SWODY2
SPC AC 261702
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1202 PM CDT TUE AUG 26 2008
VALID 271200Z - 281200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
STRONG SHORT WAVE TROUGH INITIALLY OVER SASKATCHEWAN/MANITOBA WILL
RAPIDLY EJECT NEWD IN RESPONSE TO THE INTENSIFICATION OF AN UPSTREAM
TROUGH OVER THE N-CNTRL STATES. FARTHER E...THE REMNANTS OF
TROPICAL DEPRESSION FAY WILL LIFT NNEWD THROUGH THE CUMBERLAND
PLATEAU INTO THE UPPER OH VALLEY.
...UPPER MS VALLEY SWWD INTO KS...
SURFACE COLD FRONT ATTENDANT TO LEAD SHORT WAVE MAY TEND TO WEAKEN
WEDNESDAY WHILE PROGRESSING EWD THROUGH THE UPPER MS VALLEY. THIS
FRONTAL BOUNDARY WILL EVENTUALLY BE OVERTAKEN WEDNESDAY NIGHT BY
SECONDARY COLD FRONT ASSOCIATED WITH AMPLIFYING SHORT WAVE TROUGH
OVER THE NRN PLAINS. TSTMS ONGOING AT THE ONSET OF THE FORECAST
PERIOD OVER THE MID MO VALLEY WILL WEAKEN THROUGH THE DAY AS UPPER
SYSTEM LIFTS NEWD AWAY FROM THE REGION. THEREAFTER...BOUNDARY LAYER
DEWPOINTS IN THE 60S COINCIDENT WITH ERN EXTENSION OF STEEP LAPSE
RATE PLUME WILL CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS BY
AFTERNOON WITH MLCAPES APPROACHING 500-1000 J/KG OVER SRN MN...TO AS
HIGH AS 2000-2500 J/KG OVER KS.
WHILE THE STRONGER LARGE-SCALE HEIGHT FALLS ASSOCIATED WITH
AMPLIFYING UPSTREAM SYSTEM WILL LIKELY REMAIN W OF WARM SECTOR AIR
MASS THROUGH THE DIURNAL HEATING CYCLE...SUSTAINED CONVERGENCE ALONG
FRONTAL ZONE SHOULD SUPPORT SCATTERED TSTM DEVELOPMENT BY MID/LATE
AFTERNOON. THE STRONGER DEEP-LAYER VERTICAL SHEAR /EFFECTIVE BULK
SHEAR OF AROUND 40 KT/ WILL RESIDE ACROSS NRN EXTENSION OF
INSTABILITY AXIS WITH SHEAR GENERALLY DECREASING WITH SWD EXTENT
ALONG FRONTAL ZONE WHERE CONVECTIVE INSTABILITY WILL INCREASE.
GIVEN THIS DISPLACEMENT OF STRONGER SHEAR FROM THE STRONGER
INSTABILITY...ONLY LOW SEVERE PROBABILITIES WILL BE MAINTAINED ATTM.
NONETHELESS...THE MORE INTENSE STORMS WILL BE CAPABLE OF LARGE HAIL
AND DAMAGING WINDS THROUGH WEDNESDAY EVENING.
...AZ...
A MOIST LOW-LEVEL AIR MASS WILL PERSIST ACROSS CNTRL/SRN AZ WITH
DEWPOINTS IN THE 60S AND PW VALUES OF 1.5-2.0 INCHES. THIS MOISTURE
COMBINED WITH RELATIVELY STEEP LAPSE RATES ARE EXPECTED TO
CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS WITH MLCAPES OF
1000-1500 J/KG. DIURNAL TSTMS ARE EXPECTED TO DEVELOP ALONG FAVORED
TERRAIN WITH AN ENHANCED BELT OF 20-25 KT NELY MIDLEVEL FLOW LIKELY
SUPPORTING THE SWWD MOVEMENT/PROPAGATION OF TSTMS INTO THE LOWER
DESERTS. LOCALLY DAMAGING WIND GUSTS AND/OR SOME HAIL MAY ACCOMPANY
THE MORE INTENSE STORMS.
...LOWER OH VALLEY/CUMBERLAND PLATEAU INTO NC...
LATEST MODEL GUIDANCE SUGGESTS THAT LOW-LEVEL WIND FIELDS WILL
GRADUALLY WEAKEN THROUGH THE PERIOD AS THE REMNANTS OF TROPICAL
DEPRESSION FAY LIFT NNEWD. HOWEVER...AIR MASS WILL REMAIN QUITE
MOIST FROM VICINITY OF SYSTEM CENTER ESEWD ALONG AND S OF ATTENDANT
FRONTAL BOUNDARY WHICH WILL BE SLOWLY LIFTING NWD ACROSS NC/VA.
VERTICAL SHEAR WILL NOT BE PARTICULARLY STRONG...BUT FORECAST
HODOGRAPHS DO INDICATE CONSIDERABLE VEERING THROUGH THE LOWEST 2-3
KM AGL. THIS COMBINED WITH THE MOIST BOUNDARY LAYER AND POCKETS OF
MODERATE INSTABILITY MAY BE SUPPORTIVE OF MARGINAL SUPERCELL
STRUCTURES CAPABLE OF A BRIEF TORNADO OR TWO IN ADDITION TO LOCALLY
GUSTY WINDS.
..MEAD.. 08/26/2008
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