Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 171725
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1125 AM CST WED DEC 17 2014

.DISCUSSION...
SEE THE 18Z AVIATION DISCUSSION BELOW.

40

&&

.AVIATION...
THE WARM FRONT WAS WELL SOUTH OF KGLS THIS MORNING. HOWEVER...
THERE WAS A SURFACE LOW PRESSURE TROUGH LOCATED JUST OFF THE
COAST. THE 12Z NAM12 MOVES THE WARM FRONT NORTHWARD TONIGHT WITH
THE FRONT MAKING ITS WAY INLAND TO A KCLL TO KSGR TO KGLS LINE
EITHER LATE IN THE EVENING OR BETWEEN 06Z AND 09Z. THE FRONT MAY
OR MAY NOT MAKE ITS WAY INTO KIAH AND KCXO THURSDAY MORNING.

THE MAIN IMPACTS WILL BE LIGHT RAIN AREAS DUE TO WARM AIR
ADVECTION THIS AFTERNOON...AND THEN LOWERING CEILINGS AND
VISIBILITIES TONIGHT. MVFR SHOULD DEVELOP EARLY IN THE EVENING
WITH IFR OR EVEN LIFR LIKELY OVERNIGHT TONIGHT AND THURSDAY
MORNING.

40

&&

.PREV DISCUSSION... /ISSUED 953 AM CST WED DEC 17 2014/

UPDATE...
UPPER LEVEL TROUGH DIGGING INTO THE SW COMBINED WITH WAA AND A
WARM FRONT MOVING INLAND WILL LEAD TO SCATTERED SHOWERS TODAY. LATEST
KHGX RADAR SHOWING VERY LIGHT SHOWERS MOVING INTO THE WESTERN
ZONES OF THE CWA AND HAVE INCREASED POPS TO 20S AND 30S TO REFLECT
THIS. HAVE ALSO LOWERED MAX TEMPS IN NORTHERN ZONES A COUPLE
DEGREES TO ACCOUNT FOR INCREASED CLOUD COVER. OTHER THAN THESE TWO
MINOR EDITS...FORECAST PACKAGE LOOKS ON TRACK.

PREV DISCUSSION... /ISSUED 552 AM CST WED DEC 17 2014/

AVIATION...
EARLY THIS MORNING...CEILINGS GENERALLY AROUND 8000 FEET ARE EDGING
INTO SOUTHEAST TEXAS FROM THE WEST UNDER A THICKENING CIRRUS SHIELD.
AREA RADARS ARE ALSO SHOWING SOME LIGHT RETURNS MOVING UP THE LOWER
AND MIDDLE TEXAS COAST AND ON INTO THE HILL COUNTRY. EXPECTING TO SEE
LOWERING CEILINGS AS THE DAY PROGRESSES...AND HAVE TAF SITES REACHING
MVFR LEVELS THIS EVENING. TAFS CONTINUE THE LOWERING CEILING TREND
DURING THE OVERNIGHT HOURS...BUT WILL HOLD OFF ON THE IFR LEVELS
AS SOME MODELS ARE SUGGESTING UNTIL THE DAYTIME HOURS ON THURSDAY.
ALSO BRINGING IN -RA AT CLL AND UTS OVERNIGHT...AND ANTICIPATE MOST
SITES NEEDING -RA/-SHRA ALONG WITH SOME LOWER VISIBILITIES DUE TO
SOME BR DURING THE DAY TOMORROW. AREA FORECAST SOUNDINGS INDICATE
POTENTIAL FOR LOW CEILINGS AND VISIBILITIES ALONG WITH INCREASING
SHRA/TSRA CHANCES AS WE HEAD ON INTO THURSDAY NIGHT AND FRIDAY. 42

PREV DISCUSSION... /ISSUED 434 AM CST WED DEC 17 2014/

DISCUSSION...
CLOUDS CONTINUE TO MOVE IN FROM THE WEST THIS MORNING AS AN UPPER
LEVEL DISTURBANCE APPROACHES SOUTHEAST TEXAS. ON WATER VAPOR THE
UPPER LEVEL DISTURBANCE THAT WILL HELP BRING RAIN TO THE AREA LATE
THURSDAY INTO FRIDAY CAN BE SEEN ABOUT 400 MI WEST OF THE
CALIFORNIA/ OREGON BORDER. TODAY RAIN CHANCES WILL START TO RISE
AS WIDESPREAD ISENTROPIC UPGLIDE COMMENCES. OMEGA VALUES ARE ALSO
STARTING TO SHOW SOME LIFT DUE TO WIDESPREAD WAA. THE TEXAS TECH
WRF... RAP... AND 4 KM NCEP WRF SHOW VERY LIGHT PRECIP FORMING IN
CENTRAL TEXAS AND THEN SLOWING PUSHING TO THE EAST. GLOBAL MODELS
ALSO TEND TO AGREE WITH THIS ASSESSMENT. GFS 300 K CONDENSATION
PRESSURE DEFICITS ALSO SUPPORT BEST MOISTURE IN CENTRAL TEXAS
SLOWLY PUSHING EAST. THE GENERAL THOUGHT IS TO HAVE THIS LIGHT
RAIN/ DRIZZLE START IN CENTRAL TEXAS AND PUSH INTO OUR WESTERN AND
NORTHERN COUNTIES THIS AFTERNOON INTO EVENING. AT THE SAME TIME A
WARM FRONT WILL BEGIN TO PUSH NORTH.

THURSDAY MORNING THE LIGHT RAIN FROM WAA WILL SAG TO THE
SOUTHEAST. THE LIGHT RAIN LOOKS TO CONTINUE DURING THE DAY ALONG
THE WARM FRONT. OMEGA VALUES FOR THURSDAY ARE RATHER WEAK AND
CONDENSATION PRESSURE DEFICITS DON`T LOOK AS IMPRESSIVE BUT PWATS
REMAIN ABOVE NORMAL WITH GFS FORECASTING VALUES AROUND 1.40". RAIN
CHANCES WILL THEN CONTINUE TO INCREASE THURSDAY NIGHT INTO FRIDAY
AS THE UPPER LEVEL DISTURBANCE MENTIONED ABOVE APPROACHES THE
AREA. LATE THURSDAY/ EARLY FRIDAY THE UPPER LEVEL JET STRENGTHENS
TO NEAR 120 KTS WITH SOUTHEAST TEXAS BEING IN THE RRQ. AT THE SAME
TIME FRIDAY MORNING THE UPPER LEVEL DISTURBANCE WILL MOVE OVER
HEAD BRINGING WIDESPREAD PVA WITH IT. A SURFACE LOW WILL FORM IN
SOUTHERN TEXAS WITH A WARM FRONT EXTENDED ACROSS THE AREA. GFS IS
ALSO FORECASTING PWATS NEAR 1.60" (~ +2 SD FOR THIS TIME OF YEAR).
NOT SUPRISINGLY THE WIDESPREAD PVA AND WAA ALLOWS OMEGA VALUES TO
SHOW AN IMPRESSIVE AMOUNT OF LIFT FOR FRIDAY MORNING INTO EARLY
AFTERNOON. THE TEXAS TECH WRF SHOWS WIDESPREAD RAIN FORMING ALONG
AND NORTH OF THE WARM FRONT EARLY FRIDAY. GLOBAL MODELS ARE
INDICATING RAINFALL TOTALS APPROACHING 3" IN SOME AREAS. THESE
TOTALS WILL BE HIGH DEPENDENT ON WHERE THE BEST UPPER LEVEL
DIVERGENCE OCCURS FROM THE RRQ ALONG WITH THE POSITION OF THE WARM
FRONT. GENERALLY HIGHER PRECIP AMOUNTS CAN BE EXPECTED TOWARDS
OUR NORTHERN COUNTIES WITH LOWER AMOUNTS TOWARDS THE SOUTH AND
SOUTHWEST. DEEP LAYER SHEAR VALUES ARE ABOVE 50 KTS IN BOTH GFS/
AND NAM FORECAST SOUNDINGS AND THEREFORE SPC HAS PUT SOUTHEAST
TEXAS IN A MARGINAL RISK FOR DAY 3 (FRIDAY MORNING - SATURDAY
MORNING).

AS THE SURFACE LOW MOVES TOWARDS THE NORTHEAST FRIDAY AFTERNOON IT
WILL ALSO DRAG A SURFACE COLD FRONT THROUGH THE AREA. THIS WILL
ALLOW FOR A WEEKEND WITH BELOW NORMAL TEMPERATURES. ANOTHER UPPER
LEVEL DISTURBANCE WILL MOVE ACROSS THE AREA SUNDAY BUT RAIN LOOKS
UNLIKELY GIVEN PWAT VALUES BELOW 0.70". FOR THE NEXT WORK WEEK
MODELS HAVE COME INTO AGREEMENT PUSHING ANOTHER COLD FRONT THROUGH
THE AREA TUESDAY. 23

MARINE...
ONSHORE WINDS WILL RETURN THIS AFTERNOON AS HIGH PRESSURE MOVES OFF
TO THE EAST...AND THIS FLOW WILL PREVAIL THROUGH FRIDAY AFTERNOON
WITH BOTH WINDS AND SEAS POSSIBLY REACHING CAUTION LEVELS ON FRIDAY.
A STORM SYSTEM WITH SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS THE
AREA ON FRIDAY...AND MODERATE TO STRONG OFFSHORE WINDS WILL DEVELOP
IN THE WAKE OF A COLD FRONT. AFTER THE FRONTAL PASSAGE...CAUTION
FLAGS ARE LIKELY AND ADVISORIES MIGHT BE NEEDED. OVER THE WEEKEND...
NORTH WINDS WILL GRADUALLY SHIFT TO THE NORTHEAST AND EAST.  42

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      56  54  66  57  60 /  30  50  50  80  80
HOUSTON (IAH)              61  57  71  61  68 /  20  50  50  80  80
GALVESTON (GLS)            63  62  70  63  67 /  20  30  50  50  80

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

DISCUSSION...40
AVIATION/MARINE...47


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