Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 151537 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
937 AM CST Thu Feb 15 2018

.DISCUSSION...Updated grids to take out the coastal fog for this
afternoon and evening as southerly winds have helped to lift the
fog across the region with improved visibilities. In addition, a
slight upward adjustment regarding the temperatures were made in
the valley given the latest trends and clearing skies.


.PREV DISCUSSION... /issued 445 AM CST Thu Feb 15 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Increasing surface winds produced a radical reduction
in fog and improvement in visibilities over the past several
hours, and the forthcoming TAFs will reflect this trend. VFR is
expected today as surface winds increase even further and cloud
decks rise and thin. Winds tonight appear that they will be too
strong to produce widespread or dense fog, but cloud cover could
be more and lower than the FEW020 indicated for the overnight

PREV DISCUSSION... /issued 419 AM CST Thu Feb 15 2018/

SHORT TERM (Now through Friday): A very interesting situation
occurred within the past few hours. At around midnight, stronger
winds in the lower levels of the atmosphere began mixing down,
causing an increase in surface winds. This wind, combined with a
slight increase in ambient air temperatures, resulted in rapidly
improving visibility across all of Deep South Texas and the Rio
Grande Valley as a majority of the fog that existed at that time was
scoured away. As a result, the Dense Fog Advisory will be cancelled
for the inland portions of Cameron and Willacy Counties but kept in
place everywhere else previously in effect as marine fog along the
Lower Texas Coast advects inland. Fog over the immediate coastal
area will continue to be a concern through the forecast period.
Otherwise, 500 mb high pressure over the BRO CWFA will produce dry
weather with well above normal temperatures.

LONG TERM (Friday Night through Wednesday): Large-scale pattern
features broad troughing across the eastern half of the U.S. with
another Baja California low developing this weekend. Across South
Texas, southwest flow aloft will continue as high pressure
retreats eastward into the western Atlantic. Models seem to be in
better agreement on the cold front that will likely stall just to
our north Saturday and Sunday. A 1035mb surface high out of Canada
won`t gain much southward extent as the main upper trough is
weakly amplified and moves it quickly eastward towards the
mid-Atlantic. Therefore, temperatures this weekend will likely be
several degrees above normal with highs reaching the mid 80s and
slightly cooler in northern Zapata, Jim Hogg and Brooks counties
due to more cloud cover and rain chances. Increased high temperatures
in the lower to middle Rio Grande Valley as models remain
consistent with strong S/SE flow south of the front. The best
chance of rain will be in the northern ranchlands, but can`t rule
out convection in the RGV due to the vicinity of the boundary and
a couple weak shortwave troughs aloft.

The pattern will remain largely unchanged early in the week with
southwest flow aloft and modest moisture, providing at least
slight chances of showers. Well-above-normal low and high
temperatures are expected each day as warm, moist air overspreads
the region amid strong southeast flow. The main impact will be
breezy to windy conditions as a series of storm systems develop on
the lee side of the Rockies and move across the Plains. The
pressure gradient will tighten with winds ranging from 25 to 35
mph Monday afternoon. The next cold front will be possible
Wednesday into Thursday.

MARINE (Now through Friday): Buoy 42019 reported southeast winds
around 12 knots gusting to around 16 knots with seas of 3 feet with
a period of 7 seconds at 02 CST/08 UTC. The main concern during the
forecast period will be fog. Warm and moist moderate to breezy winds
will pass over the Lower Texas coastal waters today through Friday,
allowing for the formation of fog, especially over the Laguna Madre
and Gulf of Mexico waters from 0 to 20 nautical miles offshore. A
Dense Fog Advisory is in effect for these two areas until mid-
morning today, with the possibility that the Advisory will need to
be extended in time and/or areal coverage for the remainder of the
forecast period. Otherwise, high pressure over the western Gulf of
Mexico will produce generally moderate winds and seas for the Lower
Texas Coast. Wind speeds may be high enough to warrant Small Craft
Exercise Caution for portions or all of the Lower Texas coastal
waters during the period.

Friday night through Tuesday: Light to moderate southeast winds on
Saturday will increase Sunday into Monday with seas building to 4
to 7 feet. The pressure gradient will strengthen on Monday with
low pressure developing in the Plains, leading to possible Small
Craft Advisory conditions Monday and Tuesday. There is also a
slight chance of showers each day with abundant moisture overhead
with weak upper level disturbances moving across the region.




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