Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 241625
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1025 AM CST Sat Feb 24 2018

.UPDATE...
Starting off your weekend with a muggy Saturday morning, as
southerly winds are helping to keep dew points in the mid 60s to low
70s. Mostly cloudy skies will hold tight throughout the day today,
and expecting high temperatures to reach into the upper 70s. Have
lowered our high temperatures today a tad, to account for this cloud
cover.

Low level winds will increase in speed this morning, helping to mix
out the patchy fog along the nearshore waters and both Matagorda
and Galveston Bays. Additionally, breezy conditions will be felt
across southeast Texas today as these low level winds mix down to
the surface. Low level winds speeds will decrease tonight,
allowing for the development of patchy fog to return to the
forecast shortly after sunset. The SREF and HRRR are both
indicating the potential for patchy fog returning to the coastal
waters between 00-06Z Sunday.

Upper level water vapor imagery continues to show a long strand of
disturbances, embedded in southwesterly flow aloft helping to act
as a forcing mechanism this morning. Radar imagery is pick up on
some scattered showers producing light rain in the far northern
reaches of our forecast area around College Station. Short term
guidance such as the HRRR and Texas Tech WRF are keeping most of
the shower and isolated thunderstorm activity north of a line
from Washington to Trinity county. This region will likely see
the best chance for precipitation as we move into the afternoon
hours as an area of low pressure shifts northeast of Texas. Still
cannot completely rule out a few isolated strong cells in this
region, as low level instability increases this afternoon, with
surface to 3 km lapse rates approaching 6-6.5 deg C/km. Moisture
will also be on tap with precipitable water values ranging between
1.6-1.8 inches. Gusty winds will likely be the main threat
possible beneath some of the stronger storms this afternoon.

Hathaway

&&

.DISCUSSION...


&&

.PREV DISCUSSION... /ISSUED 453 AM CST Sat Feb 24 2018/

DISCUSSION...
Onshore winds have brought warm & muggy conditions back to all of
southeast Texas. Temperatures will start out above what are
typically normal high temperatures for this time of year.
Galveston should approach a record high (76 set in 2017/1937).

Satellite imagery shows the first in a long train of upper
impulses embedded in the sw flow moving into central Texas this
morning. The tail of its associated precip should move into or
close to northern parts of the CWA this morning. A developing
low in the Texas panhandle will trek northeastward toward the
midwest later today and drag a dryline/front into northern parts
of the area late this afternoon and evening. Expect showers and
thunderstorms to accompany this boundary (more than likely a thin
band by the time it arrives this far south). Can`t completely rule
out a few isolated strong cells generally north of a Brenham-
Livingston line, but best dynamics for severe wx should be
situated well n/ne of the area. The front will likely slow/stall
before reaching the coast tonight as it loses upper support for a
continued southward push.

Another round of upper disturbances are forecast to move overhead
and parallel to the front late tonight and Sunday. High PW`s will
remain pooled along the boundary (1.6-1.9"). This, along with the
threat of some training convection we can`t rule out some localized
heavy rainfall. It looks like an initial flare up will likely
occur between 3am-9am along and south of I-10 -- then as the day
wears on possibly expand inland along a zone of convergent flow at
850mb from roughly Columbus-Trinity. Precipitation should start
tapering off from NW to SE during the evening as the upper disturbances
depart and llvl ridging eventually gives the front a southward
push.

Monday is looking like we`ll see some nice wx...precip-free,
mostly sunny with morning temps in the 50s warming into the mid
70s. Rain chances quickly return on Tuesday and continue into
early Thurs with a repeat scenario we`ve seen lately: warm front
moves in, moisture levels increase, messy sw flow aloft in place,
and approaching upper trof & surface cold front. The cold front
is penciled in for early Thursday with a few days of drier wx
expected in its wake. 47

MARINE...
Per webcams/obs, sea fog not quite as problematic this morning as it
was yesterday... likely due to the stronger onshore low-level winds.
However, will keep current configuration of the Marine Dense Fog Ad-
visory in place through it`s scheduled expiration time. And speaking
of these stronger winds, will also maintain the SCEC for the coastal
waters offshore...but will also be expecting winds over the bays and
nearshore waters to pick up through this morning/afternoon. The SCEC
could be expanded to include these areas. At this time, will probab-
ly hold off on re-issuing the Marine Dense Fog Advisory for the bays
and nearshore waters tonight as other features come into play.

All of this is setting the stage for increased showers/thunderstorms
tonight/tomorrow as a cold front moves into the coastal waters. This
boundary is forecast to stall just off/along the coast later tonight
with quite a bit of unsettled weather accompanying it for Sun. A re-
inforcing surge of cooler/drier air late Sun night/early Mon morning
is then expected to push the front into the near/offshore waters for
Mon. This should extend the break from sea fog a bit more, but, alas
the pattern changes once again on Tue as the front returns as a warm
front. Onshore winds/returning moisture should help set things up as
the lower visibilities return Tues night/Weds. Will have to wait and
see if extended guidance of a strong cold front on Thurs hold true.
41

AVIATION...
Strong onshore winds at/just above the surface (so far) this morning
are helping to keep CIGS around MVFR. Not expecting issues with VIS/
fog the rest of the morning, but have noticed an uptick with showers
developing across the central/northern portions of the CWA (via this
strong WAA). As such, will likely keep the mention of VCSH for sites
SGR/HOU northward through the rest of this morning/early afternoon.
A mix of MVFR/VFR for this afternoon/early evening...with increasing
rain chances from the north (to south) as the cold front/pre-frontal
trough approaches/moves across the area. This boundary is then fore-
cast to reach the coast by 12Z tomorrow and stall...with the mention
of SHRA/TSRA likely persisting in the LBX/GLS TAFS. 41

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      77  54  67  48  73 /  70  20  60  20   0
Houston (IAH)              79  61  67  53  74 /  40  60  80  30  10
Galveston (GLS)            77  65  70  61  69 /  20  80  60  50  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 6 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...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...08


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