Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 172344 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
544 PM CST Fri Nov 17 2017

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

.AVIATION...Satellite images and surface observations indicate
mostly clear skies across the CWA early this evening. Expect VFR
conditions to prevail across the Rio Grande valley tonight into
early Sat morning as the 500mb ridge across west-central Mexico
continues to provide subsidence across the area. Some MVFR
conditions may develop across the northern and western portions of
the CWA late tonight into early Sat morning. VFR conditions will
prevail Saturday even as a cold front moves into the RGV Sat
afternoon. Winds will shift to the southwest and diminish ahead of
the front Sat afternoon.

.PREV DISCUSSION... /issued 324 PM CST Fri Nov 17 2017/
..Big changes headed for the RGV this weekend...

SHORT TERM (Tonight through Saturday Night): Minus a few streamer
clouds along and east of I69C, a beautiful and very warm day is
occurring across the region. As of the 2pm hour, temperatures were
ranging from the middle 80 along the coast to the upper 80s to
near 90 in the upper valley/northern ranchlands.

Aloft, the stubborn 590dam heat bubble continues across northern
Mexico. This of course is helping temperatures warm well above
average. With the intense surface heating, a great deal of mixing
has taken place, which also helped warm temps, drop dewpoints, and
finally increased surface winds with some locations gusting up to 25
mph at times. Wind gusts should subside somewhat overnight, but as
pressure gradient continues to increase as a surface low deepens
across the central plains, expect winds to remain rather steady
around 10-15mph overnight, which unlike the last several nights
should preclude any fog development tomorrow morning.

Saturday will be our last very warm day before the frontal passage
late Saturday/early Sunday morning. Latest available guidance has
been showing a slight downward trend in max temps on Saturday. Think
there will be a pretty decent shot at some warming before the
frontal passage and given the lack of precip expected due to dry mid
and upper levels. This should help keep things a bit toasty for this
time year. Decided to go a few degrees above guidance/blends as
these cases tend to be underdone in terms of temps.

Again, cold front moves through mostly dry, however, can`t rule out
a widely scattered shower right on the coast. The best potential for
any rainfall will likely be offshore across our marine zones. Winds
will increase with northerly gusts perhaps as high as 30mph or so
behind the front.

LONG TERM (Sunday through Friday): A series of 500 mb short waves
will be moving over much of the lower 48 states this Sun which
will help deepen the broad troffing over the region. CAA will
prevail over the RGV into Sun and early Mon with the surface ridge
shifting eastward allowing for WAA to return later on Mon. Another
500 mb short wave will move over the RGV on Mon which could help
fire off some conv. The ECMWF and GFS differ greatly on the
handling of this feature with the ECMWF cranking out pretty high
pops for Mon versus the GFS which has only 10 % values for that
day. Another 500 mb short wave follows this one and moves over TX
late Tues/early Wed ushering through another cold front with
reinforcing CAA for the latter half of next week. Some decent
moisture levels pool ahead of this fropa later next week so will
maintain some better pops on Wed as both the ECMWF and GFS are in
better agreement for rain chcs around midweek.

For max/min temps, both the longer range models are in pretty
good agreement through around Wed with the GFS showing a warmer
bias from Wed thru Fri. The 500 mb heights from both the GFS and
ECMWF through Day 7 are in better agreement versus yesterday`s
runs. So will opt to go with a general blend of the two models for
temps throughout the extended period. Overall run to run
consistency with both the GFS and ECMWF has been pretty steady
over the last several cycles. Accordingly, forecast confidence is
a little better today versus yesterday. The main areas of concern
in the long term are the model differences with pops on Monday and
the overall temp trends for the RGV after Wed.

MARINE (Now through Saturday Night): As pressure gradient
increases across the the Gulf waters of deep south Texas tonight,
winds and seas will begin to build. In fact, winds may near Small
Craft Advisory thresholds. Decided to keep SCEC in products for
now as this is only a marginal event with a not so favorable setup
for the direction. There will be some slight improvement on
Saturday, however, this will be short lived as a strong cold front
blasts through the region late Saturday bringing near Gale force
sustained winds and building seas.

Sunday through Wednesday Night: A strong pressure gradient will
persist across the marine areas on Sun in the wake of the weekend
frontal passage maintaining SCA conditions. The gradient will then
weaken later on Sun with a weak gradient flow persisting through
Mon and Tues allowing the seas to diminish both days. The next
cold front will move through the region late Tues/early Wed
allowing for the gradient to build once again maintaining the
potential for SCA conditions through Wed night.



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