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
382 FXUS64 KHGX 182336 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 636 PM CDT Thu Mar 18 2021 .AVIATION [00Z TAF Issuance]... An excellent day for flying across SE Texas with VFR conditions prevailing throughout the TAF period. Northwesterly winds will become northerly overnight, and wind gusts will subside after sunset tonight as the boundary layer decouples. Late Friday morning, steep low-level lapse rates will extend past 1km so expecting winds to become a bit gusty once again with gusts around 15-20 kts. Hi-res model guidance shows FEW/SCT clouds around 3,500ft moving into the area in the late morning/early afternoon hours on Friday. Gusty winds subside on Friday after sunset. 26 && .PREV DISCUSSION /Issued 309 PM CDT Thu Mar 18 2021/... .SHORT TERM [Tonight through Friday Afternoon]... High pressure over the Panhandle will slide slowly eastward keeping the weather across SETX dry and cool tonight and Friday before starting the warm up. Skies should be mostly clear to clear though a few clouds should expand southward from the Arklatex Friday into the northeastern counties in the morning before eroding...the chances of them surviving to make it into SETX is slim to begin with. Temperatures will run about 5-10 degrees below climo with lows in the 40s and highs in the 60s to near 70. Good BBQ weather. 45 .LONG TERM [Friday Night Through Thursday]... A pleasant weekend is in store with a high pressure system settling in over our area. Daytime highs will be near 70 on Saturday and cooler along the coast and gradually increase to the mid-70s by Monday. Overnight lows will be in the 40s Friday and Saturday night due to clear skies enhancing radiational cooling. As the high pressure moves out by Sunday, onshore flow returns to SETX and along with it, increased cloud cover, more humidity, and higher temperatures. This trend persists until the next round of shortwave troughs begin to push early next week. Rain chances return by Monday as onshore flow, favorable upper-level dynamics, and an approaching shortwave trough lead to a stream of moisture and showers pushing inland. Global models indicate that our eastern and northern counties have the best chance of getting rain. Forecast soundings show some low-level veering/shear and a well- mixed boundary layer up to 900mb. Therefore, isolated thunderstorms cannot be ruled out despite instability and CAPE being minimal. As the aforementioned trough and its associated cold front pushes through SETX late Monday night and Tuesday, the GFS still remains more aggressive than the ECMWF, but the ECMWF is catching up and is in more of an agreeance today regarding timing, location, and intensity. Therefore, weighted the GFS slightly more today in long- term grids. PWATs will gradually reach 1.3-1.5" due to the low-level advection of a warm maritime airmass. As a result, mid-level dry air and the capping inversion will begin to erode Tuesday night. Along with daytime heating, these ingredients increase the chances for thunderstorm activity, so coverage transitions to isolated t`storms to chance t`storms. By Wednesday morning, the cap finally erodes into a thoroughly saturated profile in the midst of the frontal passage. By Wednesday and Thursday, models still disagree about another quick shortwave moving across central CONUS. Therefore, sided more with NBM for something this late in the long-term forecasting period. One noticeable difference worth mentioning is that the ECMWF places the heaviest precip over the FL panhandle and southern AL on Wednesday, which aligns more with yeserday`s and today`s GFS run, so given this trend, the two models might begin to converge in agreeance and displace the heaviest rain to the east of our CWA. By Thursday, the location of the trough axis differs too greatly between global models (GFS pushes it through Texas whereas ECMWF pushes it through Mississippi) to feel confident enough with POPs by then, so sided with the NBM once again. KBL .MARINE... As a high pressure continues to settle in, moderate offshore flow will continue through late Friday until it begins to move east and out of our area. A mixture of SCA and SCEC will be needed through at least then. Low Water Advisories may remain in effect for Galveston Bay due to moderate offshore winds. Even at high tide currently, water levels are at Low Water Advisory criteria. Winds will become NE on Saturday and then return to onshore SE winds by Sunday. Next round of rain chances will return by Monday due to an approaching front. KBL .FIRE WEATHER... Dry weather will continue and may see RH values Friday afternoon within a few percent of today...25-45 percent. Winds will be a lighter in the 5-12 mph range and still gusty though the gustiness should taper off by mid afternoon. Slow gradual warm up through the weekend and moisture return gets underway late Saturday with. more easterly flow developing. 45 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 41 66 42 71 44 / 0 0 0 0 0 Houston (IAH) 45 66 47 71 48 / 0 0 0 0 0 Galveston (GLS) 51 67 52 64 57 / 0 0 0 0 0 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...None. GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 1 AM CDT Friday for the following zones: Coastal waters from Freeport to Matagorda Ship Channel TX out 20 NM...Galveston Bay...Matagorda Bay. Low Water Advisory until 1 AM CDT Friday for the following zones: Galveston Bay. Small Craft Advisory until 1 AM CDT Friday for the following zones: Coastal waters from High Island to Freeport TX out 20 NM...Waters from Freeport to Matagorda Ship Channel TX from 20 to 60 NM...Waters from High Island to Freeport TX from 20 to 60 NM. && $$
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