074 

FXUS63 KLSX 291758

AFDLSX



Area Forecast Discussion...Updated Aviation

National Weather Service Saint Louis MO

1258 PM CDT Mon Jun 29 2026



.KEY MESSAGES...



- Dangerously hot and humid conditions continue through the end of

  the week.



- After a dry few days, chances of showers and thunderstorms begin

  to increase late in the week and this weekend.





&&



.SHORT TERM... (Through Tuesday) 

Issued at 232 AM CDT Mon Jun 29 2026



Ridging continues to build over the center of the country in

response to a digging trough over the western US and a trough over

the Northeast. With the ridge centered near the Mississippi River,

our region will continue to see some of the worst of the heat

today and Tuesday, with temperatures reaching the mid to upper 90s

in the afternoon. With a very humid air mass in place and a

continued southerly low level flow pumping moisture off the Gulf,

we'll see oppressive levels of humidity continue as well. The

combination of heat and humidity will cause heat index values to

rise well above 100 degrees today area wide, with some areas near

110. A Heat Advisory continues area wide with an Extreme Heat

Warning for the St Louis metro and areas of southern Illinois.

Areas within the warning are likely to see the most extreme heat

index values due to slightly higher humidity values. The ridge

peaks in intensity over the next 24 to 36 hours or so, likely

leading to some of the hottest temperatures of this heat wave. The

ridge also suppresses all attempts at convection, so we also have

high confidence in a dry forecast.



Kimble



&&



.LONG TERM... (Wednesday through Saturday) 

Issued at 232 AM CDT Mon Jun 29 2026



The ridge expands eastward for the middle to later part of this

week. We don't really get a break from the heat, but it does have

the effect of allowing better chances of showers and thunderstorms

to develop. More organized areas of storms are likely on the

periphery of the ridge from the Central Plains to the Great Lakes

where frequent shortwave impulses rotate around the ridge. This is

expected to stay well to the north of our area, too far away to

provide meaningful heat relief. However, with the ridge 

broadening out a bit we'll see less capping and a better chance of

air mass thunderstorms each afternoon. This doesn't really stop 

the heat as it will still get hot and humid before and after these

storms, but it may provide temporary relief locally. Some 

deterministic guidance appears to show subtle embedded troughs 

lifting northward within the tropical air mass on the western side

of the ridge, locally enhancing thunderstorm activity. Low 

resolution ensemble guidance is showing 24-hr rain chances rising 

to 30 to 50 percent by Friday and Saturday.



By this weekend, all guidance is showing some restructuring of the

ridge, with it generally reorganizing to the west across the

Rockies. This opens our area up to better potential for troughing

and even a potential cold frontal passage by Sunday. This would

bring a more solid end to the extreme heat. After coordinating 

with neighboring offices, we've extended the heat headlines 

through Friday when we still have strong confidence in dangerous 

heat continuing. While it's likely the heat lasts into Saturday as

well, there's still enough uncertainty with the better rain 

chances that we don't quite have the confidence to extend it 

through Independence Day just yet. 



Kimble



&&



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)

Issued at 1257 PM CDT Mon Jun 29 2026



VFR flight conditions and dry weather will prevail at all of the

local terminals through the TAF period.  



Elmore



&&



.LSX WATCHES/WARNINGS/ADVISORIES...

MO...Heat Advisory until 10 PM CDT Friday 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-Washington MO.



     Extreme Heat Warning until 10 PM CDT Friday for Franklin MO-

     Jefferson MO-Saint Charles MO-Saint Louis City MO-Saint 

     Louis MO-Sainte Genevieve MO-Warren MO.



IL...Heat Advisory until 10 PM CDT Friday for Adams IL-Bond IL-Brown 

     IL-Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-

     Marion IL-Montgomery IL-Pike IL.



     Extreme Heat Warning until 10 PM CDT Friday for Clinton IL-

     Madison IL-Monroe IL-Randolph IL-Saint Clair IL-Washington 

     IL.



&&



$$



WFO LSX