Area Forecast Discussion
Issued by NWS Houston/Galveston, TXVersions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000 FXUS64 KHGX 252344 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 544 PM CST Thu Feb 25 2021 .AVIATION [00Z TAF Issuance]... The presence of a stationary boundary bisecting the area and persistent conditions favorable for sea fog development will continue to make aviation conditions messy across the board. This package remains largely in sync trends-wise with the 18Z package, with widespread IFR cigs expected to develop at all terminals overnight. Conditions will be further complicated by an expected resurgence of sea fog, which should being visibilities at coastal terminals downward into the morning hours of Friday. Precipitation coverage will remain fairly scattered though an isolated thunderstorm is not out of the question in the vicinity of CLL/UTS. That being said, have maintained VCSH wording at all terminals given expected magnitude and coverage of rainfall. Cady && .PREV DISCUSSION... /ISSUED 332 PM CST Thu Feb 25 2021/ DISCUSSION... In short, the weather is a dreary mess. And it`s not likely to get better at any point for the rest of the week. And, to be honest, there`s not a real strong indication for exactly when a stronger front will sweep through next week to clear things out. The silver lining though, is that while a muddled front underneath a somewhat zonal pattern aloft tends to keep temperature shifts and rainfall amounts fairly muted. So, while a fairly dreary pattern will prevail with a sea fog threat at the coast, those should remain the primary impacts. SHORT TERM [Through Friday Night]... I am tempted to simply write "The weather through Friday night will not be pleasant" and call this section done. Cloud bases are below 1000 feet across a large majority of the area, and sea fog is beginning to encroach on the coast yet again - and this should only get worse as the sun goes down, and what little insolation was able to keep dewpoint spreads wide enough to hold the fog at bay goes away. The main challenge in this period will be temperatures. Not so much in a broad sense - it will be cool behind the front, or front-like substance, draped across our area and warm and humid ahead of it. I expect temperatures for the next day or so to remain fairly recognizable to today, with highs only reaching the upper 50s to 60s in the northwest, while spots on the coastal plain and lower Trinity Valley reaching up into the 70s. In between will depend very strongly on just where the discontinuity between these two air masses ends up. I did my best, but fully expect that someone`s forecast will be very off because they ended up on the wrong side of the boundary. As far as precipitation goes, it`s pretty safe to say that drizzly, misty, light rainy conditions will be the norm, with a chance for an embedded thunderstorm or two tonight - mainly well north of Houston - as an upper trough rolls along the Red River Valley to our north. At the coast, thunder potential will be lower to non-existent, but what we lack in flashy-flashy boom-booms, we more than make up for in fog potential. The sun is going down, winds are backing slightly to emphasize the "east" in southeasterly, and sea fog is already starting to push back towards the coast. Galveston`s visibility has dropped to 1/2 mile and visibility is worsening rapidly on coastal webcams. Will start this afternoon with a dense fog advisory for all bays and Gulf waters within 20 nm, as well as one on land for our "island" zones for everything on the Gulf side of the Intracoastal Waterway. This may need to be pushed deeper to the mainland, but will leave that to the evening shift. While we typically see at least some improvement towards mid-day, and I`d expect that tomorrow, the broadly conducive environment for sea fog is not going anywhere. LONG TERM [Saturday Through Thursday]... Weather conditions for Saturday continue to be focused on the stalled/quasi-stationary surface front over our region. With continued warm and humid onshore flow, this boundary will serve as a good source of forcing/dynamics; thus, chances for showers and perhaps a few thunderstorms will continue throughout the day and night. With the front located to our northwest and persistent WAA, will continue with a warm forecast for both Saturday and Sunday. In collaboration with surrounding offices, kept temperatures close to the 50th percentile of guidance. That is, highs mainly in the 70s. A better setup for showers and thunderstorms looks to be Sunday into early Tuesday as models bring a positive-tilted upper level low tracking sewd from the western CONUS. This upper-low will continue to surge Gulf moisture northward into the region, along its surface boundary. The frontal boundary will cross the forecast area Sunday afternoon/evening, making it near the coast by early Monday. Scattered showers and thunderstorms are likely through this period, with better opportunities north of I-10 due to better dynamics/forcing. Uncertainty arises after Monday and whether or not the front will completely move off of the coast. Latest deterministic guidance shows a reasonable agreement with the evolution of the upper-level low; however, differences persist on the evolution of the surface flow pattern. The ECMWF and Canadian suggest a surface/coastal low developing Monday into Tuesday. This will result in onshore flow along the coast through the period, as well as better/longer chances for precipitation. While confidence on local impacts (location of the heavier rainfall axis, total rainfall amounts, timing of drier airmass) is still low to moderate; a wet/active period is expected. Have increasing rain/storm chances from Sunday afternoon, continuing through Tuesday. Synoptic guidance continues to diverge significantly after Tuesday, but general consensus brings relatively drier conditions along with warmer temperatures through late Wednesday. Rain chances return late into the period as another cold front possibly moves through Wed night into Thursday. MARINE... Sea fog continues to lurk on coastal webcams and observations. Though visibility had been better for much of the day, the density of fog has become more variable of late, and is expected to degrade again tonight. A dense fog advisory for some or all of the bays and nearshore waters seems like it will be needed, but the precise timing and extent of how dense the fog will get is still somewhat uncertain. What is not uncertain, however, is that the environment will remain favorable for sea fog throughout the weekend. It can be expected that some dense fog will crop up again at times, and probably favors the overnight hours a little more than the daytime. A weak cold front has stalled north of the waters, and is unlikely to reach the coast, but its proximity will contribute to higher rain chances and perhaps even a thunderstorm near the coast. A stronger cold front next week will be needed to finally put an end to the fog threat. && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 53 64 57 75 65 / 70 20 20 30 10 Houston (IAH) 65 75 64 76 66 / 40 30 30 10 20 Galveston (GLS) 60 64 59 68 62 / 30 20 20 10 20 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Dense Fog Advisory until 9 AM CST Friday for the following zones: Brazoria Islands...Galveston Island and Bolivar Peninsula...Matagorda Islands. GM...Dense Fog Advisory until noon CST Friday for the following zones: Coastal waters from Freeport to Matagorda Ship Channel TX out 20 NM...Coastal waters from High Island to Freeport TX out 20 NM...Galveston Bay...Matagorda Bay. && $$
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