Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 140000 AAA

Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
700 PM CDT Tue Mar 13 2018

.DISCUSSION...Updated for latest /00z/ aviation discussion below.


.AVIATION...Same stuff, different day? All is `fair` for general
aviation concerns for another 24 hours, courtesy of steady-state
pattern from surface to aloft. Ridge that settled over the eastern
half of Texas on Monday remains in place tonight, and only slowly
re-orient on a northeast to southwest line from Louisiana through
the Lower RGV into Wednesday. Aloft, zonal/northwest flow will
continue to spill mid level moisture along a shear axis through
the Texas Big Bend and generally along the Rio Grande through the

What this means is an auto-pilot (pun intended) forecast through
Wednesday: Light winds overnight becoming east but still
relatively light (10 knots with a few minor gusts) and more clouds
than not, hovering well in VFR range and ceilings no lower than
6K feet as low level moisture is very slow to recover. Latest
satellite loops combined with model soundings indicate periodic
lifting of the mid decks, leaving thinner 15 to 20K decks later
tonight through midday Wednesday. Enjoy the great landing/takeoff


.PREV DISCUSSION... /issued 254 PM CDT Tue Mar 13 2018/

SHORT TERM (Tonight through Wednesday Night): 500 mb ridging will be
building over the RGV gradually throughout the short term period.
This will maintain a pretty stable pattern over the region for the
time being. Surface ridging over the central portion of the country
will drop south towards the central Gulf Coast region which will
allow the low level flow to becoming more easterly off of the Gulf
of Mexico. This will allow the low level dewpoints to gradually
rebound. Meanwhile further aloft mid level moisture will likely
persist which will maintain higher level cld cover into tomorrow. So
both of these cld decks will maintain partly cloudy to cloudy
conditions for the RGV through Wed Night.

The persistent cld cover in combination with the mild E-NE low level
flow pattern will tend to hold down the overall temp trends through
Wed Night. Short term model temp trends are in pretty decent
agreement for max and min temps through tomorrow night and will go
with a general three way model blend of the MAV/MET and ECMWF

LONG TERM (Thursday through Tuesday): The long term forecast
looks to be driven my a subtle northwesterly or even
zonal/progressive flow. Generally, a weak shear axis is forecast
to develop around or just north of the CWFA within the northwest
or zonal flow through a good portion of the long term. More about
that in a moment. As southeast return flow begins on Thursday,
there very well could be a few showers develop with the increase
in low level moisture, although the best chance looks to remain
along or just off shore, and even then POPs aren`t much above

What will be interesting on Friday will be a surface dryline
mixing eastward into the I69C vicinity. At the same time, storm
parameters are somewhat supportive of thunderstorm activity with
both adequate CAPE and 0-6km bulk shear. However, expect that a
very dry EML will develop with westerly mid level flow which will
likely be a limiting factor for convection. Additionally, at H5
the shear axis weakens so upper level support to help modify the
dry EML will be tough to overcome. That said, if storms do fire
we`ll need to watch for the potential for wind (big big "IF").

On Saturday the shear axis once again strengthens over the region,
however, dry air should remain in place in the mid levels. Model
QPF is signaling for minor precip along and east of the coastal
locations. Kept mention of slights, however, do not expect any
widespread shower or storm activity.

The progressive zonal pattern is forecast to continue through
early next week with intermittent weak vorts moving over the
region. There may be small windows of opportunity for precip right
along the coastline, however, this should be isolated and very
light. Flow should begin to transition to a more northeasterly
direction toward the end of the period as a strong low pressure is
forecast to develop across the east.

As for temperatures, with a little more sun and strong mixing,
expect temperatures to increase on Saturday and Sunday (very
similar to last weekend). We`ll need to watch the dryline as it
mixes eastward on Friday as this feature will have the final say
on max temps. As the surface flow becomes more northeasterly late
in the cycle, temperatures will be a bit closer to average.

MARINE (Tonight through Wednesday Night): ASCAT satl derived surface
winds detected generally light to moderate E-NE winds across the
lower TX Gulf waters around 17Z today. As the surface ridge pushes
southwards towards the middle Gulf Coast through the short term,
expect the low level flow to becoming more easterly and
southeasterly later in the marine forecast period. The strength of
the low level flow will remain pretty weak throughout tomorrow night
which will tend to hold down the wave action below SCA levels.

(Thursday through Tuesday): Moderate winds and seas are expected
to develop by Thursday afternoon as strong southeast flow develops
between high pressure across the eastern Gulf and a lee side low
developing just east of the front range. At this point conditions
look to be below small craft advisory thresholds. Some improvement
is expected this weekend as easterly flow slightly weakens
allowing wave heights to subside somewhat. Northeasterly flow is
forecast to increase as a frontal boundary closer to the marine
areas by the end of the period, however, there is still some
uncertainty in terms of strength and location. Regardless,
highlighted at least moderate winds/seas for the end of this




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