Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 170352 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
952 PM CST Tue Jan 16 2018

.DISCUSSION...The Winter Weather Advisory for Zapata and Jim Hogg
Counties was allowed to expire at 9 PM CST. Additionally, a Small
Craft Advisory for Winds for the Laguna Madre and a Small Craft
Advisory for the Gulf of Mexico waters from 0 to 60 nautical miles
offshore was posted and will begin after midnight tonight. No
other forecast adjustments made.
&&

.PREV DISCUSSION... /issued 626 PM CST Tue Jan 16 2018/

DISCUSSION...Surface winds have diminished below Wind Advisory
criteria, and the Advisory was allowed to expire at 6 PM CST. No
other forecast adjustments made.

PREV DISCUSSION... /issued 552 PM CST Tue Jan 16 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Surface observations indicate that freezing
precipitation is occurring or about to occur at the three major
aerodromes. With freezing temperatures in place and light
precipitation moving north out of Mexico, this trend should hold
through the overnight hours. Improved aviation conditions are
expected beginning around sunrise tomorrow with drier weather,
higher cloud decks, and lighter winds likely.

PREV DISCUSSION... /issued 415 PM CST Tue Jan 16 2018/

SHORT TERM (Now through Wednesday Night) Drier air infiltrating
the surface to 925mb level is allow for decent evaporative cooling
to take place changing rain and drizzle into a mix of snow and
sleet across the upper and mid Valley. Slight accumulation on
elevated surfaces can be expected as the precipitation persist for
the next several hours. As the surface high continues to builds
south and additional dry air moves into the area the wintry mix
should begin to end west to east this evening and push off the
coast by or shortly after sunrise Wednesday. Any residual water on
streets and bridges tonight is likely to freeze, producing black
ice. With temperatures already below freezing across the
Ranchlands and guidance continuing to lower temperatures/dewpoints
will go ahead and issue a hard freeze warning but will keep temps
in the above those levels in the RGV but can not rule out a few
hours of 27-28 degrees in exposed areas in the upper and Mid
Valley areas overnight.

Dry and cold tomorrow but with very dry arctic air overspreading
the region precipitation chances should be near zero even at the
coast. Skies remain overcast so diurnal range will be 5 to 10
degrees at most. The approach of an upper level trough Wednesday
night to help reinvigorate the coastal troughing but with east to
southeast winds increasing at 925-850mb surface temperatures are
expected to remain above freezing in the Lower Valley where
precipitation chances remain the highest. All model guidance
probabilities of freezing or frozen precipitation are low at this
time so no winter advisories expected. Freezing temperatures are
still possible over the far western areas Wednesday night but
precipitation should remain well to the east.

LONG TERM (Thursday through Tuesday):Beginning Thursday morning
the cold air mass will still be in place with light to moderate
northerly flow keeping temperatures below freezing through around
sunrise. A brief window of freezing rain or sleet will be possible
in the northwestern portions of the area before temperatures rise
above freezing a few hours after sunrise, otherwise, light rain and
drizzle will be possible in the lower Valley and along the coast as
coastal troughing strengthens. Thursday afternoon a deep mid-level
and positively-tilted trough will dig southeastward through South
Texas through Friday evening. Notable model timing differences are
leading to low confidence on the best precipitation timing, but with
strengthening of the coastal trough at the surface, PoPs will
range from 40 to 60% across the eastern half of the area. Model
guidance shows the potential for some thunder on Friday, which
makes sense if the deeper low tracks closer to our area like the
ECMWF is indicating currently. Also as the coastal troughing
enhances easterly flow across the western Gulf, we could see some
minor overwash along area beaches, especially coinciding with high
tide cycles.

This weekend, high pressure will shift off to the east, bringing
strong southerly flow back to Deep South Texas. Temperatures and dew
points will rebound back to normal with highs possible reaching near
80 degrees Sunday afternoon. The next cold front may move through
the area early next week with much drier air behind it.

MARINE:(Now through Wednesday): Gale conditions continuing over
the Laguna Madre and likely developing over the Gulf. Pressure
gradient to peak this evening and then slowly relax when surface
ridge moves into North Texas. Gales will likely be replace by
Small Craft advisories later tonight and likely to persist for the
Laguna through Wednesday morning and over the Gulf waters
Wednesday. Winds and seas continue to lower Wednesday night
however residual higher seas/swell may linger into Thursday
morning.

Thursday through Tuesday: Moderate winds and seas will
continue into Thursday with coastal troughing strengthening along
the coast. Persistent easterly flow will maintain 3 to 5 foot swells
through early Friday. Friday into Saturday southeast flow will
return with a long fetch, bringing wave heights up to Small Craft
Advisory levels potentially. Conditions will improve Sunday night
into Monday as the gradient relaxes ahead of the next front.
&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Hard Freeze Warning until 9 AM CST Wednesday for TXZ248>251.

     Wind Chill Advisory until noon CST Wednesday for TXZ248>251-256-
     257.

     Winter Weather Advisory until 1 AM CST Wednesday for TXZ250>253.

     Freeze Warning until 9 AM CST Wednesday for TXZ252>257.

     Wind Chill Warning until noon CST Wednesday for TXZ252>255.

     Winter Weather Advisory until 10 AM CST Wednesday for TXZ254>257.

GM...Small Craft Advisory for winds until 6 AM CST Wednesday for
     GMZ130-132-135.

     Gale Warning until midnight CST tonight for GMZ130-132-135-150-
     155-170-175.

     Small Craft Advisory until 6 PM CST Wednesday for GMZ150-155-170-
     175.
&&

$$

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