Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 282353
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
553 PM CST SUN DEC 28 2014

.DISCUSSION...
00Z TAF DISCUSSION IN AVIATION SECTION.

&&

.AVIATION...
LATEST RADAR TRENDS HAS RAIN ASSOCIATED WITH SHORT WAVE TROUGH
MOVING OUT OF THE AREA. THIS SHOULD ALLOW FOR VSBY/CIGS TO IMPROVE
THE NEXT SEVERAL HRS BUT STILL QUITE A BIT OF MOISTURE TRAPPED IN
COLD AIRMASS. SATELLITE IMAGERY SHOWS CLEARING LINE APPROACHING
KCLL FROM THE WEST. THIS MAY PUSH FAR ENOUGH EAST TO ALLOW FOR
IMPROVING CIGS BUT NOT SURE HOW FAR WEST IT WILL MOVE.

KCLL...THINK THERE SHOULD BE CLEARING FOR MOST OF THE NIGHT BUT
NOT SEEING MODELS INDICATE IF CIGS/VSBY FILL BACK IN THROUGH THE
MORNING WITH RADIATIONAL COOLING. WILL KEEP TAF VFR.

KUTS/KCXO/KIAH/KHOU/KSGR...WITH RAIN MOVING OUT EXPECT VSBY/CIGS
TO IMPROVE SOME. MAY BREAK OUT OF OVC IFR CONDITIONS TO BKN BUT
STILL POSSIBLE FOR IFR TO HOLD ON THROUGH MORNING. CONCERNED
CLEARING COULD OCCUR AS DRIER AIR TRIES TO MIX INTO THE AREA SO
WILL NEED TO WATCH FOR THAT AND MAY GET CIGS TO GO SCT FROM 03Z-
09Z. HRRR 19-21Z RUNS SHOW THIS TREND IN CIGS SCATTERING OUT BUT
THEN GET LOW IFR TO BUILD BACK IN FROM 09Z TO 15Z. TAFS WILL BE
GEARED TOWARDS THESE LOWER CIGS IN THE MORNING AND THEN SLOWLY
GOING IFR/MVFR WITH VFR BY LATE AFTERNOON TOMORROW. WITH HIGH
PRESSURE BUILDING IN...LIGHT WINDS EXPECTED.

KLBX/KGLS...MORE LIKELY THAT CLEARING WILL NOT OCCUR FROM THE WEST
FOR THESE TERMINALS SO HAVE MORE CONFIDENCE IN IFR CIGS HOLDING
THROUGH THE NIGHT. ALSO POSSIBLE FOR CIGS TO DROP IN THE MORNING
TO LOW IFR AS THERE WILL NOT BE ANY DRIER AIR TO MIX AS COMPARED
TO MORE INLAND SIGHTS. OTHERWISE TRENDS SHOULD BE SIMILAR TO
INLAND TERMINALS WITH IFR UNTIL LATE MORNING AND THE MVFR IN THE
AFTERNOON.

39

&&

.PREV DISCUSSION... /ISSUED 340 PM CST SUN DEC 28 2014/

DISCUSSION...
TODAY/S PERSISTENT SHOWER ACTIVITY HAS NOW STARTED TO CLEAR THE
WESTERNMOST COUNTIES AS OF 3 PM /GENERALLY AREAS WEST OF THE
BRAZOS RIVER/. THIS ACTIVITY WILL CONTINUE TO PRODUCE LIGHT
RAINFALL TOTALS INTO THE EVENING HOURS AS IT TRANSLATES EAST AHEAD
OF A COMPACT SHORTWAVE TROUGH MOVING ACROSS THE STATE. THE EDGE OF
THE CLOUD DECK ASSOCIATED WITH THE RAIN LAGS BEHIND THE END OF THE
RAINFALL AND IS NOT ANTICIPATED TO REACH SOUTHEAST TEXAS UNTIL
LATER THIS EVENING. WHILE IT SEEMS RELATIVELY BENIGN...THE
TIMING/EVOLUTION OF THIS CLOUD DECK WILL ACTUALLY PLAY A VERY
IMPORTANT ROLE IN THE SHORT TERM FORECAST IN TERMS OF OVERNIGHT
LOW TEMPERATURES AND THE POTENTIAL FOR FOG DEVELOPMENT.

SIMPLE EXTRAPOLATION OF THE WESTERN EDGE OF THE CLOUD DECK FROM
VISIBLE SATELLITE SHOWS THIS CLEARING REACHING THE WESTERN EDGE OF
THE FORECAST AREA AROUND 00-02Z...AND MODEL GUIDANCE SHOWS THE
CLEARING LINE PUSHING EAST THROUGH THE OVERNIGHT HOURS. THERE/S
STILL SOME UNCERTAINTY ON HOW FAR EAST THE LINE WILL PUSH
THOUGH...WITH GENERAL CONSENSUS SHOWING IT REACHING NEAR THE I-45
CORRDIOR EARLY MONDAY MORNING. AS THIS LINE PUSHES EAST...THE
WESTERN AREAS WILL BE ALLOWED THE OPPORTUNITY TO RADIATIONALLY
COOL ENOUGH TO EXPERIENCE A LIGHT/BRIEF FREEZE. IF THE CLOUDS DO
NOT CLEAR AS QUICKLY /OR CLEAR FASTER/...OVERNIGHT LOW
TEMPERATURES WILL BE AFFECTED WITH THE ADDITION /OR LOSS/ OF A
CLOUD BLANKET. ADDITIONALLY...RELATIVELY LIGHT WINDS OVERNIGHT
WILL KEEP MIXING TO A MINIMUM...RAISING THE POTENTIAL FOR SOME FOG
DEVELOPMENT /ESPECIALLY IN AREAS THAT CLEAR/. LATEST RAP AND HRRR
VISIBILITY PROGS OFFER CONSIDERABLE DISAGREEMENT ON WHETHER OR NOT
FOG WILL DEVELOP. FOR NOW...WILL LEAVE PATCHY FOG MENTION OUT OF
THE FORECAST BUT ISOLATED DEVELOPMENT IS STILL POSSIBLE.

THE GENERAL UPPER AIR PATTERN THIS AFTERNOON HAS CONSISTED OF A
LONGWAVE TROUGH DRAPED ACROSS THE CONUS...WITH SEVERAL
DISTURBANCES ROTATING THROUGH THIS FEATURE. THE MOST NOTICEABLE
FOR US HAS BEEN THE ONE RESPONSIBLE FOR TODAY/S RAIN. TWO
DISTURBANCES FARTHER UPSTREAM /ONE OVER THE NORTHWESTERN CONUS AND
ANOTHER OVER THE NORTHWEST TERRITORIES OF CANADA/ WILL IMPACT THE
REGION/S WEATHER LATER IN THE WEEK. BEHIND TODAY/S SHORTWAVE... A
GENERALLY ZONAL FLOW BECOMES ESTABLISHED ACROSS THE SOUTHERN
CONUS. DESPITE THE PRESENCE OF AT LEAST PARTLY CLOUDY SKIES
MONDAY... ENOUGH INSOLATION WILL REACH THE SURFACE TO ALLOW
TEMPERATURES TO REBOUND INTO THE MID TO UPPER 50S.

MONDAY/S WARM UP WILL BE SHORT-LIVED AS THE DISTURBANCE OVER THE
NW CONUS CROSSES THE CENTRAL PLAINS WITH AN ARCTIC AIRMASS OOZING
THE AREA TUESDAY THROUGH THURSDAY. NORTHERLY WINDS WILL INCREASE
AS THE LEADING EDGE OF THIS ARCTIC AIR MOVES INTO THE AREA ON
TUESDAY...AND TEMPERATURES STILL REMAIN A CONCERN WITH THIS
SYSTEM. THE EXTENT OF THE MODIFICATION OF THE AIRMASS /FROM EITHER
DIABATIC OR ADIABATIC PROCESSES/ IS STILL NOT ENTIRELY CLEAR...BUT
WILL CONTINUE THE TREND OF GOING BELOW MODEL GUIDANCE AS THE EVENT
EVOLVES. THIS LEAVES THE OUTLOOK FOR MID-WEEK CHILLY WITH HIGHS
WEDNESDAY AND THURSDAY IN THE MID 40S TO NEAR 50.

THE FORMERLY CANADIAN SHORTWAVE DROPS TOWARDS THE FOUR CORNERS
REGION BY WEDNESDAY...ESTABLISHING A SOUTHWEST FLOW ALOFT /WHICH
ALLOWS FOR SOME MID LEVEL MOISTURE RETURN INTO THE REGION/ AND
INCREASING ISENTROPIC LIFT. RAIN CHANCES WILL NOT BEGIN TO
INCREASE UNTIL THURSDAY WITH THIS LIFT...AS FORECAST SOUNDINGS
SHOW RELATIVELY DRY LOWER LEVELS WILL PREVENT ANY PRECIPITATION
THAT DEVELOPS FROM REACHING THE GROUND. GUIDANCE INDICATES A
SUBTLE SHORTWAVE TROUGH MAY TRANSLATE NORTHWEST OF THE AREA LATE
THURSDAY...POSSIBLY INCREASING RAIN CHANCES FOR THE NORTHWEST
ZONES...BUT THE REGION MAY BE TOO FAR AWAY FROM THIS EXTRA SOURCE
OF LIFT TO ENHANCE OUR CHANCES.

BY FRIDAY...THUNDERSTORM CHANCES ARE ON THE INCREASE AS A COASTAL
TROUGH AND ASSOCIATED WARM FRONT DEVELOP ALONG THE TEXAS COAST.
STILL SOME QUESTIONS REGARDING EXTENT OF GULF MOISTURE
RETURN...BUT ENOUGH INSTABILITY APPEARS PRESENT AT THIS POINT TO
CONTINUE THUNDERSTORM CHANCES FRIDAY INTO FRIDAY NIGHT. AS THE
CANADIAN SHORTWAVE CROSSES TEXAS...ANOTHER COLD FRONT WILL REACH
THE AREA AND END RAIN CHANCES HEADING INTO LATE SATURDAY.

HUFFMAN

MARINE...
BOTH NORTH WINDS AND SEAS WILL DECREASE TONIGHT AND MONDAY AS HIGH
PRESSURE MOVES OVER THE AREA. THE NEXT COLD FRONT MONDAY NIGHT THROUGH
TUESDAY MORNING WILL BRING STRENGTHENING NORTHEAST WINDS ACROSS THE
WATERS. CAUTION FLAGS ARE LIKELY...AND ADVISORIES MIGHT BE NEEDED
TUESDAY THROUGH THURSDAY NIGHT. SOUTH WINDS ARE EXPECTED TO RETURN ON
FRIDAY AND FRIDAY NIGHT AS A WARM FRONT MOVES INLAND. LIGHT TO MODERATE
NORTH WINDS COME BACK OVER THE WEEKEND. 42

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      33  58  38  51  35 /  10   0   0  10  10
HOUSTON (IAH)              36  59  42  57  38 /  10   0   0  10  10
GALVESTON (GLS)            43  57  48  56  44 /  20   0   0  10  10

&&

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

$$

DISCUSSION...40
AVIATION/MARINE...39



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