Severe Thunderstorm Warning 140, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
358 PM CDT Sun Jul 9 2017

.DISCUSSION...
Scattered showers and storms again today, and this pattern should
be expected for another couple of days until upper ridging builds
heights over the area and rain chances are tempered a bit later in
the week. Continued temperatures in the 90s can be expected.

.NEAR TERM [Through Tonight]...

Showers and storms are erupting, mainly along and east of the I-45
corridor. The storms are largely clustering in two locations -
from roughly Huntsville northward, and another emanating from
Galveston Bay. These two clusters coincide with the best
instability - the quieter areas have relatively lower MLCAPE
(1000-1500 j/kg) and even a small area shows some convective
inhibition. Suspect that means these two clusters will be the
primary focus for strong storms in the immediate term. But,
despite the lower instability elsewhere, there is still enough to
support storms, and outflow from these initial storms may be
enough to kick off continued activity into the evening hours.

Despite sufficient instability, SPC Mesoanalysis shows that both
deep layer and low level shear is relatively weak. This lack of
shear will inhibit potential for organized updrafts and make
severe wind and hail relatively unlikely. However, that does not
mean it is completely impossible. In these pools of deeper
instability, gusty and maybe even severe winds could be generated
by a particularly strong pulse storm as seen just north of our
area in Henderson and Anderson counties, as reported by the Fort
Worth forecast office. Additionally, today's storms are producing
plenty of dangerous lightning, and in air of precipitable water
around 2 inches (per GOES-16 PW product) and slow storm motion,
locally heavy rainfall are threats even in the absence of any of
more "conventional" severe weather.

This activity can be expected to continue into at least the early
evening, and should wind down later in the evening, dying down
likely around or after 9pm.

.SHORT TERM [Monday Through Tuesday Night]...

For the next couple of days, we look to remain in a relative
midlevel weakness in the height field as we have the past couple
of days, while at the surface, onshore flow continues on the edge
of high pressure to our east. As a result, Monday and Tuesday are
likely to be very similar to yesterday and today. The forecast is
a little bit cloudier, and so did nudge temperatures a bit below
the levels we've seen recently, but not much, and still right
around seasonal averages. As far as convection goes, we'll largely
be continuing the diurnal pattern, with the seabreeze and remnant
outflow boundaries providing the most likely foci for new storms.
With much of the recent storms occurring in the eastern half of
the area, will continue the keep higher PoPs in the east - with
more remnant boundaries from past convection, it seems more likely
to get development to continue for the next day or so. Also,
models prog the west-east gradient in precipitable water to
continue.

.LONG TERM [Wednesday Through Sunday]...

In the second half of the week, the GFS and Euro seem to have
gotten on board with an idea of midlevel ridging building westward
to put a flat 591/594 ridge to our north. Its proximity implies
increased subsidence that will help to suppress diurnal
convection. But, continued deep onshore flow and only a modest
step down in PW will likely keep at least isolated showers and
storms in the picture. Have tapered rain chances down as the week
goes down, but still keep some in place, focused mostly on forcing
provided by the seabreeze. As heights at 850 through 500 mb rise,
also begin to nudge temperatures back upwards, above average.

Uncertainty continues to reign at the end of the forecast period
(real shocker there, I'm sure). By this weekend, both the Euro and
GFS break down the ridge as a midlevel vort max pushes westward
across the Gulf of Mexico. The Euro even goes so far as to
generate a (very weak) surface circulation underneath it. To lend
some support to this, NAEFS shows 1000 mb heights around or below
the 10th percentile. Are we looking at a tropical cyclone here?
Nothing at this time suggests it, but I also am not going to trust
a vort max moving in from the east this time of year, so it's
something I'll be keeping my eye on in the coming days. Both
deterministic models have well timed upper troughs to yank
anything there away - as does the GEFS mean and, to a lesser
extent than I'd like to see, the EPS mean. In this period, the
NAEFS also shows near surface temperatures at the 99th percentile,
so continued heat into early next week is also in the picture,
though that may be altered if we see more significant amounts of
convection from an incoming surge of moisture.

&&

.AVIATION [18Z TAF Issuance]...

SHRA/TSRA developing across the area after reaching 91-93 degrees.
Gusty winds will be likely with the stronger storms. So far those
have been confined to the coastal areas but storms over the north
as heating intensifies should become stronger gust producers. Area
terminals will see impacts from VCTS to MVFR VISBY and gusty winds
with the passage of storms. Will probably see two windows for
storms...the first is this afternoon with a second window as
storms to the north likely coalesce and push southward through
CLL-UTS-CXO 00-04z and may reach IAH/DWH area around 03-05z. Will
carry a PROB30 for this as confidence is growing. Overnight may
see some patchy MVFR CIGS CXO-UTS-CLL as flow backs and rain
cooled moist air saturates below 2500ft.
45

&&

.MARINE...

Storms tapering off quickly over the water but still developing
along the baybreeze/seabreeze intersection near Pasadena. This may
make for some variable gusty winds around the northern portions of
Galveston bay for another hour or two.

Tonight will be watching storms over SETX moves southward and could
potentially reach Galveston bay after 9 pm. Otherwise this looks
like rinse and repeat for the most part through Wednesday.
Landbreeze (with westerly flow) edging offshore before seabreeze
develops around noon-2 pm and southerly flow returns. Winds should
be increasing a few knots by mid week but still well below SCEC.
45

&&

.PRELIMINARY POINT TEMPS/POPS...

College Station (CLL)  76  96  77  96  75 /  30  30  20  30  10
Houston (IAH)          78  94  78  94  77 /  20  50  10  40  20
Galveston (GLS)        82  89  82  89  81 /  20  40  10  30  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...

TX...None.
GM...None.

&&

NEAR TERM...Luchs
SHORT TERM...Luchs
LONG TERM...Luchs
AVIATION...45
MARINE...45

Hazardous Weather Outlook
National Weather Service Houston/Galveston TX
343 AM CDT Sun Jul 9 2017

TXZ163-164-176>179-195>200-210>214-226-227-235>238-100845-
Austin-Brazoria-Brazos-Burleson-Chambers-Colorado-Fort Bend-
Galveston-Grimes-Harris-Houston-Jackson-Liberty-Madison-Matagorda-
Montgomery-Polk-San Jacinto-Trinity-Walker-Waller-Washington-
Wharton-
343 AM CDT Sun Jul 9 2017

This hazardous weather outlook is for portions of Southeast Texas..

.DAY ONE...Today and Tonight

Scattered showers and thunderstorms will again be possible today.
The storms could be slow moving and locally heavy rain will be
possible in the stronger storms. In addition, some of the stronger
storms could produce brief gusty winds late this afternoon.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Scattered showers and thunderstorms will persist on Monday and
Tuesday. Storm motion will again be slow so a few of the stronger
storms could produce locally heavy rain.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

GMZ330-335-350-355-370-375-100845-
Coastal waters from Freeport to the Matagorda Ship Channel out
20 NM-Coastal waters from High Island to Freeport out 20 NM-
Galveston Bay-Matagorda Bay-
Waters from Freeport to the Matagorda Ship Channel from 20 to
60 NM-Waters from High Island to Freeport from 20 to 60 NM-
343 AM CDT Sun Jul 9 2017

This hazardous weather outlook is for portions of Southeast Texas..

.DAY ONE...Today and Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

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