Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 012129
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
329 PM CST SUN MAR 1 2015

.DISCUSSION...
ONLY A IMAGE CAN ACCURATELY DESCRIBE THE TEMPERATURE GRADIENT
ACROSS SE TX THIS AFTERNOON. WE WILL ATTEMPT WITH WORDS...LOW 70S
ALONG THE COAST WITH LBX AT 75F...60S TOWARDS LVJ TO HOU...50S
FROM SGR TO IAH TO CXO AND THEN 40S FOR CLL TO UTS. WARM FRONT
HAD JUST PUSHED INLAND AND CLEARED OUT FOG INLAND. WEB CAMS STILL
SHOW SEA FOG ON GALVESTON IS AND GALVESTON BAY. DECIDED TO AT
LEAST KEEP DENSE FOG ADVISORY FOR THE MARINE AREAS INTO TONIGHT.
WARM FRONT IS EXPECTED TO PUSH BACK INTO THE GULF TONIGHT/TOMORROW
AS HIGH PRESSURE BUILDS OVER THE MIDWEST AND RE-ENFORCES COLDER
AIRMASS NORTH OF THE WARM FRONT. THE FRONT WILL STILL BE A KEY
PLAYER IN KEEPING SOME RAIN CHANCES IN THE FORECAST. QUESTION WILL
BE IF FOG BUILDS BACK OVER THE COAST ONCE WARM FRONT MOVES BACK
SOUTH INTO THE GULF. FOR THAT REASON WILL LET FOG ADVISORY
CONTINUE BUT MAY BE EXPIRED IF TRENDS DO NOT SUPPORT FOG RE-
DEVELOPING.

WARM FRONT IS EXPECTED TO SURGE NORTH LATE MONDAY INTO TUE. UPPER
LOW OVER CALIFORNIA WILL SHEAR OUT WITH A PIECE OF VORTICITY
MOVING INTO THE PLAINS MON NIGHT INTO TUE. LEE CYCLOGENESIS WILL
DEVELOP IN THE HIGH PLAINS AND INCREASE THE PRESSURE GRADIENT. LLJ
INCREASES AND WARM FRONT PUSHES NORTH OVERNIGHT WITH WARM MOIST
CONDITIONS FOR TUE. AS ONE UPPER LOW LEAVES CALIFORNIA ANOTHER ONE
DEVELOPS HOLDING BACK OVER THE PACIFIC. THIS ALLOWS FOR A STRONG
WSW TO ENE ORIENT JET WITH THE MAIN JET CORE OVER THE PLAINS. THE
LLJ THEN VEERS TO THE SW WHICH WILL ALLOW FOR TEMPS IN THE 70S FOR
MUCH OF THE AREA. THIS WILL BE SHORT LIVED. A STRONG COLD FRONT
SHOULD PUSH THROUGH ON WED. THE MODELS SEEM TO BE SLOWING THE
FRONT DOWN SO TRENDED FORECAST CLOSER TO THE MODEL WITH A FASTER
FRONTAL PUSH WHICH WAS THE GFS. THE ECMWF WAS NOT FAR BEHIND BUT
THE NAM WAS SIGNIFICANTLY SLOWER BY 12 HRS. IT LOOKS LIKE THE NEW
18Z NAM IS TRYING TO CATCH UP TO THE OTHER MODELS.

TEMPS BEHIND THE FRONT WED NIGHT SHOULD DROP VERY QUICKLY. TEMPS
IN THE 30S ARE EXPECTED THUR MORNING. FREEZING TEMPS EXPECTED AT
ABOUT THE TYPICAL BRENHAM...CONROE...CLEVELAND LINE NORTHWARD.
THIS IS WHERE THE FORECAST GETS INTERESTING. WINTER IS NOT QUITE
OVER YET. WED NIGHT INTO THUR THE UPPER LEVEL LOW OVER CALIFORNIA
BEGINS TO MOVE ACROSS THE S ROCKIES AND SHEAR OUT WHILE PHASING
WITH AN UPSTREAM SHORTWAVE OVER THE C PLAINS. WHERE THERE IS NOT
MUCH LARGE SCALE ASCENT FROM PVA...JET STREAM BECOMES FAVORABLY
POSITIONED WITH THE RIGHT ENTRANCE REGION OF THE JET OVER MUCH OF
C AND E TX. THERE WILL BE QUITE A BIT OF LIFT THROUGH DIVERGENCE
WITH THE JET CORE. FRONTOGENETIC LIFT WILL ALSO SUPPORT PRECIP
DURING THIS TIME. THIS MEANS THAT THE THUNDERSTORM CHANCES WITH
THE FRONT COULD TURN INTO A WINTRY MIX BY THUR. BTW THUNDERSTORM
CHANCES FOR WED LOOK SUSPECT AS INSTABILITY WILL BE LIMITED AND
THERE SHOULD BE A DECENT CAP FROM THE ELEVATED MIXED LAYER. BASED
OFF GFS BUFR SOUNDINGS AT KCLL...AREAS NORTH OF THE FREEZING LINE
OUTLINED ABOVE WILL HAVE A CHANCE FOR A MIX OF RA/FZRA/IP. IF SUB
FREEZING LAYER DEEPENS AND THERE IS MORE SATURATION ALOFT NEAR
-10C LEVELS AND ABOVE...MAY SEE MORE OF A TRANSITION TO SLEET THAN
FZRA. BUT AT THIS TIME LOOKS LIKE THERE WILL BE A SLOW TRANSITION
FROM RA TO FZRA TO SLEET AS PRECIP ENDS THUR. THE GFS HAS MUCH
MORE PRECIP THAN THE ECMWF BUT STILL ENOUGH TO KEEP AN EYE ON
ICE/SLEET TOTALS. AT THIS TIME DO NOT THINK THERE WILL BE ENOUGH
FOR ANY SIGNIFICANT IMPACTS BUT IT USUALLY DOES NOT TAKE MUCH
AROUND HERE FOR AN IMPACT.

FOR THE END OF NEXT WEEK ANOTHER UPPER LOW FORMS OVER BAJA/DESERT
SW AND THEN MOVES ACROSS THE AREA NEXT WEEKEND. GFS SHEARS THIS
SYSTEM OUT WITH VERY LITTLE PRECIP CHANCES WHILE THE ECMWF IS
QUITE WET WITH THE SYSTEM. FORECAST WILL CARRY SOME LOW END PRECIP
CHANCES UNTIL THESE DETAILS CAN BE RESOLVED IN THE NEXT COUPLE OF
DAYS.

39


&&

.MARINE...
SEA FOG THE MAIN FCST ISSUE THESE NEXT COUPLE OF DAYS AS THE OVERALL
WX PATTERN REMAINS IN PLACE. THE WEAK COASTAL LOW OVER THE LOWER/MID-
DLE TX COAST WILL HELP TO KEEP THE STEADY SOUTH FLOW OF WARMER/MOIST
AIR OVERRIDING THE COOLER SHELF WATERS TONIGHT/MON BEFORE WEAKENING/
MOVING OFF TO THE NE. THEREAFTER STRENGTHENING ONSHORE WINDS WILL BE
ON TAP FOR TUES/WED AS THE GRADIENT TIGHTENS IN RESPONSE TO THE NEXT
COLD FRONT STILL FCST TO MOVE INTO THE COASTAL WATERS LATE WEDS NITE
INTO EARLY THURS MORNING. 41

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      43  51  51  73  61 /  40  30  30  30  30
HOUSTON (IAH)              51  58  57  74  65 /  30  40  20  20  30
GALVESTON (GLS)            56  61  60  69  63 /  30  30  20  20  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...DENSE FOG ADVISORY UNTIL 10 PM CST THIS EVENING FOR THE
     FOLLOWING ZONES: BRAZORIA...CHAMBERS...GALVESTON...
     MATAGORDA.

GM...DENSE FOG ADVISORY UNTIL 10 PM CST THIS EVENING 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.

&&

$$

DISCUSSION...39
AVIATION/MARINE...41



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