Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 151839 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1239 PM CST Mon Jan 15 2018

.DISCUSSION...With models indicating the potential for wintry
precipitation and cold temperatures, have made some changes to
the forecast this morning. Have posted a Freeze Warning, Winter
Weather Advisory and Wind Chill Advisory for much of Deep South
Texas for Tuesday into Wednesday.

&&

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

&&

.AVIATION...Visible satellite imagery indicates broken cumulus
clouds are developing over much of the area, but will remain VFR
through the day. Strong southerly flow will diminish tonight ahead
of a strong cold front Tuesday. A few patches of fog will be
possible prior to the passage of the front with very strong
northerly winds behind it. Ceilings will drop to MVFR and likely
IFR late in the morning and afternoon with scattered light showers
and drizzle.

&&

.PREV DISCUSSION... /issued 512 AM CST Mon Jan 15 2018/

SHORT TERM (Today through Tuesday): High pressure trailing southwest
from the lower Mississippi Valley into the region today will yield
seasonal weather with moderate southeast winds and a mix of clouds
and sun. High temperatures near 70 will be close to normal. That
idyllic picture will change abruptly tonight, Tuesday and beyond
when an arctic air mass brings winterlike conditions to the area. A
strong north to south ridge over the western U.S. will provide the
western buttress to a mid level low and surface cyclone diving south
from the Hudson Bay area into the northern Midwest today, then
tracking east over the great Lakes on Tuesday. An elongated mid
level trough extending west over the northern plains will move south
today and then toward the mid Mississippi Valley on Tuesday. Cold
air at the surface will track apace with the trough aloft to reach
the CWA on Tuesday.

Temperatures in the 50s tonight will represent the highs for
Tuesday, as the arrival and quick passage of the front Tuesday
morning will prevent any warmup before strong cold air advection
takes over. Steady cold air advection Tuesday during the day will
decrease temperatures to near freezing by late Tuesday afternoon,
along with wind chill values in the teens. Although 6-hourly precip
amounts are not expected to be more than a few hundredths of an inch
to around a tenth of an inch, the thin layer of freezing temperature
air near the surface could result in light freezing rain or sleet
Tuesday afternoon for interior areas.

LONG TERM (Tuesday Night through Sunday): The very strong and
deep 500 mb trough digging over central portion of the lower 48
states will continue moving east southeast. As a result of this a
large area of Arctic air will spread south and southeast over the
Gulf Coast and much of the Gulf of Mexico. Meanwhile another 500
mb trough will swing over the U.S./Mexico border region late Tues
into Wed which will help enhance UVV which will maintain pretty
decent pcpcn chances. At the surface, a coastal trough will form
up after the fropa and is expected to linger near the lower TX
coastline through the end of the work week. The border region 500
mb trough will finally clear out of the RGV as the upcoming
weekend approaches allowing for the pcpn chcs to dimish finally
and the temps to warm up a bit as the Sun reappears.

Unfortunately the pattern appears to be somewhat similar to the
cold outbreak that impacted the RGV over the first four days of
January 2018. The cold airmass will threaten to drop temps across
the region down close to near or just below the freezing mark
mainly for Tues Night and Wed Night. With the influence of the 2nd
500 mb trough digging from west to east across the region
combining with the near to sub freezing airmass over the region to
set the stage for a potential for another round of wintry mix of
pcpn mainly over the northern and western counties.

Overall confidence in the forecast is about average at this time
as is the case with winter weather in the RGV a few degrees
difference in the near surface temp can make all the difference
between a cold rain or a sleet/freezing rain/drizzle mixture.

Model consistency has been decent both between the GFS and ECMWF
for both temps and pops. Run to run consistency with both longer
range models has been pretty stable over the last several runs.

MARINE Now through Tuesday...Moderate southeast winds will prevail
Monday and much of Monday night with high pressure over the
northwest Gulf and a strong cold front moving south into north
Texas Monday aftn. Winds will slacken early Tuesday morning ahead
of the advancing cold front, which will move out over the lower
Texas coast and then from north to south Tuesday morning after
dawn to early afternoon. A gale watch is up for the Gulf waters
Tuesday, and small craft advisory conditions will be probable for
the Laguna Madre.

Tuesday Night through Friday Night...Pretty hazardous conditions
will be expected across the lower TX coastline for the bulk of
this work week as a tight PGF persists over the region in the wake
of the fropa on Tues. SCA conditions are expected for the Laguna
Madre through Tues Night with the winds gradually diminishing from
Wed through Fri. The SCA conditions for the Gulf waters will
persist on for awhile longer with the PGF not really calming down
until late Fri.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Winter Weather Advisory from 3 PM Tuesday to noon CST Wednesday
     for TXZ248>251.

     Freeze Warning from 3 PM Tuesday to noon CST Wednesday for
     TXZ248>251.

     Wind Chill Advisory from noon Tuesday to 6 PM CST Wednesday for
     TXZ248>251.

     Winter Weather Advisory from 9 PM Tuesday to 9 AM CST Wednesday
     for TXZ252>255.

     Freeze Warning from 9 PM Tuesday to 9 AM CST Wednesday for
     TXZ252>255.

     Wind Chill Advisory from 3 PM Tuesday to 6 PM CST Wednesday for
     TXZ252>257.

GM...Gale Watch from Tuesday morning through late Tuesday night for
     GMZ150-155-170-175.

&&

$$

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