Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 262322 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
622 PM CDT Thu Apr 26 2018

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


.AVIATION...Midlevel cloud deck continues to fluctuate locally due
to moisture trapped closer to the surface. This llvl moisture
remains near the sfc overnight, but the capping dry air aloft is
high enough to keep cigs from lowering significantly overnight.
Winds will drop to L/V overnight as high pressure moves into the
region. Ample moisture, especially in areas that received rainfall
yesterday, and light winds may bring some light fog to grassy
areas, but any vis reductions will be slight. Midlevel dry air
mixes out some during the day tomorrow, with thinning and rising
cloud decks through the morning.


.PREV DISCUSSION... /issued 335 PM CDT Thu Apr 26 2018/

SHORT TERM (Tonight through Friday Night): Satellite imagery shows a
punch of drier air moving south over the CWA. This drier air appears
to at the top of the boundary layer, but indications are that it
will not immediately be able to mix completely down through the
existing isothermal stable layer. Nonetheless, there will be
clearing through this evening before low level clouds redevelop. A
weak reinforcing surge of surface high pressure will push into the
area Fri morning, with a subtle extension of a shortwave over the
area extending south west from the main feature farther to the
northeast. Some moisture will remain in the area along the Rio
Grande River axis on Friday, and although the models are still
suggesting isolated light shower activity along the river Fri and
Friday night, forecast QPF amounts are relatively small, and would
not expect significant rainfall. Temps will be trending slightly
cooler over the next 36 hours however, with high temps in the lower
80s on Friday, and the lower to mid 60s Friday night, just a few
degrees below the average for this time of year.

LONG TERM (Saturday through Thursday): The 500 mb pattern over
the lower 48 states this weekend will be dominated by closed lows
over the northwestern and northeastern states. This will allow
moderate ridging to prevail over the south Central Plains states.
This blocking pattern will eventually break down as the East Coast
closed low shifts eastwards and the Pacific NW closed low opens up
into an elongated trough axis which eventually stretches out over
the northern and western states. This shift in the 500 mb pattern
will also shift the southern ridge axis farther east throughout
the rest of next week. As the western trough axis broadens and
deepens it will push an elongated frontal system down into the
central Plains states which will interact with a broad surface
ridge over the southeastern U.S. to strengthen up the PGF over the
region resulting in stronger S-SE low level flow.

With the S-SE low level flow persisting over the RGV into the
longer range period, some decent moisture levels are pushed into
the region. These higher moisture values may interact with daytime
heating to result in some patchy isold conv. The ECMWF is
maintaining a drier solution over the last several model runs
while the GFS is maintaining slightly higher pops throughout the
extended period. Will maintain the mention of slgt chc pops in the
longer range period as the GFS has been pretty persistent from run
to run maintaining some mention of isold conv.

Both the GFS and the ECMWF are in pretty good agreement in
reflecting warming overall temps throughout Day 7 as the low level
WAA is strengthening through the period. So will stay on the warm
side of guidance throughout the longer range period as see no
reason to drop down temps any.

MARINE Now through Friday night: Broad high pressure will spread over
the area, resulting in light to moderate northeast to east winds
and low to mdt seas. A weak, secondary surge of high pressure will
arrive on Friday, with minimal impact.

Saturday through Tuesday Night: The PGF will remain pretty relaxed
for the weekend as broad surface ridging pushes southeast over the
Gulf Coast. However, as surface troffing increases over the
central Plains states the PGF will then tighten up increasing the
S-SE low level flow along the lower TX coastline. This will in
turn increase the potential for some SCA conditions starting
Mon Night.




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