FXUS64 KBRO 180958

Area Forecast Discussion
National Weather Service Brownsville TX
358 AM CST Mon Dec 18 2017

.SHORT TERM (Today through Tuesday):Cloud cover and some light
drizzle/shower activity continues this morning across the region.
The 5H southwesterly flow continues to bring ample moisture into the
region from the Pacific (as seen on water vapor imagery). No real
changes in this pattern expected today or tonight. A weak frontal
boundary across the western Gulf will slowly slide west ahead of the
strong impulse currently dropping into northwest Mexico this

Temperatures will be warmer today as low level warm air advection
increases as the flow transitions to a warmer southerly/easterly
flow. This will also increase low level moisture a good bit. With
the close proximity of the warm front and ample moisture and some
upper level support, shower activity will continue through today and
into tonight. As the warm front moves just west of our area we'll
see some small reduction in showers later in the period.

Overnight tonight we'll need to watch for the possibility of some
fog development across much of the lower RGV and western/northern
ranchlands. In fact, SREF progs are rather bullish with this
potential, however, the best fog probs will reside along the coastal
bend and northeast where fog will be more effective at advecting
inland with southerly flow.

As the upper level impulse finally pushes into northern TX,
cyclogenesis will occur along the warm front. This low and parent
trough will lift eastward and northeast into the lower Mississippi
River Valley by midweek. With much of the upper level dynamics
remaining just north of our region, much of the area will begin to
dry out, however, considerable cloud cover is expected through the
end of the period.

.LONG TERM (Tuesday Night through Sunday):Mid/upper level flow
pattern over the the Lower 48 transitions from a progressive split
flow to a highly amplified pattern with a full latitudinal trough
becoming carved out across the country. Latest model consensus is
in good agreement with the pattern transition but differences
continue to show up on timing of the cold air pushing south into
Deep South Texas (if it does at all). Pattern suggest that the
coldest air remains bottled up over the Rockies and Southern
Plains with two cold fronts delivering cooler temperatures
through the Holiday weekend. Confidence in the pattern change is
above average but confidence on timing and strength of cooler
temperatures is below average.

Deep South Texas can expect a steady warming trend and dry
conditions through at least Thursday in advance of the first of
two cold fronts. GFS remains most aggressive with rain chances
and generally cooler with a Friday and Sunday/Monday Cold front
while the ECMWF remains much warmer until Monday. Temperature
guidance between the two global models continue to have large
differences next weekend with GFS indicating highs as much as 27
degrees colder in some northern/Western locations and 17 degrees
colder across portions of the RGV. To say the least, next weekends
and Christmas day forecast remains below average and will
continue a persistent course of a model blend showing a cooling
trend through the weekend (not the most desirable trend). As the
mid level flow transitions models are likely to get a better
handle on the density of the cold air and timing of its track
southward should improve.


.MARINE:(Today through Tuesday): Winds this morning were generally
10kts or less. Right along the coast northerly flow continued,
however, east of the warm front, winds have veered to more of an
easterly or southeasterly direction. Winds should begin to veer
across all marine zones through the morning as the front begins to
slide westward.

Overall, rather tranquil marine conditions expected today and
tonight. Wave heights this morning well east of our marine zones are
running just under 4 feet at Buoy 42002. Expect 2-3' feet through
much of the short term with an increase to 4' possible with
increasing surface flow as a a weak cold front nears the area just
beyond the end of this cycle.

Tuesday night through Friday...Marine fog may become an issued
Tuesday night in advance of a cold front. Drier offshore flow
push the fog out to sea Wednesday morning. General light wind and
low seas are expected Wednesday in wake of this front before winds
turn southeast and steadily increase in advance of the next front
scheduled for sometime late Friday or early Saturday. Winds may
approach marginal small craft advisory levels Friday and in wake
of the front Saturday.


BAYVIEW/PORT ISABEL 76 69 81 63 / 30 20 10 20
BROWNSVILLE 78 69 83 64 / 30 20 10 20
HARLINGEN 76 67 83 62 / 30 20 10 20
MCALLEN 74 66 81 62 / 30 20 20 20
RIO GRANDE CITY 71 64 80 57 / 40 20 20 20
SOUTH PADRE ISLAND 75 70 79 67 / 30 20 10 20




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55...short term
59...long term
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