FXUS64 KHGX 211138 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 638 AM CDT Tue Apr 21 2026 ...New AVIATION... .KEY MESSAGES... - Widespread rainfall expected on Tuesday and Wednesday with potential for locally heavy rainfall that could lead to instances of street flooding. - Daily chances for showers/storms going into the weekend. - Gradual warming trend with temperatures reaching the upper 80s by the end of the work week. && .DISCUSSION... Issued at 1111 PM CDT Mon Apr 20 2026 The radar depicted widespread moderate rain, but only light rain reached the surface. What's the deal?! Was it magic?! Nope...even better...SCIENCE! PW values gradually increased throughout the day up to near the 75th percentile (~1.38") due to the development of a coastal trough/low down near the South TX coast. Moisture gradually increased from west to east and there was even a few rumbles of thunder west of the Brazos River as elevated convection drifted in from our west earlier in the afternoon. Rainfall rates around the San Antonio metro were near 2"/hr leading to instances of flooding, but why did we only see light rain? Drier air above the surface is the answer! Forecast soundings depicted a pocket of drier air around 3km above the surface for most areas in Southeast TX. As the moisture gradually increased, the air above the surface became more and more saturated leading to some raindrops reaching the ground. This is why most of you saw light rain at most today. Now how can we tell that the majority of the rain evaporated? The answer is...our radar! Our radar (the lovely KHGX WSR-88D) is located to the southeast of Houston in northern Galveston County. The radar beam height increases the further you get from the radar...so you may have noticed high reflectivity returns out west, but those returns became lighter as they got closer to the radar. The radar was sampling moderate rain aloft, but through observations at the surface (special thanks to those that used mPING today) we were able to confirm that evaporation aloft was occuring. At times, there were enough raindrops reaching the ground to wet surfaces/roadways, but certainly not enough to cause any rainouts. You might be thinking "why did he write two paragraphs about something from the past?!" I do it for the love of the science! :) Since Tuesday is Big Word Day, I can officially say that science is supercalifragilisticexpialidocious! I can't use more than one big word though because of my hippopotomonstrosesquippedaliophobia. Before y'all ask, yes spell check did just give up on that one. Going into Tuesday though, the drier air aloft goes bye-bye as the atmospheric column becomes fully saturated with an embedded shortwave trough pushing into the region. PW values will be near or above the 90th percentile (~1.58"), so there is potential for locally heavy rainfall. Latest CAM guidance depicts the rain moving in early Tuesday morning, so plan accordingly for your morning commute. Instability on Monday was slim to none, but there will be a bit more in place on Tuesday. Not enough for any worries about strong or severe storms, but enough for some rumbles of thunder. This instability should also be enough for efficient rainfall processes. If heavy rainfall falls over an area for an extended period of time, then this could lead to localized instances of flooding. This is especially the case for urban areas or areas with poor drainage/low-lying areas. As a result, WPC has kept most of Southeast TX in a marginal risk (level 1 of 4) of excessive rainfall on Tuesday. Keep in mind that this is taking into account the somewhat more saturated soils from Saturday's heavy rainfall, which could lead to quicker transitions to runoff. Current QPF totals show a general widespread 1-2", but locally higher amounts will be possible. HREF LPMM shows the potential for isolated spots of 3+". We get a small break from the heavier downpours going into Tuesday night, but another round of rain is expected on Wednesday with another shortwave passing through. Wednesday looks to start out with sporadic showers in the morning. Daytime heating aids in the development of scattered thunderstorms in the afternoon hours. For Wednesday, the marginal risk of excessive rainfall is currently mainly for areas east of the Brazos River and south of Conroe. Convective coverage is not anticipated be as expansive as what we see on Tuesday, but it still warrants keeping an umbrella with you. As a matter of fact, go ahead and keep that with you for...*checks forecast*...ever. Even though moisture availability decreases going into the end of the work week, there will still be enough in place to pair with additional embedded shortwaves for daily chances of showers and storms. Going into the weekend, we'll be monitoring an upper level low and a frontal boundary pushing into TX. The front itself is not expected to push through our area, but it will help increase chances for showers/storms over the weekend. I know it seems like it's rained every weekend this month...and that's because it has. It's for the greater good though! ~79% of Southeast TX remains in at least a severe drought (not counting this past weekend's rainfall). This rain certainly won't be a drought buster, but every little bit helps! As far as temperatures go, widespread light rainfall led to high temperatures in the mid 60s to low 70s on Monday...so you shouldn't be surprised that the same is expected for Tuesday. Ridging aloft will be in place throughout the work week though leading to a gradual warming trend after Tuesday. High temperatures are expected to be back in the upper 80s by Friday and potentially continuing into the weekend. Just keep in mind that rain chances are present each day, so some tweaks to the temperature forecast could still occur as the week goes on. Low temperatures will be in the 50s/60s for another couple of nights, then only bottoming out in the 60s/70s midweek and beyond. Batiste && .AVIATION... (12Z TAF Issuance) Issued at 606 AM CDT Tue Apr 21 2026 SHRA continues near SGR/HOU southward to LBX/GLS. There have been occasional TS around LBX, moving toward GLS. This batch should move out in the next 2 hours or so. Another batch of SHRA is moving into CLL. Another round of redeveloping SHRA is expected late this morning after 15z affecting most sites. There is a chance of TS, but models show instability struggling with abundant cloud cover. Thus, have only included PROB30s for TS in this set of TAFs, focused on the 18-23z time frame. Cigs will remain VFR, but may drop to MVFR in SHRA/TSRA. After 01-02z, most of the SHRA should diminish for a few hours before some scattered redevelopment after 07z. Cigs will then fall as well to MVFR at all sites, possibly IFR at the northern terminals. For IAH, it appears TS probabilities don't increase again until after 18z Wed. && .MARINE... Issued at 1111 PM CDT Mon Apr 20 2026 Small craft will need to exercise caution through Tuesday afternoon in the Gulf waters. Moderate southeasterly winds persist throughout the day on Tuesday, but will subside going into Tuesday night. The elevated southeasterly winds will lead to an increased risk of rip currents early this week. An extended fetch of moderate southeasterly winds around midweek will likely lead to another round of increased seas, especially in the offshore Gulf waters. This may lead to another period of caution flags on Wednesday into Thursday for the Gulf waters. Increased chances for storms return Tuesday into Wednesday as an upper level disturbance pushes through. Water levels are expected to remain near 3.0 feet above Mean Lower Low Water during high tide cycles through at least the end of the work week. Batiste && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 66 61 80 67 / 90 40 60 0 Houston (IAH) 69 64 80 68 / 80 50 80 10 Galveston (GLS) 76 72 79 74 / 70 50 80 20 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...High Rip Current Risk through late tonight for TXZ436>439. GM...Small Craft Should Exercise Caution through this evening for GMZ350-355-370-375. && $$ DISCUSSION...Batiste AVIATION...Young MARINE...Batiste