Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000 FXUS64 KHGX 191724 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 1224 PM CDT Thu Apr 19 2018 .AVIATION [18Z TAF ISSUANCE]...
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VFR. Breezy NE winds today becoming E tomorrow. 11
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&& .PREV DISCUSSION...
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/ISSUED 958 AM CDT Thu Apr 19 2018/ DISCUSSION... Just made a couple minor changes to the grids on the morning update to match up with current observations and satellite images. See discussions below for the details. 42 PREV DISCUSSION /Issued 423 AM CDT Thu Apr 19 2018/... SHORT TERM [Today Through Sunday Morning]... A cold front working it`s way across SE TX is currently located just south of I-10 this morning separating two airmasses with dewpoints in the mid 40s to the north and upper 60s to the south. This front should move off the coast near sunrise, with moderate to strong northeasterly winds filling in behind the boundary as high pressure builds into the region. 850mb Temperatures behind this front will only drop 4-6 degrees, resulting in slightly cooler temperatures for the remainder of the week. High temperatures should top out in the mid 70s today, and the low 70s on Friday. Dry conditions can be anticipated through the remainder of the week with high pressure in play. As this ridge begins to shift east Friday, moisture will again be on the rise. Saturday will start the warming trend as onshore flow returns to the forecast. The added advection of Gulf moisture, along with a tightening moisture gradient out ahead of the approaching cold front Saturday night, will result in muggy warm conditions. Mostly cloudy skies Saturday should keep high temperatures in the upper 70s. Global guidance such as the ECMWF, GFS, and NAM bring showers ahead of the next cold front into the region as early as Saturday morning. The most recent runs of the ECMWF and GFS have both backed off on rainfall totals with the passage of this system, keeping the best accumulation northeast of the forecast area over the Piney Winds. The 00Z NAM shows a more saturated profile with showers lingering into Saturday evening with PWs increasing to 1.8-1.9 inches shortly after sunset, but low-level lapse rates only rise to near 5.5 C/km. The NAM also is a few hours faster with the front, and slightly more aggressive with rainfall totals. The GFS which is not so saturated, only increases PWs to 1.5-1.6 inches, but shows a little more in terms of instability, with low level lapse rates approaching 6.7 C/km Saturday afternoon. The best upper-level jet dynamics moves over the region late Saturday afternoon into early Sunday with decent diffluence ahead of the upper-level jet streak. It still appears as though the best dynamic forcing will be situated in a region from Colorado to San Jacinto county and northward. Ample lift should also be available out ahead of the upper-level trough axis which digs south into northern TX and southern OK, late Saturday into Sunday. Therefore, the environment will definitely have the necessary ingredients for the development of thunderstorms Saturday afternoon and into the evening hours. What remains a question is whether the best upper- level forcing, moisture, lift and instability will all be in phase to allow for the production of severe thunderstorms. SPC has just released their Day 3 Outlook, which places most of SE TX under a marginal risk of severe thunderstorms. LONG TERM [Sunday Through Thursday]... Behind the front, conditions will dry out by Sunday morning as PWs fall to near a half inch. Cold air advection behind this system will help to high temperatures just below 80 degrees to start the week. Northwesterly winds will turn out of the northeast by Tuesday, as a surface ridge builds into the NW Gulf of Mexico. This area of high pressure will slide eastward late Wednesday, and partly cloudy skies will move back into the forecast by mid- week. MARINE... Moderate to strong northeasterly winds will prevail behind a cold front expected to move across the Gulf waters this morning. A Small Craft Advisory (SCA) is in effect for both Matagorda and Galveston Bay, and the nearshore Gulf water through 11 AM. The offshore waters will hold onto a Small Craft Advisory through 3 PM this afternoon, when winds begin to lower in speed. Small craft should still exercise caution (SCEC) into early this evening. Moderate easterly winds will return as a region of high pressure shifts east of SE TX early Friday, and SCEC criteria may be necessary. Onshore flow will prevail Saturday morning out ahead of our next cold front which will push through the region late Saturday into Sunday morning. Showers and thunderstorms can be anticipated with this front, which should reach the nearshore waters shortly before sunrise on Sunday. Northwesterly winds will fill in behind this system and slowly turn out of the northeast through the beginning of next week.
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&& .PRELIMINARY POINT TEMPS/POPS...
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College Station (CLL) 51 71 55 71 56 / 0 10 20 70 60 Houston (IAH) 53 72 59 74 61 / 0 10 20 60 70 Galveston (GLS) 61 69 66 74 66 / 0 10 20 40 60
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&& .HGX WATCHES/WARNINGS/ADVISORIES...
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TX...NONE. GM...Small Craft Advisory until 1 PM CDT this afternoon 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...Galveston Bay...Matagorda Bay. SMALL CRAFT SHOULD EXERCISE CAUTION until 3 PM CDT this afternoon 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. Small Craft Advisory until 3 PM CDT this afternoon for the following zones: Waters from Freeport to the Matagorda Ship Channel from 20 to 60 NM...Waters from High Island to Freeport from 20 to 60 NM.
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&& $$ Discussion...42 Aviation/Marine...11

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