FXUS64 KBRO 290613 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
113 AM CDT Fri May 29 2020

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


.AVIATION...A conv complex pushing into the western counties will
stay clear of the RGV airports for the next few hours. However, if
this conv area holds together and maintains its eastward progress,
expect the aviation conditions across the RGV to degrade somewhat
trending towards MVFR conditions with periodic IFR conditions due
to the passing conv. The latest SPC SWODY1 outlook has removed the
marginal and slgt risk areas for the RGV but maintains the general
t-storm outlook over the region for the moment. So will maintain a
mention of conv in the upcoming TAF period later this morning into
the early afternoon hours.


.PREV DISCUSSION... /issued 653 PM CDT Thu May 28 2020/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...VFR now. Short range models suggest deteriorating
conditions after midnight through mid Friday morning as a cold
front works south through the CWA, triggering progressive
overnight convection. Ceilings will lower to MVFR after midnight
with isolated to scattered shower and thunderstorm activity
developing as dawn approaches. The main threats to aviation will
be frequent cloud to ground lightning and visibility reduction in
brief, heavy downpours. Strong, gusty winds will also be possible.
The threat for MFE will be slightly greater than the threat for
HRL and BRO, being categorized as short-lived isolated intense
storms possible. Conditions will improve later in the day Friday
as the front pushes south of the area.

PREV DISCUSSION... /issued 256 PM CDT Thu May 28 2020/

.Another round of potential strong to severe thunderstorms
tonight with the Western Ranchlands having the highest chances...

SHORT TERM (Now through Friday Night): Water vapor loops show an
upper low spinning over the Arklatex with a potent shortwave
dropping into NE New Mexico and the TX panhandle. The atmosphere
over NE Mexico and South Texas will continue to destabilize the
remainder of the afternoon with significant heating and high surface
dew points in place. Current LAPS shows CAPE values exceeding 4000
j/kg and CIN slowly eroding. A stationary front is analyzed over
South Central Texas and will begin to move south this evening as the
shortwave over NW Texas continues to move south along the western
side of the upper low. Forcing should increase tonight as the strong
disturbance combines with the front leading to an increase in
thunderstorm development. Steep lapse rates and decent shear values
should support a few stronger updrafts providing the opportunity for
severe convection. Models continue to favor the western Ranchlands
and the Upper RGV with higher probability with lower chances as you
head east. SPC Day 1 Convective Outlook also favors the wester half
of the CWA with a slight risk in place. Confidence on timing remains
about average with initial thunderstorms approaching the western
counties a few hours after sunset with better opportunity a few
hours either side of Midnight as the cold front enters the northern
portions of the CWA. The convection should follow the front with the
Mid and Lower RGV seeing the stronger convection late tonight and
possibly lingering towards sunrise Friday. Heavy rainfall will be
threat over the west as well with forecast pwats as high as 1.8
inches and the potential a few thunderstorm clusters passing over
the same area. QPF totals of 1-2 inches with isolated amounts of up
4 inches are not out of the question. Farther east one-half to one
inch of rain is possible overnight.

Friday and Friday night...GFS/EC are in decent agreement showing the
upper disturbance and the cold front moving over the CWA Friday
morning. Rain chances remain relatively high especially along the
Rio Grande in proximity of the front. Mid/upper layer wind flow
continues to show decent divergence emanating over NE Mexico as the
upper disturbance moves into NE Mexico. This may likely maintain and
continue to favor sufficient forcing and upper divergence to keep on-
going convection active through Friday morning and possibly the
afternoon. Once the front continues to move farther south convection
should begin to decrease with the majority tracking south of the
border. Rain chances lower Friday night with the upper disturbance
transitioning into a low pressure area and maintaining mid to upper
level southerly flow over our region. Any convection will likely be
reduced with model consensus showing best chances across the Upper
RGV and western ranchlands.

Temperatures tonight remain warm and very muggy in advance of the
convection. Winds are likely to be light making for a very
uncomfortable evening. Friday's highs will be lower and may not even
reach late May normals as the cold front pushes through and plenty
of cloud cover and rainfall around.

LONG TERM (Saturday through Thursday): The weather pattern
into the long term period will stay rather unsettled due to the
combination of an upper level trough/low over northern Mexico, a
nearby surface trough and low-level moisture pooling within the
southwestern Gulf of Mexico. This along with light to modest
easterly winds will promote some increased sea breeze potential.
The latest model guidance do focus the highest rain chances for
Sunday and Monday across the region, especially the Rio Grande
Valley. However, model guidance also continues to show that the
highest QPF signal remains to the south of the Rio Grande River
over northern Mexico. The rain chances will gradually diminish
midweek as the upper trough/low weakens.

With the upper level low/trough pattern over northern Mexico and
considerable cloudiness associated with the rain chances should
help to keep the temperatures at or slightly below climatological
average through early next week. Temperatures then gradually rise
into the middle of next week as the upper low weakens and rain
chances diminish.

MARINE(Now through Friday Night): Pressure gradient continue
to weakens today in advance of a slow moving cold front. Models
suggest the front moving through the coastal waters Friday morning
possibly with a line of potentially strong thunderstorms. The
front will be slow in moving south Friday with high pressure
building into NE Texas through Saturday. Northeast winds
increasing into SCEC range may approach SCA with the nearby
convection. Gradient may relax Friday evening with the front
nearby and high pressure still well removed to the north. Seas are
likely to see an increase as the northeast flow persist but
currently models keep seas at or below 5 feet. Scattered to
widespread convection is forecast for Friday.

(Saturday night through Tuesday night): Weak nearby surface
troughing will help keep the pressure gradient relaxed as high
pressure remains centered quite a distance away across the Ohio
Valley and Mid-Atlantic. Mariners should expect fair to favorable
marine conditions in the long term with low to modest easterly
winds and generally low seas. However, with the surface troughing,
opportunities for rain and thunderstorms will exist, which may
locally agitate winds and/or seas at times.




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Short Term/Aviation...60
Long Term...69
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