999
FXUS64 KHGX 251937
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
137 PM CST Sat Jan 25 2025

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

.SHORT TERM...
(This evening through Sunday Night)
Issued at 1247 PM CST Sat Jan 25 2025

This weekend`s rainfall event has moved from the long term to the
short term, and so too have I switched to the short term. We still
look on track for conditions to begin to degrade as early as
tonight ahead of a lumbering cold front, with first some light,
quick streamer showers emerging. Those showers will give way to
widespread shower (and isolated thunderstorm) development ahead of
and along this slow-moving front.

Rainfall potential will take up the bulk of this discussion
section, so let`s get all the other stuff out of the way in this
paragraph. It`s already overcast across the area, and that won`t
change for the rest of the period. Temperature-wise, we were able
to kick the freezing temp habit for all but isolated spots, but
tonight will be something else entirely: lows tonight will not
look very different from yesterday`s high temperature map!
Tomorrow night looks a bit cooler as some colder air begins to
filter in behind the front, but lows still look to range from the
mid-40s to the mid-50s. In the daytime, we are pretty on track to
see highs from around 60 degrees up north to the mid/upper 60s on
the coastal plain. Despite the clouds and rain, highs near the
coast tomorrow look even a bit warmer, with some spots not too far
inland from the coast reaching for 70 degrees. Highs should be
held back some up north as the front, slow as it is, will likely
be through early enough to keep temps chopped down in the 50s/low
60s.

Okay, now, the rain. We`ve had a roughly area-wide marginal risk
(threat level 1 of 4) for Sunday going on several days now, and
that has not changed today. What has changed is that we are now
within the range of high-res, convection-allowing models, so we
can look into that stuff some. The HREF mean precipitable water
numbers are in the 1.25-1.5 inch range, which is right there in
line with what we were getting out of the global deterministic and
ensemble guidance the last few days. As a reminder, while not
mind-bogglingly high on the grand scale of our expectations, this
type of moisture is still at/above the 90th percentile for this
time of year. Also meaningful, the 10th percentile HREF PWATs are
still in the 1-1.4 inch range. So even if moisture return is
lousier than expected, we`ve still got some unseasonably high
PWATs in the area, at least closer to the coast.

Another thing I`ve been focusing on with Gulf inflow is not just
moisture return, but how strong the flow may create widespread,
quality convergence against the incoming front. 850 mb winds are
pretty beefy today, with inflow of 30+ knots. However, those
numbers look to diminish tonight, and are down to the 20-25 knot
range tomorrow. That`s actually a bit higher than the globals had
yesterday, but one thing continues to stand out to me: this flow
is also veered a bit west of due southerly. This likely isn`t
veered enough to funnel in dry air, but it does provide two mixed
messages for us. One is that flow less perpendicular to the
incoming boundary will mitigate the tendency for low level
vertical motion, and could inhibit rain rates some. That`s good!
But more boundary-parallel flow will also encourage training,
so...we could be trading a bit off the rate for a longer duration
of whatever the higher rates end up being. That`s bad! If you get
frogurt, you can have your choice of toppings. That`s good! The
toppings contain potassium benzoate (That`s bad).

So...enough environment talk, how much is it going to rain? Well,
the lingering uncertainties still make it hard to get too precise
with it, but we`ve got some good ideas at this point. A widespread
half-inch to inch of rain broadly across the area seems like a
solid place to anchor yourself. The HREF`s 10th percentile does
show that if rain fizzles out before reaching the coast, we might
not get very much near the Gulf, but even that low-end portion of
the distribution is showing a quarter to half-inch across the
rest of the area. The HREF mean is not showing a big wash-out even
in the peak area along the coastal plain - only 1.0-1.2 inches
total. This is less than my forecast QPF, which gets up to around
1.75 inches at the high end.

But that mean is necessarily going to wash out some isolated high
totals. Let`s have some real fun and explore the HREF max! Members
of the HREF ensemble are peaking out in the 3-4 inch range, which
seems like a reasonable spot for the very highest totals in the
area to fall. Those kinds of numbers won`t be very common at all,
but uncommon doesn`t mean non-existent. Given the environment and
moisture, we could expect a couple measurements to realize this
potential. Another thing to consider is rain rate. Probability-
matched mean 3-hour QPF in the HREF does get up to 1.5 inches in
some locations from Wharton County northeastward to Polk County
Sunday afternoon and evening. And while this is a 3 hour window,
there`s a good chance most of that would fall more quickly. Given
the cold, relatively saturated grounds, this kind of rain rate
would transition to runoff pretty quickly. In a probabilistic
sense, that corridor sees a solid signal of around 30 percent for
more than an inch of rain in three hours, but fortunately is less
than 10 percent for exceeding 3 inches.

All in all, this paints a picture that is pretty much in line with
what we`ve been expecting of late. It`s gonna rain. It`s gonna
rain at least some pretty much everywhere. We could see some
heavier amounts of rain, which will more effectively convert to
runoff on the cold, saturated grounds of the area. Confidence is
not high on where specifically heavier rain would fall, but
indications are that the best potential is along the coastal plain
from Wharton County to Polk County, including the Houston metro.
Should isolated heavy rains fall on a vulnerable spot, we could
see flooding concerns emerge in those spots.

Okay, I think that`s all I got. Time for the long term. I hope
you`re not expecting to get a break there, because...it`s not
happening.

Luchs

&&

&&

.LONG TERM...
(Monday through next Friday)
Issued at 1247 PM CST Sat Jan 25 2025

Warmer weather and rising rain chances can best summarized the
forecast trend for next week. On Monday, we`ll start off with
surface high pressure draped over SE Texas/Northern Gulf coast,
courtesy of a recent cold front. We could see some showers early
in the day as that weak cold front pushes off the coast, though
thereafter we should see a lull in rain chances. Onshore flow
returns by Tuesday, with PWs rising to 1.0-1.4" over SE Texas. The
return of WAA and isentropic lifting, paired with some weaker
impulses aloft should bring periods of isolated rain chances on
Tuesday. Those impulses aloft come from a mid/upper level cutoff
low, which starts out over southern California/Four Corners/Baja
California. This system will slowly work it`s way east over the
next several days, taking on a Rex-Block pattern as ridging sets
up north of the cutoff low. Showers become more widespread and
persistent from Wednesday and onwards.

Thursday and onwards begins to look especially soggy. A deeper
trough to the northwest looks to push a cold front into SE Texas.
Deterministic guidance suggests that this boundary could stall out
over our area, or push offshore and stall out over the Gulf. Even
still, some of those more optimistic solutions depict the boundary
lifting back north as a warm front/coastal trough near the end of
the work week. Bottom line, guidance is entertaining the idea
that a stalled frontal boundary remaining in place over SE Texas,
which can act as a forcing feature to produce locally heavy rains.
Though thats not the only factor looking to enhance rainfall
rates, as PWs should reach 1.3-1.8" over the area (varying by your
model of choice). A low level jet of ~40 knots begins to set in
over the area on Thursday/Friday, with diffluence developing aloft
as the aforementioned low tracks eastward. Forecast soundings
show deep saturation and skinny MU cape profiles for both Thursday
and Friday. Even this far out, we`ve sort of checked off every
box in the "heavy rainfall" category outside of slow corfidi
vectors (which are too high at the moment). Ensemble table for
NAEFS, GEFS and ECMWF showing PWs above the 90th Climatological
and M-Climate percentile, approaching the all-time max for this
time of the year during some periods. Guidance suggests that this
possible heavy rain threat comes to a close late Friday
night/early Saturday, though LREF cluster analysis for day 7 shows
higher heights in the parent ridge of the rex block (cluster 1 &
2), with higher highs preceding the cutoff low (cluster 2),
suggesting a slower departure compared to the grand ensemble. This
suggests that the coastal trough and heavier rainfall may require
a bit more time to depart the area off to the east.

We`re several days out from this next bout of rainfall so a lot can
change. Signs point towards a relatively soggy period beginning
Wednesday, with the potential for locally heavy rainfall from
Thursday through Friday night. Street flooding is within the realm
of possibility with this pattern, though we`ll get a better idea of
the specifics with this rainfall heading into next week.

03

&&

.AVIATION...
(18Z TAF Issuance)
Issued at 1132 AM CST Sat Jan 25 2025

Still VFR across SE TX at mid-day, but we will gradually slide
into MVFR conditions this afternoon, and likely IFR conditions
later tonight. Toss in rain chances as moisture surges into an
incoming - but likely slow-moving - cold front, and we`ve got the
recipe for a TAF mess. For lack of a better way to do this, a list
of bullet points for the cycle:
- Look for lowering cloud bases this afternoon, sliding into MVFR
  21Z (ish) and even to low MVFR this evening, 00Z (ish).
- Gusty winds are already developing at issuance time, and
  10-15G20-15 should be expected until evening.
- Later this evening, moisture surges enough for some streamer
  showers to develop. This should be mostly west of the TAF sites
  with best potential to CLL, SGR, and LBX. However, think there`s
  enough of a chance that a PROB30 is in place at all sites.
- Cloud bases continue to lower, reaching IFR overnight.
- Front comes into the picture late tonight into tomorrow,
  expected to be moving slowly. Uncertainty in precise speed makes
  specific timing difficult right now, so the SHRA windows are
  broad. Hoping future shifts will be able to tighten this up.
- I`d expect a few lightning strikes here and there, but
  environment is generally not very supportive of thunderstorms,
  and so do not have any mention of TSRA explicitly in these TAFs

Luchs

&&

.MARINE...
Issued at 1247 PM CST Sat Jan 25 2025

Light to moderate onshore winds will occasionally warrant caution
flags ahead of an approaching cold front this weekend. Periods of
scattered showers and isolated storms possible today and tonight,
with rainfall becoming more widespread across the Gulf Waters on
Sunday as the front pushes towards the coast. Patchy sea fog will be
possible in the bays and nearshore waters ahead of this front,
mainly from dusk to dawn if winds end up being calmer. Northerly
winds set in behind the front with a lull in rain chances setting
in early next week as the cold front stalls offshore. Onshore
winds return by Tuesday, with winds and rain chances increasing
throughout the work week. Patchy sea fog could also return during
this period if winds stay low enough. Widespread rain chances and
locally heavy rainfall will be possible with a stronger
disturbance arriving on Thursday, continuing through Friday ahead
of a cold front. Lower tide levels will be possible at low tide
Sunday morning through mid next week.

03

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)  54  59  46  60 /  70  80  50  10
Houston (IAH)  55  67  52  63 /  50  90  70  20
Galveston (GLS)  57  64  53  60 /  30  60  50  20

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Should Exercise Caution until 9 PM CST this evening
     for GMZ350-355-370-375.

&&

$$

SHORT TERM...Luchs
LONG TERM....03
AVIATION...Luchs
MARINE...03