Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 251138 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
638 AM CDT Wed Apr 25 2018

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

.AVIATION...Some mid-level cloudiness moved over the aerodromes
during the overnight hours and has replaced the high cirrus
previously in place. Lower clouds and breezy winds will result in
VFR this morning and afternoon. Forecast models suggest that a
dying thunderstorm complex will move east out of Mexico this
evening and tonight, resulting in showers for the aerodromes.
Surface winds will become light and variable as a weak cold front
approaches from the north.

.PREV DISCUSSION... /issued 357 AM CDT Wed Apr 25 2018/

SHORT TERM (Now through Thursday): The main concern in this portion
of the forecast will be the potential for severe thunderstorms. A
500 mb shortwave is expected to ride within the northwest-to-
southeast mid-level flow over Deep South Texas and the Rio Grande
Valley this evening and early tonight just in advance of the passage
of a weak cold front at the surface. Isolated to scattered
convection will develop over the five westernmost counties of the
BRO CWFA during this time period, with the main bulk of convective
activity across the Rio Grande River in neighboring Mexico. The
Storm Prediction Center forecasts a marginal risk of severe
thunderstorms along and west of a Mission to Hebbronville line.
Therefore, have indicated strong to severe thunderstorms producing
large hail and damaging winds for Zapata, Jim Hogg, Starr, Brooks,
and Hidalgo Counties. Isolated leftover weak convection is
anticipated after midnight tonight until around sunrise Thursday
morning, before dry conditions prevail for the remainder of the
short term forecast period in the wake of the cold front. No
significant cold air advection with the cold front will result in
very warm daytime highs and mild overnight lows.

LONG TERM (Thursday night through Tuesday): An unsettled pattern
will continue across the eastern half of the U.S. with deep
troughing and several shortwave troughs moving through the upper
level flow by the end of the week. An occluded surface low in the
Northeast will bring a weakening front into South Texas on Friday
with a surface high slowly drifting across the northern Gulf
coast. A weak shortwave trough will move around the upper level
ridge across the Central U.S. and bring a chance of showers and
thunderstorms Friday night and Saturday. The GFS is currently the
wettest with much higher PoPs in the Upper Valley compared to the
last run. It also brings more intense convection over the higher
terrain of Mexico with a stationary or warm front across our area.
Will have to keep an eye on it, but decided to maintain 20 to 30%
PoPs for now with other guidance consistently staying lower.

Late in the weekend and into next week, another upper level trough
digs down across the Desert Southwest and brings southwest flow
aloft across South Texas. With plenty of moisture across the
western Gulf, isolated showers and thunderstorms will be possible
each day. Precipitation chances may be aided by seabreeze
enhancement along the coast, but the surface gradient will likely
become too strong by mid-week. Southeast winds will increase as a
storm system develops in the Central Plains and become breezy to
windy across the RGV. Slightly below normal temperatures each day
will warm up to above normal by the end of the long term with a
strong low-level jet bringing warm and humid air across the

MARINE (Now through Thursday): Buoy 42020 reported southeast winds
around 12 knots gusting to around 14 knots with seas slightly over
1.5 feet with a period of 4 seconds at 02 CDT/07 UTC. Light to
moderate winds and low to moderate seas will prevail along the Lower
Texas Coast in advance of, and behind, the Wednesday night passage
of a weak cold front. Despite the frontal passage, Small Craft
Exercise Caution and Small Craft Advisory are not likely to be

Thursday night through Monday: A weak cold front will move into
the region by Friday with a surface high moving overhead and
slowly drifting eastward. Generally light winds and low seas will
continue through Saturday. Winds will increase out of the
southeast starting on Sunday into Monday with seas building to 4
to 6 feet early in the week.



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