Area Forecast Discussion
Issued by NWS Brownsville, TX

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304
FXUS64 KBRO 152350 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
650 PM CDT Tue Oct 15 2019

.DISCUSSION...Updated for latest aviation discussion below.
&&

.AVIATION...Satellite images and surface observations indicate
mostly clear skies across the CWA early this evening. Expect VFR
conditions to prevail across the Rio Grande Valley tonight into
early Wed morning before winds diminish late tonight and low to
mid level moisture increases ahead of a cold front approaching the
northern ranchlands early Wed morning which will allow fog to
develop. Expect MVFR ceilings/visibilities with fog early Wed
morning. As the front moves into deep south Texas Wed
morning...isolated to scattered showers and thunderstorms will
develop along and ahead of the front. This will provide
showers/thunderstorms in the vicinity of local aerodromes
Wednesday.
&&

.PREV DISCUSSION... /issued 303 PM CDT Tue Oct 15 2019/
SHORT TERM (Tonight through Wednesday Night): Elongated 500-mb
ridging extends into Deep South Texas from the Gulf of Mexico
currently and will continue to dominate the weather into this
evening. A hot October day is in progress, with heat indices in
the more populated Rio Grande Valley in the 99-102F range. A cold
front, with much less thermal contrast than the one we experienced
last Friday, will be sagging southward toward the area overnight,
most likely reaching the northern-tier counties by around sunrise
on Wednesday. With winds becoming light ahead of the front and
ample boundary-layer moisture topped by drier air above, looks
like a decent setup for some patchy fog, mainly over the interior
areas. Morning low temps will be in the 70s pretty much
everywhere.

There is some discrepancy in the model solutions as far as precip
chances along and especially behind the front, but expect generally
scattered showers and a few thunderstorms.  If anything, areas
toward Zapata and Jim Hogg counties may be favored during the mid-
late morning hours, where forcing should be a bit stronger closer to
the front`s parent short-wave trough aloft.  Precipitable water
progged to rises to nearly 2.0" right along the boundary, but
instability remains modest (MUCAPE only up to 1000-1500 J/kg).  A
localized inch or even two of rainfall isn`t out of the question,
but widespread heavy rain is not anticipated.

As previous AFD mentioned, temps a bit tricky and non-diurnal with
front moving through during the middle of the day.  Went mainly with
a ConsShort/NBM blend for hourly temps, but nudged up maxes in the
RGV a degree or two (mid-upper 80s).  Front is expected to stall
just to the south of of the area for Wednesday night, with weak
coastal troughing developing as the night goes on.  Continued NW
surface winds/modest cold advection should allow temps to fall into
the 60s for most inland areas, with lower 70s along the coast.  CAPE
becomes essentially nil over land after 17/00Z, so have mentioned
only showers with no thunder that night.

LONG TERM (Thursday through Tuesday): The long term starts with
lots to cover. First, an mid/upper level low/shortwave begins to
eject eastward across the Texas Hill Country and eventually ends
up along the Sabine River by Friday. This feature will help bring
southward the modest frontal boundary highlighted in the short
term period. On the backside of the front, temperatures will cool
into the upper 70s and lower 80s. Clouds and light precipitation
will hold firm across at least the southern half of the region as
there will be some coastal troughing/isentropic upglide taking
place.

Going into the upcoming weekend all eyes will be on a tropical low
currently over the Yucatan, which will eventually push northwestward
into the Bay of Campeche. NHC has a 40 percent chance of TC
development with this feature now. The primary change with the
12z`s would be that the ECMWF has come in a bit more pronounced.
Regardless, model guidance looks to keep this feature just off our
coast with the ECM a western outlier before it move northeast
toward the central Gulf Coast region. With expected westerly
shear, we look to remain on the dry side of the system.

The Weekend looks mostly dry, however, with fewer clouds around a
a stout return flow around the subtropical high to our east,
expect temperatures to warm well above average again for the
weekend. Our next cold front will move into the region early next
week. Of course this far in advance the globals are murky in terms
of timing and strength. The GFS is a bit stronger than ECMWF. Rain
chances increase Monday through the end of the period due to not
only the front passing, but a fairly robust surface coastal trough
developing, which should keep things cooler and wetter, especially
along and east of IH69C.

MARINE (Tonight through Wednesday Night): Favorable marine
conditions, with light-to-moderate SSE winds, seas of 2-3 ft.,
and little chance of thunder, continue through early Wednesday
morning. Conditions gradually deteriorate behind a moderately
strong cold front, which should enter the northern portions of the
Lower Texas coastal waters by mid-morning. NNE winds, especially
over the Gulf, are expected to approach 20 knots by afternoon, so
Small Craft Advisories may be needed for that time through at
least part of Wednesday night. Seas build to around 5 ft. as well.
The front will also trigger scattered showers and thunderstorms.
Winds decrease to 15-20 kt. and veer a bit toward NE as coastal
troughing develops late in the night; this should help maintain
the 4-5 ft. seas and continue Small Craft Exercise Caution
conditions into early Thursday morning.

Thursday through Tuesday: Hazardous winds and seas are expected
to start the long term marine period behind a cold frontal
boundary that passes earlier on in the week. After coastal trough
develops, winds and seas will remain elevated or close to Small
Craft Advisory thresholds. At the very least, cautionary wording
will be likely at the very least. All eyes will turn to a possible
developing tropical feature in the Bay of Campeche. Although most
models seem to want to keep the tropical low to our east, any
development would likely increase seas if not both winds and seas
offshore. Some improvement will take place this weekend with only
moderate seats expected. Conditions again decline going into the
2nd half of the weekend and into early next week as a more robust
cold front is forecast to drop southward creating hazardous winds
and seas once again across the marine zones.
&&

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

$$

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