Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 010128
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
828 PM CDT Sun Apr 30 2017

.UPDATE...
Other than adjusting current T/Td trends to match ongoing
conditions...no changes were made to the short term forecast
(through Tuesday morning). Near vertically-stacked mid to upper
level low churning across eastern KS and OK this evening with
surface high pressure centered just off our coastline...weakening
inland northerly breezes through the remainder of the night. Clear
skies and calm winds within a relatively dry air mass (upper 30
to lower 40 interior dew points) should equate to northern county
lower 50 to middle-upper 50 mid to southern CWA minimum temperatures
to begin the new work week. Surface high moving east of the region
through the morning will have onshore flow/low level moisture
returning by tomorrow afternoon. Maybe an outside lunch date
tomorrow afternoon under pristine sunny skies and slightly above
normal warmth in the lower to middle 80s. Precipitation/storm
chances increase at mid week in association with the next system`s
Wednesday-early Thursday approach and passage. 31


&&

.PREV DISCUSSION... /ISSUED 623 PM CDT Sun Apr 30 2017/

AVIATION...
VFR for the next 24+ hours. 47

&&

PREV DISCUSSION... /ISSUED 354 PM CDT Sun Apr 30 2017/
Pleasant weather in the wake of yesterday`s cold front, to be
followed by warming into the mid-week. Another cold front arrives
Wednesday, and though key details are still fuzzy, at least some
of the ingredients for severe weather will be present. Afterwards,
look for more quiet weather into the weekend (and beyond).

SHORT TERM [Rest of Today Through Tuesday]...
Much cooler and drier air is surging into the area, leaving
wonderful late spring weather across the area. Highs today look to
be about 10 degrees below normal, with similar expectations for
lows tonight. Look for onshore flow to return very late tonight or
tomorrow morning, so don`t get too attached to these cooler
temps. The shift in winds will herald a warming trend into the
midweek, with temps Monday and Monday night back to near seasonal
averages, and with some spots north of Houston looking to push 90
on Tuesday afternoon underneath some mild upper ridging. With
clear skies and relatively light winds, some fog may not be out of
the question around daybreak Tuesday, but for now the forecast
doesn`t bring in quite enough moisture, and would probably only
see development in spots that fog extremely easily. More robust
moisture return than this would probably require the addition of
at least patchy fog mentions to the forecast.

MEDIUM TERM [Tuesday Night Through Wednesday Night]...
A shortwave trough looks to displace that weak ridging Tuesday
night, so look for clouds to increase from the south overnight.
Between that and the low level moisture flow from the Gulf, lows
Tuesday night will again be pretty warm - mostly in the upper 60s
and lower 70s.

Wednesday poses a conundrum for the forecast, as several
environmental factors will be present to suggest potential for
severe weather. Instability will be high - there is general
agreement for SBCAPE exceeding 1500 j/kg, and that`s from the
pessimistic Euro. The GFS and the NAM (of course the NAM) are much
more aggressive, with values easily exceeding 3000 j/kg and even
pushing 4000-5000. In reality? Expect much closer to the Euro, but
the point is that there looks to be ample instability. Shear is
less favorable, but the GFS still gives 30ish knots in the warm
sector for the majority of the area, and up to 40 knots ahead of
the cold front. In either case, it would be enough to support
organized updrafts. Capping, though it may be present, will be
weaker than we saw this weekend thanks to the late veering of
850 mb winds to southwesterly.

The limiting factor continues to be upper level wind field
support. The digging upper trough, per the Euro, may lag the
surface features just enough that it may not provide much help to
support updraft development. This would leave us dependent on lead
shortwaves to time just right with the other environmental
factors to help spark convection. Even at four days out, that`s a
tricky feature to time. If it times right, things could go
gangbusters. If it times poorly - well, look at how the other
night panned out. For what it`s worth, the GFS is much more
aggressive today with digging its trough, and actually may be
enough to provide a more direct impact. But even here, it really
only comes down deep enough to allow things to blow up in
Louisiana rather than SE Texas. That`s...a little close for
comfort. Given the supportive parameter space, this day bears
watching, but an actual severe event remains a point to be
clarified.

LONG TERM [Thursday and Beyond]...
More cooler and drier air behind Wednesday`s front, and Thursday
may be a bit breezy, though not likely as windy as we saw this
weekend. There`s pretty strong consensus for a stout midlevel
ridge to build in and stay anchored over the central US into the
middle of next week, so we may be looking at quiet weather for
some time. Of course, with 500 mb heights potentially pushing 588
dm, things may also start to get kinda toasty next week, but right
now we`re only looking for a gradual warmup into the weekend with
heights in the low to mid 80s.

MARINE... Winds relaxing faster than guidance but still have 8-10
second swell train moving into the region which has kept seas up
warranting an SCA. These swells will taper off late this afternoon
and evening and mid evening should be down 4 to 6 feet...so SCA
expires at 10 pm...though may be able to drop it earlier. Tides
have lowered and should remain so through Tuesday before edging
back up and may see a brief window Wednesday with seaward elevated
tide levels but not to be much of a problem other than perhaps
stronger rip currents and minor beach flooding. With the increase
in winds Wednesday will probably warrant at least a SCEC then the
cold front pushes out into the Gulf after 10 pm Tuesday-3 am
Thursday window with SCA winds in the wake of the front. Friday
through Monday looks benign with a light wind regime.  45

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      50  84  57  89  68 /   0   0   0   0  30
Houston (IAH)              58  85  60  88  70 /   0   0   0   0  30
Galveston (GLS)            62  78  71  82  75 /   0   0   0   0  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...Small Craft Advisory until 10 PM CDT this evening 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.

&&

$$

Discussion...31



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