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 202341 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 641 PM CDT Sat Mar 20 2021 .AVIATION [00Z TAF Issuance]... VFR conditions will continue through the period. Moderate easterly flow will persist through the evening before becoming more light and variable overnight. Southeasterly flow develops Sunday morning ushering in some higher moisture. This increase in moisture will lead to increasing cloud cover late tonight into early Sunday morning. Few to scattered clouds at 2000 to 2500ft will be possible for IAH coastward shortly after sunrise. CIGs should remain predominately VFR, but there may be some brief periods of MVFR CIGs at GLS and LBX due to a BKN 2000 to 2500ft deck. Ceiling will rise to above 10,000 feet by the afternoon area wide. Fowler && .PREV DISCUSSION /Issued 323 PM CDT Sat Mar 20 2021/... .SHORT TERM [Tonight Through Sunday]... Surface high pressure ridging into the area from the northeast will help to give Southeast Texas one more cool/cold night tonight with low temperatures ranging from the low to mid 40s most inland locations to the low to mid 50s at the beaches. Some of the latest high resolution model runs are bringing some of low level moisture (nicely seen on visible satellite imagery that has been off to our east today) into locations in/around Galveston Bay and the coast around or shortly after 3 AM and then spreading it inland during the day tomorrow as winds come back around to the southeast. Expect most areas to eventually become partly cloudy tomorrow with highs mostly in the low to mid 70s except in the upper 60s to around 70 at the coast. 42 .LONG TERM... With steady onshore flow Sunday night and into Monday, warm temps, increased cloud cover, and climbing PWATs, some streamer showers are expected to push inland through our eastern counties. This combined with an approaching upper level trough will also bring increased rain chances to our northern counties. Forecast soundings show by late afternoon, speed and directional shear combined with a well- mixed boundary layer up to 900mb could lead to some isolated storms, despite their being a cap at 900mb and decent mid-level dry air. The associated frontal boundary with this UL trough will push south and through our CWA late Mon/early Tues where it will stall somewhere near the coast or offshore. On Tuesday, another surge of moisture due to continued onshore flow along with the remnant frontal boundary will lead to more rain chances along our southern and coastal counties. By late Tuesday, the 900mb cap erodes and lapse rates remain well-mixed up to 900mb. This along with decent mid-level lapse rates will lead to more CAPE and instability, bringing back the chances for some scattered tstorms. The 12Z GFS deterministic model shows our CWA underneath the left exit region of a jet streak, leading to upper-level divergence and more convective support for thunderstorms. By Wednesday, another upper-level trough approaching from the west combined with the diffuse frontal boundary along our coast and a coastal low coming up from the Big Bend region will lead to another round of precip and tstorm chances. Afternoon forcing mechanisms are even more favorable for tstorms with forecast soundings indicating MLCAPE values ~2000 J/kg, little to no CIN, and low-level speed/directional shear. If this persists with subsequent model runs, then afternoon storms will be likely. As this conglomeration of systems moves out late Wednesday night, some trailing rain is possible, so kept POPs in through Thursday, but afterwards, the forecast period remains dry Friday and Saturday. KBL .MARINE... Winds will be gradually working their way back around from the northeast to the south southeast through Sunday night as high pressure moves off to the east. A tightening gradient in response to deepening low pressure in/around the Texas Panhandle area late Sunday night through Monday will bring increasing winds and seas that will likely require Caution and/or Advisory flags. With the approach of a weak cold front late Monday night and Tuesday, expect to see lower winds and seas along with the return of some showers and thunderstorms. The light to occasionally moderate southeast to east winds will persist until the next cold front sweeps off the coast and through the coastal waters currently scheduled to occur late Wednesday night or early Thursday morning. Caution and maybe Advisory flags will probably be needed in the wake of this front. Look for an onshore to return to the area at the end of the week. 42 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 43 73 52 75 57 / 0 0 0 20 50 Houston (IAH) 46 72 57 76 62 / 0 0 20 20 60 Galveston (GLS) 56 69 64 75 66 / 0 0 10 20 50 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$
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