Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 252345

Area Forecast Discussion
National Weather Service Brownsville TX
645 PM CDT Wed Apr 25 2018

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


.AVIATION...VFR ceilings continue into late this evening as a cold
front moves toward the Rio Grande Valley. Scattered thunderstorms
are developing along the front into northwestern portions of Deep
South Texas. While conditions aren`t as favorable in the valley,
there is an increasing chance of a few thunderstorms approaching
MFE and HRL late this evening into very early tonight, with
showers reaching BRO. MVFR ceilings are expected along the front
after midnight through Thursday morning before conditions slowly
improve. Isolated showers may continue across the lower valley
Thursday morning.


.PREV DISCUSSION... /issued 330 PM CDT Wed Apr 25 2018/

SHORT TERM (Tonight through Thursday Night): The main forecast
challenge is the advancing cold front and strong weather potential
for tonight. SPC places the upper valley under a marginal risk for
severe weather tonight, which translates to a 5% chance within 25
miles of any given point in the Zapata, Jim Hogg, and Starr county
area. Moisture, instability, and lift will be present along the
front, with gusty winds and small hail possible in the stronger
storms that may move into the upper valley from the west this
evening and tonight. An isolated severe storm is not out of the
question for the upper valley, and the threat would then be strong,
gusty winds and large hail. The front is on track to push through
the Laredo area and into Zapata county around 9 or 10 pm, and will
push through the lower valley in the pre-dawn hours of Thursday,
Rain and stronger thunderstorm chances are expected to ease as the
front progresses southeast. The best chance for unsettled weather
and a brief heavy downpour for the lower valley will be right along
the front with gusty winds of 30 to 40 mph possible.

Look for clearing skies Thursday with mild, mainly seasonal high
temperatures in the upper 70s to lower 80s with light northeast
winds. Thursday night temperatures will be in the lower to mid 60s
with light east winds under partly cloudy skies.

LONG TERM (Friday through Wednesday): The 500 mb pattern over the
lower 48 states will be dominated by deep troffing/closed lows on
the East and West Coasts this weekend. This will in turn maintain
pretty decent ridging over the South Central Plains states through
Sun. However, the East Coast trough will eventually drift
eastwards early next week while the closed 500 mb low over the
Pacific NW will open up and elongate out from SW to NE through
midweek next week. This will shift the 500 mb ridging towards the
East Coast with the South Central Plains states remaining on the
western fringes of ridging. As this broad mid level trough axis
digs to the southeast, a cold front will push into the central and
southern Plains states late in the longer range forecast period
possibly setting up for a fropa late next week. Until then expect
near to below normal temps to prevail for this weekend, with above
normal temps developing next week as the low level WAA

Some marginal moisture values remain pooled under the 500 mb
ridge axis over NE Mexico edging into southern TX. This will
likely interact with the diurnal heating to potentially fire up
some isold conv for much of the longer range period. No widespread
significant rains are expected at this time.

Run to run GFS/ECMWF consistency is pretty decent for both the
temp and pop trends. The ECMWF has a a warmer and drier bias
versus the GFS. Will maintain a general model blend for the longer
range outlook.

MARINE Tonight through Thursday night: Light to moderate southeast
winds will turn to northeast tonight after the passage of a cold
front. Light to moderate northeast to east winds will then prevail
through Thursday night. Showers and isolated thunderstorms may
develop over the marine areas tonight as the cold front moves
through, possibly superimposing strong, gusty winds and locally
rough seas on the forecast. Small craft advisory conditions will
not develop on the broader scale, however.

Friday through Monday Night: Weak to moderate surface ridging will
remain centered over the Gulf of Mexico which will likely maintain
light to moderate SE low level flow across the lower TX marine
locations throughout the weekend. However, the PGF appears to
strengthen Mon and Tues which could push the Bay and Gulf
conditions up close to SCA levels late in the forecast period.




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