Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 250837
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
337 AM CDT Wed Apr 25 2018

.DISCUSSION...

A weak cold front is expected today, and will carry along with it
some showers. We could also manage some isolated thunderstorms,
but storm potential appears fairly limited as it looks like the
best potential for precipitation will come behind the front. Once
the front is through, expect fair weather through at least the
weekend. Early next week, a series of weak disturbances will spur
a chance for showers or even thunderstorms, but the ingredients
will have to come together just right.

.NEAR TERM [Through Today]...

A compact, but fairly potent vort max in North/Northwest Texas
has sparked showers and storms well upstream this evening. Though
the activity has been on a trajectory that could impact at least
northern parts of our area, the activity has thus far fallen off
rapidly as it outruns its upper support, and even more underneath
that feature there looks to be a slow downward trend. Because of
this, keep the official forecast dry today. However, rather than
zero out PoPs as the vort max moves over our area, do leave 10ish
percent. Day shift will have to keep an eye on this feature and
see if we see any renewal of activity underneath the upper feature
through the day. Also, some guidance has hinted at a pre-frontal
trough developing and could provide a bit of a focus for any
afternoon warm sector development. Hoping that holding to dry
works out, but I can at least see a potential failure point in the
forecast here.

Beyond the rain potential today, also looking at some patchy fog
cropping up in the southwest around Matagorda Bay, where moisture
return looks strongest underneath a more potent than expected low
level jet. Expecting fog while winds are calm, but if the stronger
winds work down to the surface, could see that fog lift to low
stratus. Localized spots may briefly be fairly dense, but think

Otherwise, look for seasonable lows, rising to highs near or a
little above normal. Do paint a narrow corridor of temps
around/just above 85 near the coast in a pre- frontal temperature
bump this afternoon that guidance so frequently seems to not quite
grasp.


.SHORT TERM [Tonight Through Friday]...

Cold front that`s been advertised for some time is finally poised
to cross. If winds haven`t already turned to westerly or
northwesterly with a pre-frontal trough, winds will change this
evening. Focus my PoPs on tonight, as it appears that we may see a
better chance for elevated precip once the surface front has
already passed. Do note the development of a small upper jet
streak with us in the right entrance region, which would help
support vertical motion. Forecast soundings still don`t get too
crazy with the MUCAPE, so think thunder potential will be fairly
limited, with isolated storms. Almost all the guidance has jumped
on the bandwagon on having a broken line of showers/storms
tonight, and not confident that everyone will get wet tonight.
Because of this, I faded PoPs from the guidance slightly. Once
there`s greater confidence in how precisely things set up, some
more specificity may be possible. But for now...felt more
comfortable with describing the potential as "chance" rather than
"likely" rain.

Rain should wrap up by morning, and the rest of the short term
will be the upper trough beginning to exit the area, with ridging
from the midlevels on down getting set upstream. Highs Thursday
will be hacked back into the 70s, and should repeat for most on
Friday, although some may manage to reach 80 degrees as heights
will be a touch higher.


.LONG TERM [Friday Night Through Wednesday]...

Ridging mentioned at the close of the short term will come to
dominate most of the weekend, allow highs in the 80s to creep back
into the picture a little more each day. Lows Friday
night/Saturday morning may still be a little chilly, but as the
surface high drifts into the Deep South and winds here turn back
to onshore late Saturday, those low temperatures should begin to
move back upwards next week along with a gradual increase in
humidity. The higher temperature floors should help afternoon
highs continue to reach the 80s each day, but the midlevel ridge
from the weekend quickly shoves off, leaving us open to a series
of modest shortwave troughs in the first half of the week. Pair
that with onshore flow and deepening available moisture, and it
seems reasonable to bring at least some low PoPs back into the
picture each day next week. Each day is a little bit higher than
the last, but don`t want to get carried away here as things will
be very dependent on shortwave timing, and I have little
confidence in being able to nail that this far out.

&&

.AVIATION [06Z TAF Issuance]...

Challenging forecast unfolding for the 06Z TAFs where model
guidance has struggled to capture the development of a 25-30 know
low level jet that has developed across the region. Surface
analysis shows the sea breeze has lifted near to just north of
IAH with a weak enough surface pressure gradient in the vicinity
of this feature to produce calm to nearly calm winds at the
terminals near and north of Interstate 10. This, coupled with an
expected decreasing trend in surface winds at the terminals south
of there, has resulted in the addition of LLWS in the TAF as a
result through 08Z and will monitor trends for updates. The veered
nature of the jet raises concerns that MVFR ceilings that develop
near Matagorda Bay overnight per latest trends in the HRRR may
advect near the terminals. Not confident at all in this solution
but have added a FEW020 group to highlight potential for IAH, HOU,
SGR, LBX, and GLS. Elevated low level winds may delay or inhibit
fog development tonight, but brief MVFR visibility drops may be
possible at CXO and LBX. Regional radar mosaic shows outflow
associated with storms over West Central Texas may serve as a
focus for an isolated shower or two early this morning and
potentially a brief northerly wind shift at CLL but have not
included any mention of this in the 06Z TAF due to low confidence.

Expect VFR conditions to prevail at all terminals after 16Z with
winds becoming south to southwest around 5-8 knots ahead of an
approaching cold front. Will have to keep an eye on the remnant
outflow boundary during the morning hours for additional SHRA
development near CLL, but expect the TAF sites to remain dry until
after FROPA Wednesday afternoon and evening. Northerly winds near
10 knots will become established behind the front with a brief
window for a few elevated SHRA possible Wednesday evening before
drier air moves in Wednesday night.

Huffman

&&

.MARINE...

Light winds and low seas should persist until a weak
cold front and associated showers move through the
area tonight. Offshore winds behind the front might
reach caution levels for a short period Thursday
morning. The offshore flow will persist through the
end of the week as another cold front moves through
the area on Friday. Onshore winds that are expected
to return late Saturday or Saturday night should
persist through at least the first half of next week.
At this time, it looks like caution and/or advisory
flags might be needed beginning late Monday or Monday
night for the increasing winds and building seas. 42

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  82  51  76  53  77 /  10  40   0   0   0
Houston (IAH)          85  58  78  55  78 /   0  50   0   0   0
Galveston (GLS)        78  63  75  62  75 /   0  50   0   0   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...None.
GM...None.

&&

$$

NEAR TERM...Luchs
SHORT TERM...Luchs
LONG TERM...Luchs
AVIATION...Huffman
MARINE...42



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