Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 260337
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
937 PM CST THU DEC 25 2014

.UPDATE...
SEE DISCUSSION FOR EVENING UPDATE.

&&

.DISCUSSION...
CLOUD COVER HAS STARTED TO INCREASE TOWARDS THE CRP AREA THIS
EVENING AND IS STILL ON TRACK TO EXPAND IN COVERAGE ACROSS OUR
AREA THIS EVENING. A WEDGE OF VORTICITY EMBEDDED IN A SHORTWAVE
IS FORECASTED TO MOVE ACROSS THE WATERS TONIGHT AND MOVE OVER THE
TX/ LA BORDER TOMORROW MORNING. MOISTURE VALUES ARE STILL LIMITED
BUT LATEST HRRR RUN HAS A LINE OF SHOWERS FORMING THANKS TO THE
LIFT AND MOVING INLAND. GFS AND NAM FORECAST SOUNDINGS DO HAVE A
SATURATED LAYER UP TO AROUND 800 MB THOUGH. DUE TO THIS HAVE MADE
MINOR CHANGES TO POP GRIDS TO ACCOUNT FOR POTENTIAL OF SOME
SHOWERS FORMING THIS MORNING FROM THE SHORTWAVE. TOMORROW
AFTERNOON MODELS ARE AGAIN SHOWING STREAMER SHOWERS AND CURRENT
FORECAST HAS THIS COVERED. BESIDES MINOR CHANGES TO POP GRIDS FOR
THIS MORNING NO OTHER CHANGES REQUIRED AT THIS TIME. CURRENT
FORECAST IS ON TRACK. 23

&&

.PREV DISCUSSION... /ISSUED 544 PM CST THU DEC 25 2014/

DISCUSSION...
SEE THE 00Z AVIATION DISCUSSION BELOW.

40

AVIATION...
INCREASING MOISTURE ADVECTION AND THE DEVELOPMENT OF A LOW-LEVEL
JET WILL HELP MVFR CEILINGS TO FORM LATER TONIGHT AND FRIDAY
MORNING...MAINLY BETWEEN 08Z AND 12Z. THERE WILL ALSO BE A CHANCE
FOR ISOLATED SHOWERS MAINLY AFTER 17Z. THE NAMBUFR FORECAST
SOUNDINGS ARE SUGGESTING IFR CONDITIONS MAY DEVELOP LATE IN THE
AFTERNOON.

40

PREV DISCUSSION... /ISSUED 301 PM CST THU DEC 25 2014/

DISCUSSION...
CLOUDS WILL CONTINUE TO INCREASE OVERNIGHT AS LOW LEVEL MOISTURE
IS DRAWN BACK INTO SOUTHEAST TEXAS. SOUTHERLY WINDS...WINDS AND
CLOUD COVER WILL PRODUCE TEMPERATURES ABOUT 15 TO 20 DEGREES
WARMER THAN LAST NIGHT. PW VALUES INCREASE TO AROUND 1.1 INCHES OF
FRIDAY AND FCST SOUNDINGS SHOW A SATURATED LAYER UP TO AROUND 800
MB. PROBABLY GET SOME STREAMER SHOWERS BENEATH THE CAP. A WEAK
UPPER LEVEL DISTURBANCE WILL KEEP RAIN IN THE FCST ON FRIDAY
NIGHT. A COLD FRONT WILL APPROACH SE TX ON SATURDAY. STILL SOME
TIMING DIFFERENCES WITH THE FRONT BUT AT THIS TIME...IT APPEARS
THE FRONT WILL MOVE THRU KCLL AROUND 15Z...KIAH AROUND 20Z AND
KGLS AROUND 00Z. DYNAMICS ON SATURDAY LOOKING A BIT BETTER WITH
CAPE VALUES NEAR 1500...LI`S -3 TO -5...TT`S IN THE LOWER 50S AND
K INDEX IN THE UPPER 30S. HELICITY VALUES ARE AROUND 200 AS WELL.
SE TX WILL ALSO GET LIFT ENHANCED FROM A DEPARTING 140 KT RRQ.
RAISED POPS A BIT ON SATURDAY AND WOULD NOT BE SURPRISED IF SOME
OF THE STORMS ON SATURDAY BECOME STRONG TO SEVERE. THE GFS AND
ECMWF CONTINUE TO PUSH THE WEAK UPPER LEVEL TROUGH OVER SW TX TO
THE EAST FASTER THAN THE NAM AND CANADIAN. POST FRONTAL RAINS WILL
CONTINUE SATURDAY NIGHT INTO EARLY SUNDAY AS SOUTHWEST WINDS ALOFT
OVER RIDE COOLER N-NE SFC WINDS. THE NAM/CANADIAN DIVERGE FROM THE
GFS/ECMWF ON SUNDAY WITH THE NAM/CAN HOLDING THE UPPER TROUGH TO
THE WEST AND MAINTAINING THE SW FLOW ALOFT. THE GFS/EC MOVE THE
TROUGH EASTWARD AND THE UPPER FLOW BECOMES ZONAL ENDING THE
ISENTROPIC LIFT. HAVE LEANED TOWARD THE GFS/ECMWF SOLUTION AND
FEEL RAIN WILL DIMINISH BY SUNDAY AFTN.

THERE SHOULD BE SOME BRIEF CLEARING MON/MON NITE BEFORE CLOUDS
RETURN ON TUESDAY AS THE NEXT UPPER TROUGH DROPS SOUTH INTO AZ.
THE FLOW ALOFT WILL ONCE AGAIN BECOME SOUTHWEST AND A COASTAL LOW
WILL DEVELOP EAST OF KBRO. THE COMBINATION OF THESE FEATURES
COUPLED WITH ADDITIONAL LIFT FROM THE SLOW MOVING UPPER LEVEL
TROUGH SHOULD YIELD PATCHY LIGHT RAIN EACH DAY THROUGH FRIDAY.
TEMPERATURES WILL BE ON THE COLD SIDE AS A 1040 MB HIGH SLIDES
SOUTH INTO THE SOUTHERN PLAINS ON WEDNESDAY AND ANOTHER 1040 HIGH
APPROACHES THE AREA NEXT FRIDAY. DESPITE THE COLD TEMPERATURES...
AT LEAST FOR NOW...IT APPEARS ALL THE PRECIPITATION WILL REMAIN
LIQUID. 43

MARINE...
A DEVELOPING SURFACE LOW IN THE LEE OF THE ROCKY MOUNTAINS WILL
ENCOURAGE ELEVATED ONSHORE FLOW TO CONTINUE INTO FRIDAY
MORNING...AND MARINERS IN SMALL CRAFT SHOULD EXERCISE CAUTION OVER
THE COASTAL WATERS TONIGHT. TEMPERATURES OVER THE SHALLOWER SHELF
WATERS ARE CURRENTLY AROUND 61 TO 63 DEGREES. WITH ONSHORE FLOW
CONTINUING TO ADVECT WARM...MOIST AIR OVER THESE COOLER
WATERS...THE POSSIBILITY EXISTS FOR SEA FOG DEVELOPMENT LATE
FRIDAY NIGHT INTO SATURDAY MORNING. THE LIMITING FACTOR FOR THIS
WILL BE THE WARMER WATERS THAT ARE ALSO PUSHED CLOSER TO SHORE BY
THESE SOUTHERLY TO SOUTHEASTERLY WINDS...SO CONFIDENCE IS NOT HIGH
IN SEA FOG FORMATION AT THE MOMENT BUT WILL CONTINUE TO MONITOR
TRENDS.

AS THE AFOREMENTIONED SURFACE LOW EJECTS ACROSS THE CENTRAL PLAINS
SATURDAY...AN ATTENDANT COLD FRONT WILL PUSH INTO SOUTHEAST TEXAS
SATURDAY AFTERNOON AND REACH THE COAST SATURDAY NIGHT. ISOLATED
THUNDERSTORMS ASSOCIATED WITH THIS COLD FRONT WILL BE POSSIBLE OVER
THE BAYS AND COASTAL WATERS SATURDAY AND SUNDAY. ELEVATED OFFSHORE
WINDS BEHIND THE FRONT MAY WARRANT CAUTION FLAGS SUNDAY. A RETURN TO
ONSHORE FLOW AT THE BEGINNING OF NEXT WEEK WILL BE SHORT-
LIVED...WITH THE NEXT FRONTAL SYSTEM MOVING ACROSS THE COASTAL
WATERS BY MID-WEEK.

HUFFMAN

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      52  70  60  64  42 /  10  30  40  60  30
HOUSTON (IAH)              52  72  63  72  47 /  10  30  50  70  50
GALVESTON (GLS)            59  70  64  70  53 /  10  30  40  70  60

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 6 AM CST FRIDAY FOR
     THE FOLLOWING ZONES: GALVESTON BAY...MATAGORDA BAY...WATERS
     FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL OUT 20 NM...
     WATERS FROM HIGH ISLAND TO FREEPORT OUT 20 NM.

     SMALL CRAFT ADVISORY UNTIL 6 AM CST FRIDAY FOR THE FOLLOWING
     ZONES: WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL
     20 NM TO 60 NM...WATERS FROM HIGH ISLAND TO FREEPORT 20 TO
     60 NM.

&&

$$

DISCUSSION...23


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