Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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204
FXUS64 KHGX 161706
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
Issued by National Weather Service Lake Charles LA
1106 AM CST Thu Feb 16 2017


.AVIATION...No changes to the previous aviation package at this
time. High pressure will continue to move to the east with
southerly winds becoming more established across the region. Some
cirrus this afternoon, however increasing clouds can be expected
overnight ahead of an approaching disturbance along with
increasing moisture.

Some showers can be expected in the area by mid day.


&&

.PREV DISCUSSION... /ISSUED 522 AM CST Thu Feb 16 2017/

AVIATION...
High pressure centered over SE TX will move east today with a very
light southerly flow developing. Cirrus will continue to stream
into the area through the early aftn. Clouds will increase late
tonight as an upper level disturbance approaches. Moisture looks
deep enough for a some showers along the coast so added a VCSH at
KGLS at 17/1000z. 43

PREV DISCUSSION... /ISSUED 354 AM CST Thu Feb 16 2017/

DISCUSSION...
Early morning water vapor imagery showed a compact closed low
spinning over the Mexican states of Sonara and Sinaloa with a few
cirrus streaming across Texas ahead of this system. At the
surface, high pressure centered over South Central Texas was
resulting in light winds with 3 AM CST temperatures in the mid 30s
to low 40s. This surface high will slide east of the region later
today, allowing for onshore flow to resume and afternoon
temperatures to moderate back into the upper 60s to near 70 today.

The closed low over Mexico will lift into West Texas this
evening, crossing North Texas into Arkansas during the day on
Friday. Onshore flow will draw up moisture from the west central
Gulf tonight and Friday morning, with precipitable water values
climbing back into the 1-1.3 inch range by midday Friday (highest
along the coast and over the Gulf). Increasingly divergent flow
and the presence of a 110-120 knot jet streak across the northwest
Gulf will allow for scattered to numerous showers and
thunderstorms to spread up the Texas coast after midnight tonight
and spread across the coastal waters and into most of Southeast
Texas through the remainder of the morning hours.

Expect greatest coverage to occur over the coastal waters
(coincident with forcing from the upper jet). However, with the
proximity of the low and BUFR forecast soundings from College
Station and Lufkin showing only a weakly capped environment on
Friday, daytime heating will help encourage isolated to scattered
showers and thunderstorms north of the main activity in the Gulf.
While rain totals are expected to be highest over the Gulf, CIPS
Analog Guidance does show increased probabilities for a few
rainfall amounts exceeding 2 inches along the coast. A few of the
higher resolution models (ARW, NMM) are also attempting to develop
some kind of mesolow within the widespread convection tomorrow,
and this could be the focus for some locally enhanced rainfall
totals right along the Upper Texas Coast should it develop. Have
increased forecast rain amounts along the coast above WPC as a
result to 0.25-0.75 inches along the coast and would not be
surprised to see some minor flooding issues materialize with
stronger activity Friday morning and afternoon should locally
enhanced rainfall occur.

Additionally, 35-45 knots of 0-6 km bulk shear over the Gulf and
along the coast will promote organized thunderstorm development
and with mid-level lapse rates increasing to around 7 C/km in
response to the upper low`s arrival and a few strong thunderstorms
will be possible across the waters on Friday. Enough low level
shear may be present along the coast for a few rotating storms
that would need to be monitored for a brief isolated tornado or
waterspout threat from late morning through early afternoon as
surface winds back to the east. Expect energy from the upper low
to clear the region Friday evening as it lifts into Arkansas, with
dry conditions returning to the region as the system departs.

Patchy fog will be possible Saturday morning with morning
temperatures starting out in the mid 50s to mid 60s. Temperatures
will warm into the upper 70s to possibly mid 80s by the afternoon
as shortwave ridging amplifies over the region in the wake of
Friday`s system, with this ridging also promoting dry conditions.
By Sunday, a wave currently translating across the Central Pacific
reaches the Desert Southwest and scattered showers with a few
thunderstorms will be possible generally west of Interstate 45 as
this system approaches. Increased cloud cover and rain chances
look to keep temperatures on Sunday a few degrees cooler than
Saturday, with highs in the mid 70s to near 80.

Attention at the beginning of the work week will focus almost
exclusively on how the upper level system to our west evolves as
it moves across the state through the middle of next week. Medium
range guidance continues to offer slightly different timing
solutions for this upper low, with the 00Z Canadian offering the
most progressive (and northerly) solution as it clear the region
by late Tuesday. The 00Z GFS and European are slower and farther
south, with GFS ensemble guidance now offering better support for
the timing (although not position) of the upper low early to mid
next week. Still have concerns on the overall speed of the system
as the upper low itself (as well as the upper ridge over the East
Coast that is forecast to precede it) are not being sampled by
current upper air observations and are not being reflected in
model solutions. Should this upper ridge materialize stronger than
current guidance indicates, it would slow down the eastward
progress of the upper low and affect the current anticipated
timing for rain at the beginning of next week.

Have kept timing for rain chances fairly consistent with the
previous forecast as a result, with showers and thunderstorms
spreading across the region Sunday night through Monday and
gradually tapering them off through Wednesday as the upper low
exits. Precipitable water values are forecast to still be
anomalously high (1.6-1.8 inches) but guidance is now shifting the
deepest moisture axis east of the region and this is resulting in
a downward trend in rainfall totals seen from WPC. Regardless,
heavy rain still appears to be a very real possibility early
Monday morning through Tuesday morning given this moisture
content. Drier conditions are expected by Wednesday as the system
begins to move east of the region.

Huffman

MARINE...
Surface high pressure will bring light winds to the coastal
waters today. The high will drift east tonight and a light onshore
flow will gradually strengthen. A moderate onshore flow is
expected on Friday as low pressure over the Texas panhandle
deepens. A strong upper level disturbance will bring a good chance
of showers and thunderstorms to the coastal waters/bays on Friday.
Some of the storms could be strong late Friday morning into the
afternoon. Onshore winds will prevail through the weekend and wind
speeds will begin to increase Saturday night. A moderate to strong
onshore flow is expected both Sunday and Monday as another strong
storm system approaches the region. SCEC/SCA will likely be
required Sunday into Monday. Strong storms will again be possible
over the coastal waters on Monday. Onshore winds will prevail
through Tuesday with a weak wind shift possible Tuesday night.
There is a brief window for sea fog early Sunday but the
trajectory of sfc winds and warming water temps makes the the
threat marginal at this time. 43

&&

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

$$

Discussion...99
Aviation/Marine...99



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