SPC AC 251729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT SAT APR 25 2009
VALID 261200Z - 271200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN AND
CNTRL PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER
MIDWEST...
...SEVERE WEATHER OUTBREAK APPEARS LIKELY ACROSS PARTS OF THE SRN
AND CNTRL PLAINS SUNDAY AFTERNOON AND SUNDAY NIGHT...
...SRN PLAINS AND CNTRL PLAINS...
A WELL-DEFINED 75 TO 85 KT MID-LEVEL JET IS FORECAST TO EJECT NEWD
ACROSS THE SRN AND CNTRL PLAINS SUNDAY OUT OF THE BASE OF AN
UPPER-LEVEL TROUGH OVER THE SRN AND CNTRL ROCKIES. THIS WILL CREATE
A WIDESPREAD AREA WITH MODERATE TO STRONG VERTICAL SHEAR. AT
LOW-LEVELS...ABUNDANT MOISTURE AND LOW-LEVEL SHEAR WILL BE IN PLACE
ASSOCIATED WITH A BROAD 45 TO 60 KT LOW-LEVEL JET EXTENDING NNEWD
ACROSS THE SRN AND CNTRL PLAINS. THE LOW AND MID-LEVEL JETS WILL
BECOME JUXTAPOSED AS THE LARGE-SCALE ASCENT WITH THE MAIN
UPPER-LEVEL TROUGH MOVES EWD INTO THE PLAINS. THIS WILL BE FAVORABLE
FOR A WIDESPREAD SEVERE WEATHER EVENT SUNDAY AND SUNDAY NIGHT ACROSS
PARTS OF WRN OK...CNTRL AND ERN KS...THE ERN TX PANHANDLE AND WCNTRL
TX.
THE CURRENT THINKING IS THAT ONE OR TWO CLUSTERS OF ELEVATED STORMS
WITH HAIL POTENTIAL SHOULD BE ONGOING SUNDAY MORNING ACROSS PARTS OF
THE MODERATE RISK AREA. THIS CONVECTION SHOULD MOVE EWD AWAY FROM
THE INSTABILITY AXIS DURING THE DAY ALLOWING FOR MODERATE TO STRONG
DESTABILIZATION FROM CNTRL KS SWD ACROSS WRN OK...THE ERN TX
PANHANDLE INTO THE LOW ROLLING PLAINS OF WCNTRL TX. MODEL FORECASTS
ARE IN GENERAL AGREEMENT WEAKENING THE CAP BY EARLY TO MID-AFTERNOON
INITIATING SCATTERED TO NUMEROUS THUNDERSTORMS ACROSS THE
INSTABILITY AXIS. FORECAST SOUNDINGS FROM THE NAMKF AT 21Z ACROSS
THE MODERATE RISK AREA SHOW DEEP UNSTABLE THERMODYNAMIC PROFILES
WITH MLCAPE VALUES BETWEEN 2000 AND 2500 J/KG ACROSS MUCH OF THE
MODERATE RISK AREA. IN ADDITION...0-6 KM SHEAR ACROSS THE WARM
SECTOR AIDED BY THE MID-LEVEL JET SUNDAY AFTERNOON RANGE FROM 40 TO
55 KT WITH STRONG SPEED SHEAR IN THE BOUNDARY LAYER AND ADEQUATE
DIRECTIONAL SHEAR FOR SUPERCELLS AND TORNADOES. CURVED HODOGRAPHS
ALONG WITH LOW LCL HEIGHTS SUGGEST SOME STRONG TORNADOES WILL OCCUR
LATE SUNDAY AFTERNOON INTO THE EVENING. IF THE CONVECTION ONGOING
SUNDAY MORNING DOES INDEED MOVE EWD AWAY FROM THE AXIS OF
INSTABILITY...ALLOWING FOR MODERATE TO STRONG DESTABILIZATION...THEN
A TORNADO OUTBREAK MAY OCCUR ACROSS THE MODERATE RISK AREA.
FORECAST SOUNDINGS AT 21Z SUNDAY ALSO SUGGEST THE STORMS SHOULD BE
EFFICIENT HAIL PRODUCERS. SUPERCELLS SHOULD BE CAPABLE OF PRODUCING
VERY LARGE HAIL ESPECIALLY FROM SCNTRL KS SWD ACROSS THE ERN TX
PANHANDLE...WRN OK INTO WCNTRL TX. LARGE HAIL COVERAGE SHOULD BE
GREATEST FROM ECNTRL KS ACROSS WRN OK WITH MORE ISOLATED COVERAGE
ACROSS WCNTRL TX WHERE CONVECTIVE COVERAGE IS NOT EXPECTED TO BE AS
GREAT DURING THE EARLY EVENING. WIND DAMAGE SHOULD ALSO ACCOMPANY
SUPERCELLS AND LINE-SEGMENTS DURING THE LATE AFTERNOON AND EVENING.
A POTENTIAL FOR VERY STRONG WIND GUSTS SHOULD ALSO EXIST ESPECIALLY
ACROSS THE NRN PART OF THE MODERATE RISK AREA AS LOW-LEVEL FLOW
INCREASES AND LINE-SEGMENTS APPEAR MORE LIKELY.
...UPPER MIDWEST AND SRN GREAT LAKES...
A BROAD ZONE OF SOUTHWEST FLOW WILL EXIST ACROSS THE CNTRL
PLAINS...UPPER MIDWEST AND GREAT LAKES REGION AHEAD OF AN
APPROACHING ROCKIES UPPER-LEVEL TROUGH. AT THE SFC...A LOW SHOULD
ORGANIZE INTO THE MID-MO VALLEY WITH A COLD FRONT MOVING SEWD ACROSS
THE NRN PLAINS. THUNDERSTORMS SHOULD INITIATE ALONG AND AHEAD OF THE
COLD FRONT SUNDAY AFTERNOON WHERE MODEL FORECASTS SHOW MODERATE TO
STRONG VERTICAL SHEAR AND ENOUGH INSTABILITY FOR SEVERE STORMS.
ALTHOUGH THE DOMINATE STORM MODE REMAINS IN QUESTION...SUPERCELLS
THAT DEVELOP WILL BE CAPABLE OF PRODUCING LARGE HAIL AND PERHAPS A
FEW TORNADOES ESPECIALLY AS THE LOW-LEVEL JET STRENGTHENS IN THE
EARLY EVENING. IF THE DOMINANT MODE IS LINEAR WHICH THE HIGH RES
MODELS FAVOR...THEN THE STRONG LOW-LEVEL FLOW SHOULD SUPPORT WIND
DAMAGE POTENTIAL WITH BOWING-LINE SEGMENTS.
A WARM FRONT IS ALSO FORECAST TO EXIST ESEWD FROM THE LOW ACROSS SE
MN...FAR SRN WI INTO LOWER MI. IF SCATTERED THUNDERSTORMS CAN
INITIATE ALONG THIS BOUNDARY OR JUST SOUTH OF THE BOUNDARY WHERE
STRONGER INSTABILITY SHOULD BE PRESENT LATE SUNDAY AFTERNOON...THEN
AT LEAST A MARGINAL SEVERE THREAT WILL EXIST DUE TO ADEQUATE DEEP
LAYER SHEAR EVIDENT ON FORECAST SOUNDINGS.
...NRN APPALACHIAN MTNS...
A STRONG UPPER-LEVEL HIGH PRESSURE SYSTEM WILL REMAIN IN PLACE
ACROSS GA...THE CAROLINAS AND VIRGINIA WITH GRADUALLY INCREASING
MID-LEVEL FLOW FROM SOUTH TO NORTH ACROSS THE NRN APPALACHIANS. AT
THE SFC...A QUASI-STATIONARY FRONTAL BOUNDARY SHOULD EXIST NEAR THE
NEW YORK-PENNSYLVANIA STATE-LINE. ALTHOUGH MODEL FORECASTS DO NOT
ALL AGREE...THE POTENTIAL EXISTS FOR SCATTERED THUNDERSTORM
INITIATION DURING THE AFTERNOON ALONG THE BOUNDARY WITH THE
CONVECTION MOVING EWD INTO SRN NEW ENGLAND BY EARLY EVENING.
FORECAST SOUNDINGS ALONG THE FRONT AT 21Z SUGGEST MODERATE VERTICAL
SHEAR WILL BE IN PLACE WITH ENOUGH INSTABILITY FOR A MARGINAL SEVERE
THREAT. WLY UNIDIRECTIONAL FLOW WILL BE IN PLACE THROUGH A DEEP
LAYER SUGGESTING A THREAT FOR STRONG GUSTY WINDS WILL EXIST. HAIL
WILL ALSO BE POSSIBLE WITH THE MORE INTENSE MULTICELLS.
..BROYLES.. 04/25/2009
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