SWODY1
SPC AC 170552
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CDT WED OCT 17 2007
VALID 171200Z - 181200Z
..THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT OVER
SERN KS...PARTS OF CNTRL/ERN OK...AR AND SRN MO...
..THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE CNTRL AND SRN
PLAINS EWD INTO THE MID AND LOWER MS VALLEY...
..SYNOPSIS...
SIGNIFICANT INTENSIFICATION OF CNTRL U.S. UPPER TROUGH IS FORECAST
AS STRONG MID AND HIGH-LEVEL JET STREAKS PROPAGATE FROM THE SRN
ROCKIES INTO THE SRN PLAINS AND EWD INTO THE LOWER/MID MS VALLEY.
EMBEDDED SHORT WAVE TROUGH OVER WRN NM AS OF 17/05Z WILL LIFT
RAPIDLY NEWD INTO CNTRL/SRN PLAINS BY LATE THIS AFTERNOON OR
EVENING...AND EVENTUALLY INTO THE MIDWEST BY THURSDAY MORNING.
IN THE LOW LEVELS...PRIMARY SURFACE LOW WILL DEEPEN TODAY OVER SWRN
KS BEFORE DEVELOPING RAPIDLY NEWD INTO ERN NEB OR WRN IA BY THE END
OF THE FORECAST PERIOD. DRYLINE EXTENDING SWD FROM THIS LOW WILL
MIX/ADVECT EWD INTO WRN OK AND NWRN TX BY MID TO LATE
AFTERNOON...LIKELY PROVIDING THE FOCUS FOR SEVERE TSTM DEVELOPMENT
LATER TODAY. ELSEWHERE...WARM FRONT /EFFECTIVELY DELINEATING A
NOTABLE INCREASE IN BOUNDARY LAYER MOISTURE/ WILL LIFT NWD THROUGH
THE CNTRL PLAINS...MID MS VALLEY AND LOWER OH VALLEY THROUGH THE
PERIOD.
..CNTRL/SRN PLAINS EWD INTO THE MID/LOWER MS VALLEY...
--A POTENTIALLY SIGNIFICANT SEVERE WEATHER EPISODE IS EXPECTED THIS
AFTERNOON AND TONIGHT WITH A THREAT OF STRONG...LONG-TRACKED
TORNADOES--
17/00Z UPPER-AIR ANALYSES AND CURRENT GOES IPW DATA SHOW A RAPID
RETURN OF RICHER BOUNDARY LAYER MOISTURE NWD THROUGH THE SRN PLAINS
WITH A MARITIME TROPICAL AIR MASS /I.E. DEWPOINTS IN THE UPPER 60S
TO LOWER 70S/ NOW IN PLACE FROM SRN TX EWD ACROSS THE CNTRL GULF
COAST. STRENGTHENING SLY LOW-LEVEL FLOW FROM THE SRN/CNTRL PLAINS
EWD THROUGH THE MS RIVER VALLEY WILL ENHANCE THE TRANSPORT OF THIS
MOISTURE NWD THROUGH THE CNTRL PART OF THE NATION TODAY AND TONIGHT.
THIS INCREASE IN LOW-LEVEL MOISTURE COUPLED WITH STEEPENING
MID-LEVEL LAPSE RATES IS EXPECTED TO CONTRIBUTE TO A MODERATELY
UNSTABLE AIR MASS BY AFTERNOON E OF DRY LINE FROM CNTRL/ERN TX NWD
THROUGH OK INTO KS WITH MLCAPES OF 1000-1500 J/KG. FARTHER E OVER
THE LOWER MS VALLEY/MID SOUTH...LAPSE RATES WILL BE WEAKER...THOUGH
COMPARABLY RICHER BOUNDARY LAYER MOISTURE AND DAYTIME HEATING WILL
SUPPORT MLCAPES OF 1000-1500 J/KG.
TSTMS CURRENTLY DEVELOPING OVER THE TX PNHDL ARE EXPECTED TO BE IN
PROGRESS AT THE ONSET OF THE FORECAST PERIOD OVER PARTS OF NWRN
TX...OK AND KS IN ASSOCIATION WITH WEAKER...LEAD SHORT WAVE TROUGH
EJECTING NEWD THROUGH THE SRN HIGH PLAINS. THESE STORMS ARE
EXPECTED TO INCREASE IN COVERAGE AND INTENSITY THROUGH THE DAY WHILE
MOVING/DEVELOPING NEWD TOWARD THE LOWER MO VALLEY WITH THE POTENTIAL
FOR EMBEDDED SUPERCELLS CAPABLE OF HAIL...DAMAGING WINDS AND PERHAPS
A COUPLE TORNADOES.
MORE SIGNIFICANT...SEVERE STORM DEVELOPMENT IS ANTICIPATED IN WAKE
OF EARLIER STORM ACTIVITY LATER THIS AFTERNOON FROM VICINITY OF
SURFACE LOW OVER SWRN KS SWD/SEWD ALONG DRY LINE INTO WRN/CNTRL OK
AND FAR N-CNTRL TX. THE COMBINATION OF MODERATE INSTABILITY AND
MODERATE TO STRONG LOW AND DEEP-LAYER SHEAR SUGGEST A HIGH LIKLIHOOD
OF SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND
TORNADOES...A FEW OF WHICH COULD BE STRONG AND LONG-TRACKED. THIS
IS ESPECIALLY THE CASE FROM SERN KS AND ERN OK INTO AR AND SRN MO
THIS EVENING AND TONIGHT WHERE DEEP-LAYER FORCING FOR ASCENT WILL BE
CONCENTRATED IN ADVANCE OF PRIMARY SHORT WAVE TROUGH.
ELSEWHERE...TSTMS WILL BECOME INCREASINGLY NUMEROUS TODAY OVER PARTS
OF THE LOWER MS VALLEY INTO THE MID SOUTH WITHIN A VERY MOIST AND
MODERATELY UNSTABLE AIR MASS RETURNING NWD. FORECAST SOUNDINGS
INDICATE VERTICAL SHEAR PROFILES QUITE SUPPORTIVE OF SUPERCELLS
CAPABLE OF TORNADOES /SOME STRONG/ AND PERHAPS ISOLATED WIND AND/OR
HAIL. THIS REGIME WILL CONTINUE NWD OVERNIGHT ALONG ERN BRANCH OF
LLJ THROUGH PORTIONS OF THE MID MS AND LOWER OH VALLEYS...LIKELY
MERGING WITH OTHER STORM CLUSTERS ORIGINATING OVER THE CNTRL/SRN
PLAINS IN ADVANCE OF ABOVE-MENTIONED SHORT WAVE TROUGH. SUPERCELLS
WILL REMAIN POSSIBLE OVERNIGHT WITH A THREAT OF TORNADOES...LOCALLY
STRONG WIND GUSTS AND SOME HAIL.
.MEAD/GUYER.. 10/17/2007
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