Kirkwood, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

682
FXUS63 KLSX 280355
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1055 PM CDT Sun Jul 27 2025

.KEY MESSAGES...

- The heat will worsen early this week and peak in intensity for a
  majority of the area on Tuesday.

- The heat breaks for at least some of the area on Wednesday, with
  relief felt areawide by Thursday into Friday.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 225 PM CDT Sun Jul 27 2025

Isolated showers and thunderstorms have developed over the past
couple of hours, mainly across east central and southeast Missouri
as well as southwest Illinois. The threat for any strong to
severe thunderstorms appears low due to very weak vertical wind
shear (~10 knots). Low-level lapse rates are also slightly weaker
than yesterday along with DCAPE values (800-1000 J/kg) a bit less
as well. The axis of anomalous precipitable water values that are
near 2.00" (95th-99th percentile of climatology) has shifted more
into southeast Missouri and southwest Illinois. This means we
will still have an isolated threat for flash flooding due to
efficient rainfall processes and possible training. The chances of
true training of convection however are a bit less than yesterday
as individual storms this afternoon/evening should quickly weaken
(due to a lack of shear) and upstream convection is more likely
to weaken and/or dissipate as they head into cooler and more
stable air behind outflow boundaries from antecedent convection.

Showers and thunderstorms should gradually weaken and dissipate this
evening as daytime instability fades after sunset. Very broad, weak
low-level warm air advection in the presence of a surface
convergence zone may yield at least some isolated showers/weak
thunderstorms overnight tonight. This activity, if it forms, should
move from west to east (as the convergence zone moves) from along
the Mississippi River into south-central Illinois after midnight
into the predawn hours.

Model guidance is in very good agreement that a well-organized MCS
will be moving equatorward out of the Upper Midwest late tonight
into early Monday morning. This southward movement is buttressed by
Corfidi vectors between 0900 and 1200 UTC Monday showing nearly
due north to south propagation vectors. There is of course some
variety of how far west and how fast this system will be, but
there may be some impacts felt in northeast Missouri and west-
central Illinois by late morning. While the chances of any showers
and thunderstorms reaching these areas is very low (~10%) due to
weakening low-level moisture convergence after dawn and the
complex becoming outflow dominant due to very weak deep-layer
shear, a composite outflow boundary may move through these areas.
These outflow boundaries emanating from prior organized
convection have the capability of augmenting the surface
environment, providing a wind shift to the northwest and ushering
in (at least temporarily) cooler and less humid air. I was not
confident enough in this scenario to lower highs significantly nor
dewpoints, but this is a scenario which could yield lower heat
index values than forecast.

In the absence of a strong outflow boundary passage, dangerous heat
index values are forecast areawide. Most locations should see peak
values in the 105-110F range, with the best chances of 110F+
readings in/around metropolitan St. Louis and adjacent southwest
Illinois. Portions of northeast Missouri and west-central Illinois
(especially near the Mississippi River) also may threaten 110F due
to dewpoints near 80 degrees. Confidence though is lower due to
the possible passage of an outflow boundary detailed above.


Gosselin

&&

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 225 PM CDT Sun Jul 27 2025

(Monday Night - Tuesday Night)

It still appears likely for the magnitude of this heat event, both
in terms of temperatures as well as heat index values, to peak
Tuesday afternoon across much of the area. This is when the
mid/upper level anticyclone is strongest, located just to our
south/southwest. Highs in the mid to upper 90s are forecast, with
heat index values of 105-110F+. Once again, the worst of the heat is
expected to be located in/around metro St. Louis and adjacent
southwest Illinois as well as parts of northeast Missouri and west-
central Illinois along the Mississippi River. There were no changes
to the current heat headlines as they still looked valid. We will
have to keep an eye on the breadth of any 110+F values as 2 straight
days would meet magnitude criteria for an extreme heat warning.
However, given the uncertainty with Monday`s highs/dewpoints in
northeast Missouri and west-central Illinois as well as some
dewpoint uncertainty on Tuesday, elected to keep the heat headlines
as is for now.


(Wednesday - Wednesday Night)

There remains some uncertainty as to the exact timing of the strong
cold front moving through the area Wednesday/Wednesday night.
Guidance overall has trended a bit slower compared to yesterday, but
there definitely has been some wobbling back and forth too. There
have also been some on/off signs for a possible MCS to move out of
the mid-Missouri Valley toward the area early on Wednesday.
Something like this of course would have large ramifications on
afternoon temperatures. This is a long winded way of saying that
there remains enough uncertainty at this time range to not extend
any of the heat headlines into Wednesday. The best chances for
another day of dangerous heat/humidity is in southern sections of
the forecast area, especially along/south of the I-70 corridor.
However, not even parts of northeast Missouri and west-central
Illinois are a given to see relief if the front does not move
through until early/mid afternoon. The 75th percentile of the NBM is
around 90 degrees for daytime highs for reference even as far north
as Quincy, IL for reference.

Fairly widespread showers and thunderstorms are expected between
Wednesday and Wednesday night, but exactly when is still a question
mark due to the aforementioned uncertainty with the exact timing of
the cold front. Overall chances (40-60%) continue to creep upward,
but eventually categorical PoPs (80+%) seem likely at some point
given that 24-hr probabilities for measurable rainfall are in the 85-
95% range on the LREF ending 1200 UTC Thursday. Guidance also
diverges with respect to how much convection actually occurs
along/ahead of the front vs. post frontal. Some guidance actually
shows more of a true anafront, with basically all of the rain
occurring after the front moves through. If storms do manage to form
along/ahead of the boundary, marginally severe weather may be
possible given a very unstable environment and modest (15-25 knots)
effective shear.


(Thursday - Next Sunday)

There remains very high confidence that the entire area will see a
definitive end to the ongoing long-duration heat event by Thursday.
However, the first cold front that moves through only brings in
cooler temperatures (highs in the 80s), with the high humidity
sticking around one last day. By Friday, much lower dewpoints
(50s/60s) are forecast to advect into the area.

Medium range guidance has been pretty consistent the past couple of
days, showing an unusual upper air pattern across the CONUS. The
flow is very amplified, with strong mid/upper level ridging across
the intermountain west and anomalous troughing carving out across
southeast Canada. Strong mid/upper level confluence will be between
these two dipoles, aiding in a very strong surface anticyclone
moving into the Upper Midwest Friday morning. The strength of this
high has trended stronger and stronger, with the NAEFS now depicting
a ~1030 hPa high. This would be record-breaking for the location and
time of year and almost 3 full standard deviations above normal.
Northeast and then easterly low-level flow will come around the
southern periphery of this high into the mid-Mississippi Valley,
bringing much cooler and less humid air into the bi-state region.
High temperatures are forecast to range from the mid 70s to the low
80s for the most part Thursday through Sunday, though some
moderation may occur beginning next Sunday. There also remains the
potential for at least some areas only reaching the low 70s given
northwest flow aloft and the potential for widespread clouds/rain.
This could occur Friday or Saturday depending on the timing (and
track) of a midlevel shortwave trough.


Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1055 PM CDT Sun Jul 27 2025

Predominantly dry and VFR flight conditions are expected through the
TAF period with a few exceptions. There is a 20 percent chance of
isolated showers and thunderstorms at times tonight along/east of
the Mississippi River, but confidence is low on when or if any of
the terminals will be impacted. Additionally, a large thunderstorm
complex will quickly move southward across IA overnight with
confidence beginning to increase that its remnants will reach
northeastern MO and west-central IL Monday morning. Therefore, a
PROB30 group has been included for at least a brief period of gusty
winds MVFR flight conditions with lower ceilings and brief showers
with the outflow boundary. Aside from precipitation, patchy river
valley fog is also likely where skies remain clear, with KSUS most
favored to see a short period of impacts around sunrise.

Pfahler

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT Tuesday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Gasconade MO-Iron MO-Knox
     MO-Lewis MO-Lincoln MO-Madison MO-Marion MO-Moniteau MO-
     Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds
     MO-Saint Francois MO-Shelby MO-Warren MO-Washington MO.

     Extreme Heat Warning until 7 PM CDT Tuesday for Franklin MO-
     Jefferson MO-Saint Charles MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO.

IL...Heat Advisory until 7 PM CDT Tuesday for Adams IL-Brown IL-
     Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Montgomery IL-Pike IL.

     Extreme Heat Warning until 7 PM CDT Tuesday for Bond IL-Clinton
     IL-Madison IL-Marion IL-Monroe IL-Randolph IL-Saint Clair
     IL-Washington IL.

&&

$$

WFO LSX