Special Weather Statement, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1218 PM CDT Fri Jun 4 2021

.AVIATION...
A cluster of showers and thunderstorms, anchored near the coast
will gradually expand inland this afternoon but not much
confidence on how far inland as a weak coastal trough is basically
stationary and serving as a focus for additional development. No
lightning has been reported and lightning will be less common as
convection remains low topped. A mix of MVFR/VFR ceilings expected
today into this evening with IFR ceilings developing over the
north later tonight. Models trending drier for Saturday but will
maintain a VCSh for now. 43

&&

.PREV DISCUSSION... /ISSUED 504 AM CDT Fri Jun 4 2021/

SHORT TERM [Today Through Saturday Night]...
Heavy rains moved out into the Gulf last night and early this
morning. But a low moving along the coast early this morning is
also producing strong gusty onshore winds. These winds should be
relaxing by mid morning as low fills in and shifts east. Storms
this morning should be focused mainly over the coastal areas.
Daytime heating will help in the development of showers and
eventually thunderstorms late morning but more likely this
afternoon and evening. At this point the short term guidance has
really struggled on where rainfall was occurring and where it was
to develop and have gone with the assumption that the airmass got
worked over big time yesterday with the 2-6" of rain and moisture
shifted into the Gulf - the 925-850 flow will be increasing late
this afternoon and becoming more southerly pulling back the
moisture. Scattered showers and thunderstorms will be possible but
the heavy rainfall/greater rates will likely not reach the levels
of yesterday. The forecast could need some serious alteration as
confidence is low with how this plays out as storms could mainly
focus in the Gulf ... with the possibility that coverage is less
and lighter inland. Holding off on a Flash Flood Watch for now.

Tonight a s/w moves in from the southwest and this will likely
lead to an increase in showers and thunderstorms and then surge
inland Saturday 8am to 1pm. This may warrant a Flash Flood watch
if this continues to be the forecast as the models home in on the
solution. Rainfall rates will probably be greater on Saturday
gradually shifting east into the nighttime hours.

Temperatures will remain on the cooler side with the abundant
cloud cover and periods of rain.

45

LONG TERM [Sunday Through Thursday]...

The prevailing upper trough will continue its slow westward jog,
with its axis reaching SE TX by Sunday. While this will take the
area out of the left exit region of the associated upper jet streak
(thus losing favorable upper divergence for sustained heavy
rainfall), sustained onshore winds will nonetheless continue to
supply the area with ample Gulf moisture. Total PWs will remain in
the 1.75-2.0 in range on Sunday, with these values persisting into
the early part of next week. A series of shortwaves embedded within
the upper flow will continue to traverse the base of the longwave
trough, resulting in multiple periods of showers and storms on
Sunday and Monday. With upper-level support now favoring areas to
our east, QPF values across global model solutions diminish and the
threat of heavier rainfall diminishes slightly. Despite this, those
with any travel or outdoor plans should continue to monitor the
latest forecast information as additional clarity should be gained
when we enter into the time domain of mesoscale models later this
weekend.

While the amplitude of the upper trough looks to diminish slightly
as it continues its gradual eastward motion into the early part of
next week, a tightening of the surface pressure gradient as lee
cyclogenesis occurs in the eastern Rockies will increase onshore
flow over the Gulf of Mexico. ECMWF indicates a more robust increase
of total PWs compared to the GFS, showing 2+ in values over much of
SE TX by late Monday. Nonetheless, with values at least in the
vicinity of 2 in as additional shortwave axes traverse the region,
the potential for locally heavy downpours will continue through
Tuesday. WPC has backed off slightly on QPF values in accordance
with recent model trends, forecasting values of 3-5" over the next 5
days. That being said, we continue to monitor the potential for
flash flooding as this situation evolves in the coming days.

Upper ridging will begin to build into the central CONUS, albeit
slowly, by mid-week. Despite this, precipitation chances will
continue with the support of diurnal processes as moisture
availability remains plentiful. Drier conditions look to finally
take hold towards the end of the week.

Temperature forecast remains similar to the trend of late, with
daytime highs generally unchanged in the mid-upper 80s and nighttime
lows in the lower to mid-70s.

Cady

MARINE...
Messy with surface low near the coast and have hoisted an SCA for
the nearshore waters and Galveston bay. Storms over the Gulf move
east and start reloading for the next system arriving from the
southwest Saturday. Should be active over the Gulf waters Saturday
as this moist axis traverses the coastal waters. Winds of 5-15
knots should prevail through the weekend.
45

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      79  69  80  69  85 /  60  60  80  50  60
Houston (IAH)              80  70  80  71  85 /  70  60  80  40  60
Galveston (GLS)            82  74  80  76  83 /  70  80  80  50  60

&&

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

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

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