Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000 FXUS64 KHGX 231752 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 1152 AM CST Fri Feb 23 2018 .AVIATION... Visible satellite imagery late this morning shows ceilings beginning to scatter at CXO, IAH, HOU, SGR, and LBX. Intermittent MVFR conditions will be possible at these terminals through early afternoon but decent mixing will allow for VFR conditions to prevail for at least a few hours before sunset. Daytime heating may also contribute to isolated SHRA developing near these terminals this afternoon. VLIFR conditions continue to impact CLL and UTS (located north of a stationary boundary also evident on visible satellite bisecting Southeast Texas from VCT to LFK) and are expected to linger through mid- afternoon before the stationary boundary begins to lift north as a warm front and allows for ceilings to lift to MVFR. Periods of VLIFR sea fog will continue to impact GLS through the afternoon. Webcams have shown some improvement around the island and expect a window for IFR/MVFR this afternoon before fog rolls back in this evening. A developing 40 knot low level jet overnight and associated mixing should help mitigate against overall fog potential, but should result in ceilings lowering to IFR after 06Z. Associated moisture advection may result in a few SHRA developing again early Saturday morning. Southerly winds 8-12 knots this afternoon should decrease into the 6-10 knot range after sunset. Southerly winds are expected to increase into the 10-15 knot range during the day Saturday ahead of a cold front approaching the terminals after 21Z. Huffman && .PREV DISCUSSION... /ISSUED 932 AM CST Fri Feb 23 2018/ UPDATE... Fog fog and more fog. Dense fog advisory was expanded and extended though mixing is developing around Hobby which has improved visibility to 10 miles. Elsewhere though 1/8 to 1/2 mile was the norm for visibility in the fog. As the warm front (PSX-ARM-IAH-6R3 line) lifts north this morning and afternoon areas of improved visibility will expand northward though fog will likely linger until after 12 or 1 in the far northern counties probably not dense though. S/W moving past the CLL area could bring a few showers though it is dissipating as well. This afternoon expect some light spotty sprinkles or WAA showers but very sparse in coverage. Temperatures are a going to be very strongly influenced by the location of the warm front. Areas farther to the north of the warm front will be the last to warm up and may not hit their highs until 4 or 5 pm whereas areas around the Metro could hit their highs 1 to 3 pm. Last but not least the sea fog along the coast will be slow to clear and may need to extend the dense fog advisory along the immediate coast an hour. In addition the sea fog will probably linger even with mixing this afternoon though not as dense. Tonight with winds relaxing slightly the sea fog will probably return. Guidance does show stronger winds a little veering and mixing Saturday which could help to lessen the sea fog threat. 45 PREV DISCUSSION... /ISSUED 447 AM CST Fri Feb 23 2018/ DISCUSSION... At 4am a stationary front is currently draped along a line from roughly Matagorda-Hobby Airport-Cleveland. Temperature differences around 20 degrees are being observed within short distances of this boundary. It will be lifting northward today and expect areas of fog, drizzle, and -ra to follow. A cluster of shra/tstms near San Antonio is associated with an upper level impulse embedded in the sw flow. This precip may clip our nw zones (CLL area) later this morning. Forecast highs across extreme northern parts of the CWA will have the potential for significant forecast busts should the front not push through by late afternoon. Closer to the coast, warm conditions will persist and would expect to see some breaks in the cloud cover later today. Low pressure developing near the TX/OK panhandles later tonight & Sat will track northeastward toward the Great Lakes by Sunday. A trailing dryline/front will make its way into se TX late Saturday and Saturday night. Strong llvl jet, ample moisture and upper jet positioning may allow for a few strong storms to develop along the boundary across n/ne parts of the area, but appears conditions would be much more favorable for that further north toward the Arklatex where there will be more instability. Locally we`ll probably just see a thin band of precip along the front that should be slowing as it approaches the coast late Sat night. Latest model guidance suggests increasing precip coverage along and north of the front during the day on Sunday with the aid of isentropic lift and a series of disturbances riding thru the sw flow aloft. Of course, there`s always uncertainty as to where the front will be and also timing/intensity of the upper impulses this far out, but in general, locations south of a Livingston-Brenham line look fairly wet. Precip should taper off Sunday night and the front should get a secondary push offshore which should provide a day of dry wx Monday. But rain chances return by Tuesday it heads back north, moisture levels increase, sw flow remains aloft, and another weak front approaches midweek. 47 MARINE... Will be keeping the Marine Dense Fog Advisory in place for both the bays and nearshore waters through 11 AM this morning...and then for just the nearshore waters the rest of the afternoon. Sea fog should roll back into the bays tonight as the generally light/moderate on- shore remains in place. Winds are expected to increase Saturday (in response to the next upper level storm system moving across the SRN Plains), with SCEC/SCA flags possible. As this system moves east it will help to drag a weak cold front into the area late Sat night or early Sun morning. At this time, confidence is shaky with regard to how far offshore this boundary will get (or if at all). However, we could see less fog Sat/Sat night given the increased mixing. 41 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 69 65 77 50 66 / 40 30 70 20 30 Houston (IAH) 78 67 80 59 66 / 20 20 30 40 70 Galveston (GLS) 75 67 75 61 65 / 20 20 20 60 70 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Dense Fog Advisory until 1 PM CST this afternoon for the following zones: Austin...Brazoria...Brazos...Burleson... Chambers...Colorado...Galveston...Grimes...Houston... Jackson...Madison...Matagorda...Trinity...Waller... Washington...Wharton. GM...Dense Fog Advisory until 1 PM CST this afternoon for the following zones: Galveston Bay...Matagorda Bay. Dense Fog Advisory until 6 PM CST this evening for the following zones: Coastal waters from Freeport to the Matagorda Ship Channel out 20 NM...Coastal waters from High Island to Freeport out 20 NM. && $$ Discussion...25 Aviation/Marine...14

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