Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 041756
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1256 PM CDT MON MAY 4 2015

.AVIATION...
ANOTHER DAY OF A HIGH LOWER ALTITUDE CUMULUS DECK...MODERATE
SOUTHEASTERLIES THE GENERAL BACKGROUND WIND FIELD. EASTERLY MID-
LEVEL STEERING WINDS HAS ADVECTED IN A RELATIVELY DRIER WESTERN
GULF AIR MASS TODAY BUT...AS THESE WINDS VEER MORE SOUTHERLY
TONIGHT...LOWER TO MID LEVELS WILL BEGIN TO SATURATE UP. A TIGHT
ONSHORE SURFACE PRESSURE GRADIENT PROVIDING THE MODERATE ONSHORE
TRANSPORT OF SOUTHERN(WEST)-BASED HIGHER MOISTURE...WITH A STRENGTHENED
EARLY TUESDAY LOW LEVEL JET...WILL THICKEN CLOUDS TO MVFR CATS THROUGH
THE LATTER PERIOD. EITHER A SOUTHWESTERN WEAK DISTURBANCE RIDING
ACROSS EASTERN TEXAS...OR THE WESTERN PERIPHERY OF AN EASTERLY
WAVE...WILL INCREASE TUESDAY MORNING PRECIPITATION PROBS. MODEL
FORECAST SOUNDINGS DEPICT AN UNSTABLE ENOUGH ATMOSPHERE TO MENTION
LATE MORNING THROUGH LATE TUESDAY AFTERNOON THUNDER. 31

&&

.PREV DISCUSSION... /ISSUED 1033 AM CDT MON MAY 4 2015/

UPDATE...
SEE MORNING UPDATE.

DISCUSSION...
12Z CRP SOUNDINGS SHOWED A SATURATED PROFILE BENEATH 700 MB AND PW
VALUES NEAR 1.50 INCHES. 12Z LCH SHOWED A PW VALUE OF 0.75 INCHES
AND A DRY PROFILE. SATELLITE DERIVED PW CONFIRMS THE SHARP
MOISTURE GRADIENT ACROSS THE HGX CWA TODAY. FEEL THE MOISTURE IS
DEEP ENOUGH NEAR MATAGORDA BAY TO GENERATE A FEW SHOWERS
THROUGHOUT THE DAY SO WILL CARRY 20 POPS FOR THAT AREA THROUGH THE
AFTN. INCREASED SKY GRIDS OUT WEST AS WELL. MAX TEMP FCST LOOKS ON
TRACK SO NO CHANGES PLANNED THERE. NEW ZONES OUT BY 1045 AM.  43

&&

PREV DISCUSSION... /ISSUED 542 AM CDT MON MAY 4 2015/

UPDATE...
QUICK MORNING UPDATE.

DISCUSSION...
SHOWERS OFF THE COAST OF MATAGORDA HAVE SLOWLY MADE PROGRESS TOWARDS
THE COAST. UPDATED FORECAST FOR 17 POPS AND MENTION OF ISO SHOWER
OR THUNDERSTORM. ACTIVITY SHOULD DECREASE LATER THIS MORNING. 39

&&

PREV DISCUSSION... /ISSUED 353 AM CDT MON MAY 4 2015/

DISCUSSION...
SOUTHEAST TO SOUTH BOUNDARY LAYER FLOW WITH A 30KT LLJ WILL
CONTINUE TO SUPPORT INCREASED MOISTURE OFF THE GULF. OVERALL
SOUTHERLY WINDS HAVE KEPT TEMPS FROM DROPPING TOO MUCH THIS
MORNING WITH MIN TEMPS IN THE 60S EXCEPT FOR KCXO WHERE TEMP HAS
DROPPED TO THE UPPER 50S AND CALM WINDS. TODAY WILL CERTAINLY FEEL
MORE HUMID THAN THE LAST SEVERAL DAYS WITH DEW POINT TEMPS
CLIMBING INTO THE LOW 60S. DEW POINTS IN THE MID/UPPER 60S WERE
FOUND JUST ALONG THE COAST AND OFF THE UPPER TX COAST. TODAY
SHOULD BE PRECIP FREE EXCEPT FOR MAYBE AN ISO SHOWER THAT DEVELOPS
IN THE AFTERNOON THROUGH C TX WHICH COULD CLIP AREAS FROM COLUMBUS
TO CALDWELL.

WATER VAPOR IMAGERY SHOWS RIDGING OVER THE AREA BUT TWO UPPER
LEVEL TROUGHS THAT WILL BE TRACKED. THE FIRST IS JUST OFF THE
COAST OF CALIFORNIA AND THE SECOND IS NW OF THE PAC NW. SYNOPTIC
MODELS GFS/ECMWF/CANADIAN ARE ALL IN PRETTY GOOD AGREEMENT WITH
THE EVOLUTION OF THESE SYSTEMS. THE FIRST TROUGH WILL PUSH ACROSS
THE S ROCKIES TONIGHT AND THEN INTO THE C PLAINS AND C ROCKIES
TUESDAY. THE SECOND LOW WILL THEN CONTINUE TO DROP SOUTH INTO THE
PAC NW. THE FIRST TROUGH WILL CONTINUE NORTHWARD THROUGH THE
PLAINS ON WED AS THE SECOND WAVE DEVELOPS INTO MORE OF A CLOSED
LOW OVER N CALIFORNIA. ANOTHER SHORT WAVE TROUGH WILL PUSH INTO
THE PLAINS ON THUR BETWEEN THE TWO SYSTEMS. THE CLOSED LOW WILL
MOVE OVER THE GREAT BASIN ON FRI AND FINALLY OPEN UP INTO THE
PLAINS LATE SUN INTO NEXT MONDAY. AS THIS SYSTEM EXITS A COLD
FRONT MAY PUSH INTO THE AREA.

OVERALL THERE HAS NOT BEEN TOO MUCH CHANGE IN RAIN CHANCES WHICH
WILL BE CONVECTIVELY DRIVEN. FORECAST WILL KEEP 40 POPS ON TUE AS
INITIAL SURGE OF HIGHER MOISTURE REACHES SE TX FROM THE GULF.
PRECIP WATER VALUES TOP OUT AROUND 1.6 INCHES AND WILL LITTLE
CAPPING...SHOULD SEE SCT SHOWER/THUNDERSTORM ACTIVITY. INSTABILITY
LOOKS TO TOP OUT AROUND 1000-1500 J/KG SO THERE MAY BE A COUPLE
STRONG STORMS ESPECIALLY SINCE THERE IS LITTLE CAPPING WITH 850MB
TRAJECTORIES COMING FROM THE GULF. THIS CORRESPONDS WELL WITH THE
PASSING OF THE FIRST UPPER LEVEL TROUGH INTO THE PLAINS. STORMS
MAY PRODUCE SOME GOOD RAIN RATES BUT THINK WITH STORM MOTIONS OF
20KTS FLOODING SHOULD NOT BE AN ISSUE.

BY WEDNESDAY MOISTURE LOOKS TO DROP TO AROUND 1.4-1.5 INCHES OF
PRECIP WATER AND REALLY WEAK IF ANY LARGE SCALE ASCENT FOR LIFT.
WHILE A JET STREAK COMES INTO W TX THERE IS STILL SOME
ANTICYCLONIC CURVATURE TO THE JET OVER E TX LEADING TO SOME
SUBSIDENCE. THIS WILL LIMIT LAPSE RATES AND MID LEVEL FLOW BECOMES
ENOUGH SW FOR THERE TO BE A WEAK ELEVATED MIXED LAYER IN MODEL
SOUNDINGS. WEAK SHORTWAVE PASSES WELL NORTH OF THE AREA ON THUR
BUT STILL DEALING WITH WEAK RIDGING ALOFT. JET DOES BECOME A BIT
MORE DIFFLUENT IN THE AFTERNOON SO COULD BE ENOUGH LIFT FOR SCT
SHOWERS/THUNDERSTORMS TO FORM. OVERALL KEPT 30 POPS IN THE
FORECAST THROUGH THE END OF THE WEEK GIVEN THIS PERSISTENT UPPER
LEVEL PATTERN.

UPPER LOW OVER THE GREAT BASIN FINALLY MOVES INTO THE PLAINS WITH
TROUGH AXIS CROSSING THE AREA SUN NIGHT INTO MONDAY ON DAY 8 OF
THE FORECAST. LOOK FOR HIGHER THUNDERSTORM CHANCES DURING THIS
TIME AS JET STRUCTURE BECOMES MUCH MORE FAVORABLE FOR LIFT AND
TROUGH AXIS SHOULD DROP FAR ENOUGH SOUTH TO ERODE ANY CAPPING.
WILL NEED TO MONITOR THIS TIME FRAME FOR POSSIBILITY OF
STRONG/SEVERE STORMS NOT TO MENTION HEAVY RAINFALL. THIS IS STILL
A WEEK OUT SO PLENTY OF TIME FOR GFS/ECMWF TO CHANGE THEIR
SOLUTIONS BUT THE AGREEMENT THIS FAR OUT IS WELL NOTED. 39

&&

MARINE...
EXPECT INCREASING WINDS AND SEAS THIS WEEK UNDER A TIGHTENING PRESSURE
GRADIENT. CAUTION FLAGS ARE IN EFFECT...AND ADVISORIES MIGHT BE NEEDED.
LOW SHOWER AND THUNDERSTORM CHANCES RETURN TO THE FORECAST TONIGHT
AND PERSIST THROUGH MOST OF THE WEEK. 42

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      64  81  67  82  68 /  20  40  30  40  20
HOUSTON (IAH)              67  81  68  84  69 /  30  40  30  40  10
GALVESTON (GLS)            71  79  73  81  73 /  30  40  30  30  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION THROUGH LATE TUESDAY NIGHT
     FOR THE FOLLOWING ZONES: WATERS FROM FREEPORT TO THE
     MATAGORDA SHIP CHANNEL 20 NM TO 60 NM...WATERS FROM
     FREEPORT TO THE MATAGORDA SHIP CHANNEL OUT 20 NM...WATERS
     FROM HIGH ISLAND TO FREEPORT 20 TO 60 NM...WATERS FROM HIGH
     ISLAND TO FREEPORT OUT 20 NM.

&&

$$

DISCUSSION...43
AVIATION/MARINE...31



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