Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 151843
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1243 PM CST Fri Dec 15 2017

.UPDATE...
Big picture forecast is on track, but have made some cosmetic
changes to better integrate the forecast with observations. Light
rain showers may remain possible this afternoon on the immediate
coast, but will continue to trend down as the bulk of the echoes
on radar push southward. Additionally, have nudged high temps down
slightly. But as satellite shows some breaks in the clouds
farther north, have not taken temps down as much as short range
guidance suggests - instead opt for meeting the old highs and the
consensus of short range models in the middle.

Luchs

&&

.PREV DISCUSSION... /ISSUED 1151 AM CST Fri Dec 15 2017/

AVIATION...
VFR conditions are expected to prevail for the next 24 to 30
hours at the Southeast Texas terminals, with southwest flow in the
mid and upper levels promoting periods of broken to overcast
skies between FL150-FL250. Surface high pressure sliding east
across the region will allow northerly winds 5-10 knots inland
this afternoon to become light and variable overnight. Winds are
expected to increase into the 5-10 knot range out of the
east/southeast mid to late morning Saturday as a surface low lifts
up the Texas coast. For GLS, expect slightly stronger winds
generally in the 10-15 knot range this afternoon, falling below 10
knots overnight.

Huffman

PREV DISCUSSION... /ISSUED 509 AM CST Fri Dec 15 2017/

DISCUSSION...
Cold front has pushed well offshore this morning. Radar indicates
areas of -ra streaming near/off the coast in association with
some impulses embedded in the messy flow aloft. Other than some
locations south of I-10 & closest to the coast, I`d anticipate a
mostly dry day.

Surface high pressure moves off to the east later tonight. Expect
a coastal trof/low to begin developing along the lower & middle
Texas coast as this occurs. Further aloft, the upper trof currently
near Baja will make its way ewd over cntl Mexico, begin filling
and eject northeast across cntl and ne Tx Sat night. Look for
precip coverage to begin expanding across southeast Texas later
Saturday afternoon in association with the increase in large scale
lift.

Low level jet ramps up to 40-50kt, PW`s increase to 1.5-1.8" east
of the Highway 69/59 corridor and the region becomes situated
near the RRQ of a 120kt jet by Saturday night. Forecast soundings
show very impressive turning in the llvls and helicity values...but
a significant inversion & lack of instability will be limiting
factors for widespread severe wx. That being said, we`ll need to
closely monitor the eventual track of the surface coastal low and
whether the warm sector makes its way inland or not as
spinning/tornadic cells could be a possibility. Models have been
showing some run-to-run differences as of late, but for now, are
in general agreement that could occur roughly along a Matagorda
Bay-Liberty line. Otherwise...the primary issue will be some
moderate to occasionally heavy December rain with PW`s nearing
close to 2 standard deviations above norms.

The bulk of precip will be pushing off to the east by early Sunday
morning with a trailing moisture axis lingering near and off the
coast. By Sunday evening onshore winds will resume and transport
some of this moisture and showers back inland through Monday.
(Would also expect some sea fog to develop away from precip
areas).

Forecast becomes more uncertain Mon night-Wed. GFS & CMC swing the
next trof and associated sfc front thru late Monday...effectively bringing
an end to rain chances Monday night. ECMWF on the other hand is less
progressive with the trof and keeps rain/fog chances going well into
the middle of next week. In general, the fcst has been more in line
w/ GFS reasoning as of late, but did nudge POPs up a touch Tue and
Wed in case ECMWF is onto something.

A strong cold front is penciled in for next Friday.   47

MARINE...
Strong offshore winds (and building seas) will prevail this morning
across the bays/coastal waters early this morning (in the wake of a
cold front last night). As high pressure builds into the area (from
the north), we should begin to see the gradient weaken and winds de-
crease through the rest of the morning from the north. The offshore
waters will remain under SCA flags through the afternoon.

Winds to veer to the E then SE by Sat as the forecast calls for the
development of a coastal trof/low off of the lower/middle TX coast.
This system is then expected to eventually track NE up the coast...
bringing unsettled weather to the area Sat night in the form of ele-
vated winds/seas, strong storms and possibly sea fog. Conditions to
improve Sun as this disturbance pushes east of the region. However,
sea fog could return to the bays/nearshore waters late Sun and then
persist through Mon (ahead of the next cold front on Tues). 41

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      59  40  56  46  66 /  10   0  50  90  10
Houston (IAH)              57  41  59  50  67 /  10   0  20  80  10
Galveston (GLS)            55  48  60  58  67 /  50   0  20  80  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...Small Craft Advisory until 2 PM CST this afternoon 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 6 PM CST 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...25


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