SWODY2
SPC AC 090557
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT THU APR 09 2009
VALID 101200Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A LARGE PART OF THE OH/TN
VLYS INTO THE DEEP S/SERN STATES...
...SYNOPSIS...
UPR LOW OVER MO AT 12Z FRIDAY IS PROGGED TO GRADUALLY WEAKEN AS IT
EJECTS NEWD AND PHASES WITH A NRN STREAM TROUGH OVER NEW ENGLAND AND
THE MID-ATLC STATES FRIDAY NIGHT. NEXT IN A SERIES OF STORM SYSTEMS
WILL AMPLIFY ALONG THE CA CST FRIDAY AFTN AND EVENTUALLY CLOSE INTO
A LOW OVER THE DESERT SW BY THE END OF THE PD.
AT THE SFC...A LOW ATTENDANT WITH THE LEAD SYSTEM WILL TRAVEL FROM
SERN MO AT THE START OF THE PD TO THE MID-OH VLY BY FRIDAY EVE...AND
THEN REDEVELOP OVER SERN VA BY DAYBREAK SATURDAY. TO THE S OF THE
LOW...A CDFNT WILL MOVE SEWD INTO VA AND THE CAROLINAS BY EARLY
SATURDAY. TAIL-END OF THE FRONT WILL SETTLE MORE SLOWLY SWD ACROSS
DIXIE AND THE SERN TX CST. WRN PORTIONS OF THE FRONT WILL BEGIN TO
MIGRATE NWD VERY LATE IN THE PD ACROSS CNTRL TX AS A WRMFNT.
...OH/TN VLYS...DEEP SOUTH...CAROLINAS...
MODEST WSW LLVL FLOW WILL ADVECT MODIFIED GULF MOISTURE NWD FROM THE
LWR MS VLY INTO THE OH VLY ALONG/E OF THE SFC LOW/CDFNT THROUGH
FRIDAY. BY FRIDAY AFTN...SFC DEW POINTS WILL LIKELY RANGE FROM NEAR
50 DEG F IN THE OH VLY AND 60+ FROM PARTS OF NRN AL/GA SWD TO THE
CNTRL GULF CST. ATOP THE MOISTENING BOUNDARY LAYER...A PLUME OF
STEEP MID-TROPOSPHERIC LAPSE RATES /7.5 DEG C PER KM/ WILL FLOW EWD
ALONG SRN QUADRANT OF THE UPR LOW CONTRIBUTING TO MLCAPES RANGING
FROM 750 J PER KG IN THE OH VLY INTO THE 1500- 2000 J PER KG RANGE
ACROSS PARTS OF MIDDLE TN...AL AND PERHAPS NW GA.
AN AREA OF ELEVATED CONVECTION WILL BE IN THE PROCESS OF EXPANDING
ACROSS AREAS N OF THE OH RVR AT THE BEGINNING OF THE PD. SRN
FRINGES OF THIS ACTIVITY ACROSS WRN PORTIONS OF KY/TN ALONG/W OF THE
50 KT SWLY LLJ MAY YIELD LOCAL DMGG WIND GUSTS/HAIL EARLY FRIDAY
MORNING.
DESTABILIZING AIR MASS AHEAD OF THE MORNING STORMS COMBINED WITH
MODEST HEIGHT FALLS ASSOCD WITH THE UPR TROUGH SHOULD LEAD TO
RENEWED TSTM INTENSITY FROM CNTRL KY SWD INTO WRN-MIDDLE TN BY EARLY
AFTN. ACTIVITY WILL TEND TO BACKBUILD SWWD INTO PARTS OF AL BY
MID-AFTN WHERE SBCINH WILL BE STRONGER...BUT ERODIBLE. SUPERCELL
STORM MODES WILL BE LIKELY...PARTICULARLY FROM SCNTRL KY SWD WHERE
STRONGEST DEEP LAYER SHEAR IN EXCESS OF 50 KTS BECOMES COINCIDENT
WITH STRONGEST INSTABILITY /VERY LARGE HAIL/. STORM MODE WILL
GRADUALLY TRANSITION INTO LINE SEGMENTS OVER THE OH VLY WITH DMGG
WINDS BECOMING A THREAT AS FAR EAST AS THE WV/KY COALFIELDS.
FARTHER S...EVENING KINEMATIC SET-UP FEATURING A VEERING-WITH-TIME
LLJ BLOWING FROM A STEEP LAPSE RATE ENVIRONMENT AND WLY H5 FLOW OF
60+ KTS WILL YIELD BOTH BACKBUILDING...SEMI-DISCRETE SUPERCELLS
/VERY LARGE HAIL/ AND FORWARD-PROPAGATING BOWS /HIGH WINDS/.
STRONGEST POTENTIAL FOR TORNADOES WILL OCCUR MID-AFTN INTO THE
EVENING WITH THE MORE DISCRETE STORMS FROM MIDDLE TN SWD INTO NRN AL
AND NWRN GA. HERE...FRINGE OF LWR-MID 60S DEW POINTS SHOULD BE
EDGING NWD INTO THE REGION AMIDST 0-1KM SRH OF 250 M2/S2. FARTHER
TO THE N...ALONG THE TRACK OF THE SFC LOW IN THE OH VLY...ISOLD
TORNADOES CANNOT BE RULED OUT...BUT WILL TEND TO BE LESS LIKELY
OWING TO RATHER MEAGER BOUNDARY LAYER MOISTURE AND POTENTIAL FOR
MORE LINEAR STORM MODES.
OVERNIGHT FRIDAY/EARLY SATURDAY...PORTIONS OF THE ACTIVITY THAT
DEVELOP OVER THE TN VLY/DEEP S WILL CONTINUE ENE ACROSS THE SRN
APLCNS AND INTO THE CAROLINAS. IT IS UNCLEAR HOW MUCH BOUNDARY
LAYER MOISTENING/DESTABILIZATION WILL OCCUR ACROSS THIS REGION AHEAD
OF THE STORMS. BUT...PRIND THAT AT LEAST A FEW HUNDRED J PER KG OF
MLCAPE AND STRONG SHEAR WILL MAINTAIN AT LEAST A DMGG WIND/ISOLD
TORNADO THREAT AS FAR NE AS PARTS OF NC BY LATE IN THE PD.
..RACY.. 04/09/2009
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