Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 051514 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
914 AM CST Mon Dec 5 2016

.DISCUSSION...Made a few tweaks to timing of precipitation this
morning as well as sky cover. Expect mostly cloudy/cloudy skies to
continue through noon or so as low level cold advection keeps
drier air from mixing out the stratocumulus decks that are in
behind the precipitation, whose last band was moving into the
Lower Valley just after 9 AM.

Also, split morning grids into two sections to cover end of
precipitation which has occurred mainly west of US 77/IH 69E at 9
AM. As the drier air helps to erode clouds and increase sunshine,
blended sky cover to show more rapid decrease in cloud cover from
west to east beginning late morning and really getting going
between noon and 3 PM.

Remainder of forecast left alone.
52/BSG

&&

.AVIATION...Updated all TAFs to remove thunder as elevated nature
of convection ended overnight, and also to match current mainly
VFR ceilings with the forecast to remove any fuel restrictions
that may have occurred because of the low MVFR forecast late into
the morning and early afternoon. General timing of clearing
conditions looked fine (after 17/18Z)so left this alone, as well
as winds which indicated some pickup with the clearing/mixing
during the afternoon before laying down around sunset.
52/BSG


&&

.PREV DISCUSSION... /issued 609 AM CST Mon Dec 5 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...IFR/MVFR conditions continue for the region this
morning, with passing showers and a possible clap of thunder
through the morning. Dry air moves in quickly from the west late
this morning, with quickly clearing skies expected this afternoon.
Light winds and clear skies tonight, with some fog formation
possible areawide before dawn Tuesday.

PREV DISCUSSION... /issued 400 AM CST Mon Dec 5 2016/

SHORT TERM (Now through Tuesday): H5 low continues to trek across
far northern Mexico this morning, with deep moisture plume racing
out ahead of it across southeastern Texas. This is resulting in
areas of showers racing northeastward. Also noted in the water vapor
imagery is the approaching dry slot wrapping around the low. With
the progression of the low to the northeast later today, this should
bring the dry slot across our area later this morning. There will be
an abrupt shutdown of precipitation as it arrives, with quickly
clearing skies this afternoon. Even with modest cold air advection
continuing, temperatures should still be able to rise into the mid
60s once the sky clears.

Weak high pressure moves off to the east behind the departing
surface low reflection on Tuesday, with a gradual wind shift back to
the south later in the afternoon. This will bring the warmer airmass
back into the region, with highs in the lower 80s.

LONG TERM (Tuesday Night through Sunday):The long term will be
characterized as a warm start, a chilly and wet mid-portion
followed by a warm and dry end. Models are all on board with a
late Wednesday night early Thursday morning polar/arctic cold
frontal passage. A broad mid level trough anchored from a deep
cold low over Quebec will combine with a strong ridge building
north along the Pacific Northwest to send a 1045+ surface ridge
South into the Central Plains. Folks should not be fooled by the
warm temperatures Wednesday which could be 10 degrees above
normal and prepare for the coldest airmass of the season thus
far. Once the front moves through the CWA, off the lower coast
around sunrise Thursday, temperatures to plummet and might not
recover until Saturday. Strong north winds and deepening moisture
(thickening cloud cover) along with a decent chance of drizzle and
light rain (mainly over the Southern tier counties especially the
RGV), push temperatures down into in the 40s and 50s with wind
chills in the 30s and 40s Thursday with only slight recovery
Friday mainly due to lighter winds. Minimums Friday morning bottom
out just above freezing across the Northern and Western
Ranchlands thanks to an expected thickening cloud cover. This will
have to be watched closely because any partial clearing could
allow some areas to reach or dip slighlty below freezing for a few
hours. Across the RGV lows to approach the upper 30s to lower 40s
in some urban areas. Both GFS/EC temperatures guidance looking
like they collaborated but could see even colder temperatures or
at least a faster fall in the RGV as the overrunning conditions
are indicated to worsen on Friday.

As fast as this airmass moves in it should retreat and modify
quickly as the mid level flow over the Conus goes zonal and the
typical warming trend commences Saturday and accelerates Sunday
and Monday. As the surface ridge moves east Saturday a weak but
noticeable surface trough or even a warm front develops along the
Gulf Coast. Southerly winds return to the region with the cold air
retreating. Once again the major deterministic models are on board
with the timing of this warming trend so confidence is above
average as of this forecast cycle.

MARINE:(Now through Tuesday): The surface low pressure building
across the northwest Gulf will continue to provide gusty northwest
winds during the remainder of the day Tuesday. Small craft
advisories are in effect for the open Gulf waters through noon for
winds around 20 knots providing wave heights of 7 to 9 feet. As the
surface low departs to the northeast, lighter northwest flow will
remain through Tuesday morning before switching back to the south
during the day. Winds are expected to remain around 10 knots tonight
and tomorrow, so seas will relax, falling to around 2 feet by noon
Tuesday.

Tuesday night through Friday...the calm before the storm will be
evident this forecast cycle as interest along the Western gulf
should brace themselves for a strong surge of polar air late
Wednesday night and lasting through Friday. Confidence in Gale
conditions Thursday are increasing as a strong surface ridge
builds into Southern Plains. Once marine conditions deteriorate
after midnight Wednesday/Thursday no improvement is expected
until Saturday morning.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory until noon CST today for GMZ150-155-170-175.

&&

$$

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

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