The SPC is forecasting ...intense severe thunderstorms expected over parts of the southeastern texas panhandle...western...north-central oklahoma...and south-central kansas late this afternoon into tonight.... Please read the latest public statement about this event.
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SPC AC 252000 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0300 PM CDT SAT APR 25 2009 VALID 252000Z - 261200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF WRN OK...SRN KS AND THE ERN TX PANHANDLE... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN AND CNTRL PLAINS...MID-MS VALLEY AND SRN GREAT LAKES REGION... ...LATEST THINKING FOR SRN KS/OK... ALTHOUGH SOME QUESTION REMAINS CONCERNING THE EXACT TIMING OF INITIATION...THUNDERSTORMS MAY INITIATE IN THE 22 TO 23Z TIMEFRAME ACROSS THE ERN TX PANHANDLE WITH SUPERCELLS MOVING INTO FAR WRN OK ALONG A FRONTAL BOUNDARY LOCATED FROM NEAR ALVA OK SWWD TO THE SERN TX PANHANDLE. THIS IS SUPPORTED BY THE LATEST 12Z HIGH RES NMM MODEL WHICH THEN INITIATES STORMS WITH LARGE HAIL AND WIND DAMAGE POTENTIAL ACROSS SRN AND ERN KS. THE THINKING CONTINUES THAT SUPERCELLS WITH VERY LARGE HAIL ARE LIKELY WITH AN ISOLATED STRONG TORNADO POSSIBLE IN WRN OK ESPECIALLY AS THE LOW-LEVEL JET CRANKS UP JUST AFTER DARK. ...CHANGES TO THE OUTLOOK... THE GREATEST CHANGE TO THE OUTLOOK IS TO EXTEND THE 5 PERCENT TORNADO PROBABILITY INTO NERN KS AND 10 PERCENT TORNADO PROBABILITY NEWD ACROSS THE SRN KS WHERE MODERATE INSTABILITY AND LOW-LEVEL SHEAR WILL BE FAVORABLE FOR A FEW TORNADOES WITH SUPERCELLS THAT INITIATE LATE THIS AFTERNOON OR EARLY THIS EVENING. OTHER MINOR CHANGES INCLUDE BETTER ALIGNING THE MODERATE AND SLIGHT RISK TO THE LATEST SFC ANALYSIS...SHORT-TERM THUNDER GUIDANCE AND INITIALIZED RUC FIELDS. THIS CUTS SOME OF NRN LOWER MI OUT OF THE SLIGHT...ADDED PART OF NRN KS INTO THE SLIGHT AND MOVED THE 5 PERCENT HAIL AND WIND PROBABILITIES WWD INTO AREAS SOUTH OF MIDLAND TX. ANOTHER CHANGE IS TO NARROW THE 5 PERCENT PROBABILITY ACROSS NE TX AND THE ARKLATEX TO FAVOR THE MOST LIKELY STORM INITIATION AND GREATEST COMBINATION OF INSTABILITY AND VERTICAL SHEAR. ALSO EXTENDED THE 5 PERCENT HAIL AND WIND PROBABILITIES NEWD ACROSS SRN MD WHERE THE COMBINATION OF SHEAR AND INSTABILITY APPEARS FAVORABLE FOR A MARGINAL SEVERE THREAT IF STORMS CAN INITIATE. ..BROYLES.. 04/25/2009 .PREV DISCUSSION... /ISSUED 1119 AM CDT SAT APR 25 2009/ ...SYNOPSIS... SW MID/UPR LVL FLOW WILL CONTINUE OVER THE CNTRL STATES...DOWNSTREAM FROM STRONG UPR LOW NOW IN SRN NV. THE LOW SHOULD EVOLVE INTO AN OPEN WAVE LATER TODAY...AND ACCELERATE ENE TO THE CNTRL HI PLNS BY 12Z SUN. FARTHER S...WEAK SRN STREAM VORT SHOULD FURTHER WEAKEN AS IT CONTINUES SLOWLY E FROM E TX TO THE LWR MS VLY. AT THE SFC...COLD FRONT NOW EXTENDING FROM THE UPR GRT LKS TO THE NRN TX PANHANDLE SHOULD BE THE MAIN FOCUS FOR SVR TSTMS THIS PERIOD. THE FRONT SHOULD MOVE STEADILY SE ACROSS WI/MI TO LWR GRT LKS THROUGH EARLY SUN. THE WRN PART OF THE BOUNDARY WILL SLOW AND BY LATE THIS AFTERNOON EXTEND FROM JUST S OF ICT TO NEAR A GAG AND S OF AMA LINE. ..CNTRL/SRN PLNS... SVR TSTMS...INCLUDING SUPERCELLS WITH POTENTIAL FOR VERY LARGE/DAMAGING HAIL AND A FEW TORNADOES...SHOULD DEVELOP LATE THIS AFTN THROUGH EARLY TONIGHT A LITTLE FURTHER S AND E THAN EXPECTED IN 13Z OUTLOOK DUE TO EVENTUAL LOCATION OF FRONTAL ZONE ACROSS NWRN OK THAN WWD CENTRAL TX PANHANDLE. AFTER INITIATION VICINITY THE INTERSECTIONS OF FRONTAL ZONE AND N/S DRY LINE WHICH SHOULD SET UP NEAR OK/TX BORDER THE STORMS SHOULD MOVE NE AND INCREASE IN COVERAGE AFTER DARK. IN THE MDT RISK AREA...POTENTIAL WILL EXIST FOR TORNADIC SUPERCELLS NEAR INTERSECTION OF STALLING SFC FRONT AND LEE TROUGH/DRY LINE. AN INCREASINGLY CONDITIONAL THREAT /DUE TO EML CAP/ WILL EXTEND SWD ALONG DRY LINE TOWARD NW TX. EXPECT CONSIDERABLE HEATING IN WARM SECTOR S OF FRONT TODAY WHICH COUPLED WITH LOW-MID 60S SFC DEW POINTS THAT HAVE ALREADY BECOME WELL ESTABLISHED ACROSS OK WHICH COMBINED WITH STEEP MID LVL LAPSE RATES...SHOULD YIELD AFTN SBCAPE AOA 2500 J/KG. AT THE SAME TIME...40-50 KT WSWLY MID LVL FLOW WILL CONTRIBUTE TO SUBSTANTIAL DEEP WLY SHEAR...WITH 0-1 KM SRH OF 150-250 M2/S2 LIKELY BEFORE 00Z. A CONDITIONAL POTENTIAL WILL EXIST FOR STG TORNADOES...ESPECIALLY JUST AFTER DARK WHEN SSWLY LLJ APPRECIABLY STRENGTHENS... SEASONABLY RICH MOISTURE INFLOW CONTINUES /KEEPING STORMS SFC-BASED/...AND LARGE SCALE ASCENT INCREASES WITH CONTINUED ENE MOVEMENT OF GRT BASIN UPR TROUGH. LLJ-RELATED BOOST IN HODOGRAPH SIZE MAY YIELD 300-500 M2/S2 0-1 KM SRH BY MID EVE. NOCTURNAL/NWD SPREAD OF FAVORABLE WARM SECTOR AIR MASS NWD ACROSS KS MAY BE AFFECTED ON THE MESOSCALE BY STORMS OVER WRN/NW OK AND SRN KS...LENDING TO SOME UNCERTAINTY REGARDING DEGREE OF OVERNIGHT SVR IN CNTRL/ERN KS. NEVERTHELESS...STRENGTHENING WIND FIELD AND ASCENT WITH APPROACHING UPR TROUGH...AND CONTINUED RICH MOISTURE INFLOW...SUGGEST A BETTER THAN EVEN RISK FOR A CONTINUING SVR THREAT /HAIL...WIND..AND ISOLD TORNADOES/ INTO EARLY SUN IN KS. ...SRN/CNTRL KS NE TO LWR MI... SCTD SFC-BASED TSTMS SHOULD FORM THIS AFTN THROUGH EARLY TONIGHT ALONG AFOREMENTIONED FRONTAL ZONE FROM NE KS TO LWR MI. ENVIRONMENT WILL BE CHARACTERIZED BY 30-40 KT DEEP WSWLY SHEAR ON SRN FRINGE OF NRN STREAM JET...AND 1500-2000 J/KG SBCAPE. DEVELOPMENT MAY BE ASSISTED BY ASCENT IN RIGHT ENTRANCE REGION OF SPEED MAX CROSSING THE UPR GRT LKS. A FEW SUPERCELLS WILL BE POSSIBLE INITIALLY...BUT DOMINANT EVOLUTION SHOULD BE TOWARD BROKEN LINEAR/BANDED STRUCTURES WITH EMBEDDED BOWING SEGMENTS YIELDING SVR WIND/HAIL...ESPECIALLY IN LWR MI. ISOLD TORNADOES WILL BE POSSIBLE...BUT LIKELY TIED TO LOCALIZED STORM SCALE EFFECTS. THE SVR THREAT SHOULD DIMINISH AFTER DARK...EXCEPT OVER CNTRL/ERN KS WHERE MOIST/60 KT LLJ LIKELY WILL SUPPORT AN OVERNIGHT SVR MCS EVOLUTION FROM THE SRN PLNS STORMS DESCRIBED ABOVE. ...SE TX INTO ARKLATEX/ERN OK... WEAK CIN IS EXPECTED OVER THIS REGION...WHICH WILL BE LOCATED ON ERN FRINGE OF ELEVATED MIXED LAYER. STG HEATING INVOF SRN STREAM UPR TROUGH AND/OR ALONG SUBTLE BOUNDARIES LEFT FROM PRIOR CONVECTION WILL LEAD TO SCTD CLUSTERS OF DIURNAL STORMS. WIND PROFILES SHOULD EXHIBIT CONSIDERABLE LOW LVL SHEAR...BUT WEAKER FLOW ALOFT. COUPLED WITH RICH LOW LVL MOISTURE /AVERAGE PW OVER REGION NOW AOA 1.25 INCHES/...SETUP COULD YIELD A FEW SPOTS OF SVR HAIL/WIND...IN ADDITION TO A LOW/CONDITIONAL TORNADO THREAT. ...CNTRL/ERN UT INTO WRN CO... A BAND OF TSTMS SHOULD FORM OVER CNTRL/ERN UT THIS AFTN...JUST AHEAD OF NV UPR VORT/TROUGH. THE LINE SHOULD MOVE RAPIDLY ENE...WITH MODERATE UNIDIRECTIONAL SSW FLOW AND SIZABLE TEMPERATURE-DEWPOINT SPREADS POSSIBLY PRODUCING A FEW STG/SVR GUSTS. SUSTAINED MESOSCALE ASCENT AND ASSOCIATED STEEPENING OF MID LVL LAPSE RATES SHOULD YIELD 100-500 J/KG MLCAPE DESPITE LIMITED MOISTURE. THE LINE SHOULD WEAKEN AFTER 00Z AS IT MOVES TOWARD CNTRL CO. ...CNTRL/SRN APPALACHIANS... ISOLD TO WDLY SCTD DIURNAL STORMS SHOULD FORM IN ENVIRONMENT OF MODEST LOW LVL MOISTURE AND STG SFC HEATING/STEEP LOW LVL LAPSE RATES OVER ELEVATED TERRAIN. PROXIMITY OF UPR RIDGE WILL KEEP DEEP WIND FIELD WEAK. BUT PULSE/MULTICELL STORMS COULD YIELD A FEW LOCAL DOWNBURSTS/SVR HAIL EVENTS. ...WRN/CNTRL/NRN NY AND NW WRN NEW ENGLAND... WEAKENING CIN THROUGH THE DAY...ALONG WITH LOW LVL MOIST INFLOW FROM THE WSW...MAY LEAD TO WDLY SCTD DIURNAL STORMS OVER THE REGION. LIMITED BOUNDARY LAYER MOISTURE WILL KEEP MLCAPE TO BELOW 1000 J/KG DESPITE RELATIVELY STEEP MID LVL LAPSE RATES. BUT WELL-MIXED SUB CLOUD LAYER AND RELATED EVAPORATIONAL COOLING MAY ENHANCE DOWNDRAFTS ENOUGH FOR A MRGL SVR WIND CONCERN. NEARLY UNIDIRECTIONAL DEEP WIND FIELD WILL FAVOR EWD-MOVING CELLS AND SHORT LINE SEGMENTS. CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z