327
FXUS64 KBRO 150923
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
323 AM CST Wed Jan 15 2025

...New SHORT TERM, LONG TERM, MARINE...

.SHORT TERM...
(Today through Thursday)
Issued at 316 AM CST Wed Jan 15 2025

Due to the presence of a coastal low in the Gulf, moisture
continues to be advected onshore resulting in cloudy, drizzly
conditions that will continue overnight. Overnight rain chances
are between 60-80% for the entire Valley. Tomorrow, an upper level
shortwave will begin to push the coastal low away from Deep South
Texas, which will decrease our precipitation chances. However,
some lingering drizzle could persist (especially in the earlier
hours), and there remains a 30-60% chance of precipitation, with
the highest chances being in the Coastal counties. Skies are
expected to remain cloudy through the day, keeping temperatures
lower, and should slightly clear in the afternoon into the
evening. There will not be much variance in high and low
temperatures due the low cloud cover, and temps are expected to
get up to the mid-50s tomorrow, with low temps in the upper
40s/lower 50s

Thursday is expected to be warmer and drier, with less cloud cover
(skies should be partly cloudy). With more sun getting to the
surface, temperatures Thursday are expected to be warmer, with high
temperatures getting up into the lower to mid 60s.  There is little
to no chance of precipitation on Thursday.

&&

.LONG TERM...
(Thursday night through Tuesday)
Issued at 316 AM CST Wed Jan 15 2025

Key Messages:

- Arctic air cold front Saturday night.

On Thursday, the remains of a coastal trough will fill as a mid
level ridge weakens over Texas. The CWA will see mostly clear
skies on Thursday night with low temps in the 40s and 50s.
Meanwhile, Arctic air will move out of Canada into the northern
High Plains behind an eastward moving Canadian trough and
underlying low pressure system. Local temperatures will feel warm,
with Friday highs in the 70s and Friday night lows in the 50s and
60s. Even on Saturday high temps will be in the 70s to near 80.

A cold front with air derived from the arctic will arrive on
Saturday and we will have a McFarland clone (referring to the
classic 1976 paper by M.J. McFarland describing a synoptic setup
that produces unusually cold weather for deep South Texas). Once a
cold front moves through, the mid-level trough axis from Hudson
Bay southwest across the United States with a north-south blocking
ridge to the west allows very cold air to plummet south through
nothing but barbed wire fencing over the Plains. The resulting
"signature" is often present when extreme cold devastates local
agriculture, especially when that industry was of major
importance.

Temperatures will "free-fall" starting Saturday night creating a
winter weather threat that will persists through much of the
week. Though initially dry, cold air nosing south into the CWA
will dance with warmer and moister marine air to set up a
deepening coastal trough. That will enhance rain chances and, when
combined with the colder temperatures which are expected to reach
a nadir Wednesday and Thursday, will up the chances for pockets
of wintry precip.

Used an NBM baseline for the forecast, realizing that there is
still a lot of uncertainty. Some of the models (like the NAM)
handle the colder temps better, and those have yet to come into
prime range. For now, the ECMWF and the NBM50 seem to be tracking
well. A bit concerning is that the lower end NBM probabilities (25
and 10 percent) which might be considered reasonable worst case
scenarios, take temps well below freezing for the coldest
nights/mornings. For now, however, we are looking at freezing
temps (around 32 degrees) for the Ranchlands Monday morning, a
light freeze across the northern tier and Starr Counties Tuesday
morning, and a light (possible hard) freeze for that same area
Wednesday morning along with a light freeze reaching Hidalgo,
Willacy, and northern Cameron Counties.

In terms of weather, look for light, patchy fog Thursday and Friday
mornings. Other precip threats will occur in the 5 to 7 day
range. We can`t get around the possibility of freezing drizzle
across the Ranchlands and Upper Valley Monday morning (rain
elsewhere). Too, the wintry precip chances occur during the
overnight hours. Freezing rain will be featured Monday night for
the Northwest Ranchlands and Zapata County. The freezing rain
threat will shift east to Kenedy and Brooks Counties Tuesday
night, with even a slight chance of freezing drizzle for Cameron
County early Wednesday. A fresh surge of high pressure will spread
over the area late next week and will end the influence of the
coastal trough and the associated rain chances.

&&

.AVIATION...
(06Z TAFS)
Issued at 1050 PM CST Tue Jan 14 2025

Conditions have become LIFR at KHRL and KBRO tonight with ceilings
of 400 ft while KMFE has still maintained IFR with ceilings at
500 ft, but is expected to eventually drop down to LIFR (400ft
ceilings) over the next couple of hours. Light intermittent
showers, mist and patchy fog will continue overnight, bringing
periods of reduced visibility of less than 2-4 SM, potentially
less than 1 SM at KHRL. LIFR conditions are anticipated to linger
through sunrise, gradually rising to IFR ceilings (500 ft)
throughout the morning. Chances of showers decrease in the
afternoon along with a pick up in north-northwesterly winds. Winds
settle later Wednesday evening, with conditions possibly
beginning to improve towards the end of the TAF cycle as trough
moves to northeast.

&&

.MARINE...
Issued at 316 AM CST Wed Jan 15 2025

Today through Tomorrow...A Small Craft Advisory is currently in
effect for the northern nearshore and offshore waters (Port
Mansfield up to Baffin Bay) until 6 pm today. Guidance is
suggesting that this advisory may need to be extended to all Gulf
Waters overnight as wave heights are expected to increase to up to
8 feet tonight. Thursday will slightly improve but still remain
dangerous for small craft, with heights between 4 to 7 feet
expected. Winds will remain north-northeasterly today and
tomorrow, with the highest anticipates (20-25 knots) expected
tonight.

Thursday night through Sunday night...Moderate to fresh (offshore
zones) winds and moderate to slightly elevated seas will
initially prevail, prompting mainly small craft should exercise
caution conditions. A Saturday cold front will bring strong north
winds and high seas, producing small craft advisory conditions.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             55  51  63  52 /  30  20   0   0
HARLINGEN               53  49  63  48 /  40  10   0   0
MCALLEN                 53  51  66  51 /  30  10   0   0
RIO GRANDE CITY         53  50  66  48 /  30  10   0   0
SOUTH PADRE ISLAND      59  56  62  58 /  50  30   0   0
BAYVIEW/PORT ISABEL     56  52  62  52 /  50  20   0   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk through Thursday afternoon for TXZ451-454-
     455.

GM...Small Craft Advisory until noon CST Thursday for GMZ130-132-135-
     150-155-170-175.

&&

$$

SHORT TERM...55-MM
LONG TERM....54-BHM
AVIATION...55-MM