Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 181833 AAA
AFDBRO

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
1233 PM CST Sun Feb 18 2018

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

&&

.AVIATION...The strengthening southerly low level flow will mix
out the low level cld cover allowing for VFR conditions to prevail
this afternoon and early this evening. The moist low level layer
will persist into the overnight hours. As the surface winds
decouple later tonight, expect low clds to reform once again over
the RGV airports reducing the ceilings down to near IFR levels for
several hours later tonight through sunrise Mon. As the low level
nocturnal inversion mixes out after sunrise tomorrow, the low clds
will mix out once again allowing for a return of VFR conditions by
the mid to late morning.

&&

.PREV DISCUSSION... /issued 545 AM CST Sun Feb 18 2018/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Low-level jet continue to bring warm, moist air across
the region with low clouds and patchy fog this morning. Ceilings
at BRO are varying between IFR and LIFR and will likely continue
through the morning. As the winds increase late this morning,
conditions will improve to VFR in the afternoon with a few
stronger wind gusts in the lower Rio Grande Valley. Ceilings will
drop again late tonight with moderate winds keeping any fog from
becoming dense.

PREV DISCUSSION... /issued 449 AM CST Sun Feb 18 2018/

SHORT TERM (Now through Monday): A weak front is currently
analyzed just north of the CWA with very little in the way of
precipitation. The main impacts affecting the region tonight have
been the low clouds and fog near the coastline. Dew points in the
upper 60s to low 70s continue to stream northward over relatively
cooler water temperatures, therefore causing another round of
dense marine fog. Some of the fog could advect inland and affect
portions of coastal Cameron and Willacy counties through mid-
morning. This afternoon, the leftover surface boundary will
retreat northward with the pressure gradient strengthening. Well-
above-normal temperatures and breezy southeast winds can be
expected with highs in the upper 80s to low 90s across the Upper
Valley and cooler along the coast. High temperatures yesterday
(Saturday) broke 90 degrees in the McAllen area, which was well
above all MOS guidance. With a similar pattern expected today,
will go with near persistence. A few showers will be possible in
the northern Ranchlands from Falfurrias to Hebbronville in the
vicinity of the front, but moisture is very limited with RH values
in the 25% range above 800mb.

Monday, a surface low will develop in the Central Plains, leading to
a windy day across Deep South Texas. A Windy Advisory still looks to
be a strong possibility with sustained winds ranging from 25 to 30
knots and gusts to near 40 knots at times in the lower RGV.
Temperatures will also be very warm and likely a tad warmer than
this weekend as low-level winds veer from the south to south-
southwest from 850 to 700mb, which is ideal for some good
downsloping off the higher terrain of Mexico. Once again models are
likely going too cool, so went several degrees above guidance, with
highs ranging from the upper 80s to low 90s.

LONG TERM (Monday Night through Saturday): 500mb trough across
the western United States Monday and a 500mb ridge across the
southeast U.S. will provide a south to southwest flow aloft across
south Texas. Low to mid level moisture is expected to increase
across northeast TX Monday and across portions of central and
southwest TX Mon night. Convection will develop across portions of
north and central TX as a result with most of the showers and
thunderstorms well to the north of the CWA Mon night into Tuesday.
Rain chances are expected to increase across south TX Tues night
into Wednesday as a cold front moves into central TX Wed morning.
The global models continue to show differences in timing on the
front moving through deep south TX with the ECMWF continuing to be
slower and farther north than the GFS. This will affect
temperatures on Wednesday so have blended MOS guidance between
the two models as the ECMWF continues be warmer than the GFS. Rain
chances will increase Wed night either along or in the wake of
the front with a high chance of showers and thunderstorms as the
models are at least in better agreement with instability across
the area. Cooler temperatures Thursday will be brief with a
lingering chance of elevated convection. The front will retreat
northward Thurs night into Friday providing warm temperatures
through the rest of the forecast period. Will continue to mention
a slight chance of showers or thunderstorms Friday and Saturday as
the GFS 700mb omega fields prog some moderate to strong vertical
motion through the rest of the week into the weekend.

MARINE (Now through Monday): Dense marine fog will continue
through mid-morning across the nearshore Gulf waters and Laguna
Madre as moist air advects northward over cooler water
temperatures. A Dense Fog Advisory is in effect through 10 AM CST.
Pressure gradient will strengthen this afternoon with winds
possibly reaching 15 to 20 knots at times across the Bay. Cooler
water temperatures should keep winds slightly lower over the Gulf
waters. On Monday, winds will increase as a storm system deepens
in the Central Plains, with southeast winds nearing Small Craft
Advisory criteria. Seas will also build to 5 to 6 feet Sunday
night through Monday.

Monday night through Thursday...Moderate to strong southeast winds
will prevail across the coastal waters Mon night into Tuesday with
surface low pressure across the southern plains and high pressure
across the eastern Gulf of Mexico providing a strong pressure
gradient across the lower Texas coast. The pressure gradient
should weaken across the western Gulf Wednesday before a cold
front moves offshore the lower TX coast Wed night. Small craft
advisories will likely be needed for the offshore waters Mon night
through Tues night and possibly Wed night into Thursday. Moderate
northeast winds should prevail across the coastal waters in the
wake of the front on Thursday.

&&

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

&&

$$

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

Short Term/Aviation...60
Long Term...55
Graphicast/Upper Air...62



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