032 
FXUS63 KLSX 221112
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
612 AM CDT Sun Jun 22 2025

.KEY MESSAGES...

- Confidence is increasing in heat index values around 100 degrees
  lasting through the end of this week. 


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 218 AM CDT Sun Jun 22 2025

Dangerous heat continues to plague the region as an upper level 
ridge continues to spin over the eastern half of the CONUS. This 
feature and its surface reflection will remain largely in place for 
the next few days and will keep today's sensible weather very 
similar to yesterday's. Heat index values are again forecast to 
reach 100 areawide with the St. Louis area and southwest Illinois 
peaking around 105 degrees. Lows remain steady as well with 
widespread mid-70s forecast. 

A cold front is forecast to push through the northern Plains tonight 
and stall just north of the forecast area by Monday night. Ahead of 
the front, isolated showers are possible Monday afternoon. The best 
upper level support will be along the front to our north, so any 
convection will be driven by diurnal heating. Locations that see 
rain have the potential to temporarily cool. If it falls in the 
early afternoon, this may be enough to shave a degree or two off the 
high temperature, but it won't be enough provide relief from the 
heat. If it falls past mid-afternoon, afternoon highs will be 
established and it won't matter. Areawide broken diurnal cumulus is 
expected outside of the showers. This in itself will inhibit 
heating. On top of this, the center of the mid-level ridge slides 
east and 850 mb temperatures fall slightly. With these factors in 
mind, I inched Monday's high temperatures down by a couple of 
degrees. A failure point in my forecast is if deep boundary layer 
mixing negates the cooling factors discussed.

Jaja

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 218 AM CDT Sun Jun 22 2025

Tuesday will be a very similar day to Monday albeit with a slightly 
higher potential for showers and thunderstorms. The same forecast 
holds true in terms of the nature and impacts of convection, a 
widespread broken cumulus deck, and mixing being a factor in the 
forecast. I did pull Tuesday's temperatures down a degree or two as 
well due to the similarities. Regardless of Monday and Tuesday's 
highs being lowered, heat index values will still meet criteria both 
days so the Heat Advisory and Extreme Heat Warning have not been 
edited.

Confidence is increasing that the mid-level ridge will stick around 
beyond mid-week. This is corroborated by consensus in deterministic 
models which depict the ridge eroding and sliding east on Thursday. 
This translates to greater confidence in the heat lasting longer 
than initially anticipated. Our current maximum heat index values on 
Wednesday and Thursday both have portions of the forecast area 
reaching 100 degrees again. If confidence in this continues to grow, 
parts of the Heat Advisory will need to be extended. The only 
mitigating factor is the potential for more convection during the 
mid to late week that may dampen the potential of meeting
criteria.

Jaja

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 610 AM CDT Sun Jun 22 2025

Dry and VFR conditions will prevail through the TAF period. Some
VFR diurnal cumulus is expected this afternoon. Otherwise, winds 
will pick up from the south again today and will become gusty in 
portions of central and northeast Missouri as well as west-central
Illinois. Cumulus and winds will diminish after sunset.

Jaja

&&

.CLIMATE...  
Issued at 1225 PM CDT Thu Jun 19 2025

Record maximum temperatures at St. Louis, MO (STL), Columbia, MO (COU), 
and Quincy, IL (UIN) along with the year of the record:

    |    6/22    |    6/23    |    6/24    |    6/25   
-------------------------------------------------------
STL | 102 (1930) | 101 (1930) | 102 (1988) | 103 (2024) 
    |            |            |            |            
COU | 100 (1988) | 100 (1988) | 103 (1988) | 102 (1988)
    |            |            |            |            
UIN | 100 (1930) | 100 (1934) |  99 (1988) | 102 (1931)


Record high minimum temperatures at St. Louis, MO (STL), Columbia, MO (COU), 
and Quincy, IL (UIN) along with the year of the record:

    |    6/22    |    6/23    |    6/24    |    6/25   
------------------------------------------------------
STL | 80 (2016)  | 80 (2010)  | 80 (1914)  | 82 (1988) 
    |            |            |            |            
COU | 77 (1944)  | 76 (2010)  | 77 (1937)  | 77 (1988)
    |            |            |            |            
UIN | 78 (1944)  | 80 (1944)  | 79 (1931)  | 80 (1937)


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 9 PM CDT Tuesday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin 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-Sainte Genevieve MO-Shelby 
     MO-Warren MO-Washington MO.

     Extreme Heat Warning until 9 PM CDT Tuesday for Jefferson MO-
     Saint Charles MO-Saint Louis City MO-Saint Louis MO.

IL...Heat Advisory until 9 PM CDT Tuesday for Adams IL-Bond IL-Brown 
     IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Macoupin IL-
     Marion IL-Montgomery IL-Pike IL-Randolph IL-Washington IL.

     Extreme Heat Warning until 9 PM CDT Tuesday for Jersey IL-
     Madison IL-Monroe IL-Saint Clair IL.

&&

$$

WFO LSX