DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 291730
SWODY2
SPC AC 291728

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT WED AUG 29 2012

VALID 301200Z - 311200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR THE LOWER MS VALLEY...

...SYNOPSIS...
A MID-LEVEL ANTICYCLONE SHOULD SHIFT FROM THE MID-MS VALLEY TO THE
SRN APPALACHIANS...AS TC ISAAC TRACKS NNW ACROSS LA INTO WRN AR PER
LATEST NHC FORECAST. QUASI-ZONAL FLOW REGIME WILL EXIST ACROSS THE
NRN CONUS WITH A LOW-AMPLITUDE SHORT WAVE IMPULSE PROGRESSING
RAPIDLY FROM THE SRN PRAIRIE PROVINCES TO QUEBEC BY EARLY FRI. AN
ATTENDANT COLD FRONT WILL PUSH ACROSS THE UPPER GREAT LAKES AND
BECOME QUASI-STATIONARY ALONG THE SD/NEB BORDER.

...LOWER MS VALLEY...
ALTHOUGH TC ISAAC IS FORECAST TO BE IN A WEAKENING PHASE...STRONG TO
INTENSE LOW-LEVEL WIND FIELDS WILL PERSIST THROUGH THE PERIOD. IN
FACT...A RELATIVE INCREASE IN THE TORNADO THREAT MAY OCCUR AS ISAAC
MOVES FARTHER INLAND...WITH POTENTIAL FOR STRONGER DIURNAL HEATING
IN THE SERN QUADRANT. THIS SCENARIO WILL BE PREDICATED ON THE
OCCURRENCE OF GREATER INSOLATION RESULTING IN INCREASING
DESTABILIZATION. ALTHOUGH THE NAM TRACK APPEARS TO BE A WWD
OUTLIER...CONVECTION-ALLOWING NAM NESTS AND WRF HI-RES WINDOWS DO
SUGGEST THAT GENERALLY N/S-ORIENTED BANDS OF STRONG CONVECTION
SHOULD INDEED DIURNALLY INCREASE. AS SUCH...FOLLOWING THE NHC TRACK
AND GFS/ECMWF GUIDANCE FOR THE STRENGTH/SPATIAL EXTENT OF LOW-LEVEL
SLYS...HAVE SHIFTED AND SOMEWHAT EXPANDED THE SLIGHT RISK EWD.

...UPPER GREAT LAKES...
ISOLATED ELEVATED TSTMS ROOTED AROUND 600-650 MB MAY DEVELOP THU
MORNING AND THEN AGAIN EARLY FRI WITHIN A RESIDUAL MID-LEVEL
MOISTURE PLUME TRAILING THE FAST-MOVING IMPULSE ACROSS S-CNTRL/SERN
CANADA. NAM FORECAST SOUNDINGS SUPPORT THE SYNOPTIC PATTERN SETUP
WHICH SHOULD RESULT IN A VERY STOUT CAPPING INVERSION FOR
SURFACE-BASED CONVECTION AS THE PLAINS EML SPREADS EWD.

..GRAMS.. 08/29/2012

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