SWODY2
SPC AC 140559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT THU APR 14 2011
VALID 151200Z - 161200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL GULF
COAST STATES AND TN VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER TO
MID-MS VALLEY...CNTRL TO ERN GULF COAST STATES...SRN APPALACHIAN
MTNS AND OH VALLEY...
...TORNADO OUTBREAK BECOMING INCREASINGLY POSSIBLE ACROSS THE CNTRL
GULF COAST STATES ON FRIDAY INTO FRIDAY NIGHT...
...CNTRL GULF COAST STATES/SRN APPALACHIAN MTNS...
AN IMPRESSIVE NEGATIVELY-TILTED UPPER-LEVEL LOW IS FORECAST TO MOVE
FROM THE CNTRL PLAINS EWD INTO THE OZARKS. THE EXIT REGION OF A 75
TO 90 KT MID-LEVEL JET ROUNDING THE BASE OF THE UPPER-LEVEL TROUGH
WILL OVERSPREAD THE CNTRL GULF STATES FRIDAY AFTERNOON CREATING VERY
FAVORABLE DEEP LAYER SHEAR PROFILES FOR SEVERE STORMS OVER A BROAD
AREA. AT THE SFC...A LOW WILL DEEPEN AND MOVE NEWD ACROSS THE OH
VALLEY AS A TRAILING COLD FRONT ADVANCES EWD ACROSS THE MS VALLEY.
ELEVATED THUNDERSTORM ACTIVITY MAY BE ONGOING ACROSS THE WARM SECTOR
FRIDAY MORNING IN AL AND MIDDLE TN WITH THIS CONVECTION BEING
SHUNTED EWD AWAY FROM THE MODERATE RISK AREA AROUND MIDDAY. AS THIS
OCCURS...MODEL FORECASTS ARE CONSISTENT WITH DEVELOPING NUMEROUS
THUNDERSTORMS ALONG THE WRN EDGE OF AN AXIS OF MODERATE TO STRONG
INSTABILITY FROM WRN TN SWD ACROSS NRN AND CNTRL MS. THIS ACTIVITY
SHOULD SPREAD EWD ACROSS THE MODERATE RISK AREA LATE FRIDAY
AFTERNOON INTO THE EVENING.
FORECAST SOUNDINGS ALONG THE INSTABILITY AXIS SHOW MLCAPE VALUES
FROM 2000 TO 3000 J/KG IN CNTRL MS TO 1500 TO 2000 J/KG ACROSS WRN
KY AND WRN TN. THIS IS COMBINED WITH 55 TO 70 KT OF DEEP LAYER SHEAR
AND STRONG LOW-LEVEL SHEAR SHOULD RESULT IN SUPERCELL DEVELOPMENT
WITH TORNADOES ACROSS THE MODERATE RISK AREA. 0-3 KM STORM RELATIVE
HELICITIES ARE FORECAST TO BE 400 TO 500 M2/S2 WITH LOOPING
HODOGRAPHS ACROSS MUCH OF ERN MS AND WRN AL SUGGESTING A POTENTIAL
FOR LONG-TRACK STRONG TORNADOES WILL EXIST. 500 MB TEMPS ARE
FORECAST TO BE FROM -12C IN SRN MS AND SRN AL TO -16C IN WRN TO
MIDDLE TN. THIS ALONG WITH THE STRONG DEEP LAYER SHEAR SHOULD ALSO
BE FAVORABLE FOR LARGE HAIL. VERY LARGE HAIL WILL BE POSSIBLE
ESPECIALLY IN ERN MS AS SUPERCELLS DEVELOP DURING THE MID TO LATE
AFTERNOON WHERE THE STRONGEST INSTABILITY IS FORECAST. ALTHOUGH
DISCRETE CONVECTION IS ANTICIPATED EARLY IN THE EVENT...LINEAR
DEVELOPMENT SHOULD INCREASE ALONG THE COLD FRONT BY EARLY EVENING
WITH A SQUALL-LINE MOVING EWD ACROSS THE REGION. DISCRETE STORMS
AHEAD OF THE LINE SHOULD CONTINUE TO HAVE TORNADO THREAT THROUGH THE
EVENING.
ONE CONCERN IS THAT THE LOW-LEVEL JET IS FORECAST TO BE MAXIMIZED
OVER KY AND TN DURING THE EARLY EVENING. LOW-LEVEL SHEAR PROFILES
WILL STILL BE VERY FAVORABLE FURTHER SOUTH IN MS AND AL BUT THE
LOW-LEVEL JET RESPONSE MAY BE FOCUSED FURTHER TO THE NORTH. ANOTHER
CONCERN IS FOR THE SRN EDGE OF THE MODERATE RISK. MODEL FORECASTS
DIFFER ON CONVECTIVE COVERAGE WITH THE NAM ISOLATED BUT THE ECMWF
DEVELOPS NUMEROUS STORMS. IN SPITE OF THE UNCERTAINTIES...WILL ISSUE
A MODERATE RISK ACROSS MUCH OF THE CNTRL GULF COAST STATES DUE TO
THE POTENTIAL FOR A HIGHER-END EVENT.
...MID-MS VALLEY/OH VALLEY...
AN UPPER-LEVEL LOW WILL MOVE ACROSS THE OZARKS FRIDAY WITH A MOIST
AXIS IN PLACE ACROSS KY...IL AND IND. THE DEVELOPMENT OF NUMEROUS
SEVERE THUNDERSTORMS APPEARS LIKELY TO THE EAST OF THE UPPER-LEVEL
LOW AS STRONG LARGE-SCALE ASCENT MOVES ACROSS THE REGION FRIDAY
AFTERNOON. FORECAST SOUNDINGS ALONG THE MOIST AXIS SHOW SFC
DEWPOINTS IN THE UPPER 50S F WITH DEEP LAYER SHEAR OF 40 TO 50 KT.
THIS ENVIRONMENT ALONG WITH COLD TEMPS ALOFT SHOULD SUPPORT THE
DEVELOPMENT OF SUPERCELLS WITH LARGE HAIL. BACKED SFC WINDS AND
STRONG LOW-LEVEL SHEAR ALSO SHOULD BE FAVORABLE FOR A TORNADO THREAT
WITH ROTATING STORMS. HOWEVER...STRONG LOW-LEVEL CONVERGENCE ALONG A
COLD FRONT MAY FORCE A LINEAR MCS. THIS WOULD RESULT IN A WIDESPREAD
WIND DAMAGE THREAT WITH THE LINE MOVING INTO IND...CNTRL KY AND
ECNTRL TN DURING THE EVENING.
..BROYLES.. 04/14/2011
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