Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 211202
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
702 AM CDT Thu Mar 21 2024

...New AVIATION...

.SYNOPSIS...
Issued at 349 AM CDT Thu Mar 21 2024

A typical springtime week around Southeast Texas, with roughly
seasonable temperatures, and a mix of fair weather stretches and
windows for showers and storms. Of course, springtime storms
frequently carry potential for severe weather and/or flooding, and
right now is no different. Here are some key points for today and
beyond:

- Showers and thunderstorms become something to watch for very
  early this morning, and carry through the day today. The bulk of
  our area has a slight risk for severe weather (threat level 2 of
  5), with a marginal risk (level 1 of 5) around and north of Lake
  Livingston. The primary hazard from the strongest storms today
  will be large hail. Damaging wind gusts are a secondary threat.
  A brief tornado can`t be ruled out near the coast, but even
  there is a tertiary threat behind the other two hazards.
- In addition to severe weather, locally heavy rainfall is
  possible from the day`s strongest storms. Should the heaviest
  rains fall over vulnerable, poor-drainage locations, some
  isolated spots of ponding and minor flooding could emerge.
- After a weekend of fair weather, look for another shot for rain
  and storms on Monday with a frontal passage. In a bit of a
  mirror to today`s activity, it is beginning to look as if the
  focus for Monday`s action will be farther north towards the
  Pineywoods.

&&

.SHORT TERM...
(Today through Friday Night)
Issued at 349 AM CDT Thu Mar 21 2024

Well...

Not a lot going on over SE TX at this time, but this should be chang-
ing soon enough given the trends to our west and southwest. All this
activity will continue to move in this direction through the morning
(strengthening/becoming organized with time). These rains/storms are
courtesy of the approaching mid/upper trof from the west and likely
a strong short-wave embedded in the southern stream jet. As such, we
should be looking at two rounds of storms for today...the first now,
and another just a bit later this evening/tonight.

Per the bulk of latest hi-res models, the strongest development with
this first round could be concentrated more across the southern half
of the CWA and the nearshore waters...with mainly widespread showers
and isolated thunderstorms for inland areas. However, due to the un-
certainty with this track, portions of SE TX are in a Slight Risk of
strong to severe storms (level 2 of 5) for today. A Marginal Risk is
in place elsewhere for the CWA (level 1 of 5). Deep layer shear com-
bined with deepening moisture and daytime heating are indicating the
primary severe weather threat as large hail, with an isolated threat
of damaging winds or a tornado with the formation of a supercell.

As this system tracks east of the CWA this afternoon, we are likely
going to see the second round of organized storms this evening into
the overnight hours. But unlike the first round, the better chances
of storms will be over our northern half of the CWA (given the path
of the trough aloft). The potential intensity of this next round of
activity is going to be very dependent on the timing and other meso
scale factors with the earlier storms. However, will be keeping the
mention of severe with these storms as a precaution.

By Fri morning, POPs will be falling as skies begin to clear. A cold
front in the wake of the exiting mid/upper trof will bring drier and
cooler air back into SE TX through the day. But...wrap around clouds
with some embedded isolated showers will be possible across northern
parts of the area Fri morning before clearing by the afternoon. Cool
and dry conditions will prevail areawide for Fri night.

&&

.LONG TERM...
(Saturday through Wednesday)
Issued at 349 AM CDT Thu Mar 21 2024

This weekend will mostly be an activity in trying to peg
temperature trends, as stacked ridging should be passing across
the region Saturday into early Sunday. This will keep weather
fair, and mostly sunny for the most part. That should start to
change on Sunday as the ridge moves off, and more zonal flow sets
up aloft. At the surface, onshore flow resumes Sunday morning,
boosting low level moisture and beginning the cycle anew.

On the troughy side of this cycle, guidance is coming into some
more agreement on how things evolve for Monday. The incoming upper
trough looks somewhat disjointed across the deterministic
guidance - which is somewhat interesting, given that the scenario
is somewhat complex. Adding into the chorus, taking a look at the
ensemble cluster analysis mostly just seems to back up what the
deterministics are showing. Each cluster is a little different in
its placement of heaviest precipitation, but all feature a pattern
that would occur from this particular upper level setup. The
primary cluster is perhaps a bit slower than the multi-ensemble
mean, but that`s about it. It is worth noting that there may be a
bit of a dispersiveness concern here, as a solid majority of Euro
members are in the primary cluster, half the Canadian members are
in the second cluster, and half of the GEFS members are in the
third cluster. But given the relatively minor differences at play
here, I`ve not got a ton of heartburn about that.

What this boils down to is that a faster, lead impulse/vort max
comes spurs lee cyclogenesis more in the Central Plains to
Oklahoma Panhandle, still ejecting it towards the Great Lakes
Sunday night and Monday. Meanwhile, a slower, trailing vort max
digs into the Big Bend, or even deeper into Northern Mexico. With
the main impulse so far north, I`m looking up to our northern edge
from Lake Livingston up into the Pineywoods for the most vigorous
convection along the front on Monday. As you head farther south,
I`d expect capping to be an issue, and simply a greater distance
from the better upper support to dwindle our storms down to
showers, and eventually perhaps even to nothing down around
Matagorda Bay.

As that trailing vort max rounds the trough base and ejects
northeastward, we may need to keep an eye on Monday night. I keep
slight chance PoPs lingering into late Monday night to account for
this, though I`m much less confident in how this goes given that
the surface front will be through, with northwest flow in the
boundary layer. I`d expect that if we get anything at all, it
would be more in nature of elevated development of showers and
maybe an isolated thunderstorm in there. In looking back at the
cluster analysis, the primary (Euro-dominated) cluster, as well as
the fourth cluster, is pessimistic about this and staying drier
than the grand mean. But the following two clusters, accounting
for 53 percent of the ensemble members, do indicate we`ll squeeze
something out from this trailing vort, so there`s a chance my
slight PoPs might be a bit underdone.

Tuesday will be another post-frontal day with generally fair
weather and a clearing sky. That clearing sky will largely
counteract whatever post-frontal cold advection we can manage, so
if you`re only looking at high temps, you`d be forgiven for not
even noticing a front went through. The fingerprint shows up in
the overnight lows, as drier air and a mostly clear sky will allow
for effective radiational cooling. Monday night and Tuesday night
should see lows back down into the 50s for most, with even some
upper 40s up in our north. Finally, Wednesday *should* be another
warm, fair weather day. But, another vort max will shoot through
the still-troughy wave pattern that day, and some guidance is
aggressive enough to produce some light, high-based rain. I`m not
buying it, and chose to keep PoPs below 10 percent and even keep
sky conditions mostly sunny. But if that changes in the future,
let`s all try to remember that I at least mentioned here, right?

&&

.AVIATION...
(12Z TAF Issuance)
Issued at 635 AM CDT Thu Mar 21 2024

Widespread showers/thunderstorms will persist across SE TX for much
of today as a strong upper level disturbance moves in from the west.
We`ll be seeing lowering ceilings/visibilities through the next few
hours as all this activity strengthens and moves into the CWA. Have
tweaked the timing of TEMPO groups for our southern terminals based
on current trends (from IAH to the coast). Have also switched times
for these TEMPO groups at our northern terminals to tonight (as per
the passage of the main upper trough). And from SPC`s Day 1 outlook,
there`s a potential for severe weather with the storms this morning
(with large hail as the main threat). Safe to say, there`s probably
going to be amendments through the day. 41

&&

.MARINE...
Issued at 349 AM CDT Thu Mar 21 2024

Winds on the waters are largely in the 10 to 15 knot range early
this morning, but some folks are bumping right up against the
caution flag threshold. Indeed, with the pressure gradient
expecting to tighten with the developing/incoming low pressure
center, I have gone ahead and put up caution flags for Galveston
Bay and the 0-60 NM waters adjacent to it through tonight. Both
winds, and even some seas of 5-6 feet on the Gulf can be expected,
and of course, locally higher near any of the day`s thunderstorms.
Speaking of that low, expect showers and storms to increase and
overspread the waters from the southwest, then wind down from west
to east over the next 24 hours. High-res models suggest the
heaviest rains in the area are likely to fall over the Gulf
waters, so that will be another hazard to consider, particularly
in the strongest storms which will be capable of producing gusty
winds, hail, and even waterspouts. All thunderstorms will be able
to produce locally higher winds and seas.

In the wake of the exiting low pressure, light to moderate
offshore winds will emerge Friday, persisting into Saturday night,
before onshore winds return ahead of the next weathermaker, an
incoming cold front. Caution flags, and even a small craft
advisory seem likely at some point late in the weekend and Monday
before the next frontal passage.

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)  65  57  71  52 /  80  70   0   0
Houston (IAH)  67  59  74  56 /  80  60  10   0
Galveston (GLS)  68  63  73  59 /  90  40   0   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...None.
GM...Small Craft Should Exercise Caution through this evening for
     GMZ335-355-375.

&&

$$

SHORT TERM...41
LONG TERM....Luchs
AVIATION...41
MARINE...Luchs


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