Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 040107
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
707 PM CST Sat Dec 3 2016

.UPDATE...
Per radar and surface/marine observations, the frontal boundary
continues to sag farther offshore, and the heaviest rain is
currently over our Gulf waters, extending into Southwest
Louisiana. Over land, numerous light to moderate showers are still
falling across the entire area. These showers will continue
through the evening, but we should at least be looking at a brief
respite from the heavy rain this evening into at least the early
overnight hours.

That said, multiple convection allowing models fill back in with
more precip over the area after midnight and towards Sunday
morning. Like Saturday, both the boundary near the coast and
(to a lesser extent) farther inland near the 850mb front will be
the foci for precipitation. There is general consensus that the
surface front/coastal trough will be forced back towards shore
some overnight, and if it sets up in a similar spot, we could see
a repeat rain performance. On the plus side, recent runs of the
HRRR seem to be trending to the heaviest rain setting up more
offshore than right on the coast, which would be very welcome.
Regardless, the heavy rain in coastal communities Saturday create
a saturated situation in which lesser rains Sunday still look to
pose flooding problems. And even if the axis of heaviest rain just
misses, rain will fall.

Luchs

&&

.PREV DISCUSSION... /ISSUED 549 PM CST Sat Dec 3 2016/

AVIATION...
Still looking at periods of SHRA/TSRA and associated IFR ceilings and
visibilities overnight and on into tomorrow. Hard to pinpoint the spots
that will have the most impact, but current thinking is that the locations
closest to the coast (LBX and GLS) and offshore might be at the greatest
risk for periods of TSRA while the rest of the area has mostly SHRA.
In the stronger activity, LIFR conditions will be possible. Do not anticipate
significant improvement until Monday and Monday night when this storm
system finally moves off to the east.  42

PREV DISCUSSION... /ISSUED 332 PM CST Sat Dec 3 2016/

DISCUSSION...

Note to users of HGX radar: Rainfall estimates are running 15-40%
too LOW so use w/caution.

Tonight through Monday...
Swath of significant rainfall along the coast today with 3-11"
fallen thru 3pm. Frontal boundary has sagged back offshore, but
just a gradual slope behind it is still allowing some training
heavy rain which will probably continue at the coast this evening.
The next disturbance will move in from the w/sw overnight
spreading another batch of precip across the area and into the
day Sunday.

Will maintain the Flash Flood Watch that`s out across the CWA.
That being said, vast majority of folks will see just stratiform
light/moderate rain. Totals will gradually add up thru the weekend
and once grounds become saturated enough...any heavier downpours
will runoff to cause flooding. Highest concern for the next 12-24
hours is Brazoria, Galveston, Chambers and SE Liberty where we`re
already at and above the point of ground saturation. To complicate
things there, higher water/tide levels won`t allow for efficient
drainage.

Upper trough kicks out of Mexico and across Texas Sun night-Mon
night. Coastal trof & gradient tightens back up near the coast,
and depending on eventual details, may produce a somewhat similar
scenario as we saw last night & this morning. Improving
conditions anticipated beginning Mon night. 47

Tuesday through Saturday night...
Tuesday should be pretty dry and sunny, but rain chances return
to the forecast Wednesday ahead of a cold front that should pass
through SE Texas overnight Wednesday night. Temps will cool off
significantly behind the front with highs on Thursday only
forecast in the 40s and 50s. The northern counties may experience
their first freeze so far this season on Friday morning, and these
freezing temperatures may extend southward into the Houston metro
area. Dry conditions and slowly rebounding temps are expected
through the rest of the period. 11

MARINE...
Areas of rain with embedded thunderstorms continued to occur over
most of the nearshore Gulf waters and Galveston Bay at mid
afternoon. The rain was occurring along a warm frontal boundary that
was nearly stationary just off the immediate coast. Isolated
stronger storms with wind gusts and waterspouts will continue to be
possible into this evening east of the warm frontal boundary.
Periods of rain and embedded thunderstorms will continue through
Sunday night into Monday and end late Monday as the storm system
moves east of the area.

Tidal flooding will continue to be a threat along low-lying areas
at the coast through tonight. Problems may persist into Sunday and
Monday.

Other impacts expected are advisory conditions due to winds and seas
over the Gulf waters. The pressure gradient weakens slightly tonight
and may lead to diminishing winds; however, seas will probably stay
up at least over the offshore waters tonight. Winds may pick back up
later Sunday into Monday. 40

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      49  54  48  56  45 /  80  90  90  80  10
Houston (IAH)              53  56  50  59  48 /  80  80  90  90  10
Galveston (GLS)            59  61  57  64  56 /  90  90 100  90  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flash Flood Watch through Sunday evening for the following
     zones: Austin...Brazoria...Brazos...Burleson...Chambers...
     Colorado...Fort Bend...Galveston...Grimes...Harris...
     Houston...Jackson...Liberty...Madison...Matagorda...
     Montgomery...Polk...San Jacinto...Trinity...Walker...
     Waller...Washington...Wharton.

     Coastal Flood Advisory until 6 AM CST Sunday for the following
     zones: Brazoria...Chambers...Galveston...Harris.

GM...Small Craft Advisory until 7 PM CST this evening for the
     following zones: Coastal waters from Freeport to the
     Matagorda Ship Channel out 20 NM...Coastal waters from High
     Island to Freeport out 20 NM.

     Small Craft Advisory until midnight CST tonight 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...25



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