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Area forecast discussion...updated 
National Weather Service Brownsville Texas
635 PM CDT Thursday Aug 21 2014

Discussion...updated for latest aviation discussion below.

Aviation...visible satellite imagery shows a batch of high cirrus
moving towards the north from neighboring Mexico...while surface
winds are continuing at breezy levels. The cirrus should persist
through the next several hours as winds become light for the
overnight hours. Tomorrow...conditions similar to Thursday are
predicted...although lower cloudiness should rule. VFR is likely
through the next 24 hours.

Previous discussion... /issued 249 PM CDT Thursday Aug 21 2014/

Short term /now through Friday night...weak upper level disturbance
over the western Gulf Coast is moving northwest into Mexico
enhancing scattered convection over the area while abundant dry air
shown in the 12z kbro sounding with precipitable waters of around 1.53 inches were
observed. This has limit the convection activity over deep south
Texas at this time. Southeast winds have increased as expected due to the
low level jet increasing between 25 to 30 knots mixing to the surface leading to
this breeze conditions. Kept only a low 20 percent across the Lower
Valley as a few isolated showers could move into the area. The
southeast winds will begin to lower tonight as the gradient weakens
and high pressure slightly retrogrades west. Low temperatures will stay in
the low 80s across much of the County Warning Area. The dry air embedded within the
periphery of this high pressure will move inland Friday lowering the
chance of showers even more. Temperatures will be above 100 west of
Highway 281 and upper 90s along the coast. Heat index or feel like
temperatures will be between 108 to 110. The pressure gradient will
not be as strong Friday allowing for southeast winds to remain moderate
during the day.

Long term /Friday night through Thursday/...
dried forecast out until Thursday with especially dry air over Gulf of
Mexico...breezy windy through Saturday.

Friday night into Saturday good agreement amongst NAM/GFS/ECMWF on a
shortwave trough diving into the intermountain west and aiding in
amplifying ridging over the midwestern states. This shifts the 500mb
and associated lower level ridging from its perch on the northern
Gulf Coast to the arklatex region. This will help relax the low
level pressure gradient a little...but it will still be strong
enough to generate persistent breezes and make setting up a stronger
seabreeze front difficult. GFS/NAM model soundings are decent for
convection but the 850/700mb region is pretty dry and the lack of
extra help from the seabreeze should keep rain chances limited. Sref
and MOS guidance agree and the run to run trend is drier so pared
back the slight chance of showers to a more favored zone inside of a
Falfurrias Sarita Raymondville Triangle. Temperatures will be close
but slightly cooler than the last few days.

Sunday the 500mb ridge axis will be a little further north but the
overall synoptic pattern is expected to be close to Sunday. Low
level moisture will likely remain a little too low for much in the
way of precipitation with 850/700mb flow sourcing in the currently rather
dry western Gulf of Mexico and the low level pressure gradient will
still be a little too strong for seabreeze convection. Played the
temperatures and probability of precipitation similar to Saturday in the new forecast with a Dry
Valley and small area of the ranchlands that may pop a late
afternoon seabreeze shower.

Monday the ridge moves to the middle Mississippi Valley with low level
wind speeds decreasing more noticeably and orienting more east to
west. High temperatures will be a touch cooler...although still in
the middle/upper 90s to low 100s. Middle level convergence in the area
will be lower with the ridge moving ahead but when GFS/European model (ecmwf) shift
the low to middle level flow more easterly it only advects in still
relatively dry air. AMSU/SSMI blended precipitable water
estimates...GOES sounder... ND current weather over the Bay of
Campeche appear to support that concept with a fairly dry 850mb
layer across that entire region so kept the valley dry with another
small area of seabreeze showers over the ranchlands given the
unusually dry airmass to our southeast.

Tuesday a reinforcing Pacific jet maximum begins to dig western US
troughing a little further east and south which appears to flatten
the eastern US ridge. This leads to deeper more easterly flow over
the region but still only draws in the dry air from the central Gulf
and does not really appear to increase precipitation chances much. Winds
will be fairly light out of the east with temperatures moderated
slightly by the easterly flow. Kept probability of precipitation a little below guidance
consensus feeling that climatology may be playing too big a role at
that range compared to our current abnormally dry airmass.

Wednesday GFS/European model (ecmwf) still differ in the progression of the middle level
shortwave that moves over the plains in response to the previous
days events but the 12z European model (ecmwf) did trend closer to the GFS. Set up
the forecast based on a synoptic solution closer to the GFS ensemble
whereas the European model (ecmwf) flattens and deepens ridging in a way to usher in
much Richer eastern Gulf moisture and GFS brings in at least a
little higher middle/low level relative humidity valuesbut not quite as much in terms
of richness and depth. Wind speeds should be favorable for a sea
breeze but I suspect that Lee troughing will be stronger than
forecast in day 7 guidance and bumped wind speeds up a bit. Went
with a nearly valley wide 20 pop. /68-jgg/

now through Friday night...southeast winds will prevail
through the short term period with slight chance of showers over the
Gulf waters in the afternoon. Small Craft Advisory is in effect over
the Laguna Madre through the evening. Conditions improve tonight but
winds pick up again Friday but pressure gradient will not be as
strong as today with possible scec over the Laguna and the near
shore waters. Seas will remain up to 5 feet over the Gulf waters but
will begin to lower to around 4 feet into tomorrow as the winds
begin to decrease.

Friday night through Tuesday...
breezy southeast winds are expected to prevail through Sunday before
becoming lighter and more southeasterly Monday and Tuesday. Current
forecasts suggest wind speeds below advisory criteria however for
the entire period Friday night through Tuesday but periods of
moderate seas and small craft exercise caution level winds will be

Fire weather...on Friday dry air embedded within the high pressure over the
Gulf will move inland. Relative humidity values between 1000 to 500 mb lower to
around 30 to 25 percent. In addition...the southeast winds will begin to
increase in the afternoon with gust up to 20 miles per hour. Due to the dry
fuels in the western counties and moderate to strong southeast winds weather conditions will not be elevated to
critical over the western counties but could enhance fire danger may
be issued as the dry conditions continue over the area. The
precipitable water values have also lower to around 1.5 inches.
Minimum relative humidity values for tomorrow range from 25 to 30 percent
especially for Zapata...Jim Hogg and western Starr counties. Relative humidity
recoveries for the western counties remain in the lower 80 percent
with a few locations along the river remaining in the 70 percent

Bro watches/warnings/advisories...
GM...Small Craft Advisory for winds until 8 PM CDT this evening for


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