SWODY1
SPC AC 221617
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1117 AM CDT SUN MAY 22 2011
VALID 221630Z - 231200Z
...THERE IS A MDT RISK OF SVR TSTMS OVER SERN MN...ERN IA...PARTS OF
WI/IL/MO...NERN OK AND NWRN AR...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE GREAT LAKES INTO THE
SRN PLAINS...
...UPPER GREAT LAKES INTO THE MID MS AND OH VALLEYS...
DEEP-LAYER CYCLONE OVER ERN SD WILL TRANSLATE EWD INTO THE UPPER MS
VALLEY BY THIS EVENING WITH AN ASSOCIATED 50-60 KT MIDLEVEL JET
STREAK OVERSPREADING THE UPPER MIDWEST THROUGH THE PEAK OF THE
DIURNAL HEATING CYCLE. SURFACE CYCLONE WILL ACCORDINGLY DEVELOP EWD
TO CNTRL MN BY 23/00Z WITH ASSOCIATED WARM FRONT RAPIDLY LIFTING NWD
THROUGH ERN IA/IL INTO WI AND LOWER MI TODAY. HEIGHT FALLS/DYNAMIC
FORCING FOR ASCENT ATTENDANT TO MIDLEVEL SYSTEM COUPLED WITH FRONTAL
UPLIFT WILL FOSTER SCATTERED SVR TSTMS BY EARLY AFTERNOON INITIALLY
FROM PORTIONS OF E-CNTRL/SERN MN AND ERN IA/NERN MO INTO WI/IL.
THE COMBINATION OF A MOIST...MODERATELY TO STRONGLY UNSTABLE AIR
MASS --I.E. MLCAPE RANGING FROM 1000-1500 J/KG OVER MN/WI TO
2000-3000 J/KG ACROSS MO/IL-- COUPLED WITH 40-50 KT DEEP-LAYER SHEAR
ORIENTED ORTHOGONAL TO SURFACE FRONT WILL YIELD A BAND OF SUPERCELLS
CAPABLE OF TORNADOES...LARGE HAIL AND DAMAGING WINDS. THE GREATEST
TORNADO POTENTIAL --SOME POTENTIALLY SIGNIFICANT-- APPEARS TO BE
ACROSS CNTRL/SRN WI INTO IL THIS AFTERNOON AND EVENING WHERE
LOW-LEVEL SHEAR WILL BE ENHANCED BY A GRADUALLY STRENGTHENING LLJ.
STORMS MAY GROW UPSCALE INTO A QLCS TONIGHT WITH A CONTINUED THREAT
FOR MAINLY HAIL AND DAMAGING WIND GUSTS SPREADING EWD THROUGH LOWER
MI AND THE OH VALLEY.
FOR ADDITIONAL NEAR TERM GUIDANCE...SEE MCD 849.
...SRN PLAINS...
12Z REGIONAL SOUNDINGS SHOWED THE POTENTIAL FOR EXPLOSIVE TSTM
DEVELOPMENT LATER TODAY WITH A VERY MOIST BOUNDARY LAYER BENEATH
STEEP MIDLEVEL LAPSE RATES...RESULTING IN MLCAPE OF 3000-4000 J/KG.
GIVEN THAT LARGE-SCALE FORCING FOR ASCENT WILL REMAIN NEGLIGIBLE
THROUGH THE DIURNAL HEATING CYCLE...THE PRIMARY UNCERTAINTIES ARE
LOCATION AND EVENTUAL COVERAGE OF SEVERE STORMS.
DRYLINE LOCATED FROM WRN OK INTO W-CNTRL AND SWRN TX AS OF MID
MORNING WILL MIX MOST RAPIDLY EWD TODAY ACROSS NRN HALF OF OK WITH
THE BOUNDARY EXTENDING FROM E OF THE I-44 CORRIDOR INTO W-CNTRL TX
BY MID/LATE AFTERNOON. CURRENTLY THE HIGHEST PROBABILITY FOR
DIURNAL TSTM DEVELOPMENT APPEARS TO BE FROM NERN OK NEWD INTO MO
WHERE AREA WILL BE INFLUENCED BY LEFT EXIT REGION OF UPPER JET
STREAK STRETCHING FROM THE SRN ROCKIES INTO SRN PLAINS.
HOWEVER...GIVEN THE POTENTIAL FOR STRONG HEATING W OF DRYLINE AND A
BREAKABLE CAP /SEE 12Z FWD SOUNDING/...ISOLATED SEVERE STORMS WILL
BE POSSIBLE ALONG THE LENGTH OF THE DRYLINE.
LATEST MODEL GUIDANCE SUGGESTS DEEPER PBL MIXING MAY LEAD TO
DECREASING LOW-LEVEL MOISTURE CONTENT THIS AFTERNOON...LARGELY
ACROSS PORTIONS OF CNTRL/ERN TX. WHILE THIS MAY TEMPER THE DEGREE
OF INSTABILITY...EXPECT AFTERNOON MLCAPE VALUES OF 3000-4000+ J/KG.
WHEN COUPLED WITH 35-40 KT OF DEEP WLY SHEAR...SETUP WILL FAVOR THE
DEVELOPMENT OF SUPERCELLS WITH VERY LARGE HAIL BEING THE PRIMARY
HAZARD. THE TORNADO THREAT WILL INCREASE IN THE 23/00-03Z TIME
PERIOD AS A STRENGTHENING SLY LLJ ENHANCES LOW-LEVEL SHEAR.
...LOWER MS/TN VALLEYS INTO SRN APPALACHIANS...
REGENERATIVE TSTM DEVELOPMENT IS OCCURRING THIS MORNING ACROSS AR
WITHIN A ZONE OF LOW-LEVEL WAA ASSOCIATED WITH A SWLY LLJ
ORIGINATING OVER SRN TX. CONTINUED HEATING/DESTABILIZATION ALONG
THE SRN/ERN PERIPHERY OF ONGOING STORMS IN CONCERT WITH A
GROWING/DEEPENING COLD POOL MAY ALLOW FOR THE DEVELOPMENT OF A
FORWARD-PROPAGATING MCS WITH EMBEDDED SUPERCELLS WHICH WOULD TRACK
ACROSS THE TN VALLEY AND NRN GULF COAST STATES WITH ATTENDANT
THREATS OF DAMAGING WINDS AND HAIL AND PERHAPS A COUPLE TORNADOES.
FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 850.
...LOWER GREAT LAKES INTO NC...
THE EWD PROGRESSION OF A COUPLE OF WEAK MIDLEVEL IMPULSES WILL
PROVIDE SUFFICIENT BACKGROUND FORCING TO SUPPORT DIURNAL TSTM
DEVELOPMENT WITHIN A WARMING/DESTABILIZING AIR MASS WHERE AFTERNOON
MLCAPE WILL RANGE FROM 1000-2000 J/KG OVER NC TO AROUND 500 J/KG
ACROSS PORTIONS OF NY/PA. THE STRONGEST VERTICAL SHEAR WILL RESIDE
ACROSS THE LOWER GREAT LAKES...DIMINISHING WITH SWD EXTENT. AS
SUCH...THE POTENTIAL WILL EXIST FOR A FEW STRONG-MARGINALLY SEVERE
STORMS THIS AFTERNOON INTO EVENING WITH THE PRIMARY THREATS BEING
HAIL AND LOCALLY STRONG WIND GUSTS.
..MEAD/GRAMS.. 05/22/2011
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