Scientific Forecaster Discussion
fxus64 kbro 130030 aaa
Area forecast discussion...updated
National Weather Service Brownsville Texas
630 PM CST Tue Dec 12 2017
Discussion...updated for latest aviation discussion below.
Aviation...VFR tafs. High pressure will spread over the area the
next 24 hours, yielding relatively unremarkable aviation weather
conditions. A weak return flow will develop Wednesday afternoon,
shifting winds from north to southeast as high pressure over Texas
moves farther east and lower pressure develops upstream, but
moisture will still be rather limited at that point, as will any
significant cloud development.
Previous discussion... /issued 253 PM CST Tue Dec 12 2017/
.Weak cold front moves through the lower Rio Grande Valley...
Short term (tonight through Wednesday night): the cold front has
passed through the region earlier this morning, but there was
minimal visible signal to its passing. Winds remain from the north
around 10 knots, while dewpoint temps are only slowly decreasing
this afternoon. Skies will remain mostly clear tonight, and with
dewpoints falling into the 30s, expect lows tonight to be about 5
degrees below this mornings low, generally in the low 40s
areawide. The core of the surface high behind the front will be
in the vicinity during the day tomorrow, keeping skies clear and
providing light and variable winds. Wednesday night will see the
surface ridge gently slide east, allowing some southeast flow to
return, with modest returns of Gulf moisture. Lows will still fall
into the lower 50s with clear skies.
Long term (thursday through tuesday):
The prior uncertainty with diverging solutions within the GFS and
European model (ecmwf) seem to be smoothing out slightly with the 12z update this
morning. Both the GFS and ecm now have the upper level cut off low
across northwest Mexico finally being picked up this weekend and
moved across central/northern Texas. Ahead of the parent "kicker"
wave, another cold front will slide through the region late
Thursday and early Friday. The front doesn't get far before
stalling along or just south of the river. As the front stalls,
isentropic upglide will keep the area rainy, gloomy, and quite
cool. In fact, I dropped the maximum temps Fri-sun as much as 10
degrees across board to compensate for this. That said, I didn't
go as far as MOS guidance would like, but there is notably a big
trend downward with temps this cycle.
By late Saturday and into Sunday, the surface front will begin
lifting northward across the eastern Gomex. Surface cyclogenesis will
occur under the strong wave pushing eastward (finally) and over
the natural baroclinic zone in the northwest Gulf. Once this
occurs, the low should slide northeastward away from the region.
Models then diverge once we get into early to midweek next week.
GFS is a bit wetter and keeps some quantitative precipitation forecast signal across our Gulf
zones. Ecm is much drier. Decided to split the difference here.
Bottom line, confidence is increasing in a wet, cloudy, and
perhaps brisk weekend ahead. Temperatures are certainly trending
below average from Friday through early next week...and could even
go cooler than what we are currently advertising.
Marine: (now through Wednesday night): the cold front has passed
earlier this morning, with northerly winds in its wake. Speeds
are running 10 to 15 knots, so no advisories will be needed with
this front. Tomorrow the surface high moves into the northwest
Gulf, providing light and variable winds, allowing wave heights to
drop to 2 feet or less through the remainder of the short term
(Thursday through tuesday): marine conditions will gradually
decline as we move closer toward the weekend. A stronger cold
front will slide through and eventually stall out across or just
south of the border. A strong northeasterly flow will take shape
allowing for likely Small Craft Advisory conditions to set up through much of the
weekend. Eventually, a surface low will develop and rocket
northeastward into the southeast U.S. By Sunday and into Monday.
There will be some improvement early next week, however, the
surface flow will eventually shift easterly. With a long fetch
across the Gomex, this may help produce increased swell later on
in the period. Frye/55