Area Forecast Discussion
Issued by NWS Brownsville, TX
FXUS64 KBRO 192340 AAA
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
640 PM CDT Wed Oct 19 2016
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...Mostly clear skies and light southeast winds
prevail across Deep South Texas this evening. VFR conditions
expected for much of the night. A pre- frontal trough will
approach the Rio Grande Valley late tonight. This will result in
very light northeast winds which may allow some patchy fog to
develop at local TAF sites. Model guidance continues to suggest
periods of MVFR visibility between 10-14Z. Showers and thunderstorms
will develop on Thursday afternoon ahead of a cold front, but
should be mainly beyond the TAF period.
.PREV DISCUSSION... /issued 257 PM CDT Wed Oct 19 2016/
SHORT TERM (Now through Thursday night): A cold front, now
nearly stationary across NW TX and southern NM, will get a kick in
our direction beginning tonight as an upper-level trough emerges
from the Rockies into the Plains. This while bring widespread
chances for rain to Deep S. Texas, mainly from tomorrow afternoon
through tomorrow night. Rainfall amounts will generally be around
0.5"...perhaps closer to an inch in the SE coastal areas.
Meanwhile, another warm night in store as with lows in the 70`s
most locations. SE winds this evening go nearly slack as a pre-
frontal trough approaches from the north around dawn. With
elevated dewpoints in place, patchy fog is again expected for the
Northern Ranchlands and perhaps the outlying areas around
Harlingen and McAllen. There will a slight chance for showers in
coastal areas as well late tonight, as Gulf moisture increases
Timing of front`s arrival continues to slow a bit, so one more
day with above-normal temps is in store for Thursday, with low-mid
90`s across the RGV. A pre-frontal trough, with winds shifting to
the NE, is progged to arrive around mid-day. This, along with
decent destabilization from daytime heating and perhaps sea-breeze
convergence, will allow scattered showers and thunderstorms to
develop in the afternoon, even before the front itself arrives.
12Z runs of NAM/GFS put this arrival mid-late afternoon (21-00Z)
for the northern counties and evening for the RGV (03-06Z). No
severe storms are expected, with the upper-level support far
removed from the local area yielding very low vertical shear.
Rainfall amounts will be mostly in the "beneficial" range of
0.5-1.0", with coastal areas favored with better moisture.
Flooding concerns fairly minimal with little recent rain and PW
ahead of the front holding around 1.5-1.8". North winds of
15-20mph also likely to accompany the front.
For Thursday night, upper-level moisture remains in place, at
least for the RGV, though instability will be on the decrease as
lower dewpoints move in from the north. Gradually trended PoP`s
down overnight from NW to SE. Moisture will hang on in the
Brownsville vicinity, with scattered showers through he night.
LONG TERM (Friday through Wednesday): The cold front should be
through the CWA and offshore by the beginning of Friday, based on
winds, thicknesses, and relative humidity. Slight rain chances
will linger over the lower valley through about noon however, and
winds will stay moderate through afternoon with the prevailing
pressure gradient. Temperatures will bottom out pretty much
diurnally, near dawn, but may be a little slow to warm Friday
morning, especially along the coast and the Tipotex as winds veer
to northeast and keep an orientation that brings cooler Gulf air
across areas that are not far enough inland to quickly counteract
the cooling effect through daytime heating. That said, most areas
should see upper 70s to lower 80s for high temps for the day under
partly cloudy skies. Friday night, being essentially the second
night behind the front, will see the coolest temps, which will
range from the mid 50s across the ranchlands and brush country to
the mid and even upper 60s along the coast. Look for low to mid
80s on Saturday under mostly sunny skies with light northeast to
H5 ridging will build over the Southwest United States as the
front weakens offshore. The axis of the ridge will slide east
slowly overhead during the remainder of the long term. Thus, a
slow warming trend to above normal temperatures will ensue over
the weekend, with low rain chances. Winds will veer to southeast
again as early as Sunday, however, bringing low level moisture
back over the CWA and even deeper into South Central Texas.
Coastal showers will make a comeback by Monday, but models
indicate that any sea breeze may not be enough to produce any
showers farther inland until Wednesday.
Now through Thursday night...Current light to moderate SE winds
will back to the NE as a pre-frontal trough moves through the
waters Thursday morning. Moisture will also be on the increase
from the Gulf overnight with scattered showers and thunderstorms.
Winds become northerly behind the front on Thursday night and
increase to 20-25 kt., so Small Craft Advisories will be needed
at that time. 2-3 ft. seas remain the rule until becoming more
adverse Thursday night with the increased winds. Seas approach 7
ft. by early Friday morning. Mariners should be aware of rapidly
changing conditions around any showers and thunderstorms.
Friday through Monday...A cold front pushing through to the coast
Thursday night will set up small craft advisory conditions on
Friday, as high press settles in behind the front. Strong
northeast winds will persist Friday, eventually dropping below 20
knots late in the day. Wave heights on the Gulf will likely remain
at or above seven feet into Friday night, however, extending
small craft advisory conditions. Conditions will then improve
slowly through the rest of the weekend and into early next week.
Winds will become light to moderate east southeast on Saturday
with moderate seas.
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