Area Forecast Discussion
Issued by NWS Houston/Galveston, TX
Issued by NWS Houston/Galveston, TX
175 FXUS64 KHGX 212346 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 646 PM CDT Thu Aug 21 2025 ...New AVIATION... .KEY MESSAGES... Issued at 1204 PM CDT Thu Aug 21 2025 - Increase in shower/storm coverage today through Friday with locally heavy rainfall possible. - Rain chances lower over the weekend, but should rise again next week as another weak boundary approaches the area. && .DISCUSSION... Issued at 1204 PM CDT Thu Aug 21 2025 A weak, diffuse, slow-moving (and even stationary at times) boundary will be progressing southwards through the region through late tomorrow night. This will allow for higher rain chances across SE Texas, however what will ultimately be driving the when and where of thunderstorm development will be daytime heating and mesoscale interactions like boundary collisions. These boundary collisions will be either outflows between the storms themselves, or with the daily sea breeze. The boundary pushing southwards across the region is really only helping by increasing upper-level support for development as weak vort maxes slide across the boundary. While activity will be possible across the area, coverage is still expected to be highest along and south of I-10 where I-10s. High PWATs will lead to the possibility of locally heavy rainfall of up to 1-2" in isolated strong storms. WPC maintains a Marginal Risk (level 1 of 4) of excessive rainfall for today and Friday. Rain chances continue through the weekend, but coverage is expected to be less with activity confined along the coast associated with the sea breeze. Rain chances increase by Tuesday or Wednesday of next week as another boundary approaches from the north with upper-level northwest flow developing. This northwest flow pattern will likely lead to increased thunderstorm chances through the remainder of the week as weak disturbances embedded in the flow pass through the area. Continued summer-time heat will persist with highs generally in the 90s and lows in the 70s. Afternoon heat indices will rise into the triple digits, so be sure to stay hydrated if preforming strenuous outdoor activities. Fowler && .AVIATION... (00Z TAF Issuance) Issued at 627 PM CDT Thu Aug 21 2025 A messy afternoon/early evening with scattered showers and thunderstorms. A few of these storms are strong, capable of producing small hail, gusty winds, and heavy downpours. This activity will continue at some terminals through 02-03Z. The next aviation concern arrives late this evening into the overnight. Some Hi-res models bring a complex of storms moving NE to SW across the area, impacting IAH, HOU and CXO terminals after 05Z Friday. At the moment, the probability of occurrence remains low, therefore, did not mention this activity in TAFs. Will continue to monitor trends in the next few hours and amend accordingly. Another round of showers and storms are possible on Friday with the best chances in the afternoon. Given uncertainty in coverage and timing, will continue with PROB30, mainly in the afternoon. JM && .MARINE... Issued at 1204 PM CDT Thu Aug 21 2025 A weak, diffuse boundary slowly making its way through the area will lead to increased coverage of showers and thunderstorms through Saturday. Light winds and low seas will continue to prevail through the start of next week. Even though this boundary will be moving through the coastal waters over the next couple of days, it is so diffuse that wind directions will still ultimately be decided by the land breeze/sea breeze: offshore in the overnight and morning periods, and onshore in the afternoons and evenings. Locally higher winds and seas, and locally heavy rainfall will be possible with any storms. Fowler && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 74 92 73 93 / 30 60 20 30 Houston (IAH) 75 92 76 92 / 40 70 30 50 Galveston (GLS) 80 89 81 89 / 60 70 70 70 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$ DISCUSSION...Fowler AVIATION...JM MARINE...Fowler