Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 151628
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1028 AM CST Mon Jan 15 2018


.DISCUSSION...
Today conditions will feel like spring only to get slapped in the
face with reality that it is the warm up before another freeze.
Temperatures are in the 50s and should reach low/mid 60s most
areas. MLK Day is shaping up to be one to enjoy outside before
rushing to the store to grab milk and bread.

All joking aside, arctic front is on its way located from the
Ozarks down through central Oklahoma into the Texas Panhandle.
High pressure of ~1052mb over Montana will be pushing into the
northern Plains behind the front by Tuesday morning. Broad
positive tilt trough continues to develop on water vapor imagery
with upper low over the Great Lakes and vorticity max/jet streak
coming down through the Plains. Front should push through the area
late tonight into Tuesday morning. We are still monitoring new
model data for winter precipitation development. The 12Z NAM and
GFS seem to be hinting at freezing temperatures occurring sooner
in the day. We are not sure how this may impact our current winter
weather advisory or how this affects precipitation types, but
there will be some adjustments for the afternoon forecast. Early
analysis shows quite a bit of frontogenesis through 925-850mb and
850-700mb layers so mesoscale precip banding is a growing concern.
The real trick is timing these precip bands versus the intrusion
of dry air from the north through the boundary layer. This may
determine when precip may end on Tuesday.

Overpeck

&&

.PREV DISCUSSION... /ISSUED 612 AM CST Mon Jan 15 2018/

AVIATION...
Changes on the way during this TAF period...more specifically
during the second half of the period. An approaching cold front
will thicken up VFR clouds this afternoon into evening...eventually
introducing overnight scattered showers. Terminals from metro
northward will likely begin experiencing a wintry mix of light
rain...sleet and/or snow from roughly 09Z on through Tuesday
morning. The cold front will pass across CLL around midnight
Tuesday...city just before dawn...and to the coast shortly after
sunrise. As cold air advection kicks in behind this boundary...the
lower near surface layer will begin falling below freezing from
just before sunrise (northern hubs) to shortly after sunrise
(around Houston). Thus...any light precipitation falling during
this time will begin to freeze or partially freeze on its way to
the ground. Anticipating a wintry mix that may eventually transition
to all sleet or snow over far northern terminals during the pre-dawn
hours...a mix to all -PL or -SN over metro hubs late Tuesday morning.
If still precipitating within post-frontal northerly winds Tuesday
afternoon...winter precipitation (likely light blowing snow) will
continue through Tuesday night as cold air advection strengthens/
sub-freezing layer deepens. 31

PREV DISCUSSION... /ISSUED 445 AM CST Mon Jan 15 2018/

DISCUSSION...
Light mainly east to southeast winds early this morning will become
mainly southeast and increase a bit during the day today as high
pressure continues moving off to the east. This flow will bring warmer
temperatures, increasing cloud cover and maybe some afternoon and
evening showers to the area. The strong arctic cold front will enter
our northern counties late this evening (probably before midnight)
and will then race to the coast and be offshore before sunrise. Falling
temperatures and increasing north winds (eventually increasing to just
under wind advisory levels) can be expected during the day behind the
front. Areas of rain possibly changing over to a wintry mix up north
can be expected as early as around 3 AM with activity building southward
as the day progresses. By sunset, anticipate the wintry mix to possibly
be flirting with the coastal counties. Tuesday night will be very cold
with temperatures falling into the upper teens to around 20 up north
and in the upper 20s at the coast. Drying can be expected from the
north overnight as strong high pressure builds into the area, but there
is a risk for the wintry mix to continue across parts of our central
and southern counties. Will go ahead and issue a Winter Weather Advisory
for the entire area from early Tuesday morning through Tuesday night
(little to no accumulation expected), and upgrades to watches and/or
warnings might need as this event unfolds if accumulation and/or the
hazard risk increases. We`ll also need to be watching for possible
wind chill advisories as readings drop into a 10 to 20 range. Any
precip chances should stay offshore during the day on Wednesday while
very cold morning temperatures warm into the upper 30s to lower 40s.
Precip chances come back into the forecast Thursday through Friday
morning as a shortwave trough moves across the area and brings another
shot of a wintry mix across our northern counties Thursday morning
and better rain chances toward the coast/offshore. The next cold front
moves through the area on Sunday. 42

MARINE...
Weak albeit slightly strengthening onshore flow today as the waters
fall downstream of an approaching cold front. Early Tuesday winds
will back easterly briefly until the frontal boundary comes across
the nearshore and bay waters shortly after sunrise Tuesday. Strong
Advisory level offshore winds in the wake of the front will occur
during the day Tuesday...likely reaching gale gusts across the far
offshore waters Tuesday afternoon. Strong northerlies with elevated
seas in the 6 to 8 foot range nearshore...around 10 or 11 feet offshore
.will persist through mid to late Wednesday. Early week precipitation
is forecast to remain light rain or periodic passing rain showers.

High pressure centered across the southeastern U.S. will maintain a tight
enough east-to-west NW Gulf pressure gradient to allow for a Caution level
easterly fetch to linger on through late Thursday or early Friday. A
developing western Gulf coastal low will take this easterly fetch and
veer it going into the weekend...stronger southeasterlies along the low`s
eastern side on Friday. Once the low either moves east or washes out by
Saturday...onshore flow will pick up going into Sunday ahead of the next
cold front that is timed to pass across the waters Sunday. 31

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      64  30  32  20  38 /  20  60  50  20  10
Houston (IAH)              64  40  41  24  41 /  20  30  50  30  10
Galveston (GLS)            64  47  48  29  41 /  10  30  50  40  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Winter Weather Advisory from 3 AM Tuesday to 6 AM CST Wednesday
     for the following zones: Austin...Brazoria...Brazos...
     Burleson...Chambers...Colorado...Fort Bend...Galveston...
     Grimes...Harris...Houston...Jackson...Liberty...Madison...
     Matagorda...Montgomery...Polk...San Jacinto...Trinity...
     Walker...Waller...Washington...Wharton.

GM...Gale Watch from Tuesday afternoon through Wednesday morning 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...39



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