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 152318 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 518 PM CST Fri Jan 15 2021 .AVIATION... VFR, SKC and weaker winds overnight. VFR, SKC and WNW to NW winds around 10 knots or less tomorrow. 42 && .PREV DISCUSSION... /ISSUED 305 PM CST Fri Jan 15 2021/ SHORT TERM [Tonight through Sunday]... Gusty conditions will gradually decrease late this afternoon/early evening as the surface pressure gradient relaxes and surface high builds in from western TX. Will allow the current Wind Advisory headlines to expire at 6 PM CST. With clear skies and light winds we should see sufficient radiational cooling to drop temperatures into the low to mid 30s. Trended towards the mean/colder guidance. Strong surface high pressure along with quasi-zonal flow aloft will keep the weekend dry for SE TX. A progressive shortwave trough will move northwest of the region on Sunday, bringing only a period of mid to high clouds. Highs will be in the 50s to low 60s on Saturday and a few degrees warmer on Sunday with values mainly in the low 60s. 05 LONG TERM... (Sunday Night through Friday) High pressure over the western Gulf of Mexico will bring generally clear skies on Sunday night. As the surface high drifts east, onshore winds will return and this will also allow low level moisture to return to the region. There should be an increase in clouds on Monday but moisture profiles look to meager to offer much in the way of precipitation. Warm air advection and warming at 850 mb should allow MaxT values to warm to near 70 degrees on Monday. Moisture levels deepen Monday night beneath a stout capping inversion at 700 mb. The moisture profile again looks too shallow to offer up much in the way of rain chances. Cloud cover should keep MinT values on the warm side with low temps only cooling into the mid/upper 50`s. By Tuesday, a weak cold front over North Texas and a weak warm front over South Texas will aid in lifting air over SE TX. PW values reach 1.20 inches and the moisture profiles look semi saturated beneath 700 mb. It continues to remain dry in the 700-500 mb layer with a strong cap remaining in place near 700 mb. The lift from the two fronts and the deeper low level moisture should allow for some showers to develop across SE TX. The ECMWF and GFS differ with regards to the position of a cold front on Wednesday with the GFS faster and further south with the fropa. The main upper level trough remains well west over Baja CA so am not seeing the upper level support necessary to drive the front this far south. The ECMWF is supported by the Canadian and ICON model so leaned toward the global model consensus keeping the front to the north for now. Another area of low pressure will develop in the lee of the Rockies late Wednesday and this feature will move east and drag another cold front into the state on Thursday. Continued warm air advection (WAA) should keep showers in the forecast Wednesday through Thursday. Jet dynamics not looking all that impressive so not expecting heavy rain at this time. Speaking of WAA, if the global model consensus is correct, MaxT values will remain on the warm side next week with high temperatures in the mid/upper 70`s for much of the week ahead. The cold front over North Texas will edge into SE TX on Friday and is expected to stall over the region before reaching the coast. The front will likely serve as a focus for additional showers and thunderstorms next Fri-Sat. 43 MARINE... A strong offshore flow will persist tonight as the pressure gradient between low pressure over NE MO and high pressure over West Texas remains tight. The gradient will begin to relax on Saturday as the surface high edges toward South Texas. Winds have struggled to increase today and have yet to reach SCA criteria but that should change over the Gulf waters as the 850 mb cold front reaches the waters around 21-22z. Will drop the SCA over the bays and issue a SCEC as winds will only exceed 20 knots for about an hour or so around sunset and then begin to diminish. The moderate to strong offshore flow will also produce below normal water levels and Morgans Pt and the Galveston Bay entrance will fall 1.5 to 2.0 feet below MLLW. Other sites in the bay and along the coast will also endure low water levels and marine navigation will become difficult in spots. A Low Water Advisory is in effect through 6 PM Saturday. Winds will diminish quickly on Saturday as surface high pressure develops over the western Gulf. The surface high will meander over the Gulf through Monday with a light NE-E flow. The sfc high will move toward the eastern Gulf on Monday and onshore winds will return late in the day. The onshore flow will strengthen on Monday night into Tuesday as low pressure develops over West Texas. An SCA may be required for parts of the coastal waters Monday night. The winds will back a bit late Tuesday in response to weak low pressure developing over Deep South Texas and a weak cold front moving toward SE TX Tuesday night. Models diverge significantly with regard to the strength, timing and location of the front. 43 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 32 58 36 63 40 / 0 0 0 0 0 Houston (IAH) 35 59 37 63 41 / 0 0 0 0 0 Galveston (GLS) 44 58 46 60 50 / 0 0 0 0 0 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Wind Advisory until 6 PM CST this evening for the following zones: Austin...Brazoria Islands...Brazos...Burleson... Chambers...Coastal Brazoria...Coastal Galveston...Coastal Harris...Coastal Jackson...Coastal Matagorda...Colorado... Fort Bend...Grimes...Houston...Inland Brazoria...Inland Galveston...Inland Harris...Inland Jackson...Inland Matagorda...Madison...Matagorda Islands...Montgomery... Northern Liberty...Polk...San Jacinto...Southern Liberty... Trinity...Walker...Waller...Washington...Wharton. Wind Advisory until 9 PM CST this evening for the following zones: Galveston Island and Bolivar Peninsula. GM...Low Water Advisory until 6 PM CST Saturday for the following zones: Galveston Bay...Matagorda Bay. Small Craft Advisory until 9 AM CST Saturday 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...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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