[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 180602
SWODY1
SPC AC 180600

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT TUE APR 18 2006

VALID 181200Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE LOWER MO VALLEY TO
THE OZARKS/LOWER TN VALLEY REGION...

...SYNOPSIS...
HIGH AMPLITUDE LARGE SCALE PATTERN WILL CONTINUE ACROSS THE U.S.
TODAY...CHARACTERIZED BY OMEGA BLOCK EXTENDING FROM WRN ATLANTIC WWD
TO THE PLAINS. WRN EXTENT OF THIS BLOCKING PATTERN WILL BE A MID/
UPPER LEVEL TROUGH MOVING EWD AND INTENSIFYING INTO A CLOSED LOW
ACROSS NRN/CENTRAL PLAINS.  80+ KT MID-LEVEL JET WITH THIS SYSTEM
WILL TRANSLATE NEWD TODAY AND EXTEND FROM WRN KS TO MID MO VALLEY BY
EARLY EVENING.

IN THE LOW-LEVELS...OCCLUSION OF NRN MOST SURFACE LOW IS EXPECTED
OVER THE ERN DAKOTAS THIS MORNING AS STRONG COLD FRONT OVERTAKES NRN
EXTENT OF WARM FRONT WHICH WILL EXTEND ALONG THE MID/LOWER MO VALLEY
INTO THE LOWER TN VALLEY AND SERN STATES.  SECONDARY SURFACE LOW AT
OCCLUSION POINT OF PROGRESSIVE COLD FRONT IS EXPECTED TO BE LOCATED
ACROSS NWRN MO BY LATE AFTERNOON...WITH THIS LOW TRACKING SEWD INTO
LOWER TN VALLEY TONIGHT.

...MID AND LOWER MO VALLEY INTO OZARKS/LOWER TN VALLEY...
LATEST SURFACE OBSERVATIONS INDICATED DEWPOINTS IN THE UPPER 60S AS
FAR NORTH AS SERN OK/SRN AR.  SLY LOW-LEVEL FLOW WITHIN THE WARM
SECTOR WILL ALLOW THIS MOISTURE TO RETURN NWD TODAY WITH UPPER 60S
DEWPOINTS POTENTIALLY REACHING AS FAR N AS CENTRAL/NRN MO THIS
AFTERNOON.  PLUME OF STEEP MID-LEVEL LAPSE RATES ASSOCIATED WITH THE
NRN/CENTRAL PLAINS UPPER SYSTEM WILL ADVECT EWD CAPPING THE WARM
SECTOR THROUGH MUCH OF THE DAY.  THESE LAPSE RATES COMBINED WITH
STRONG SURFACE HEATING AND SURFACE DEWPOINTS IN THE 60S EXPECTED TO
RESULT IN SBCAPE AOA 3000 J/KG FROM MO SSWWD TO THE ARKLATEX REGION.

THUNDERSTORMS MAY BE ONGOING AT THE BEGINNING OF THE PERIOD ACROSS
PARTS OF THE CENTRAL/ERN DAKOTAS.  LARGE SCALE ASCENT AHEAD OF THE
INTENSIFYING UPPER TROUGH AND LOW-LEVEL WAA SHOULD SUPPORT A
CONTINUATION OF THIS ACTIVITY EWD TOWARD SWRN MN AND SEWD
DEVELOPMENT INTO ERN NEB/WRN IA WITH GRADUAL INCREASE IN COVERAGE. 
FORECAST SOUNDINGS SUGGEST THIS ACTIVITY SHOULD REMAIN ELEVATED
GIVEN COOLER/MORE STABLE BOUNDARY LAYER.  STEEP MID-LEVEL LAPSE
RATES WITH MODERATE ELEVATED INSTABILITY WILL SUPPORT HAIL AS THE
PRIMARY THREAT WITH THIS ACTIVITY.

SURFACE BASED STORM DEVELOPMENT IS EXPECTED INITIALLY NEAR THE
SECONDARY SURFACE LOW/OCCLUSION POINT OVER NWRN MO BY MID-LATE
AFTERNOON...AND THEN SWD ACROSS WRN MO TO FAR ERN OK/WRN AR AS THE
COLD FRONT MOVES EWD.  ALTHOUGH THE WARM SECTOR IS EXPECTED TO BE
LOCATED S OF STRONGER FLOW ALOFT...DEEP LAYER SHEAR VECTORS WILL BE
SUFFICIENT FOR SUPERCELLS GIVEN THE STRONG INSTABILITY.  ANY STORMS
THAT DEVELOP/MOVE IN THE VICINITY OF THE OCCLUSION POINT AND WARM
FRONT WILL ENCOUNTER STRONG LOW-LEVEL SHEAR /0-3 KM SRH 250-400
M2/S2/ FOR AN ENHANCED TORNADO THREAT...WITH A FEW POTENTIALLY
STRONG.  LARGE HAIL...SOME VERY LARGE...WILL BE LIKELY ACROSS MUCH
OF MO/NRN AR...AND WITH ACTIVITY THAT SPREADS EWD INTO WRN IL THIS
EVENING.

POTENTIAL EXISTS FOR UPSCALE GROWTH INTO AN MCS THIS EVENING/
OVERNIGHT EWD ACROSS MID MS/LOWER OH VALLEYS.  GREATEST SEVERE
THREAT SHOULD BE ALONG SWRN PERIPHERY OF THIS MCS ACROSS SERN MO/
NRN-ERN AR AS SECONDARY SURFACE LOW TRACKS TOWARD THE LOWER TN
VALLEY.  LLJ VEERING TO SWLY AND INCREASING ACROSS AR INTO SRN IL
WILL MAINTAIN THREAT FOR TORNADOES THROUGH THIS REGION INTO THE 
MID-LATE EVENING...IN ADDITION TO LARGE HAIL/DAMAGING WINDS.

...FL NWWD INTO SWRN GA/PARTS OF AL...
BOUNDARY WILL EXTEND FROM WRN TN ACROSS AL/SWRN GA.  SRN EXTENT IS
EXPECTED TO MOVE SWD THROUGH THE NRN-ERN PORTIONS OF THE FL
PENINSULA.  STRONG SURFACE HEATING ALONG THIS BOUNDARY COMBINED WITH
RICH MOISTURE EXPECTED TO SUPPORT MODERATE INSTABILITY.  WATER VAPOR
IMAGERY INDICATED A WEAK MID-LEVEL IMPULSE CURRENTLY OVER THE
ARKLATEX REGION.  LARGE SCALE ASCENT WITH THIS FEATURE AS IT TRACKS
SEWD TOWARD FL COMBINED WITH STRONG SURFACE HEATING ALONG THE
SURFACE BOUNDARY EXPECTED TO SUPPORT SCATTERED THUNDERSTORM
DEVELOPMENT.  STRONG DEEP LAYER SHEAR WITHIN NW FLOW REGIME SHOULD
ALLOW FOR A FEW STRONG TO SEVERE STORMS INTO THE EARLY EVENING.

..PETERS/JEWELL.. 04/18/2006