Excessive Heat in Texas, June 24 to 27, 2023

Area Forecast Discussion
National Weather Service Houston/Galveston TX
600 AM CDT Sat Jun 24 2023

...New AVIATION...

.SYNOPSIS...
Issued at 321 AM CDT Sat Jun 24 2023

After sharing the stage with isolated severe thunderstorms the
past few days, heat returns as the main start in the week to come.
Rain chances will trend towards nil, and temperatures around and a
little above the century mark will be back.

An area-wide heat advisory continues again today, and an excessive
heat watch covers the large majority of the area tomorrow. Look
for heat index values to peak in the 108-111 degree range today,
and most look to see those step up to a 111-116 degree range on
Sunday. This need will likely extend into the next week, and
we'll continue to monitor trends for the most appropriate
configuration of watches, advisories, and warnings.

It's also important to consider nighttime conditions! Overnight
lows will struggle to fall much below 80, if they do at all. This
removes a critical time for the human body to recover if you
cannot get into an air-conditioned space to sleep.

I know, it's summer and we all want to get out and enjoy the fair
weather this weekend and we're all kinda sick of just how hot
it's been and will continue to be. But we need to continue to
keep heat safety at the fore when it comes to the weekend plans.
Even though we're used to hot summers, this stretch continues to
be high end even by our already high standard for excessive heat.

&&

.SHORT TERM...
(Today through Sunday Night)
Issued at 321 AM CDT Sat Jun 24 2023

Well, hope y'all have enjoyed the "break" in this heatwave the
last couple of days, because it looks to be coming to an end. Of
course, we've got the scare quotes around break and say that
firmly tongue in cheek; though we toned down the peak levels of
heat index enough to leave behind excessive heat warnings, area-
wide advisories still has meant that without taking precautions,
it's still plenty dangerous at times. From here, things look to
trend back upwards again.

The slight weakening in this heatwave pattern also opened us up to
thunderstorms, so let's talk about that real quick before diving
into what the heat has in store for us - trust me, it won't take
that long. The storm complexes to our northwest have fizzled out.
Ridging is still building in, so I do have some slight chances for
showers or a stray storm up around the Pineywoods before dawn, but
that's largely a hedge. After that, King Ridge and the subsidence
(dibs on that for a band name) should choke off rain chances for
the rest of the short term, and beyond. Some guidance does still
develop some showers over the Gulf in the late night/early morning
hours this weekend in keeping with the diurnal pattern, and I
gave some consideration to leaving in some slight chances.
Ultimately decided against it, however.

Alright, with that out of the way, now for the star of the
weekend: the heat. As we're still in a bit of transition to the
big ridge stuff, my guide for today was yesterday, but no rain
and a little hotter. I used persistence as a floor, and worked in
an even parts mix of NBM, median NBM, and NBM 75th percentile.
With less cloud cover, no rain chances, and probably some more
aggressive mixing, I did get more aggressive in taking dewpoints
down in the afternoon - more in the lower 70s than the middle 70s
for inland locations. As a result, widespread heat index values
top out in the 108-111 degree range. This justifies continuing the
advisory already in place. I'd fully expect isolated hot spots to
see the heat index reach heat warning thresholds, particularly in
localized hot spots and higher moisture areas, but probably not
over a broad enough area to support the issuance of an excessive
heat warning. But knowing these spots exist is why we do still
hit heat safety roughly as hard whether we have advisories or
warnings out. It may be overkill for many, but for some, it's
still very relevant information.

Tomorrow is a different picture. Where today I have highs mostly
in the middle to upper 90s with some spotty 100s, the heat becomes
even more aggressive tomorrow, with fairly widespread highs of
99-102, particularly in the coastal plain just beyond the reach of
the Gulf's moderating influence. I'm also a touch less aggressive
with my afternoon mixing out of dewpoints as well. Onshore flow
looks a little bit stronger Sunday, and one thing that really
stuck with me last week is how easily those winds overwhelmed any
mixing and replenished surface moisture to keep dewpoints high and
heat index excessive. I think we'll see something more like that
on Sunday compared to today.

The end result is a band of peak heat index values of 111-116 for
much of the area, and only slightly lower at the coast and our
northernmost row of counties in the forecast area. Because of
this, I've chosen to issue an excessive heat watch for the large
majority of the area on Sunday, and continue the heat advisory for
everywhere else.

&&

.LONG TERM...
(Monday through Friday)
Issued at 321 AM CDT Sat Jun 24 2023

The major story in the extended period (as has generally been the
case this month) will continue to surround the prolonged period of
excessive heat that is expected to last at least through the
duration of the upcoming week.

Synoptically, little change is anticipated as a robust midlevel
ridge with maximum 500mb heights in the 594-96dam range will
continue to remain dominant over the South Central CONUS. With SE TX
remaining directly under the influence of this feature throughout
the week, thereby bringing strong subsidence aloft and moderate
onshore flow at the surface, it remains a near-persistence forecast.
High temperatures will continue to break into the triple digits for
most locations, while areas along the immediate coast will generally
reach the mid/upper 90s. While elevated dew points in the 70s are
still expected, latest NBM appears to be continuing to under-
represent afternoon mixing and thus have brought those values down
into the mid 70s as we have seen in recent days. Despite this, heat
index values are still expected to approach 110 on most afternoons
and at a minimum I anticipate the need for a Heat Advisory each day
throughout the course of the week as things currently stand.
Overnight lows will continue to hover near 80, potentially
threatening daily high minimum temperature records at times.

With the position of the ridge overhead, subsidence aloft should
generally stifle precipitation chances over the duration of the week
and thus have not included any mentionable PoPs in this morning's
forecast package. Of course, we can't completely rule out the
development of any very isolated mesoscale/diurnally driven
convection but as a whole rain chances should remain minimal.

Heat safety precautions should remain a priority...remaining
hydrated, avoiding strenuous activity during the hottest parts of
the day, and being able to recognize the signs of heat exhaustion
remain critical actions! Heat-related illnesses account for over
60,000 hospitalizations across the US each year.

&&

.AVIATION...
(12Z TAF Issuance)
Issued at 600 AM CDT Sat Jun 24 2023

A mix of MVFR and VFR across the region, with FEW-BKN sky around
015 early this morning as well as some patchy fog cropping up.
Fog dissipates and clouds lift/scatter through the morning,
setting us up for VFR area-wide for most of the day. Light/VRB
winds early this morning pick up in strength generally out of the
south, reaching around 10 knots. Winds expected to stay up higher
than typical tonight.

&&

.MARINE...
Issued at 321 AM CDT Sat Jun 24 2023

With high pressure generally remaining overheat, light to moderate
onshore winds and seas of around 2-4 ft should continue for the
remainder of the weekend and throughout the course of next week.
Wind speeds may approach caution thresholds at times, but will
likely not reach advisory levels. Rain chances over the course of
the next 7 days will remain minimal.

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL)	  98  77 100  78 /   0   0   0   0
Houston (IAH)			  99  80 100  78 /  10   0   0   0
Galveston (GLS)			  90  82  90  82 /  10   0   0   0

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Heat Advisory until 9 PM CDT Sunday for TXZ163-176-195-196-214-
     335>338-438-439.

     Heat Advisory until noon CDT Sunday for TXZ164-177>179-197>200-
     210>213-226-227-235>238-300-313.

     Excessive Heat Watch from Sunday afternoon through Sunday
     evening for TXZ164-177>179-197>200-210>213-226-227-235>238-
     300-313.

     Heat Advisory from noon to 9 PM CDT Sunday for TXZ436-437.

GM...None.
&&

SHORT TERM...Luchs
LONG TERM....Cady
AVIATION...Luchs
MARINE...Cady