Area Forecast Discussion
Issued by NWS Brownsville, TX

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000 FXUS64 KBRO 231117 AAA AFDBRO Area Forecast Discussion...UPDATED National Weather Service Brownsville TX 617 AM CDT Fri Apr 23 2021 .DISCUSSION...Updated for latest aviation discussion below. && .AVIATION...IFR to MVFR conditions continue near daybreak this morning as southeasterly winds are just beginning to increase. Morning sounding shows a low level jet of 30 kts up to 2k feet. Expect these winds to mix down at times into this evening. MVFR to brief VFR ceilings are likely this afternoon, before MVFR to IFR ceilings return tonight. Patchy fog is possible late tonight as a cold front approaches, with IFR to LIFR conditions near daybreak Saturday. Isolated thunderstorms are possible this afternoon north of the RGV. && .PREV DISCUSSION... /issued 407 AM CDT Fri Apr 23 2021/ SHORT TERM (Today through Saturday): A 500mb shortwave spins through Texas and into the Southeastern US into Saturday. Low pressure develops across North Texas and the Southern Plains today with severe weather expected, strengthening the pressure gradient along the lower Texas coast. A cold front arrives on Saturday, weakening the pressure gradient and bringing very dry air through the CWA. Isolated coastal showers are possible early today across eastern counties with minimal rainfall. Hot and dry southwesterly flow aloft will likely cap off any thunderstorm chances, especially across the RGV, but have left a 20 percent chance across northern ranchlands counties due to increasing instability through the afternoon. The cold front arrives late tonight into Saturday, potentially breaking the cap and allowing a couple of thunderstorms to develop. Have continued a 20 percent rain chance through the valley with the frontal boundary. Temperatures warm today with the moderate to at times strong southerly flow, and despite the front and any northerly winds on Saturday, warm even more due to the arrival of very dry air. This will present an elevated fire weather concern as humidity values drop below 15 percent across most of the CWA. Have held off on a Fire Watch, as the 20 foot wind speeds fall short of 15 mph on Saturday. A Fire Danger Statement should probably still be issued tomorrow, due to the near explosive fuel state and well above normal temperatures expected. LONG TERM (Saturday Night through Thursday): 500 mb ridging will strengthen over the RGV this weekend through Mon/Tues. This will maintain pretty hot and stable conditions over the region throughout at least the first half of next week. Meanwhile to the west, a major 500 mb trough axis will start digging into the Rockies Mon and Tues. This feature eventually pushes into central portion of the country around midweek. This trough eventually moves into the the Miss River Valley around Wed/Thur which will likely set the stage for a potential fropa for the region. The longer range forecast models continue to show some very marginal moisture return occurring ahead of this trough axis around midweek. So will maintain some low end pops there. Overall rainfall potential over the next 7 days looks relatively low. The main issue continues to be the timing differences of the West Coast trough by the GFS and the ECMWF. The GFS continues to be faster with the eastward progression of the trough versus the ECMWF. Good agreement shows up through next Wed from both the ECMWF and GFS for both temps and pops with bigger differences showing up from Thurs onwards. Overall forecast confidence is above average through next Wed and then drops quite a bit for Thurs. MARINE (Now through Saturday): The pressure gradient strengthens along the lower Texas coast today as low pressure develops across North Texas and the Southern Plains. Expect seas to build through the day and remain elevated into tonight, especially offshore. Have hoisted a Small Craft Advisory through the afternoon across bay and nearshore waters and through this evening for offshore waters. Offshore waters may not full diminish until Saturday morning, and the advisory may need to be extended. A cold front arrives early Saturday with light northerly winds turning easterly on Saturday, weakening the pressure gradient and allowing marine conditions to improve. Saturday Night through Tuesday Night: The PGF remains fairly weak as surface ridging spreads over the NW Gulf of Mex. As the West Coast 500 mb trough axis moves in the central Plains States, A surface low pressure area developing with the trough will strengthen potentially resulting in a round of near SCA conditions for both the Bay and Gulf Waters. && .PRELIMINARY POINT TEMPS/POPS... BAYVIEW/PORT ISABEL 84 72 89 66 / 20 20 10 0 BROWNSVILLE 87 73 94 66 / 10 20 10 0 HARLINGEN 90 72 95 64 / 20 20 10 0 MCALLEN 92 72 98 65 / 10 20 0 0 RIO GRANDE CITY 97 71 99 62 / 10 20 0 0 SOUTH PADRE ISLAND 78 72 80 69 / 10 20 10 0 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...High Rip Current Risk through this evening for TXZ256-257-351. GM...Small Craft Advisory from 1 PM this afternoon to 8 PM CDT this evening for GMZ130-132-135. Small Craft Advisory from 3 PM this afternoon to 1 AM CDT Saturday for GMZ170-175. Small Craft Advisory from 3 PM this afternoon to 8 PM CDT this evening for GMZ150-155. && $$ This product is also available on the web at: HTTP://WEATHER.GOV/RGV 56-Hallman...Aviation

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