Severe Thunderstorm Warning 18, NWS Brownsville, TX

DEEP SOUTH TEXAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
215 PM CST SAT FEB 21 1998

STRONG STORM SYSTEM AS SHOWN BY CURRENT WATER VAPOR AND VISIBLE LOOP
TO BE JUST SOUTH OF THE BIG BEND OVER NORTHERN MEXICO.  THIS
VERIFIES NICELY FROM WHAT WAS FORECASTED BY THE 15Z RUC.  THE RUC
TAKES THE VORT TO A POSITION OVER THE RIO GRANDE NEAR LRD BETWEEN
00 AND 03Z TONIGHT. ETA GRIDDS AND HOURLY SOUNDINGS SHOW CAP TO
DIMINISH QUICKLY THIS AFTERNOON AS COLD ADVECTION ALOFT MOVES OVER
THE AREA AS STORM APPROACHES. FORECASTED CAPES NEAR 2000 AND LIS
NEAR -10 MEAN THAT ANY STORMS THAT DO BREAK THE CAP WILL LIKELY GO
SEVERE.

SATELLITE DERIVED LIS AT 1800GMT SHOW -6 NEAR FALCON LAKE WITH
CAPES NEAR 1500.  SATELLITE DERIVED BRO SOUNDING FOR 1730GMT SHOWS
MID LEVEL CAP NEARLY ERODED.  CURRENT SE WINDS OF 30 KNOTS WILL
OBVIOUS FEED STORMS SOMEWHERE...QUESTION IS WHERE.  LATEST ADAP
SHOWS GOOD SURFACE MOISTURE CONVERGENCE JUST TO OUR NORTH WITH LIS
DROPPING.
MOUNTAINS SOUTH OF DRT.  CLEARING NOW OVER THE WESTERN VALLEY WILL
AID IN DESTABILIZING THE ATMOSHPHERE

MODELS ARE DEVELOPING MOST RAIN TO THE NORTH OF AREA BUT FEEL THAT
ACTIVITY WILL DEVELOP OVER OUR CWA...IF NOT AHEAD OF THE SFC
TROF/FRONT...MAYBE ALONG THE TROF THIS EVENING AS IT PUSHES THROUGH
SOMETIME AROUND 03Z. TIME SECTIONS OVER BRO SOME STRONG STABILITY
AND A DRY ATMOSPHERE TO QUICKLY DEVELOP AS THE SFC LOW MOVES INTO
THE NORTHWEST GULF OF MEXICO TOWARD THE LA COAST BY 12Z MON.  THIS
SHOULD MEAN DECREASING CLOUDS AFTER MIDNIGHT WITH MOSTLY SUNNY ON
SUN AND MON.  SFC LOW DOES NOT DEVELOP INTO SOMETHING EXTRAORDINARY
SO NW WINDS ON SUN WILL ONLY BE MODERATE.

HEAVY RAIN AND FLOOD POTENTIAL WILL BE MAX TO THE NORTH WHERE
RAINFALL HAS OCCURRED THE PAST FEW MONTHS.  SPEED OF SYSTEM AND
RELATIVELY LOW PW VALUES WILL LIKELY KEEP FLOODING TO A MINIMUM
ALTHOUGH LOW WATER AREAS COULD FILL UP QUICKLY WITH THE STRONG
STORMS.

IN THE EXTENDED...TROF MOVES QUICKLY TO THE EAST COAST BY MONDAY
EVENING AS NEXT STORM MOVES INTO THE GREAT BASIN ON TUESDAY. STRONG
SFC LOW DEVELOPS OVER THE EASTERN SLOPES OF THE ROCKIES.  THIS
COMBINED WITH WEAK HIGH PRESSURE OVER THE GULF WILL MAKE FOR A
WINDY MID WEEK. TUES SHOULD BE MOSTLY SUNNY AND WINDY.  WED...PC
AND WINDY.  THURS...PC WITH SLIGHT CHANCE SH/TS.  TEMPS SHOULD WARM
NICELY WITH THE STRONG SOUTH WINDS.

TONIGHT...MOSTLY CLOUDY WITH A 50 PERCENT CHANCE FOR SH/TS.
         SOME POSSIBLY SEVERE.  SE WIND 15 TO 25 MPH AND GUSTY
         SHIFTING TO THE NORTHWEST LATE.
SUNDAY...MOSTLY SUNNY.  NORTHWEST WINDS 10 TO 15 MPH.
SUNDAY NIGHT...MOSTLY CLEAR
MONDAY...MOSTLY SUNNY.

BRO  UU  53/78/54/82  50/00/00/00
MFE  UU  53/79/53/83  50/00/00/00
RGC  UU  51/81/52/84  50/00/00/00
SPI  UU  55/73/57/76  50/00/00/00

67