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Area Forecast Discussion (AFD)

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

FXUS64 KBRO 161008

Area Forecast Discussion
National Weather Service Brownsville TX
408 AM CST Wed Jan 16 2019

.SHORT TERM (Today through Thursday): Coastal trough lingers but 
continues to weaken as surface high pressure shifts east. Isentropic 
upglide is trending weaker with the southerly thermal advection 
weakening as winds veer a bit more southwest and with boundary layer 
flow becoming more parallel to the pressure surfaces. Condensation 
pressure deficits at the 295K level remain relative narrow so some 
lingering light rain and drizzle is still possible mainly along the 
coastal counties this morning before tapering off this afternoon. In 
the mid layers a weak disturbance has passed to the east with modest 
dry layer developing between 700-400mb which should maintain a 
surface inversion over much of the CWA. Even with south winds 
becoming established later this afternoon, albeit light, the thick 
lower cloudiness is expected to hang around all day with maybe a few 
breaks in the overcast out west late in the day. With all this said 
temperatures will  have a tough time recovering with GFS/EC guidance 
trending lower on highs. A blend of the guidance with a bit more 
weight from the NAM has lowered today's highs into the low to mid 

Tonight just a cloudy night with some patchy fog developing late 
with plenty of low level moisture in place and light southerly winds 
expected. Temperatures to fall very slowly overnight due to the 
blanket of clouds and the light southerly flow. For Thursday 
expecting warmer conditions but still clouds lingering with the 
southerly flow becoming more established. A weak disturbance in the 
persistent southwest flow aloft may be enough to spark a few showers 
in the east during the afternoon hours but these should not amount 
to much and most locations should remain dry. Highs to rebound back 
into the 70s but have kept highs in slightly below guidance with the 
expected overcast conditions.

.LONG TERM (Thursday Night through Tuesday): Southwesterly flow
will be over head Thursday night ahead of our next upper level 
wave and surface cold frontal boundary. At the surface southerly 
return flow around the western side of high pressure building over
the Florida Peninsula will help continue to increase boundary 
layer moisture across the region into early Friday. Within this 
rich low level flow, a few isolated to widely scattered showers 
will be possible...though these should be on the light side given 
the shallow depth. 

As the trough begins to translate eastward across the high plains
of TX/OK...a cold front will begin to slide through the region
late Friday and especially early Saturday morning. Along and ahead
of the front expect some increase in rain chances, however, the
QPF isn't currently overly impressive in any of the globals. Think
most of the region will experience some type of shower activity,
however, the better chances will be offshore where the highest QPF
signal resides.

Behind the front, drier air will rush southward clearing skies by
later afternoon Saturday. Temperatures will need to be monitored
carefully on Saturday as any upward adjustment may lead to more 
of a fire weather concern, especially as winds may gust to near 
30mph during the day on Saturday (perhaps more if we can 
effectively warm and consequently mix stronger winds aloft to the 
surface). The real cool down holds off until early next week 
(Sunday and Monday AM) as surface high pressure begins to settle 
into South TX. Globals have been trending higher with the 
overnight low Sunday/Monday AM. We'll need to pay close attention 
to surface winds during this time as this will dictate the light 
freeze potential (more easterly flow will be a warmer flow and may
be a limiting factor). 

A brief warm up is expected by Monday afternoon and especially 
Tuesday ahead of our next strong cold frontal boundary due into 
the region toward the end of this forecast period on Wednesday. 
The origin of this front is the northeast Pacific so not expecting
an exceptional cool down, but it should be noticeable after a warm
Tuesday. Left POPs low at this time as GEM and ECM are showing a 
little something, however, this appears to be a similar frontal 
passage as expected this weekend with much of the precipitation 
likely developing/staying offshore.


.MARINE (Today through Thursday): Pressure gradient to slacken today 
as the coastal trough weakens. Winds and seas to lower through 
tonight. Surface high pressure settles to the east Thursday with 
light southeast winds and low seas becoming established. 

(Thursday Night through Tuesday): Marine conditions start off very
benign on Thursday evening and into early Friday. This, however,
is short lived as winds and seas begin to increase out a head of
our next strong cold front due into the region on Saturday.
Indeed, by midday Saturday winds will have transitioned to a
northwesterly flow and increase to around 30 knots with frequent
gusts over Gale force expected. This should help build seas to
around 12 to 13 feet at times in our offshore waters before seas 
finally begin to subside late Sunday and especially into the day 
Monday as high pressure begins to settle into the region.

Beyond Monday, marine conditions will become somewhat tranquil,
however, like before, this too will only be short lived as winds
again increase on Tuesday ahead of our next strong cold front due
into the region by midweek. 


BAYVIEW/PORT ISABEL  64  60  73  64 /  20  10  20  10 
BROWNSVILLE          65  61  75  65 /  20  10  20  10 
HARLINGEN            66  59  75  63 /  20   0  20  10 
MCALLEN              67  59  76  65 /  10   0  10  10 
RIO GRANDE CITY      64  56  76  63 /  10   0   0  20 
SOUTH PADRE ISLAND   63  62  69  65 /  20  10  20  10 




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Short Term/Aviation...59
Long Term...Frye-55