SPC 1300Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0740 AM CDT WED SEP 26 2012 VALID 261300Z - 271200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE SRN AND CNTRL PLNS... ...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE OH VLY INTO THE MID ATLANTIC... ...SYNOPSIS... WEAK SPLIT FLOW PATTERN WILL CONTINUE OVER THE CNTRL AND ERN STATES...DOWNSTREAM FROM UT/CO UPR LOW AND ON SRN FRINGE OF QUE/GRT LKS TROUGH. A SRN STREAM ZONAL JET WILL PERSIST FROM THE SRN RCKYS/SRN PLNS INTO THE LWR OH VLY/MID ATLANTIC STATES...WHERE IT WILL MERGE WITH STRONGER BAND OF FLOW MARKING BASE OF QUE TROUGH. AT LWR LVLS...WRN PART OF FRONTAL ZONE NOW EXTENDING FROM THE LWR GRT LKS THROUGH NRN/CNTRL IL INTO CNTRL KS SHOULD REMAIN QSTNRY TODAY...WHILE ERN PART CONTINUES E TO OFF THE NEW ENGLAND CST BY 12Z THU. SCTD AREAS OF SHOWERS AND TSTMS LIKELY WILL PERSIST INVOF THE BOUNDARY THROUGH THE PERIOD...WITH ACTIVITY MODULATED BY BOTH DIURNAL HEATING AND NOCTURNALLY-ENHANCED LLJ. THE GREATEST SFC-BASED INSTABILITY SHOULD DEVELOP FROM THE SRN PLNS INTO THE OH VLY. WEAKER BUOYANCY IS EXPECTED OVER THE APPALACHIANS AND MID ATLANTIC REGION...WHERE SOMEWHAT GREATER DEEP SHEAR WILL EXIST. ...SE CO SE INTO PARTS OF THE SRN PLNS/WRN OZARKS THIS AFTN/EVE... ONGOING TSTMS ALONG AND S OF STNRY FRONT EXPECTED TO PERSIST THROUGH AT LEAST MIDDAY FROM ERN PARTS OF KS/OK ENE INTO THE LWR OH VLY...SUPPORTED BY WAA/MOISTURE TRANSPORT ALONG BROAD WSWLY LLJ. MOST OF THE ACTIVITY SHOULD REMAIN SUB-SVR...BUT ISOLD MARGINALLY SVR HAIL OR WIND COULD OCCUR. SFC HEATING OCCURRING W OF THE ABOVE ACTIVITY SHOULD SUPPORT SCTD TO NUMEROUS NEW STORMS ALONG OUTFLOW BOUNDARIES OVER NRN/WRN OK AND SW/S CNTRL KS...AND ALONG DRY LINE IN W TX. OTHER STORMS MAY FORM A BIT LATER IN THE DAY INTO TNGT IN ZONE OF STRENGTHENING UPSLOPE FLOW OVER SE CO. WHILE DEEP SHEAR WILL BE SOMEWHAT WEAKER THAN YESTERDAY /DUE MAINLY TO DECREASED 700 MB FLOW/...RELATIVELY COOL AIR WILL REMAIN PRESENT AT MID-LVLS ATOP A MODERATELY MOIST BOUNDARY LAYER. COUPLED WITH INCREASING UPR DIVERGENCE ASSOCIATED WITH EXIT REGION OF HIGH-LVL...SRN BRANCH SPEED MAX APPROACHING FROM THE SRN RCKYS...SETUP MAY YIELD A FEW LONG-LIVED CLUSTERS OF STORMS CAPABLE OF SVR HAIL/WIND. ISOLD SVR WEATHER MAY PERSIST INTO LATE EVE...ESPECIALLY IN PARTS OF OK...NW TX...AND PERHAPS SE CO. IN GENERAL...HOWEVER...STORM STRENGTH SHOULD DIMINISH BY MID EVE. ...MID/UPR OH VLY INTO THE MID ATLANTIC THIS AFTN/EVE... SEASONABLY STRONG /50 KT/ 700-500 MB UNIDIRECTIONAL WLY FLOW WILL PREVAIL FROM OH/NRN KY TO THE MID ATLANTIC CST IN BASE OF QUE UPR TROUGH. INSTABILITY WILL...HOWEVER...REMAIN MODEST RELATIVE TO POINTS W...OWING LARGELY TO MORE LIMITED BOUNDARY LAYER MOISTURE AND MID/UPR LVL CLOUD COVER. NEVERTHELESS...SUFFICIENT BUOYANCY LIKELY WILL DEVELOP TO SUPPORT DEVELOPMENT OF SCTD AREAS OF DIURNALLY-ENHANCED STORMS IN A NARROW CORRIDOR ALONG THE EFFECTIVE COLD FRONT...I.E. ALONG COMPOSITE OUTFLOW BOUNDARY THAT ATTM EXTENDS FROM CNTRL/NRN KY ENE INTO PARTS OF WV/VA/MD. GIVEN THE STRENGTH OF THE LOW TO MID TROPOSPHERIC WIND FIELD...AND RELATIVELY STEEP MID LVL LAPSE RATES/RESIDUAL EML...POTENTIAL WILL EXIST FOR A FEW STORMS WITH SMALL-SCALE BOWS AND POSSIBLY LOCALLY DMGG WIND. FARTHER N...MORE WIDESPREAD CLOUDINESS AND SOMEWHAT WEAKER DEEP WIND FIELD EXPECTED TO LIMIT STORM STRENGTH/LONGEVITY ALONG IMMEDIATE COLD FRONT FROM NRN OH INTO NRN PA/NY...ALTHOUGH ISOLD STRONG TO SVR GUSTS CANNOT ENTIRELY BE RULED OUT. ..CORFIDI/GRAMS.. 09/26/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1300.html
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