SWODY3
SPC AC 040730
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 AM CDT THU OCT 04 2007
VALID 061200Z - 071200Z
..THERE IS A SLGT RISK OF SVR TSTMS SAT AFTN/EVE ACROSS THE NRN AND
CNTRL PLAINS....
..SYNOPSIS...
A SIGNIFICANT IMPULSE...EMERGING FROM THE BASE OF THE LARGE-SCALE
WESTERN U.S. UPPER TROUGH BY EARLY SATURDAY...IS FORECAST TO LIFT
ACROSS THE CENTRAL ROCKIES DURING THIS FORECAST PERIOD. AS THIS
OCCURS...AND ANOTHER STRONG WESTERLY POLAR JET STREAK NOSES THROUGH
BRITISH COLUMBA AND THE CANADIAN ROCKIES...MODELS SUGGEST THAT THE
UPPER TROUGH AND AN EMBEDDED DEVELOPING CLOSED LOW WILL SLOWLY SHIFT
INTO THE ROCKIES BY 07/00Z SATURDAY EVENING. BEYOND THIS TIME...THE
SPREAD AMONG VARIOUS MODEL FORECASTS INCREASES CONCERNING THE
PROGRESSION OF THIS LOW...DUE TO UNCERTAIN INTERACTION WITH THE MAIN
BELT OF WESTERLIES TO THE NORTH...AND THE CONTINUING PRESENCE OF A
STRONG SUBTROPICAL RIDGE OVER THE EASTERN HALF OF THE NATION.
..PLAINS...
A STEEP LAPSE RATE ENVIRONMENT IS EXPECTED TO PERSIST AT LEAST
THROUGH SATURDAY FROM THE SOUTHERN HIGH PLAINS THROUGH THE EASTERN
NORTHERN PLAINS AND PARTS OF THE UPPER MISSISSIPPI VALLEY...BEFORE A
SHARP COLD FRONT ADVANCES EAST OF THE NORTHERN/CENTRAL ROCKIES. A
LOWER/MID TROPOSPHERIC PRE-FRONTAL THERMAL RIDGE IS EXPECTED TO
BECOME THE FOCUS FOR STRONG DAYTIME HEATING AND CONSIDERABLE
DESTABILIZATION BY MID TO LATE SATURDAY AFTERNOON...ALONG AN AXIS
FROM WEST CENTRAL NEBRASKA INTO EASTERN NORTH DAKOTA. GIVEN A
FAVORABLY MOIST BOUNDARY LAYER WHICH IS ALREADY EXPECTED TO BE
PRESENT...MIXED LAYER CAPE ON THE ORDER OF 1000-2000 APPEARS
PROBABLE. AND...THIS MORE THAN LIKELY WILL BE SUPPORTIVE OF
VIGOROUS CONVECTIVE DEVELOPMENT AS LARGE-SCALE ASCENT CONTRIBUTES TO
WEAKENING INHIBITION.
BENEATH 50-70 KT SOUTH SOUTHWESTERLY MID-LEVEL FLOW...AND 30-50 KT
SOUTHERLY 850 FLOW...DEEP LAYER SHEAR WILL BE SUFFICIENT FOR
SUPERCELLS. ALTHOUGH SHEAR WILL GENERALLY BE UNIDIRECTIONAL...
LOW-LEVEL HODOGRAPHS WILL BE LARGE ENOUGH TO SUPPORT A RISK FOR
TORNADOES...MAINLY WITH INITIAL ACTIVITY. HOWEVER...AT THE PRESENT
TIME IT APPEARS THE PRIMARY THREATS WILL BE DAMAGING WIND GUSTS/
LARGE HAIL...WITH THE EVOLUTION OF A NARROW BROKEN SQUALL LINE
SEEMING PROBABLE BY EARLY SATURDAY EVENING. THE SEVERE THREAT MAY
CONTINUE INTO THE EVENING HOURS...WITH A GRADUALLY EASTWARD SHIFT
..BEFORE STORMS WEAKEN DUE TO STABILIZATION ASSOCIATED WITH THE
LOSS OF DAYTIME HEATING.
.KERR.. 10/04/2007
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