Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 302343
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
643 PM CDT Thu Jun 30 2022

.AVIATION [00Z TAF ISSUANCE]...

Mix of VFR to MVFR conditions expected through the TAF period.
Light ESE winds tonight will turn SSE and increase to 6-12 KTS
Friday morning. The SH/TS that rolled through SE Texas earlier
today have either dissipated or continued eastward into E Texas.
Only a few light to moderate showers remain along the waters and
in/around GLS. Another round of SH/TS associated to the low
pressure system over the NW Gulf waters can be expected to move
into the region during the overnight hours or early morning hours
as the low pressure approaches the Mid to Upper Texas Coasts.
There might be some decrease in activity in the afternoon/evening,
if the bulk of the moisture/rain veers more to the east. For now,
kept mention of either VCSH or VCTS through the end of the period
for most of the sites.

24

&&

.PREV DISCUSSION... /ISSUED 345 PM CDT Thu Jun 30 2022/

DISCUSSION...

Today`s forecast can largely be divvied up into two sections - the
95L part, and the not-95L part. Though there is still potential
for 95L to briefly become a tropical depression before it moves
inland, whether it does or not is fairly irrelevant. What`s more
or less locked in for our area is a broad area of rain, heavy at
times near the coast, fueled by a surge of tropical moisture. For
most of the area, this rain will be welcomed (and far enough
inland probably not as much as you`d like). But in spite of recent
drought conditions, rain rates could be enough to still cause some
isolated flooding concern closer to the coast. A flood watch is in
place for this area, with a particular eye on urban, low-lying,
and other areas with poor drainage.

Once the mess that is 95L pulls north out of the area and the
final lingering showers come to an end - probably sometime early
on Saturday - we transition into the other part of the forecast.
This will be dominated by a strengthening summertime ridge, fair
weather, and hot temperatures. At this time we`re not expecting
things to get quite as unseasonable as they were for most of
June, but we should still look to see most of next week dominated
with temperatures near or a little above normal, and heat index
values peaking out above 100 degrees.

SHORT TERM [Through Saturday]...

Radar and Satellite have thankfully been quieting up some from
this morning. We still have some light to moderate rain around
Galveston Bay, but otherwise the bulk of the rain has retreated
back to the Gulf and even drifted eastward a bit.

This is good, because for all the lack of tropical cyclone-ness of
Invest 95L, there are some worrying features. The key one is the
apparent long moisture plume feeding from the southwest Gulf,
all the way up the Gulf on the right side of the "center" of the
Invest, and pointed at Galveston Bay. And even in a drought, I do
not feel particularly good about having a moisture cannon with
that much fetch pointed right at me. As the area of low pressure
begins to make its way more to the north, we`ll see that moisture
impinge more on the coast, and begin to spread into Southeast
Texas. The best potential for heavy rain will likely come in a 15
or so hour period after midnight tonight into early tomorrow
afternoon.

This scenario has been hinted at, really since this timeframe came
into the extended portion of the HRRR. And while the run to run
consistency hasn`t necessarily been there from a deterministic
standpoint, we`ve seen an increasing signal the CAM-ensemble HREF
showing at least a potential for several inches of rain near the
coast. Even in a drought, rain-rate driven flooding is a real
threat. The ground may be able to soak up a lot, but not if it all
comes at once.

Of course, it can still be tricky to get too specific with high
rain rates. The environment certainly is very supportive, with
this long fetch of moisture pushing precipitable water easily
above two inches, around the 90th percentile with an incoming
tropical low. Forecast soundings are your quintessential tropical
downpour soundings, with a ton of moisture and a very skinny CAPE
profile. Probability matched mean QPF in the HREF suggests at some
point tonight, potential for getting three inches of rain in less
than three hours exceeds 70 percent around Galveston Bay. So...it
seems reasonable to expect some big rain somewhere. If we`re
lucky, it will be over locations built to take it. But if it comes
over something with a lot of concrete, very low-lying, or in some
other spot that causes poor drainage, we could start seeing
problems.

The teal dear on it all is that with this environment, even in
spite of the longer-term drought conditions, it seems reasonable
to have a flood watch in place at the coast. While the watch
covers broad areas bounded by political boundaries, those that
really should focus on a flooding threat are for those susceptible
to flash flooding: urban areas, small and flashy streams, low-
water crossings, etc.

Though the flood watch is set to end tomorrow evening, lingering
showers seem likely to persist through the night and even Saturday
morning before fully coming to an end. The HREF actually still
shows a bit of a heavy rain signal up around Lake Livingston, but
the rain appears to be more isolated to scattered by this point,
and this would fall in an area more able to handle some heavier
rain.

With everything pulling out of the area, we can look for clouds to
begin to scatter out deeper into the day and temperatures to push
their way back towards 90 degrees. This will be our transition day
back into summer.

LONG TERM [Saturday Night Through Thursday]...

Saturday evening into Sunday will really feature the return of
mid-level ridging to the area, with 500 mb heights over the
northwestern Gulf beginning to exceed 594 dm again. This sets us
up for some solid warming into next week, with this ridge expected
to stop, drop, shut it down and open up shop around North Texas.
Meanwhile, at the surface, we should see surface high pressure
with onshore flow continue.

Now, this doesn`t necessarily look to be quite like the
unseasonably hot and dry weather that came to define the month of
June, even though in many ways they share some similarities.
That`s probably because a lot of our June looked like a typical
July. So, now that we`re finally in July, it`s not so weird. And
fortunately, at least next week, it looks like conditions should
fall pretty close to - perhaps a bit warmer than - seasonal
averages. NAEFS and the EPS do start to flash in some 90th
percentile temps towards middle/late next week, and so this may be
something for us to watch for once we get through this rain event.

AVIATION [18Z TAF Issuance]...

Incoming, loosely organized tropical moisture makes for a high
confidence forecast in the big picture, but very tricky to hit
precise details. Morning rain is beginning to retreat a bit back
towards the coast, so only have shower mentions from HOU/SGR
coastward (and might even have to be amended back to just GLS). Do
have brief MVFR mentions where obs merit it, but most should see
VFR take hold this afternoon. However, expect rain to return late
tonight into tomorrow as tropical moisture is dragged inland. As
rain returns, so should MVFR CIGs.

MARINE...

Invest 95L is degrading conditions on the waters with stronger
onshore winds, higher seas, higher tides, as well as numerous
showers and thunderstorms across the waters today. We look to be
entering a brief lull this evening, but conditions should get
worse again overnight into Friday as the low pressure begins to
move northward into, then through Texas. The National Hurricane
Center continues to indicate that there is a medium chance of this
system developing briefly into a tropical depression before it
pushes inland along the middle Texas Coast, but the expected
conditions are expected to be about the same regardless of whether
or not this occurs. As the system exits the area to the north,
conditions are expected to improve over the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)      72  86  75  93  76 /  10  40  30  40  10
Houston (IAH)              74  85  77  93  78 /  60  80  40  50  10
Galveston (GLS)            78  85  82  90  83 /  80  80  40  40  10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Flood Watch through Friday evening for the following zones:
     Bolivar Peninsula...Brazoria Islands...Chambers...Coastal
     Brazoria...Coastal Galveston...Coastal Harris...Coastal
     Matagorda...Fort Bend...Galveston Island...Inland
     Brazoria...Inland Galveston...Inland Harris...Inland
     Matagorda...Matagorda Islands...Southern Liberty...Wharton.

GM...NONE.
&&

$$

Discussion...99
Aviation/Marine...99


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