498
FXUS63 KLSX 300356
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1056 PM CDT Tue Jul 29 2025

.KEY MESSAGES...

-Heat index values as high at 110 will continue south of I-70
 Wednesday, while temperature relief will kick off north of I-70.

-There is a marginal risk for severe thunderstorms across much of
 the area tomorrow afternoon with damaging wind gusts and heavy
 rain the main threats.

-Widespread cool and comfortable conditions will prevail
 Thursday- Sunday.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 210 PM CDT Tue Jul 29 2025

Afternoon showers and thunderstorms are possible again this
afternoon, mainly across southeast Missouri where a small mid-level
disturbance within the ridge will interact with leftover boundaries
from this morning`s convection. If anything develops it`ll be weak
and short-lived thanks to the weakly sheared environment (5-10
kts of 0-6 km shear).

Patchy fog is possible tonight across the area, particularly where
locations see afternoon thunderstorms. Many locations will come
close to their crossover temperature, combined with light winds and
a clear overnight sky. Fog will dissipate tomorrow morning.
Meanwhile, a mid-level shortwave will usher an MCS through Iowa
overnight into Wednesday morning, stretching the outflow into
northern Missouri and central Illinois. Convection is expected to
pop up along that outflow tomorrow morning, though how much remains
uncertain given the weak surface moisture convergence along the
boundary.

The remnants of the MCS will meld with the approaching cold
front, which will move south into the forecast area during the
day. North of the cold front during the day, clouds, showers and
thunderstorms, and the first tastes of cold air advection will
keep temperatures near normal, but cooler than previous days with
highs in the mid to upper 80s. Hi-resolution models continue to
show the front making it to I-70 by peak heating.

South of the front, another day of hot and humid conditions will
lead to 1500-2500 J/kg of surface based instability. Lift along the
front and from the mid-level shortwave overhead is expected to fire
some convection along lingering outflow boundaries during the
afternoon hours. Of the storms that form, a few will be able to
organize in the 25-35 kts of 0-6 km shear to produce damaging wind
gusts and heavy rainfall. Heavy rainfall may lead to localized flash
flooding, particularly where thunderstorms move over the same
location. This scenario is certainly in the cards given the largely
parallel deep layer shear vector and frontal boundary, within an
environment with deep warm cloud depths and precipitable water
values between 1.5-2.0". Severe convection will wane during the
evening, but the flash flood threat will remain as the cold front
continues to sink southward overnight.

Delia

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 210 PM CDT Tue Jul 29 2025

The front will push through the remainder of the forecast area
Thursday morning and cold air advection behind the front will be
able to take hold of the region. Lingering showers and cloud cover
will also help to cool temperatures, dropping them into the 70s to
mid 80s across the area Thursday. While northwesterly mid-level flow
will establish aloft, a strong surface high will settle in over the
Great Lakes through the weekend. Continued cold air advection from
this high will cool 850mb temperatures into the lower teens (C)
Friday through Sunday, resulting in high temperatures in the mid 70s
to low 80s despite dry and mostly sunny conditions. Simply put, it
will be a marvelous weekend.

By late Sunday warm air advection will return to the region as the
low-level high shifts eastward and the flow becomes southwesterly
once again. The impacts of this shift will be felt Monday as a
gentle warm up kicks off, which will last through the work week. A
pattern shift will also take place in the mid-levels with the
approach of another mid-level shortwave and increasing chances for
showers and thunderstorms. But the depth, location, and timing of
this feature remains uncertain, as does the pattern beyond the start
of next week.

Delia

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1056 PM CDT Tue Jul 29 2025

Conditions are favorable for areas of fog to develop overnight into
Wednesday morning, especially in the Ozarks and river valleys. Fog
is likely to impact KSUS and KCPS with MVFR to briefly IFR
visibilities. A weakening thunderstorm complex is expected to track
across IA/northern MO into IL on Wednesday morning, including
through KUIN. Thunderstorms will eventually redevelop during he
afternoon and evening across the region, but there is uncertainty
exactly when and where they will occur. PROB30 groups are used at
all terminals to capture when the chances of thunderstorms are
generally highest/increasing through the afternoon and evening. The
strongest thunderstorms will be capable of IFR flight conditions and
gusty winds. Winds will be light and variable outside of
thunderstorms and outflow boundaries.

Pfahler

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT Wednesday for Boone MO-Callaway MO-
     Cole MO-Crawford MO-Gasconade MO-Iron MO-Lincoln MO-Madison
     MO-Moniteau MO-Montgomery MO-Osage MO-Reynolds MO-Saint
     Francois MO-Warren MO-Washington MO.

     Extreme Heat Warning until 7 PM CDT Wednesday 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 Wednesday for Calhoun IL-Fayette IL-
     Greene IL-Jersey IL-Macoupin IL-Montgomery IL.

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

&&

$$

WFO LSX