Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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377
FXUS64 KHGX 270919
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
419 AM CDT Sat May 27 2017

.DISCUSSION...
Persistent southerly flow and cloudy skies this morning have kept
temperatures in the upper 70s to low 80s (about 10 degrees above
normal for this time of year) and a few record high minimum
temperatures may be in danger of being reached or broken today.
Cannot rule out one or two light streamer showers along the coast
this morning, but another hot, humid, and generally dry day is
expected for the region as upper ridging further builds over
Southeast Texas from the southwest. Similar to yesterday, cloud
cover will play a critical role in how high temperatures will rise
this afternoon. However, a weaker inversion today between 950-850
MB should allow for more breaks in the clouds and temperatures a
few degrees warmer than yesterday in the low to mid 90s inland and
mid to upper 80s along the coast. Combined with ample low level
moisture, this will translate to afternoon heat index values in
the 98 to 105 degree range but breezy 10-15 MPH winds should help
provide some relief to individuals outdoors today. Regardless,
heat safety should still be practiced with individuals drinking
plenty of water and taking frequent breaks to allow their bodies
to cool off if working (or playing) outdoors.

Subjective surface analysis as of 05Z/12 AM CDT showed a surface
trough stretching from Colorado south into the Low Rolling Plains
of Texas, with associated drylines across West Texas and eastern
New Mexico and a warm/ nearly stationary front stretching from
southeastern Colorado across northern Oklahoma into Arkansas.
Early morning water vapor imagery showed an upper trough axis
stretching from California northeast towards an upper low over
Manitoba. As this upper trough axis swings into the Southern
Plains tonight and Sunday, it will send the frontal boundary
located across Oklahoma south into Texas as a cold front. Rain
chances will begin to increase with the approach of this front.
For areas north of Interstate 10, rain chances result from
thunderstorms developing along the cold front and possibly
growing upscale into a thunderstorm complex that may reach parts
of the Brazos Valley or Piney Woods region Saturday night into
Sunday morning. For areas south of Interstate 10, rain chances
are the result of streamer/ warm air advection type showers along
the coast early Sunday morning as onshore flow increases ahead of
the front. Rain chances through this time only remain around 20
percent but will continue to increase during the day with the
front`s arrival. Otherwise, another morning of elevated onshore
flow and cloudy skies will mean record high minimum temperatures
will again be in danger of being reached on Sunday.

The cold front and its associated thunderstorm activity will
progress into the region from the north sometime during the
afternoon hours on Sunday, and a few strong to severe
thunderstorms will be possible along the front during this time.
Ample moisture pooling ahead of the front combined with diurnal
destabilization looks to result in strong instability (MLCAPE
values in excess of 3500 J/kg and mid-level lapse rates 7.5-8
C/km). Bufr forecast soundings also show quite a bit of dry air
between 900 and 500 MB, which would enhance evaporational cooling
leading to acceleration of downdrafts and the lowering of the
freezing level (aiding hail production). As a result, storms that
are able to develop along the front appear to be capable of a
damaging wind gust or large hail... should they develop. Overall
shear profiles are only marginally supportive of organized
thunderstorms and 700 MB temperatures are a warm 11-12 degrees C
south of a Brenham to Cleveland line, which raises questions about
the actual coverage of severe thunderstorms. Given the amount of
instability that is forecast to be present during this time
however, think at least an isolated strong to severe thunderstorm
will be possible north of a Brenham to Cleveland line during the
afternoon hours. This severe weather threat may linger into the
evening hours, with the threat translating south with the cold
front.

As the front begins to outrun its upper level support during the
evening and overnight hours, it will begin to slow its progress
towards the Upper Texas Coast. However, ongoing thunderstorm
activity and the potential for thunderstorms to produce
downbursts/outflow may be able to drive the cold front farther
south than where deterministic model guidance places it by Monday
morning (roughly between Interstate 10 and the coast). Where the
front is Monday morning will be key to determining where best rain
chances will materialize as a disturbance lifts across the region
for Mexico, but based on latest guidance this appears to be along
the Upper Texas Coast. Continued moisture advection during this
time will result in precipitable water values climbing to the 1.7
to 1.9 inch range on Monday and this atmospheric moisture content
combined with weak mid level flow and a slow-moving to nearly
stationary boundary will result in the potential for at least
locally heavy rain across parts of the region (which will be
better defined when the frontal position becomes more certain).

Periods of showers and thunderstorms will continue through the end
of the week as weak southwest flow aloft allows embedded
disturbances to translate across the region. Will possibly need to
raise rain chances for Wednesday into Thursday in subsequent
forecasts (should guidance remain consistent) as most medium range
guidance advertises upper level diffluence overspreading the
region (possibly signaling the passage of a weak wave) with
1000-500 MB relative humidity progs advertising a deep saturated
layer in place. Another widespread round of rain is possible
during the upcoming weekend as another wave translates across
Southeast Texas from the west. Both periods will also need to be
monitored for the threat of at least locally heavy rain... but the
evolution of these portions of the forecast will be heavily
dependent on mesoscale features that evolve from the early week
portion of the forecast.

Huffman

&&

.MARINE...
S-SW flow 15 to 20 knots should prevail early this morning then
gradually diminish to 10 to 15 knots by late morning. As gradient
tightens back up tonight will likely see winds climb back up into
SCEC criteria between 7p-7a. Seas have diminished to 4 feet at both
bouys. Overall this general pattern of 3 to 4 foot with winds
between 10 and 15 knots should be norm Sunday morning through Sunday
evening. Weakening frontal boundary slides into SETX and nears the
coast Sunday night with the potential for mesoscale convective
complexes to push it further south into the Gulf Sunday night/Monday
and Bays and Nearshore waters may have fairly significant impacts
with storms...potentially Offshore waters as well depending on how
those play out. Tuesday-Thursday persistent SE flow 10-15 increasing
to 15-20 by Thursday morning. Guidance (ECMWF) in the extended also
brings a system out of the Pacific southwest of Guatemala northward
across southern Mexico and into the Gulf becoming a fairly
impressive low Saturday with some very impressive moisture streaming
across the coastal waters into SETX Thu-Sat...could be some very
unsettled weather (GFS confines big moisture to Yucatan area). Stay
tuned.

Beach hazards continue with stronger rip currents and slightly
elevated tide levels.  Water temperature this morning was 80 at
Galveston Pleasure Pier. If heading to the beaches, swim near life
guards and stay away from jetties and piers.

45

&&

.AVIATION...
MVFR ceilings blanket the region as expected 1200-2100ft. This
should continue through mid morning then slowly rise with with MVFR
transitioning over the VFR around noon at most sites...LBX/GLS more
problematic. Winds will be accelerating inland with strongest winds
probably from PSX-CLL but even at the main hubs SSE 11-15 sustained
with gusts around 20 knots. Rinse and repeat with MVFR ceilings
redeveloping this evening 28/02-04z and prevailing throughout the
night. Will probably be adding VCSH to upcoming suite of TAFS for
CLL-UTS Sunday morning 09-12z and IAH 13z.

45

&&

.CLIMATE...
Near to record high minimum temperatures are possible at all of
the first order climate sites this morning and again Sunday
morning. A listing of the current records is provided below.

May 27
LOCATION           RECORD HIGH MINIMUM     YEAR
City of Houston           80               1996
Houston Hobby             78               1996
College Station           77               1924
Galveston                 80               2000

May 28
LOCATION           RECORD HIGH MINIMUM     YEAR
City of Houston           81               1996
Houston Hobby             79               1996
College Station           77               1996
Galveston                 81               1996

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      94  75  90  70  82 /  10  10  30  70  60
Houston (IAH)              93  77  90  74  82 /  10  10  30  70  70
Galveston (GLS)            87  80  85  76  82 /  10  10  20  60  80

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 9 AM CDT this morning
     for the following zones: 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/Climate...14
Aviation/Marine...45



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