Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 260534 AAC

Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
1234 AM CDT Mon Sep 26 2016

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


.AVIATION...Rain shield across the western valley has been slowing
during the past couple hours, and is looking less likely to reach
KMFE overnight. Models continue to show redevelopment starting
right along the coast later tonight and continuing into the day
Monday. Hvea kept the tempo group startin at 10z, but may need to
bump that forward for BRO as showers already forming off to the
southeast of town. Overnight showers will be more isolated in
nature, with only small time periods of passing showers. More
numerous showers Monday will bring more predominant rain into the
TAFs for the afternoon hours.


.PREV DISCUSSION... /issued 926 PM CDT Sun Sep 25 2016/

DISCUSSION...A weak cold front currently extends from near
Texarkana to Zapata. Numerous showers and thunderstorms continue
to develop along the boundary mainly across Zapata, Starr and Jim
Hogg Counties. The latest HRRR and NAM suggests that this
convection will move east and gradually weaken overnight.
However, the NAM shows some additional development near the coast
around sunrise. Have updated the overnight grids to reflect
current thinking and for observational trends. A flash flood
watch may be needed later tonight or Monday due to the high
rainfall rates, precipitable water values over 2 inches, and the
slow moving boundary across the area.

PREV DISCUSSION... /issued 705 PM CDT Sun Sep 25 2016/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...Moderate and gusty southeast winds prevail across deep
south Texas this evening. Latest BRO radar indicates scattered
showers and thunderstorms the extreme western portions of the CWA.
This activity is associated with a weak cold front approaching the
area. THe latest HRRR and NAM models suggest that some of this
activity could reach the TAF sites after midnight, mainly after
09z. Otherwise, winds will gradually diminish by later this
evening with some brief MVFR ceilings possible overnight. Rain
chances will increase on Monday as the front approaches from the
west and moisture pools ahead of it.

PREV DISCUSSION... /issued 221 PM CDT Sun Sep 25 2016/

SHORT TERM (Tonight through Monday Night): A negative tilt H5
trough is moving laterally from west to east across the upper plains
today. It extends a weakness southwest to a cutoff low over North-
west Mexico. High pressure is over the central high plains and a
cold front is pushing out ahead of that high pressure over North
Central Texas. High pressure is also over the Gulf of Mex, driving a
moderate southeast flow over the CWA, pumping moisture ashore.
Marine showers are ongoing over the Gulf adjacent to the CWA, while
isolated to scattered afternoon convection is developing over the

Daytime convection should decrease this evening as heating subsides,
however, there is enough moisture such that it may not entirely
disappear, especially over the Gulf and along the coast tonight.
Plus, a few showers may push south ahead of the front, whose
transection of the Rio Grande should end up between Del Rio and
Laredo tonight. Despite somewhat more robust pop percentages than
usual of late, QPF amounts will remain relatively low, at a quarter
of an inch or less. Overnight low temperatures will be in the mid
70s with a light east southeast wind.

The NAM starts out the work week Monday morning with ongoing Gulf
showers and streamers moving onto the coast and over the Lower
Valley, even reaching the southern Mid Valley. Though convective
coverage will be in the numerous category, overall QPF still looks
manageable at under a half an inch, though some locally heavier
downpours will be possible. Light winds will back from east
southeast early Monday morning to east northeast through the day.
Max temperatures will be slightly lower than today, mainly in the
mid to upper 80s.

A shift to north winds Monday night signals that the front will edge
into the area, but marginally drier air will not push all the way
through, and the front may hang up at the coast. QPF amounts again
still look modest at less than half an inch, although heavier
amounts look feasible over the Gulf. Overnight low temperatures will
be a bit less than tonight, in the lower to mid 70s.

LONG TERM (Tuesday through Sunday): The main effort in the long
term portion of the forecast was to reduce rain chances and shift
the focus of the precipitation to along the immediate coastal area
and the adjacent coastal waters in the wake of the above-mentioned
cold front. Isolated to scattered thunderstorms and/or showers
are forecast Tuesday through Thursday as deep tropical moisture
remains in place near the coast in the wake of the front. The
atmosphere will then rapidly dry beginning Thursday night and
afterwards, leading to dry weather at that time and through the
remainder of the forecast. Temperatures tempered to near normal
levels immediately in the wake of the front will gradually warm to
above normal levels by the end of the forecast period courtesy of
abundant sunshine and limited cloud cover.

MARINE (Tonight through Monday night): High pressure over the
Gulf will be countered by a weak area of low pressure over the
Southwest Gulf and by the approach of a weak cold front pushing
slowly through South Central Texas tonight. Moderate southeast
winds today will weaken and shift to east tonight, and will then
become light to moderate northeast on Monday. Winds will back to
north and will become moderate Monday night as the front moves
near to and over the lower Texas Coast. Seas will remain low to
moderate through the short term. Isolated to scattered showers
with embedded thunderstorms will continue over the marine areas.

Tuesday through Sunday: Moderate generally northeast winds and
moderate seas will prevail through the period in the wake of the
cold front discussed above. Wind speeds may be strong enough on
all or portions of the Lower Texas coastal waters Tuesday and
Tuesday night to warrant a Small Craft Exercise Caution.




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