SWODY1
SPC AC 062004
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0304 PM CDT SAT JUN 06 2009
VALID 062000Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM NEB/IA TO WEST
CENTRAL/SOUTHWEST TX...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SOUTHERN FL
PENINSULA...
...CENTRAL/SOUTHERN PLAINS...
SURFACE FRONTAL ZONE CONTINUES TO SLOWLY SAG SOUTHWARD ACROSS
SOUTHEAST NEB THIS AFTERNOON...WHILE REMAINING QUASI-STATIONARY
ACROSS IA. WHILE A CAP WAS NOTED PER 18Z OBSERVED RAOBS FROM
OMAHA/TOPEKA...IT STILL SEEMS PROBABLE THAT SCATTERED TSTMS SHOULD
DEVELOP LATE THIS AFTERNOON/EARLY EVENING ACROSS PORTIONS OF
SOUTHEAST NEB/FAR NORTHEAST KS AND SOUTHWEST/CENTRAL IA. SEE
MESOSCALE DISCUSSION 960 FOR ADDITIONAL DETAILS.
FARTHER WEST...OTHER DEVELOPMENT MAY OCCUR ACROSS SOUTHWEST NEB
ALONG/NORTH OF THE SURFACE FRONTAL ZONE. A FEW SUPERCELLS ARE
POSSIBLE...WITH HAIL AS THE PRIMARY THREAT. THIS ACTIVITY COULD
CONSOLIDATE/SPREAD EASTWARD WITH ADDITIONAL DEVELOPMENT TONIGHT
ACROSS CENTRAL NEB/FAR NORTH KS AS A SOUTHERLY LOW LEVEL JET
INTENSIFIES ACROSS KS.
FARTHER SOUTHWEST...DEEPLY MIXED CU FIELD HAS BEEN INCREASING ACROSS
PORTIONS OF WEST/SOUTHWEST TX THIS AFTERNOON WITHIN THE POST-DRYLINE
AIRMASS. RELATIVELY ISOLATED TSTMS SHOULD DEVELOP IN VICINITY OF THE
DRYLINE BY LATE AFTERNOON...WITH SOME HIGH BASED
SUPERCELLS/ORGANIZED MULTICELLS POSSIBLE.
...SOUTH FL...
AS UPPER LOW REMAINS ACROSS NORTH FL...SEVERE TSTMS WILL REMAIN
POSSIBLE MAINLY ACROSS THE SOUTHEAST FL PENINSULA THROUGH EARLY
EVENING.
..GUYER.. 06/06/2009
.PREV DISCUSSION... /ISSUED 1128 AM CDT SAT JUN 06 2009/
...KS/NE/MO/IA THIS AFTERNOON INTO TONIGHT...
MORNING SURFACE ANALYSES AND 12Z SOUNDINGS SHOW RATHER MEDIOCRE
LOW-LEVEL MOISTURE ACROSS THE SRN/CENTRAL PLAINS WITH 100 MB MEAN
MIXING RATIOS AROUND 10 G/KG AND SURFACE DEW POINTS IN THE UPPER 50S
TO NEAR 60 F. SHORT TERM MODEL FORECASTS CONTINUE TO SHOW MIXING
RATIOS INCREASING TO 14-15 G/KG BY 21-00Z FROM NE KS INTO SW IA/ERN
NEB. THIS INCREASE SEEMS EXCESSIVE GIVEN NO UPSTREAM SOURCE REGION
CLOSER THAN S TX.../EXCLUDING THE LESS RELIABLE AWOS DEW POINT
OBSERVATIONS/. A CORRESPONDING BOUNDARY LAYER PW INCREASE OF
0.15-0.20 INCHES LIKEWISE APPEARS TOO HIGH FOR ONLY A FEW HOURS OF
EVAPOTRANSPIRATION THIS AFTERNOON. THEREFORE... EXPECT SLIGHTLY
MORE SUBDUED AFTERNOON MLCAPE VALUES OF 1500-2000 J/KG S OF THE
FRONT IN NEB/IA/KS/NW MO...AS OPPOSED TO THE 2500-3000 J/KG VALUES
SHOWN IN THE 12Z NAM/RUC FORECASTS.
MEANWHILE...THE LARGE SCALE FORCING FOR ASCENT WILL REMAIN DIFFUSE
OVER THIS SLIGHT RISK AREA THIS AFTERNOON AS AN INITIAL SHORTWAVE
TROUGH EJECTS ENEWD AWAY FROM THE REGION...AND THE PRIMARY UPSTREAM
TROUGH IS STILL WELL TO THE W/NW OVER THE ROCKIES AND GREAT BASIN.
THAT SUGGESTS THAT ANY STORM DEVELOPMENT THIS AFTERNOON WILL RELY ON
SURFACE HEATING AND LOW-LEVEL ASCENT ALONG THE FRONT/DRYLINE TO
REMOVE CONVECTIVE INHIBITION FROM S CENTRAL NEB/N CENTRAL KS ENEWD
INTO ERN NEB/W CENTRAL IA. THE MODERATE INSTABILITY AND 0-6 KM BULK
SHEAR IN EXCESS OF 50 KT WILL FAVOR SUPERCELLS WITH LARGE HAIL AND
DAMAGING WINDS. THE TORNADO THREAT IS MORE UNCERTAIN GIVEN
POTENTIALLY LARGE TEMPERATURE-DEW POINT SPREADS AOA 25
F...ESPECIALLY ACROSS KS/NEB WHERE SURFACE TEMPERATURES WARM INTO
THE 85-90 F RANGE...AND A WEAKENING OF LOW-LEVEL FLOW/SHEAR DURING
THE DAY.
CONVECTIVE COVERAGE WILL LIKELY INCREASE BY EARLY TONIGHT AS THE LLJ
REFORMS AND CONTRIBUTES TO INCREASING WAA ALONG THE BAROCLINIC ZONE.
THIS CONVECTION SHOULD EVOLVE INTO ONE OR MORE CLUSTERS WITH AN
ACCOMPANYING RISK OF DAMAGING WINDS AND LARGE HAIL...AND PERSIST
INTO EARLY SUNDAY WHILE SPREADING EWD/ENEWD FROM NE KS/SE NEB INTO
NW MO/SW IA.
...CENTRAL KS TO NW TX THIS AFTERNOON/EVENING...
STRONG SURFACE HEATING IS EXPECTED ALONG THE DRYLINE THIS AFTERNOON
AS TEMPERATURES WARM INTO THE 95-100 F RANGE. THE RESULTANT
WEAKENING OF CONVECTIVE INHIBITION SHOULD ALLOW FOR THE DEVELOPMENT
OF WIDELY SCATTERED...HIGH-BASED THUNDERSTORMS FROM CENTRAL/W
CENTRAL KS SWD ACROSS WRN OK INTO NW AND W CENTRAL TX LATE THIS
AFTERNOON. DEEP LAYER VERTICAL SHEAR WILL BE AT LEAST MARGINALLY
FAVORABLE FOR SUPERCELLS /ESPECIALLY FARTHER N TOWARD KS/...AS WELL
AS ORGANIZED MULTICELL CLUSTERS. ISOLATED LARGE HAIL AND DAMAGING
GUSTS WILL BE POSSIBLE THROUGH EARLY TONIGHT...AND STORM CLUSTERS
THAT PERSIST INTO TONIGHT COULD ALSO PRODUCE ISOLATED HEAT BURSTS.
...CENTRAL/S FL THIS AFTERNOON...
WATER VAPOR IMAGERY AND MORNING UPPER AIR ANALYSES REVEALED A COLD
CORE MID LEVEL LOW MOVING OVER FL FROM THE ERN GULF OF MEXICO. 12Z
SOUNDINGS FROM TBW/MFL/EYW REVEALED 1-3 C COOLING ALOFT /500-300
MB/...WITH RESULTANT STEEPENING OF LAPSE RATES ALOFT AND AN INCREASE
IN BUOYANCY COMPARED TO 12Z YESTERDAY. THERE HAS ALSO BEEN A MODEST
INCREASE IN LOW-MID LEVEL SWLY FLOW WHICH WILL HELP KEEP THE E COAST
SEA BREEZE CLOSE TO THE COAST AND PROVIDE A FOCUS FOR THUNDERSTORM
DEVELOPMENT THIS AFTERNOON. SIMILAR TO YESTERDAY...THE FOCUSED
CONVERGENCE ALONG THE SEA BREEZE AND MODEST SWLY DEEP LAYER MEAN
FLOW WILL ALLOW STORMS TO BACK-BUILD ALONG THE BOUNDARY WITH THE
POTENTIAL FOR LARGE HAIL AND DAMAGING DOWNBURST WINDS. OTHER
SCATTERED STORMS COULD ALSO OCCUR INLAND ACROSS SRN/CENTRAL FL IN
RESPONSE TO DAYTIME HEATING WITHIN CLOUD BREAKS.
...NRN MAINE THIS AFTERNOON/EVENING...
A STRONG MID LEVEL TROUGH AND ASSOCIATED COLD FRONT WILL MOVE EWD
FROM QUEBEC TO NRN MAINE THIS AFTERNOON/EVENING. THOUGH LOW-LEVEL
MOISTURE IS LIMITED IN ADVANCE OF THE FRONT...STEEP LOW-MID LEVEL
LAPSE RATES AND STRONG UNIDIRECTIONAL WIND PROFILES COULD SUPPORT
SOME LOW-TOPPED CONVECTION ALONG THE FRONT WITH THE POTENTIAL FOR
MARGINALLY SEVERE HAIL AND ISOLATED DAMAGING GUSTS.
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