SPC AC 061245
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0745 AM CDT WED MAY 06 2009
VALID 061300Z - 071200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN TX INTO THE SOUTHEAST
AND APPALACHIANS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE UPPER MS
RIVER VALLEY...
...SYNOPSIS...
VERY COMPLEX FORECAST THIS MORNING WITH SERIES OF MORNING SEVERE
MCSS ALONG AND NEAR EFFECTIVE WARM FRONT ARCING FROM THE SRN
APPALACHIANS INTO NERN TX AT DAYBREAK. THIS IS OCCURRING AHEAD OF
BROAD MID/UPPER LEVEL TROUGH WHICH IS FORECAST TO EJECT NEWD ACROSS
THE GREAT LAKES/OH RIVER VALLEY AND CENTRAL GULF COAST STATES TODAY.
SYNOPTIC SURFACE LOW IS FORECAST TO DEEPEN OUT OF THE TN VALLEY AND
INTO THE UPPER OH RIVER VALLEYS TODAY...AS 60+ KT SWLY LLJ EJECTS
FROM THE TN VALLEY ACROSS THE CENTRAL APPALACHIANS/VA INTO THE
EVENING. IN ADDITION...FAST MOVING NRN STREAM IMPULSE NOW MOVING
OVER THE NRN PLAINS MAY FOCUS ADDITIONAL AREA OF STRONG/SEVERE
THUNDERSTORM DEVELOPMENT INTO THE UPPER MS RIVER VALLEY REGION LATER
TODAY.
...RED RIVER VALLEY OF OK/TX INTO THE CENTRAL GULF COAST STATES...
SEVERE THUNDERSTORM FORECAST FOR REMAINDER OF DAY WILL BE STRONGLY
INFLUENCE BY ONGOING MORNING MCS ACTIVITY. SMALL BOWING MCS OVER
NERN TX IS ALREADY BEING FED BY A VERY UNSTABLE AIR MASS SOUTH OF
MAIN SURFACE WARM FRONT...WITH SUFFICIENT INFLOW/INSTABILITY FOR
CONTINUED THREAT OF WIND DAMAGE INTO ERN TX/WRN-CENTRAL LA THROUGH
THE EARLY AFTERNOON. ADDITIONAL LINEAR MCS OVER MS/AL IS BEGINNING
TO ORIENT ITSELF A BIT MORE NORMAL TO MODERATE WSWLY FLOW ALOFT OVER
E-CENTRAL MS. THIS ACTIVITY IS ALSO BEING FED BY VERY
MOIST/UNSTABLE AIR WITHIN WARM SECTOR AND SHOULD SUPPORT THREAT OF
DAMAGING WINDS ACROSS CENTRAL AL INTO PORTIONS OF WRN/NRN GA THROUGH
THE AFTERNOON. ISOLATED TORNADOES MAY ACCOMPANY ANY LEADING
SUPERCELLS/OR FROM CIRCULATIONS ALONG LEADING EDGE OF THE LINE WITH
BOTH MCSS. LARGE HAIL THREAT CAN ALSO BE EXPECTED WITH ELEVATED
STORMS TRAILING SYSTEMS AND NORTH OF CONVECTIVELY-STABILIZED AIR.
...SRN APPALACHIANS/GA INTO THE CAROLINAS...
ANOTHER MESSY CONVECTIVE DAY LIKELY ACROSS THIS REGION WITH ONGOING
MCS ACROSS NRN GA POSSIBLY INCREASING ACROSS UPSTATE SC AS AIRMASS
BECOMES MARGINALLY UNSTABLE AND WEAKLY CAPPED AHEAD OF IT.
ADDITIONAL STORMS MAY DEVELOP INVOF STATIONARY SURFACE TROUGH AND/OR
SEA BREEZE OVER THE CAROLINAS AS AFTERNOON HEATING OVERCOMES WEAK
CAP. DEEP LAYER SHEAR SHOULD INCREASE THROUGH THE DAY AS MID/UPPER
TROUGH APPROACHES...SUGGESTING STORM-SCALE ORGANIZATION INTO
BOWS/SUPERCELLS WITH MYRIAD OF SEVERE THREATS EVOLVING WITH ANY
PERSISTENT CLUSTER. ADDITIONAL SEVERE THREAT MAY EVOLVE LATER
TODAY/THIS EVENING WITH ANY MCS DEVELOPMENT SHIFTING NEWD AWAY FROM
THE SRN APPALACHIANS/CENTRAL GULF COAST STATES.
...TN VALLEY INTO PORTIONS OF WV/VA AND THE UPPER OH ALLEY...
HAVE EXTENDED SLGT RISK AND RELEVANT PROBABILITIES NEWD INTO THIS
REGION GIVEN THE EXTREME LOW LEVEL SHEAR AND POSSIBILITY OF
SURFACE-BASED THUNDERSTORMS WITHIN LOW-CAPE ENVIRONMENT LATER
TODAY/EVENING INVOF SURFACE LOW AND LLJ MENTIONED ABOVE. THREAT IS
CONDITIONAL ON DEVELOPMENT OF SURFACE-BASED INSTABILITY AND
QUESTIONS OF OVERALL IMPACT FROM LARGE MCSS TO THE SW THIS MORNING.
INSTABILITY MAY BE A BIT GREATER EAST OF THE APPALACHIANS INTO VA AS
INFLUX OF RICHER LOW LEVEL MOISTURE NOW OVER NC ADVECTS NWD THROUGH
THE DAY. HOWEVER...LAPSE RATES ARE FORECAST TO REMAIN QUITE WEAK
THROUGH THE PERIOD. ALTHOUGH...SHOULD EVEN MODEST SBCAPE EVOLVE
LATER TODAY...FORECAST SOUNDINGS INDICATE VERY LARGE/LOOPING LOW
LEVEL HODOGRAPHS SUPPORTIVE OF AT LEAST AN ISOLATED TORNADO THREAT.
NWD EXTENT OF SEVERE THREAT MAY BE LIMITED INTO THE MID
ATLANTIC/PA...ALTHOUGH INFLUX OF MODEST SURFACE THETA-E AND LARGE
LOW LEVEL SHEAR WARRANTS AT LEAST LOW SEVERE PROBABILITIES NWD INTO
THIS REGION.
...PORTIONS OF CENTRAL PLAINS INTO THE UPPER MS RIVER VALLEY...
FORECAST SOUNDINGS INDICATE AIR MASS WILL DESTABILIZE SUFFICIENTLY
FOR 500-1000 J/KG MLCAPE AHEAD OF APPROACHING MID LEVEL SHORTWAVE
TROUGH AND ASSOCIATED SURFACE FRONT OVER THIS REGION. ISOLATED
SEVERE THUNDERSTORMS SHOULD EVOLVE DURING THE LATE AFTERNOON ONCE
AGAIN AND CONTINUE EWD INTO THE EARLY EVENING. ADDITIONAL CLUSTER OF
ELEVATED STORMS MAY ACCOMPANY LATE NIGHT IMPULSE SHIFTING SEWD
ACROSS THE CENTRAL PLAINS EARLY THURSDAY MORNING...WITH HAIL
POSSIBLE WITH THE STRONGER CORES.
..EVANS/GARNER.. 05/06/2009
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
|
