Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 171738
AFDHGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
1238 PM CDT FRI APR 17 2015

.DISCUSSION...
SEE 18Z AVIATION DISCUSSION.

&&

.AVIATION...
SHORT TERM GUIDANCE REMAINS BULLISH WITH AN EAST-WEST LINE OF
SHRA/TSRA DEVELOPING LATE THIS AFTN. NOT EXACTLY SURE WHERE THESE
SHRAS WILL DEVELOP AND BROAD BRUSHED THE AREA WITH VCSH/VCTS WITH
A TEMPO GROUP BETWEEN 22-02Z. SOME OF THE STORMS COULD PRODUCE
GUSTY WINDS THIS EVENING. AN MCS WILL APPROACH SE TX LATE TONIGHT
INTO EARLY SATURDAY. SINCE TIMING THESE FEATURES IS TOUGH...WILL
JUST GO WITH A VCTS FOR NOW. 43

&&

.PREV DISCUSSION... /ISSUED 1125 AM CDT FRI APR 17 2015/

UPDATE...
THE ANTICIPATION FOR ANOTHER ACTIVE DAY IS BRIMMING...MORNING
UPDATE SHOWS MINOR TWEAKS TO POPS/QPF TO COMMUNICATE THE THREAT
FOR THE PASSAGE OF A LATE DAY INTO EVENING MCS OR QLCS. VICIOUS
LOOKING SHORTWAVE DISTURBANCE MOVING ACROSS BAJA THAT...WHEN
COUPLED WITH THE SPEED MAX WORKING ITS WAY INTO WESTERN TEXAS...
WILL LIKELY BE ALL THE TRIGGER NEEDED IN RE-DEVELOPING LATE AFTERNOON
THROUGH EVENING REGIONAL RAIN AND NUMEROUS STORM ACTIVITY. UPPER
LEVEL SUPPORT WILL COME FROM SE TEXAS FALLING UNDER THE LF QUAD
AND FROM AMPLE SPREADING OF 25-3H WINDS/DIFFULENCE IN RESPONSE TO
THE LARGE SLOW-MOVING MID-UPPER LOW CENTERED OVER THE FOUR CORNERS.
RECENT SUBSIDENCE FROM LAST NIGHT`S ACTION HAS CREATED A EASTERN
MESO-HIGH THAT HAS AIDED IN CLEARING MORNING SKIES OUT. PLENTY OF
MORNING SUN WILL SPIKE TEMPERATURES INTO THE 80S OVER THE NEXT
HOUR OR TWO...SO THERE SHOULDN`T BE MUCH PROBLEM OF BREAKING THE
MID-LEVEL CAPPING NOTED ON THE 12Z CRP SOUNDING. 1.7 TO 1.8 INCH
PWATS ARE LOCKED IN PLACE WITH THE BACKGROUND OF LL SE FLOW
SUPPORTING CONTINUED MOISTURE FLUX AND MAY LIKELY PROVIDE THE
NEEDED INFLOW INTO ANY MCV/MCD THAT TRUCKS THROUGH BETWEEN 20Z AND
06Z TONIGHT. WIND PROFILE IS VEERED AND THIS WAA REGIME ADDS
PLENTY OF SUPPORT TO THE ARGUMENT THAT THE MAIN THREATS WILL BE
HEAVY RAINFALL LEADING TO FLOODING AND STRONG STORM WINDS.
SECONDARY THREATS WILL BE LARGE HAIL...ESPECIALLY IF ANY DISCRETE
CELLS PULSE UP QUICKLY (LIKE YESTERDAY AFTERNOON OVER WESTERN
HARRIS COUNTY). THE PROG SOUNDINGS ALSO DISPLAY SUB 11K FT WBZ
HEIGHTS THAT LEAN TOWARDS MANY STRONGER CELLS (SAY 50 DBZ ABOVE
20K FT) PRODUCING AT LEAST NICKELS. OVERALL...THERMO PROFILES ARE
VERY AGGRESSIVE ONCE AGAIN WITH LARGE CAPE AND SEVERE INDICES
(ONCE LOW 80S CONVECTIVE TEMPS AREA MET).

NATIONAL CENTERS SPC AND WPC HAVE CENTERED AN ENHANCED OUTLOOK FOR
SEVERE AND MODERATE EXCESSIVE RAINFALL CHANCES...RESPECTIVELY...
OVER THE FORECAST AREA TODAY. THERE IS AN AREAWIDE FLOOD WATCH IN
EFFECT THRUOGH TOMORROW MORNING. FLASH FLOOD GUIDANCE STATES THAT
HARRIS...FORT BEND...CHAMBERS AND LIBERTY COUNTIES ARE THOSE COUNTIES
THAT CAN RECEIVE THE LEAST AMOUNT OF SHORT TERM RAINFALL...1 TO 2
INCH HOURLY RAIN AMOUNT OVER THESE AREAS WILL LIKELY PRODUCE RUN-
OFF FLOODING ISSUES. THROUGH SATURDAY MORNING...THE ENTIRE CWA
(SANS ABOVE COUNTIES) CAN ONLY HANDLE AN ADDITIONAL 2 TO 3 INCHES
OF NEW RAINFALL OVER A COUPLE OF HOURS BEFORE FLOODING WILL OCCUR.
PLEASE STAY AWARE AND CLOSELY MONITOR LOCAL GOVT AND MEDIA OUTLETS
FOR UPDATED FORECASTS AND INFORMATION. 31

PREV DISCUSSION... /ISSUED 724 AM CDT FRI APR 17 2015/

UPDATE...
A QUICK UPDATE TO LOWER RAIN CHANCES THIS MORNING ACROSS THE AREA.
BUT BY LATE MORNING STILL EXPECTING SCATTERED SHOWER AND
THUNDERSTORMS WITH THE POTENTIAL FOR HEAVY RAIN.
45

PREV DISCUSSION... /ISSUED 459 AM CDT FRI APR 17 2015/

DISCUSSION...
VERY HEAVY RAINS YESTERDAY AFTERNOON AND OVERNIGHT JUST A TASTE OF
WHAT IS TO COME. SHOWERS AND THUNDERSTORMS THIS MORNING FROM
AROUND THE NEARSHORE WATERS OFF OF MATAGORDA BAY TO FREEPORT TO
MONT BELVIEU TO DAYTON WITH A GENERAL WEAKENING TREND INLAND WHILE
THE STORMS IN THE OFFSHORE WATERS HAVE BEEN GETTING A LITTLE MORE
ORGANIZED WITH DEEPER ROTATION. MESO HIGH OVER SW LA APPARENT UP
THROUGH 850MB APPEARS TO BE HELPING REINFORCE THE DEEPER AND
STRONGER EASTERLY LL FLOW BUT AS THE LA SYSTEM PULLS AWAY THE LL
EASTERLY FLOW SHOULD WEAKEN. AS THIS S/W THAT GOT THESE STORMS
FIRED UP OVERNIGHT DEPARTS TO THE EAST AM EXPECTING THE LL FLOW TO
GRADUALLY WEAKEN AND BEGIN TO VEER TO THE SOUTHEAST AND SOUTH.
THIS WILL BRING BACK IN THE ANOMALOUSLY HIGH PW VALUES AND SET THE
STAGE FOR MORE STORMS THIS AFTERNOON AND TONIGHT. AS THE
SUBTROPICAL JET PROGRESSES EASTWARD TODAY AND THE SPEED MAX OVER
MEXICO AND RIO GRANDE AREA NEAR DRT SHIFTS INTO THE AREA EXPECTING
THAT STORMS SHOULD REDEVELOP OVER THE REGION THIS AFTERNOON BUT BE
MORE SCATTERED IN NATURE AND NOT WELL ORGANIZED...BUT LATE THIS
AFTERNOON AND TONIGHT WILL BE A DIFFERENT STORY. A LARGE MCS
SHOULD DEVELOP IN THE AREA TO THE WEST OF SAN ANTONIO GETTING
LARGER AND MORE ORGANIZED AS IT MOVES TOWARD SETX. IT SHOULD GET
INTO THE WESTERN AREAS EARLY THIS EVENING (OR POSSIBLY LATE THIS
AFTERNOON...AS SOME OF THE HIGH RES MODELS INDICATE) AS MOST OF
THE LARGER SCALE GUIDANCE SUPPORTS. VERY LARGE SCALE LIFT WITH
THE STRONGLY DIFFLUENT PATTERN ALOFT AND ABUNDANT INSTABILITY TO
WORK WITH SHOULD PROMPT WIDESPREAD RAINFALL FOR SETX. THE FLOOD
WATCH HAS BEEN EXTENDED TO 12Z SATURDAY BUT IT MAY NEED EXTENDING
INTO SATURDAY AFTERNOON...FOR THE POSSIBILITY OF MORE STORMS
SATURDAY MORNING AND EARLY AFTERNOON THOUGH MAINLY OVER THE
CENTRAL AND EASTERN AREAS. RAINFALL TOTALS FROM THIS MORNING
THROUGH SATURDAY MORNING - WIDESPREAD 0.5-1 INCH WITH ISOLATED TO
SCATTERED TOTALS OF 3 TO 6 INCHES. OBVIOUSLY IF THESE HEAVIER
AMOUNTS FALL ON THE AREAS HARDEST HIT YESTERDAY AND THIS MORNING
(OR FOR THAT MATTER THE COASTAL AREAS FROM EDNA TO CLEAR LAKE)
THEN SIGNIFICANT FLOODING WILL BE MUCH MORE LIKELY.

SEVERE THREAT STILL ON FOR TODAY...PRESENCE OF THE LL BOUNDARY
LIFTING NORTH THROUGH THE AREA-VERY HIGH INSTABILITY WITH CAPE
VALUES OF 2200-3700 J/KG AND LI OF -5 TO -10-SHEAR STARTS OUT HIGH
THIS MORNING BUT DECREASE THROUGH THE AFTERNOON HOURS AS LL FLOW
VEERS BUT STILL ENOUGH TO SUPPORT SEVERE THREAT. IF WE REACH ANY
POCKETS OF MID 80S WE MAY SEE MORE PULSE SEVERE THIS AFTERNOON. TODAY
IT RANGES FROM DAMAGING WINDS AND BRIEF TORNADOES THIS MORNING...SHIFTING
TO HAIL AND DAMAGING WINDS THIS AFTERNOON...STORMS OVERNIGHT MAY
POSE MORE OF A DAMAGING WIND AND HAIL THREAT THAN TORNADO BUT
CAN`T RULE BRIEF ONES OUT.

SUNDAY AND BEYOND SURFACE LOW MOVES FROM TX/OK INTO GREAT LAKES
REGION AND 850 FLOW SWINGS AROUND TO THE NORTH WITH DRYING AS
A COLD FRONT PUSHES OFF THE COAST EARLY MONDAY. GUIDANCE SHOWING
SOME DIFFERENCES AFTER THE FROPA GOING INTO TUESDAY AND WEDNESDAY.
EXPECT MONDAY AFTERNOON AND TUESDAY MORNING TO BE PLEASANT ACROSS
THE AREA THEN RAIN CHANCES INCREASE AGAIN AS ENTRANCE REGION OF
THE SUBTROPICAL JET CROSSES THE REGION TUESDAY AFTERNOON. WARMING
BACK UP AND GETTING MORE HUMID AGAIN WITH THE RETURN OF SE FLOW.
ANOTHER DEEP TROUGH SETTING UP SHOP OVER THE DESERT SW AND
POSSIBLY THE FOUR CORNERS AREA AGAIN FRIDAY AND SATURDAY...FOR MORE
RAIN AGAIN NEXT SATURDAY. 45

MARINE...
ELEVATED WINDS CONTINUE ACROSS PORTIONS OF THE COASTAL
WATERS EARLY THIS MORNING AND A SMALL CRAFT ADVISORY IS IN EFFECT
FOR THE NEARSHORE WATERS FROM HIGH ISLAND TO FREEPORT THROUGH 7 AM
CDT. THUNDERSTORMS OVER THE COASTAL WATERS THIS MORNING WILL
CONTINUE TO PRODUCE STRONG WINDS AND SEAS... IN ADDITION TO HEAVY
RAINFALL THAT WILL LIMIT VISIBILITIES. THUNDERSTORM CHANCES WILL
CONTINUE OVER THE COASTAL WATERS OVER THE NEXT SEVERAL DAYS AS A
SERIES OF DISTURBANCES APPROACH THE REGION FROM THE WEST. THE NEXT
ROUND OF THUNDERSTORMS IS EXPECTED OVER THE COASTAL WATERS THIS
EVENING AND INTO THE OVERNIGHT HOURS AS A THUNDERSTORM COMPLEX
DEVELOPS OVER CENTRAL TEXAS AND PUSHES EAST TOWARDS THE GULF...
WITH A SECOND THUNDERSTORM COMPLEX POSSIBLY REACHING THE COASTAL
WATERS AGAIN ON SATURDAY AFTERNOON AND EVENING. FREQUENT
LIGHTNING... STRONG WINDS... AND HEAVY RAIN WILL BE POSSIBLE WITH
ANY THUNDERSTORM.

ONSHORE FLOW WILL PERSIST THROUGH THE WEEKEND WITH HIGH PRESSURE
OVER THE EASTERN GULF AND LOW PRESSURE OVER THE HIGH PLAINS. BY
MONDAY... A PASSING UPPER TROUGH WILL HELP SEND A COLD FRONT ACROSS
THE COASTAL WATERS. OFFSHORE FLOW WILL BE SHORT-LIVED IN THE WAKE OF
THIS FRONT HOWEVER... WITH AN EASTERLY FETCH IN PLACE BY TUESDAY AS
SURFACE HIGH PRESSURE SLIDES OVER THE SOUTHEASTERN CONUS.
THUNDERSTORM CHANCES INCREASE OVER THE COASTAL WATERS BY THE MIDDLE
OF NEXT WEEK AS THE NEXT STORM SYSTEM APPROACHES THE SOUTHERN
PLAINS. 14

&&

.PRELIMINARY POINT TEMPS/POPS...
COLLEGE STATION (CLL)      81  66  78  63  83 /  60  80  50  20  20
HOUSTON (IAH)              83  68  79  65  84 /  60  90  60  20  20
GALVESTON (GLS)            80  71  78  70  78 /  50  80  50  30  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...FLASH FLOOD WATCH THROUGH SATURDAY MORNING FOR THE FOLLOWING
     ZONES: AUSTIN...BRAZORIA...BRAZOS...BURLESON...CHAMBERS...
     COLORADO...FORT BEND...GALVESTON...GRIMES...HARRIS...
     HOUSTON...JACKSON...LIBERTY...MADISON...MATAGORDA...
     MONTGOMERY...POLK...SAN JACINTO...TRINITY...WALKER...
     WALLER...WASHINGTON...WHARTON.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL 1 PM CDT THIS
     AFTERNOON 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...31
AVIATION/MARINE...43



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