Area Forecast Discussion
Issued by NWS Brownsville, TX

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000
FXUS64 KBRO 190514
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
1114 PM CST Sat Feb 18 2017

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

&&

.AVIATION...The 00z BRO sounding shows a pretty saturated layer
between the 2kft and 3kft levels. The model forecast soundings
maintain this saturated layer throughout the night into sunrise
Sun. Expect the ceilings to continue lowering slowly through
sunrise tomorrow potentially falling into IFR levels. The surface
winds will stay strong enough overnight to limit any serious fog
formation. The increasing daytime heating tomorrow and
strengthening low level S-SE winds will mix out the early morning
ceilings pretty quickly allowing a return of VFR conditions later
in this current TAF period.

&&

.PREV DISCUSSION... /issued 709 PM CST Sat Feb 18 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...The last few vsbl satl images from the RGV this
evening indicate that some SC decks are already forming up as a
result of the increasing low level dewpoints from the SE surface
flow. The 00z BRO sounding shows a pretty saturated layer forming
up between the 2kft and 3kft levels. The model forecast soundings
maintain this saturated layer throughout the night into sunrise
Sun. Expect the ceilings to continue lowering steadily through
sunrise tomorrow likely falling into IFR levels. The surface winds
will likely stay strong enough overnight to limit any serious fog
formation. The increasing daytime heating tomorrow and
strengthening low level S-SE winds will mix out the early morning
ceilings pretty quickly allowing a return of VFR conditions later
in this current TAF period.

PREV DISCUSSION... /issued 252 PM CST Sat Feb 18 2017/

SHORT TERM (Tonight through Sunday Night): The main issue in the short
term will be the potential for strong to severe storms across
portions of Deep South Texas late Sunday afternoon through early
Monday morning. Current water vapor satellite imagery shows a 500mb
short wave ridge axis moving over the region this afternoon. The
ridge overhead and the dry westerly winds aloft has allowed
temperatures to climb into the 80s under sunny skies. The very warm
and breezy conditions will continue for the rest of this afternoon.
South to southwest flow aloft develops over the area tonight ahead
of the strong mid to upper level storm system approaching from the
west. Near-surface moisture will continue to increase tonight as
southeast flow prevail. Low temperatures will generally range from
the mid 60s across the west to the lower 70s along the coast under
mostly cloudy skies. Patchy fog is possible late tonight towards
sunrise but dense fog is not expected as winds should remain around
10 mph.

Very warm and breezy conditions will prevail on Sunday, as the 500mb
trough and the associated pacific cold front moves closer to the
region. High temperatures Sunday will range from the mid to upper
80s near the coast to the lower 90s inland. Latest model guidance
suggests that Sunday could be slightly warmer than today. The record
high temperature at Harlingen Valley international Airport for
Sunday is 90 degrees which could be reached. High dewpoints and the
very warm temperatures will support afternoon heat indices reaching
the mid-90s during the afternoon across the Mid/Lower Valley. Sunday
should remain rather dry but some isolated convection is possible
across the northern ranchlands in the afternoon. However, the region
will remain under a strong capped due to warming at 850mb.

The weather could become a little more interesting by Sunday evening
as stronger forcing arrives. Steepening mid-level lapse rates and
increasing Gulf moisture will support higher instability, especially
along and west of the I-69C corridor. The Storm Prediction Center
continues to keep a marginal risk of severe weather across Deep
South Texas for Sunday and Sunday night. Some initial convection may
develop from general instability around sunset Sunday evening, but
most of the activity will likely develop Sunday evening through
early Monday morning as the 500mb trough axis moves closer. There is
a small chance of strong to severe storms developing across the area
with the main threats being damaging wind gusts of 60 to 80 mph and
hail up to golf ball size. Brief heavy rain is possible but flash
flooding is not expected. Overnight low temperatures Sunday night
will generally be in the 60s.

LONG TERM (Monday through Saturday): Convection...some possibly
strong to severe...will be ongoing across the southern and eastern
portions of the CWA Mon morning but rain chances will diminish
from west to east Mon afternoon as the 500mb trough across west
Texas and northern Mexico moves eastward during the day bringing
dries air across west and southwest TX Mon afternoon into Mon
evening. A cut-off low is expected to develop across southwest TX
Mon night and this will provide convection well offshore the lower
TX coast but isolated showers will linger across the coastal
sections of the CWA Mon evening. The 500mb low across deep south
TX and northeast Mexico Tuesday will eventually move eastward into
the western Gulf of Mexico Wednesday but some wrap around
moisture around the backside of the upper low will provide some
isolated convection offshore the lower TX coast Tues night into
Wednesday. Subsidence will prevail across south TX Wednesday
before a 500mb trough across the western United States Thursday
moves across the central U.S. Friday bringing a dry cold front
through south TX Friday. An onshore flow is progged to return
towards the end of the forecast period.

MARINE (Now through Sunday Night): Buoy 42020 reported south-
southwest winds around 10 knots with gusts near 12 knots and seas of
2.6 feet with a period of 6 seconds at 14 CST/20 UTC. Winds will
gradually increase tonight, especially across the Gulf waters, as
the pressure gradient tightens. A exercise caution headline for the
Gulf waters may be needed for tonight. Moderate winds and building
seas will continue for Sunday with exercise caution conditions
likely for all of the coastal waters, as the weak cold front moves
closer. Winds will begin to diminish Sunday night as the gradient
weakens.

Monday through Thursday...Winds will be shifting to the northeast
and increasing across the coastal waters Monday as a weak Pacific
cold front moves offshore the lower Texas coast early Mon morning.
Light to moderate north to northeast winds across the western Gulf
of Mexico Mon night will back to the northwest Tuesday as low
pressure develops along the frontal boundary across the western
Gulf and moves northeast. Winds will remain northerly with low
pressure across the northern Gulf of Mexico. An onshore flow is
expected to return Thursday as the low over the Gulf weakens and
stronger low pressure develops across the southern plains.

&&

.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...69


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