Scientific Forecaster Discussion
fxus64 kbro 170540 aaa
Area forecast discussion...updated
National Weather Service Brownsville Texas
1240 am CDT Tue Oct 17 2017
Discussion...updated for latest aviation discussion below.
Aviation...light northwest winds and clear skies prevail across
deep south Texas early this morning. Surface high pressure
across the region will result in VFR conditions for the next 24
hours. Light north winds this morning will gradually become
northeast by this evening.
Previous discussion... /issued 607 PM CDT Mon Oct 16 2017/
Discussion...updated for latest aviation discussion below.
Aviation...VFR conditions expected through this taf cycle. As
high pressure takes control of the weather across the region, sky
conditions should clear and the northerly surface flow will
lighten (generally below 10kts).
Previous discussion... /issued 300 PM CDT Mon Oct 16 2017/
Short term (now through Tuesday night): more Fall-like weather
will continue for the next 36 hours, with nil chance of measurable
rain through the period. Cloud cover continues to erode from northwest
to southeast across the forecast area, and clear skies are expected
pretty much everywhere by sunset or just afterward. Dewpoints
crashed more quickly than expected overnight, falling to the low
50s f even near the coast. An even drier (column) airmass exists
upstream, over south-central Texas, but dewpoints are not
drastically lower than those being observed currently.
Had to tweak Max temps for this afternoon down a bit, per trends in
obs. Overnight, good conditions for radiational cooling will exist,
with the northerly breezes becoming light, the dry air in place, and
clear skies. Blended in the adjmet guidance (which is on the lower
side of the suite) with inherited mins. This yielded values in the
low-mid 50s across the cwa, except some low 60s right along the
coast. Will be a refreshingly cool morning with these temps about 8-
10 degrees below the norms.
For Tuesday, light northerly flow at the surface continues, though
not much temp advection will be left. Very dry air above 850mb
continues to move in on northwest flow at mid-levels on the front side of a
ridge over the desert SW. Temps rebound nicely into the mid-80s f
(near 80 along the coast) for a beautiful, sunny day. These readings
will be just below climo. Bumped up inherited temps ever-so-
slightly given the dryness of the airmass coming in.
Heading into Tuesday night, flow turns light onshore as the surface
high migrates to the mid-Atlantic coast. Dewpoints start to creep
up toward 60f again in the Lower Valley. Some of the guidance shows
temps cooling all the way to the dewpoint, but not confident enough
yet to forecast any fog formation.
A coastal flood statement remains in effect until 6pm. Measured
water levels have begun to slowly trend down since high tide at
12:30pm, though are still running more than a foot above predicted.
The decline should continue through next low tide around 7:30pm.
With few beach-goers in the water today, main impact would seem to
be poor beach driving conditions.
Long term (wednesday through monday): 500mb ridge of high
pressure will remain over the Southern Plains with subsidence
keeping rain chances virtually inexistent for the first couple
days of the long term. Beautiful weather will continue during the
day on Wednesday with highs in the 80s with dew points in the
upper 50s to low 60s for most areas. As surface winds turn more
easterly and eventually southeasterly, higher dew points will
return to deep south Texas with temperatures also rebounding to
near normal or slightly above. Latest 12z model guidance is a bit
in disagreement on moisture with the European model (ecmwf) being the wetter
solution and GFS being much drier as a weak trough moves overhead.
Decided to go slightly on the drier side with pops ranging from
20 to 30% east and over the marine areas towards the end of the
week. Regardless of exact magnitude of moisture, it should be
enough to allow for at least isolated showers and thunderstorms
with seabreeze enhancement due to light surface flow along the
This weekend, the forecast becomes slightly trickier with the
possibility of another cold frontal passage. Models are in more
agreement today versus yesterday, bringing a deep 500mb low
pressure system into central/eastern Texas on Sunday. An
associated surface low would move eastward north of the great
light north winds to northeast winds at lakes with a trailing
front through the Southern Plains. It's still too early to know
how strong the front will be, but models show a pretty tight
gradient and higher rain chances than our last notable front.
Marine (now through Tuesday night): earlier on, had extended
Small Craft Advisory for winds on the Laguna Madre through 5pm,
which looks to be in pretty good shape. Northerly winds on the
northern Laguna have fallen to around 15 knots, but are still near
20 knots with some higher gusts further south near South Padre
Winds over the Gulf will be a bit slower to subside, but still on a
downward trend through the evening. Small Craft Advisory there has been extended
through 4am Tuesday, mainly for seas (which are now near their Max
for this event). Tough to gauge how well the wave models are doing,
especially nearshore, though the trends seem reasonable. Capped off
forecast wave heights at 8 ft. Small craft exercise caution
conditions may persist on the outer Gulf waters into Tuesday morning
before more benign conditions take hold Tuesday afternoon Onward
with light-to-moderate NE winds and seas of 3-4 ft.
Wednesday through saturday: surface high pressure will continue to
move eastward towards the mid-Atlantic, shifting winds back to the
east/southeast across the Lower Texas coastal Gulf waters. Low
seas on Wed/Thu will slowly build to 3 to 6 feet Friday and
Saturday due to the persistent easterly fetch. Small craft
exercise caution conditions will be possible.
GM...Small Craft Advisory until 4 am CDT early this morning for