Severe Thunderstorm Warning 1, NWS Brownsville, TX

DEEP SOUTH TEXAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
315 PM CST THU FEB 22 2001

SYNOPSIS...AN UPPER LEVEL LOW CONTINUES TO SPIN ALONG THE NORTHERN
CALIFORNIA COAST. SUBTROPICAL JET BRINGING COPIOUS AMOUNTS OF
MOISTURE INTO THE SOUTHWEST UNITED STATES AHEAD OF THE LOW. A SHORT
WAVE TROUGH CURRENTLY OVER NORTHERN MEXICO MOVING EASTWARD AS
EVIDENT ON WATER VAPOR IMAGERY WITH POSITIVE VORTICITY ADVECTION
ACROSS NORTHEAST MEXICO INTO DEEP SOUTH TEXAS. AT THE SURFACE...A
WEAK COLD FRONT WAS LOCATED JUST NORTH OF THE REGION OVER THE RIO
GRANDE PLAINS...WHERE TEMPERATURES WERE IN THE 50S AND 60S. SOUTH OF
THE FRONT...ACROSS THE LOWER RIO GRANDE VALLEY...WERE IN THE 70S AND
80S. SKIES WERE MOSTLY CLOUDY ACROSS THE VALLEY WITH A FEW
CONVECTIVE SHOWERS ACROSS EASTERN PORTIONS OF DEEP SOUTH TEXAS.
WINDS WERE MOSTLY SOUTHEAST AT 10 TO 15 MPH.

SHORT TERM...WITH INCREASING DEEP MOISTURE ASSOCIATED WITH PVA AND
A SERIES OF VORTICITY MAXIMA CROSSING DEEP SOUTH TEXAS...SURFACE
BOUNDARY TO THE NORTH TO HELP FOCUS CONVERGENCE FOR CONTINUED
CONVECTION TONIGHT. WITH THE MOIST UNSTABLE AIR AT THE SURFACE AND A
DEVELOPING LOW LEVEL JET...SHOWERS WILL CONTINUE TO DEVELOP THIS
AFTERNOON AND EVENING WITH THE POTENTIAL FOR SOME HEAVY RAINFALL
AMOUNTS TONIGHT. NO SEVERE WEATHER EXPECTED AS PER LATEST SPC
DISCUSSION WITH CWA UNDER GENERAL THUNDERSTORM OUTLOOK. WILL
INTRODUCE HIGHER POPS WITH AN ISOLATED THUNDERSTORMS A POSSIBILITY.
FRONTAL BOUNDARY TO STALL TONIGHT POSSIBLY OVER NORTHERN PORTIONS OF
DEEP SOUTH TEXAS AND RETREAT TO THE NORTH AS A WARM FRONT
FRIDAY...AS THE UPPER LOW OVER NRN CA COAST DROPS SE OVER SRN CA AND
OPENS UP AS A TROUGH. RAIN CHANCES TO CONTINUE FRIDAY THROUGH FRIDAY
NIGHT AS THE TROUGH OVER THE SW UNITED STATES MOVES EAST AND LIFTS
NE AS A NEGATIVE TILTED TROUGH SATURDAY. DRIER AND SUBSIDENT AIR TO
FILTER IN SATURDAY FOR A NICE WEEKEND...AS A WEAK PACIFIC
FRONT/SURFACE DRYLINE MOVES THROUGH THE VALLEY. NO SIGNIFICANT
CHANGE IN MAV TEMP GUIDANCE FROM PREVIOUS RUN. ALSO...MAV HIGH TEMP
GUIDANCE ON TARGET WITH TODAY. LOOKS REASONABLE FOR NOW.

EXTENDED...UPPER LEVEL RIDGE TO MOVE OVER WESTERN U.S. AS THE UPPER
LEVEL TROUGH LIFTS OUT OF THE SOUTHERN PLAINS SUNDAY. THE RIDGE WILL
SHIFT OVER THE CENTRAL U.S. WITH ANOTHER UPPER TROUGH DEVELOPING
OVER CA/NV. RETURN FLOW TO DEVELOP MONDAY NIGHT AS SURFACE HIGH
PRESSURE RIDGE OVER TEXAS SHIFTS EAST OVER THE SOUTHEAST U.S. LOW
LEVEL MOISTURE TO INCREASE WITH THE SOUTHEAST TO SOUTH SURFACE FLOW.
MRF 00Z MODEL RUN SPLITS THE WESTERN U.S. TROUGH WITH THE NORTHERN
BRANCH LIFTING INTO THE NORTHERN PLAINS AND THE SOUTHERN BRANCH
DROPPING OVER NORTHERN MEXICO. ANOTHER WEAK PACIFIC FRONT WILL MOVE
THROUGH THE VALLEY WEDNESDAY WITH INCREASING BOUNDARY LAYER RELATIVE
HUMIDITY THURSDAY AHEAD OF THE SOUTHERN STREAM TROUGH ENERGY OVER
NORTHERN MEXICO. RAIN CHANCES MORE LIKELY THURSDAY THAN WEDNESDAY
WITH THE DEEPER MOISTURE LEVELS AND SURFACE TROUGH MOVING INTO SOUTH
TEXAS.

MARINE...CURRENT BUOY OBS REFLECT EAST WIND AT 12 KTS WITH 2 FOOT
WAVES. A WEAK COLD FRONT NEAR BAFFIN BAY THIS AFTERNOON...WILL
STALL AND MOVE BACK NORTH AS A WARM FRONT TONIGHT THROUGH TOMORROW.
SHOWERS AND ISOLATED THUNDERSTORMS WILL DEVELOP IN THE VICINITY OF
THIS FRONT. LOW PRESSURE WILL BEGIN TO DEVELOP OVER THE LEE OF THE
ROCKIES FRIDAY...RESULTING IN AN INCREASE OF SOUTH WINDS TOMORROW
THROUGH SATURDAY NOON. SCA LIKELY NEEDED FRIDAY WITH INCREASING
WINDS AND SEAS. WINDS WILL BECOME SOUTHWEST AS THEY WEAKEN SATURDAY
AFTERNOON...DUE TO A SURFACE TROUGH THAT WILL MOVE THROUGH AHEAD OF
THE COLD FRONT. THE FRONT WILL BRING A PERIOD OF STRONG NORTH WINDS
BY EARLY SUNDAY...VEERING EAST AND WEAKENING MONDAY.

PRELIMINARY NUMBERS:
BRO EE 068/081 070/085 060    40/30/20/00/00
HRL EE 067/082 071/086 060    40/30/20/00/00
MFE EE 068/086 072/088 061    40/30/20/00/00
RGC EE 066/086 070/088 059    40/30/20/00/00
SPI EE 070/078 072/080 065    40/30/20/00/00

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

SYNOPTIC-MARINE-AVIATION...CASTILLO.61/MESO...MARTINEZ

.BRO...NONE.