Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 060523 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1123 PM CST Tue Dec 5 2017

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

.AVIATION...Aviation conditions to deteriorate overnight with MVFR
cigs falling to IFR or below by sunrise and remaining IFR or lower
through Thursday morning. Rain chances increase and becoming
widespread Wednesday with periods of MVFR to possible IFR vsby
during persistent patches of rain.  North winds increase with gusts
of 20-25 knots at time with stronger gusts near the coastal
sections.
&&

.PREV DISCUSSION... /issued 546 PM CST Tue Dec 5 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Cold front extending south of KAPY to Sarita line
moving steadily south. The front is likely to move through the
regional airports between 0130z-0300Z. Aviation conditions to
deteriorate overnight with IFR conditions before or shortly
after sunrise. IFR or LIFR conditions will likely persist all day
and well into Wednesday night. Winds may gusts near 25 knots with
the initially surge of the front then back off overnight before
increasing Wednesday morning and afternoon. Stronger wind gusts
are possible Wednesday night.

PREV DISCUSSION... /issued 250 PM CST Tue Dec 5 2017/

SHORT TERM (Tonight through Wednesday Night): A strong cold
front is just north of the CWA this afternoon, anchored by a 1031
mb high over north Texas and Oklahoma. The front will sweep
through this evening, reaching the vicinity of Brownsville by
about midnight, based on short term model guidance. Moderate to
breezy north winds will develop under overcast skies, with light
rain and lowering temperatures. Overnight low temperatures will be
in the 40s, and won`t recover very much on Wednesday, as the
connection to high pressure from the Pacific Northwest and the
Canadian Rockies continues. Low temperatures Wednesday night will
dip a few more degrees, with a few upper 30s possible across the
ranchlands and brush country. Light to moderate north winds will
support wind chill readings in the 30s Wednesday night, however.

LONG TERM (Thursday through Tuesday): Isentropic upglide
continues on Thursday, continuing to produce light rain and
drizzle areawide through the day. CAA and low clouds will keep
temperatures well below normal, struggling to reach 50 degrees
even during the afternoon. The weather gets a little more
interesting Thursday night. After midnight, the large-scale H5
trough drives southward across Texas. There is a considerable cold
core with this trough aloft, with the freezing level dropping to
1500 to 2000 feet overnight during passage. During this time,
rainfall will still be falling across the area, as mixture and
instability are still high. With wet bulb effects minimizing some
melting, would not be surprised to see some -SN mixing in with
the -RA in the northwest Ranchlands, areas that will have the
smallest distance between the freezing level and the surface. Now
with the limited amount of time of potential -SN and still warm
ground conditions, expect only a dusting of snow, with no
accumulation. Now subtle timing differences are leading to very
different solutions on the non- liquid precip, generally relating
to how fast the trough axis sweeps through. GFS remains the
fastest with the trough, drying things out Thursday night, while
EC, Canadian, and NAM are step things back slowly Thursday night.
Seeing that the GFS is initializing the cold air mass poorly
already, will shy away from the faster progression, keeping closer
to the slower EC prognosis (and associated -SN to the north).
With the slower progression, will hold on to precipitation chances
into the day Friday, with temperatures continuing to struggle to
rise until late in the afternoon once some cloud breaks start to
arrive. Drier airmass arrives in earnest Saturday morning, with
clear skies expected all weekend. Northerly flow continues to keep
a tap of cooler air sweeping through the region, so highs will
only reach the 60s both afternoons.

MARINE:
Now through Wednesday night: Very few changes were made to the
inherited forecast. A strong cold front will drive deteriorating
conditions when it arrives this evening. Used a slightly lower
multiplier which lowered the magnitude of wind gusts. Based on
that, decided to go with a small craft advisory for the Laguna
Madre instead of a gale watch.

Thursday through Sunday: Strong north winds continue Thursday and
Friday, with winds likely remaining above 25 knots through the
latter half of the week. Gusts will still be threatening the Gale
force criteria, so expect any Gale warning to continue into
Friday. Small Craft Advisories will continue beyond this time into
Friday night, finally allowing seas to start relaxing. All
advisories should be finished by dawn Saturday, with continued
decreases in wave action through the weekend. Seas should be down
to 2 to 3 feet by Sunday morning.
&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory for winds until 6 PM CST Wednesday for
     GMZ130-132-135.

     Gale Watch from 9 AM CST Wednesday through Thursday evening for
     GMZ150-155-170-175.

     Small Craft Advisory until 9 AM CST Wednesday for GMZ150-155-170-
     175.
&&

$$

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