Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 251747 AAB
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1247 PM CDT Tue Apr 25 2017

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

&&

.AVIATION...A strong low level inversion is keeping a lid on the
boundary layer, though strong low level southeast to south winds
have been able to mix out low cloud decks except at BRO. Winds
will diminish to moderate later today, but south southwest winds
at 850 mb should keep a cap in place. Thus, MVFR ceilings will
form this evening at all sites. Winds will further decrease to
light overnight, with light haze possible. Ceilings will lift
Wednesday as winds shift to moderate northwest and drier air works
into the area, scouring out the inversion in the process.

&&

.PREV DISCUSSION... /issued 634 AM CDT Tue Apr 25 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Variable CU continue to drift northward across the
region, with KBRO and KHRL varying from SCT to BKN around 2500
feet. Satellite data shows KMFE has cleared, and no upstream
redevelopment is expected in the next couple hours. Daytime CU
will return midmorning, with cigs around 4000 feet. Winds will
initially start from the southeast, with KBRO reaching 20 to 25
knots, KHRL around 20, and KMFE 15 to 20. The dryline will move
into the western valley later this morning, bringing lighter winds
to KMFE and pushing the strongest winds right along the coast.
Gusty winds will continue through most of the overnight hours
Tuesday night.

PREV DISCUSSION... /issued 410 AM CDT Tue Apr 25 2017/

SHORT TERM :(Now through Wednesday): Surface high pressure
continues to slowly get pushed eastward across the Gulf by
developing surface low across western Oklahoma. Latest model runs
indicate winds just off the surface of 40 to 45 knots, which
correlates decently with the current KBRO VWP readings near 50
knots. The jet stretches well inland currently, but the jet is
expected to get forced eastward later this morning as a dryline
drifts into the western valley. This will keep the stronger winds
along the immediate coast and offshore late this morning and
afternoon. As the dryline sweeps to the coast, inland areas will
see much warmer and drier air, with highs above 95 degrees
generally west of US 77, and a couple 100 degrees readings in the
Rio Grande City vicinity. Southeast winds return to the region
overnight tonight, pushing the dry air briefly back to the west.
Wednesday morning the next boundary of airmass change sweeps
through south Texas. This will shift winds to the northwest and
reintroduce even drier air to the entire region. This will drive
temperatures upwards quickly, with high temperatures reaching 100
degrees for all locations north and west of Harlingen.

LONG TERM (Wednesday Night through Monday): Latest model package
remain in good agreement and consistency for the long term. Two
cold fronts, yes we are in a static active cyclonic pattern, will
"bookend" a very hot to possibly extreme heat days Friday and
Saturday. No rain is expected with either the weak front Wednesday
night/Thursday or the stronger front Sunday with the atmosphere
remaining rather dry with a persistent strong west to southwest
AOA 850mb.

The first front will allow for temperatures to moderate 5 to 10
degrees Thursday as winds turn briefly northeast. Upstream
shortwave trough deepens the Western longwave trough Friday and
Saturday allow for winds aloft to become increasing southwest over
South Texas. 850mb temperatures begin to climb upward ranging
from 24-28 degrees. This can translate between to 95 to 110
degrees at the surface if all conditions come together. Confidence
is not there for the extreme end of maximums but the latest blend
of models remain consistent with the last few deterministic
packages. Will continue to monitor the trends and may have to go
higher, especially Saturday, if better downslope conditions are
indicated. Wind to be player at the end of the week and into the
weekend, especially Friday, as the pressure gradient strengthens
through the day as surface low pressure deepens over the southern
Plains. Will be monitoring for wind advisory conditions.

Models are showing a more significant cold front barreling through
Deep South Texas this coming Sunday. Strong upper low pushes
through the Central Plains surging another shot of much cooler
Canadian South of the Mexican border. This front looks very
similar in timing and strength to this past Sunday. Max and min
temperatures to fall up to 20 degrees Sunday and Monday in some
locations. Rain chances look minimal at best with some low chances
showing up across the northern Ranch lands. At this time have kept
chances below 20 percent with moisture amounts and depth remaining
limited. Winds may be an issue in wake of the front but look to
weaken considerably during the afternoon...this will have to be
watched.

MARINE:(Now through Wednesday): Brisk southerly winds will ramp up
later this morning as a strong low level jet along the coast mixes
down to the surface. Small Craft Advisories will be hoisted with the
next update to start mid-morning, as winds reach 20 to 25 knots for
all waterways. This will push Gulf swells quickly to 5 to 7 feet and
cause a considerable chop on the Laguna. The low level jet continues
to influence the marine zones overnight, with advisories continuing
through at least midnight, possibly through sunrise Wednesday. Wind
conditions improve considerably on Wednesday as a weak front stalls
right along the coast. This will bring a minimal gradient to the
nearshore waters, dropping winds to 5 to 10 knots depending on the
final location of the boundary. Seas will only slowly relax, with 4
to 5 foot swells still expected through the day Wednesday.

Wednesday night through Saturday...The first of two cold fronts
this week weakly moves offshore Wednesday into Thursday morning.
Light to moderate northeast winds to quickly turn southeast by
Thursday night. Winds and seas begin to increase Friday and peak
Saturday as low pressure strengthens over the Southern Plains. An
extended period of small craft advisory conditions, Friday
through Sunday, is looking more probable with strong onshore flow
prior to a strong cold front Sunday morning.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory for winds until midnight CDT tonight for
     GMZ130-132-135.

     Small Craft Advisory until midnight CDT tonight for GMZ150-155-
     170-175.

&&

$$

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