Tornado Warning 27, NWS Houston/Galveston, TX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1151 AM CST Thu Nov 24 2022

...New AVIATION...

.SHORT TERM...
(Today through Friday Night)
Issued at 401 AM CST Thu Nov 24 2022

Currently, sea fog and low cloud ceilings are impacting Southeast
Texas as deep moisture advection from a 20-35kt LLJ is setting up
across Texas and pushing into the Southern Plains. These ceiling and
visibility impacts will persist throughout most of the day until the
pre-frontal trough pushes off the coast around midnight and washes
out sea fog along the coast. However, low ceilings will remain
through tomorrow.

Overall, the forecast is shaping up as expected. A mid level trough
over the 4-Corners Region of the Rockies continues to dig south and
will become a cutoff low in West Texas today and tomorrow. This will
generate a surface low over North Texas and a corresponding cold
front over Central and East Texas. At the same time, a southwesterly
300mb jet streak will place Southeast Texas in a favorable region
for upper level divergence which will enhance convection along this
front. With the cut-off low located over West Texas, this also puts
Southeast Texas in a PVA regime, which will also enhance convection
later today. These favorable forcing mechanisms will push south and
towards the coast as the pre-frontal trough also marches towards the
coast later today. At the same time, a warm front is draped across
our coastal counties, leading to some light rain showers south of I-
10 currently. This warm front will gradually lift north throughout
the day, bringing with it higher dewpoint air, an unstable airmass,
and low-level veering winds.

Sounds a little messy with several features to track, but to
simplify it as much as possible, showers and storms ahead of the
cold front that are currently located over the Brazos Valley will
push Southeast and towards the coast today. At the same time, the
warm front near the coast will lift north and towards the I-10
corridor. These two features are expected to converge and enhance
the potential for strong to severe storms and heavy rainfall. By
sunrise, most of southeast Texas has 20-40% rain chances with the
higher values across our northern counties where those pre-frontal
showers and storms will start to push south. Streamer showers near
the coast will push inland and bring some light rain showers as far
north as Conroe. The coverage of these showers and isolated storms
will continue to increase throughout the day. A few isolated
thunderstorms are possible this morning, but around 10-12pm, the
likelihood for thunderstorms gradually increases as the
aforementioned jet dynamics and PVA enhance this convection.
Therefore, by noon, we can expect widespread showers and scattered
storms for Southeast Texas. These rain chances don't begin to taper
off until around 9pm as the pre-frontal trough pushes off the coast.
Some lingering light showers are possible late tonight and through
the overnight hours as we remain in a PVA regime and a coastal
trough/low over the Corpus area starts to push east and into our
area. This coastal low will bring another round of heavy rain
showers and storms to our area on Friday, this time with showers and
storms originating west of I-45 and gradually pushing east
throughout the day on Friday. This coastal low will be slow to
depart until the cutoff low towards our west pushes it out later
this weekend.

Regarding the potential for strong to severe storms today, SPC has
placed most of of HGX in a Marginal Risk for severe storms. Although
there will be plenty of effective bulk shear at 50+ knots and enough
0-1km low level helicity at 150-200 m2/s2, SBCAPE and MLCAPE will be
lacking with values struggling to reach 500-1000 J/kg. Should some
of these storms become strong to severe, then the main hazards
expected will be a few isolated tornadoes (mainly south of Conroe
and offshore as waterspouts) and damaging wind gusts. The best
window for these strong to severe storms appears to be from 12pm to
6pm today.

In addition to strong to severe storms, there is also the potential
for heavy rainfall and flash flooding. High PW values above 1.6+
inches, 12,000ft warm cloud layers, upper level diffluence, and
"skinny" CAPE are just some of the few ingredients coming together
to enhance the potential for heavy rainfall today. Storm motion of
these showers and storms also seem to align parallel to the two
boundaries/fronts pushing through today which is why hi-res model
reflectivity is showing training storms developing. Overall, plenty
of ingredients are in place for WPC to put all of Southeast Texas in
a Slight Risk for excessive rainfall today. Expected rainfall totals
range from 1-3 inches, but a few bands of 5-7+ inches or higher is
possible where these training storms set up later today. It's hard
to pinpoint an exact location for these higher swaths, but the best
likelihood appears to be South of Huntsville and east of Brenham.
Moving onto tomorrow, a coastal trough/low will bring another round
of heavy rainfall to our area. Most of the aforementioned flash
flooding "ingredients" remain in place tomorrow as well, prompting
another Slight Risk for excessive rainfall from WPC and an
additional 1-3+ inches expected for most counties. Obviously, areas
that received higher rainfall amounts today as well as urban areas
will have a lowered threshold for flash flooding potential.

Given the Thanksgiving holiday today and people likely shopping for
the upcoming winter holidays tomorrow, it's important to monitor the
weather before heading out and to stay weather aware over the next
few days. Have an emergency plan in place, have multiple ways to
receive warnings, and make sure to never drive through water of
unknown depth.

Walts

&&

.LONG TERM...
(Saturday through Wednesday)
Issued at 401 AM CST Thu Nov 24 2022

This upper trough just will not quit me. Another long term shift,
and another day where it looks as if the trough looks to dig a
little bit deeper (Mexico, now!) and take a little bit longer to
eject. As it is, the long term begins in a similar spot, just a
little bit later, with likely showers and some embedded storms
across the area, gradually coming to an end through the day
Saturday as the low expected to form up in the remains of the
initial front ejects to the northeast along with the upper low.

With a sluggish initial front, the deeper dig of the upper trough,
and the development of a little coastal low, it looks like the
best we'll do for winds on Saturday is westerly. It'll take a
reinforcing front Sunday evening to well and turn winds more
northwesterly or northerly. Even here, the upper trough driving
this reinforcing front doesn't look to support a real deep cold
pool, so we'll probably get a chillier couple of nights this
weekend, and heck, the full sun will probably mean Saturday is the
cooler day of the weekend with a slow warming trend bringing us
into the new week.

Winds should be quickly back around to onshore on Monday as
surface high pressure makes its way east of the area, and aloft we
are under roughly zonal flow, with upper ridging to our east over
the Bahamas. This should accelerate the warming trend into
Tuesday, with widespread highs back into the upper half of the
70s...just in time for the next cold front to arrive, and this one
looks to have a beefier push behind it.

So...strong, dynamic front capable of supporting strong lift and
shear...potential for unseasonably high boundary layer warmth
enhancing instability...precipitable water around 1.5 inches, or
above 150 percent of normal...oh yeah, you bet we're starting to
tick the severe thunderstorm boxes. There's a lot of details to
work out here, and a ton of ways this scenario could break down,
so I don't want to speculate too much this far out. But if you're
looking at the extended SPC outlook and see that Day 6 "slight"?
Yeah, there's a reason for that, and something we'll have to keep
an eye on as the details resolve themselves.

Luchs

&&

.AVIATION...
(18Z TAF Issuance)

Issued at 1151 AM CST Thu Nov 24 2022

Periods of SHRA/TSRA and low ceilings can be expected with increasing
coverage/intensity gradually working its way toward the coast later
this afternoon and this evening. Ceilings could fluctuate with LIFR/
IFR/MVFR possible. Winds will shift to the N and NNE this afternoon
through early this evening, and this could help to improve visibilities.
Less rain coverage is anticipated tonight, especially near the CLL
and UTS areas. More scattered development can be expected tomorrow,
but at this time tomorrow night through Saturday morning looks like
the next best chance of SHRA/TSRA.

42

&&

.MARINE...
Issued at 401 AM CST Thu Nov 24 2022

Areas of sea fog, dense in some areas, has developed on the
nearshore waters, as well as both Galveston and Matagorda bays
tonight. This fog is expected to continue on and off through late
Friday night. An approaching storm system will generate multiple
rounds of showers and thunderstorms to finish off the holiday
week. The first round is expected today, particularly in the
afternoon as a front drops into the area. The next round is
expected Friday into Friday night as the front stalls and a weak
coastal low develops among the remnants. Though visibilities will
improve with the onset of rain, some of the storms on Thursday
could be strong at times with locally stronger and variable winds.
On Saturday, look for that weak low to lift north of the area,
ending rain and bringing moderate to strong west winds in its
wake. A reinforcing front on Sunday will continue to veer winds to
northwesterly and northerly. However, onshore flow will quickly
resume and strengthen Monday.

Luchs

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)	  70  59  62  55 /  90  70  70  90
Houston (IAH)			  73  62  66  59 /  90  70  70  90
Galveston (GLS)			  72  64  67  62 /  80  70  80  90

&&

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

Special Weather Statement
National Weather Service Houston/Galveston TX
206 PM CST Thu Nov 24 2022

TXZ213-227-237-242030-
Inland Brazoria TX-Inland Harris TX-Fort Bend TX-
206 PM CST Thu Nov 24 2022

...A strong thunderstorm will impact portions of southeastern Fort
Bend, northern Brazoria and south central Harris Counties through 230
PM CST...

At 205 PM CST, Doppler radar was tracking a strong thunderstorm over
Brazos Bend State Park, or 14 miles south of First Colony, moving
northeast at 40 mph.

HAZARD...Winds in excess of 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Western Pearland, southeastern Sugar Land, Missouri City, Alvin,
Stafford, Manvel, Fresno, Arcola, Iowa Colony, Fairchilds, Thompsons,
Westbury, Fifth Street, Sienna Plantation, Riverstone, Fort Bend
Houston, Fondren Gardens, Brazos Bend State Park, Meyerland Area and
southwestern Central Southwest.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 2925 9566 2941 9578 2968 9548 2941 9524
TIME...MOT...LOC 2005Z 234DEG 33KT 2937 9565

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH