Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 231755
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1155 AM CST Thu Feb 23 2017

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

&&

.AVIATION...Moderate southerly winds will continue to increase
this afternoon, especially along the coastal counties, as a storm
system developing across the Central Plains tightens the pressure
gradient. Winds will drop to around 10 knots overnight and veer to
the south/southwest ahead of an approaching cold front early
Friday afternoon. Moisture pooling ahead of the front may allow
for patchy fog development Friday morning, but winds will likely
be too strong for widespread dense fog. VFR conditions are
expected to prevail.

&&

.PREV DISCUSSION... /issued 545 AM CST Thu Feb 23 2017/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...IFR to LIFR visbys and cigs will continue at KBRO and
KHRL for the next one to two hours. However...conditions will
rapidly scatter out shortly after sunrise...with VFR conditions
prevailing. A tightening surface pressure gradient will bring
gusty SE to SSE winds through the afternoon. Winds will lessen
overnight overnight...but stay a bit elevated a head of a dry cold
front that will move through the Lower RGV just beyond this
period.

PREV DISCUSSION... /issued 428 AM CST Thu Feb 23 2017/

SHORT TERM (Today through Friday): Hot and dry weather continues to
be the story of the day as persistent mid-level ridging continues to
slowly move across the region. Meanwhile...surface high pressure has
moved east and southerly flow has returned to the Lower RGV and
coastal areas. This has allowed for some patchy dense fog too form
early this morning across portions of Cameron County.
However...winds will remain around 5 to 7 knots early this morning
due to the increasing pressure gradient and will quickly increase
through the morning...allowing fog to mix out quickly.

As the 500mb ridge continues to pull away from Deep South
Texas...flow through the lower to mid layers becomes increasingly
southwest. With exceedingly dry air and downsloping
compression...more widespread...warmer temps are expected. Highs
across the river valley region of Starr and Zapata Counties will
easily warm into from around 100 to 102 given triple digits were
already reached yesterday. We will likely see high temperature
records at least tied if not broken at Brownsville with high of 92
(previous record of 92 set in 2016 and 1917) and at Harlingen with a
high of 93 (previous record of 93 set in 2016). With south winds
return and just the slight increase in moisture...coastal
temperatures are a little hard to nail down. What little moisture
there is will not back it farther west...and McAllen will have a
good shot at reaching triple digits at 100 degrees (previous record
of 98 set in 1996).

The hot temperatures and dry conditions will lead to some fire
weather concerns today as well. Rh values will range in the single
digits to lower teens from areas along I-69C and west. However...20-
foot winds in these areas should remain below any critical
thresholds. Meanwhile...east of I-69C towards the coast will have
higher RH values in the upper teens to mid 30s. The difference here
is that 20-foot winds will be near or just below Red Flag Criteria.
Will issue a Fire Danger Statement this morning to highlight the
potential for erratic fire behavior and wildfire concerns...and
allow the oncoming shift to monitor conditions.

The 500mb pattern shifts on Friday as weak trough/nearly zonal flow
is in place as a strong 500mb low passes across the Central Plains.
This system will drag a dry cold front into the region by Friday
morning with winds becoming northwest. The winds will increase and
become gusty through the day...mainly across the Western Ranchlands
and Upper level. Given a reinforcing surge of dry air...it is likely
that Red Flag Warnings will be need across the western half of the
region at the very least. On a positive note...temperatures should
be a few to several degrees cooler.

LONG TERM (Friday Night through Wednesday): A deep 500 mb closed
low will be exiting the central portion of the country late
Friday. This pattern will allow a pretty zonal pattern to continue
over the RGV into the weekend with pretty dry surface ridging
spreading south and southeast. This will drop temps down somewhat
this weekend in comparison to the hotter temps observed this
week. However overall temps this weekend even with the cooler
airmass in place over the region will still likely average above
climo for late Feb. A series of 500 mb short waves will then dig
across the western and central state early next week which will
tend to rebuild the mean ridge axis over the Gulf of Mex and the
southeastern states through Tues and Wed. As these short waves
push further into the central portion of the country...a somewhat
dry cold front will move through the RGV on Wed resulting in a
reinforcing shot of cooler air moving over the region.

Overall moisture levels throughout the longer range period remain
pretty limited with the exception of the fropa expected next Wed.
For now the only significant pops mentioned during the longer
range period will be only a 20 % chc for next Wed which is a blend
of the ECMWF and the GFS numbers.

The ECMWF continues to maintain a warmer bias for temps versus the
GFS. Will lean closer to the hotter ECMWF numbers as this model
has had a better handle on exceptionally hot temps the RGV has
witnessed over the last several weeks/months. The nighttime lows will
be more of a blend of the GFS and ECMWF.

Overall confidence in the longer range forecast wording is above
average this morning.

MARINE (Now through Friday): At 4 AM...Buoy 42020 is currently
reporting SSE winds of 10 to 15 knots and seas of 2 feet. As the
surface high pressure departs and surface low pressure develops
across West Texas...the pressure gradient will increase through the
day. Small Craft Should Exercise Caution conditions will develop
Thursday afternoon for winds. Seas will remain elevated Thursday
night ahead of an approaching dry cold front which will move through
the Lower Texas Coastal Waters Friday morning. Moderate winds and
seas will continue through Friday morning before conditions briefly
improve in the afternoon.

Friday night through Monday night...The marine surface wind flow
will be returning to a more southeasterly direction from late
Saturday night through next Monday as a surface high shifts
further east. The strengthening southeasterly flow this weekend
will be due to the development of a series of surface lows across
the Midwest. This interaction may push the winds and seas across
the lower TX Gulf waters back up close to SCA levels this weekend
continuing into early next week mainly for the lower Texas Gulf
waters.

&&

.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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