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 100024 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 624 PM CST Tue Mar 9 2021 .AVIATION [00Z TAF Issuance]... Moderate SSE winds and gusty this afternoon should be gradually relaxing and losing much of the gusts in the next 2 hours. Clouds will be the primary issue with this package of TAFs. AMDAR soundings clearly showing a very moist layer 1800-6000ft then dry subsidence inversion atop that. Pattern looks to change very little the next 30 hours so other than a gradual lowering of ceiling heights tonight then rising ceilings mid to late morning. MVFR conditions setting in between 02z and 07z and expanding into many of the TAF sites. Throughout the afternoon can`t rule out --R with shallow convection but insignificant for flight ops. Still some concerns with sea fog but the afternoon model runs have swung back to drier air aloft and not the surge of low level moisture. Dewpoints well offshore still only 61 and with the rising SST nearshore sea fog threat looks low. 45 && .PREV DISCUSSION /Issued 236 PM CST Tue Mar 9 2021/... .SHORT TERM [Today Through Wednesday Night]... High pressure off to the east has allowed for onshore flow to persist. The southerly winds have developed a layer of clouds around 4,000-6,000ft across SE Texas. Even with the cloud cover, suitable WAA will be enough to get afternoon temperatures into the mid 70s. Speaking of advection, the southerly winds will be a bit gusty today thanks to steep lapse rates past 1km. Moderate winds aloft will be able to mix down to the surface, so gusts of 20-25 kts are likely for today. For tonight, the SREF is hinting at fog along the coast, especially near Galveston Bay. Otherwise, no significant weather is expected over the next 24 hours. Cloud cover increases tonight, so overnight lows will remain rather mild in the upper 50s/low 60s. For tomorrow, expect more of the same except with slightly stronger winds as the pressure gradient tightens between a developing area of low pressure to our north and high pressure to the east. Winds will transition to a bit more southerly as well, and afternoon temperatures will be a touch higher with highs in the upper 70s/low 80s. There is a small chance (we`re talking around 10% at most) that we could see some warm advection showers tomorrow afternoon, but only a few models are hinting at this including the ECMWF. The ECMWF also shows warm advection showers for today, but as of right now there are only a couple of small, short-lived showers in the area so this is why I have largely leaned against that scenario and kept low PoPs in the grids through tomorrow night. With the increase in cloud cover tomorrow night, leaned a bit higher for low temperatures with lows in the mid 60s. Sea surface temperatures in the nearshore waters are still in the low 60s and by tomorrow night, dew points will be approaching the mid 60s. Included patchy sea fog in the grids during this timeframe, but the risk is very marginal at least for now. Batiste .LONG TERM (Thursday through Monday)... A broad upper level ridge will be located over the western Gulf on Thursday with a slow moving upper level over central CA. At the surface, high pressure will remain anchored over the SE US with low pressure developing in the TX panhandle. A tight pressure gradient will foster a moderate to strong onshore flow bringing a surge in low level moisture. The moisture will remain shallow, staying below 850 mb with considerably drier air between 850 and 500 mb. Could get some streamer showers from time to time but most of the area will remain dry. 850 mb temps support a MaxT values of around 80 degrees. There`s really not a lot of change for Friday as moisture and thermal profiles look similar. Some minor change for Saturday as the upper low over CA moves toward the 4 corners region. That said, the moisture profile actually looks a bit drier on Saturday with PW values falling to less than an inch. But the lowering of PW values doesn`t last long as moisture deepens quickly Saturday night reaching 1.50 inches by Sunday morning. Surface low pressure over the TX panhandle will begin to move east on Sunday and this will aid in moving the dry line into SE TX. This feature will serve as a focus for showers and thunderstorms late Sunday into Sunday night. Jet dynamics which looked very favorable yesterday looks much less so today. The upper level support is a bit further north taking the best splitting jet structure north. Even the RRQ is looking out of phase with the surface feature. Low level instability is also looking rather paltry but things could change by Sunday. As for temps, think the GFS is trending too cool and have leaned toward the warmer side of guidance as there doesn`t look like much of a cold air intrusion. Another weak short wave will move into the area late Monday into Tuesday and depending on the timing of the dry line and front, thinks it`s best to keep slight rain chances in the forecast Monday into Tuesday. Lastly, some potential for some sea fog near the coast but it looks like those chances will be small. Water temps is up to 62 degrees this afternoon and with a persistent S-SE wind, feel water temperatures will only become warmer. It`ll become increasingly difficult for dew pts to be much warmer than the water thus reducing the fog threat. That said, the potential is not zero and will carry patchy fog from 06-12z into Saturday. 43 .MARINE... A moderate to occasionally strong onshore flow will persist through the end of the week as high pressure remains over the eastern US and low pressure develops in the lee of the Rockies. Warm and moist air overriding the cooler shelf waters could yield some patchy fog at times but widespread dense fog is looking less likely as water temperatures slowly warm by the weekend. Sustained winds will exceed 15 knots offshore and a SCEC will be required probably into Saturday. Due to the persistent onshore fetch, seas will also be building in excess of 7 feet so an SCA may be needed before all is said and done. There may be a brief offshore flow late Sunday into Monday associated with some storms but onshore winds will return quickly for the first half of next week as low pressure develops in North Texas. 43 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 58 79 64 80 64 / 0 0 0 20 10 Houston (IAH) 61 79 65 79 65 / 0 10 0 20 10 Galveston (GLS) 62 71 64 72 64 / 0 0 0 10 10 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...None. GM...SMALL CRAFT SHOULD EXERCISE CAUTION through Wednesday afternoon for the following zones: 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. && $$ AVIATION...45
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