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000
FXUS64 KBRO 102343
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
643 PM CDT Wed Apr 10 2024

...New AVIATION...

.SHORT TERM...
(Tonight through Thursday night)
Issued at 336 PM CDT Wed Apr 10 2024

The closed 500 mb mid-level low and associated mid-upper level
trough over east Texas will lift east-northeastward throughout the
short term period. The 30 to 50 knot low level jet (LLJ), behind the
cold front, which passed through early this morning, will continue
to roar above Deep South Texas overnight tonight and then gradually
translate east-northeastward with the trough early tomorrow morning
and throughout Thursday, thus diminishing winds aloft. At the
surface, north-northwesterly winds on the backside of a low pressure
system, currently over the southern Gulf states, will bring
southward a surge of high pressure late tonight and a high pressure
will emerge from the southern Rockies tomorrow as the low departs to
the northeast.

Due to the boundary layer heights mixing down strong winds from the
LLJ aloft, strong and gusty northwesterly winds will continue into
this evening. A Wind Advisory remains in effect till 9 PM CDT
tonight for winds of 20-30 mph with gusts up to 50 mph. Along with
the strong wind, relative humidity values (RH) continue to range
from 15% to 20% with slightly higher values in coastal areas; a Red
Flag Warning also continues till 9 PM CDT tonight for the entire CWA
outside of the Coastal and Island Counties. Overnight, as boundary
layers heights lower and decouple from the LLJ, surface winds will
diminish significantly overnight and from the north as a surge of
high pressure arrives near the coast. Overnight lows will range the
low 50s across the northwestern half of the CWA and from the mid to
upper 50s for the southeastern half with low to mid 60s across the
coastal areas.

Behind the surge of high pressure, a light westerly wind will settle
over the CWA by sunrise and remain throughout the day. As the high
pressure mentioned above emerges from the Rockies, winds will veer
from the northeast tomorrow evening then transition to southeasterly
at night and become southerly by Friday morning, remaining light
throughout this timeframe. Thursday`s highs will range from the mid
to upper 80s with upper 70s along the coast and Friday morning lows
will range from the low to mid 50s across the CWA with low to mid
60s at the coast.

&&

.LONG TERM...
(Friday through next Wednesday)
Issued at 336 PM CDT Wed Apr 10 2024

*Key Messages
-Dry and breezy Friday supports additional wildfire spread concerns
-"Valley Wind Machine" takes over from the weekend through mid-week,
with sultry nights and warm to hot and humid afternoons
-South-to-north longshore currents dominate the weekend and next
week at the beach
-Difficult boating conditions due to wind on Laguna Madre and wind
waves in the Gulf

Mid-April across the Valley brings a somewhat common refrain for the
region, with increasingly warm to hot temperatures, building
humidity, and plenty of wind by day with fresh breezes overnight.
The culprits are a strengthening (for April) and broad subtropical
500 mb ridge which initially is centered over eastern Mexico through
early Sunday, which shifts into the western Gulf Sunday night and
parks there through at least next Wednesday. Meanwhile, speedy flow
initially rides over the ridge through Sunday, and re-orients on a
southwest-northeast trajectory from western Mexico through
west and central/north Texas Sunday night through next Wednesday. At
the surface, this is a "classic" Valley Wind Machine setup, favoring
persistent southeast to south flow for most of the period. As for
precipitation?  No luck in this forecast, as the stronger
forcing...when it appears early next week...remains well north of
the RGV. This has been the general trend this spring so far (fewer
rain events compared with this time last year) and it remains to be
seen how long this general pattern persists.

As for sensible weather...Friday will be the last of the pure sunny
days with average temperatures as surface winds begin picking up
from the east-southeast.  Lower level moisture arrives over the
weekend...gradually at first as Saturday should see a mix of sun and
clouds with limited haze even as surface flow veers southeasterly.
That changes Sunday as the aforementioned 500 mb ridge begins to
slide east...opening the door to a tightening gradient between the
somewhat strong surface ridge in the Gulf and lowering pressures
along the west Texas/Sierra Madre trough. Expect more filtered
sunshine through more clouds and haze to arrive then. The clouds
will likely hold temperatures back a bit, especially where thickest
(Hidalgo/Brooks and points east) and counter the rising 1000-500 mb
thicknesses. In the end, near average temperatures (mid to upper 80s
east to mid 90s Rio Grande Plains) covers it.

A small but somewhat potent 500 mb trough will rip through
southern/central Plains later Monday and Monday night, with
intensifying surface trough tightening the gradient further. GFS
indicated a period of 50 knot 850 mb southerly jet late Monday
through early Tuesday...which could bring near Wind Advisory
conditions to the lower Valley which could persist overnight.
Daytime cloud cover will determine just how hot it gets Monday as
thicknesses sneak above 583 dm and 850 temperatures push toward 28C.
Typically, we see a few more breaks ahead of such systems,
especially from the mid Valley through the Rio Grande Plains...and
triple-digit heat is possible in Zapata and southern Starr Monday.

Tuesday`s deterministic forecasts from the ECMWF and GFS differ
slightly as the ECMWF nudges a weak boundary toward the Brush
Country, while the GFS says no. The main difference would be in
gusty winds, as the GFS continues the trend from Monday, even as the
core of the 850 mb jet eases into the Gulf - while the ECMWF dips
winds a bit (though still southeasterly).  Either way...still plenty
of soupy haze following a very sultry overnight Monday where
temperatures may not drop below the mid to upper 70s if winds stay
up and the expected overcast at night verified.

More heat, humidity, and sultry breeziness on Wednesday.

With the increasing heat and humidity, we`ll be watching apparent
temperatures rising to or above 100 degrees across portions of the
mid/upper Valley, beginning Monday and most likely Tuesday and
Wednesday. In addition, expect air quality to worsen...a combination
of viscous air and overnight inversions trapping pollutants from
agricultural and industrial burning in Mexico, which begins to peak
this time of year.  Finally...south to north longshore currents
arrive Saturday and peak Sunday through Wednesday at South Padre
Island.

&&

.AVIATION...
(00Z TAFS)
Issued at 643 PM CDT Wed Apr 10 2024

VFR will prevail through the forecast period at all TAF sites.
Breezy north to northwest winds with gusts up to 30 knots will
persist through the early evening hours, but should begin to
subside as high pressure settles in across the region. Wind speeds
will remain around or below 10 knots through Thursday evening,
generally out of the west northwest early Thursday, shifting to
the north by Thursday afternoon.

&&

.MARINE...
Issued at 336 PM CDT Wed Apr 10 2024

Adverse marine conditions continue through tonight for the coastal
waters. Strong northwesterly winds this afternoon will settle down
for a brief period in the evening. However, a surge of high pressure
will re-enhance northerly winds with a moderate-to-fresh breeze into
the late night hours, but more concentrated over the Gulf Waters.
Small Craft Advisories remains in effect till 1 AM CDT Thursday
morning for the Laguna Madre and till 7 AM CDT Thursday morning for
the nearshore (0-20 nm) and offshore (20-60 nm) Gulf Waters.
Tomorrow, winds will diminish across all marine zones and turn
westerly by sunrise, easterly by the evening and becoming
southeasterly overnight as a high pressure settles across the
region.

Friday through Monday Night...Increasing east southeast winds may
require caution on Laguna Madre Friday and Friday night before
veering southeast Saturday, increasing gradually, and continuing
through Sunday night.  Viscosity and a still decent marine layer
nearshore (analyzed SST are still in the 68-71 range) will knock
down daytime winds to around 15 knots, while Laguna Madre reaches
Advisory levels each afternoon and evening Saturday-Sunday.

By Sunday night...caution conditions (15-20 knot and gusty) are
likely just about everywhere...continuing into Monday over the Gulf
with Advisory conditions likely on Laguna Madre. Aforementioned low
level jet arrives Monday night which may be enough for 20-25 knot
(or even higher) advisory conditions in all waters...something we`ll
need to keep an eye on.

As for seas...low to moderate seas Friday into Friday night before 4-
5 foot levels with plenty of wind wave begins Saturday and persists
through Sunday, rising to 5-7 feet...perhaps higher...late Sunday
night and Monday.

&&

.FIRE WEATHER...
Issued at 336 PM CDT Wed Apr 10 2024

Rest of Today through Thursday...Continuation of the Red Flag
Warning has been mentioned above as conditions are right in line
with expectations. Thursday will see lighter winds but continued
very low afternoon humidity...increasing the fuel dryness and
setting the stage for some potential concerns Friday (below).

Friday: The "flash" drying today (Wednesday) which continues with
very low RH Thursday will set the stage for at least a Fire Danger
situation (just below Red Flag Criteria...check out
https://weather.gov/rgv/mapcolors#fire for the matrix) Friday
afternoon as afternoon humidity drops below 30 percent with winds
back up to 15-20 mph and temperatures well into the 80s. Best
opportunity will be along/west of IH-69C/US281 with a pocket of
southern Hidalgo/southern Starr an area of continued concern where
greenup has yet to be fully realized and conditions there may be
reverting to more fully cured.

Saturday: Humidity should return from east to west along with the 15-
20 mph winds now from the southeast...but we`ll need to watch Starr
and at least southern Zapata for some potential fire weather
concerns.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             59  84  61  82 /   0   0   0   0
HARLINGEN               55  86  56  84 /   0   0   0   0
MCALLEN                 58  88  59  86 /   0   0   0   0
RIO GRANDE CITY         55  87  58  87 /   0   0   0   0
SOUTH PADRE ISLAND      65  76  67  76 /   0   0   0   0
BAYVIEW/PORT ISABEL     59  82  61  80 /   0   0   0   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Wind Advisory until 9 PM CDT this evening for TXZ248>255-351-
     353>355-451-454-455.

     Red Flag Warning until 9 PM CDT this evening for TXZ248>255-353.

     High Rip Current Risk through Thursday evening for TXZ451-454-
     455.

GM...Small Craft Advisory until 1 AM CDT Thursday for GMZ130-132-135.

     Small Craft Advisory until 7 AM CDT Thursday for GMZ150-155-170-
     175.

&&

$$

SHORT TERM...65
LONG TERM....52
AVIATION...22-Garcia