SPC AC 161721
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1221 PM CDT TUE JUN 16 2009
VALID 171200Z - 181200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE CNTRL PLAINS
SEWD INTO THE OH/TN VALLEYS AND SRN APPALACHIANS...
...SYNOPSIS...
CURRENTLY FLATTENED UPPER RIDGE WILL INTENSIFY NWD INTO THE CNTRL
CONUS WITH THE PASSAGE OF MIDLEVEL TROUGH /NOW OVER THE MIDWEST/
THROUGH THE GREAT LAKES REGION. UPSTREAM...POSITIVELY TILTED TROUGH
FROM THE GREAT BASIN TO OFF BAJA WILL BECOME INCREASINGLY
SHEARED....WHILE FARTHER N...A SERIES OF MIDLEVEL IMPULSES TRANSLATE
EWD THROUGH THE PACIFIC NW AND NRN INTERMOUNTAIN REGION AND WRN
CANADA.
AT THE SURFACE...LOW INITIALLY NEAR CHI WILL DEVELOP EWD INTO THE
UPPER OH VALLEY DURING THE DAY WITH AN ATTENDANT N-S ORIENTED WARM
FRONT INTENSIFYING FROM ERN OH/WRN PA SWD INTO THE CNTRL
APPALACHIANS. TRAILING FRONTAL BOUNDARY WILL SETTLE SWD THROUGH THE
MID/LOWER OH VALLEY WHILE WRN EXTENSION OF BOUNDARY LIFTS NWD
THROUGH THE CNTRL PLAINS IN RESPONSE TO DEEPENING SURFACE LOW OVER
KS.
...CNTRL PLAINS INTO MID MS VALLEY...
CAPPING WILL STRENGTHEN OVER THE SRN INTO CNTRL PLAINS BENEATH
BUILDING MIDLEVEL RIDGE AXIS WHICH WILL LIMIT STORM DEVELOPMENT TO N
OF ABOVE-MENTIONED SURFACE BOUNDARY. CURRENT GOES SOUNDER AND GPS
PW DATA INDICATE THAT THE RICHEST MOISTURE NOW RESIDES ALONG AND E
OF THE MS RIVER. DEEPENING KS LOW SHOULD ALLOW FOR THE NWWD
ADVECTION OF THIS MOISTURE THROUGH THE LOWER AND MID MO
VALLEYS...BENEATH STEEP MIDLEVEL LAPSE RATES...CONTRIBUTING TO
MODERATE TO STRONG INSTABILITY WITH MLCAPE OF 2000-4000 J/KG INVOF
BOUNDARY.
LATEST MODEL GUIDANCE CONTINUES TO INDICATE THAT A WEAK MIDLEVEL
IMPULSE WILL CREST BUILDING RIDGE OVER THE CNTRL PLAINS NEAR THE
PEAK IN THE DIURNAL HEATING CYCLE. FORCING FOR ASCENT ASSOCIATED
WITH THIS FEATURE COUPLED WITH PERSISTENT LOW-LEVEL WAA ARE EXPECTED
TO FOSTER STORM DEVELOPMENT FROM MID AFTERNOON INTO EARLY EVENING
FROM WRN NEB EWD THROUGH THE MID MO VALLEY.
FORECAST HODOGRAPHS INDICATE CONSIDERABLE VEERING IN THE LOW-LEVELS
AND 40-50 KT OF DEEP-LAYER SHEAR WHICH WILL SUPPORT THE DEVELOPMENT
OF SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND A FEW
TORNADOES. THE GREATEST TORNADO THREAT WILL EXIST WITH ANY
SUPERCELLS N OF SURFACE BOUNDARY DURING THE EVENING OVER S-CNTRL
INTO ERN NEB WHERE BOUNDARY LAYER WILL BE MORE MOIST/UNSTABLE AND
MODERATELY SHEARED. OTHERWISE...EXPECT UPSCALE GROWTH INTO ONE OR
MORE LARGE TSTM CLUSTERS OVERNIGHT WITHIN STRENGTHENING WAA REGIME
WITH A WIND AND HAIL THREAT SPREADING EWD/SEWD INTO PARTS OF THE MID
MS VALLEY.
...OH/TN VALLEYS INTO SRN APPALACHIANS...
SCENARIO IS A BIT MORE COMPLICATED ACROSS THIS REGION DUE TO
EXPECTED ONGOING STORMS WEDNESDAY MORNING AND THEIR EFFECTS ON AIR
MASS DESTABILIZATION AND BOUNDARY LOCATIONS. AS MENTIONED
ABOVE...CURRENT OBSERVED PW DATA INDICATE A MOIST AIR MASS IN PLACE
E OF THE MS VALLEY. THIS MOISTURE WILL BE DRAWN NWD INTO THE UPPER
OH VALLEY IN ADVANCE OF EWD-MIGRATING SURFACE LOW...CONTRIBUTING TO
A MODERATELY UNSTABLE AIR MASS /MLCAPE OF 1000-2000 J PER KG/ W OF
WARM FRONT AND E/SE OF COLD FRONT TRAILING LOW. MOREOVER...A LOCAL
N-S CORRIDOR OF STRONGER LOW-LEVEL SHEAR WILL COINCIDE WITH THIS
INSTABILITY FROM NERN KY INTO OH WITH THE POTENTIAL FOR A FEW
SUPERCELLS CAPABLE OF HAIL...DAMAGING WINDS AND PERHAPS TORNADOES
DURING THE AFTERNOON INTO EVENING.
OTHER EPISODIC STRONG/SEVERE STORMS WILL BE POSSIBLE FROM VICINITY
OF TRAILING FRONTAL BOUNDARY OVER KY/TN SSEWD ALONG RETREATING WEDGE
FRONT OVER PORTIONS OF GA/SC. THIS AREA WILL RESIDE TO THE S OF
STRONGER MID/HIGH-LEVEL FLOW...BUT THE PRESENCE OF A MODERATELY
UNSTABLE AIR MASS INVOF SURFACE BOUNDARY WILL BE SUPPORTIVE OF A FEW
ORGANIZED TSTM CLUSTERS CAPABLE OF DAMAGING WINDS AND SOME HAIL.
..MEAD.. 06/16/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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