SPC AC 121251
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0751 AM CDT WED AUG 12 2009
VALID 121300Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS ALONG THE S ATLANTIC CST...
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE CNTRL/SRN HI PLNS...
...SYNOPSIS...
THE MAIN BELT OF THE WLYS WILL BE CONFINED TO THE PACIFIC NW AND S
CNTRL/SE CANADA THIS PERIOD AS OH VLY TROUGH CONTINUES E AND
ELONGATES NE/SE OVER THE APPALACHIANS. IN THE WLYS...IMPULSE NOW
OVER WA/ORE EXPECTED TO SHEAR ENE ACROSS NW MT AND SRN AB/SK LATER
TODAY/TONIGHT AS STRONGER UPSTREAM SYSTEM DEVELOPS SE ALONG THE BC
CST. FARTHER S...SATELLITE SHOWS AN ILL-DEFINED IMPULSE NOW OVER WY
THAT SHOULD CONTINUE E INTO THE CNTRL HI PLNS BY EVE...AND INTO THE
MID MO VLY EARLY THU.
AT LWR LVLS...WEAK FRONT ALONG THE CAROLINA CST WILL SERVE AS THE
FOCUS FOR SCTD TO NUMEROUS TSTMS TODAY. OVER THE CNTRL HI PLNS...
MORE ISOLD STORMS ARE EXPECTED LATE THIS AFTN AND EVE ALONG/E OF LEE
TROUGH. OTHER ISOLD DIURNAL STORMS MAY OCCUR ALONG STRENGTHENING
COLD FRONT IN MT.
...S ATLANTIC CST...
AXIS OF RICH MOISTURE /PW AOA 2.00 INCHES/ WILL PERSIST ALONG THE S
ATLANTIC CST TODAY AS OLD FRONT DISSIPATES OVER REGION. THIS
MOISTURE SHOULD SUPPORT MODERATE INSTABILITY /SBCAPE TO 2500 J PER
KG/ AS HEATING OCCURS OVER REGION E OF MID/UPR LVL CLOUD BAND
ASSOCIATED WITH OH VLY TROUGH. WEAKLY CAPPED ENVIRONMENT WITH 25-30
KT DEEP SWLY SHEAR...AND ASCENT IN ENTRANCE REGION OF 80 KT UPR LVL
JET STREAK SHOULD SUPPORT FAIRLY WIDESPREAD STORM COVERAGE BY AFTN.
SETUP COULD SUPPORT ORGANIZATION OF STORMS INTO BANDS...SOME WITH
PRODUCING WET MICROBURSTS.
...CNTRL/SRN HI PLNS TO MID MO VLY...
CONTINUED EWD MOTION OF OH VLY TROUGH WILL ALLOW UPR RDG TO REBOUND
OVER THE SRN/CNTRL RCKYS TODAY. THIS FACT...AND EXISTING
EML...CASTS SOME UNCERTAINTY REGARDING POTENTIAL FOR LATE AFTN/EVE
STORM ALONG LEE TROUGH OVER THE CNTRL HI PLNS INTO THE OK/TX
PANHANDLES. NEVERTHELESS PRESENCE OF PREVIOUSLY-MENTIONED WY
IMPULSE WITH UNIMPEDED HEATING AND SUSTAINED CONVERGENCE ALONG LEE
TROUGH SHOULD BE SUFFICIENT FOR AT LEAST ISOLD STORMS.
MODERATE INSTABILITY /SBCAPE TO 2000 J PER KG/ WILL DEVELOP ALONG
LEE TROUGH AS LIGHT SSELY LOW LVL FLOW MAINTAINS SFC DEWPOINTS IN
THE 50S TO LOW 60S F. 25-30 KT NNWLY MID LVL FLOW IS FORECAST OVER
REGION ON NE SIDE OF SRN RCKYS RDG...RESULTING IN HODOGRAPHS WITH
AMPLE DEEP SHEAR AND LOW LVL TURNING FOR ORGANIZED/ROTATING STORMS
WITH HAIL AND LOCALLY DMGG WIND.
THE THREAT FOR HAIL MAY REDEVELOP NEWD INTO PARTS OF NEB LATER
TONIGHT/EARLY THU AS LLJ STRENGTHENS AND VEERS IN RESPONSE TO
CONTINUED EWD MOVEMENT OF WY IMPULSE. ALTHOUGH AMPLE MOISTURE AND
ELEVATED INSTABILITY SHOULD BE PRESENT FOR ISOLD SVR HAIL...WEAK
CLOUD LAYER SHEAR SHOULD LIMITED STORM INTENSITY/LONGEVITY.
...WRN/CNTRL MT...
SPARSE MOISTURE WILL LIMIT DEGREE OF CONVECTIVE INSTABILITY
OVER WRN AND CNTRL MT TODAY AHEAD WA/ORE IMPULSE...KEEPING SBCAPE
AOB 1000 J/KG. BUT STEEP LOW TO MID LVL LAPSE RATES...TERRAIN
INFLUENCES...AND SUSTAINED FORCING FOR ASCENT SHOULD SUPPORT ISOLD
TO PERHAPS SCTD STORMS ALONG ASSOCIATED COLD FRONT LATE THIS AFTN
AND EVE. 40-45 KT DEEP WLY SHEAR ON SRN EDGE OF THE WLYS MAY
SUPPORT MARGINAL/HIGH-BASED SUPERCELLS AND/OR BOWING STRUCTURES
CAPABLE OF ISOLATED DMGG WIND AND MARGINALLY SVR HAIL.
..CORFIDI/BOTHWELL.. 08/12/2009
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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