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 212351 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 551 PM CST Thu Jan 21 2021 .AVIATION [00Z TAF Issuance]... Widespread IFR to LIFR conditions continue this evening due to -RA, -DZ and/or FG. Visibility will once again drop to 1SM or less across the coastal terminals overnight. Inland terminals may see visibility in the 1-5SM range. Showers will continue through Friday morning before a cold front moves through bringing a drier airmass and MVFR to VFR conditions. Winds will generally remain calm; increasing from 5-10 knots across the coastal terminals by Friday. 05 && .PREV DISCUSSION /Issued 355 PM CST Thu Jan 21 2021/... .UPDATE... It has only been a few minutes since the AFD issuance but have already issued a Dense Fog Advisory for Bolivar/Galveston/Freeport as webcams clearly showing the anticipated advection fog "overperforming". This is unlikely to the last word on fog tonight. 45 && .SHORT TERM [Tonight through Tomorrow Night]... Weak shallow frontal boundary has pushed into the central areas of SETX this afternoon bringing some slightly drier air to the northern areas with dewpoints down into the mid-upper 50s...closer to the coast in the warm sector 63-69 dewpoints with south and southwesterly winds. Some patchy light rain ongoing in the warm sector beneath and mainly east of the LLJ axis - CRP-CXO. Cloudy skies have been the norm today and overnight should continue with lowering cloud bases and fog becoming more widespread again. Anticipate that the evening shift will be issuing Dense Fog advisories for the eastern/southeastern areas. Not as confident over the western areas where mixing may be enough to keep it in the more nuisance category. Weak upper troughing slides through the area Friday and this should bring more drying aloft but cooler temperatures for the northern areas in the morning and much warmer over the southwest as even some sunshine makes an appearance. Rain chances will be high tonight with light rain and possibly a few showers again along and east of the LLJ then rain chances taper down quickly Friday morning as it shifts east/southeast through 6-11 am. Possibly some patchy light rain or drizzle will be developing up north where a band of isentropic upglide develops in the afternoon otherwise much lower rain chances over land. And accumulations through Friday night look to be on the light side with trace amounts up to around 0.25 amounts thanks to the abundance of drizzle and some of the light rain. Friday afternoon/night the frontal boundary pushes out into the Gulf and becomes a focus for showers and takes the fog threat with it. Moist SW flow aloft does remain and will be looking for high clouds to continue along with increasing low/mid clouds thanks to the upglide in the east/northeast. That sea fog may not be far offshore just lurking... 45 .LONG TERM [Saturday morning through Thursday]... The offshore stalled front will allow for easterly/southeasterly winds to flow along the coastline and since water temperatures are still in the upper 50s and dew points will be in the low 60s, sea fog will still be possible into Sunday morning. Fortunately, some relief is on the way as a developing area of low pressure in West Texas will tighten the pressure gradient along the Gulf Coast. Forecast soundings still indicate the capping inversion around 850 mb with dry air aloft. With the unidirectional flow and steep lapse rates, should get enough mixing to diminish fog. Consequently, I have removed fog from the grids after 18z on Sunday. Let`s talk rain! The previously mentioned stalled frontal boundary will drift back over the area as a warm front and return southeasterly flow to the area on Saturday afternoon. This will increase PWATs to 1.2"-1.4" by Sunday morning. Instability will be on the rise as well from west to east with Theta-E increasing and CAPE building up to 800-1000 J/kg by Sunday. Rain will be more isolated and light on Saturday for as we`ll still be dealing with a subsidence inversion around 700 mb. As the instability builds up going into Saturday afternoon, the chances of scattered thunderstorms goes up as well. We talked previously about an area of low pressure developing in West Texas. This low will increase our chances of thunderstorms for Monday morning by bringing in a cold front to the area that will be our source of lift for all of the moisture and instability. We will be in the favorable right entrance region of a jet streak as well, so expect heavier rain and increased probabilities of thunderstorms along the frontal boundary. The front will be through the CWA by Monday night. After days of cloudy skies and warm overnight temperatures, we`ll finally get a break from both! High pressure builds in following FROPA and clears out the skies and drops overnight lows for early next week into the upper 40s/low 50s. This front will also stall off of the coast due to mid-level flow becoming zonal. On Tuesday night/Wednesday morning, the front will head back to the north as a warm front and bring rain chances back to the CWA. This won`t last too long though as an area of low pressure developing on the lee side of the Rockies will push another cold front through the area on Wednesday night with help from a weak shortwave trough. High pressure builds in behind this front and gives us at least one day with dry northerly flow before sliding off quickly to east and putting us back into a moist, onshore flow by Thursday night. Due to the two cold fronts, temperatures next week look much more pleasant with afternoon highs in the 60s and overnight lows in the 40s/50s. 26. .MARINE... The passage of a weak upper level disturbance (and its associated showers/drizzle from the Gulf) appears to have helped to decrease the sea fog over the bays/nearshore waters today However, will be expecting visibilities to fall once again early this evening with sea fog redevelops in the wake of the precipitation. Overall con- ditions won`t be improving unless/until the next cold front makes it down to the marine waters. Current timing has the line pushing off the coast late tomorrow afternoon (between 3-6pm or so) and a most likely brief break from the sea fog as slightly cooler/drier air moves into the region. This boundary is forecast to stall in/ around the nearshore waters tomorrow night and act as a focus for increasingly unsettled weather across the coastal waters by early Sat morning into the afternoon. Rain chances should decrease with the boundary moving back inland as a warm front Sat afternoon and evening. However, this pattern does favor a return of sea fog and lower visibilities for the rest of the weekend and most likely in to Mon. All ahead of the next cold front, who`s timing the models have had some issues with (i.e. 12Z runs with the faster FROPA vs the 00Z runs with a slower one). As any rate, we`ll see strong N/ NW winds develop over the coastal waters sometime late Mon or Tue morning and SCEC/SCA flag will likely be needed in its wake. 41 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 56 73 55 68 61 / 70 30 20 30 50 Houston (IAH) 62 72 57 68 61 / 60 50 10 30 50 Galveston (GLS) 64 65 58 65 60 / 50 50 20 30 40 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Dense Fog Advisory until 9 AM CST Friday for the following zones: Brazoria Islands...Galveston Island and Bolivar Peninsula. GM...Dense Fog Advisory until 9 AM 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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