SWODY1
SPC AC 181249
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT THU OCT 18 2007
VALID 181300Z - 191200Z
..THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF THE LWR OH AND LWR
TN VLYS...
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE ERN GULF CST THROUGH
THE MID MS VLY TO THE GRT LKS...
..SYNOPSIS...
LEAD SHORTWAVE TROUGH THAT AFFECTED THE PLNS/OZARKS YESTERDAY WILL
MOVE NE ACROSS THE UPR GRT LKS LATER TODAY AS UPSTREAM SPEED MAX NOW
OVER THE CO/NM BORDER REDEVELOPS E ACROSS THE SRN PLNS TODAY...AND
INTO THE MID/LWR MS VLY TONIGHT.
AT LWR LVLS...IA SFC LOW SHOULD TRACK N TO NRN MN BY THIS EVENING AS
ATTENDANT COLD/OCCLUDED FRONT MOVES E TO LK MI...ERN IL...SE MO AND
NRN LA. THE FRONT SHOULD CONTINUE E/NE ACROSS THE OH AND TN VLYS
TONIGHT AS LOW REMAINS NEARLY STATIONARY OVER THE MN ARROWHEAD.
..LWR TN VLY/LWR OH VLY NWD INTO MI LATE THIS AFTN/TONIGHT...
A VERY STRONG WIND FIELD WILL EXIST TODAY THROUGH EARLY FRIDAY FROM
THE LWR MS VLY NNE TO GRT LKS REGION...IN BROADENING WARM SECTOR OF
DEEP IA LOW. 500 MB WIND SPEEDS IN EXCESS OF 75 KTS WILL PREVAIL
THIS AFTERNOON FROM AR TO MI. AND...SPEEDS SHOULD INCREASE TO
NEARLY 100 KTS BY THIS EVENING AND CONTINUE THROUGH TONIGHT OVER
PARTS OF IL/IND AND MI AS CO/NM JET STREAK REDEVELOPS NEWD. COUPLED
WITH EXISTING BROAD BELT OF 40 KT SWLY LOW LVL FLOW THAT WILL
PERSIST THROUGH THE PERIOD...KINEMATIC SETUP WILL BE FAVORABLE FOR
STRONG ROTATING STORMS IN UNSEASONABLY WARM AND HUMID AIR STREAMING
N AHEAD OF COLD FRONT.
HOWEVER...WEAK SHORTWAVE RIDGING IN WAKE OF LEAD UPR DISTURBANCE
LIKELY WILL PREVAIL THROUGH MUCH OF THE DAY OVER NRN PARTS OF THE
WARM SECTOR. THIS WILL LIMIT DEGREE OF LARGE SCALE FORCING FOR
ASCENT DURING MAX HEATING TIME...AND MAY LIMIT COVERAGE OF
DIURNALLY-DRIVEN STORM DEVELOPMENT...ESPECIALLY OVER MI/IL AND IND.
LATE THIS AFTERNOON AND CONTINUING THROUGH TONIGHT...EXPECT THAT
FORCING FOR ASCENT WILL MARKEDLY INCREASE FROM THE LWR MS/LWR TN VLY
NE INTO THE LWR OH VLY AS JET ENTRANCE REGION EVOLVES IN ASSOCIATION
WITH EWD REDEVELOPMENT OF CO/NM SPEED MAX. GIVEN PREVIOUSLY
MENTIONED KINEMATIC AND MOISTURE SETUP...THIS SHOULD SUPPORT
INITIATION OF SVR STORMS INVOF COLD FRONT VERY LATE THIS AFTN OR
EARLY TONIGHT OVER SE MO/SRN IL/SW IND/WRN KY AND WRN TN.
THE STORMS SHOULD BUILD BOTH N AND S ALONG FRONT LATER TONIGHT
..WITH SOME OF THE ACTIVITY REMAINING STRONG TO SVR THROUGH EARLY
FRIDAY.
BREADTH OF WARM SECTOR...60-70 KT DEEP SWLY SHEAR AND QUALITY OF
MOISTURE INFLOW SUGGEST GOOD LIKELIHOOD FOR DISCRETE SUPERCELLS FOR
PERHAPS A 2-3 HOUR PERIOD EARLY TONIGHT...BEFORE STORMS MERGE INTO
BROKEN LINES. STRONG LOW LVL SPEED SHEAR AND LOW LCLS SUGGEST
POTENTIAL FOR A FEW STRONG TORNADOES...IN ADDITION TO HIGH WIND AND
HAIL...DESPITE LESS THAN OPTIMAL TIME OF DAY. THE STORMS MAY
CONTINUE TO POSE A THREAT FOR HIGH WIND AND ISOLATED TORNADOES
THROUGH EARLY FRIDAY...ESPECIALLY IN THE LWR TN VLY.
..ERN IA/SE MN/WI/NRN IL THIS AFTN/EVE...
MID LVL DRY SLOT WITH IA LOW WILL ROTATE NNE ACROSS ERN IA/NRN IL
AND SRN WI LATER TODAY. COUPLED WITH COOL MID LVL TEMPERATURES
/MINUS 16C AT 500 MB/ ON CYCLONIC SIDE OF UPR JET...SFC DEWPOINTS IN
THE UPR 50S TO LOW 60S...AND CONVERGENCE INVOF OF DEEP SFC
LOW...SETUP MAY SUPPORT DEVELOPMENT OF AFTN STORMS DESPITE WEAK UPR
LVL FORCING FOR ASCENT.
MODEST INSTABILITY /SBCAPE AOB 1000 J PER KG/ SHOULD LIMIT STORM
INTENSITY. BUT 35-45 KT DEEP SWLY SHEAR WILL SUPPORT A CONDITIONAL
RISK FOR SUPERCELLS WITH HAIL/HIGH WIND AND PERHAPS A TORNADO IF
SUSTAINED UPDRAFTS DO INDEED DEVELOP.
..GULF CST STATES THROUGH THE PERIOD...
A BROAD AREA OF LOW LVL WAA WILL PERSIST OVER MUCH OF MS/AL AND WRN
GA AND UPR TN VLY THROUGH THE PERIOD AS DEEP WSW FLOW PREVAILS ON
SERN SIDE OF EVOLVING CNTRL U.S. TROUGH. VERY RICH BOUNDARY LYR
MOISTURE AND LOW LVL VEERING PROFILES MAY SUPPORT STORMS THAT
OCCASIONALLY DEVELOP LOW LVL ROTATION. THIS WILL BE ESPECIALLY TRUE
THIS AFTN AS HEATING BOOSTS SFC-BASED INSTABILITY...AND INVOF WEAK
INVERTED TROUGH NOW ALONG THE AL/MS BORDER...WHERE LOW LVL
DIRECTIONAL SHEAR WILL BE MAXIMIZED. WHILE DEEP SHEAR WILL BE WEAK
RELATIVE TO POINTS FARTHER NW...IT WILL BE SUFFICIENT TO SUPPORT
SUSTAINED UPDRAFTS/POSSIBLE SUPERCELLS WITH A CONDITIONAL THREAT FOR
TORNADOES.
..ERN NEB/NE KS/NW MO...
STEEP LOW TO MID LVL LAPSE RATES AND FORCING FOR ASCENT ASSOCIATED
WITH RECONFIGURATION OF UPR JET AS CO/NM SPEED MAX CONTINUES EWD MAY
SUPPORT A BAND OF LOW-TOPPED STORMS WITH MARGINALLY SVR HAIL/WIND
THIS AFTN ACROSS THE LWR MO VLY.
.CORFIDI/GUYER.. 10/18/2007
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