Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 151821 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1221 PM CST Wed Nov 15 2017

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

&&

.AVIATION...The daytime heating has mixed out the morning fog
leaving behind some fair wx cu VFR/MVFR conditions across the
region. These conditions should persist on into the early evening
hours. Afterwhich the persistent boundary layer moisture levels
will combine with the decreasing overnight surface winds to allow
for another round of late night/early morning fog. The latest NAM
and GFS LAMP guidance hints at some potential for a few hours of
IFR/LIFR conditions early Thurs morning. The GFS guidance is a
little more optimistic on the vsbys tomorrow morning but still
reflects a similar trend to the NAM and GFS LAMP numbers. For now
will lean towards the more pessimistic guidance especially for the
HRL and MFE TAF sites which showed lower vsbys earlier this
morning. As with this current pattern, the diurnal heating
tomorrow morning will help mix out any fog that forms allowing for
conditions to return to MVFR/VFR categories after 14-15z.

&&

.PREV DISCUSSION... /issued 550 AM CST Wed Nov 15 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Patchy fog continues to develop across the area this
morning, but it`s been very local up to this point. Light winds
and moist low-levels should allow fog to expand through sunrise,
so have kept TEMPO MVFR groups for the three airports. Conditions
should improve by mid-morning with daytime heating and light to
moderate southeast winds. With a similar pattern expected tonight,
another round of fog will be possible, especially from HRL to MFE
Thursday morning.

PREV DISCUSSION... /issued 438 AM CST Wed Nov 15 2017/

SHORT TERM (Now through Thursday): Mid-level high pressure will
remain over Baja California with northwest flow over South Texas,
keeping mostly warm and dry conditions across the area. Near the
surface, however, a shallow moist layer and weak to calm winds will
continue to produce mist and fog across Deep South Texas this
morning. Observations from Harlingen to McAllen show occasionally-
patchy fog since midnight, and it should expand across the middle
valley and northern ranchlands through sunrise as radiational
cooling continues amid clear skies. This afternoon, temperatures
will warm up to well above normal with highs in the middle to upper
80s and near-zero chances of rain. Another round of fog is expected
tonight into Thursday morning with light winds and dry air above a
moist surface continuing. Models indicate increasing moisture ahead
of a very weak surface boundary, which is expected to dissipate
before it moves into South Texas. With model time-heights showing 70
to 80% RH almost up to 700mb and light ESE flow at the surface,
isolated convection is possible mainly along the coastal counties.

LONG TERM (Thursday Night through Tuesday): At least the long
term portion of the forecast remains consistent. A cold front is
still progged to affect Deep South Texas and the Rio Grande Valley
on Saturday, producing isolated showers Saturday afternoon and
night. Daytime high and overnight low temperatures are expected
to be suppressed into the near normal range in the wake of the cold
front. In advance of the front, expect above normal temperatures
and dry weather. Just beyond the end of the long term forecast
period, some model guidance suggests the approach and passage of a
mid-level disturbance, with brief but copious rainfall. Will have
to monitor this as Tuesday night and Wednesday slips more into
the official forecast period.

MARINE (Now through Thursday): A weak pressure gradient with a
surface high over the eastern U.S. will maintain light southeast
winds across the coastal waters. Seas will generally range from 2 to
4 feet. Increasing moisture and a very weak dissipating surface
front may produce isolated showers Thursday afternoon.

Thursday Night through Tuesday: The passage of a cold front
through the Lower Texas coastal waters Saturday night will produce
Small Craft Advisory winds and/or seas Saturday night through
early Sunday night. Outside of this period, generally moderate
winds and seas are anticipated.

&&

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

$$

This product is also available on the web at:
HTTP://WEATHER.GOV/RGV

Short Term...60
Long Term...55
Graphicast/Upper Air...56



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