Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000 FXUS64 KHGX 310914 AFDHGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX 414 AM CDT FRI JUL 31 2015 .DISCUSSION... OVERNIGHT CONVECTION OVER THE BRAZOS VALLEY CONTINUES TO DIMINISH AS IT EXITS THE FORECAST AREA... WITH VERY WARM TEMPERATURES PERSISTING ACROSS SOUTHEAST TEXAS EARLY THIS MORNING. SURFACE ANALYSIS AT 05Z SHOWED A PLUME OF 75+ DEGREE DEW POINTS DRAPED ALONG THE TEXAS COAST AND EXTENDING INTO NORTHEAST LOUISIANA. THIS... COMBINED WITH LEFTOVER CLOUDS FROM LAST NIGHT/S STORMS... WAS CONTRIBUTING TO HEAT INDICES IN THE LOW TO MID 90S AS OF 3 AM CDT AT A FEW SITES. A WEAK FRONTAL BOUNDARY WAS ALSO ANALYZED ON THIS MAP STRETCHING NORTH TEXAS AND ON INTO NORTHERN LOUISIANA. THIS FRONT WILL PLAY A MAJOR ROLE IN HOW THE WEATHER EVOLVES TODAY FOR THE REGION... BOTH IN TERMS OF THUNDERSTORM CHANCES AS WELL AS CONCERNS ABOUT HEAT. THE 00Z LAKE CHARLES SOUNDING REPORTED A PRECIPITABLE WATER VALUE OF 2.26 INCHES... WITH OVERNIGHT GPS-MET MEASUREMENTS ACROSS THE REGION SHOWING A SIMILARLY MOIST AIRMASS /2.1 TO 2.3 INCHES AROUND THE HOUSTON METRO AND ALONG THE COAST/. HIGH RESOLUTION GUIDANCE IS FAIRLY CONSISTENT WITH DEVELOPING SCATTERED SHOWERS AND THUNDERSTORMS ALONG THE FRONT AS IT SLOWLY DROPS SOUTHWESTWARD TODAY... BUT AGREEMENT IS POOR IN THE ACTUAL TIMING OF THIS FEATURE AND CONSEQUENTLY THE LOCATION OF THE GREATEST AREAL COVERAGE. THE GFS APPEARS TO BE BY FAR THE MOST AGGRESSIVE AND SWEEPS MOISTURE AWAY FROM THE INTERSTATE 45 CORRIDOR AND POINTS EAST BY 18Z. COMPARISON OF SURFACE THETA-E FIELDS HOWEVER /WHICH REPRESENT MOISTURE AND INSTABILITY PRESENT/ REVEAL STABILIZATION FOR THE EASTERN HALF OF THE REGION CLOSER TO 00Z... WITH RELATIVELY GOOD AGREEMENT BETWEEN BOTH HIGHER RESOLUTION AND SYNOPTIC MODELS ON THIS SOLUTION. BASED ON THIS... HIGHLIGHTING HIGHEST RAIN CHANCES WEST OF THE INTERSTATE 45 CORRIDOR TODAY ALONG AND AHEAD OF THE ANTICIPATED FRONTAL POSITION. ADDITIONALLY... A DRY SUB-CLOUD LAYER AND DCAPE VALUES 1100-1300 J/KG THIS AFTERNOON RAISES CONCERNS FOR AT LEAST AN ISOLATED GUSTY WIND THREAT FROM STRONGER THUNDERSTORM ACTIVITY. A LATER FRONTAL PASSAGE ALSO MEANS THAT STIFLING CONDITIONS WILL PERSIST AHEAD OF THE FRONT TODAY AND HAVE GONE AHEAD AND ISSUED A HEAT ADVISORY FOR THE COASTAL COUNTIES OF MATAGORDA... BRAZORIA... GALVESTON... AND CHAMBERS. HEAT INDICES IN THESE AREAS REACHED 109 TO 111 DEGREES YESTERDAY. WITH THE ANTICIPATED SLOW PROGRESSION OF THE FRONT TODAY COMBINED WITH NAEFS ANOMALIES HIGHLIGHTING ANOMALOUS TEMPERATURES AGAIN ALONG THE COAST /A RETURN INTERVAL OF APPROXIMATELY ONCE EVERY 10 YEARS/... WANTED TO HIGHLIGHT THE INCREASED POTENTIAL FOR HEALTH IMPACTS. IF THE FRONT MOVES THROUGH FASTER THAN ANTICIPATED HOWEVER... DRIER AIR FILTERING IN BEHIND THE FRONT WILL ACTUALLY HELP LOWER HEAT INDEX VALUES AND ADVISORY CRITERIA MAY NOT BE MET. FOR THE REMAINDER OF THE SHORT TERM... THE FRONT IS EXPECTED TO PUSH OFF THE COAST TONIGHT. DRIER AIR FILTERING IN BEHIND THE FRONT WILL HELP LIMIT RAIN CHANCES OVER ALL BUT THE COASTAL WATERS ON SATURDAY. THIS SLIGHTLY DRIER AIR MAY ALSO ALLOW FOR SOME OVERNIGHT LOWS IN THE UPPER 60S IN THE PINEY WOODS REGION... WITH LOW 70S TO NEAR 80 POSSIBLE ELSEWHERE. HIGH TEMPERATURES ARE NOT EXPECTED TO DIFFER MUCH FROM TODAY ON SATURDAY BUT A DRIER AIRMASS IN PLACE WILL HELP MITIGATE AGAINST HIGHER HEAT INDEX VALUES. THE REGION WILL REMAIN ON THE EASTERN PERIPHERY OF THE UPPER RIDGE ON SUNDAY AND THROUGH THE REST OF THE FORECAST PERIOD... WITH THE CENTER OF THIS FEATURE SHIFTING A BIT AROUND THE SOUTHERN PLAINS DURING THIS TIME. LOW THUNDERSTORM CHANCES WILL CONTINUE IN THE VICINITY OF THE STALLED FRONTAL BOUNDARY WITH DRY CONDITIONS AND ABOVE NORMAL TEMPERATURES INLAND PERSISTING INTO THE MIDDLE OF NEXT WEEK. HUFFMAN && .MARINE... STORMS HAVE DEPARTED THE WATERS BUT MORE COULD COMING LATE THIS MORNING THROUGH EVENING. WINDS WILL GENERALLY BE VARIABLE NORTHERLY TO EASTERLY ACROSS THE UPPER TEXAS COASTAL WATERS WITH AN AFTERNOON SEABREEZE FORMING. EVENTUALLY A DIFFUSE COLD FRONT SAGS OUT INTO THE GULF WATERS LATE TONIGHT AND WINDS INCREASE SLIGHTLY. 850MB FRONT APPEARS TO STALL WELL OFFSHORE AND SHOULD BECOME A FOCUS FOR REDEVELOPMENT OF SHOWERS AND THUNDERSTORMS BUT PROBABLY JUST SE OF THE UPPER TEXAS COASTAL WATERS. WILL NEED TO KEEP AN EYE ON THE REMAINS OF THE BOUNDARY SATURDAY AFTERNOON-SUNDAY AS THE GULF IS PLENTY WARM ENOUGH AND SHEAR RELAXES. MOISTURE SURGES BACK INTO THE AREA LATE SUNDAY AND SOUTH TO SOUTHEASTERLY FLOW RETURNS AND CONTINUES THROUGH FRIDAY. 45 && .AVIATION... VFR FOR NOW BUT MAY GET A FEW SPOTS WITH MIFG AROUND SUNRISE MAINLY THE MORE RURAL SITES CXO NORTHWARD. CHALLENGING FORECAST FOR TODAY. DRY AIR SHOULD INTRUDE INTO THE REGION FROM THE NORTHEAST BUT A FEW OF THE MODELS APPEAR TOO QUICK TO DRY THINGS OUT. L/V WINDS WILL BE THE NORTH UNTIL THE DIFFUSE FROPA. AM THINKING THAT CLL-HOU-SGR-LBX MAY SEE SOME THUNDER CLOSE BY THIS AFTERNOON AND WILL LIKELY ADD THIS IN THE 12Z PACKAGE IF NOT SOONER. IAH MAY BE ON THE NORTHERN FRINGE OF WHERE POOLED MOISTURE AND SAGGING BOUNDARY INTERACT SO FOR NOW WILL PROBABLY LEAVE VCTS OUT BUT IT WILL BE CLOSE. DEEP MIXING AGAIN TODAY WITH LIGHT WINDS IN THE PROFILE SO STORMS SHOULD BE SLOW MOVING. DRYING NORTHEASTERLY TO EASTERLY FLOW SHOULD OVERSPREAD IAH/HOU BY LATE AFTERNOON/EARLY EVENING LEADING TO CLEAR SKIES. 45 && .PRELIMINARY POINT TEMPS/POPS... COLLEGE STATION (CLL) 98 73 98 74 99 / 30 10 10 10 10 HOUSTON (IAH) 98 74 98 75 99 / 20 10 10 10 10 GALVESTON (GLS) 95 80 94 81 92 / 30 10 10 10 10 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...HEAT ADVISORY FROM 1 PM THIS AFTERNOON TO 7 PM CDT THIS EVENING FOR THE FOLLOWING ZONES: BRAZORIA...CHAMBERS...GALVESTON... MATAGORDA. GM...NONE. && $$ DISCUSSION...14 AVIATION/MARINE...45

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