Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Brownsville Texas
254 PM CDT Thursday Sep 18 2014
Short term... /tonight through Friday night/...plenty of rich Gulf
moisture trapped under the middle level high pressure ridge but little
in the way of a significant trigger to lift the moisture to get
showers and thunderstorms going. Besides a few streamer showers
this morning little in the way of convection has fired today.
Moisture remains somewhat shallow and just enough subsidence and
afternoon warming due to the middle level ridge overhead has currently
kept any convection at Bay.
Tonight...surface dewpoints to remain rather high with middle 70s to
near 80 degrees overnight. Southerly flow to slacken off at bit but
maintain at least a light component to keep overnight lows 5 to 8
degree above normal. Some stratus clouds to form in the boundary
layer overnight or more likely before sunrise so mostly clear to
partly cloudy overnight before some areas see cloudiness increase.
Any showers that might form will likely be offshore as some
streamers might form. Will be watching any convection that forms
over the west central and south central Texas overnight. Any mesoscale convective system
that develops could work its way southeastward possibly having an
impact on our area Friday.
Friday...upper ridge shifts slightly westward leaving eastern and
southern Texas on the eastern periphery. Perturbations /parts of the
remnants of Pacific Hurricane Odile/ to traverse northwest Texas
producing clusters of thunderstorms. Models are in not in best
agreement if any of these disturbances work there way into our County Warning Area.
NAM remains the most aggressive with a strong disturbance tracking
into deep south Texas under a more impressive northwest flow. GFS
and European model (ecmwf) although keep the stronger disturbances northeast of our
area both indicate some quantitative precipitation forecast with low probability of precipitation. Any combination of
outflow from the northern thunderstorms any disturbances working
there way into the region and seabreeze and daytime heating could be
a trigger to get a few showers or thunderstorms developing.
Localized heavy rain remains in the equation with precipitable waters not budging
from the 2 inch mark. Model consensus focuses low end chance probability of precipitation
over the northern and eastern counties with western counties having
the least chances. A bit more cloud cover to possibly keep temperatures
down a degree or two but with the higher due points heat indices to
range from 100-105. Still Summer for 3 more days at least by the
Friday night...any convection that fires during the day should begin
to dissipate with instability weakening as the temperatures cool
off. The western counties will be the favored locations through the
evening. Another warm and muggy night will make local football games
a bit uncomfortable.
Long term /Saturday through Wednesday/...
Saturday into Sunday...mid/upper level ridging remains over the area
through Sunday providing some subsidence. Precipitable waters remain above 2
inches through early Sunday before drier air briefly moves into the
midlevels and decreases precipitable waters to around 1.8 inches. The lack of a
focus mechanism will prevent widespread rainfall. However...light
onshore east/southeast winds should allow for a daily seabreeze to develop and
for isolated to scattered showers and thunderstorms to develop along
Monday into Wednesday....by Monday the middle/upper level ridging
slides west and flattens as the next upper level trough swings over
the northeastern US...pushing the associated cold front south across
the plains and North Texas. At the same time disturbances push west
over the Gulf of Mexico increasing easterly flow and moisture...with
precipitable waters surging to 2.2 inches Monday into Wednesday. Front continues
to appear weaker in the last few model runs. European model (ecmwf) keeps the front
well to our north...while the GFS pushes it a little further south.
Looking at midlevel winds there is little northerly flow to push the
front south through the County Warning Area. Believe with little support to move it
through the County Warning Area...the front will stall/wash out north of the area.
However...if the front moves closer to the County Warning Area it could enhance
shower and thunderstorm activity for the first half of the week.
Have maintained probability of precipitation at 20 to 30 percent for the time being.
tonight through Friday night...a weak to moderate gradient to
persist between broad high pressure over the Gulf and the remnants
of Pacific Hurricane Odile expected to move across the Texas
Panhandle Friday. The lighter than normal south to southeast flow to
continue through Friday evening maintaining the slight seas.
Isolated to scattered showers or thunderstorms are possible.
Stronger winds and higher seas will accompany any thunderstorm.
Saturday through Tuesday...light east to southeast winds will prevail
through Sunday and seas will remain low. As high pressure
strengthens over the plains...moderate east to northeast winds will
develop late Sunday night into Monday and wave heights begin to
build. Isolated to scattered showers and thunderstorms are possible
through the period.
Preliminary point temps/pops...
Bayview/Port Isabel 80 90 80 90 / 20 30 10 20
Brownsville 78 91 78 92 / 10 30 10 30
Harlingen 77 92 76 92 / 10 30 10 30
McAllen 78 92 78 92 / 10 20 10 30
Rio Grande City 79 93 78 94 / 10 20 20 20
South Padre Island 80 88 80 87 / 20 30 20 20
This product is also available on the web at: