Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 302055

Area Forecast Discussion
National Weather Service BROWNSVILLE TX
255 PM CST Wed Nov 30 2016

.SHORT TERM (Tonight through Thursday Night):
November is going out like a mild, though somewhat breezy, lamb -
which is welcome relief from yet another round of summer-like heat
that ensured another top-five hottest month for most of the
Valley. So, how will December begin? Rather seasonable, with
daytime temperatures in the "normal" mid to upper 70s and still
rather comfortable humidity.

The gusty northerlies that brought refreshingly drier and noticeably
cooler compared with the recent record-obliterating high
temperatures on the 28th and 29th are settling down late this
afternoon, and will lay down completely this evening under clear
skies. But those clear skies will be the last for awhile come
Thursday mid morning, as southerly flow at the inversion level
jamming moisture there and combining with a veering flow to easterly
brings broken to overcast stratocumulus.  Warm advection will be
enough to bring temperatures back to the aforementioned mid to upper
70s during the afternoon.

By Thursday night, the moisture remains locked in down low ensuring
an overcast condition with ceilings lowering a bit, which combined
with surface east/southeast flow will hold both dew points and
temperatures up mainly in the 60s with just a couple of upper 50s
across the northern ranchlands. By late night, moisture thickens at
the same time a weak shear axis rides across the Valley as
mid/upper flow shifts to the southwest. Not sold on rain chances
everywhere just yet, but elected to keep mention (slight chance)
across the RGV counties after midnight, probably leaning toward
daybreak. Did not mention thunder, just showers as atmosphere far
too stable at the start.

.LONG TERM (Friday through Wednesday): Longer term forecast
beginning to focus better on rainfall chances over the weekend and
return of cooler air to the valley. The models are settling into
the slower progression of the H5 low cutting off into NW Mexico,
but there`s always one model that`s a bit too antsy to sweep it
right back out before the remaining models. While the low spins
out west, the southwest flow aloft around the low will sweep ample
moisture across the region between Friday and Monday. At the
surface, weak coastal troughing begins to form along the coast.
With the low in the vicinity, some good daytime heating is progged
for the region, so convective activity is a possibility Friday
into Saturday morning. Overall pattern for early weekend shifting
away from overrunning scenario and into a more convective
scenario, so rain chances paring back a bit, but slightly better
chance for some thunder both days. The general consensus is the
upper low will eject through west and north Texas during the day
Monday. As the low approaches Sunday it will induce rapid
cyclogenesis here in the valley and just offshore, which will
sweep to the northeast. Once the low is immediately east of the
region, strong overrunning sets up. PW values above 2 inches this
time of year is the signal for some reasonably higher rainfall
totals Saturday night and Sunday. Have focused rainfall on those
periods. Wraparound cold air surge behind the sfc low will pull
temperatures downward Sunday, struggling into the 60s during the
afternoon. As the low departs Sunday night into Monday, drier air
will sweep into the midlevels during the day Monday, shutting down
 precipitation and clearing out skies.


Now through Thursday night: After peaking at 10 feet at both NOAA
buoy 42020 and TABS K buoy (42045) about 40 nm east of South Padre
around noon, seas are slowly subsiding late this afternoon as
winds also begin to slacken. That said, values still in the 8 to 9
feet level and may well continue at or above 7 feet for another
few hours. For this reason, will extend the Gulf Small Craft
Advisory for another 4 hours (through 10 PM) to cover the

Thereafter, winds and seas dip below Small Craft Exercise Caution
levels (15-20+ knots and 6 feet) by or just after midnight, with
moderate winds (mainly easterly) and seas continuing late tonight
through Thursday night. Lowest winds will be late tonight and
Thursday morning before easterlies increase slightly toward 15 knots
by Thursday afternoon/night.  Some spotter showers are expected
toward daybreak Friday.

Friday through Sunday: Weekend conditions depend highly on the
developing surface low pressure in the lower valley and when it
departs. Models are showing the low starting to spin up inland
Friday morning, which will keep winds from the south across marine
areas. Since the low won`t be building quickly Friday, winds
shouldn`t be reaching significant levels early in the weekend. By
Saturday night, the low quickly deepens and moves to the
northeast. Winds will shift from the south to the northwest
overnight into Sunday, with gusty winds expected. Small Craft
advisories are possible during the day Sunday, with seas staying
agitated throughout the period.


BAYVIEW/PORT ISABEL  61  75  67  79 /   0   0  20  60
BROWNSVILLE          58  76  66  80 /   0   0  20  60
HARLINGEN            56  77  64  81 /   0   0  20  60
MCALLEN              56  78  65  81 /   0   0  20  40
RIO GRANDE CITY      52  78  62  81 /   0   0  20  40
SOUTH PADRE ISLAND   65  74  70  77 /   0   0  20  70


GM...Small Craft Advisory for winds until 3 PM CST this afternoon for

     Small Craft Advisory until 6 PM CST this evening for GMZ150-155-



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