Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 271816
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
116 PM CDT MON APR 27 2015

.AVIATION...
MAIN AVIATION CONCERNS FOR THE 18Z SOUTHEAST TEXAS TAFS CENTER
AROUND THE POTENTIAL FOR TSRA THIS AFTERNOON AND EVENING... AND
THEN INCREASING WINDS/ LOWERED CIGS WITH A COLD FRONT MOVING
ACROSS THE REGION TONIGHT.

LATEST OBSERVATIONS SHOW A MIX OF MVFR AND VFR CEILINGS IN PLACE
ACROSS THE REGION... WITH SHRA/TSRA DEVELOPING FROM NEAR LBX
TOWARDS THE NORTHEAST. ANTICIPATE COVERAGE TO INCREASE THROUGH THE
AFTERNOON WITH ADDITIONAL HEATING. GIVEN ANTICIPATED ISOLATED TO
SCATTERED NATURE OF ACTIVITY... WILL ADVERTISE VCTS MENTION AT ALL
TERMINALS AND HANDLE TSRA IMPACTS AT TERMINALS WITH AMENDMENTS.
AMPLE SHEAR AND INSTABILITY IN PLACE TODAY RAISE CONCERNS FOR
STRONG TO SEVERE THUNDERSTORMS TO POTENTIALLY IMPACT THE
TERMINALS /HIGHEST LIKELIHOOD BETWEEN 21 AND 03Z/... WITH ISOLATED
INSTANCES OF LARGE HAIL POSSIBLE FROM MORE ROBUST ACTIVITY.

AS AN AREA OF SURFACE LOW PRESSURE EJECTS TOWARDS THE GULF COAST
STATES LATER TONIGHT... IT WILL DRAG A COLD FRONT ACROSS THE
TERMINALS TONIGHT WITH WINDS BECOMING NORTHERLY 10 TO 15 KNOTS
/WITH STRONGER GUSTS POSSIBLE/ IN ITS WAKE ON TUESDAY MORNING.
EXPECT THE FRONT TO REACH THE HOUSTON TERMINALS AROUND 03Z...
CLEARING THE COASTAL SITES BETWEEN 06 AND 09Z. A PERIOD OF MVFR
TO EVEN IFR CEILINGS WILL ALSO BE POSSIBLE BEHIND THE FRONT...
BEFORE IMPROVING TOWARDS/AFTER THE END OF THE TAF PERIOD.

HUFFMAN

&&

.PREV DISCUSSION... /ISSUED 1100 AM CDT MON APR 27 2015/

UPDATE...
SOME ADDITIONAL INFORMATION...AN NWS STORM SURVEY IS ENROUTE TO
THE GRIMES COUNTY AREA TO ASSESS DAMAGE. WE WILL UPDATE WITH
INFORMATION AS WE RECEIVE IT FROM THE ASSESSMENT.

PEAK WINDS MEASURED LAST NIGHT
CONROE ASOS        62 MPH AT 435 AM
8SE OF NAVASOTA    55 MPH AT 412 AM
HUNTSVILLE ASOS    54 MPH AT 452 AM
1N OF WALLER       50 MPH AT 422 AM
BRENHAM AWOS       49 MPH AT 335 AM

45

PREV DISCUSSION... /ISSUED 1040 AM CDT MON APR 27 2015/

UPDATE...
THE AREA HAS BEEN STABILIZED FOR THE MORNING HOURS. HAVE PARED
BACK THE RAIN CHANCES THIS MORNING...BUT...THIS AFTERNOON IS A
VERY DIFFERENT STORY. A SQUALL LINE THAT RACED THROUGH THE REGION
KNOCKING DOWN TREES IS WELL INTO LA WITH SUBSIDENCE/DRYING ACROSS
THE NORTHERN CWA. OUTFLOW BOUNDARY (WITH A SMALL CLUSTER OF
STORMS) IN THE NEARSHORE WATERS WITH SURFACE DEWPOINTS DOWN TO
63-67 OVER SETX. LOW LEVEL CONVERGENCE CURRENTLY STRETCHES FROM
THE NEARSHORE WATERS UP THROUGH MATAGORDA BAY TO GIDDINGS TO JUST
WEST OF FORT WORTH. WATER VAPOR/UA CLEARLY SHOWS A DRYING TREND
ALOFT WITH STRONG SW FLOW OF 50+ KNOTS AT 500MB AND 80+ KNOTS AT
300MB. AS WE HEAT UP AND THE UPPER LOW NEAR WICHITA FALLS
CONTINUES TO TREK EAST THIS SHOULD PLACE SETX IN A FAVORABLE
REGION FOR SEVERE WEATHER WITH SYNOPTIC SCALE LIFT...LL
CONVERGENCE AND A RAPIDLY DESTABILIZING ATMOSPHERE. SB CAPE
VALUES SOAR TO 3500-4500 J/KG OVER THE NORTH WITH THE
AFOREMENTIONED SHEAR ALOFT AND LOW LEVELS ONLY SOMEWHAT SHEARED
HIGHLIGHT THE POTENTIAL FOR HAIL/DAMAGING WINDS/ISOLATED
TORNADOES...THOUGH PROBABLY A LOWER THREAT FOR TORNADOES BUT THAT
IS A LOT OF CAPE IF WE CAN REACH THE 80 DEGREE MARK. THE STORMS
SHOULD SWING EASTWARD THROUGH THE EVENING HOURS ENDING THE THREAT
OF SEVERE WEATHER. SPC HAS KEPT THE AREA IN A SLIGHT RISK. HEAVY
RAIN THREAT POSSIBLE BUT SHOULD BE MORE ISOLATED IN NATURE. COLD
FRONT SHOULD ARRIVE IN THE HOUSTON AREA AFTER 2 AM WITH MODERATE
COLD ADVECTION. BREEZY CONDITIONS EXPECTED TUESDAY.

45

PREV DISCUSSION... /ISSUED 717 AM CDT MON APR 27 2015/

AVIATION...
CONFIDENCE IN THE FORECAST IS LOW DUE TO THE VARIABILITY IN MODEL
SOLUTIONS. THE HIGH RESOLUTION HRRR MODEL AGREED WITH THE GLOBAL
MODELS IN MOVING THE CURRENT CONVECTION EAST OF THE AREA WHILE
POSSIBLY DEVELOPING MORE SHOWERS AND THUNDERSTORMS THIS AFTERNOON
AS THE UPPER LOW IN NM MOVES INTO THE SOUTHERN PLAINS.

FOR THIS MORNING...DO EXPECT VFR CONDITIONS FROM KIAH NORTHWARD.
THE MVFR TO IFR CONDITIONS FROM KHOU TO THE COAST SHOULD IMPROVE
BY THE MID MORNING PERIOD. WILL ADD THE MENTION OF SHOWERS OR
THUNDERSTORMS THIS AFTERNOON INTO THE EARLY EVENING.

ALTHOUGH GUIDANCE WAS FORECASTING LOW CEILINGS...RAW MODEL OUTPUT
SUGGESTED BEST CHANCES WILL BE MORE TOWARD THE COAST. AT LEAST
MVFR CONDITIONS ARE POSSIBLE FROM KHOU TO THE COAST AHEAD OF THE
COLD FRONT. THE FRONT IS EXPECTED TO AT LEAST MOVE THROUGH KCLL
AND KUTS BY AROUND 08Z...AND SHOULD MOVE THROUGH KCXO AND KIAH BY
12Z.

40

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      60  67  49  72  53 /  40  20  10   0  10
HOUSTON (IAH)              63  70  49  74  54 /  40  20  10   0  10
GALVESTON (GLS)            69  73  56  71  63 /  20  10  10   0   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 4 PM CDT THIS
     AFTERNOON FOR THE FOLLOWING ZONES: GALVESTON BAY...WATERS
     FROM HIGH ISLAND TO FREEPORT 20 TO 60 NM...WATERS FROM HIGH
     ISLAND TO FREEPORT OUT 20 NM.

&&

$$



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