SPC AC 121708

   DAY 1 CONVECTIVE OUTLOOK  

   NWS STORM PREDICTION CENTER NORMAN OK

   1108 AM CST SUN MAR 12 2006

   VALID 121630Z - 131200Z

   ...THERE IS A HIGH RISK OF SVR TSTMS ACROSS EASTERN KANSAS...MUCH OF

   MISSOURI...SOUTHEAST IOWA...AND WEST CENTRAL AND NORTHWESTERN

   ILLINOIS...

   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS EASTERN OKLAHOMA...FAR

   NORTHEAST TEXAS..ARKANSAS..MISSOURI...SOUTHEAST NEBRASKA...SOUTHERN

   IOWA...ILLINOIS...INDIANA...AND WESTERN KENTUCKY...

   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS ERN PORTIONS OF THE

   CENTRAL AND SRN PLAINS EWD ACROSS THE MID MS AND OH VALLEYS...

   ...SYNOPSIS...

   LARGE UPPER TROUGH OVER THE WRN U.S. WILL SHIFT ENEWD ACROSS THE

   PLAINS STATES TOWARD THE MIDDLE AND UPPER MS VALLEY THIS

   PERIOD...ACCOMPANIED BY VERY STRONG DEEP-LAYER WIND FIELD /H5 JET

   100 TO 120 KT/.

   AT THE SURFACE...WELL-DEVELOPED LOW IS FORECAST TO SHIFT ENEWD OUT

   OF ERN CO...WHILE WARM FRONT NOW EXTENDING W-E ACROSS SRN KS/SRN MO

   MOVES NWD WITH TIME.  THIS BOUNDARY WILL CONTINUE TO SERVE AS A

   FOCUS FOR CONVECTIVE DEVELOPMENT...WITH DRYLINE ALSO FORECAST TO ACT

   AS A CONVECTIVE FOCUS LATER THIS AFTERNOON AS IT MIXES EWD ACROSS

   CENTRAL AND INTO ERN OK/SERN KS.

   ...CENTRAL AND SRN PLAINS EWD ACROSS THE MID MS AND OH VALLEYS...

   VERY STEEP LAPSE RATES -- 8 TO 8.5 C/KM IN THE 850 TO 500 LAYER

   ACCORDING TO MORNING RAOBS -- WILL CONTINUE TO SPREAD ENEWD ACROSS A

   MOIST WARM SECTOR /SURFACE DEWPOINTS IN THE LOW TO MID 60S/ THIS

   PERIOD.  LOW-LEVEL JET ADVECTING WARM/MOIST AIR ISENTROPICALLY NWD

   INTO NRN KS/NRN MO COMBINED WITH VERY STRONG DEEP-LAYER WIND

   PROFILES HAS YIELDED A CLUSTER OF ELEVATED SUPERCELLS...WHICH HAVE

   PRODUCED SIGNIFICANT SEVERE WEATHER.  SUPERCELLS/SEVERE THREAT

   SHOULD PERSIST/SHIFT SLOWLY EWD ALONG AND N OF RETREATING WARM FRONT

   AS UPPER TROUGH AND ASSOCIATED JET STREAK MOVES EWD INTO THE PLAINS.

   MEANWHILE...DRYLINE NOW LYING ACROSS WRN OK/WRN N TX WILL ALSO SERVE

   AS A FOCUS FOR SEVERE CONVECTIVE DEVELOPMENT LATER THIS

   AFTERNOON...AS IT MIXES EWD ACROSS N TX/OK/SERN KS INTO

   DESTABILIZING AIRMASS /1500 TO 3000 J/KG MEAN-LAYER CAPE/.  THOUGH

   WARM SECTOR AIRMASS REMAINS CAPPED ATTM...DAYTIME HEATING OF MOIST

   BOUNDARY LAYER COMBINED WITH INCREASING LARGE-SCALE ASCENT SHOULD

   WEAKEN CAP SUFFICIENTLY TO ALLOW STORM DEVELOPMENT TO OCCUR BY

   20-21Z.  

   AS STRONG MID-LEVEL SWLYS SHIFT EWD ACROSS THE WARM SECTOR ABOVE 35

   TO 50 KT SLY/SSWLY LOW-LEVEL JET...VERY FAVORABLE WIND SHEAR WITH

   HEIGHT WILL SUPPORT INTENSE SUPERCELLS -- PARTICULARLY GIVEN DEGREE

   OF INSTABILITY.  ATTM...AREA OF MAXIMUM SEVERE THREAT APPEARS TO

   EXIST FROM ERN KS ENEWD ACROSS CENTRAL AND NRN MO INTO SERN IA/W

   CENTRAL AND NWRN IL.  WITH SURFACE LOW FORECAST TO SHIFT ENEWD WITH

   TIME ACROSS THIS REGION...BACKING LOW-LEVEL FLOW IN THE WARM SECTOR

   -- AND ELY WINDS N OF WARM FRONT -- WILL YIELD VERY FAVORABLE

   LOW-LEVEL SHEAR SUPPORTIVE OF VIOLENT/LONG-TRACK TORNADOES ALONG A

   BROAD AXIS ON EITHER SIDE OF WARM FRONT.  ALONG WITH

   TORNADOES...VERY LARGE HAIL AND STRONG/DAMAGING WINDS CAN ALSO BE

   EXPECTED.

   THOUGH LOW-LEVEL FLOW SHOULD REMAIN MORE SLY -- AND MID-LEVEL FLOW

   LESS INTENSE -- FURTHER S ACROSS ERN OK AND INTO N TX...SHEAR

   PROFILES WILL REMAIN MORE THAN ADEQUATE FOR SUPERCELL STORMS.  GIVEN

   DEGREE OF SHEAR AND INSTABILITY...A FEW STRONG/DAMAGING TORNADOES

   ARE ANTICIPATED...ALONG WITH VERY LARGE HAIL AND LOCALLY DAMAGING

   WIND GUSTS.

   THIS EVENING/OVERNIGHT...70 KT LOW-LEVEL JET IS FORECAST TO DEVELOP

   ACROSS THE MID MS VALLEY.  EXPECT STORMS TO INCREASE IN

   COVERAGE...EVOLVING INTO ONE OR MORE SEVERE STORM CLUSTERS.  ALONG

   WITH LARGE HAIL...DAMAGING WINDS AND ISOLATED TORNADOES WILL BE

   POSSIBLE ALONG AND N OF WARM FRONT AS FAR E AS SRN LOWER MI/NRN OH.

   FURTHER S...DRYLINE WILL CONTINUE SHIFTING EWD ACROSS MO/ERN OK/NERN

   TX THIS EVENING/OVERNIGHT.  COLD FRONT SHOULD OVERTAKE THE DRYLINE

   OVERNIGHT ACROSS MO...WHERE SQUALL LINE SHOULD EVOLVE. ALONG WITH

   LARGE HAIL AND ISOLATED TORNADOES...A MORE WIDESPREAD THREAT FOR

   VERY STRONG/DAMAGING WINDS APPEARS LIKELY.  A MORE BROKEN LINE OF

   STORMS SHOULD CONTINUE EWD OVERNIGHT FROM ERN OK AND NERN TX ACROSS

   AR/NRN LA AND TO THE MS VALLEY BY THE END OF THE PERIOD.  LARGE HAIL

   AND LOCALLY DAMAGING WINDS ALONG WITH AN ISOLATED TORNADO THREAT

   SHOULD PERSIST THROUGH THE END OF THE PERIOD.

   ..GOSS.. 03/12/2006