Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 161717

Area Forecast Discussion
National Weather Service Brownsville TX
1217 PM CDT Thu Mar 16 2017

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


.AVIATION...CU field has developed across the region as have the
gusty south to southeasterly winds with most TAF sites gusting 30
to 25 knots. BKN to SCT cloud decks expected through this
afternoon with VFR conditions prevailing. Moving into the evening
and overnight hours,skies expected to clear out and winds will
diminish, but stay in the 10 knot range. The southeasterly flow
may bring enough moisture overnight for some MVFR ceilings to
develop, but they should not be long lived. Gusty winds resume by
midmorning Friday.


.PREV DISCUSSION... /issued 643 AM CDT Thu Mar 16 2017/

DISCUSSION...Updated for latest /12Z/ aviation discussion below.

AVIATION...Only minor changes to the prior forecast this morning.
MVFR ceilings have largely remained north of the Valley terminals
overnight, though a patch is headed into the Lower Valley as I
write. Quick glance at partially arrived sounding indicates cloud
heights would be somewhere between 3500 and 5000 feet, so went
with this idea for a few hours of broken skies.

Thereafter, as mentioned earlier and now verified by the sounding,
the layer of moisture (saturation) is pencil thick compared with
the 1,000 foot thick layer we observed on Wednesday which was the
"transition day" from east southeast flow to the more typical
Valley Wind Machine. So still expect any brief broken skies to
quickly mix out by mid to late morning. McAllen carrying patchy BR
(mist) and will do the same for a few hours early this morning.

Thereafter, the wind machine takes over with no change in the
forecast through midnight with scattered decks lifting to between
5 and 6 thousand feet. Winds stay up overnight in the 8 to 12 knot
range which ensures no fog even though skies will be mostly clear.
Model soundings hinting at just enough moisture toward daybreak to
introduce MVFR broken conditions.

PREV DISCUSSION... /issued 345 AM CDT Thu Mar 16 2017/

SHORT TERM (Today through Friday): It`s classic mid spring
weather for the next couple of days, more like late March/early
April than mid March but for those who like their days easy and
breezy this weather is for you. Deep South Texas/Rio Grande Valley
remains on the east (subsident) side of the 500 mb ridge through
the period as fast-moving disturbances cut across the
northwesterly flow at 500 mb through the central Plains. A modest
surface trough moving through the southern Plains today helps to
crank up the Valley Wind Machine with southerly flow increasing to
20 to 30 mph in the preferred areas mainly between US 77/IH 69E
and US 281/IH 69C by late morning through late afternoon today.
The trough slips south into west Texas Friday, with similar
gradient supporting another round of the Wind Machine following a
balmy night with fresh but lighter breezes as low level southerly
flow is just strong enough to maintain them.

As for sky cover, unlike Wednesday when there was some thickness to
the saturation between 925 and 825 mb and led to mostly cloudy
skies, any early morning clouds will mix out to few to scattered by
late morning/afternoon with the beaches clearing completely. Mean
layer relative humidity drops as well today and remains overnight
which should keep skies generally clear with perhaps a few passing
cumulus as low level moisture increases a hair.  With the fuller
sunshine will come higher temperatures today, ranging through the
80s with overnight lows ranging through the 60s.  A carbon copy on
Friday with atmospheric parameters the same; perhaps one or two
degrees warmer but that`s about it.

For the beaches...the wind machine will be tempered by the marine
layer though with full sunshine and deep dry air expect some mixing
but more likely in the 13 to 17 mph range vs. the 20 to 30 mph
gustiness just several miles inland. Same situation on Friday as
longshore current becomes more noticeable.

LONG TERM (Friday Night through Wednesday):The weather pattern
remains status quo through the long term as high pressure aloft
continues to dominate the regime and keeps the 500mb flow either
light or zonal in nature. Meanwhile, high pressure near the
coastal bend of Florida will beginning shift west in to the North-
Central Gulf Friday night, remaining through early next week.
This will generally keep southeast or onshore flow across the
region. Low level moisture will be enough to bring us some clouds
here and there, but deep layer moisture is significantly lacking.
As such, have continued with a rain-free forecast.

The high pressure will shift back towards the Eastern Gulf by mid
week as cold front and low pressure system sets up in near the
in the Southern Plains near the Panhandles region. This will
increase the gradient over Deep South Texas with southerly winds
increasing for Tuesday and Wednesday.

As for as temperatures go, the dry air aloft, combined with warm
southerly flow, will keep both highs and lows above normal through
the period.


Now through Friday: Southerly flow has begun to take hold and
winds now gusting over 20 knots at Buoy 42020 and likely carrying
in toward the coast in favorable diurnal late night situation.
Current forecast carries 15 to 20 knot winds offshore today and
will likely push into advisory levels across parts of the Laguna
Madre as well by late morning/early afternoon. That said situation
is a fence-sitter so will hold off on advisories for now over
Laguna Madre and roll caution (near 20 knots and gusty) as well as
over the open Gulf waters. For the overnight, however, gradient
associated with enhancement from the southern Plains trough should
be enough to support advisory winds over at least the offshore
waters, and will add a headline stating as much. Nearshore waters
will be on the fence but caution speeds (15 to 20 knots) look
reasonable. Winds ramp down a smudge over the Gulf on Friday;
seas will ramp up today and remain moderate (5 to perhaps 6 feet)
into Friday in persistent southerly flow.

Friday Night through Monday: By Friday night, the surface pressure
gradient should be weakening as low pressure across the Southern
Plains moves farther to the northeast. This will allow for winds
and seas to relax. For the weekend and into early next week,
surface high pressure will take control of the North-Central Gulf.
Mariners can generally expect light to moderate SE winds and low
to moderate seas due to some swell activity.




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