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May 11, 2014 1630 UTC Day 1 Convective Outlook

May 11, 2014

May 11, 2014 1630 UTC Day 1 Convective Outlook

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DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1122 AM CDT SUN MAY 11 2014

VALID 111630Z – 121200Z

…THERE IS A MDT RISK OF SVR TSTMS OVER CNTRL KS INTO PARTS OF ERN NEB…WRN/CNTRL IA AND FAR NWRN MO…

…THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MIDWEST AND OH VALLEY INTO SRN PLAINS…

…SUMMARY…
SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP FROM PARTS OF THE CENTRAL AND SOUTHERN PLAINS THROUGH THE MID-MISSISSIPPI VALLEY INTO THE OHIO VALLEY TODAY THROUGH TONIGHT. THE GREATEST CONCENTRATION OF SEVERE WEATHER SHOULD EXTEND FROM CENTRAL AND NORTHERN KANSAS THROUGH SOUTHEAST NEBRASKA INTO MUCH OF IOWA. VERY LARGE HAIL…DAMAGING WIND…AND TORNADOES WILL OCCUR. A COUPLE OF INTENSE TORNADOES WILL BE POSSIBLE THIS AFTERNOON INTO EVENING OVER PARTS OF EASTERN NEBRASKA INTO WESTERN AND PERHAPS CENTRAL IOWA.

…SYNOPSIS…

12Z UPPER-AIR DATA INDICATE MID AND UPPER-LEVEL JET STREAKS PROGRESSING THROUGH THE BASE OF THE PARENT TROUGH OVER THE LOWER CO VALLEY. THESE WIND MAXIMA WILL CONTINUE EWD/NEWD INTO THE CNTRL/SRN HIGH PLAINS BY 12/12Z…IN TANDEM WITH THE SRN EXTENSION OF FULL-LATITUDE TROUGH. A 40-50+ KT SLY LLJ WILL BE MAINTAINED AHEAD OF THE TROUGH ACROSS THE CNTRL/SRN PLAINS TODAY WITH THIS FEATURE MIGRATING EWD/NEWD INTO THE UPPER MIDWEST AND OZARK PLATEAU REGION BY EARLY MONDAY.

AT THE SURFACE…A LEE CYCLONE OVER WRN KS MAY WEAKEN SLIGHTLY WHILE DEVELOPING NEWD INTO N-CNTRL IA OR S-CNTRL/SERN MN BY THE END OF THE DAY ONE PERIOD. AN ASSOCIATED WARM FRONT /REINFORCED BY CONVECTIVE OUTFLOW/ WILL ATTEMPT TO MOVE NWD THROUGH PARTS OF ERN NEB AND SRN/CNTRL IA WHILE A COLD FRONT SURGES SWD THROUGH THE CNTRL INTO SRN HIGH PLAINS. THE COLD FRONT WILL GRADUALLY OVERTAKE A DRYLINE WHICH WILL BECOME ESTABLISHED FROM N-CNTRL KS SSWWD INTO THE FAR ERN OK/TX PNHDLS INTO W-CNTRL TX BY MID/LATE AFTERNOON.

…MID/LOWER MO VALLEY INTO CNTRL PLAINS TODAY THROUGH TONIGHT…

MORNING RAOB DATA FROM TOP AND SGF SHOW THAT CONSIDERABLE MOISTENING OF THE WARM SECTOR HAS OCCURRED OVERNIGHT WITH LOWEST 100-MB MEAN-MIXING RATIOS OF AROUND 13 G/KG AND BOUNDARY LAYER DEWPOINTS IN THE MID 60S. THIS MOISTURE WILL COMBINE WITH DAYTIME HEATING AND STEEP MIDLEVEL LAPSE RATES TO YIELD AFTERNOON MLCAPE VALUES APPROACHING 2500-3500+ J/KG.

THE REMNANTS OF A NOCTURNAL MCS ONGOING OVER WRN/CNTRL IA HAVE RECENTLY SHOWN SIGNS OF RE-INTENSIFICATION OWING TO THE GRADUAL DESTABILIZATION OF THE AIR MASS ALONG THE NWD-MOVING WARM FRONT. A GROWING RISK FOR DAMAGING WINDS…LARGE HAIL AND PERHAPS A TORNADO OR TWO WILL EXIST WITH THIS SYSTEM AS IT CONTINUES EWD TODAY. FOR ADDITIONAL NEAR-TERM GUIDANCE…SEE MCD 561.

IN THE WAKE OF THE MORNING STORMS…RAPID TSTM DEVELOPMENT IS ANTICIPATED FROM THE VICINITY OF THE SURFACE TRIPLE POINT OVER S-CNTRL NEB SWWD ALONG THE COLD FRONT AND DRYLINE INTO WRN KS. AMPLE VERTICAL SHEAR WILL EXIST FOR SUPERCELLS AS THE INITIAL STORM MODE WITH A RISK FOR VERY LARGE HAIL AND TORNADOES. HOWEVER…THE LARGELY PARALLEL ORIENTATION OF THE DEEP-LAYER SHEAR VECTOR TO THE COLD FRONT AS IT OVERTAKES THE DRYLINE SUGGESTS A FAIRLY QUICK UPSCALE GROWTH OF STORMS INTO A LINEAR MCS. THE EXCEPTION MAY BE ACROSS PARTS OF ERN NEB INTO WRN AND CNTRL IA THIS AFTERNOON AND EVENING WHERE STRONG LOW-LEVEL SHEAR /I.E. EFFECTIVE SRH VALUES OF 300-400 M2 PER S2/ AND A MORE FAVORABLE DEEP-LAYER SHEAR VECTOR ORIENTATION SUGGEST A GREATER RISK FOR TORNADOES /SOME POSSIBLY INTENSE/ GIVEN A
MORE DISCRETE STORM MODE.

EXPECT ONE OR MULTIPLE BOWING MCS/S TO EVOLVE TONIGHT WITH A HAIL AND DAMAGING WIND THREAT SPREADING EWD INTO THE MIDWEST/UPPER MIDWEST AND LOWER MO VALLEY.

…SRN PLAINS THIS AFTERNOON INTO TONIGHT…

STRONG HEATING W OF THE DRYLINE COUPLED WITH WEAK HEIGHT FALLS ALOFT WILL LIKELY PROMOTE ISOLATED STORM DEVELOPMENT BY LATE AFTERNOON/EARLY EVENING. FORECAST SOUNDINGS INDICATE THAT CONSIDERABLE BOUNDARY LAYER MIXING WILL RESULT IN 30+ T-TD SPREADS JUST E OF THE DRYLINE WITH STEEP LOW TO MIDLEVEL LAPSE RATES CONTRIBUTING TO MLCAPE OF 1500-3000 J/KG. ASSOCIATED HODOGRAPHS EXHIBIT A VERTICALLY VEERING WIND PROFILE WITH 30-40 KT OF DEEP-LAYER SHEAR WHICH WILL BE SUFFICIENT FOR SUPERCELLS CAPABLE OF VERY LARGE HAIL.

THE MAJORITY OF THESE DIURNALLY DRIVEN STORMS ARE EXPECTED TO DIMINISH WITH NIGHTFALL OWING TO THE DE-COUPLING OF THE BOUNDARY LAYER. HOWEVER…SOME TSTM ACTIVITY –INCLUDING AN ISOLATED RISK FOR DAMAGING WINDS AND HAIL– MAY PERSIST OVERNIGHT ALONG THE EWD/SEWD-MOVING COLD FRONT.

…UPPER MIDWEST INTO MID MS/OH VALLEYS THIS AFTERNOON INTO TONIGHT…

DESPITE THE PRESENCE OF MIDLEVEL RIDGING DOWNSTREAM FROM THE EVOLVING WRN U.S. TROUGH…INCREASING LOW-LEVEL MOISTURE…DAYTIME HEATING AND STRENGTHENING MIDLEVEL LAPSE RATES FROM THE WEST WILL PROMOTE MODERATE INSTABILITY BY AFTERNOON WITH MLCAPE OF 1000-2000 J/KG. SPECIFIC DETAILS REGARDING STORM DEVELOPMENT AND EVOLUTION REMAIN UNCLEAR…BUT THE PRESENCE OF A NWD-MOVING WARM FRONT AND EXISTING CONVECTIVE OUTFLOWS MAY SERVE AS FOCI FOR TSTM DEVELOPMENT LATER TODAY. OTHER STORMS ONGOING ACROSS IA/NRN MO WILL LIKELY BEGIN TO AFFECT PARTS OF THE REGION THIS AFTERNOON INTO EVENING. WHILE VERTICAL SHEAR WILL BE WEAKER THAN POINTS TO THE W…THE DEGREE OF INSTABILITY WILL SUPPORT ORGANIZED STORM STRUCTURES WITH A RISK FOR PRIMARILY DAMAGING WINDS AND SEVERE HAIL.

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