Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS64 KHGX 152138

Area Forecast Discussion
National Weather Service Houston/Galveston TX
338 PM CST Fri Dec 15 2017


Unsettled weather looks to continue through at least the next week
(and likely longer) in Southeast Texas, with only brief periods of
fairer weather interspersed between more active stretches.
Tomorrow night looks to provide some - albeit highly conditional -
potential for strong to severe weather on the immediate coast.
Additionally, look for a weak front towards mid-week, and finally
a more substantial front comes into the picture at the end of the
week, but there is low confidence in this timeframe due to
significant inconsistency in the guidance both between models and
from run to run. How this front behaves will likely set the stage
for weather through the Christmas holiday.

.NEAR TERM [Through Tonight]...

Radar shows most showers have pushed offshore this afternoon, though
there may be some light showers or drizzle around Matagorda Bay.
However, there`s a good chance that none of these returns are even
reaching the ground. Satellite imagery shows overcast skies are
beginning to break from north to south, though perhaps too late to
allow for much more significant warming this afternoon.

Sky cover will be a fairly important consideration overnight as far
as overnight temperatures go. At this time things look open enough
for the far north to radiate down to the upper 30s to around 40,
while the immediate coastline will be hung up around or just above
50, with the rest of the area in the 40s. Rain chances look to be
quite low except for a slight chance of showers offshore growing
towards dawn.

.SHORT TERM [Saturday Through Sunday Night]...

Northeast winds early look to veer towards easterly or just south of
easterly, aided by the development of a weak surface low off the
coast towards Brownsville. Look for that low to quickly scoot up the
coast Saturday night, and its precise path may become dreadfully
important for the severity of any storms in the late night hours. A
low that is able to move onshore and track just inland will allow
coastal areas to briefly enter into the warm sector - in a window
roughly from 3Z-7Z - which will help surge dewpoints above 66
degrees and create a thermodynamic situation which would allow for
storms to become surface-based. This track would also severely back
surface winds and create a situation with significant low level
shear and a very largely curved hodograph - a perfect situation for
transient, low-topped supercells with potential for tornadic
waterspouts and even some brief tornadoes very near the coast. The
Texas Tech WRF would be a prime example of this scenario.

On the other hand, a track that stays offshore, or even scrapes
right on the coastline would limit the potential intrusion of
warmer, moister air. The LLJ in this scenario would actually more
likely result in a surface layer inversion, and any thunderstorms
would become elevated and unable to tap into any low level shear.
We`d still see storms, and potentially locally heavy rain - indeed,
of the models that follow this scenario, some use convergence on the
northeast side of the quickly moving low to generate or at least
imply something like a QLCS that could have some briefly torrential
rain. On the plus side here, the dynamic wind fields involved should
keep everything moving quickly. While isolated points of street
flooding could occur, it seems unlikely that we`d see anything worse
than that as we just won`t have time for rain to pile up.

With the low clearing out quickly on Sunday, that day should
generally be quiet, though perhaps with some lingering shower
potential near the coast. But, winds will also very quickly become
onshore Sunday night, and begin to pump warmer, high moisture air
back in. Because of this, we could see the development of sea fog
overnight, and low temperatures across the area look to stay above
50 degrees.

.LONG TERM [Monday Through Friday]...

As we go into next week, the closed upper low near Mexico`s Pacific
coast should start to eject, though there is some difference of
opinion as to how much interference/phasing we`ll see with the
northern jet as it does so. Beneath that low, a surface low, or at
least a trough may develop that will result in upglide from the
onshore Gulf flow and result in a new bout of showers. Monday looks
pretty solid for some of this rain, while Tuesday is a little more
up in the air. The GFS has a pretty solid surge of northwesterly
winds Monday night as the upper trough moves quickly by and dries us
out very rapidly. The Euro is a bit more deliberate with the upper
low, and though perhaps it has a better defined surface low, a post-
frontal northwesterly surge doesn`t look as significant, keeping us
from drying out until Tuesday night. Though I would tend towards a
slower evolution when it comes to these closed/cutoff lows to our
west, I did tamp down PoPs somewhat for Tuesday as the GFS` solution
is at least plausible. There will be time to adjust up (or, perhaps
down) as we gain greater consensus on this evolution.

Despite some deviation here, there is strong consensus in a quick
return to onshore flow for the back half of the week. Thursday looks
to be relatively drier, but there is a slight chance of a shower.
However, potential should increase Friday as lee cyclongenesis over
the Oklahoma Panhandle should result in the development of a new low
and trailing cold front that is on our doorstep by Friday morning.
Look for showers to develop near the front and persist for some time
in the front`s wake. This will set the stage for an unsettled period
leading up to Christmas. And while there`s fairly high confidence in
that, and generally good confidence that colder air will push into
the area, there is significant uncertainty about how that may
translate into wintry precipitation. At this point, there is so much
inconsistency both between models and between individual runs of the
same model, that it`s impossible to state much beyond that it will
be colder, there will be periods of precipitation, and some sort of
wintry precip is possible (but by no means certain!). Indeed, just
to make things more fun, the GFS doesn`t even bring the 850 front
far into our area, if at all, keeping 850 temps well above freezing
for all but our northwest. In the words of my esteemed shift
partner, this is a "warm and gross rain" scenario. Not so sure I`m
convinced about this as reality compared to the Euro, but I put it
there to illustrate that in a place where wintry weather hangs on
razor thin margins, those margins are totally swamped by range of
potential scenarios at this time. Much like in tropical season
with potential threats in the extended period, keep calm, make
sure you have a plan, and stay tuned.


.AVIATION [18Z TAF Issuance]...

VFR conditions are expected to prevail for the next 24 to 30
hours at the Southeast Texas terminals, with southwest flow in the
mid and upper levels promoting periods of broken to overcast
skies between FL150-FL250. Surface high pressure sliding east
across the region will allow northerly winds 5-10 knots inland
this afternoon to become light and variable overnight. Winds are
expected to increase into the 5-10 knot range out of the
east/southeast mid to late morning Saturday as a surface low lifts
up the Texas coast. For GLS, expect slightly stronger winds
generally in the 10-15 knot range this afternoon, falling below 10
knots overnight.




Offshore winds will continue to decrease this afternoon and tonight,
but veer to the east and increase back to near advisory levels
during the day Saturday as surface low pressure lifts up the Texas
coast. Scattered to numerous showers and thunderstorms will be
possible as this low shifts towards the east Saturday night with a
few stronger thunderstorms capable of producing waterspouts Saturday
night through early Sunday morning. A brief period of offshore flow
behind this front will quickly become onshore by Sunday night with
warmer, moist air moving across the cooler shelf waters resulting in
periods of sea fog through Tuesday or Wednesday before a cold front
moves off the coast.




College Station (CLL)  40  57  45  67  53 /   0  70  90  10  20
Houston (IAH)          42  59  49  69  58 /   0  30  90  20  30
Galveston (GLS)        50  61  57  66  62 /   0  20  90  40  50



GM...Small Craft Advisory until 4 PM CST this afternoon for the
     following zones: Waters from Freeport to the Matagorda Ship
     Channel from 20 to 60 NM...Waters from High Island to
     Freeport from 20 to 60 NM.

     for the following zones: Waters from Freeport to the
     Matagorda Ship Channel from 20 to 60 NM...Waters from High
     Island to Freeport from 20 to 60 NM.



MARINE...Huffman is the U.S. government's official web portal to all federal, state and local government web resources and services.