729
FXUS64 KHGX 110933
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
433 AM CDT Sat May 11 2024

...New SYNOPSIS, SHORT TERM, LONG TERM, MARINE...

.SYNOPSIS...
Issued at 433 AM CDT Sat May 11 2024

The unsettled, frequently rainy pattern that has been a prominent
feature recently doesn`t appear to really being going anywhere
anytime soon. Over the next week, we can expect multiple
opportunities for showers and thunderstorms around Southeast
Texas. Given all the recent rain and lingering flooding issues on
the Trinity and Brazos rivers, we`ll certainly need to be on the
lookout for the aggravation or return of flooding concerns, and
some of the week`s stronger storms will carry some potential for
severe weather as well. A quick summary of what to look for:
- Amongst the broader unsettled pattern, we`re looking at two
  windows with relatively higher potential for locally heavy rain.
  The first is Sunday into Monday. The second is later in the
  week, Wednesday into Thursday. WPC highlights at least a portion
  of the area with a slight risk of excessive rainfall (threat
  level 2 of 4) for both Sunday and Monday. There is also a
  portion of the area highlighted in their Day 5 outlook with a
  slight risk.
- These same windows will also have to be watched for some
  thunderstorms becoming strong to severe. On Sunday, SPC`s severe
  weather outlook indicates a marginal risk area across Southeast
  Texas (threat level 1 of 5), which increases to a slight risk
  (threat level 2 of 5) on Monday. There is also some concern
  about the midweek window mentioned above, but there is not
  enough confidence yet to highlight a specific threat level at
  this time.

&&

.SHORT TERM...
(Today through Sunday Night)
Issued at 433 AM CDT Sat May 11 2024

We ended up having to make some changes to the forecast today which
lead to increased rain chances, particularly across the southern
half of the CWA. So let`s talk about it! Sfc high pressure dominates
the low levels this morning. Northeast flow on the east side of the
high has pushed drier dew points (50s and 60s) down into SE TX.
Therefore, conditions should feel relatively pleasant early this
morning. As the aforementioned high progresses east, LL flow will
veer more easterly. Meanwhile offshore, a building gradient between
the high to the north and lower pressure over S TX will result in
increasing easterly winds. For those of us on land, this will impact
us in two different ways. 1) Expect conditions to become quite
breezy at the coast, possibly gusting to around 30 MPH this
afternoon at the beaches. 2) A LL convergence zone will become
enhanced over our coastal counties, possibly providing enough lift
for shower and isolated thunderstorm development by the afternoon.
Large scale forcing won`t be too impressive today. However, PWs
across our southern / coastal counties may be approaching 2.0 inches
as early as this afternoon. These PWs coupled with the LL
convergence and weak disturbances embedded in the flow aloft have
warranted the addition of PoPs in today`s forecast. Today`s PoPs
range from ~10% over the Piney Woods to ~20% for the I-10 corridor
and ~30% near the coast. Model guidance varies a lot with today`s
precip. If the NBM had its way, I wouldn`t have added PoPs.
Meanwhile, many of the overnight HRRR runs suggest that our current
PoPs could be conservative. Temperatures this afternoon are expected
to warm into the low/mid 80s.

The strong easterly winds across the Gulf Waters and adjacent coast
will ease as we head into this evening, weakening LL convergence
over our coastal zones. However, a stalled frontal boundary offshore
is expected to lift northward as a warm front overnight,
reintroducing LL convergence to the area. Meanwhile, a mid/upper
trough over SW CONUS will approach from the west. Large scale lift
and mid/upper shear will gradually increase as a result. The trough
will also induce a sfc low over Kansas and Oklahoma. Deep, moist, LL
S to SE flow ahead of the low will result in a PW surge across SE
TX. ECMWF deterministic / ensembles guidance is particularly
aggressive with this surge, showing widespread PW values of at least
2.0 inches by Sunday morning. GFS global/ensemble guidance as well
as HREF means are a tad more conservative (though still quite juicy)
with widespread 1.8-2.0 inches. While the lower levels remain warm
and moist, the upper levels are likely to cool as the trough
approaches. Guidance indicates there will be no shortage of LL/ML
instability, setting the stage for deep convection Sunday afternoon
and evening. There does appear to be some model variance regarding
how far south deep convection will occur on Sunday with the GFS
keeping it over our northern counties while the ECMWF shows areas as
far south of I-10 partaking in the action. This is why Sunday`s PoPs
are highest over the northern CWA, ranging from 80-90% in our Brazos
Valley / Piney Woods counties, to 70-80% near I-10, and 50-60% near
the coast.

The primary concern on Sunday will be heavy rainfall. WPC has kept
much of the region under a Slight Risk (Level 2 of 4) for excessive
rainfall on Sunday. Our southwest most counties near Matagorda Bay
are under a Marginal Risk (Level 1 of 4) of excessive rainfall.
Given the instability and shear parameters, we cannot rule out
locally strong to severe thunderstorms. Hail and damaging winds will
be the primary concerns. The impact Sunday`s rains have on our SE
TX rivers will largely depend on where the heaviest showers /
thunderstorms occur. There exists some uncertainty regarding the
exact location of these storms. But generally speaking, the best
chance of heavy rainfall will be north of I-10.

&&

.LONG TERM...
(Monday through Friday)
Issued at 433 AM CDT Sat May 11 2024

If you`re looking for the long term portion of the forecast to
give you some fairer weather to look forward to...I haven`t got a
whole lot to give you. Although if you read the synopsis section
up top, you probably already know I don`t have much to offer but
more chances for showers and storms.

While Sunday`s activity does look to generally move off to the
east, we`ve still got ourselves an upper trough over the Great
Plains to deal with on Monday. While I certainly won`t stop you
from hoping that Sunday`s rains work over the atmosphere, you also
won`t find me promoting any of that hope, either. Low level flow
looks to stay primarily onshore to continue pumping in warm and
humid boundary layer air, and mid-level heights look to fall with
the upper trough making its way across the Plains. This should
hammer out a thicker CAPE profile for us, with NBM SBCAPE numbers
in excess of 3000 J/Kg. and largely create an environment that
just reloads for another round of showers and storms, and likely
is one that could better support severe weather than Sunday.

Indeed, with such ample moisture and instability, the primary
bottleneck on severe potential might actually be that we get
convective initiation too early and too numerous, creating a
situation where many storms are battling for "clean" air, and
only allowing fewer individual cells to fully realize their
potential. That`s...not an ideal way to do it, especially since we
are already dealing with lingering flooding issues that Sunday
will aggravate, and will only be further aggravated by numerous
storms on Monday. We can likely peg the primary hazard to be large
hail earlier in the day thanks to the instability present - though
if things do cluster on an incoming front, that may be far enough
back to largely spare us of that threat, except for up in our far
north/northwest. That threat will likely shift to damaging wind
gusts later, as storms grow upscale into some sort of convective
complex. I don`t want to write of tornado potential entirely, and
that will pose a secondary threat...but the anticipated evolution
here has me focusing more on the hail and wind hazards.

Tuesday, at least, does give us a brief break from this seemingly
unending train of storm events. A weak front (weak, weak, all
these fronts are weak) will usher Monday`s storms off to the east,
and give us (most of) a day with offshore winds and a modest
decrease in humidity. I`m not too confident we`ll actually see
temperatures drop at all...and may even be warmer than the
days before and after if enough sun can break in. In fact, this is
explicitly in the forecast, where Tuesday is arguably one of the
warmest days of the week across the area with a mostly sunny sky.
I didn`t even have to step in and force it on this one. It`s so
obvious that this outcome popped right out of the deterministic
NBM output. Often I find myself have to make some sort of tweaking
to the NBM`s numbers to better highlight this scenario, but not
this time...I largely just let its temperatures ride this time
around.

Don`t get too used to Tuesday, though. In fact, you`ll want to
savor it. Onshore winds return quickly, by Tuesday night most
likely. This will put us back into an environment ready to support
showers and thunderstorms again, we`ll just be waiting for the
next instigator to move in. That will likely be in the form a
shortwave trough, and that should move in at some point on
Wednesday. I`ve got PoPs coming up as early as Wednesday
afternoon, but for now, it appears that Wednesday night into
Thursday is the prime time to look for. Wednesday during the day
may yet be a little too early - though Tuesday`s post-frontal
airmass isn`t very effective at scouring out moisture, it may
knock precipitable water down just enough that Wednesday will be
more iffy, while both the NAEFS and Euro ensembles prog
precipitable water to be back up around or above the 90th
percentile late Wednesday night into Thursday. At this point,
we`re at too far a range and models have too much spread to be too
confident in specifics, but the increase in moisture certainly
points to another locally heavy rain threat emerging, though
it looks like it would be the less significant one of the week?
That`s starting to get a bit speculative, though. Similarly
speculative would be a severe threat. I see some of the
ingredients there - the Euro ensembles Extreme Forecast Index does
show a signal for an enhanced CAPE and shear environment, so we`ll
have to watch and see how things play out in the days to come.

&&

.AVIATION...
(06Z TAF Issuance)
Issued at 1101 PM CDT Fri May 10 2024

VFR conditions continuing through tonight. Light patchy fog
possible overnight. Light easterly winds will continue, becoming
easterly to southeasterly through Saturday. Clouds will increase
Saturday night as moisture funnels into SE TX. CIGs begin to
transition to MVFR around 20Z.

&&

.MARINE...
Issued at 433 AM CDT Sat May 11 2024

Moderate northeasterly winds will modestly increase and veer more
easterly through the day today, with an attendant increase in
seas. This will lead to conditions in which small craft will need
to exercise caution through at least the evening. Conditions are
expected to degrade enough, that any additional increase in winds
or seas over what is expected will necessitate a small craft
advisory. Some low rain chances may begin to creep into the
picture as early as today, particularly around the coast.

More shower and thunderstorm activity is anticipated Sunday into
Monday. Tuesday looks to feature some fairer weather and a brief
amount of offshore flow, but onshore winds return quickly,
followed shortly by the next window for showers and storms and
poorer marine conditions.

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)  84  68  80  71 /  10  30  80  50
Houston (IAH)  84  69  82  73 /  20  30  80  50
Galveston (GLS)  81  74  81  76 /  30  40  60  30

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Should Exercise Caution through this evening for
     GMZ350-355-370-375.

&&

$$

SHORT TERM...Self
LONG TERM....Luchs
AVIATION...Adams
MARINE...Luchs