Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 261137

Area Forecast Discussion
National Weather Service Houston/Galveston TX
637 AM CDT Sat May 26 2018

.AVIATION [12Z TAF Issuance]...

With only very little amounts of low stratus and/or fog developing
this morning, have gone ahead and taken most places that were at
MVFR originally up to VFR at the outset. The lone exception is
CXO, which has a history of BKN015, and there appears to be a
patch of thicker low clouds very near the site that could push us
back to an MVFR ceiling. Otherwise, have also added a brief VCSH
mention to GLS and LBX with showers cropping up fairly early this
morning. However, think decreased coverage relative to past days
will preclude needing a similar reference later today.

Some guidance suggests fog in the pre-dawn hours tomorrow. That
said, the same guidance was very aggressive with fog yesterday,
and that has largely not come to pass. Will hold off on any
mention of restricted visibility for now and give later shifts
more time to evaluate the true fog potential.



.PREV DISCUSSION /Issued 406 AM CDT Sat May 26 2018/...

.NEAR TERM [Through Today]...

Upper air analysis at 00Z has upper level ridge centered over
Mexico with northwest flow aloft over Texas. Water vapor imagery
shows a strong short wave trough dropping down through the
southern Plains into Texas which has initiated convection across
north Texas last night. Some of this activity continues to push
south to the north of the area while the central Texas prolific
hail producing supercell has already decayed. Cirrus blow off from
these storms should continue to drift into southeast Texas this
morning and has been limiting radiational cooling. Latest 08Z
observations still show temperatures in the upper 70s and
Galveston holding steady at 80F. Then there is Palacios with a
temperature of 82F dewpoint 77F or heat index of 90F. A certain
reminder that summer is here to stay and what is likely still
ahead of the area.

Forecast for today will keep high temperatures in the low 90s
with less cloud cover than the last couple of days. GOES
precipitable water imagery shows values of 1.6 to 1.8 inches
across the area. Shortwave trough over the southern Plains and
Ozarks will drop south into the mean trough over the Gulf. It
should shear out as it does so lift may be limited with the
system. Forecast will keep some 20/30 PoPs for areas east of I-45.
Again mainly looking for isolated showers and storms due to the
vorticity with the shearing shortwave and enough moisture.

.SHORT TERM [Tonight Through Monday]...

Upper level ridge is still expected to build over Texas and the
Plains as a closed low forms over the Great Basin upstream of the
ridge. Downstream of the ridge will be another weak closed low
that will support Sub-Tropical Storm Alberto. This system should
track towards the northern Gulf coast Sunday into Monday. This
will leave SE Texas in northerly flow aloft getting the subsidence
from the ridge. This means no rain chances for the Memorial Day
holiday and high temperatures getting into the mid 90s and may
need to go a degree or two higher into the upper 90s.

.LONG TERM [Monday Night Through Saturday]...

Model consensus through the coming week shows the upper level
ridge building through the week and peaking over the area by the
end of next week. Again will keep rain chances out of the forecast
due to the ridge and gradually increase high temperatures closer
to the century mark. Ensemble and MOS guidances from both the GFS
and ECMWF are holding steady with temperatures in the mid 90s but
wouldn`t take much for a few spots to hit 98-100 for the end of
the week.

Main weather messages this weekend and next week will be beach
and heat safety. People on area beaches need to be aware of
possible rip currents, especially true for Sunday to Tuesday time
frame when swells from Alberto could affect the coast and
increase the threat for rip currents. Being late May, high
temperatures in the 90s with the humidity puts heat index values
in the low 100s this weekend and approaching 105F for most of the
coming week. Even with heat advisory criteria at 108F for the
area, we may need to think about a heat advisory since we are
getting these conditions in end of May and beginning of June.



Moderate onshore winds look to give way to light southwesterly winds
to develop towards dawn from a weak land breeze influence. With
this, a diurnal pattern typical of the summer should set up for the
next several days, with the flip side of the cycle being afternoon
seabreezes turning winds back onshore. Seas will remain relatively
light through the weekend with the light to occasionally moderate

Seas may increase some next week, depending on the strength and
track of Subtropical Storm Alberto. At this time, the forecast
brings 4-5 foot seas into the offshore waters late Monday morning or
mid-day. This influence does not look to be significant closer to
shore, having little to no impact on tide levels. This should be the
extent of impacts of Alberto on our coastal waters. If your plans
take you to the central or eastern Gulf, continue to follow the
latest forecasts from the National Hurricane Center and local NWS



Subtropical Storm Alberto is located in the NW Caribbean near the
Yucatan Straight. It should track north and then northwest the
next couple of days with no impacts to SE Texas. The system will
continue to organize in the lower half of the atmosphere while
most of the convection will remain removed from the center to the
north and northeast with a broad upper level trough over the Gulf.
Just to clarify a subtropical storm is only different from a
tropical storm in its structure. A tropical cyclone will be a
fully warm core system with low pressure near the surface and high
pressure (ridging) aloft in which the ocean heat content and
latent heat release drive convection. Extratropical cyclones are
generally cold core in nature with low pressure at the surface and
an upper level trough (low) over top of it with lift driven by a
baroclinic zone and strong jet stream aloft. The subtropical
classification basically takes a warm core low at the surface so
that the heat content from the ocean and latent heat release drive
convection but there is a cold core upper level trough over top
of it. This trough also helps support convection due to
baroclinicity but generally allows for the convection to be
displaced from the surface low pressure center. In the end despite
classification, the impacts can be the same as a tropical storm
with tropical storm force winds, minor storm surge, flooding rains
inland and tornadoes. Alberto looks to be a heavy rainfall and
flood threat for much of the northern Gulf Coast from the
Mississippi delta to the Florida Panhandle.




College Station (CLL)  93  73  94  73  96 /  10  10  10   0   0
Houston (IAH)          93  74  94  75  95 /  20  10  20   0  10
Galveston (GLS)        87  79  90  80  90 /  20  10  20   0  10






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