Tornado Warning 31, NWS Houston/Galveston, TX

SOUTHEAST TEXAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
944 AM CST MON DEC 23 2002

CURRENT HOT SPOT FOR TORNADOES WAS ENTERING INTO THE WESTERN FRINGES
OF SE TX AT THIS HOUR.  FORECAST PROBLEM OF THE DAY CONCERNS THE
TORNADO AND SEVERE THREAT...THOUGH A SECONDARY CONCERN IS THE FLOOD
POTENTIAL.  THE 12Z CRP SOUNDING HAD HELICITY VALUES OF 419...A CAPE
OF 2554...AND A PW OF 1.42.  THE 1.42 INCH PW IS CLOSE TO 2 STANDARD
DEVIATIONS ABOVE NORMAL FOR THIS TIME OF YEAR.  THE RUC HAS VERIFIED
THE BEST SO FAR THIS MORNING OVER THE GFS AND ETA.

THE RUC PLACES HELICITY VALUES IN EXCESS OF 400 FOR ALL OF SE TX
THROUGH 21Z THIS AFTERNOON.  THE SURFACE WARM FRONT AT 15Z WAS LOCATED
FROM JUST NORTH OF AUS EASTWARD ACROSS THE NORTHERN THIRD OF SE TX
WITH A SURFACE LOW SOUTH OF JCT.  ALSO...THE UPPER JET WAS KEEPING THE
AREA UNDER THE BEST LIFT.  THIS SCENARIO WILL KEEP SE TX IN THE BEST
AREA FOR SEVERE WEATHER.  AM EXPECTING THE SHOWERS STARTING TO POP
OVER THE SOUTHEASTERN THIRD OF THE FORECAST AREA TO BUILD AS THEY MOVE
NORTHWARD.  ONE CONCERN WE HAVE IS THAT THE CONVECTION CURRENTLY
FIRING WILL BUILD INTO AN MCS WHICH WILL HIGHLIGHT THE HEAVY RAINFALL
THREAT.  A NEW WATCH WILL BE ISSUED SHORTLY AND WILL UPDATE THE PUBLIC
FORECAST BY THE TOP OF THE HOUR.  WILL TWEAK TEMPERATURES AND WINDS AT
THAT TIME AS WELL.

.HGX...FLASH FLOOD WATCH  ALL OF SOUTHEAST TEXAS.
       SCA GALVESTON AND MATAGORDA BAYS.
       SCA 00 TO 60 NM HIGH ISLAND TO THE MATAGORDA SHIP CHANNEL.

PREV DISC...
THE BIG STORY IS THE WEATHER TODAY AND TONIGHT. TORNADO OUTBREAK
TAKING SHAPE FOLLOWED BY A SQUALL LINE TO CLEAR THINGS OUT LATE THIS
AFTERNOON-MIDNIGHT.

THUNDERSTORMS DEVELOPING OVER THE HILL COUNTRY ALONG THE WARM FRONT
FROM SOUTH OF SAN ANTONIO TO SUGARLAND TO NEAR GALVESTON. SPEED MAX
SOUTHWEST OF BIG BEND WILL SHIFT EAST AS THE UPPER TROUGH SLIDES EAST.
THIS JET WILL BE SPLITTING AS IT GETS INTO THE AREA AROUND NOON. AT
06Z LLJ AXIS FROM THE EXTREME WESTERN GULF AIMED AT SAN ANTONIO WHERE
THE DEVELOPING CONVECTION IS OCCURRING. GPS DERIVED PW ALONG THE
COAST FROM CRP TO GLS INDICATES 1.15-1.3 PW ALREADY SURGING
INLAND. THE LLJ AXIS MOVES EAST INTO THE FA AROUND 18Z WITH PW RISING
TO AROUND 1.4 TO 1.5 WITH RICHER MOISTURE AIMED AT LA. LOW LEVEL
SHEAR WITH HELICITIES THIS MORNING 200-240M2 INCREASING THIS AFTERNOON
TO PERHAPS AS HIGH AS 300M2...WITH LCL 1200FT OR LESS. LI PLUNGES FROM
AROUND -2 TO -8 WITH NO CAP. UNFORTUNATELY THE AREA LOOKS LIKE IT WILL
GET DRY SLOTTED AT AROUND 21Z THIS SHOULD OPEN THE GATES TO RAPIDLY
INCREASE THE SEVERITY OF THE TORNADO THREAT OVER THE CENTRAL AND
EASTERN ZONES. CURRENT PACKAGE ALREADY CARRIES 100 POPS FOR INLAND
AREAS AND 80 POPS COAST WITH SEVERE AND A FOCUS ON TORNADOES. ETA AND
GFS BOTH SUPPORT A SCENARIO WHERE THE CORRIDOR OF SUPERCELLS SHIFTS
ACROSS SOUTHEAST TEXAS LEAVING BEHIND ENOUGH MOISTURE FOR A SQUALL
LINE TO DEVELOP EMBEDDED IN A VERY STRONG WIND FIELD LATE THIS
AFTERNOON AND RACING ACROSS BETWEEN 6 PM AND MIDNIGHT. VERY DRY/COLD
AIR ALOFT SHOULD MAKE THE DOWNDRAFT IN THE SYSTEM VERY EFFECTIVE SO
WILL ADJUST THE FORECAST CONCERNING THIS ISSUE. LOCALLY HEAVY RAINFALL
STILL AN ISSUE. EXTREMELY MOIST ATMOSPHERE FOR THIS TIME OF YEAR AND
1000-500MB THICKNESS VALUES AROUND 5660M AND DECREASING AS LLJ
TRAVERSES THE AREA WITH THE ABOVE MENTIONED UPPER JET STRUCTURE AND
THE EXPECTED WIDESPREAD DEVELOPMENT SUPPORTS THE CONTINUED MENTION OF
LOCALLY HEAVY RAINFALL. WILL ISSUE A FLASH FLOOD WATCH BUT WILL
LIKELY NEED DAY SHIFT TO REFINE THE THREAT AREA BASED ON LOCATION
OF AND THE DEEP CONVECTIVE DEVELOPMENT ON AND NORTH OF THE WARM
FRONT.

THE SHOW SHOULD BE OVER BY 6-9Z TUE AS IT ROARS OUT OVER THE GULF AND
INTO LA. WRAP AROUND TRAPPED MOISTURE SHOULD DRAG IN CLOUDS THROUGH
MOST OF TUESDAY WITH CLEARING LATE AFTERNOON. AREA REMAINS DRY IN THE
WAKE AS WESTERLY FLOW VEERS TO NW AND PRECIP CHANCE DROP. WEATHER
SHOULD GOOD FOR SANTA TO DELIVER TOYS TO SOUTHEAST TEXAS ON CHRISTMAS
EVE. NEXT SHOT AT RAIN MAY NOT COME AROUND TIL SUNDAY BUT MRF LOOKS
LIKE IT IS TOO FAST AND TOO DEEP WITH THIS SYSTEM SO WILL CONTINUE THE
PARTLY CLOUDY FORECAST GOING FOR SUNDAY MORE IN LINE WITH THE ECMWF.

PREV PRELIMS...
CLL TE 065/042 052/030 050 +71
IAH TE 071/045 054/033 050 +92
GLS TE 073/052 057/041 051 892

45/36

GMZ300-330-335-350-355-370-375-TXZ163-164-176>179-195>200-210>214-226-
227-235>238-241300-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
553 AM CST MON DEC 23 2002

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST TEXAS AND
THE UPPER TEXAS COASTAL WATERS.

...TORNADO OUTBREAK ACROSS SOUTHEAST TEXAS APPEARS IMMINENT...

.DAY ONE...
.TODAY...A WARM FRONT DRAPED ACROSS SOUTHEAST TEXAS AND VERY STRONG
SOUTHERLY WINDS THAT VEER FROM SOUTH TO WEST IN THE LOWER PORTIONS OF
THE ATMOSPHERE WILL COMBINE WITH COOLING TEMPERATURES ALOFT TO AID THE
DEVELOPMENT OF THUNDERSTORMS ACROSS THE AREA THIS MORNING. A POWERFUL
DISTURBANCE IN THE JETSTREAM WILL MOVE INTO THE AREA THIS AFTERNOON
BRINGING A LAYER OF COLDER AND DRIER AIR ALOFT THAT WILL ENHANCE THE
POTENTIAL FOR VERY DANGEROUS THUNDERSTORMS THAT COULD HAVE LONG LIVED
STRONG TO SEVERE TORNADOES. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE
AND A FLASH FLOOD WATCH IS IN EFFECT THROUGH TONIGHT. A SQUALL LINE
WILL LIKELY DEVELOP LATE THIS AFTERNOON OR EARLY EVENING TO THE WEST
OF THE REGION AND RACE EAST THROUGH THE AREA. STRONG DAMAGING WINDS
WILL LIKELY ACCOMPANY THIS SYSTEM. THE SQUALL LINE SHOULD BE NEARING
THE COAST LATE TONIGHT OR VERY EARLY TUESDAY MORNING. MARINERS SHOULD
AVOID GOING OUT ON THE WATER TONIGHT.

.DAYS TWO THROUGH SEVEN...
.TUESDAY THROUGH SUNDAY...HAZARDOUS WEATHER IS NOT EXPECTED.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS ANTICIPATED BY AROUND 9 AM. SPOTTERS AND
EMERGENCY MANAGEMENT SHOULD PLAN FOR ACTIVATION TO CONTINUE THROUGH
MIDNIGHT.