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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 141746

Area Forecast Discussion
National Weather Service Brownsville TX
1246 PM CDT Sun Oct 14 2018

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


.AVIATION...VFR and breezy SE winds will prevail through the
afternoon at the RGV terminals. Meanwhile, a strong cold front
will continue pushing into Texas from the northwest. Ahead of this
front, some moisture pooling overnight into Monday morning may 
lead to intermittent MVFR ceilings (per RAP BUFKIT soundings and
SREF probabilities) and passing, light coastal showers at BRO and
HRL. The front may edge into MFE by very late in the TAF period, 
bringing stronger northerly winds, steady rain, MVFR ceilings, 
and possibly a thunderstorm. These conditions are likely to spread
to HRL and BRO by mid-afternoon Monday.


.PREV DISCUSSION... /issued 648 AM CDT Sun Oct 14 2018/ 

..12z Aviation Update...

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Mainly VFR conditions will prevail through this 
cycle. Only concern looks to be gusty southeasterly winds, 
especially from late morning through around sunset. Winds may 
gust up to 20-25kts at times. We will need to watch toward the end
of the cycle for perhaps an isolated shower or two, especially 
closer to the coast, however, given uncertainty and low 
probabilities at this time left any mention of convection out of 
the forecast.

PREV DISCUSSION... /issued 411 AM CDT Sun Oct 14 2018/ 

SHORT TERM (Today through Monday):As the upper level high 
continues to gradually build eastward, relatively active southwest 
flow will set up across the region, especially as a trough across 
the western US/N Mexico continues to amplify. 

For today, expect a very similar day as yesterday. The 00z BRO 
sounding shows a good bit of dry air in the middle and upper levels. 
Unless something can develop within the moist boundary layer right 
along the sea breeze (it would likely be isolated if so) think much 
of the region should be rainfree today. The dry conditions will 
likely last through tonight, however, POPs begin to increase pretty 
quickly as we get into the day Monday. This increase in POPs comes 
from a strong surface Canadian frontal boundary. This front and 
parent shortwave, currently located from the Cornbelt to the high 
plains of Kansas will continue to surge southward. Again, as the 
front surges southward toward the area, this should be the focus for 
shower and thunderstorm activity. 

Timing of the front is a bit of a concern. The global spectrals and 
GEM show a slower progression of the front with a passage through 
the entire CWFA around or just after sunset Monday (or just beyond 
the short term period). However, mesoscale models show the frontal 
boundary passing through the entire forecast area between 21z and 
00z respectively. That said, mesoscale models tend to have a better 
handle on timing as well as temperatures behind the front than the 
more coarse resolution globals. Went with mostly the NAM this 
package for the frontal passage and cool down behind the front. 
Speaking of temperatures, did bump temperatures a few degrees for 
Monday in lower RGV locations. Given the delay in the front making 
it into the lower valley, think that by late morning and early 
afternoon temperatures will have the opportunity to warm into the 
upper 80s or lower 90s. That said, clouds and precipitation will 
quickly increase from the north limiting the window to go even 

LONG TERM (Monday Night through Saturday):The cold front should
be offshore by the beginning of the Long Term which will lead to a
wet and much welcomed cooler pattern for much of next week. Main
concerns will be for the potential of heavy rain Monday night with
the initial surge of the front and again Thursday as disturbance
moves along the Texas from the Gulf of Mexico. 

A very unstable and moist atmosphere and increasing divergence 
aloft should lead to widespread convection along and behind the 
front Monday night into Tuesday morning. Heavy rainfall with 
amounts of 1-3 inches are not out of the question favoring mainly
the coastal sections but any location could see heavy rain. WPC 
has added the region in a marginal risk excessive rainfall due to 
tropical nature of the airmass in place. Wet soils from the 
previous 6 weeks of rain may cause some local flooding issues if 
the heavy rain materializes. Temperatures will continue to fall 
with 40s and 50s overspreading the region add in some gusty north 
winds and conditions will be outright nasty to say the least. 

No change in the mid level flow pattern with South Texas to remain
between an upper low over the Desert Southwest and mid level
ridging extending across the Gulf. A steady flow of moisture
overriding the cool surface air will keep a good chance of rain
across the region for foreseeable future. Lighter rain looks to
materialize later Tuesday and Wednesday with a more isentropically
driven pattern setting up. However, can not rule out some elevated
convection (shwrs/tstorms) at times due to the warm southerly 
flow aloft. With a coastal trough developing not too far offshore
the coastal counties are likely to have the better opportunity to
see moderate rainfall at times. GFS/EC continue to advertise a
tropical disturbance, or a surge of moisture, moving in from the
Gulf Wednesday night and Thursday with rain chances increasing 
and providing the opportunity of heavy rainfall. Once again the 
coastal counties seems to be the favored location. Rainfall 
amounts could exceed 2 inches in some locations with coastal 
trough strengthening setting the stage for localized flooding.
WPC's 1-7 day rainfall amounts indicate 4-7 inches along the
coast and 2-4 inches Mid and Upper Valley's as well as the
Northern and Western Ranchlands. Flooding potential will be a
possibility and Flash Flood watches may have to be issued if the
initial swath of heavy rain (with the front) does indeed develop.

The cold air will be entrenched across the region Tuesday and
Wednesday with lows in the 40s and 50s and highs mainly in the 50s
to lower 60s. A slow recovery of temperatures is expected Thursday
and Friday and into Saturday as the surface ridge moves east and
the airmass modifies with the tropical disturbance moving into the
region. Another cold front could arrive later Saturday or Sunday
but models differ on timing and uncertainty resides on the density
of the colder air associated with it. 

MARINE:(Today through Monday): Moderate seas/winds expected today 
across the marine zones of Deep South Texas. The only concern today 
will come during the afternoon and early evening as winds begin to 
increase over the Laguna. At this time, Small Craft Advisories 
aren't expected today or tonight, however, cautionary wording may be 
needed in the coastal waters products. Moderate marine conditions 
will continue through early Monday and perhaps into the afternoon 
hours before a cold frontal boundary moves into the adjacent coastal 
waters. It appears behind the front winds will reach as high at 20-
30 knots at times with locally higher gusts up to Gale strength may 
be possible from time to time.

Monday night through Thursday...Strong cold front will be moving 
through the coastal waters Monday night with a sharp increase in
winds and seas. Strong northerly winds to persist into Wednesday
while seas approach or briefly exceed 10 feet. An extended period
of small craft advisories are highly likely with occasional gale 
force gusts anticipated Monday night and Tuesday. Coastal trough
moves over the coastal waters Thursday which results in a slight
weakening of the northerly flow allow for seas to begin to
subside. Widespread rain with heavier showers and thunderstorms
at times are expected through much of the period. 




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