Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 281510 AAB

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1010 AM CDT Fri Oct 28 2016

.DISCUSSION...Made a couple tweaks to forecast for remainder of
today. First was to remove mention of thunder for land areas
through this afternoon. Dry air aloft extends out about 250 miles
into the Gulf ahead of inverted low/trough. Only lightning
detected currently is on back side of the trough, and this won`t
reach us during daylight today. Subsidence inversion with base at
800mb also evident on 12Z BRO sounding. Consensus of short-term
model soundings also leans hard against enough instability for
thunder this afternoon. Second change was to bump up max temps a
couple of degrees (above guidance), to around 90, for the mid-
Valley/McAllen metro area. Record high of 94 was reached
yesterday. Thicknesses nudge down today and morning min was 65,
but should still be able to recover to near 90. Updated products
already sent.


.DISCUSSION...Updated for latest marine discussion below.


.MARINE...Raised combined seas to 5 feet for zones 20-60nm out.
Latest obs from Buoy 020 suggest easterly swell is building
slightly faster than previously forecast. Change is reflected in
latest Coastal Waters Forecast.


.PREV DISCUSSION... /issued 711 AM CDT Fri Oct 28 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...The 00z BRO sounding shows a pretty dry atms in place
over the RGV with only some shallow low level moisture evident. A
more moist and unstable atms is located out over the lower TX Gulf
waters where KBRO radar shows isold marine conv moving west
towards the coastline. This conv appears to be dissipating as it
meets up with the drier and more stable air in place over the
inland areas. 500 mb ridging looks to remain in place over the RGV
over the upcoming 12 to 18 hours while an inverted trough over the
marine areas will start to build in along the coastline from the
18 to 24 hour portion of the current TAF package. Some MVFR
ceilings may be possible late in the current TAF period as the
troffing gets a little closer to the region. For now will go with
VFR conditions until the inverted troffing over the Gulf of Mex
gets a little further inland over the RGV airports.

PREV DISCUSSION... /issued 459 AM CDT Fri Oct 28 2016/

SHORT TERM (Today through Saturday):The short term 500 mb fields
indicate that a ridge axis will remain in place over the RGV
throughout today and early tonight. IR satl imagery over the Gulf of
Mexico indicates that a broad inverted trough axis is producing a
pretty decent area of conv over much of the Gulf. This inverted
trough axis will steadily build west later tonight into Saturday as
the 500 mb ridge over the region weakens. As this trough builds west
deeper layer tropical moisture will start encroaching along the
lower TX coast. The combination of the approach of the Gulf trough
axis and the deepening tropical moisture will start in boost up the
conv potential over the region late tonight into Saturday.

Short term guidance from the NAM/GFS and ECMWF differ a bit on the
timing of the approach of the inverted trough. The ECMWF is the
quickest of the three models with the GFS being the slowest. The NAM
splits the difference between the two. Despite the timing
differences between the three models...all three check in today with
fairly similar max and min temp trends. So will opt for a general
blend of the short term model sets for both temps and pops through

Will include a mention of patchy fog across the northern counties
both for this morning and Saturday morning. The light surface winds
will combine with elevated dew points to maintain the threat of
some patchy fog across the climatologically more favorable areas
in the northern counties.

LONG TERM (Saturday Night through Thursday):The first decent
push of moisture will be Saturday night into Sunday as an inverted
mid level trough continues to move westward across Deep South
Texas/Northeast Mexico and have kept chances POPs going. The H5
ridge of high pressure will retreat northward in response...and
gradually shifts over the Southern CONUS and Gulf Waters as the
trough moves inland. Deeper layer moisture will continue to be
ushered into the RGV through the weekend and into early next week
as precipitable water values increase to near the 2" mark. The
best chances for showers/storms still looks to be Monday.
However...with the RGV in the western periphery of the
high...moisture influxes will continue through mid week...with
scattered showers and thunderstorm chances. By late in the
period...the high pressure will begin to recenter over
Texas...with precip chances decreasing.

Furthermore...beach run-up is expected through the late weekend
and into next week as swell heights increase due to a
prolonged...nearly due east fetch. The water run up maybe
significant during high tide and could approach the dunes or maybe
make it into the dunes. This situation will continued to be


Today through Saturday: The persistent surface ridging over the
Gulf of Mex will interact with elongated surface troffing located
further south to maintain a fairly persistent easterly low level
flow over a large portion of the Gulf of Mex. This will maintain a
steady runup of long period swells on the lower TX coastline. This
may push conditions across the lower TX Gulf waters up close to
SCEC criteria either today or Saturday.

Saturday Night though Tuesday Night...The surface pressure
gradient will increase in response to surface high pressure over
the Northern Gulf interacting with weaker/low pressure over the
Southern Gulf/Bay of Campeche. A long fetch of easterly flow will
maintain elevated seas with swell heights of 4 to 6 feet...or
possibly higher. SCEC conditions will likely be meet...although
Small Craft Advisories may be needed at times. Meanwhile...ENE to
ESE winds will continue to be light to moderate through the
forecast period. There will also be increased convective activity.




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