SWODY1
SPC AC 091620
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1120 AM CDT SAT AUG 09 2008
VALID 091630Z - 101200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN ROCKIES AND
ADJACENT HIGH PLAINS OF MT...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE
CENTRAL/LOWER GREAT LAKES...
...THERE IS A SLGT RISK OF SVR TSTMS OVER SRN FL...
...NRN ROCKIES INTO THE NRN HIGH PLAINS...
NEGATIVELY TILTED SHORTWAVE TROUGH EJECTING ACROSS THE PAC NW IS
ALREADY ENHANCING DEEP ASCENT/THUNDERSTORM DEVELOPMENT INTO THE NRN
ROCKIES EARLY TODAY. AIR MASS IS SEASONABLY MOIST ACROSS THE NRN
ROCKIES AND ADJACENT HIGH PLAINS WITH PW/S IN EXCESS OF 1 INCH AND
SURFACE DEW POINTS LIKELY HOLDING IN THE 50S F DESPITE STRONG
AFTERNOON HEATING. THIS WILL BOOST INSTABILITY TODAY AS MID LEVEL
THERMAL TROUGH OVERSPREADS THE REGION...WITH MLCAPE IN THE 1000-2000
J/KG LIKELY BY THE MID TO LATE AFTERNOON. EXPECT GENERAL INCREASE
IN DEEP MOIST CONVECTION THROUGH THE LATE MORNING/EARLY AFTERNOON
WITH SEVERE THREAT LIKEWISE INCREASING WITH STRENGTHENING
INSTABILITY AND STEEPENING LOW LEVEL LAPSE RATES. VERTICAL SHEAR
REMAINS MODEST THROUGH THE MID LEVELS WITH SFC-6 KM SHEAR FORECAST
IN THE 30-40 KT RANGE AS 40-50 KT MID LEVEL SWLY JET OVERSPREADS THE
NRN ROCKIES. EXPECT MORE DISCRETE STORMS WILL DEVELOP AT LEAST
BRIEF LOW-MID LEVEL ROTATION THIS AFTERNOON...WITH ACTIVITY LIKELY
ORGANIZING INTO ONE OR MORE LARGER LINEAR COMPLEXES SPREADING
QUICKLY NEWD ACROSS THE NRN HIGH PLAINS LATE TODAY/THIS EVENING.
DAMAGING WINDS WILL BE PRIMARY SEVERE THREAT...ALONG WITH ISOLATED
LARGE HAIL.
...CENTRAL/LOWER GREAT LAKES REGIONS...
UNSEASONABLY STRONG MID/UPPER LOW AND ASSOCIATED TROUGH APPEAR TO BE
GAINING AMPLITUDE...WITH MID LEVEL HEIGHT FALLS OVERSPREADING THE
CENTRAL AND LOWER GREAT LAKES THROUGH THE PERIOD. VERY COLD MID
LEVEL AIR WILL OVERCOME SEASONABLY COOL SURFACE CONDITIONS AND
SUPPORT MARGINAL INSTABILITY ACROSS THE REGION...AND MAINTAIN A FEW
STRONGER STORMS ESEWD THROUGH THE DAY. LOW-DEEP LAYER SHEAR FROM
20-30 KT MAY SUPPORT ORGANIZATION INTO CLUSTERS/LINES...WITH DEEP
WLY COMPONENT SUPPORTING PRIMARY THREAT OF DAMAGING WINDS.
ALTHOUGH...STRONGER CORES SHOULD ALSO PRODUCE MARGINALLY SEVERE HAIL
GIVEN THE COLD AIR ALOFT. GREATEST CONCENTRATION OF DEEP MOIST
CONVECTION...AND ASSOCIATED SEVERE THREAT...SHOULD OVERSPREAD
CENTRAL/SERN LOWER MI ACROSS ONTARIO AND THE LOWER GREAT LAKES
REGIONS. HOWEVER...WIDELY SCATTERED STORMS MAY DEVELOP WWD ALONG
ASSOCIATED SURFACE COLD FRONT ACROSS SRN LAKE MI INTO SRN WI/NRN
IL/IA TODAY WHERE SUFFICIENT INSTABILITY AND STEEP LOW LEVEL LAPSE
RATES MAY SUPPORT ISOLATED/BRIEF HAIL/WIND EVENTS NEAR SEVERE
LEVELS.
...FL...
LATEST SURFACE OBSERVATIONS AND MORNING RAOBS SUGGEST THAT THE VERY
MOIST BOUNDARY LAYER...CHARACTERIZED BY MID 70S SURFACE DEW
POINTS...IS BECOMING MODERATELY UNSTABLE AND WEAKLY CAPPED ACROSS
MUCH OF THE CENTRAL/SOUTHERN PENINSULA. ONGOING THUNDERSTORMS
ACROSS WESTERN AND INTERIOR SECTIONS IS LIKELY AIDED BY AN AREA OF
STRONGER FORCING FOR UPWARD VERTICAL MOTION IN THE BASE OF
LARGE-SCALE EASTERN U.S. UPPER TROUGH. WITH 20-25 KT MEAN WESTERLY
FLOW IN THE 850-500 MB LAYER...STORM MOTIONS WILL BE RELATIVELY
FAST...LIKELY ENHANCING THE RISK FOR AT LEAST LOCALIZED DAMAGING
DOWNBURSTS AS THE BOUNDARY LAYER NEAR EASTERN COASTAL AREAS BETWEEN
MIAMI AND MELBOURNE BECOMES MORE FULLY MIXED BY 18-19Z. AN OFFSHORE
LOW-LEVEL WIND COMPONENT ALONG THE EAST COAST WILL TEND TO MINIMIZE
LOW-LEVEL CONVERGENCE ALONG CONVECTIVELY GENERATED
OUTFLOWS...PROBABLY LIMITING THE POTENTIAL FOR A MORE WIDESPREAD
SEVERE THREAT. REGARDLESS...ISOLATED HAIL/DAMAGING WINDS CAN BE
EXPECTED WITH THE MORE ROBUST UPDRAFTS...WITH SOME POTENTIAL FOR
ORGANIZATION INTO SMALL LINES AS STORMS DEVELOP EWD THROUGH THE
AFTERNOON.
...PORTIONS KS INTO ADJACENT AREAS OF NRN OK/SWRN MO...
CONVECTIVELY ENHANCED LOW-MID LEVEL VORT MAX WILL CONTINUE TO DRIFT
SEWD ACROSS WRN KS TODAY...WITH ASSOCIATED LOCAL MAXIMUM IN SSWLY
H85 FLOW PERSISTING OVER SRN KS/NRN OK. ONGOING MCS WILL LIKELY
CONTINUE RIDING SEWD ACROSS THE OZARK PLATEAU REGION TODAY AND
UNDERGO SLIGHT WEAKENING THROUGH THE DAY. REDEVELOPMENT IS LIKELY
NEAR THE LOW-MID LEVEL CIRCULATION IN WAKE OF EARLIER STORMS WHERE
AUGUST HEATING AND ABUNDANT MOISTURE SUPPORT MODERATE TO STRONG
INSTABILITY BY LATE TODAY. ALTHOUGH RELATIVELY WARM AIR ALOFT AND
WEAK MID LEVEL LAPSE RATES WILL TEND TO LIMIT OVERALL SEVERE
THREAT...LARGE LOW LEVEL HODOGRAPHS INVOF H85 WIND MAX WARRANTS SOME
POTENTIAL FOR BRIEF ORGANIZATION/ROTATION WITH ISOLATED STRONG
DOWNBURSTS WITH THE MORE INTENSE CORES.
...SWRN U.S...
PW VALUES REMAIN QUITE HIGH FROM THE SRN ROCKIES INTO THE LOWER CO
RIVER VALLEY/SRN GREAT BASIN EARLY TODAY. THIS WILL BOOST
INSTABILITY THIS AFTERNOON IN AREAS OF STRONGER HEATING ON FRINGES
OF MOISTURE PLUME...I.E. OVER PARTS OF SE CA/SRN NV AND NRN AZ/SW
UT. THESE AREAS MAY EXPERIENCE LOCALLY DAMAGING WIND GUSTS...BUT
WEAK DEEP FLOW ACROSS THE REGION WILL LIMIT ORGANIZATION WITH THIS
ACTIVITY AND MAINTAIN PRIMARY THREAT OF HEAVY RAINFALL.
..EVANS/SMITH.. 08/09/2008
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