[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 201612
SWODY1
SPC AC 201611

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1111 AM CDT THU APR 20 2006

VALID 201630Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM TX TO THE SRN
APPALACHIANS...

...TN RIVER VALLEY/CENTRAL GULF COAST STATES INTO THE SRN
APPALACHIANS...

CONVECTION WILL CONTINUE TO BUILD UPSCALE INTO AN MCS INTO MUCH OF
MIDDLE TN/CENTRAL KY AND SPREAD ENEWD INTO THE APPALACHIANS THIS
AFTERNOON.  THIS ACTIVITY WILL INCREASE AHEAD OF SHORTWAVE TROUGH
NOW MOVING OVER THE MID SOUTH. INCREASING CONVECTION/CLOUDS WILL
HINDER HEATING AND OVERALL DESTABILIZATION OVER MUCH OF THE TN RIVER
VALLEY AND POINTS EWD. IN ADDITION...THIS WILL LIMIT NEWD RETURN OF
RICHER MOISTURE NOW CONFINED TO REGIONS EAST OF N-E ORIENTED OUTFLOW
BOUNDARY FROM YESTERDAYS STORMS.  LARGE HAIL WILL BECOME SCATTERED
NORTHEAST OF THIS BOUNDARY...THOUGH MUCH OF IT WILL REMAIN MARGINAL
IN SEVERITY.  IF AREA DESTABILIZES MORE THAN EXPECTED...LARGE HAIL
THREAT WOULD INCREASE IN COVERAGE AND SEVERITY.  STORMS ROOTING INTO
NRN EXTENT OF MODERATE MLCAPE AXIS INTO NRN MS/NRN AL WILL BE MORE
LIKELY TO BECOME MORE ORGANIZED AS WLY FLOW ALOFT MAINTAINS 40 KT OF
EFFECTIVE SHEAR.  DURING THE MID TO LATE AFTERNOON...HEATING AND
MIXING OF SWLY FLOW ALOFT WILL ERODE NRN EDGE OF PERSISTENT SURFACE
BOUNDARY AND DESTABILIZE AHEAD OF OUTFLOW BOUNDARY NOW SHIFTING
SSEWD INTO NRN MS.  TAIL END OF SHORTWAVE TROUGH AND CONVERGENCE
WILL LIKELY INITIATE MORE VIGOROUS SEVERE THUNDERSTORMS FROM NRN MS
ACROSS NRN/CENTRAL AL...POSSIBLY BY 18Z.  FORECAST SOUNDINGS AGAIN
FAVOR VERY LARGE HAIL AND PERHAPS A FEW PERSISTENT
SUPERCELLS/ORGANIZED CLUSTERS. THIS ACTIVITY SHOULD SPREAD
GENERALLY EWD INTO THE SRN APPALACHIANS THROUGH THE EVENING...WITH
THREATS OF DAMAGING WINDS AND LARGE HAIL.

...TX INTO THE LOWER MS RIVER VALLEY...
COMPLEX EVOLUTION ANTICIPATED ACROSS TX TODAY. STRONG UPPER LOW IS
NOW MOVING INTO THE SRN HIGH PLAINS...WITH SUBSEQUENT MID/UPPER
LEVEL JET OVERSPREADING TX.  SURFACE PATTERN IS QUITE MESSY DUE TO
EARLIER CONVECTION...THOUGH EXPECT PRIMARY SURFACE WARM FRONT WILL
BECOME BETTER DEFINED FROM THE UPPER TX COAST INTO THE HILL COUNTRY
DURING THE AFTERNOON.  SOUTH OF THIS BOUNDARY RICH GULF MOISTURE
REMAINS IN PLACE WITH SURFACE DEW POINTS AROUND 70F.

SLY LLJ OBSERVED ON MORNING UPPER AIR ANALYSES WILL REMAIN ANCHORED
INTO THE BIG BEND REGION/EDWARDS PLATEAU THROUGH THE DAY AND
MAINTAIN ELEVATED STRONG TO SEVERE THUNDERSTORMS INTO WRN AND NWRN
TX.  ACTIVITY NOW ONGOING IN THE HILL COUNTRY NEAR THE FRONT MAY
BECOME INCREASINGLY SURFACE BASED AND PERSIST EWD INTO CENTRAL TX
THROUGH THE AFTERNOON. OTHER VIGOROUS DEVELOPMENT IS EXPECTED TO
OCCUR NEARER THE DRY LINE AND AHEAD OF STRONG UPPER LOW INTO
SWRN/CENTRAL TX LATER TODAY.  THIS ACTIVITY WILL BECOME INCREASINGLY
WIDESPREAD WITH INITIAL DEVELOPMENT AS SUPERCELLS AND ORGANIZED
CLUSTERS.  VERY LARGE HAIL AND A FEW TORNADOES SHOULD ACCOMPANY
THESE STORMS.  SUPERCELLS MAY PERSIST NEAR THE FRONT...THOUGH
OVERALL ACTIVITY SHOULD MORPH INTO ONE OR TWO LARGE MCSS AND SPREAD
INCREASED SEVERE THREAT EWD TOWARDS THE MIDDLE TX COAST AND ERN TX
THROUGH THE EVENING/OVERNIGHT.

..EVANS/CROSBIE.. 04/20/2006