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-- Discussion containing changed information from previous version are highlighted. --
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