Friday, April 16, 2021

Apr. 16 21

 Area Forecast Discussion

Issued by NWS Houston/Galveston, TX

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000
FXUS64 KHGX 162357
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
657 PM CDT Fri Apr 16 2021

.AVIATION [00Z TAF Issuance]...

We`re starting to see some intensification of storms along the
pre-frontal boundary with an occasional lightning strike noted
with the activity. Will keep the mention of TSRA/VCTS at sites
from IAH south to the coast. Expecting only SHRA with the cold
front itself which is only lagging behind the other line by an
hour or so. Extrapolated timing has this boundary at/along the
coast just before midnight...with rain chances ending with its
passage. However, will keep a mix of MVFR to LIFR in place for
most of SE TX overnight even with N winds developing/strenght-
ening. With the generally zonal upper flow remaining in place,
BKN/OVC overrunning clouds are progged to prevail through much
tomorrow...with rain chances likely returning as embedded weak
disturbances move across as well. 41

&&

.PREV DISCUSSION... /ISSUED 341 PM CDT Fri Apr 16 2021/

SHORT TERM [Through Saturday Night]...

Cold front and associated band of shra & embedded tstms will be
making its way into the northern parts of southeast Tx in the next
hour or two. Though not very likely, any isolated stronger cells
that manage to develop will probably be situated east of a College
Station-Liberty line between now and early evening. Beyond that,
better lift & moisture works its way further east. As the front
approaches the I-10 corridor and the coast, precip should evolve
to mainly just thin band of shra right along the wind shift.
Cooler and breezy conditions overnight with a break in the precip
post-fropa.

On Saturday...cloudy, breezy and cool conditions will prevail.
Model guidance is still supporting some disturbances embedded in
the wsw flow aloft moving up the coast from south Tx during the
day. Areas of light precip will develop to the sw and move across
the southern 2/3 - 1/2 of the region during the late morning
through evening hours. Highest rain chances & coverage should be
situated south of the H85 front (I-10 and offshore). Rain should
taper off toward mid evening Saturday. Some locations may see some
partial clearing, but still expect some mid/high cloud cover
streaming overhead in the flow aloft. 47

LONG TERM (Sunday through Friday)

A return to cooler than average temperatures is expected on
Sunday. Northerly light winds and low humidity will lead to a
pleasant day with highs in the upper 60s to low 70s. These
forecast highs will be around 10 degrees below average for this
time of year.

The extended period features dry and cooler conditions through at
least mid-week. This is thanks to a surface ridge building in
over the southern Plains and 850 mb temperatures in the 5 to 10 C
range. Zonal flow aloft brings a shortwave trough over southwest
TX on Monday, while a northern trough over the MS Valley drags a
surface front over the region Monday night into Tuesday. Low to
mid-level moisture is limited with PWATS around 1.0 inch or lower.
Therefore, this frontal boundary is not expected to bring
precipitation.

The pattern is expected to become more favorable for showers and
thunderstorms after Thursday. Upper-level low moves across the
desert southwest, then into the southern Plains Thursday into the
weekend. Southerly flow develops at the surface, surging warmer
and more humid air across the region into the weekend. While
deterministic models differ a bit in terms of timing and strength
of this trough; overall forecast indicates unsettled conditions
continuing into the upcoming weekend. 05


MARINE...

Early this morning, moderate east winds produced gusty conditions
around Galveston Bay and nearshore waters from High Island to
Freeport out 20 nm. Winds are beginning to veer to the southeast this
afternoon, resulting in a decrease in gusts through the evening.
Will keep caution flags for all our nearshore waters and bays
through this evening as gusts from 15- 20 knots may persist.

The main marine concern is anticipated later tonight with the
arrival of a cold front. The FROPA will reach the coastal waters
after midnight, bringing a chance for showers ahead and along the
boundary. Moderate to strong offshore winds are likely behind the
front and will persist through Sunday. Winds may reach Gale
criteria at times, mainly offshore. Elevated seas from 4 to 7 ft
are also expected in the wake of the front. That said, a Small
Craft Advisory has been issued for the bays and all Gulf waters
from late tonight into Saturday night.

Showers will persist through Saturday as another disturbance
moves along the coast throughout the day. Light to moderate
northeasterly to easterly flow begins to develop on Monday as the
high pressure builds in over TX. This pattern will continue
through at least, Thursday. Next chance for precipitation returns
Thursday into the weekend.
05

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      53  63  47  68  47 /  40  20  10  10   0
Houston (IAH)              59  65  51  69  52 /  60  50  30  10  10
Galveston (GLS)            64  67  58  70  62 /  40  40  50  10  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk until 7 PM CDT this evening for the
     following zones: Bolivar Peninsula...Brazoria Islands...
     Galveston Island...Matagorda Islands.

GM...Small Craft Advisory from 1 AM Saturday to 1 AM CDT Sunday for
     the following zones: Coastal waters from Freeport to
     Matagorda Ship Channel TX out 20 NM...Coastal waters from
     High Island to Freeport TX out 20 NM...Galveston Bay...
     Matagorda Bay.

     Small Craft Advisory from 4 AM Saturday to 1 AM CDT Sunday for
     the following zones: Waters from Freeport to Matagorda Ship
     Channel TX from 20 to 60 NM...Waters from High Island to
     Freeport TX from 20 to 60 NM.

&&

$$

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