Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 280516
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1216 AM CDT THU MAY 28 2015

.DISCUSSION...
PLEASE SEE 06Z AVIATION DISCUSSION...

&&

.AVIATION...
A QUIET NIGHT ON TAP FOR AVIATION INTERESTS. SCATTERED CIRRUS
CLOUDS EXTEND OVER THE FORECAST AREA WITH CLEAR SKIES BENEATH.
MVFR CIGS MAY FORM DURING THE EARLY MORNING HOURS...HOWEVERTHERE
SHOULD NOT BE ANY OBSTRUCTIONS TO VISIBILITY WITH LIGHT SOUTHEAST
WINDS AT 5 TO 10 KNOTS PRODUCING ENOUGH MIXING TO PREVENT FOG
FORMATION.

MVFR CIGS SHOULD LIFT ABOVE VFR CRITERIA BY MID MORNING. THE TERMINALS
MAY EXPERIENCE A FEW WIDELY SCATTERED SHOWERS AND THUNDERSTORMS BY
LATE MORNING AND EARLY AFTERNOON AS THE CONVECTIVE TEMPERATURE IS
REACHED AND PRECIPITABLE WATER REMAINS ELEVATED AT 1-.7 TO 1.9
INCHES. WINDS SHOULD BE FROM THE SOUTHEAST NEAR 10 KNOTS. 44

&&

.PREV DISCUSSION... /ISSUED 902 PM CDT WED MAY 27 2015/

DISCUSSION...
NO SIGNS OF ANY SHOWERS OR THUNDERSTORMS CLOSE TO OUR AREA THIS EVENING...
AND ALL NORTH TEXAS ACTIVITY IS SHOWING NO INDICATION OF ORGANIZING
INTO A SYSTEM THAT WILL HEAD ON DOWN HERE OVERNIGHT. FOR THE UPDATE...WILL
KEEP SOME VERY LOW POPS IN THE FORECAST IN CASE ONE OR MORE OF THE AFTERNOON
STORMS THAT WERE A COUPLE COUNTIES OUTSIDE OUR AREA SENDS A WEAK BOUNDARY
OUR WAY AND SETS OFF A STORM OR TWO. HOWEVER...CURRENT THINKING IS THAT
THIS HAS A LOW CHANCE OF HAPPENING.  42

PREV DISCUSSION... /ISSUED 717 PM CDT WED MAY 27 2015/

DISCUSSION...
PLEASE SEE 00Z AVIATION DISCUSSION.

AVIATION...
VFR CONDITIONS THIS EVENING WILL GRADUALLY TRANSITION TO MVFR OVER
NIGHT. MOST TERMINALS WILL DEVELOP CIGS IN THE 015-025 RANGE AFTER
06Z. WINDS WILL BE FROM THE SE AT 5-10 KNOTS OVER NIGHT.

ON TUESDAY...MVFR CIGS SHOULD LIFT ABOVE VFR THRESHOLD BY MID
MORNING. WITH DAYTIME TEMPERATURES FORECAST THE MID 80S AND
PRECIPITABLE WATER VALUES IN THE 1.7-1.9 INCH RANGE. SCATTERED
SHOWERS AND THUNDERSTORMS ARE POSSIBLE TOMORROW AFTERNOON. EXACT
TIMING AND EXTENT OF COVERAGE ARE UNCERTAIN...SO WILL CONTINUE TO ADDRESS
CONVECTIVE ACTIVITY WITH VCSH/VCTS AT THIS TIME. 44

PREV DISCUSSION... /ISSUED 406 PM CDT WED MAY 27 2015/

DISCUSSION...
A LINE OF STORMS PUSHED THROUGH THE AREA THIS MORNING DUMPING
ANOTHER 2-4 INCHES OF RAINFALL ACROSS PORTIONS OF THE AREA.
PORTIONS OF MONTGOMERY CO AREA HAD 3-4 INCHES NEAR LAKE CONROE
WITH 2-3 INCHES IN NW HARRIS CO. HOUSTON IAH HAD 1.41 INCHES SO
FAR TODAY BRINGING THE MAY TOTAL TO 13.59 INCHES OR 5TH WETTEST
MAY ON RECORD. YEARLY TOTAL NOW UP TO 29.86 INCHES.

FORECAST TONIGHT INTO THE WEEKEND WILL BE CRITICAL FOR RIVER
LEVELS GIVEN RELEASES FROM LAKES. TONIGHT THERE IS LOW CONFIDENCE
IN ANOTHER LINE OF STORMS ORGANIZING IN C AND N TX. SOME OLDER WRF
MODEL RUNS HINT AT THE IDEA OF SOMETHING HAPPENING TONIGHT BUT
HAVE BACKED OFF ON THAT EVOLUTION. EVEN THE RAP/HRRR SEEM TO
PRODUCE CONVECTION IN C/N TX BUT FAILS TO ORGANIZE OR MOVE INTO SE
TX. STILL WILL LEAVE SOME THUNDERSTORM CHANCES OVERNIGHT TO COVER
THE POSSIBILITY BUT NOT SEEING A STRONG FORECAST SIGNAL FOR
ANYTHING ORGANIZING.

DAYS 2-7 FORECAST...
OVERALL MODELS SHOW SCT THUNDERSTORM ACTIVITY THURSDAY MAINLY IN
THE AFTERNOON. TEMPS IN THE MID/UPPER 80S SHOULD BE ENOUGH FOR
BOUNDARY LAYER TO DESTABILIZE AND FOR CONVECTION TO FORM. MAIN
FOCUS WILL BE ALONG ANY OUTFLOW BOUNDARIES FROM PREVIOUS
CONVECTION. BEST CHANCES LOOK TO BE FOR HOUSTON/INTERSTATE 10
NORTHWARD WHERE INSTABILITY WILL BE BETTER AND NOT AS CAPPED IN
MIDLEVELS. PRECIP WATER VALUES EXPECTED TO BE AROUND 1.7 INCHES SO
ENOUGH TO SUPPORT SOME HEAVY RAINFALL...BUT HOPEFULLY NOT ENOUGH
TO CAUSE FLOODING. MAIN ISSUE WILL BE IF STORMS MOVE SLOWLY AND
CONTINUE TO PULSE IN INTENSITY PRODUCE HIGHER RAIN RATES.

FOR FRIDAY THROUGH SUNDAY...TRACKING 2 UPPER LEVEL TROUGHS.
LATEST WATER VAPOR IMAGERY SHOWS THE FIRST OVER THE DESERT SW AND
THE SECOND OVER THE INTER MTN WEST. THE FIRST LOOKS TO ARRIVE
FRIDAY WHICH WILL INCREASE LARGE SCALE ASCENT. PRECIP WATER VALUES
COULD RANGE FROM 1.7-1.9 INCHES WHICH IS STILL BELOW THE SEASONAL
2 STANDARD DEVIATIONS FROM NORMAL OF 2.2 INCHES. THE TROUGH WILL
STILL PROVIDE LIFT AND COOLING ALOFT. TEMPS AT 500MB DROP TO
AROUND -10 TO -12C WHILE CAPPING WEAKENS WITH LARGE SCALE LIFT.
AGAIN THE ISSUE WILL NOT BE SO MUCH HOW MUCH PRECIP BUT HOW
QUICKLY RAINFALL OCCURS. QUITE POSSIBLE THAT STRONGER STORMS COULD
PRODUCE 2 INCHES AN HR SO WILL NEED TO AGAIN LOOK AT FLASH FLOOD
WATCHES. MODELS HAVE NOT BEEN PRODUCING ANY HEAVY RAINFALL SIGNALS
IN QPF OUTPUT BUT PATTERN CERTAINLY SUPPORTS A THREAT FOR SE TX.

SATURDAY NIGHT INTO SUNDAY A FRONTAL BOUNDARY PUSHES INTO SE TX
ALONG WITH A SECOND TROUGH DROPPING DOWN FROM THE ROCKIES THROUGH
THE PLAINS. THE BOUNDARY WILL ONLY ADD MORE SUPPORT FOR
THUNDERSTORM ACTIVITY AND THE POSSIBILITY OF HEAVY RAINFALL. THIS
WILL AGAIN BE MONITORED FOR FLOOD WATCHES BUT LARGELY DEPENDS ON
HOW CONVECTION EVOLVES FRIDAY. AGAIN THE CAP WILL BE WEAK...TROUGH
AXIS WILL NOT HAVE PUSHED OUT OF THE AREA YET AND DEEP MOISTURE
WILL STILL CONVERGE ALONG THE FRONT. UPPER LEVEL LOW LOOKS TO
LINGER OVER THE MISS RIVER VALLEY SO SUBSIDENCE ON THE BACK SIDE
OF THE TROUGH MAY HELP SUPPRESS SOME THUNDERSTORM ACTIVITY OR AT
LEAST LOWER THE CHANCE. GIVEN THE FRONT STALLED ACROSS THE ARE AND
DEEP MOISTURE IN CLOSE PROXIMITY...FORECAST WILL KEEP A LEAST SOME
CHANCES GOING FOR EARLY NEXT WEEK.

39

MARINE...
WILL BE RESURRECTING THE SCEC FOR THE COASTAL WATERS FOR THE REST OF
THE AFTN INTO TONIGHT AS WINDS AND SEAS/SWELLS HAVE COME UP ONCE AG-
AIN. THERE IS ALSO STILL A THREAT FOR RIP TIDES AS THE ONSHORE WINDS
PERSIST AND ELEVATED SWELLS HEAD TOWARD THE SHORE. TIDES WILL REMAIN
ELEVATED DUE TO THE SWELLS AND THE DISCHARGE OF RAIN/FLOOD WATERS IN
TO THE BAYS. PER LONG RANGE MODELS...NOT A LOT OF CHANGES WITH LARGE
SCALE PATTERN WITH THE SFC HIGH TO THE EAST AND LOWER PRESSURES WEST
WHICH WILL HELP MAINTAIN A DEEP/STEADY SELY FLOW OVER THE REGION.
41

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      72  87  73  86  72 /  30  40  20  50  30
HOUSTON (IAH)              73  87  73  86  72 /  20  40  20  50  30
GALVESTON (GLS)            77  86  77  85  76 /  10  30  20  40  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 1 AM CDT THURSDAY FOR
     THE FOLLOWING ZONES: WATERS FROM FREEPORT TO THE MATAGORDA
     SHIP CHANNEL 20 NM TO 60 NM...WATERS FROM HIGH ISLAND TO
     FREEPORT 20 TO 60 NM.

&&

$$

DISCUSSION...42
AVIATION/MARINE...44



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