SWODY2
SPC AC 160546
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1246 AM CDT SUN SEP 16 2007
VALID 171200Z - 181200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MS VALLEY SWWD
INTO NERN NEB...
..SYNOPSIS...
AN EWD PROGRESSION OF BROAD...WRN CONUS TROUGH IS FORECAST DURING
THE DAY TWO PERIOD WITH THE STRONGEST HEIGHT FALLS OCCURRING OVER
THE NRN PLAINS INTO THE UPPER MS VALLEY. THESE HEIGHT FALLS WILL BE
ASSOCIATED WITH A LEAD SHORT WAVE TROUGH/JET STREAK THAT WILL
TRANSLATE FROM THE CNTRL HIGH PLAINS NEWD INTO WRN ONTARIO BY
TUESDAY MORNING. MEANWHILE...NEXT UPSTREAM SHORT WAVE TROUGH/JET
STREAK WILL ORIGINATE OVER NRN CA MONDAY MORNING AND INTENSIFY AS IT
DIGS SEWD INTO THE FOUR CORNERS REGION LATE MONDAY NIGHT.
IN THE LOW LEVELS...PRIMARY SURFACE LOW WILL CONSOLIDATE ALONG THE
ND/MANITOBA BORDER MONDAY WITH A N-S ORIENTED PRESSURE TROUGH
EXTENDING SWD INTO CNTRL NEB. A WEAK FRONTAL WAVE ATTENDANT TO
ABOVEMENTIONED...LEAD SHORT WAVE TROUGH MAY FORM ALONG THIS PRESSURE
TROUGH...SUPPORTING THE NWD MOVEMENT OF A WARM FRONT THROUGH CNTRL
MN/WRN WI. AS THIS OCCURS...A COLD FRONT MOVING OUT OF THE NRN HIGH
PLAINS WILL EVENTUALLY OVERTAKE PRESSURE TROUGH OVER THE CNTRL
DAKOTAS DURING THE LATTER HALF OF THE FORECAST PERIOD.
..UPPER MS VALLEY SWWD INTO CNTRL NEB...
LATEST MODEL GUIDANCE INDICATES THAT A PLUME OF STEEP MID-LEVEL
LAPSE RATES /7.5-8 C PER KM/ WILL RESIDE ATOP AN INCREASINGLY MOIST
BOUNDARY LAYER...SUPPORTING A MODERATELY UNSTABLE AIR MASS MONDAY
AFTERNOON FROM ERN NEB/WRN IA NWD INTO SRN MN WITH MLCAPES OF
2000-2500 J/KG. INITIAL TSTM DEVELOPMENT IS EXPECTED TO OCCUR N OF
WARM FRONT OVER CNTRL INTO NRN MN...DRIVEN LARGELY BY WAA ALONG
STRENGTHENING LLJ. THESE STORMS WILL LIKELY BE ELEVATED WITH THE
PRIMARY SEVERE WEATHER THREAT BEING LARGE HAIL.
INITIALLY STRONG CAP ACROSS SYSTEM WARM SECTOR OVER SRN MN/ERN
SD/NERN NEB/NWRN IA IS EXPECTED TO WEAKEN THROUGH THE AFTERNOON
OWING TO DIABATIC HEATING AND INCREASING HEIGHT FALLS ASSOCIATED
WITH ARRIVAL OF LEAD SHORT WAVE TROUGH. MORE INTENSE...
SURFACE-BASED STORM DEVELOPMENT WILL BECOME INCREASINGLY LIKELY BY
LATE AFTERNOON OR EARLY EVENING NEAR TRIPLE POINT /I.E. WEAK SURFACE
WAVE/ WHERE WARM FRONT WILL INTERSECT PRESSURE TROUGH
OVER E-CNTRL SD/SWRN OR W-CNTRL MN. FORECAST SOUNDINGS INDICATE A
VERY FAVORABLE THERMODYNAMIC AND KINEMATIC ENVIRONMENT FOR
SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND A FEW
TORNADOES. STORMS SHOULD GRADUALLY EVOLVE INTO AN MCS MONDAY NIGHT
WITH THE SEVERE WEATHER THREAT DEVELOPING EWD/NEWD THROUGH E-CNTRL
MN INTO NWRN WI.
ADDITIONAL...ISOLATED/SCATTERED TSTM DEVELOPMENT WILL BE POSSIBLE
SWWD ALONG PRESSURE TROUGH INTO CNTRL NEB MONDAY EVENING. THIS MAY
NOT OCCUR UNTIL NOCTURNAL LLJ BEGINS TO STRENGTHEN...ENHANCING
CONVERGENCE ALONG PRESSURE TROUGH. THE PRESENCE OF THE STEEP LAPSE
RATES AND SUFFICIENTLY STRONG DEEP LAYER SHEAR INDICATE POTENTIAL
FOR ORGANIZED/ROTATING UPDRAFTS CAPABLE OF DAMAGING WINDS AND LARGE
HAIL.
..FOUR CORNERS REGION...
TERRAIN FORCING AND INCREASED LARGE-SCALE FORCING FOR ASCENT
ASSOCIATED WITH APPROACHING SHORT WAVE TROUGH FROM THE GREAT BASIN
ARE EXPECTED TO CONTRIBUTE TO FAIRLY WIDESPREAD TSTM DEVELOPMENT
MONDAY AFTERNOON INTO MONDAY NIGHT. WHILE AIR MASS WILL NOT BE
OVERLY MOIST /PW VALUES OF .6-.9 INCH/...STEEP LOW TO MID-LEVEL
LAPSE RATES WILL EXIST. MOREOVER...VERTICAL SHEAR WILL STRENGTHEN
THROUGH THE PERIOD AND SOME POTENTIAL WILL EXIST FOR A FEW ORGANIZED
STORMS WITH A THREAT OF LOCALLY STRONG WIND GUSTS AND SOME
MARGINALLY SEVERE HAIL.
.MEAD.. 09/16/2007
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