Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 031758
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1258 PM CDT SUN MAY 3 2015

.AVIATION...
VFR THROUGH MOST OF THE PERIOD. MID-LEVEL CU FIELD THROUGH DAYTIME
HOURS...DISSIPATING OVERNIGHT. SLIGHTLY STRENGTHENED ONSHORE WINDS
WILL DISPLAY MORE OF A SOUTHEAST COMPONENT AS THE LARGE SCALE
GRADIENT BECOMES MORE WEST-TO-EAST BETWEEN SOUTHEASTERN STATES
HIGH PRESSURE AN LOWERING WEST TEXAS PRESSURE. EARLY MONDAY MORNING
WINDS SHOULD STAY UP JUST ENOUGH TO INHIBIT ANY SIGNIFICANT FOG
FORMATION...ALTHOUGH MORE INTERIOR RURAL HUBS MAY EXPERIENCE BRIEF
MVFR SHALLOW BR DEVELOPMENT. REPEAT PERFORMANCE TOMORROW...EXTENSIVE
INLAND CU FIELD (WITH MORE WESTERN CI STREAMING OVER) AND MODERATE
SOUTHEAST WINDS. 31

&&

.PREV DISCUSSION... /ISSUED 1031 AM CDT SUN MAY 3 2015/

UPDATE...
SEE MORNING UPDATE.

DISCUSSION...
SATELLITE DERIVED PW SHOWS A PLUME OF SLIGHTLY DEEPER MOISTURE
MOVING UP THE COAST TOWARD SE TX. UPPER LEVEL WINDS ARE WEAKLY
DIVERGENT OVER COASTAL TEXAS AS WELL. THE TEXAS TECH WRF AND THE
HRRR SHOW SCATTERED SHOWERS DEVELOPING LATER TODAY AND FEEL THIS
IS REASONABLE BASED ON THE INCREASING MOISTURE LEVELS. TWEAKED SKY
GRIDS TO SHOW A BIT MORE CLOUD COVER. MAX TEMPS FCST LOOKS REASONABLE
SO NO CHANGES PLANNED THERE. NEW ZONES OUT BY 1045 AM. 43


&&

PREV DISCUSSION... /ISSUED 427 AM CDT SUN MAY 3 2015/

DISCUSSION...
SFC ANALYSIS THIS MORNING SHOWS HIGH PRESSURE OVER THE SE U.S.
WITH A FRONTAL BOUNDARY THROUGH THE N PLAINS. THIS HAS ALLOWED FOR
SOUTHERLY WINDS TO DEVELOP OVER SE TX WITH MOISTURE RETURN OFF THE
GULF. SFC DEW POINT TEMPS HAVE INCREASED TO THE LOW 60S ALONG THE
COAST AND LOOK FOR DEW POINTS IN THE 60S TO BECOME WELL
ESTABLISHED LATER TODAY AND MONDAY. WINDS ARE STILL LIGHT/CALM
INLAND SO MAY GET SOME PATCHY FOG THIS MORNING.

PRECIP CHANCES REALLY DO NOT INCREASE UNTIL MOISTURE DEEPENS
THROUGH THE ATMOSPHERIC COLUMN. HIGHER PRECIP WATER VALUES DO NOT
BECOME ESTABLISHED OVER TX UNTIL TUE INTO WED. PRECIP WATER VALUES
OF GREATER THAN 1.5 INCHES WILL PERSIST TUE THROUGH THE END OF THE
WEEK. THIS SHOULD BE ENOUGH MOISTURE FOR SCT SHOWER AND
THUNDERSTORM ACTIVITY THROUGH THE WEEK. THE QUESTION OF HEAVY
RAINFALL WILL DEPEND UPON LIFT/INSTABILITY THROUGH THE WEEK.

WATER VAPOR IMAGERY STILL SHOWS ONE UPPER LEVEL LOW WEST OF
CALIFORNIA AND A MORE POTENT SYSTEM IN THE GULF OF ALASKA. ALL OF
THE SYNOPTIC MODELS ARE IN GOOD AGREEMENT WITH BRINGING THE FIRST
UPPER LOW ACROSS THE S ROCKIES WITH A BIT OF A NEG TILT ON TUE.
THERE IS A BROAD AREA OF DIFFLUENCE ALOFT OVER TX ASSOCIATED WITH
THE TROUGH AND JET STREAM COMING INTO TX FROM ACROSS MEXICO. WITH
850MB FLOW LARGELY FROM THE SE/S...THERE SHOULD NOT BE MUCH OF AN
EML FOR CAPPING. MODEL SOUNDINGS SHOW THAT AN EML NEVER REALLY
ESTABLISHES ITSELF OVER THE REGION FOR THE COMING WEEK. THIS MEANS
THAT EVEN SYNOPTIC SCALE LIFT MAY BE ENOUGH TO INITIATE CONVECTION
OVER THE AREA ESPECIALLY WITH DAY TIME HEATING SUPPORTING MAX
TEMPS IN THE MID 80S.

THE BIGGEST DIFFERENCE IN MODEL DATA FROM YESTERDAY TO TODAY IS
THAT LARGE SCALE LIFT DOES NOT APPEAR TO BE AS FAVORABLE. THE JET
STREAM IS MORE ANTICYCLONICALLY CURVED OVER THE REGION THAN
YESTERDAY WITH SUGGESTS SOME SUBSIDENCE. DIFFLUENCE ALOFT DOES NOT
LOOK A GREAT AND JET STREAKS ASSOCIATED WITH THE UPPER LOW OVER
THE GREAT BASIN DO NOT LOOK TO MAKE AN IMPACT UNTIL LATER IN THE
WEEK ON FRI/SAT. DURING THIS TIME UPPER FLOW STILL HAS SOME
RIDGING OR AT LEAST SOME ANTICYCLONIC CURVATURE TO IT WHICH WOULD
LIMIT LARGE SCALE ASCENT. FINALLY THERE ARE REALLY NOT ANY STRONG
BOUNDARIES TO FOCUS CONVECTION WHICH MEANS THERE MAY NEED TO BE
SOME MESOSCALE FORCING TO FOCUS CONVECTION. SO THE FORECAST HAS
TRENDED DOWN A BIT IN RAIN CHANCES. FORECAST DOES KEEP MAINLY 40
POPS FOR TUE/WED BUT TRIMMED BACK CHANCES TO 30 PERCENT FOR THE
END OF THE WEEK.

MAIN HAZARDS FOR THE COMING WEEK HAD BEEN MAINLY HEAVY RAINFALL
WHICH IS STILL POSSIBLE BUT EVEN TEMPERED THOSE EXPECTATIONS SINCE
LIFT MAY BE LIMITED. POSSIBLE THAT A STORM OR TWO COULD APPROACH
SEVERE LEVELS OR BECOME SEVERE WITH HAIL/DAMAGING WINDS FROM TUE
THROUGH THE END OF THE WEEK. HOWEVER IT LOOKS LIKE INSTABILITY
WILL BE LIMITED A BIT MORE THAN BEFORE. CAPE EACH DAY MAY REACH
1000-1500 J/KG WHERE YESTERDAY EVEN 2500 J/KG COULD BE EXPECTED.
THIS IS WHERE RIDGING OR ANTICYCLONIC FLOW WILL AFFECT
INSTABILITY. THIS TYPE OF FLOW WILL HINDER STEEP LAPSE RATES FROM
DEVELOPING AND COLDER AIR ALOFT WILL BE EXPECTED TO BE FARTHER
NORTH OVER THE PLAINS ASSOCIATED WITH THE TROUGH. 39

MARINE...
LIGHT TO MODERATE SOUTH TO SOUTHEAST FLOW WILL CONTINUE THROUGH
THE FORECAST PERIOD. WINDS AND SEAS WILL INCREASE INTO AT LEAST
SMALL CRAFT SHOULD EXERCISE CAUTION LEVELS AND POSSIBLY ADVISORY
LEVELS BY TUESDAY NIGHT AS PRESSURE GRADIENT INCREASES BETWEEN
HIGH PRESSURE OVER THE SOUTHEAST UNITED STATES AND TROUGH OF LOW
PRESSURE TO THE WEST. SHOWER AND THUNDERSTORM CHANCES WILL RETURN
TO THE FORECAST BEGINNING TUESDAY GIVEN INCREASING MOIST
SOUTHEASTERLY FLOW AND LIFT ASSOCIATED WITH WARM AIR ADVECTION.
46

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      64  83  65  81  68 /  10  10  10  40  30
HOUSTON (IAH)              63  83  67  82  69 /  10  10  10  40  30
GALVESTON (GLS)            70  81  71  81  73 /  10  10  10  40  30

&&

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

$$

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


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