260 FXUS64 KHGX 180129 AFDHGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX 829 PM CDT SUN APR 17 2016 .AVIATION... SHOWERS AND THUNDERSTORMS DEVELOPING IN A SWATH FROM NEAR BYY-BAY CITY TO LVJ-PEARLAND TO CLL-COLLEGE STATION WHERE LL CONVERGENCE APPEARS TO BE MAXIMIZED. BROAD DIFFLUENCE ALOFT WITH A MOIST SOUNDING TO NEAR 600 MB WITH ONGOING DEEP CONVECTION. HAVE MADE SOME CHANGE TO TAFS TO HIGHLIGHT THE PREVAILING NATURE OF STORMS THROUGH THE NEXT 12-24 HOURS. GUIDANCE IS ALL OVER THE PLACE ON WHERE THE HEAVIEST RAINFALL WILL OCCUR AND TIMING...AM EXPECTING THE SWATH OF STORMS TO CONTINUE AND PROBABLY SLOWLY SHIFT FURTHER NW AND N WHICH WILL KEEP MOST TERMINALS IMPACTED BY AT A MINIMUM SHOWERS AND PROBABLY TSRA AT TIMES. SOUNDING FROM TAMU CLL JUST CAME IN AND IT IS JUICY...1.8 PW/K INDEX 40/CAPE 1650 AND 0-1KM SRH OF 200. THINK THAT BIG IMPACTS FROM STORM CLUSTERS MAY OCCUR AFTER 12Z FOR IAH/HOU (AFTER THIS EVENINGS). CIGS SHOULD LOWER OVER THE EVENING AND MVFR WILL PREVAIL BETWEEN 1000-2000FT. LOWER CIGS/VISBY WITH STORMS. 45 && .PREV DISCUSSION... /ISSUED 358 PM CDT SUN APR 17 2016/ DISCUSSION... RECENT THINKING IS THAT...WITH ALL OF THE METEOROLOGICAL INGREDIENTS IN PLACE...THE (FLASH) FLOOD THREAT IS STILL ALIVE AND WELL FROM THIS EVENING THROUGH TUESDAY. THE SLOW CHURNING BROAD UPPER LOW CENTERED OVER THE FOUR CORNERS REGION IS THE WESTERN LOW IN WHAT HAS BECOME AN OMEGA BLOCKING PATTERN. THE NEAR ZERO MOVEMENT OF THE WESTERN ATLANTIC LOW...WITH A CENTRAL CONUS RIDGE WEDGED IN BETWEEN THESE TWO LOWS...WILL ULTIMATELY BE THE IMPETUS TO WHAT IS SHAPING UP TO BE AN ACTIVE 36 HOURS. AS MENTIONED ABOVE AND IN PREVIOUS AFDS...ALL OF THE ELEMENTS THAT YOU NEED FOR FLASH FLOODING LEADING TO RIVER FLOODING ARE IN PLACE. SECONDARY THREATS WILL BE DAMAGING STORM DOWNBURST WINDS AND HAIL. UNLESS THIS DOWNSTREAM RIDGE AND ATLANTIC LOW SUDDENLY DECIDE TO SHEAR OUT AND RELEASE THIS BLOCKING FLOW PATTERN...HIGH RAINFALL WILL NOT BECOME A MATTER OF 'IF' BUT OF 'WHEN AND WHERE'. AS OF NOW THE RECENT HIGH RESOLUTION MODELING HAVE BEEN OF LITTLE TO NO HELP...CONFIDENCE IS GREATEST THAT EITHER A CENTRAL TEXAS FORMING MCS OR LARGE SCALE NORTH TO SOUTH QLCS WILL DEVELOP SOMETIME MONDAY. TRAINING THUNDERSTORMS WILL LIKELY PRODUCE 2 TO 3 INCH PER HOUR AMOUNTS...LOCALLY UPWARDS OF 3 TO 4 INCHES (AS EVIDENCED BY THIS AFTERNOON'S CLUSTERING OVER THE BASTROP/SMITHVILLE AREA). THUS ..WITH SLOW STEERING VECTOR MOTION...IT WILL NOT TAKE MUCH TIME TO PRODUCE GREATER THAN 8 INCH AMOUNTS OVER THOSE AFFECTED COUNTIES. THIS EVENT COULD COMMENCE AS EARLY AS THIS EVENING AND PERSIST THROUGH MID WEEK. SINCE THIS SCENARIO WILL BECOME MORE MESO-DRIVEN IN TIME...THE FINER DETAILS OF THE TIMING AND LOCATION OF THE HIGHEST RAINFALL WILL COME WITH SHORT TERM FORECASTS WHILE CLOSELY MONITORING RADAR/RAINFALL RATES. THE UPSTREAM RIDGE BREAKS DOWN GOING INTO MIDWEEK...ALLOWING SOUTHWESTERLY /DIFFULENT FLOW ALOFT TO BECOME MORE ZONAL WEDNESDAY. A COLD FRONTAL PASSAGE INTO A SOMEWHAT RE-CHARGED RESIDENT AIR MASS (1.4-1.5 INCH PWATS) WILL PICK THURSDAY'S RAIN CHANCES BACK UP TO HIGH CHANCE- LOW LIKELY PROBABILITIES. BACKING HIGH PRESSURE WILL DESCEND DOWN FROM THE SOUTHERN PLAINS AND BEGIN FEW DAYS OF DRY WEATHER GOING INTO THE WEEKEND. DAY-TO-DAY TEMPERATURE FORECASTS WILL FOLLOW A NEAR SIMILAR DIURNAL CURVE...UPPER 60 TO LOW 70 DEW POINTS WILL MAINTAIN HIGHER HUMIDITY LEVELS THROUGH FRIDAY MORNING...OR BEFORE THE THURSDAY BOUNDARY PASSAGE. DAILY MINIMUMS TEMPERATURES WILL GENERALLY BE IN THE MID-UPPER 60S WITH DAILY MAXIMUM TEMPERATURES IN THE UPPER 70S TO NEAR 80 F. MARINE... A COASTAL FLOOD WARNING REMAINS IN EFFECT FROM PORT OCONNOR TO HIGH ISLAND AS TIDE LEVELS REMAIN 1.5 TO 3.0 FEET ABOVE NORMAL. THIS WILL BRING WATER LEVELS TO NEAR 4 FEET IN A FEW PLACES AT HIGH TIDE. HWY 87 HAS BECOME WATER COVERED AT TIMES AND TODDVILLE ROAD HAS BEEN WATER COVERED AT TIMES. WINDS ARE EXPECTED TO BECOME SE AND GRADUALLY DECREASE ON MONDAY AND THREAT FOR COASTAL FLOODING SHOULD BEGIN TO DIMINISH DURING THE DAY. A TIGHT PRESSURE GRADIENT BETWEEN LOW PRESSURE OVER SW TX AND HIGH PRESSURE TO THE EAST WILL MAINTAIN MODERATE TO STRONG E-SE WINDS TONIGHT. A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE GULF WATERS AND ADJACENT BAYS THROUGH 12Z MONDAY AND MAY NEED TO BE EXTENDED FOR THE GULF WATERS ON MONDAY MORNING. SEAS WILL RANGE BETWEEN 6 AND 9 FEET TONIGHT. WINDS SHOULD DROP BELOW ADVISORY CRITERIA ON MONDAY NIGHT AND SPEEDS WILL SLOWLY FALL THROUGH THE END OF NEXT WEEK. IN ADDITION TO THE WINDS...WAVES AND ELEVATED TIDES...MARINE REPORTS INDICATE SOME LIGHT SEA FOG WITH VISIBILITIES BELOW 3 MILES IN A FEW LOCATIONS. STRONG WINDS SHOULD PROVIDE ENOUGH MIXING TO LIMIT THE FOG THREAT AND MAINTAIN VSBY AOA 3 MILES. 43 && .PRELIMINARY POINT TEMPS/POPS... COLLEGE STATION (CLL) 68 75 66 78 66 / 100 100 90 60 20 HOUSTON (IAH) 70 77 67 77 67 / 90 90 90 70 30 GALVESTON (GLS) 70 75 70 75 70 / 60 70 80 80 30 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...FLASH FLOOD WATCH THROUGH TUESDAY 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. COASTAL FLOOD WARNING UNTIL 1 PM CDT MONDAY FOR THE FOLLOWING ZONES: BRAZORIA...CHAMBERS...GALVESTON...HARRIS...MATAGORDA. GM...SMALL CRAFT ADVISORY UNTIL 7 AM CDT MONDAY FOR THE FOLLOWING ZONES: GALVESTON BAY...MATAGORDA BAY. SMALL CRAFT ADVISORY UNTIL 11 AM CDT MONDAY FOR THE FOLLOWING ZONES: WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL 20 NM TO 60 NM...WATERS FROM FREEPORT TO THE MATAGORDA SHIP CHANNEL OUT 20 NM...WATERS FROM HIGH ISLAND TO FREEPORT 20 TO 60 NM...WATERS FROM HIGH ISLAND TO FREEPORT OUT 20 NM. && $$ DISCUSSION...41 AVIATION/MARINE...45