ACUS03 KWNS 210657
SWODY3
SPC AC 210655
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0155 AM CDT SAT APR 21 2007
VALID 231200Z - 241200Z
..THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CNTRL AND SRN
PLAINS...
..SYNOPSIS...
LATEST SHORT TO MEDIUM-RANGE MODEL GUIDANCE IS RELATIVELY CONSISTENT
IN THE EVOLUTION OF MID- AND UPPER-LEVEL LOW WHICH WILL MOVE FROM
THE GREAT BASIN INTO THE CNTRL/SRN ROCKIES BY TUESDAY MORNING.
DOWNSTREAM RIDGING FROM THIS FEATURE WILL RESULT IN A CONTINUED
WEAKENING OF SHORT WAVE TROUGH TRANSLATING EWD FROM THE UPPER GREAT
LAKES INTO NEW ENGLAND.
IN THE LOW-LEVELS...ELONGATED LOW PRESSURE OVER THE HIGH PLAINS
MONDAY MORNING WILL CONSOLIDATE INTO A DEEPENING LEE CYCLONE OVER
SERN CO DURING THE LATTER HALF OF THE PERIOD. ATTENDANT DRYLINE
WILL LIKELY SHAPEN THROUGH THE DIURNAL HEATING CYCLE FROM WRN KS SWD
THROUGH THE TX/OK PNHDLS INTO WRN TX. MEANWHILE...WARM FRONT WILL
LIFT NWD THROUGH THE CNTRL PLAINS IN RESPONSE TO DEEPENING SURFACE
LOW. FARTHER E...COLD FRONT WILL PUSH EWD THROUGH THE LOWER GREAT
LAKES AND NEW ENGLAND WITH THE SWRN EXTENT OF THIS BOUNDARY
GRADUALLY WEAKENING NEAR OR JUST S OF THE OH RIVER.
..CNTRL/SRN PLAINS...
INGREDIENTS APPEAR TO BE COMING TOGETHER FOR A POTENTIALLY ACTIVE
SEVERE WEATHER DAY ACROSS THE REGION AHEAD OF INTENSIFYING UPPER
SYSTEM OVER THE INTERMOUNTAIN W. CONSIDERABLE AIR MASS
DESTABILIZATION IS FORECAST THROUGH THE DAY E OF DRYLINE AS A MOIST
BOUNDARY LAYER AIR MASS /UPPER 50S TO LOWER 60S DEWPOINTS/ IS
ADVECTED NWD BENEATH STEEP MID-LEVEL LAPSE RATES. VERTICAL SHEAR
WILL CONCURRENTLY INCREASE AS EXIT REGIONS OF MID AND HIGH-LEVEL JET
STREAKS ATTENDANT TO WRN U.S. SYSTEM BEGIN TO PROPAGATE INTO THE
CNTRL/SRN HIGH PLAINS.
FORECAST SOUNDINGS SUGGEST THAT CAPPING ARISING FROM THE PRESENCE OF
AN ELEVATED MIXED LAYER WILL LIKELY INHIBIT DEEP MOIST CONVECTION
THROUGH MUCH OF THE AFTERNOON. HOWEVER WITH TIME...SUSTAINED
CONVERGENCE ALONG DRYLINE AND WARM FRONT SHOULD SUPPORT ISOLATED
STORM DEVELOPMENT WITHIN A MODERATELY UNSTABLE AND INCREASINGLY
SHEARED ENVIRONMENT. FORECAST SOUNDINGS SUGGEST THE LIKELIHOOD OF
SUPERCELLS CAPABLE OF TORNADOES AND LARGE HAIL SHOULD SURFACE-BASED
STORMS INITIATE AND BECOME SUSTAINED.
MODEL GUIDANCE INDICATES THAT TSTMS /LIKELY SLIGHTLY ELEVATED/ WILL
BECOME MORE NUMEROUS MONDAY NIGHT ACROSS PARTS OF NRN KS INTO NEB AS
STRENGTHENING LLJ ENHANCES WAA AND ISENTROPIC ASCENT NEAR AND N OF
WARM FRONT. LARGE HAIL WOULD APPEAR TO BE THE PRIMARY THREAT WITH
THESE STORMS.
THE OPERATIONAL NAM/WRF OFFERS A SCENARIO FOR POTENTIALLY EARLIER
CONVECTIVE DEVELOPMENT OVER THE ERN TX PNHDL INTO WRN OK MONDAY
AFTERNOON APPARENTLY IN ASSOCIATION WITH A LEAD SHORT WAVE TROUGH
ORIGINATING OVER NRN MEXICO. CURRENTLY...CONFIDENCE IN THIS
SCENARIO IS LOW DUE TO UNCERTAINTIES IN EXISTENCE AND TIMING OF THIS
FEATURE.
..LOWER GREAT LAKES INTO OH VALLEY...
WHILE MID-LEVEL LAPSE RATES AND RESULTANT INSTABILITY ARE NOT
FORECAST TO BE PARTICULARLY STRONG AHEAD OF COLD FRONT...LATEST
MODEL GUIDANCE DOES SUGGEST AN INCREASE IN CONVECTIVE DEVELOPMENT
ALONG FRONTAL ZONE MONDAY AFTERNOON. SOME STEEPENING OF THE
LOW-LEVEL LAPSE RATES COUPLED WITH MODESTLY STRONG DEEP LAYER
VERTICAL SHEAR SUGGESTS SOME POTENTIAL FOR A FEW ORGANIZED STORMS
CAPABLE OF DAMAGING WINDS. THIS THREAT SHOULD TEND TO DIMINISH
MONDAY NIGHT AS BOUNDARY LAYER COOLS AND STABILIZES.
.MEAD.. 04/21/2007
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