Severe Thunderstorm Warning 20, NWS Brownsville, TX

DEEP SOUTH TEXAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
300 PM CDT MON MAY 21 2001

WELL-DEFINED UPPER TROUGH DIGGING SOUTHEAST ACROSS THE CENTRAL
PLAINS HAS ALLOWED AN UNSEASONABLY COLD AIRMASS TO MOVE INTO CENTRAL
PORTIONS OF TEXAS.  AT 19Z THE POLAR FRONT EXTENDED FROM TEXARKANA
TEXAS...TO LUFKIN...TO SOUTH OF AUSTIN...TO SOUTH OF DEL RIO...WITH
MUCH COLDER TEMPERATURES LAGGING THE INITIAL WINDSHIFT BY ROUGHLY 75
NM.  STRONG LOW-LEVEL COLD ADVECTION AND ASSOCIATED SURFACE PRESSURE
RISES OF 5 MB/3 HOURS ACROSS CENTRAL TEXAS WILL ACCELERATE THE
SOUTHWARD PROPAGATION OF THE FRONT...WITH FRONT LIKELY CROSSING THE
RIO GRANDE RIVER AROUND MIDNIGHT.

SHOWERS AND THUNDERSTORMS ARE POSSIBLE...ESPECIALLY FROM LATE THIS
AFTERNOON THROUGH MIDNIGHT.  THE 21/12Z RUNS OF THE MESO-ETA AND AVN
ARE BOTH ADVERTISING WEAK 500 MB FLOW.  HOWEVER...BOTH MODELS ALSO
GENERATE DECENT QPF ACROSS THE ENTIRE AREA...POSSIBLY DUE TO A
SUBTLE 500 MB SHORTWAVE TROUGH AND FAVORABLE LOCATION OF 300 MB JET
APPROACHING THE AREA BY 22/06Z.  CURRENT THINKING IS THAT A SQUALL
LINE WILL FORM ALONG A PRE-FRONTAL WINDSHIFT LINE IN SOUTH CENTRAL
TEXAS...AND WILL BACKBUILD INTO NORTHERN MEXICO WITH TIME.

21/12Z KBRO RAOB REVEALS WEAK MID-LEVEL FLOW...WHICH WILL LIKELY
PRECLUDE DEVELOPMENT OF SUPERCELLULAR STORM STRUCTURES...AND SHOULD
LIMIT DAMAGING WIND THREAT FROM THUNDERSTORMS.  HOWEVER...CAPE
GREATER THAN 4000 J/KG...AND A MODIFIED SOUNDING YIELDING CAPE OF
5500 J/KG SUGGEST THAT SEVERE HAIL THREAT IS A DISTINCT POSSIBILITY
WITH ANY ORGANIZED CONVECTION.  AS ALWAYS...STRENGTH OF INVERSION
WILL DICTATE STRENGTH AND AREAL COVERAGE OF CONVECTION.  MOST
PRECIPITATION SHOULD BE OVER SHORTLY AFTER MIDNIGHT...WITH SOME
LIGHT RAIN POSSIBLE INTO MID-MORNING ON TUESDAY.  A CLEARING TREND
WILL BEGIN BY LATE TUESDAY.

UPPER NORTHWEST FLOW WILL KEEP THE UPPER TROPOSPHERE DRY THROUGH THE
WEEKEND...WHILE RETURN FLOW WILL BEGIN ON WEDNESDAY AND PERSIST
THROUGH THE BEGINNING OF NEXT WEEK.  FOR NOW...WILL MAINTAIN A
PARTLY CLOUDY AND RAIN-FREE FORECAST...WITH A GRADUAL WARMING TREND.

MARINE...CURRENT OBS FROM BUOY020 INDICATE SOUTHEAST WINDS AT 8
KNOTS PRODUCING 5 FOOT SEAS.  SCA WILL LIKELY BE CONTINUED THROUGH
TOMORROW...WITH STRONG NORTHEAST WINDS EXPECTED BEHIND COLD FRONT.
SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE THROUGH TUESDAY
MORNING.

PRELIMINARY NUMBERS:
BRO EB 068/079 063/083 067  50/20/00/00/00
HRL EB 067/079 062/084 066  50/20/00/00/00
MFE EB 066/077 061/086 066  50/20/00/00/00
RGC EB 064/075 059/087 066  50/20/00/00/00
SPI EB 072/079 066/079 069  $50/20/00/00/00

SYNOPTIC...DD (65) / AVIATION-MARINE...60 / MESO...SM

INTERNET ADDRESS...WWW.SRH.NOAA.GOV/BRO

.BRO...SCA FOR GMZ130-150-155-170-175 TODAY.

TXZ248>257-220100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BROWNSVILLE TX
415 PM CDT MON MAY 21 2001

...SEVERE WEATHER REMAINS A POSSIBILITY TONIGHT ACROSS DEEP SOUTH
TEXAS...

A STRONG COLD FRONT MOVING THROUGH SOUTH CENTRAL TEXAS LATE THIS
AFTERNOON WILL MOVE THROUGH DEEP SOUTH TEXAS LATER THIS EVENING.

WARM...MOIST AND UNSTABLE AIR OVER THE REGION AHEAD OF THE FRONT...WILL
PROVIDE THE POTENTIAL FOR SCATTERED SHOWERS AND THUNDERSTORMS THIS
EVENING AND TONIGHT...AS THE FRONT APPROACHES FROM THE NORTHWEST. SOME
OF THESE THUNDERSTORMS WILL BE STRONG WITH SOME POSSIBLY REACHING SEVERE
LEVELS. THE GREATEST THREAT WITH ANY STRONG TO SEVERE STORMS THAT
DEVELOP IS LIKELY TO BE LARGE HAIL AND THE POSSIBILITY OF STRONG
DAMAGING WINDS.

LAW ENFORCEMENT AGENCIES...EMERGENCY MANAGEMENT OFFICIALS...STORM
SPOTTER GROUPS...AND OTHER INTERESTED CONCERNS SHOULD MONITOR THIS
SITUATION AND TAKE APPROPRIATE ACTION SHOULD SEVERE WEATHER THREATEN
YOUR AREA.

SPEECE

TXZ248>257-220300-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BROWNSVILLE TX
523 PM CDT MON MAY 21 2001

...A SEVERE THUNDERSTORM WATCH HAS BEEN ISSUED FOR ALL OF DEEP SOUTH
TEXAS...

THE NATIONAL WEATHER SERVICE HAS ISSUED A SEVERE THUNDERSTORM WATCH
VALID UNTIL 10 PM CDT MONDAY EVENING FOR ALL OF DEEP SOUTH TEXAS. THIS
WATCH INCLUDES THE COUNTIES OF BROOKS...CAMERON...HIDALGO...JIM HOGG...
KENEDY...STARR...WILLACY AND ZAPATA COUNTIES.

THIS WATCH INCLUDES THE CITIES AND TOWNS OF...FALFURRIAS...
HEBBRONVILLE...MCALLEN...WESLACO...RIO GRANDE CITY...ZAPATA...
BROWNSVILLE...HARLINGEN...SAN BENITO...RAYMONDVILLE...SARITA...PORT
MANSFIELD...SOUTH PADRE ISLAND...PORT ISABEL...LAGUNA VISTA AND LAGUNA
HEIGHTS.

THIS SEVERE THUNDERSTORM WATCH INCLUDES THE BAYS AND INLAND WATERWAYS...
FROM BAFFIN BAY TO THE RIO GRANDE...AS WELL AS THE NEAR SHORE WATERS
FROM BAFFIN BAY TO THE RIO GRANDE OUT TO 20 NAUTICAL MILES OFFSHORE.

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE FAVORABLE
FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. PERSONS IN
THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING WEATHER CONDITIONS
AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS.  SEVERE
THUNDERSTORMS CAN AND OCCASIONALLY DO PRODUCE TORNADOES.

SPEECE