Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 290218
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
918 PM CDT THU MAY 28 2015

.DISCUSSION...
AT 9 PM...A SOLID LINE OF STRONG/SEVERE THUNDERSTORMS OFF TO OUR NORTHWEST
CONTINUES TO MARCH TOWARD THE EAST AND SOUTHEAST. THIS LINE SHOULD WEAKEN
AS IT APPROACHES OUR NORTH AND NORTHWEST COUNTIES AFTER MIDNIGHT...BUT
IT COULD STILL BE CAPABLE OF DUMPING SOME BRIEF HEAVY RAINFALL ACROSS
PARTS OF SOUTHEAST TEXAS AS IT TRIES TO MAKE PROGRESS TOWARD THE COAST.
DUE TO ITS CURRENT SPEED AND EXPECTED WEAKENING TREND...WILL HOLD OFF
ON ISSUING A FLASH FLOOD WATCH WITH THE EXPECTATION OF RAINFALL TOTALS
PEAKING UNDER ONE INCH. IF THE COMPLEX DOES NOT MAKE IT OFF THE COAST...
WE COULD BE SETTING THE STAGE FOR POSSIBLE TRAINING ACTIVITY SOMEWHERE
IN OUR AREA LATE TONIGHT AND ON INTO TOMORROW RESULTING IN SEVERAL INCHES
OF RAIN AND AN INCREASING FLOOD THREAT DUE TO THE SATURATED GROUNDS.
FOR THE UPDATE...WENT AHEAD AND RAISED EVERYONE`S RAIN CHANCES A GOOD
10% TO 20% FOR THE OVERNIGHT HOURS RESULTING IN LIKELY POPS NORTHWEST
AND CHANCE POPS AT THE COAST. FUTURE FORECAST UPDATES ARE GOING TO DEPEND
HOW EVERYTHING UNFOLDS OVER THE NEXT SEVERAL HOURS.  42
&&

.PREV DISCUSSION... /ISSUED 714 PM CDT THU MAY 28 2015/

DISCUSSION...
PLEASE SEE 00Z AVIATION DISCUSSION...

AVIATION...
VFR CONDITIONS OVER NIGHT...WITH A LAYER OF MVFR CIGS LIKELY TO
FORM JUST BEFORE SUNRISE. BIG QUESTION IS WHETHER OR NOT THE
CONVECTION CURRENTLY IN WEST TEXAS MAKES IT TO SOUTHEAST TEXAS ON
TUESDAY MORNING AS SUGGESTED BY SUBSEQUENT HRRR MODEL RUNS. I
ADDED PROB30 TSRA GROUPS FOR KCLL AND KUTS BETWEEN 10 AND 15Z IN
DEFERENCE TO THE HRRR. IF THE THUNDERSTORMS CONTINUE TO HOLD
TOGETHER AFTER SUNSET AND ADDITIONAL MESOSCALE MODELS SUPPORT THE
HRRR SOLUTION...I MAY HAVE TO MORE AGGRESSIVELY BRING IN MORNING
SHRA/TSRA IN THE HOUSTON METRO AREA DURING THE 03Z TAF UPDATE.

ON FRIDAY...VFR CONDITIONS SHOULD PREVAIL AFTER 15Z. SIMILAR TO
TODAY THE HOUSTON METRO TERMINALS MAY EXPERIENCE SOME ISOLATED TO WIDELY
SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS. 44

PREV DISCUSSION... /ISSUED 406 PM CDT THU MAY 28 2015/

DISCUSSION...
BEFORE WE TALK ABOUT ALL THE UPCOMING THUNDERSTORM CHANCES FOR THE
WEEKEND...HOUSTON IAH DID REACH 90F TODAY WHICH IS THE FIRST TIME
HITTING 90 DEGREES IN 2015. THE LAST TIME HOUSTON IAH HAD A 90
DEGREE DAY WAS OCTOBER 10 2014. AVERAGE 1ST DAY OF 90 DEGREES AT
HOUSTON IAH IS AROUND MAY 7.

HOPEFULLY EVERYONE ENJOYED SOME BREAK IN THE RAINFALL. THIS
WEEKEND LOOKS TO BE ANOTHER WET WEEKEND WITH PROBABLY 2 PERIODS OF
WHEN HEAVY RAINFALL COULD OCCUR. CURRENT WATER VAPOR IMAGERY SHOWS
2 UPPER LEVEL TROUGHS...ONE MOVING THROUGH THE S ROCKIES AND W TX
WHICH SHOULD IMPACT THE AREA TOMORROW AND A SECOND TROUGH MOVING
THROUGH THE N ROCKIES WHICH WILL SUPPORT THUNDERSTORM ACTIVITY
LATE SAT INTO SUN.

WE ARE ALSO MONITORING THUNDERSTORM ACTIVITY IN W TX WHICH MAY
FORM INTO A SQUALL LINE. LAST FEW RUNS OF THE HRRR CONTINUE TO
HOLD THIS LINE OF STORMS TOGETHER AND HAVE IT REACHING WESTERN
PORTIONS OF SE TX AFTER MIDNIGHT. IT LOOKS LIKE THIS ACTIVITY MAY
WEAKEN BEFORE REACHING HOUSTON BUT STILL SOMETHING TO MONITOR.
SHOULD IT HOLD TOGETHER...STRONG WINDS AND SMALL HAIL WILL BE A
THREAT ALONG WITH HEAVY RAINFALL. GIVEN THE UNCERTAINTY A FLASH
FLOOD WATCH WILL NOT BE ISSUED AS IS THE CASE IN C TX AND N TX.

MODELS STILL HAVE THE INFLUENCE OF THE UPPER TROUGH OVER SE TX
TOMORROW. ALOFT THERE SHOULD BE AT LEAST SOME COOLING WITH LARGE
SCALE ASCENT AND DIFFLUENCE IN THE THE JET TO SUPPORT BROAD LIFT.
DAY TIME HEATING ALLOWING FOR TEMPS IN THE MID/UPPER 80S SHOULD
AGAIN SUPPORT CONVECTIVE INITIATION. PRECIP WATER VALUES SHOULD BE
AROUND 1.6-1.8 INCHES WITH A SWATH OF 1.8 INCH PW FROM COLLEGE
STATION TO LUFKIN. THIS SEEMS TO BE THE MORE LIKELY AREA FOR HEAVY
RAINFALL ALTHOUGH THERE IS NOT A BOUNDARY TO FOCUS CONVECTION.
MESOSCALE INTERACTIONS WILL BE A BIG KEY FOR FURTHER CONVECTIVE
DEVELOPMENT TOMORROW. MODEL SOUNDINGS DO INDICATE WEAK CAPPING
ALONG THE COAST WITH THE CAP WEAKEST NORTH OF HOUSTON. ORIENTED 50
POPS FOR HOUSTON NORTHWARD BASED ON CAPPING AND LOWER PRECIP
WATER ALONG THE COAST.

MORE FAVORABLE SET UP FOR HEAVY RAINFALL LOOKS TO BE LATE SATURDAY
INTO SUNDAY. BY 00Z SUN MODELS ARE IN PRETTY GOOD AGREEMENT WITH
UPPER LEVEL TROUGH AXIS DROPPING INTO THE S PLAINS. A COLD FRONT
WITH THIS SYSTEM ALSO PUSHES INTO TX AND LOOKS TO STALL ACROSS THE
AREA OVERNIGHT. THE FRONT MAY MAKE SOME SLOW PROGRESS SOUTHWARD
AND OFF THE COAST LATER ON SUNDAY. UPPER LEVEL WINDS WILL BE WEAK
AND DIFFLUENT DURING THIS TIME. THE FRONT WILL LIKELY FOCUS
THUNDERSTORM ACTIVITY LATE SAT AFTERNOON GOING INTO THE OVERNIGHT.
PRECIP WATER VALUES LOOK TO BE CLOSER TO 1.8 INCHES AREA WIDE.
MISSING FROM THIS SET UP IS A STRONG LLJ OFF THE GULF BUT STILL
THINK GIVEN FORCING FROM THE FRONT...VENTING ALOFT WITH DIFFLUENCE
AND HIGH MOISTURE WILL SUPPORT THUNDERSTORM ACTIVITY CAPABLE OF
HEAVY RAINFALL. STORMS CAPABLE OF 1-2 INCHES AN HR RAINRATES CAN
NOT BE RULED OUT AND WITH SLOW STORM MOTIONS...HIGH RAINFALL
TOTALS CAN BE ACHIEVED. WE WILL BE WATCHING THIS TIME FRAME FOR A
FLASH FLOOD WATCH. ANY STORMS OF THESE STORMS COULD PRODUCE OVER 3
INCHES OF RAIN VERY QUICKLY WHICH WILL CAUSE FLOODING PROBLEMS.

WITH THE FRONT SLOWLY MOVING OFF THE COAST...MORE STORMS MAY BE
EXPECTED SUNDAY. EXPECT THERE TO BE SOME BREAK IN CONVECTION
DURING THE MORNING BUT COULD SEE MORE ACTIVITY ALONG THE COAST
WITH DAY TIME HEATING. TROUGH AXIS ALOFT WILL STILL BE OVER THE
AREA AS THE UPPER TROUGH BEGINS TO SLOWLY CLOSE OFF FROM THE MAIN
FLOW. DRIER AIR MAY FILTER INTO THE REGION LATE SUNDAY INTO MONDAY
BEHIND THE FRONT. WHILE WE WISH WE COULD END THUNDERSTORM
CHANCES...MAIN PROBLEM IS THAT UPPER LOW CLOSES OFF MON INTO TUE
OVER LOUISIANA. ECMWF TAKES THIS LOW A BIT FARTHER EAST. IT IS
STILL POSSIBLE THAT SE TX WILL BE ON THE BACK SIDE OF THE TROUGH
AND SUBSIDENCE MAY LIMIT ACTIVITY. DESPITE THAT MODELS STILL
CONTINUE TO DEVELOP PRECIP AND CONVECTION WITH DAY TIME HEATING.
POSSIBLY BY WED/THU NEXT WEEK WE WILL GET A BREAK FROM
THUNDERSTORM CHANCES.

MARINE...
THE SLIGHT TIGHTENING OF THE PRESSURE GRADIENT TONIGHT (IN RESPONSE
TO THE FIRST OF A SERIES OF UPPER LEVEL DISTURBANCES FROM THE WEST)
WILL HELP TO INCREASE WINDS A BIT TONIGHT. AT THIS TIME NOT EXPECT-
ING MUCH MORE THAN MARGINAL SCEC CONDITIONS OVERNIGHT...BUT ANOTHER
SYSTEM LATE FRI/EARLY SAT COULD BE STRONG ENOUGH FOR SCEC FLAGS FOR
THAT TIMEFRAME. MODELS STILL CALLING FOR A WEAK COLD FRONT TO STALL
OVER SE TX SUNDAY...AND ITS PROXIMITY MAY BRIEFLY BACK WINDS TO THE
EAST AT THAT TIME. OTHERWISE...THE VERY WEAK PRESSURE GRADIENT WILL
PRODUCE LIGHT ONSHORE WINDS INTO NEXT MON/TUES. 41

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      72  85  70  83  67 /  60  50  20  60  50
HOUSTON (IAH)              72  86  71  85  69 /  40  50  20  60  60
GALVESTON (GLS)            77  85  76  84  74 /  30  30  20  30  40

&&

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

$$

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


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