Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 192343
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
543 PM CST Sun Feb 19 2017

.AVIATION...
Not too many changes to the TAFs for the 00z package. Primary
short term issue will be lowering cigs, and possibly some sea fog
at the coast. Later tonight we`ll be keeping a close eye on
evolution of storms expected to organize into a line west of the
region and then move into SE Tx after 8z. Latest HRRR runs are a
bit faster with timing of the line & closer to what the Tx Tech
WRF has been depicting. (maybe leading edge CLL 8-10z, UTS/CXO
10-12z, IAH/SGR 11-13z, HOU/LBX 12-14z, & GLS >14z). We`ll watch
trends and update for timing best we can, but there is uncertainty
with a lot of variables in play. Will likely see the heaviest
rain along the leading band, but possibility for steady moderate
rains for several hours in its wake are expected as well. Should
see slowly improving conditions later in the afternoon. 47

&&

.PREV DISCUSSION... /ISSUED 250 PM CST Sun Feb 19 2017/
Cloud cover starting to break up this afternoon with some mixing.
Where we are seeing the sun, temps have already made it to the
upper 70s, so SE areas will likely see some 80 degree temps this
aft. It is breezy and very humid as well for Feb with sfc dw pts
in the mid/upper 60s areawide.

Model guidance is in fairly good agreement that widespread showers
and storms will develop early this eve well west of SE TX across
central/north TX ahead of a slow eastward moving longwave
mid/upper level trough. Meso models show that an area of showers
and storms will develop out ahead of this main precip. band across
western portions of Se Texas just after midnight and this lead
band will be a slow mover across our W/NW areas during the early
morning hours. With PW values peaking around 1.8 inches Mon
morning, and upper level divergence increasing Mon morning as well
as a split jet structure develops, key parameters are in place
for heavy rainfall. The fairly unidirectional s/sw flow in the
low-mid layers of the atmosphere points to the possibility of
cell training in this very moist airmass. Think this all equates
to widespread 1 to 3 inches late tonight and tomorrow as well as
the threat for localized 4 to 6 amounts. Given that the ground is
fairly moist from previous rainfall, have issued a flash flood
watch for most of SE TX beginning during the early morning hours
on Mon and continuing through most of the aft.

The heavy rainfall threat should end by the eve hours. A trailing
mid/upper low that hangs around on Tue and this feature will
extend the chc of showers into Tues, but no heavy rainfall is
expected with this feature. Dry conditions with above normal
temperatures are expected on Wednesday and Thursday. A cold front
will move through on Friday aft/eve and bring a brief cooler
airmass to the region early next weekend. 33

MARINE...
Southeasterly flow very slow to come up this afternoon. Throughout
the evening hours expect winds to increase and will continue with
the SCEC for winds increasing to 15-20 knots...lighter in the bays.
Moisture still rich but with shorter residency over the warming
shelf waters and more mixing expect fog to be lighter throughout the
night with areas from around Freeport to Galveston probably dropping
to 1 to 3 miles. Will hold off on a Marine Dense Fog Advisory as it
isn`t as clear cut as last night. Seas building to 5 to 6 feet
toward morning. Storms will move in from the west and will be
capable of gusty conditions and significant reduction in visibility
in heavy downpours. Shear is a little higher over the southwest
waters between midnight and 8 am and will have to keep an eye out
for fast moving spinners/waterspouts over the far waters. Pacific
cold front eventually pushes through Monday night with a gusty
northwesterly winds probably below SCEC. Another Pacific cold front
late Friday may boost offshore winds to SCEC for Saturday morning.
Long southeasterly fetch develops Sunday and may see a period of
elevated seas/tides/sea fog late Sunday through Tuesday.
45

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      64  72  57  76  55 /  90  70  10  20  10
Houston (IAH)              69  72  61  76  59 /  80 100  30  30  10
Galveston (GLS)            68  70  63  72  62 /  60  90  50  30  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flash Flood Watch from 3 AM CST Monday through Monday afternoon
     for the following zones: Austin...Brazoria...Brazos...
     Burleson...Chambers...Colorado...Fort Bend...Galveston...
     Grimes...Harris...Jackson...Liberty...Madison...Matagorda...
     Montgomery...San Jacinto...Walker...Waller...Washington...
     Wharton.

GM...SMALL CRAFT SHOULD EXERCISE CAUTION through late tonight 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...Waters from Freeport to the
     Matagorda Ship Channel from 20 to 60 NM...Waters from High
     Island to Freeport from 20 to 60 NM.

&&

$$



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