Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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121
FXUS64 KHGX 031202
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
602 AM CST Sat Dec 3 2016

.AVIATION...
Messy flight conditions expected for the next 24-30 hours for the
Southeast Texas terminals. Scattered to numerous SHRA with
isolated embedded TSRA continue to spread across the terminals
early this morning as a result of strong isentropic lift, with IFR
to MVFR ceilings in place. Expect these trends to continue through
the period, but drops to LIFR will be possible in heavier
SHRA/TSRA activity from heavy rain. Have prevailed SHRA or TSRA
through the TAF period at all sites, but breaks in this activity
are expected as passing mid-level disturbances in the flow aloft
provide enough subsidence to temporarily suppress rain. Winds at
the inland terminals are expected to range from north to northeast
10-15 knots, but coastal terminals (LBX and GLS) may see winds
more southeast 10 to 15 knots as a warm front located just off the
Upper Texas coast lifts inland today. As this boundary then pushes
off the coast tonight, expect all sites to carry a northerly wind
around 10 knots.

Huffman

&&

.PREV DISCUSSION... /ISSUED 433 AM CST Sat Dec 3 2016/

DISCUSSION...
Heavy rain event underway and will continue through the weekend.

Warm front/coastal trough poised near the coast and showing some
efforts of moving into the Matagorda Bay area...dewpoints of 73-75
aimed at the coast there with more northeasterly flow in place
along/up the coast from there. Tides are elevated and a Coastal
Flood Warning was issued earlier...see marine section below for
more on that. So far the LLJ 35-45 knots has been focusing most
of the rainfall near the coast around Galveston but that should
shift eastward somewhat and with that the widespread rain with
embedded and elevated heavy showers and thunderstorms will expand
out of the Hill country and develop overhead in the inland areas
of SETX. Rainfall rates may not be as high but the thunderstorms
that form will still be capable of 2+" per hour rates. Expecting
two areas of heavier rainfall through the afternoon hours. A
corridor from around Brenham through Crockett and a second where
the richest moisture axis impinges on the stationary front
probably from around Freeport to Houston to Liberty. Side note:
the NCAR ensembles appear to be converging on this solution as
well between 15-19z. Still think that rainfall totals of 8-11
inches are within reach today across the area possibly slightly
favoring the more southern corridor given the available PW (near
2" record values for this time of year and greater CAPE/Shear)
and proximity to the frontal boundary. Galveston Scholes Field
already reporting 2.44" as of 1028z nearing the daily record of
2.64" (1965) and will probably surpass that record. Other records
may be in jeopardy as well.

OLD MAX RAINFALL RECORDS

.....SAT............SUN
CLL   3.02/1949      7.54/1913* (*RECORD FOR DECEMBER)
IAH   2.50/1949      1.96/1930
HOU   2.13/1965      2.55/1930
GLS   2.64/1965      2.11/1887

Severe threat mainly in the form of brief tornadoes will be
possible near the coast today along with waterspouts over the
coastal waters. Frontal boundary with easterly winds and LLJ from
the SSW will yield very high shallow helicity. Already quite a few
storms in the Gulf have exhibited supercell characteristics and
with the expectation that the coastal trough/warm front will creep
northward likely moving into the coastal counties will add the
mention of severe for the coastal counties. Hail and damaging wind
threat looks fairly low at this time.

Tonight and Sunday the axis of heaviest rainfall will probably
focus across the central and southern areas as the frontal
boundary eases out into the Gulf (lowering the severe threat
for SETX) which may focus any spinners over the Gulf waters.
Widespread rainfall overnight and Sunday with deeper convection
mainly southern areas and stratiform and a few embedded bands of
deeper convection north. As the upper low slowly marches east it
will finally begin to accelerate Monday and this should push a
Pacific cold front across S TX and through SETX Monday
afternoon...but across SETX that will be putting one final squeeze
on the atmosphere to produce another round/large band of showers
and thunderstorms. Severe threat may be increasing with the cold
front and mainly in the central and eastern counties where greater
instability may be available.

Drying weather Monday night into Tuesday as weak Pacific high
builds into the area. A much stronger cold front plunges south
late Wednesday with very chilly temperatures on tap as this cold
airmass blankets TX and may see our first freeze in the northern
counties Friday morning. Freeze line may make it into the Houston
area so stay tuned.

45

MARINE...
Early this morning, a tightening pressure gradient north of a slowly
lifting warm front has resulted in frequent wind gusts to gale force
across the eastern 0-20 NM waters. Have issued a short Gale Warning
through 6 AM CST in response, with a somewhat relaxing pressure
gradient in the wake of this feature allowing winds to decrease
later this morning. Seas remain in the 8-10 feet range and expect
seas to begin to decrease during the day as winds relax. However,
have extended the ongoing Small Craft Advisory through most of the
day with seas expected to remain above 7 feet for most of the day.

Tides are running above to much above normal this morning, with
water levels at Galveston Pier 21 peaking around 3.75 feet above
MLLW. While winds are expected to decrease during the day, expect
tidal issues to persist into Sunday as swell from the Gulf keeps
water levels elevated.

Otherwise, periods of showers and thunderstorms are expected to
continue across the marine areas through Monday. Some of these
storms may be strong to marginally severe and capable of gusty winds
and a waterspout or two. Drier conditions are expected by Tuesday as
a Pacific front sweeps into the western Gulf.

Huffman

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      54  48  54  50  60 / 100 100  90  70  70
Houston (IAH)              65  54  59  54  65 / 100 100 100  90  90
Galveston (GLS)            69  65  67  61  69 / 100 100 100 100  90

&&

.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 3 AM CST Sunday for the following
     zones: Brazoria...Chambers...Harris.

     Coastal Flood Warning until 6 AM CST early this morning for the
     following zones: Galveston.

     Coastal Flood Advisory until 3 AM CST Sunday for the following
     zones: Galveston.

GM...Small Craft Advisory until 6 AM CST early this morning for the
     following zones: Matagorda Bay.

     SMALL CRAFT SHOULD EXERCISE CAUTION until noon CST today for the
     following zones: Matagorda Bay.

     Small Craft Advisory until 6 PM CST this evening for the
     following zones: Coastal waters from Freeport to the
     Matagorda Ship Channel out 20 NM...Galveston Bay...Waters
     from Freeport to the Matagorda Ship Channel from 20 to 60
     NM...Waters from High Island to Freeport from 20 to 60 NM.

     Small Craft Advisory until 6 PM CST this evening for the
     following zones: Coastal waters from High Island to
     Freeport out 20 NM.

     Gale Warning until 6 AM CST early this morning for the following
     zones: Coastal waters from High Island to Freeport out 20
     NM.

&&

$$

Discussion...45
Aviation/Marine...14



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