Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 080551 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1251 AM CDT Thu Jun 8 2023

...New AVIATION...

(Tonight through Thursday night)
Issued at 250 PM CDT Wed Jun 7 2023

Key Messages:
-Heat continues to build.
-Thunderstorm chances are down, but not out.

What seemed to be a straightforward forecast now has a wrinkle or
two thrown in.  The main message will continue to be the building
heat.  Here at BRO, for example, we have already hit 93F today.
Regarding shower and thunderstorm chances, enhanced flow aloft will
keep at least limited coverage around for this evening, mainly along
the Rio Grande near Starr County, then perhaps again tomorrow
evening, more focused toward the Brooks/Kenedy ranches.

In the bigger picture, currently, ridging aloft with axis roughly
along the Pecos River valley is actually weakening a bit, especially
at 250mb, as it is undercut by a subtropical jet moving in from the
Pacific.  However, NAM/GFS both rebuild a larger-scale subtropical
ridge across northern Mexico as early as tonight.  Jet-level NW flow
is progged to reach 80-90 knots on the front side of this ridge on
Thursday, before weakening somewhat Thursday night as the larger-
scale ridge axis begins to translate eastward.

Regarding temperatures and building heat, overnight lows generally
expected to be in the lower 70s for interior areas, with more mid-
70s along the Rio Grande (still actually a degree or two below
normal).  For Thursday, with the aforementioned ridging aloft
upstream, 1000-500mb heights nudge up, which generally supported the
increasing trend in max temps seen in NBM guidance.  High temps
should reach the mid-90s pretty much everywhere away from the coast
(going with 95F at BRO and 97 at MFE), with the Falcon Lake/Zapata
areas reaching 100-101F.  Heat indices top out in the 102-106F
range, except slightly lower in Jim Hogg where dewpoints dip into
the mid-60s.

As far as those thunder chances...been a bit tough to find consensus
amongst the global/regional models and CAM`s.  After collaborating
with WPC on QPF placement, appears that most likely spot for remnant
showers or perhaps a thunderstorm affecting the area this evening is
along the Rio Grande, from western Hidalgo up through Zapata
counties, so have inserted a few hours of mentionable PoP`s there.

Of potentially greater interest, SPC has placed much of the CWA
(except Zapata and most of Starr counties) into a Marginal (Level 1
of 5) risk of severe weather for Thursday, with the focus on the
evening hours.  At his point, confidence is on the lower side,
however.  There is some concern that storms developing across
central/south-central TX may move S/SE into our area.  Due to the
enhanced NW flow mentioned above, deep-layer shear is actually
stronger over Deep South TX vs. further north. On the other hand,
the competing influence of the approaching ridging aloft, and
associated drying of the column (evident especially in the NAM),
really decreases confidence with the potential southward extent of
any storms.  So, thunderstorm chances are relatively low, but
conditionally, any storms that form have a decent chance of becoming
strong-to-severe and producing strong winds and large hail.  Gridded
guidance not catching onto this scenario very well, so edited in
mentionable PoP`s/thunder chances for Kenedy and eastern Brooks as a
starting point.  Stay tuned for changes on this in future updates.


(Friday through next Wednesday)
Issued at 250 PM CDT Wed Jun 7 2023

-Hot temperatures will lead to Heat Advisories likely through
 much of the period.

Dry and hot conditions will be the main story through the long term
period. A midlevel ridge will push east into south Texas. The good
news is that this will suppress thunderstorms chances through the
period. The bad news is that this means the heat is on.
Temperatures will continue to climb through the weekend into next
week. High temperatures will range from the mid 90s across our
eastern counties to low 100s across the Rio Grande Plains. As we
head into the middle of next week expect uppers 90s to low 100s
across the eastern counties and temperates nearing 110 across the
Rio Grande Plains. Couple these hot temperatures with high
dewpoints and high humidity, heat indices will likely hit Heat
Advisory criteria for at least some portion of our CWA most days.


(06Z TAFS)
Issued at 1242 AM CDT Thu Jun 8 2023

VFR will be the rule at the aerodromes through the next 24 hours.
Light to moderate winds are also anticipated.


Issued at 250 PM CDT Wed Jun 7 2023

Now through Thursday Night: Light NE winds and flat/nearly glassy
seas persist on the Gulf waters, per observations from Buoy
42020. Slight breezes of 10-12 knots have picked up on the Laguna
Madre behind the sea-breeze. Weak high pressure over the NW Gulf
should maintain these quiescent conditions in the short- term. A
few showers and thunderstorms could impact the northern waters
Thursday evening, but confidence on this is low.

Friday through Tuesday...Light to moderate southeasterly winds
are expected through the forecast period. We could see Small Craft
Caution conditions at times as winds become slightly more
elevated, especially each afternoon. Expect seas to increase
through this weekend into next week to 2-4 ft.


BROWNSVILLE             75  95  77  93 /  10   0   0   0
HARLINGEN               73  98  74  97 /  10   0   0   0
MCALLEN                 76  99  77  98 /  10   0   0   0
RIO GRANDE CITY         74 101  75 101 /  10   0   0   0
SOUTH PADRE ISLAND      79  88  80  88 /  10   0   0   0
BAYVIEW/PORT ISABEL     75  93  76  92 /  10   0   0   0




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