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Area Forecast Discussion (AFD)

Issued by Brownsville/Rio Grande Valley, TX (BRO)

                            
000
FXUS64 KBRO 150941
AFDBRO

Area Forecast Discussion
National Weather Service Brownsville TX
341 AM CST Fri Feb 15 2019

.SHORT TERM (Now through Saturday): A broad 500 mb short wave 
moving over the central Plains states today will develop an 
elongated surface frontal system over the south Central and 
southeastern States. As this 500 mb trough moves eastwards, the 
surface low and frontal system will result in a shift of the low 
level flow over the RGV to a more S-SW direction later this 
afternoon. This wind configuration will combine with relatively 
low humidity values throughout the atms to set the stage for 
afternoon high temps going with above climo for mid February. The 
SW low level component will help maintain good potential 
downsloping of the airflow off of the higher terrain in NE Mex 
which will in turn maintain good potential for an afternoon heat 
spike across the RGV. So the main forecast question is how high to
go for max temps this afternoon. 

Most of the short term model blends tend to produce max temps in the 
lower 90s mainly west of the I69E corridor with generally mid 90s 
centered over western Starr County. Believe that these model blends 
may be a bit underdone for the max temps today as the models may 
not be handling the potential downslope effect off of the 
mountains to our west. So will edge these values up a bit for 
highs this afternoon. All of these high temp values for today are 
well above all of the short term NAM/GFS and ECMWF MOS numbers for
today. Will not mention any potential for record highs today as 
the current records for the RGV sites are still a bit out of reach
for the forecast highs today. However, if the afternoon high 
temps warm up a few more degrees, the records for the day could be
threatened. 

The surface frontal system will sag steadily southwards towards the 
Gulf Coast tomorrow. This will likely allow the low level winds to 
shift around more from the SE which will likely result in the 
surface dewpoints starting to rebound a bit more on Sat. This will 
likely limit the potential warmup for Sat as the humidity levels 
increase. However, still expect max temps on Sat to remain well 
above climo for mid Feb. 

Deep level moisture will remain pretty limited throughout the short 
term period. So single digit pops are expected through Sat. 

Areas of fog are forming up across the Coastal Bend area of TX this 
morning. Some of this fog will likely edge down into the northern 
Ranchlands early this morning, possibly pushing down into portions 
of the lower RGV. At this time do not expect any widespread dense 
fog formation. However some patchy dense fog is possible through 
sunrise. 

.LONG TERM (Saturday Night through Thursday): Low pressure in the
Northern Plains works into the Great Lakes with a weak cold front
passing through Deep South Texas Sunday morning before stalling 
just south of the border. A larger trough drops out of the Pacific
NW into the Desert SW by Monday, keeping 500mb flow out of the SW
across Texas. With a stalled frontal boundary, onshore flow, 
increasing moisture, and coastal low pressure developing at the 
surface, expect overrunning precipitation and increased cloud 
cover to develop by Monday and potentially continue through late 
next week. Models have been fairly consistent early in the week 
with scattered light rain, mainly along the coast. Mid to late 
week model output is a little less cohesive on the timing of the 
trough digging out of the SW. Earlier model runs with a frontal 
passage on Wednesday have slid back into this overrunning pattern 
persisting along the coast, with a slight increase in rain chances
Tuesday night into Wednesday, and a gradual taper to rain through
the end of the week.

Temperatures on Sunday afternoon rebound above normal behind the 
front, still a fair amount cooler than Saturday, before thicker 
cloud cover settles in. Near normal temperatures are expected on 
Monday, and with little change in the pattern, expect each night 
and day to lose a few degrees, leading into below normal 
temperatures Tuesday and Wednesday. Model trends have some warming
by the end of the week with drier air working in aloft, but 
confidence remains lower beyond Wednesday due to model 
discrepancies on the SW trough. A tighter PGF with low pressure in
the Plains would increase southerly flow and provide a better 
chance of near normal temperatures on Thursday. 

Have once again tossed in fog for Saturday night into Sunday
morning, with areas of fog possible near the coast out ahead of
the frontal passage. SREF and NAM guidance keeps the best chance
of fog across nearshore waters. 

&&

.MARINE (Today through Saturday): Surface ridging over the Gulf of 
Mex will interact with the frontal boundary over the southeastern 
States to maintain a light to moderate S-SE flow along the lower TX 
coastline into Sat. This will maintain moderate Gulf swells 
through the short range period. No SCA conditions expected 
throughout Sat. Some marine fog will still remain a threat along 
the lower TX coastline throughout Fri and Sat mornings.

Saturday Night through Thursday: A weak cold front approaches on
Sunday, with relatively light winds and seas prior to and after
the frontal passage. Patchy to areas of fog across nearshore
waters are possible into Sunday morning. As coastal low pressure 
develops on Monday, winds and seas become elevated, creating 
potentially hazardous conditions Monday night into Tuesday, with 
SCAs possible. SCEC conditions possibly continue through the rest
of the week, with seas generally 3 to 5 feet, and occasionally 6 
feet across offshore Gulf waters. 

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  82  66  81  66 /   0   0   0  10 
BROWNSVILLE          89  68  87  66 /   0   0   0  10 
HARLINGEN            91  67  89  66 /   0   0  10  10 
MCALLEN              94  67  92  66 /   0   0   0  10 
RIO GRANDE CITY      94  66  93  66 /   0   0   0   0 
SOUTH PADRE ISLAND   79  65  77  66 /   0   0  10  10 

&&

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

$$

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HTTP://WEATHER.GOV/RGV

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