Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 220048
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
748 PM CDT Sat Apr 21 2018

.DISCUSSION...
Quick update sent to raise POPS tonight for line of storms moving
through area.


&&

.AVIATION...
Mix of VFR/MVFR with winds slowly veering from the ESE to S
tonight as line of storms ahead of the dryline pushes eastward and
through the area. Expect an additional line near the surface low
and cold front to rotate eastward and swing through the northern
sites. VCSH/VCTS will prevail in the TAFS through around 06z north
and 10-11z south based on current timing. Brief IFR conditions
possible with the storms. MVFR ceilings should linger after FROPA
tonight thru 12-16z window then expect those to erode as drier air
spreads quickly southeastward through the region. High clouds from
Pacific tap will likely blanket a good chunk of the area but still
VFR.
45

&&

.PREV DISCUSSION... /ISSUED 346 PM CDT Sat Apr 21 2018/

DISCUSSION...
Light warm air advection showers will continue through the
afternoon as the warm front progresses farther northward out of
Southeast Texas. AMDAR soundings indicate the warm nose near 700
mb is still in place, inhibiting the thunderstorm potential. As
the upper level trough axis moves into Central Texas, the
divergence aloft has translated northeastward over Arklatex. The
surface low has moved into Central Texas with its trailing cold
front through North Texas.

Dew points in the upper 60s to 70 have moved inland along a
Brenham-Intercontinental-Baytown line. This increase in moisture
at the surface increases the likelihood of surface-based
convection this evening and tonight. The 18Z HRRR and NAM-Nest
represented the enhanced surface moisture well, and show CAPE
values tonight peaking at 700-1000 J/kg. While CAPE values are
still marginal for severe weather, wind profiles continue to look
more favorable with 0-3 km SRH near 200 m2/s2, even as high as
400 m2/s2 along the coast this evening. That said, if any
thunderstorms were to develop, they may become strong to severe.
Strong winds and isolated tornadoes are possible.

For timing, thunderstorms will develop near 6 to 7 PM this
evening. These showers and thunderstorms will continue moving
from southwest to northeast until late tonight. Additional
convection lingering near the coast through early Sunday morning
is possible. Ahead of the approaching cold front, there will be a
broken line of showers and thunderstorms, heavy at times. MUCAPE
is near 1000 J/kg with surface-based CAPE closer to 500 J/kg, so
any convection should be elevated, limiting the threat for
tornadoes and severe wind. The cold front will move into our
northern counties near midnight and continue to track toward the
coast. The front will move offshore near 6 AM Sunday. Rainfall
totals of 0.5"-1.5" will be common, with isolated totals of 2"-3"
with the heavier thunderstorms.

Behind the front, high pressure will build in from the northwest
and upper level ridging will dominate our weather for the early
work week. Skies will stay mostly clear with high temperatures in
the upper 70s to low 80s and minimum temperatures ranging from
the upper 50s to low 60s, near climatological average. Moisture
builds back into the area on Wednesday as surface high pressure
progresses eastward. A series of cold fronts will pass through the
area late next week. There is low confidence in the timing of
these fronts and the expanse of precipitation. 22

MARINE...
Moderate to strong E-SE winds will persist into the evening and
will extend the SCEC for the Gulf waters through 06z. Winds will
drop off in advance of a weak cold front that will cross the
coastal waters around 12z. An offshore flow will develop in the
wake of the front but sustained wind speeds are expected to remain
below Advisory criteria and another Caution statement appears
likely. Offshore winds will prevail through Tuesday with a weak
onshore flow developing Tuesday night. Not much confidence
Wednesday and beyond as models diverge in handling a strong upper
level storm system and associated surface features. At this time,
it appears a cold front will cross the coastal waters with an
offshore flow expected Wednesday night and Thursday. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      53  72  52  77  55 /  70   0   0   0   0
Houston (IAH)              61  75  56  78  57 /  70   0   0   0   0
Galveston (GLS)            65  74  61  76  64 /  70  20   0   0   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 1 AM CDT Sunday 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.

&&

$$

Discussion...41
Aviation/Marine...45


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