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Area Forecast Discussion (AFD)

Issued by Brownsville/Rio Grande Valley, TX (BRO)

FXUS64 KBRO 211007

Area Forecast Discussion
National Weather Service Brownsville TX
407 AM CST Mon Jan 21 2019

.SHORT TERM (Now through Tuesday): High pressure remains in 
control across South Texas, as the eastern trough continues to 
move northeastward. Dry air aloft keeps plenty of sunshine in the 
mix, with little to no cloud cover expected. The next system drops
into the Desert SW today and deepens into Northern Mexico Tuesday
as surface low pressure settles into the Plains, increasing the 
pressure gradient. Southerly winds pick up into tomorrow due to 
the strengthening gradient, continuing the warming trend well 
above normal. 

Winds have already shifted southeast across the board, and should
pick up shortly after sunrise, boosting high temperatures a 
degree or two above normal into the low 70s. Low temperatures 
Tuesday morning only dip into the upper 50s and low 60s, with 
breezy southeast winds continuing. As the pressure gradient 
further strengthens and southerly winds increase on Tuesday, high 
temperatures top off into the upper 70s and low 80s. Model 
soundings and time height guidance have winds Tuesday afternoon 
ranging from 30 to 40 kts off the surface to 950 and 925 mb. For 
now, conditions will likely fall just shy of Wind Advisory 
criteria, but should remain monitored for Tuesday afternoon into 
Tuesday evening along the coastal counties. High cloud cover 
should increase as well on Tuesday with an approaching front.

LONG TERM (Tuesday night through Sunday): The main event this 
forecast will be a cold front pushing through the CWA Tuesday 
night. The front will bring a noticeable cool down. Tuesday night 
low temps will drop into the 40s and 50s with a chance of rain, 
and with a few wind chill values in the upper 30s across the 
ranchlands and brush country. High temperatures on Wednesday are 
forecasted to be in the mid 50s under partly to mostly cloudy 
skies with a chance of rain, mainly east early, and breezy to 
windy north winds, especially near the coast. Clearing is expected
late in the day Wednesday and then Wednesday night. Nonetheless, 
the weather Tuesday night into Wednesday morning will feel rather
raw, but with improvement by Wednesday afternoon. Rainfall 
accumulations will be light for the most part, measured mainly in 
hundredths of an inch. High pressure will then spread over the 
area, and the mid level trough axis will pass overhead, both 
bringing drier air, with Wednesday night low temps in the mid 30s 
to near 40 under mostly clear, good radiational cooling skies.

Conditions will be cool but otherwise pleasant on Thursday, with 
light winds swinging around to southeast in advance of a 
reinforcing source of high pressure forecast to reach to coast 
Friday morning around dawn. Thursday night low temperatures will 
be in the 40s. While this secondary front will be dry, it will 
bring breezy north winds and additional cooler air, which will 
keep high temperatures from climbing out of the 60s on Friday. Yet
another front plunging out of Canada will move into the Southeast
United States, with the base of the mid level trough and tail of 
the front moving mainly over east Texas, but extending far enough 
south to bring a wind shift to north and a possible shower to the 
coastal areas Saturday night. By Sunday mid level flow will once 
again be northwest with drier air moving into the CWA and high 
temperatures down in the 60s once more.


Now through Tuesday: Pressure gradient strengthens today into
Tuesday as one system moves east and the next drops into the SW
US. Southerly winds pick up this afternoon and increase into
Tuesday, allowing seas to gradually increase through the period.
Small Craft Exercise Caution conditions are likely by this
afternoon, with Small Craft Advisory conditions possible across
Gulf of Mexico waters late this evening or tonight, and building
through Tuesday. SCA conditions likely across bay waters by
Tuesday afternoon.

Tuesday night through Friday night: Moderate south 
winds will switch to north and increase after midnight as a surge 
of high pressure behind a cold front pushes across the lower Texas
Coast. Already large wave heights from Tuesday will build further
Tuesday night into Wednesday in the wake of the front. Gusts to 
gale force will be possible mainly Wednesday morning in the wake 
of the front. Winds and seas will decrease to below small craft 
advisory conditions by Thursday as high pressure spreads over the 
area, and will then remain more modest, though not insignificant, 
through Friday night.


20 foot winds will increase from the southeast around 15 knots
this afternoon as temperatures in the 70s and dewpoints in the
upper 40s to low 50s provide relative humidity values generally
near 40 to 45 percent across inland counties. These conditions are
below Red Flag Warning criterion, and no fire weather watch is
needed. A fire danger statement may be needed for portions of Deep
South Texas if winds are higher and relative humidity values are
lower than currently forecast. Similar concerns exist on Tuesday,
with relative humidity values near 40 to 45 percent and 20 foot
winds increasing to 15 to 20 knots Tuesday afternoon.

On Wednesday, the models suggest that post frontal conditions on 
Wednesday will be dry, with relative humidity values across inland
areas bottoming out in the 20s Wednesday afternoon. Winds at 20 
feet over those inland areas are forecast to be in the 10 to 15 
mph range. These conditions, combined with cured fine fuels, will 
enhance the threat of erratic wildfire behavior and the potential
for wildfire growth and spread. it's too early to say if Red Flag
Warning criteria will be achieved; it appears marginal for now, 
but conditions will be monitored.


BAYVIEW/PORT ISABEL  70  62  76  50 /   0  10  10  60 
BROWNSVILLE          72  61  78  52 /   0  10  10  50 
HARLINGEN            72  60  78  50 /   0  10  10  50 
MCALLEN              73  60  80  53 /   0  10  10  40 
RIO GRANDE CITY      75  58  82  51 /   0  10  10  20 
SOUTH PADRE ISLAND   68  63  74  55 /   0  10  10  60 




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