Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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758
FXUS64 KHGX 221130
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
630 AM CDT Wed Mar 22 2017

.AVIATION...
Low clouds and fog have overspread much of SE TX this morning. The
fog is shallow and should burn off within an hour or two of
sunrise. Fcst soundings show a bit more cloud cover today and will
carry a scattered deck into the afternoon. Not expecting any
ceilings this aftn once the morning fog/clouds erodes. Winds
should be relatively light through the day and very light tonight.
The light winds coupled with clear skies should allow for more
fog development prior to sunrise. 43

&&

.PREV DISCUSSION... /ISSUED 402 AM CDT Wed Mar 22 2017/

DISCUSSION...
Another morning of low clouds and fog is underway for the region,
with split channel IR satellite imagery showing a stratus deck
rapidly expanding north of Interstate 10. South of this deck,
visibilities have fallen below 2 miles in a few locations and
additional deterioration of visibilities is expected through the
morning as radiational cooling continues with several locations
likely seeing dense fog development before the morning is out.
Given a weaker low level jet this morning, cannot rule out needing
a brief Dense Fog Advisory before sunrise. Onset of daytime
heating once again allow the fog to lift/mix out by mid-morning.
Similar to today, more fog and low clouds will be possible
Thursday morning.

The upper ridge axis has wobbled towards West Texas over the past
24 hours, but will build back east later today and push east of
the region on Thursday as an upper trough pushes onto the West
Coast. As a result, today and Thursday will both see mostly sunny
to partly cloudy skies and temperatures rising to near record
levels along the Upper Texas coast with highs in the upper 70s to
mid 80s. Given the ridge`s westward displacement today and
forecast soundings showing precipitable water values rising to
nearly 1 inch inland, a stray shower or two could be possible
during the late morning into the afternoon hours. However,
anything that develops would be the exception and not the norm as
subsidence across the region increases today and have only covered
this possibility with a 5 percent chance of rain in an otherwise
dry forecast.

As the West Coast trough reaches the Rocky Mountains on Thursday,
surface cyclogenesis will be induced over the High Plains. This
surface cyclone is expected to eject across the Southern Plains
during the day on Friday with its parent upper level system and
will drag a dryline and cold front across Texas. Strong ascent
associated with the upper level trough (height falls on the order
of 10-15 decameters across West Central Texas) will allow for
thunderstorms to develop along the dryline and grow upscale into a
larger complex as it moves east across Texas. The 00Z suite of
model guidance brings this this complex into Southeast Texas
sometime Friday afternoon, clearing the region by early Saturday
morning.

Southerly flow will increase dramatically in response to the
development of the surface cyclone and breezy to windy conditions
are expected across the region during the day Friday ahead of this
system. This strong onshore flow will also result in a dramatic
increase in moisture with precipitable water values surging back
to nearly 1.5 inches inland. Shear associated with this system is
also strong (60 to nearly 70 knots 0-6 km bulk shear) north of
Interstate 10. Both of these environmental conditions mean gusty
to possibly damaging winds and locally heavy rain would be the
main concerns with this complex Friday afternoon and evening.
There are still concerns about how far south this complex will be
able to extend into the region as the amount of instability that
will be present across the region on Friday as cloud cover is
keeping CAPE values below 1000 J/kg. Additionally, mid-level
southwest flow ahead of this system may result in a stronger cap
than model guidance is recognizing, especially across the southern
and southwestern counties. Continuing to advertise rain chances
across the region on Friday, with best chances for areas north of
Interstate 10. However, have concerns that some locations south
of I-10 may not see rain on Friday.

A weak cold front looks to push into the region Friday night
behind the storms and stall along the coast Saturday morning with
little fanfare, but increasing deep westerly flow in the wake of
the upper trough will result in dry and warm conditions resuming
for Saturday and Sunday as highs climb into the upper 70s to mid
80s. A shortwave trough looks to reach the Southern Plains by
Sunday night, with showers and thunderstorms returning to the
forecast on Monday as it sends a cold front into the region.
Medium range model guidance starts to fall out of phase by the
middle of next week as another upper level trough approaches the
Southern Plains, but the passage of this system could bring
widespread showers and thunderstorms back to Southeast Texas
during this time.

Huffman

MARINE...
High pressure over the central Gulf and lower pressures over West
Texas will maintain light to moderate onshore winds through early
Thursday. The pressure gradient will tighten significantly
Thursday evening into Friday as the high moves east and low
pressure over the western plains intensifies. The low will move
toward the mid Mississippi Valley on Saturday and drag a cold
front into Texas. The front never makes it to the coast but it
does get close enough to weaken the gradient and all the winds to
veer to the southwest and weaken by Saturday afternoon. Another
area of low pressure will develop over eastern New Mexico on
Sunday and the gradient is expected to tighten once again. Winds
will back to the SE and increase in response to the deepening low.
The low over NM will move east but associated cold front with
this feature will also stall before reaching the coast. Overall, a
moderate to occasionally strong onshore flow is expected through
early next week. Caution flags will be possible Thursday with SCA
conds possible Thu night and Friday. More Caution/SCA flags
possible Sunday. 43

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      84  65  83  66  78 /   0  10   0  10  80
Houston (IAH)              84  65  84  68  80 /   0  10   0  10  50
Galveston (GLS)            77  68  76  70  75 /   0  10   0  10  40

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Dense Fog Advisory until 9 AM CDT this morning for the following
     zones: Austin...Brazoria...Chambers...Colorado...Fort
     Bend...Jackson...Liberty...Matagorda...Waller...Wharton.

GM...NONE.
&&

$$

Discussion...14
Aviation/Marine...43



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