Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 172145
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
345 PM CST Sun Dec 17 2017

.DISCUSSION...
Temperatures have been slow to warm this afternoon in parts of the
Brazos Valley and Piney Woods owing to persistent cloud cover.
Elsewhere, breaks in the clouds have allowed for temperatures to
warm into the mid 50s to lower 60s. Limited heating today is also
resulting in very small dewpoint depressions across the Brazos
Valley this afternoon, which means that another round of fog will
be possible this evening and tonight (with onset much earlier
than last night). Low level ridging over the Gulf building west
tonight will help increase isentropic lift on the 295 K surface,
allowing for bands of showers to develop along the coast and
across the coastal waters by late this evening. Should any of this
activity be able to tap into some of the elevated instability
present (around 1000 J/kg MUCAPE along the coast), a few embedded
thunderstorms will be possible as well. How far south fog will be
able to spread (and how dense it will get) will be dependent on
the rain that develops along the coast and for now highlighting
areas north of the Highway 59 corridor as having the best
potential to see dense fog tonight.

A developing warm front tonight over the Gulf may also result in
periods of sea fog returning to the nearshore waters before it
lifts inland Monday. Southwest flow aloft will persist Monday and
Tuesday, allowing for periods of showers, isolated thunderstorms,
and sea fog to persist. The upper trough encouraging this
southwest flow lifts across Texas on Tuesday, becoming negatively
tilted as it does. This will drag a cold front across the region
as the upper trough passes late Tuesday into early Wednesday. A
few strong to severe thunderstorms are possible ahead and along
the front as returning moisture ahead of the front contributes to
SBCAPE values approaching 1500 J/kg and 0-6 km bulk shear values
increase into the 50-60 knot range in response the trough`s
passage. Primary threats appear to be gusty winds, locally heavy
rain, and possibly an isolated tornado before the system shifts
east of the region Wednesday.

Drier air behind the front will also result in a brief break in
sea fog Wednesday, but onshore flow quickly returns Thursday and
Friday and returning moisture may allow for sea fog to redevelop
late in the week. Warm air advection will also result in showers
again spreading north into the region from the Gulf during this
time. The cold front expected to cross the region on Friday has
come in dramatically weaker and drier than 24 hours ago and have
trended with a blend of model guidance for the extended portion of
the forecast due to the extreme variability being observed in
model solutions. A second, stronger cold front may arrive closer
towards Christmas... but any impacts from this front are
indiscernible at this time.

Huffman

&&

.MARINE...
Light easterly winds will veer becoming southeasterly winds
overnight tonight. With higher dewpoints situated in the northern
Gulf of Mexico associated with the remnant moisture from the coastal
trough that moved through the region yesterday, warm moist air will
be advected over the cooler shelf waters this evening. This will
result in possible sea fog development over the coastal waters and
bays, beginning this evening and continuing into Monday. This set up
for potential sea fog should remain in place through the
beginning of the week until late Tuesday when the next cold front
is expected to move across SE TX. Additionally, the potential for
isolated shower coverage will increase to scattered showers, as a
warm front slides north across the northwestern Gulf of Mexico
late tonight through Monday. These scattered showers will linger
through the day Tuesday out ahead of our next cold front. Light
to moderate winds will turn out of the northwest becoming north
behind the front Tuesday evening and continue through the day
Wednesday. Wave heights should remain between 2 to 4 feet through
most of next week.

Onshore flow returns early Thursday, and wind speeds should
strengthen enough that a SCEC may be necessary in the offshore
waters late Thursday through early Friday. Additionally, wave
heights should increase to 3 to 5 feet late Thursday through
Saturday. Model guidance has slowed the arrival of Friday`s cold
front to late in the afternoon into the early evening hours. Based
off the most recent model solutions, the winds should shift out of
the northwest along the coast around 00Z Saturday. Moderate to
strong northerly winds will fill in behind this frontal passage. At
this time, wind speeds should strengthen enough that a SCA would be
needed over both the coastal and offshore waters.

Hathaway

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      51  64  60  71  54 /  10  60  60  90  40
Houston (IAH)              56  67  64  74  58 /  30  60  40  60  70
Galveston (GLS)            60  66  64  70  61 /  40  60  20  30  60

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

Discussion...14
Aviation/Marine...08


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