Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 250227
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
827 PM CST Fri Feb 24 2017

.DISCUSSION...Clearly the cold front proper did not make it
through the CWA today, with a record high temp for the day tied at
BRO and broken at HRL. Seems that a dryline (sharpened later in
the afternoon by the sea-breeze boundary) moved out ahead of the
front. Front analyzed by WPC across the northern boundary of the
CWA as of 00Z. Not much thermal contrast immediately across this
boundary, but northerly winds behind it will bring in a drier and
eventually cooler airmass overnight. This boundary should reach
the mid-Lower RGV by around midnight. Updated wind, temp, and
moisture fields through 12Z Saturday with a short-term blend which
had a better handle on the observed trends. Little net change in
overnight min temps. Updated text products have been disseminated.

&&

.DISCUSSION...Updated for latest marine discussion below.

&&

.MARINE...Freshened up wind grids through the overnight and seas
from 09-12Z with latest wave guidance. Kept inherited timing of
SCA for the Gulf Waters and issued product. Updated winds have
increased confidence in the SCA conditions developing this
evening.

&&

.PREV DISCUSSION... /issued 549 PM CST Fri Feb 24 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Winds shifted to the NE a little more quickly than
expected late this afternoon at BRO and HRL, with dewpoints
quickly jumping back into the lower 60s F. Dry north winds still
prevail at MFE with dewpoint in the 30s. Still anticipating VFR to
prevail through the period, but might need to give this a closer
look later in the evening as far as the overnight period goes.
With winds staying up in the 7-8 knot range, don`t think that
fog/mist will become an issue (even with the higher dewpoints),
but lower CIG`s could come into play. Will hedge with SCT020 at
BRO and HRL for now. NE winds pick up a bit at all three terminals
from mid-day Saturday onward, with perhaps just a few cumulus and
passing high clouds from time-to-time.

PREV DISCUSSION... /issued 320 PM CST Fri Feb 24 2017/

.A Brief Break in the Heat for the Weekend then Returning in
Force to Close out a Record Warm February...

SHORT TERM (Tonight through Saturday Night): As of early afternoon, the
dry surface cold front had moved completely offshore with northwest
to north winds developing behind the front and running generally in
the 20 to 30 mph range. Relative humidities were dropping area-wide
with Red Flag Warning criteria being met (and veryifying current
warning) out west. RFW in its current form looks good for the
remainder of the warned area and will leave as it is set up through
6 pm. Winds will begin to diminish and relative humidities will
begin to slowly recover with the setting sun this evening.

Overnight tonight, surface winds will become northeasterly as high
pressure builds southward from north TX/OK. Drier air moving into
deep south TX behind the front will allow temperatures to cool into
the upper 50s near the coast with lower to mid 50s inland. Saturday
will be a very pleasant day as the surface high pressure slowly
slides eastward toward Arkansas and winds turn easterly. Highs look
to be anywhere from 7 to 13 degrees lower than readings we will have
reached today. Highs will range from the mid/upper 70s over the
extreme northern ranchlands with lower/mid 80s elsewhere. Pleasant
and cool conditions will prevail Saturday night into Sunday morning
with lows getting into the lower 60s along the coast with mid 50s to
near 60 inland. Mid and high clouds will be on the increase Saturday
night but will not have a significant impact on the weather.

LONG TERM (Sunday through Friday): It`s quite appropriate that
February 2017 finishes with a hot flourish; after all, persistent
warmth and flat out hot days have dominated much of the second half
of the month and the last few days of the month will be no
exception.  March looks to come in like a lamb as well, but some
changes are afoot as the week comes to a close.

In the big picture, Deep South Texas and the RGV will be on the back
side of back building subtropical 500 mb ridge across the central
Gulf (Monday) and into the Western Gulf (Tuesday and Wednesday).
The ridge flattens later Wednesday into Wednesday night and allows a
front to sweep through the region, followed by zonal flow aloft into
Thursday.  GFS/ECMWF differ slightly on the handling of downstream
featurs ahead of a weak short wave that dips along the coast of Baja
California later Thursday and Friday.  The GFS wants to stream
moisture east-northeast along a channel that extends from the Sierra
Madre Oriental through Deep South Texas and into the northern Gulf
in a typically classic overrunning setup. The ECMWF keeps a more
west-northwest to east southeast flow initially which allows surface
front to surge through, mostly dry, before 500 mb flow begins to
back to the west-southwest by Friday. One has to think that the
region is due at least one more overrunning type event even into
early to mid March - but they`ve been fleeting this winter, and the
ECMWF has handled the warm and dry "lean" better in a winter headed
for record warmth in many areas.  Bottom line?  Will maintain the
current forecast trends with only a gradual cooling into Thursday
and the best chance for below average (average being mid 70s overall
by) temperatures by Friday.

For the sensible weather:  We`ll actually see more low clouds than
we`ve seen in days on Sunday, which will tend to erode across the
Upper Valley/Rio Grande Plains by afternoon but could be more pesky
toward the coast. A hint of the Valley Wind Machine returns but
nothing out of the ordinary, and as the atmosphere warms overall
temperatures will have no problem reaching the 80s in most areas,
except near 90 near the river west of US 281.

By Monday, lee side troughing sets up and pushes out into the mid
Valley by afternoon, setting the stage for more building heat. ECMWF
carrying the higher values and current forecast reflects this, so
may tease up a degree especially out west but mid 90s west of 281
and 90 to 95 east of 281, except toward the coast with Gulf
influence, should cover it.

Tuesday looks to be the hottest day of the week with impressively
high atmospheric heat parameters.  Upper 90s and even triple digits
are within reason along the river west of McAllen; McAllen will
probably hold a bit short based on a more viscous airmass. Only
slight tweaks are expected, perhaps a degree or two higher.

For Wednesday, the ECMWF and now the GFS are rather bearish on any
frontal precipitation that comes with the wind shift; ECMWF solution
of dry heat for one more day will continue to be accepted for the
upper Valley with only slightly lower temperatures elsewhere. As for
rain chances, will likely drop to 20 percent and only for the coast
and Gulf waters, but will keep thunder mentioned based on potential
lift along the boundary.

Thursday and Friday will see more clouds overall and increasing
chances for rain especially toward the coast. Will continue the
current trend of more gradual increases in clouds per the ECMWF on
Thursday vs. the wetter and somewhat cooler GFS; GFS is more bullish
in all areas Friday but the aforementioned west southwest flow aloft
does make a presence felt with the ECMWF.  Will broad brush low
chances (20/30 percent, perhaps some 40 percent near the coast) for
rain showers and hold temperatures in the upper 60s to low/mid 70s
for now.

One thing to note about this week`s upcoming heat return: Unlike the
beautiful evenings and early mornings with dry comfortable and cool
conditions, the soup will be on with evening temperatures in the mid
to upper 70s and daybreak temperatures in the upper 60s to around 70
through Wednesday before easing down toward normal (50s by morning)
Thursday and Friday.

MARINE: (Now through Saturday night): Observations at Buoy 42020
early this afternoon were showing NNW winds from 8 to 14 knots in
the wake of a weak and dry cold front. Seas were still running over
5.5 feet in response to elevated winds in the morning, but were
slowly subsiding. North to northeast winds look to strengthen late
tonight into Saturday morning as strong surface high pressure builds
toward the waters from the north. Small Craft Should Exercise
Caution conditions, if not Small Craft Advisory conditions, will be
possible late tonight through early Saturday for winds.

Sunday through Wednesday: With region being on the back side of
the expanding 500 mb ridge, low level wind fields and marine layer
should combine to keep conditions fairly copacetic (for
winter/early spring) especially over the Gulf. Sunday could see
the highest seas (4 to 6 feet) as air mass transitions back in
southerly flow, but Monday through Wednesday should see winds and
seas dip back below 15 knots and 5 feet, respectively. On Laguna
Madre, each afternoon could see 15 to 20 knot and gusty winds in
the squeeze zone between the cooler Gulf and warmer inland region.
Shifting north/northeast winds Wednesday night could kick up
enough to 20 knots but uncertainty remains on timing for now.

CLIMATE...As of February 23rd, the Valley`s main data points all
ranked number 1, with a bullet in some cases (McAllen/Miller, for
example, 2.5 degrees above the prior record for max temperature and
total average temperature.  The remainder of the month is likely to
push those differences even higher, and winter (December-February)
averages should reach the mountaintop at Brownsville and approach
even at Rio Grande City and McAllen/cooperative.  The current data
for Brownsville, Harlingen, and McAllen, through Feb. 23:

February     Current     Prior Record
Brownsville:    72.5 (1)  70.8 (1962)
Harlingen:      72.7 (1)  72.2 (1962)
McAllen/Miller  74.5 (1)  71.8 (1962)

Winter       Current     Prior Record
Brownsville:    68.5 (2)  69.6 (1890)
Harlingen:      67.8 (1)  67.6 (1957)
McAllen/Miller  69.6 (1)  66.4 (2013)

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Advisory until 6 AM CST Saturday for GMZ150-155-170-
     175.

&&

$$

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

53-Schroeder...Short-term/Marine
66-Tomaselli...Long-term


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