Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 270526
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1126 PM CST Sun Feb 26 2017

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

&&

.AVIATION...Southeast winds will remain slightly elevated tonight
at around 8 to 11 knots. Low level moisture will continue to move
into the region tonight...with low MVFR clouds expected to develop
overnight. The stronger winds should prevent any significant
widespread fog from forming although visbys may lower slightly
around daybreak. Otherwise...gusty winds will be breezy again on
Monday...with VFR conditions expected.

&&

.PREV DISCUSSION... /issued 539 PM CST Sun Feb 26 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...The afternoon cloud field has begin to dissipate late
this afternoon with the loss of solar heating. Gusty winds will
settle down over the next one to two hours...with southeast winds
of 5 to 10 knots over night. Low level moisture will creep into
the region with cigs and visbys lowering to at least MVFR
criteria...although some guidance does suggest IFR values towards
daybreak. The higher winds speeds should preclude any widespread
or dense fog formation across the area.

PREV DISCUSSION... /issued 238 PM CST Sun Feb 26 2017/

.February 2017 Now Certain to Break Record Warmth for Many Rio
Grande Valley Locations...

SHORT TERM (Now through Monday Night): The heat quickly returned
to most of the region Sunday afternoon and has been joined by
late spring-like humidity as zonal 500 mb flow leaning from the
west southwest with Deep South Texas on the southern edge between
the flow and subtropical ridge in the southern Gulf induces low
level southerlies which once again pushed today`s overall average
temperature more than 10 degree above the 30-year (1981-2010)
averages for this date. And this is just the start of a four-day
stretch which will appropriately peak on Tuesday, when the average
daily temperature just about everywhere is likely to be nearly 20
degrees above what it should be for February 28th. These final
three days are likely to push the three primary sites for long
term climate record (Brownsville, Harlingen, and McAllen) to or
above 10 degrees higher than the monthly average, and in some
cases *3 degrees higher* than the prior record set 55 years ago!
For what it`s worth, the monthly average highs in McAllen so far
are similar to those of early to mid April, and helps to explain
why all of the spring tree, brush, and flower blooms are fully out
now.

Confidence in this scenario is high, as model consensus continues
to show the unusually strong Gulf subtropical ridge lifting north
and west to along 26N latitude by Monday afternoon and night,
bringing not only additional heat but continued southerly flow of
true tropical air which will keep overnight temperatures from
falling much below 70 tonight, and likely to stay in the 70s all
night Monday night into daybreak Tuesday. In fact, record *high*
minimums are in jeopardy February 28th at Brownsville (72),
Harlingen (72), and McAllen/Miller (68), all which were set this
decade.

For this afternoon and evening, expect clearing skies to spread
from west to east with winds staying gusty until just after
sunset. After dark, expect scattered cumulus to scoot northward
for a time with temperatures falling into the 70s. Overnight, sky
and temperature forecast is a little tricky with dry air expanding
toward the surface and low level southerlies weakening below 10
knots. The lighter winds especially out west should allow morning
lows to reach the low/mid 60s and assuming skies remain generally
clear patchy to perhaps areas of fog can`t be ruled out. Farther
east where just enough wind remains (i.e. near 10 knots) expect
some fuzzy haze in the soupy airmass but not true fog. Temps
should be able to fall to or just below 70s with fewer clouds than
in a typical southerly event with the very dry air just above the
deck able to mix down.

For Monday, based on persistence of hot temperatures this month
and accuracy of the ECMWF vs. the catching up GFS, have kept the
forecast alone, with low to mid 90s along/west of US 281 and upper
80s to lower 90s elsewhere except the beaches. Deep dry air means
little more than fair weather cumulus amidst the hazier skies,
and while the Valley Wind Machine is present its speeds are about
5 to 10 mph lower than today, closer to 12 to 18 mph and gusty vs.
the 18 to 25 mph and gusty speeds this afternoon. Across the Rio
Grande Plains/Brush Country, afternoon winds will slacken and dew
points will dip. ECMWF/NAM are onto the analog case best and left
the lower dewpoints (and RH crashing near 20 percent) for
Zapata/western Jim Hogg/western Starr). Light winds keep the
wildfire behavior threat down, fortunately.

The low level wind fields increase again Monday night as southwest
U.S./Baja California trough begins to dig while the Gulf ridge nears
its peak. This will keep speeds up to preclude fog but also hold
temperatures well into the 70s all night.  Skies should see nothing
more than fast moving patchy cumulus below the stars.

LONG TERM (Tuesday through Sunday): Though not the only item of
interest this week, a cold front on Wednesday will be the primary
focus of the long term forecast. The front will bring a quick shot
of rain on Wednesday as it passes through, followed by a cooler,
cloudier and wetter period for the latter half of the week and the
weekend.

Southeast to south southeast flow will be established on Tuesday,
supporting warm weather with a moderate breeze. High temperatures
will reflect this, ranging from the upper 80s to the middle 90s,
a solid 10 to 15 plus degrees above normal. Little relief will be
on tap Tuesday night, with low temperatures in the upper 60s to
lower 70s. The Wednesday cold front should arrive in time for the
modified maritime polar airmass to moderate afternoon high
temperatures some, with forecast high values in the mid 80s. As
has been the recent trend, upper dynamics will be weak or lacking,
so initial weather should be limited to showers and a possible
thunderstorms along the front as it moves through from dawn to
early afternoon. Strong, 1029 mb high pressure will settle over
East Texas Wednesday night and will begin shifting east on
Thursday. Most of deep South Texas will clear out Wed. night,
though a few clouds may remain near the Lower Valley along the
coast.

As high pressure shifts east, the low level northeast winds will
continue on Thursday and Fri., being overrun by west southwest flow
aloft. Winds aloft would have to be a bit more from the northwest to
allow for a rapid clearing. Despite the removal of the high pressure
center toward the East Coast, a coastal trough will help maintain
nearby low level convergence and cloudy skies, except for the
possibility of some clearing across the ranchlands and brush
country, along with enhanced rain chances Thursday through Sunday.
This will also help keep temperatures a little more reasonable, and
closer to normal, than they have been. Thursday night and Friday
should be the coolest days of the period, with 50s Thursday night
and 60s on Friday.

Coastal concerns: The arrival of a robust cold front late Wednesday
will produce strong north northeast winds Wed. night into Thursday,
along with offshore wave heights of up to 10 feet. Winds will remain
in an unfavorable northeast direction through Fri., when reinforcing
high pressure will bolster winds again, also rebuilding seas on Sat.
Predicted tides during this interval are forecast to rise to above
one foot above mean lower low water each mid afternoon from Thursday
through Sunday. The addition of another foot to foot and a half of
swell water approaching the beach will produce a total tide of two
feet or more, enough to produce tidal overwash and some coastal
flooding.

MARINE:
Now through Monday: The deciding point on Small Craft Advisory vs.
Caution is 20 knot+ sustained wind, and given that it`s a Sunday
we probably could have been fine with an advisory for the outer
waters. That said, TABS Buoy 45 (40 nautical miles east of South
Padre) has held below while NOAA buoy 20 has been just above, and
conditions are starting to come down as would be expected in
afternoon marine layer influence. With low level wind fields
fading overnight into Monday, expect a continued period of caution
(15 to 20 knot/gusty) through sunset on Laguna Madre with similar
winds likely continuing over the Gulf during the more favorable
diurnal period despite slowly weakening 850-925 mb flow overnight.

Monday`s winds should be at or below 15 knots everywhere for the
most part, though we could see some 20 knot gusts in thin channels
of the Laguna Madre by afternoon. Seas will dip, too, but still
remain moderate and a bit difficult for small craft. The low level
winds pick up again especially late Monday night across the Gulf,
so early morning excursions Tuesday beyond 20 nm out could be a
bit tough.

Tuesday through Friday: Moderate to fresh south southeast winds will
be in play Tues., supporting moderate seas. Conditions will improve
briefly and slightly Wed. morning ahead of a cold front arriving in
the late afternoon or early evening. Small craft advisory conditions
will develop, with north northeast winds becoming strong by midnight
Wednesday, and building seas to 10 feet offshore by Thursday morning.
Conditions will improve Thurs., but will still be rough for mariners
with elevated winds and seas. Reinforcing high pressure will arrive
Thursday night into Fri., reinvigorating northeast to east winds and
building seas to 10 feet again Friday night. Thus, much of the week
will not be favorable for marine interests.

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...None.
&&

$$

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

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