Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 182346 AAA

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
646 PM CDT Tue Oct 18 2016

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


.AVIATION...Afternoon CU fields are beginning to erode with only
some lingering high clouds expected. A lower cloud deck will
likely develop some time overnight at KBRO and KHRL given more
low level moisture towards the coastline. However...VFR
conditions will prevail and SE winds will remain in place.


.PREV DISCUSSION... /issued 306 PM CDT Tue Oct 18 2016/

SHORT TERM (Tonight through Wednesday Night):Another hot mid-October
afternoon in progress across the Rio Grande Valley and Deep South
Texas, but looks like temps will stay below record territory, which
was well-handled in the going forecast.  Latest water-vapor
satellite imagery and model objective analyses show that mid-level
high center has moved off to the east over Louisiana.  Meanwhile, at
the surface, high pressure centered over the SE CONUS is driving
breezy SSE winds this afternoon.  Overall atmospheric column
moisture remains paltry, with 1.18" precipitable water measured on
the 12Z BRO sounding.  Only shower activity to speak of today has
occurred offshore.  NAM and GFS hint at a modest increase in
moisture over the offshore waters tonight, so another round of late
night/morning showers is possible, but land areas should stay mostly
rain-free.  Patchy fog again possible for just a few hours around
sunrise for the ranchlands.

Thicknesses decrease slightly for Wednesday as an upper-level trough
moves into the Plains states.  This should knock a couple of degrees
off the afternoon max temps, though Brownsville and McAllen will
still be approaching records for the date.  Heat indices will reach
100-103F in the afternoon.  Models indicate that perhaps a modest
moisture deepening and a weak vort max rotating around the back side
of the high will trigger isolated shower activity in the afternoon.
Moving into Wednesday night, a frontal boundary currently across NW
TX will get a finally get a push southward.  This front is expected
to be in south-Central TX by 12 Thursday, so most impacts hold
off until daytime. Moisture will be pooling offshore and along
coastal areas after midnight, though, so scattered showers and
isolated thunder will be possible.

LONG TERM (Thursday through Tuesday):Cold front will be making
is way slowly across South Texas and the the CWA Thursday with it
moving south of the Rio Grande River as early as 3 pm and as late
as midnight Thursday night. GFS seems to be the faster model,
showing a 3-7 pm passage, with NAM and ECMWF the slowest (9pm-
midnight)at this time. All models show a pre- frontal trough
moving well in advance of the front with winds gradually backing
east to northeast. This should allow for at least some slow down
of the diurnal heating but still expect another day in the 90s
for most of the CWA. Latest model package is hinting at a slighlty
weaker front as it advances into Deep South Texas as the mid and
upper level trough over the central portions of the country
quickly moves eastward. 500-1000mb thicknesses becoming more
diffuse as the front moves south and as the surface high also
tracking more east then south which might result in a slowing of
the front. This may result in clouds and some rain lingering
across the RGV, especially the Lower RGV, longer. Even with the
weaker front and some indication of warmer guidance temperatures
clouds and rain should allow for cooler temperatures on Friday.
Coldest morning will be Saturday as skies clear and center of
surface ridge

Moisture continues to pool ahead of the front and will likely
interact with the prefrontal trough (convergence line)maintaining
the decent chance of rain Thursday. Models guidance has trended
slighlty lower on the pops Thursday but with the slower front models
are trending with higher pops Thursday night into Friday, especially
across RGV which will remain within the frontal zone. Forecast will
show a slight bump in pops over the RGV through at least Friday
morning to accommodate this trend.

Cooler and drier air to move in for Friday night and the first half
of the weekend with high pressure reaches it farthest point south.
As surface high shifts farther east and a weak mid level trough
moves into NW Mexico Gulf moisture will be on the return with clouds
likely to increase. As for rain chances ECMWF and GFS show this weak
mid level trough moving into Big Bend and West Texas region with
deepening moisture over the CWA. Rain chances are already in the
offering so will not vary from this trend. Temperatures to
rebound as the moisture increases.

MARINE:(Now through Wednesday night):  Generally moderate SE winds
will persist through most of the period before backing to the E and
slackening late Wed. night as a pre-frontal trough moves through the
coastal waters.  Easterly swell has subsided to about 1-1.5 ft. so
total seas remain in the 2-3 ft. range.  Isolated showers expected
tonight and into tomorrow morning.  Showers become more scattered in
nature with isolated thunderstorms on Wednesday night.

Thursday through Sunday...Cold front to move through the coastal
waters Thursday with a steady increase in northeast winds.
Strongest winds are anticpated for Thursday evening through Friday
morning. Seas are likely to build through Friday peaking by sunset
Friday. Small craft advisories are likely as early as Thursday
afternoon and continuing into early Saturday for some lingering
higher seas. Winds begin to veer east Saturday and turn southeast
returning to moderate southeasterlies Sunday and early next week.




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