Area Forecast Discussion
Issued by NWS Houston/Galveston, TX
Issued by NWS Houston/Galveston, TX
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992 FXUS64 KHGX 091121 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 621 AM CDT Thu May 9 2024 ...New AVIATION... .SYNOPSIS... Issued at 340 AM CDT Thu May 9 2024 Early season heat takes center stage for one more afternoon, then we look warily northwest to see what...if anything...comes our way tonight bearing any threat for severe storms. Temperatures will tone down going into the end of the week after a weak cold front, turning the focus of the forecast to rainfall potential Sunday into Monday. A few key takeaways: - Look for peak heat index values to again rise to around or over 100 degrees away from the Gulf this afternoon thanks to humid conditions and high temperatures around 90 degrees. This first multi-day stretch of above-average heat is a good chance to stretch out those heat safety muscles, as summer is rapidly arriving. - Meanwhile, over North and Central Texas, we expect storms to get going late in the afternoon, and make their way eastward. In general, the highest threat is to the north, with a less favorable environment southward. A threat level 3 of 5 (Enhanced Risk) exists northward of a line roughly from College Station to Livingston. A threat level 2 of 5 (Slight Risk) exists southward of there to roughly I-10. A threat level 1 of 5 (Marginal Risk) is in place for much of the area south of I-10. The primary threat in the afternoon will be large hail, potentially even significant hail larger than 2 inches in diameter. The primary threat will shift more towards damaging wind gusts in the evening. An isolated tornado is a lesser concern, but cannot be ruled out. - We`re also still watching the potential for locally heavy rainfall on Sunday and Monday from another round of showers and thunderstorms. WPC indicates a Marginal to Slight risk of excessive rain each day (threat levels 1 and 2 of 4). Continue to monitor the forecasts heading into the weekend for the latest analysis. && .SHORT TERM... (Today through Friday Night) Issued at 340 AM CDT Thu May 9 2024 Oh, it`s starting to feel a lot like summer...everywhere you sweat... We`ve been talking about this for several days now, so I don`t want to risk beating this point too frequently, but early season heat continues to be a sneaky threat for heat exhaustion and heat stroke, as the numbers are lower than we see in the teeth of summer, but our bodies aren`t quite acclimated to it yet. The same situation is there today, thanks to highs again around 90 degrees with a peak heat index around or just over the century mark (except on the Gulf, things look a bit cooler there). Hang in there, today will be last day with widespread above average heat, and things will continue to moderate just a bit into next week. But if you love it hot, don`t worry - there`s a lot more where this came from. Of course, with temperatures this high and ample moisture in place, evidenced by widespread dewpoints in the middle 70s, we`ve got a deep pool of thunderstorm fuel in place, but like yesterday, we`ll largely be in search of a mechanism for initiation. That mechanism exists off to the northwest of our area along a dryline, and eventually, an incoming "cold" front. Eventually, storms that fire away from our area, may become a concern as they push eastward off the initiating boundary. mean HREF SBCAPE values exceed 4000 J/Kg in our northwest closest to the initiation region. The max values start to get a little stupid, exceeding 5000 J/Kg. Should any storms manage to push their way in from the west/northwest, that instability combined with shear in excess of 30 knots should sustain any storms that come into the area. The big question again is...do any storms get in here at all? Convective initiation should again focus well to the north of the area, where there`s much better forcing. Still, late this afternoon into the overnight hours does look to feature a small shortwave trough passing aloft, which could be enough to get some isolated storms going. Given the big amounts of instability at play, the initial threat...mostly out of our area, but perhaps sneaking into the northwest if they move in early enough, will be large hail, potentially greater than 2 inches in diameter. Eventually, as the sun sets, and we lose that pool of extreme instability, we`ll likely see any development there is grow upscale along/ahead of the incoming front for the overnight hours. The threat should then transition from hail to large swaths of damaging straight line wind gusts, though a brief tornado can`t be totally ruled out either. One important note with today`s setup - because our primary question is convective initiation, many of us, even in the enhanced risk area, may well see nothing at all. Can`t have severe storms if there aren`t any storms to begin with! But also, with our north on the edge of the pool of extreme instability, if we get a couple storms to pop up, we can expect them to cook. Any storms that do make their way through the area should be moving on to the east and out of our portion of Southeast Texas not too long after midnight. Behind them, a weak "cold" front looks to push its way through the area to the Gulf by Friday morning. It will help tamp down temperatures modestly, but do not get too excited here. Cold air advection behind the front will be limited, and while the post-frontal airmass will also be modestly drier, our main achievement will be to see dewpoints drop out of the 70s. Indeed, this time of year, while we can expect to see some slight cooling well inland, the day after a cold front on the coastal plain is often just as...or even a bit hotter than the day before, thanks to seeing more sun and the more efficient heating of drier air. I was pleasantly surprised to see the NBM actually catch onto that for once, and mostly rolled with its temperatures rather than trying to Frankenstein together an inland and a coastal high temperature forecast. Finally, we should see whatever modest relief we`re going to see behind this front settle deeper into the area Friday night. Except within a county of so of the Gulf, we can expect low temps Friday night to make it below 70 degrees. && .LONG TERM... (Saturday through Wednesday) Issued at 340 AM CDT Thu May 9 2024 Surface high pressure slides east through the Southern Plains on Saturday, allowing onshore flow to gradually return during the day. Remnants of the frontal boundary will gradually lift north as a warm front Saturday night, suppling additional moisture and bringing PWs of 1.5-2.0 inches. Lifting from the boundary will be further supplemented by weak impulses aloft from a cutoff low over the Desert Southwest. This should produce scattered showers and storms, beginning over out west/southwestern counties early Sunday and spreading to the remainder of SE Texas later that morning. Around this point, the closed low/trough will be near the TX/OK Panhandle, providing additional lift as stronger impulses pass over the area. Combining this forcing with the lifting warm sector should allow for more widespread showers/thunderstorms to develop during the afternoon/evening. Forecast soundings also suggest high precipitation efficiency in this environment, favoring the potential for locally heavy rainfall. WPC has portions of SE Texas under a Slight (level 2/4) to Marginal (level 1/4) Risk of excessive rainfall for Mother`s Day on Sunday. Shower/storm activity should briefly decreases during the overnight hours as the main forcing axis from the upper level trough slides eastward towards the Mississippi River Valley. Global models indicate another shortwave trough passing overhead on Monday, bringing an additional round of thunderstorms. Forecast soundings seem to suggest sufficient shear & instability available for stronger storms to develop during this period. Additionally, these storms will still be capable of producing locally heavy rainfall, and thus WPC has maintained a Slight (level 2/4) to Marginal (level 1/4) Risk of Excessive rainfall over portions of SE Texas on Monday. Forecasted rainfall totals from Sunday through Monday night will be around 1-3" with the highest amounts expected generally north of the I-10 corridor. Rain chances diminish into early Tuesday morning as PWs drop under 1.0" in the wake of the shortwave & upper trough. This will bring calmer, more benign weather for Tuesday with highs in the 80s to lower 90s. However, moisture begins to return Tuesday night, with rain chances returning on Wednesday and continuing late into the week. && .AVIATION... (12Z TAF Issuance) Issued at 621 AM CDT Thu May 9 2024 Frustration potential with this forecast is high to say the least. MVFR at best around the area early this morning, with pockets of IFR or LIFR. This is likely to be a bit variable but remaining in this range to start, gradually improving to a hazy VFR for the afternoon. Big uncertainty in possible storms this evening. May see severe storms...or may see nothing, and probably nothing in between. Went conservative and sketched out VCTS at sites where, if storms do occur, are most likely to be in the neighborhood. Certainly not enough confidence for even a TEMPO at this point. Once storms clear, weak front will move through. Eventually will turn winds more north/northeasterly, but will likely get a stretch of light/VRB winds first. Incoming airmass likely not enough of a change to prevent return to MVFR conditions overnight. && .MARINE... Issued at 340 AM CDT Thu May 9 2024 Light to moderate onshore flow is expected today ahead of a frontal boundary. This persistent fetch will bring seas of 3-6 feet in the Gulf and elevated tide levels along the coast. High flows from rivers, creeks and streams will lead to above normal water levels in the bays and intercoastal water way this week, which may make navigation difficult at times. A cold front will push offshore during the early morning hours of Friday. Moderate offshore winds behind the front may warrant caution flags into the weekend. Onshore flow returns Saturday night/Sunday as a warm front moves onshore. Periods of showers and thunderstorms will be possible from Sunday through early next week. && .HYDROLOGY... Issued at 426 PM CDT Wed May 8 2024 Updated 340 AM CDT Thu May 9 2024 A slightly higher chance for thunderstorms exists again today, but is still not expected to be widespread enough to result in any additional areal flooding. Although there have been decreases in the water levels along the rivers, some will remain swollen for days (possibly weeks). Do NOT go around barricades and stay out of the floodwaters. Do NOT return to homes until officials deem that it is safe. River flooding continues for parts of Southeast Texas, particularly along portions of the Trinity river. The following river points are at Moderate or Major flood stage as of Wednesday afternoon: - Trinity River (Liberty): Major Flood Stage - Trinity River (Goodrich): Moderate Flood Stage - Trinity River (Moss Bluff): Major Flood Stage - Trinity River (Riverside): Moderate Flood Stage Remember to heed any instructions from your local officials and to never travel through flooded areas or roadways. TURN AROUND, DON`T DROWN. Please monitor updated forecasts via the NWS AHPS website and/or the new NWS NWPS webpage (https://water.noaa.gov/) as the river flood threat continues. Also of note is that the downstream runoff from the previous rainfall will cause continued rises along the Brazos River through the end of the week. 24/Luchs && .CLIMATE... Issued at 340 AM CDT Thu May 9 2024 Hobby Airport keeps the record high minimum train rolling, breaking the daily record again yesterday. The low of 78 degrees eclipsed the previous record of 77, set all the way back in 2022. && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 89 69 83 64 / 20 30 10 10 Houston (IAH) 90 72 88 68 / 10 10 10 10 Galveston (GLS) 82 75 84 72 / 10 10 10 0 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$ SHORT TERM...Luchs LONG TERM....03 AVIATION...Luchs MARINE...03