Area Forecast Discussion
Issued by NWS Houston/Galveston, TX
FXUS64 KHGX 252055
Area Forecast Discussion
National Weather Service Houston/Galveston TX
355 PM CDT Sat Mar 25 2017
Expect a brief respite from active weather tomorrow, but the
theme of the week will continue to be a rapid progression of upper
troughs to keep things active. For now, it appears that tomorrow
night/Monday, Wednesday/Thursday, and next weekend are the most
likely timeframes for passing bouts of precip. The first should
have relatively minor impact in our corner of Texas, but be sure
to keep an eye on the midweek and late week rounds as we refine
the details, as they could potentially have stronger implications
for the area.
Satellite and radar show that the cold front has passed into the
Gulf, and any remaining showers/storms have withered over the
more stable airmass over the waters. While we can see that a
Gulf/Bay breeze has kept a boundary present just onshore, the
post-frontal airmass appears to be sufficiently dry/capped to
prevent any cells from popping up this afternoon and evening.
Expect a quiet night and light winds as high pressure drifts over
the area and off to the east, allowing onshore flow to resume by
morning. Model guidance is ambivalent about fog potential tonight.
However, given that the post-frontal airmass is not significantly
drier, and we have wettened soils from last night`s rains, we
should have a good moisture pool to draw from. Tack on the clear
skies and calm/light winds, and patchy fog seems a pretty good bet
for much of the area. Right on the coast may stay clearer with
enough wind to mix that surface moisture up, but that would be the
exception in Southeast Texas. Did also draw in a small patch of
more widespread fog to the east of Houston, where this morning`s
rains were able to saturate the ground per NASA SPoRT LIS data.
Otherwise, look for weather to remain dry tomorrow and for heat to
come roaring back.
Sunday night through Tuesday...
Our brief time with upper ridging and surface highs end Sunday,
and another upper trough looks to swing through, introducing some
modest height falls for Sunday night. However, the best moisture
axis looks to curl around to our west and north, and jet streaks
aloft miss us well to the north and south. All told, focus for
active weather tomorrow will be in Oklahoma and North Texas, while
a weak cold front attached to a surface low moving through
Oklahoma may not even make it to our area. All told, have brought
in some low chances for thunder in case we do see rain crop up on
a frontal boundary and/or its remnants, but don`t expect serious
concerns. The forecast doesn`t even cool temperatures off too much
for the early week.
Wednesday through Friday...
Yet another upper trough rolls into the Southern Plains midweek.
However, this one looks to have more in common with this last
trough, than the upcoming early week trough. This means more
significant height falls and cyclonic vorticity advection into
Southeast Texas, paired with a more potent - albeit fairly narrow
moisture axis streaming through the area. There`s pretty good
agreement amongst the guidance in this general scenario, but
considerably more disagreement about the details. The Canadian and
Euro are a bit faster and perhaps a bit shallower than the GFS.
Indeed, while certainly bringing a shot of rain, the Canadian is
perhaps the least significant of the three. The GFS worryingly
pairs a split jet Wednesday night with 1500-2000 j/kg of CAPE,
while placing the nose of a 30 knot low level jet into SE Texas.
This seems to check a lot of the boxes for severe weather,
particularly with flow from the surface through 700 mb looking
relatively backed. Additionally, though it`s focused more to our
northeast, there`s a pretty good QPF signal associated with this
as well. The Euro shows a less favorable upper jet, is a bit more
veered at 850 and 700, and has higher midlevel heights, which
would limit instability some. Still, it cranks out 1000-1500 j/kg
for most of the area, even pushing 2000 j/kg towards Matagorda
Bay. This implies a sounding with skinnier CAPE, and perhaps more
of a heavy rain threat than severe weather. Indeed, Wednesday
evening shows a QPF bullseye roughly along I-45. So, whether
things more closely resemble the Euro or the GFS, this
Wednesday/Thursday timeframe is worth keeping an eye on. After
this, expect heights to rebound towards ridging for Friday, but
this is mostly in advance of yet another trough to come...
The trough train continues to roll down the track, with yet
another hit looking to come next weekend. With a couple pops of
precip coming ahead, and at such a long range, don`t want to
speculate too much at this point. Have simply gone with temps in
the low 80s, and POPs around 30%. For what it`s worth, the GFS
drops some real big rains offshore Sunday night, and the Euro
shows a bit of a QPF signal too. But at this time it`s better to
just keep in mind that the weekend may have some more unsettled
weather, while focusing more on potential at nearer range.
The cold front finally made it off the coast and skies have nearly
cleared. Moisture will return though as winds become onshore tonight
and continue through the coming days. Seas of 4 to 6 feet this
afternoon will continue to diminish but the underlying 2-4 foot
swells will be slower to diminish. Have dropped SCA/SCEC. Winds come
up Sunday afternoon/night and will likely be back into SCEC
conditions and then flirt with them off and on through Tuesday
night. Gradient tightens dramatically Wednesday as next storm system
approaches and will warrant SCA flags with winds near 20 knots and
seas of 5-8 feet.
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 57 85 66 84 64 / 10 10 20 10 10
Houston (IAH) 61 85 68 86 67 / 10 10 10 10 10
Galveston (GLS) 69 82 71 81 71 / 10 10 10 10 10
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 4 PM CDT 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.