Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 191545
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1045 AM CDT TUE MAY 19 2015

.UPDATE...
MORNING RADAR SHOWS TWO DIFFERENT SETS OF SHOWER AND THUNDERSTORM
ACTIVITY OCCURRING OVER AND JUST WEST OF THE BRAZOS VALLEY. THE
FIRST ROUND CONTINUES TO DRIFT NORTHEAST ACROSS THE BRAZOS VALLEY...
AND THE SECOND A COMPLEX OF SHOWERS AND THUNDERSTORMS THAT/S
DEVELOPED EAST OF BASTROP /SLOWLY DRIFTING NORTH/. MORNING
SOUNDINGS FROM CORPUS CHRISTI... FORT WORTH... AND LAKE CHARLES
ALL MEASURED PRECIPITABLE WATER VALUES GREATER THAN 1.6 INCHES...
BUT SOUNDING PROFILES THEMSELVES WERE NOT SATURATED IN THE MID
LEVELS. SOMEWHAT DRIER MID-LEVEL AIR MAY HELP TO LIMIT RAINFALL
INTENSITY A BIT BUT SLOW STORM MOTIONS TODAY /850-300 MB WINDS WSW
AROUND 10 TO 15 KNOTS/ WILL CREATE A LOCALIZED FLOODING THREAT FOR
ANY STORM THAT IS ABLE TO MAINTAIN ITSELF OVER AN AREA.

EXPECT SHOWERS AND THUNDERSTORM CHANCES TO CONTINUE ACROSS THE
REGION TODAY AND THE 20-40 POPS CURRENTLY IN THE FORECAST HANDLE
THIS WELL. MORNING SURFACE ANALYSIS /13Z/ SHOWED A WEAK AREA OF
SURFACE CONVERGENCE /POSSIBLY REMNANTS OF OUTFLOW FROM YESTERDAY/
STRETCHED FROM NEAR AUSTIN TO COLUMBUS TO GALVESTON. HRRR/RAP
CONTINUE TO SHOW DEVELOPMENT ALONG THIS FEATURE WITH INCREASING
COVERAGE ACROSS THE REGION AS CONVECTIVE TEMPERATURES ARE REACHED.
FORECAST SOUNDINGS DO SHOW A SHALLOW INVERTED-V SIGNATURE DURING
THE AFTERNOON HOURS AND CAN/T RULE OUT A GUSTY WIND THREAT /20 TO
40 MPH/ AS WELL WITH SOME OF THE STRONGER STORMS. OTHERWISE...
REMAINDER OF FORECAST ON TRACK WITH MINOR ADJUSTMENTS TO HOURLY
TEMP/DEW POINT GRIDS BASED ON OBSERVATIONS WITH AFTERNOON
TEMPERATURES RISING INTO THE MID 80S. UPDATED PRODUCTS ALREADY
OUT.

HUFFMAN


&&

.PREV DISCUSSION... /ISSUED 519 AM CDT TUE MAY 19 2015/

DISCUSSION...
THIS RATHER ACTIVE WX PATTERN EXPECTED TO CONTINUE THROUGH THE UP-
COMING FCST CYCLE. LOOKING FOR ANOTHER ROUND OF PCPN TODAY...THEN
A BRIEF BREAK WEDS WITH MORE UNSETTLED WX FCST FOR THURS/FRI.

AS PER WV/RADAR LOOPS THIS MORNING...AN EMBEDDED SHORTWAVE IN THE
PERSISTENT SW FLOW ALOFT LOOKS TO BE MOVING INTO SE TX LATER THIS
MORNING/AFTN. LINGERING OUTFLOW BOUNDARIES FROM STORMS LAST NIGHT
ALONG WITH DAYTIME HEATING IN THE ALREADY UNSTABLE AIRMASS ACROSS
THE REGION SHOULD ALLOW FOR THE DEVELOPMENT OF STRONG STORMS THIS
AFTN. OF SOME CONCERN IS THE DIFFLUENT PATTERN AT THE UPPER PARTS
OF THE ATMOSPHERE...EVEN IF IT IS NOT QUITE AS STRONGLY DIFFLUENT
AS YESTERDAY. ANY SORT OF TRAINING COULD QUICKLY LEAD TO FLOODING
PROBLEMS GIVEN THE VERY WET GROUNDS/LOW FLASH FLOOD GUIDANCE. THE
ISSUANCE OF A FLOOD WATCH FOR PARTS OF SE TX IS A POSSIBILITY.

SLIGHTLY WARMER MID LEVELS WITH THE DEVELOPMENT OF AN UPPER RIDGE
SHOULD HELP TO LIMIT PCPN FOR WEDS...BUT RAIN CHANCES EXPECTED TO
RETURN THUR AS THIS PATTERN HELPS TO PUSH A WEAK FRONTAL BOUNDARY
INTO OUR NRN ZONES. AS THE NEXT UPPER TROF DEEPENS NEAR THE CALI-
FORNIA BAJA AND RE-ESTABLISHES THE SWLY WINDS ALOFT OVER THE AREA
THURS...WE WILL SEE INCREASED TSRA CHANCES THROUGH FRI. LINGERING
FRONT COMBINED WITH EMBEDDED DISTURBANCES BEING THE MAIN CULPRITS.

EXTENDED GUIDANCE INTO THE WEEKEND WOULD SEEM TO INDICATE THAT WE
WILL NEED SOME MENTION OF POPS AS THE ACTIVE SRN STREAM JET STAYS
IN PLACE OVER THE STATE. 41

MARINE...
LIGHTER WIND REGIME IN PLACE FOR A FEW DAYS. HIGH PRESSURE OVER
THE GULF WILL MAINTAIN THE ONSHORE FLOW. IN GENERAL SHOWERS AND
THUNDERSTORM COVERAGE SHOULD DECREASE THROUGH WEDNESDAY. MAY HAVE
TO WATCH FOR A SURGE OF MOISTURE MOVING THROUGH THE CENTRAL GULF
AND INTO THE UPPER TX COASTAL WATERS THURSDAY WHICH MAY LEAD TO AN
INCREASE IN COVERAGE OF SHOWERS. GRADIENT BEGINS TO TIGHTEN OVER
THE WEEKEND AND SCEC CONDITIONS MAY BE POSSIBLE.
45

AVIATION...
MESSY FORECAST FOR THE EARLY MORNING HOURS. MVFR TO IFR CIGS
COVERING IAH TERMINALS NORTHWARD AND VFR TO MVFR FOR HOU SOUTHWARD
AT 09Z. EXPECT THAT SOME SLIGHT NORTHWARD DRIFT OF LOWER THE CIGS
COULD OCCUR FOR IAH AS REMNANT BOUNDARY WITH MORE EASTERLY WINDS
DRAPED OVER THE REGION FROM 11R-ARM-HOU-BPT SLOWLY LIFTS NORTHWARD
THIS MORNING. THEN MODEL SOUNDINGS (ASSUMING THEY ARE EVEN CLOSE
TO REALITY) SHOW THE CAP ERODING WITH DAYTIME HEATING BY 16-17Z
AND VCTS APPEARS TO BE IN ORDER. SOUNDINGS ALSO SHOW THE POTENTIAL
FOR HEAVY DOWNPOURS AND RELATIVELY SLOW STORM MOTIONS...BY 21Z NAM
SOUNDING DEPICTS SBCAPE OF 3400-3900J/KG/K-INDEX OF 30-33/WEAK
SHEAR SO THINK THAT PULSE TYPE STORMS ARE LIKELY WITH PRIMARY
IMPACTS GUSTY WINDS AND VISBY REDUCTIONS DUE TO HEAVY DOWNPOURS.
NO TEMPOS FOR TSRA YET IN THE FORECAST AS DIFFERENTIAL
HEATING/RETREATING BOUNDARY WILL PROBABLY BE THE MAIN DRIVERS.
45

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      86  72  87  71  84 /  40  10  20  20  40
HOUSTON (IAH)              87  73  88  74  87 /  30  10  20  10  30
GALVESTON (GLS)            84  77  85  77  84 /  20  10  10  10  20

&&

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

$$

DISCUSSION...14



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