SPC AC 241726
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT FRI APR 24 2015
VALID 251200Z - 261200Z
...THERE IS AN ENH RISK OF SVR TSTMS FOR PARTS OF THE LOWER OH
VALLEY AND UPPER TN VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE MID MS VALLEY SEWD
INTO GA AND THE CAROLINAS...
...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PORTIONS OF THE LOWER MO
VALLEY AND THE GULF COAST STATES...
...SUMMARY...
SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP DURING THE AFTERNOON
ACROSS PORTIONS OF THE LOWER OHIO VALLEY AND TENNESSEE VALLEY. VERY
LARGE HAIL...DAMAGING WINDS...AND TORNADOES ARE POSSIBLE. THE
SEVERE THREAT MAY CONTINUE INTO THE EVENING ACROSS THE SOUTHERN
APPALACHIANS AND PARTS OF THE CAROLINAS.
ISOLATED SEVERE THUNDERSTORMS ARE ALSO POSSIBLE ACROSS MUCH OF THE
SOUTHEAST AND GULF COAST REGIONS.
...SYNOPSIS...
A MID-LEVEL WAVE INITIALLY OVER THE LOWER MO VALLEY IS FORECAST TO
DEAMPLIFY AND REACH THE LOWER OH VALLEY DURING THE OVERNIGHT. THE
ASSOCIATED SPEED MAX IS FORECAST TO MOVE FROM AR INTO THE SRN
APPALACHIANS DURING THE PERIOD WITH 60-90 M HEIGHT FALLS FOCUSED
FROM THE MID MS VALLEY INTO THE SRN APPALACHIANS. A WARM FRONT WILL
LIKELY ADVANCE NWD REACHING THE LOWER OH VALLEY EARLY IN THE DAY AND
A LOWER MO VALLEY SURFACE LOW WILL DEVELOP ESEWD REACHING THE LOWER
OH VALLEY BY MID AFTERNOON. POSSIBLE SECONDARY LOW DEVELOPMENT
INVOF THE SRN APPALACHIANS MAY ALSO SERVE TO CONCENTRATE STRONG TO
SEVERE THUNDERSTORM ACTIVITY LATE IN THE DAY INTO THE EVENING.
...MID MS INTO THE LOWER OH AND TN VALLEY...
A LOW LEVEL JET STREAM /40-50 KT/ WILL ACT TO TRANSPORT LOW-LEVEL
MOISTURE NNEWD INTO THE REGION BY THE START OF THE DAY 2 PERIOD.
RESIDUAL OVERNIGHT THUNDERSTORMS OWING TO STRONG LOW-LEVEL WARM
ADVECTION/ISENTROPIC ASCENT WILL LIKELY SPREAD E ACROSS THE OH
VALLEY DURING THE MORNING. MODELS SHOW A PRONOUNCED MID-LEVEL DRY
SLOT IN WAKE OF THE EARLY DAY ACTIVITY WITH SOME CLEARING AND
HEATING EXPECTED. MODEL GUIDANCE SHOWS MID 60S DEWPOINTS
OVERSPREADING THE AREA S OF THE WARM FRONT AND CONTRIBUTING TO
MODERATE TO STRONG BUOYANCY /1000-3000 J PER KG SBCAPE/. COUPLED
WITH STRONG AND DEEP WLY MID- TO HIGH-LEVEL FLOW /50-70 KT EFFECTIVE
SHEAR/...SUPERCELLS WILL LIKELY BE THE PREFERRED STORM MODE AND POSE
A RISK FOR LARGE TO VERY LARGE HAIL AND DMGG WIND GUSTS. RELATIVELY
BACKED NEAR-SURFACE WINDS ALONG THE WARM FRONT WILL ENLARGE
HODOGRAPHS AND POTENTIALLY LEAD TO A HEIGHTENED THREAT FOR SUPERCELL
TORNADOES --A FEW OF WHICH COULD BE STRONG-- WITH ANY ROBUST STORM
TRACKING INVOF THE BOUNDARY. HOWEVER...DUE TO UNCERTAINTY AT THIS
TIME...WILL REASSESS AND DEFER PROBABILISTIC/CATEGORICAL TIER
ADJUSTMENTS TO LATER OUTLOOKS.
FARTHER S INTO THE WARM SECTOR...NEGLIGIBLE CONVERGENCE IN PART DUE
TO VEERED SWLY LOW-LEVEL WINDS WILL PROBABLY LEAD TO CONSIDERABLY
LOWER TSTM PROBABILITIES AS THE BULK OF LARGE-SCALE FORCING REMAINS
CONCENTRATED IN THE OH VALLEY. ADDITIONALLY...BOUNDARY LAYER MIXING
AND ENLARGING OF SURFACE TEMP-DEWPOINT SPREADS MAY LESSEN THE
TORNADO RISK WITH ISOLD LARGE HAIL/WINDS BEING THE PRIMARY THREAT.
...SRN APPALACHIANS INTO THE CAROLINAS...
LARGELY COINCIDENT WITH THE EWD PROGRESSION OF FORECAST OVERNIGHT
DAY 1 THUNDERSTORMS AND CONVECTIVE DEBRIS ACROSS AL/GA DURING THE
MORNING...THE EWD EXTENSION OF THE WARM FRONT WILL LIFT NEWD THROUGH
NRN GA INTO SC DURING THE DAY. STRONG HEATING AND INCREASED
LOW-LEVEL MOISTURE /BOUNDARY LAYER DEWPOINTS IN THE MID-UPPER 60S/
WILL PROBABLY LEAD TO MODERATE TO STRONG BUOYANCY DEVELOPING BY PEAK
HEATING AND THE WEAKENING OF THE CAP BY LATE AFTERNOON. LOW LEVEL
VEERING WINDS BENEATH INCREASING TROPOSPHERIC FLOW WITH HEIGHT WILL
STRONGLY FAVOR SUPERCELL DEVELOPMENT WITH ANY STORMS THAT MANAGE TO
DEVELOP AND AN ASSOCIATED SEVERE THREAT. ALTHOUGH THE CONDITIONAL
PARAMETER-SPACE ENVIRONMENT WOULD SUPPORT SIGNIFICANT SEVERE
HAZARDS...THE MAIN FACTOR PRECLUDING HIGHER PROBABILITIES ATTM
INVOLVES UNCERTAINTY REGARDING CONVECTIVE COVERAGE.
...GULF COAST STATES...
A MARITIME AIRMASS FEATURING UPPER 60S AND 70S DEWPOINTS WILL BE IN
PLACE BENEATH STRONG WLY FLOW ALOFT. THE LACK OF A LOW-LEVEL
FORCING MECHANISM FOR DIURNAL STORM INITIATION AND THIS REGION BEING
LARGELY REMOVED FROM MID-LEVEL WAVE DISPLACED TO THE N...CASTS
CONSIDERABLE DOUBT IN MORE THAN A FEW STORMS DEVELOPING.
NONETHELESS...STRONG SHEAR/INSTABILITY WOULD ENABLE STORMS TO
ACQUIRE CHARACTERISTICS SUPPORTIVE OF AN ISOLD STRONG/SEVERE THREAT
AND WILL MAINTAIN LOW PROBABILITIES THIS FORECAST.
..SMITH/MEAD.. 04/24/2015
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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