101
FXUS64 KBRO 170910
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
410 AM CDT Fri May 17 2024

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

.SHORT TERM...
(Today through Saturday)
Issued at 407 AM CDT Fri May 17 2024

Key Messages:

* Low to medium (20-50%) chance for showers and thunderstorms today
  (greatest chance Northern Ranchlands)

* All of Deep South Texas including the Rio Grande Valley is under a
  Marginal (Level 1 out of 5) Threat for Severe Thunderstorms today

* Saturday will mark the beginning of another stretch of very warm
  and hot conditions

The main forecast concern for Deep South Texas and the Rio Grande
Valley will be the potential for showers and thunderstorms today and
again later this afternoon/evening. A stalled out cold frontal
boundary over the Northern Ranchlands and a shortwave overhead will
be the focus of showers and thunderstorms potentially developing
over the local forecast area today. Currently, there is a low to
medium chance ranging from 20-50% for showers and thunderstorms
today with the lower chances along the Rio Grande Valley and the
higher chances over the Northern Ranchlands (in closer proximity to
the aforementioned frontal boundary).

With the local forecast area placed on/near the right entrance region
of an 80-100 kt jet overhead, Showalter values indicating a
moderately to very unstable atmosphere, MLCAPE values between 500-
1,000 J/kg, MUCAPE values between 1,000-3,000 J/kg, and decent mid-
level lapse rates of around 7C/km, there is enough large scale
forcing and instability in place for storms to develop.
Additionally, with 0-6km bulk shear values between 50-60 kts, any
storms that develop will have the potential for becoming strong to
severe with the capabilities of some hail and/or damaging winds.
Given the overall atmospheric dynamics and synoptic pattern in
place, all of Deep South Texas and the Rio Grande Valley run the
risk of isolated severe weather today. The Storm Prediction Center
(SPC) in Norman, OK has placed the entire area under a "Marginal
(Level 1 out of 5) Risk" for severe weather today. Again, the main
threats will be isolated damaging wind gusts and hail. Finally, any
storms that do form will also have the capabilities of producing
heavy rainfall with PWAT values between 1.75-2.30 inches (1 to 3
STDEVs above normal).

Otherwise, expect for today to be mostly cloudy, warm, humid, and
hazy. High temperatures are expected to range between 90-95F this
afternoon (cooler near/along the coast due to continued onshore flow
out of the east-northeast).

The storm threat comes to an end later this evening/tonight as the
frontal boundary lifts northward and high pressure begins to
strengthen. Tonight will once again be another warm and muggy night.
Given the copious amounts of low level moisture in place, some
patchy mist/fog is also possible once again tonight as well. Low
temperatures are expected to be in the 70s most places with similar
dewpoint values (narrow dewpoint depressions).

After a day of relatively cooler temperatures, Saturday will begin
another stretch of very warm to hot days as forecast models and
ensembles show ridging strengthening and 500 mb geopotential heights
increasing over the region. During the day on Saturday, the northern
fringe of a 591 dam heat dome will encompass most, if not all of the
area. Additionally, the 1000-500 mb thickness values increase over
the area as well with values returning to around 580 dam. This
implies 850 mb temperatures reaching the lower 20s (degree Celsius)
which will translate to surface temperatures in the mid 90s to near
lower 100s on Saturday across Deep South Texas and the Rio Grande
Valley. This coupled with dewpoints in the 70s will result in heat
indices ranging between 103-111F on Saturday (just below Heat
Advisory criteria).

&&

.LONG TERM...
(Saturday night through Thursday)
Issued at 407 AM CDT Fri May 17 2024

Mid-level ridging will build over Texas through the period leading
to warming temperatures with triple digits across the Rio Grande
Plains on Sunday afternoon with mid to upper 90s across the rest of
the area, except for the 80s near the coast. The triple digits will
expand eastward through the week, reaching the I-69c/US 77 corridor
by Tuesday. High humidity combined with the hot temperatures will
lead to "feels like" temperatures exceeding 110 degrees in many
areas and Heat Advisories will likely be needed Monday through
Friday. Overnight temperatures each night will remain warm with lows
falling into the upper 70s to low 80s. The NWS HeatRisk tool
highlights a major risk of heat-related impacts for those that are
not properly hydrated or do not have effective cooling in place
through the week. The combination of lack of moisture and subsidence
will generally maintain rain-free conditions across Deep South Texas
through the long term.

&&

.AVIATION...
(06Z TAFS)
Issued at 1246 AM CDT Fri May 17 2024

Through 06z Sunday....MVFR conditions were taking place at the TAF
sites under a SCT-BKN deck of stratus clouds with ceilings between
1,000-1,500 feet AGL and haze which is restricting visibilities down
to 4-6 statute miles. Much of the TAF period including the next 6-9
hours will continue to experience MVFR cigs and/or visibilities. There
could be times especially during the day today where VFR conditions
are seen.

There is a non-zero, low grade probability of showers and
thunderstorms to develop this morning and then again this
afternoon/evening as a frontal boundary approaches. Opted to keep
headlines out of the TAFs given the continued uncertainty with the
likelihood and coverage of storms. If confidence for storm
chances increase in the hours ahead, will make amendments in the
form of a TEMPO or Prob30 to the TAFs to reflect the increase
confidence.

Winds are currently out of the southeast at 5-10 kts. An outflow
boundary from earlier convection to our north could shift winds out
of the east-northeast towards daybreak. Otherwise, expect for light
and variable winds during the morning hours. During the afternoon
hours today, expect for winds to become east-northeasterly between 5-
10 kts.

&&

.MARINE...
Issued at 407 AM CDT Fri May 17 2024

Today through Saturday: Light to moderate winds will yield low to
moderate seas today through Saturday. While marine conditions are
mostly favorable today through Saturday, there remains a
"Moderate Risk" for rip currents along the are beaches through
Saturday.

Saturday night through Thursday: Light to moderate winds with
moderate seas of generally 3 to 5 ft will persist through late in
the week. A slighlty enhanced pressure gradient each afternoon,
especially next week, could lead to periods of Small Craft
Caution.

&&

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE             92  78  94  78 /  20  20  10   0
HARLINGEN               92  75  95  75 /  30  20  10   0
MCALLEN                 94  77  98  78 /  40  20  10   0
RIO GRANDE CITY         92  74  99  76 /  40  20   0   0
SOUTH PADRE ISLAND      85  80  85  80 /  20  30  10   0
BAYVIEW/PORT ISABEL     88  77  90  78 /  30  20  10   0

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

SHORT TERM...23-Evbuoma
LONG TERM....63-KC
AVIATION...23-Evbuoma