIL OVER THE NRN INTERMOUNTAIN REGION
TODAY...DOWNSTREAM FROM CONSOLIDATING TROUGH IN ORE/NV. MODEST
DESTABILIZATION AHEAD OF TROUGH SHOULD LEAD TO AFTERNOON STORM
DEVELOPMENT FROM NE NV/NRN UT NEWD INTO PARTS OF ID/WRN MT AND WRN
WY. 30-40 KT DEEP SSWLY SHEAR WILL FOSTER ORGANIZATION OF
CONVECTION INTO ONE OR MORE BANDS/CLUSTERS. EMBEDDED STRONGER/
SUSTAINED STORMS COULD YIELD ISOLATED DAMAGING WINDS AND LARGE HAIL
THROUGH THE EARLY EVENING.
FARTHER EAST OVER THE HIGH PLAINS...SUFFICIENT VERTICAL MOTION AND
MODEST INSTABILITY SHOULD SUPPORT CLUSTERS OF STRONG TO ISOLATED
SEVERE STORMS INVOF LEE TROUGH OVER WRN ND AND INTO SERN WY/NERN CO.
HOWEVER...OVERALL THREAT APPEARS TOO ISOLATED TO WARRANT GREATER
SEVERE PROBABILITIES ATTM.
...MID/UPPER MS RIVER VALLEY INTO SRN APPALACHIANS/SC-GA COAST...
PERSISTENT SE-NW ORIENTED SURFACE FRONT TOPPED BY MODEST NWLY
MID/UPPER LEVEL FLOW WILL MAINTAIN A THREAT OF ISOLATED SEVERE
ACROSS THIS CORRIDOR THIS AFTERNOON. LITTLE OR NO LARGE SCALE
SUPPORT IS EVIDENT ON WV IMAGERY THIS MORNING. HOWEVER AS CAP
WEAKENS AND ISOLATED STORMS DEVELOP VIA AFTERNOON HEATING...DEEP
LAYER SHEAR WILL BE SUPPORTIVE OF ORGANIZATION AND POSSIBILITY OF
ISOLATED WIND DAMAGE. ALTHOUGH WEAK LAPSE RATES AND LACK OF FOCUSED
ASCENT WILL TEND TO HINDER OVERALL SEVERE THREAT ACROSS THE BROADER
AREA.
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