[SWODY2] SWODY2

[Severe Weather Outlook - Day 2]

ACUS02 KWNS 181734
SWODY2
SPC AC 181733

DAY 2 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1233 PM CDT TUE APR 18 2006

VALID 191200Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS WED/WED NIGHT ACROSS A LARGE
PORTION OF THE GULF STATES INTO THE TENNESSEE VALLEY....

A ZONAL BELT OF WESTERLIES PERSISTS ACROSS THE FAR SOUTHERN TIER OF
THE U.S...WHILE A BLOCK DEVELOPS IN A BRANCH OF THE POLAR WESTERLIES
FROM THE NORTH CENTRAL U.S. INTO THE WESTERN ATLANTIC. A
STRENGTHENING UPPER RIDGE IS EVIDENT IN LATEST WATER VAPOR IMAGERY
NEAR JAMES BAY...WITH CLOSED LOWS DEVELOPING OFF THE NORTH ATLANTIC
COAST...AND ACROSS THE NORTH CENTRAL PLAINS.

MODELS SUGGEST LITTLE CHANGE TO THE LARGE-SCALE PATTERN WILL OCCUR
THROUGH THIS FORECAST PERIOD...BUT THE RIDGE MAY BEGIN TO WEAKEN AS
NORTHERN PLAINS CLOSED LOW SHIFTS TOWARD THE UPPER MISSISSIPPI
VALLEY.  THIS SEEMS LIKELY TO OCCUR MAINLY IN RESPONSE TO A
SIGNIFICANT IMPULSE ROTATING AROUND THE SOUTHERN/EASTERN PERIPHERY
OF THE CYCLONIC CIRCULATION.  AMPLIFICATION OF AN UPPER TROUGH IS
FORECAST UPSTREAM...OVER THE EASTERN PACIFIC...LATE WEDNESDAY INTO
EARLY THURSDAY.  THIS IS PROGGED TO FORCE A SOUTHERN BRANCH CLOSED
LOW INLAND ACROSS THE LOWER COLORADO VALLEY/SOUTHERN PLATEAU BY 12Z
THURSDAY...PERHAPS IN PHASE WITH AN IMPULSE IN THE WEAKER
SUBTROPICAL STREAM.

...TEXAS THROUGH EASTERN GULF STATES/TENNESSEE VALLEY...
A CLUSTER OF THUNDERSTORM ACTIVITY APPEARS LIKELY TO BE SPREADING
INTO PARTS OF THE TENNESSEE VALLEY EARLY WEDNESDAY IN ASSOCIATION
WITH AN EVOLVING ZONE OF STRONGER LOW-LEVEL WARM ADVECTION.  THIS
FORCING MAY BE ENHANCED BY A WEAK LOWER/MID TROPOSPHERIC IMPULSE
EMBEDDED WITHIN BELT OF FLOW UNDERCUTTING BLOCK.  MODELS SUGGEST
THIS FEATURE WILL EVENTUALLY TURN SOUTHEASTWARD ACROSS THE SOUTHERN
APPALACHIANS/SOUTH ATLANTIC COAST STATES...MERGING INTO CYCLONIC
REGIME SOUTH OF NORTH ATLANTIC CLOSED LOW.

WHILE A BROADER AREA OF CONVECTION SEEMS LIKELY TO SPREAD ABOVE
LINGERING SURFACE RIDGING ACROSS PARTS OF THE SOUTH ATLANTIC COAST
STATE...FORCING FOR ADDITIONAL ACTIVITY AHEAD OF STALLING  UPSTREAM
FRONT ACROSS THE LOWER MISSISSIPPI VALLEY IS MORE UNCERTAIN. 
HOWEVER...INHIBITION ACROSS PARTS OF THE TENNESSEE VALLEY AND
NORTHERN GULF STATES MAY BECOME WEAKENED ENOUGH TO SUPPORT
DEVELOPMENT OF THUNDERSTORMS BY WEDNESDAY AFTERNOON IN RESPONSE TO
DAYTIME HEATING.

MIXED BOUNDARY LAYER WITH MID/UPPER 60S DEW POINTS IS EXPECTED TO
BECOME MODERATELY UNSTABLE...WITH CAPE IN EXCESS OF 2000 J/KG BY
PEAK HEATING.  THIS SHOULD BE SUFFICIENT FOR SCATTERED SEVERE
STORMS.  ISOLATED SUPERCELLS APPEAR POSSIBLE WHERE SHEAR PROFILES
WILL BE MORE SUPPORTIVE NEAR 30 KT WESTERLY LOW-LEVEL JET
AXIS...ACROSS PARTS OF FAR SOUTHERN TENNESSEE/NORTHERN ALABAMA INTO
NORTHWEST GEORGIA.  A TORNADO OR TWO IS POSSIBLE...BUT DAMAGING WIND
GUSTS AND LARGE HAIL SEEM TO BE PRIMARY SEVERE THREATS.

WIDELY SCATTERED STRONG/SEVERE THUNDERSTORMS APPEAR POSSIBLE FARTHER
UPSTREAM...ALONG STALLED FRONT ACROSS SOUTHEAST TEXAS INTO THE HILL
COUNTRY AND BIG BEND REGION.  SOUTHEASTERLY SURFACE FLOW ACROSS
AREAS TO THE EAST/SOUTHEAST OF DEL RIO WILL CONTRIBUTE TO ISOLATED
SUPERCELL POTENTIAL BENEATH MODERATELY STRONG WESTERLY MID-LEVEL
FLOW.  THIS ACTIVITY SHOULD DIMINISH DURING THE EVENING...BUT
ADDITIONAL...PERHAPS MORE WIDESPREAD...CONVECTIVE DEVELOPMENT IS
EXPECTED WEDNESDAY NIGHT WITH APPROACH OF UPSTREAM SOUTHERN BRANCH
TROUGH.  THIS IS EXPECTED TO OCCUR IN ZONE OF STRONGER WARM
ADVECTION...NORTH OF RETREATING SURFACE FRONT ACROSS CENTRAL TEXAS. 
CAPE OF 1000 TO 2000 J/KG FOR PARCELS BASED IN MOIST LAYER ABOVE
FRONTAL INVERSION IS EXPECTED TO SUPPORT VIGOROUS UPDRAFTS WITH RISK
OF LARGE HAIL.

..KERR.. 04/18/2006