[SWODY2] SWODY2

[Severe Weather Outlook - Day 2]

ACUS02 KWNS 211749
SWODY2
SPC AC 211748

DAY 2 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1248 PM CDT THU SEP 21 2006

VALID 221200Z - 231200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS ERN IA/SRN WI/NWRN
INDIANA/IL/MO/NRN AR/NERN OK...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN UPPER GREAT LAKES
REGION SSWWD INTO NERN TX...

...SYNOPSIS...
UPPER SHORT-WAVE TROUGH FORECAST ACROSS THE MID MO VALLEY REGION AT
THE START OF THE PERIOD SHOULD CONTINUE NWD...WHILE SECOND
SHORT-WAVE TROUGH MOVES ESEWD ACROSS THE ROCKIES TOWARD THE CENTRAL
PLAINS AROUND LARGER MID-LEVEL VORTEX. STRONG MID-LEVEL SPEED MAX
ASSOCIATED WITH THIS TROUGH WILL  SHIFT EWD ACROSS THE SRN
ROCKIES/SRN PLAINS...AND INTO THE MID MO VALLEY REGION BY THE END OF
THE PERIOD.

AT THE SURFACE...MODELS DIFFER IN LOCATION OF PRIMARY SURFACE LOW
DUE TO SMALLER-SCALE COMPLEXITY WITHIN THE LARGE UPPER TROUGH. 
HOWEVER...GENERAL AGREEMENT EXISTS THAT RICH BOUNDARY LAYER MOISTURE
WILL SPREAD NWD ACROSS THE CENTRAL THIRD OF THE CONUS AHEAD OF AN
EWD-MOVING COLD FRONT. COMBINATION OF RICH BOUNDARY LAYER MOISTURE
SPREADING NWD BENEATH A VERY STRONG/FAVORABLY-VEERING WIND FIELD
WITH HEIGHT SUGGESTS THAT A SIGNIFICANT/WIDESPREAD SEVERE WEATHER
EVENT WILL UNFOLD THIS PERIOD.

...SRN PORTIONS OF THE UPPER GREAT LAKES SSWWD INTO NERN TX...
CONVECTION IS FORECAST TO BE ONGOING AT THE START OF THE PERIOD
ACROSS PARTS OF AR/MO/IL/IA AND VICINITY...IN CONJUCTION WITH
STRONG/SLY LOW-LEVEL JET AND BROAD/ASSOCIATED ZONE OF WARM
ADVECTION.  ATTM...IT APPEARS THAT ONGOING STORMS SHOULD BE LARGELY
SUB-SEVERE...EXCEPT POSSIBLY ACROSS AR ON LEADING EDGE OF RETURNING
MOISTURE.

THOUGH THIS ONGOING PRECIPITATION INJECTS A DEGREE OF UNCERTAINTY
INTO THE DAY 2 FORECAST...MODELS GENERALLY AGREE THAT MOST OF THE
CONVECTION SHOULD SHIFT N AND E WITH TIME...WHILE VERY MOIST
BOUNDARY LAYER ADVECTS NWD ACROSS AN EXPANDING WARM SECTOR. 
ATTM...IT APPEARS THAT AT LEAST SOME DAYTIME HEATING WILL OCCUR
ACROSS THE WARM SECTOR...RESULTING IN MODERATE DESTABILIZATION
ACROSS THE MDT RISK AREA.  THOUGH A STRONG MID-LEVEL FEATURE DOES
NOT APPEAR LIKELY TO AFFECT THIS REGION...SMALLER/MORE SUBTLE
FEATURES WILL MOVE NEWD IN SWLY FLOW AROUND SERN FRINGES OF
LARGE/POSITIVELY-TILTED TROUGH.  THIS SHOULD SUPPORT THE DEVELOPMENT
 ALONG PRIMARY LOW-LEVEL CONVERGENCE AXIS WHICH SHOULD BE MOVING
ACROSS ERN KS/ERN OK INTO WRN MO AND NWRN AR DURING THE AFTERNOON.

WITH THE LACK OF A PRONOUNCED SMALL-SCALE UPPER FEATURE...IT APPEARS
ATTM THAT DISCRETE STORM DEVELOPMENT SHOULD OCCUR WITHIN POCKETS OF
GREATER INSTABILITY.  WITH VERY STRONG/WEAKLY DIFFLUENT SWLY FLOW
ALOFT ABOVE VERY STRONG SSWLY LOW-LEVEL WIND FIELD...DEGREE OF SHEAR
WILL ALLOW STORMS TO RAPIDLY ACQUIRE STRONG ROTATION.  ALONG WITH
THREAT FOR DAMAGING WINDS AND HAIL...MOIST BOUNDARY LAYER/LOW LCLS
COMBINED WITH VERY STRONG LOW-LEVEL SHEAR WILL SUPPORT TORNADOES. 
THOUGH SOME UNCERTAINTY STILL EXISTS -- PARTICULARLY REGARDING
EARLIER CONVECTION AND ITS EFFECT ON THE THERMODYNAMIC
ENVIRONMENT...IT WOULD APPEAR THAT A SIGNIFICANT TORNADOES WILL BE
POSSIBLE -- PARTICULARLY ACROSS MO AND INTO IL DURING THE AFTERNOON
AND EVENING.

LOW-LEVEL JET IS FORECAST TO FURTHER STRENGTHEN OVERNIGHT...WITH
STRONGEST WARM ADVECTION FORECAST TO SHIFT NWD AND EWD INTO THE
UPPER GREAT LAKES/OH VALLEY REGION.  THOUGH THIS WILL LIKEWISE ALLOW
CONVECTION -- AND SOME SEVERE THREAT -- TO EXPAND NWD AND EWD...MAIN
THREAT SHOULD PERSIST FROM IL SSWWD...WHERE MOST FAVORABLE
COMBINATION OF INSTABILITY AND SHEAR SHOULD REMAIN.

..GOSS.. 09/21/2006