827 
FXUS63 KLSX 211047
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
547 AM CDT Sat Jun 21 2025

.KEY MESSAGES...

- A prolonged period of dangerous heat will continue today and
  last through at least Tuesday. Widespread heat index values of
  100+ degrees are expected each day.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 248 AM CDT Sat Jun 21 2025

Upper level ridging is currently amplifying across the eastern 2/3 
of the CONUS with a longwave trough spinning over the Pacific 
Northwest. As a result, the Mid-Mississippi Valley sits sandwiched 
between high pressure to our east and low pressure to our northwest. 
This places us in an area of enhanced southwest pressure gradient 
winds which will continue to advect warm air and moisture into the 
region today. This will cause hotter conditions than what we saw 
yesterday, with widespread 90s expected and mid-70s dewpoints 
equaling heat index values of 100 to 110 degrees areawide. 
Because of this, an areawide Heat Advisory and an Extreme Heat 
Warning for the St. Louis metro area will take effect at noon 
today. This morning will be our first low temperature > 70 degrees
during the hot stretch. In the city's urban heat island, the low 
will remain above 75 degrees. These values will threaten if not 
break record warm minimum temperatures at STL, COU, and UIN (see 
CLIMATE section).

Jaja

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 248 AM CDT Sat Jun 21 2025

As mentioned previously, hot weather will continue Sunday through 
early next week as upper level ridging continues to build and the 
low-level pattern remains largely stagnant. Though it won't be as 
warm as today, widespread heat index values of 100 degrees are 
expected Sunday and Monday with low temperatures in the 70s. This 
combination of hot days and warm nights does not allow the body to gain 
the necessary reprieve it needs to withstand heat. Vulnerable 
populations and individuals without access to air conditioning 
will be at most risk of heat related illness and death during the 
coming days and need to take preventative actions against this.

The length of the dangerous heat comes into question during the 
middle of next week. A shortwave trough ejects from the mid-level 
longwave referred to in the short term, causing low pressure in the 
northern Plains to become more progressive send a cold front our 
way. This cold front is forecast to stall to the north of us Monday 
night into Tuesday with convection along it staying in Iowa. 
However, if the aforementioned shortwave trough is able to 
sufficiently erode the northwest edge of the ridge, the chance for 
precipitation will increase, both from the front and from warm 
sector showers. Deterministic and ensemble guidance are beginning to 
lean toward an eroding ridge, with most guidance showing at least a 
chance of rain Tuesday afternoon. If this does come to fruition, the 
Heat Advisory and Extreme Heat Warning may conclude earlier than forecast. The ridge will 
continue to slowly erode and shift east through mid-week, albeit 
possibly more slowly than originally anticipated. With the possible 
exception of Tuesday, 100+ degree heat index values are still 
forecast for portions of the forecast area on Wednesday and 
Thursday. Confidence in this verifying is low at this juncture, but 
I feel it's important to mention given how long that would make the 
hot streak in some locations.

Jaja

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 544 AM CDT Sat Jun 21 2025

Dry and VFR conditions with clear skies are forecast for the TAF
period. Winds today will pick up from the southwest with gusts of
20 to 30 kts forecast. Winds will be strongest in northeast
Missouri and west-central Illinois where the pressure gradient
will be strongest. Gusts will diminish after sunset today.

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:

     |   6/21    |    6/22    |    6/23    |    6/24    |    6/25   
--------------------------------------------------------------------
STL |  99 (1988) | 102 (1930) | 101 (1930) | 102 (1988) | 103 (2024) 
    |            |            |            |            |
COU |  98 (1988) | 100 (1988) | 100 (1988) | 103 (1988) | 102 (1988)
    |            |            |            |            |
UIN | 100 (1988) | 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:

     |   6/21    |    6/22    |    6/23    |    6/24    |    6/25   
--------------------------------------------------------------------
STL |  81 (1901) | 80 (2016)  | 80 (2010)  | 80 (1914)  | 82 (1988) 
    |            |            |            |            |
COU |  76 (1937) | 77 (1944)  | 76 (2010)  | 77 (1937)  | 77 (1988)
    |            |            |            |            |
UIN |  77 (1937) | 78 (1944)  | 80 (1944)  | 79 (1931)  | 80 (1937)


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon today to 9 PM CDT Tuesday for Crawford 
     MO-Franklin MO-Gasconade MO-Iron MO-Lewis MO-Lincoln MO-
     Madison MO-Marion MO-Montgomery MO-Pike MO-Ralls MO-
     Reynolds MO-Saint Francois MO-Sainte Genevieve MO-Warren MO-
     Washington MO.

     Extreme Heat Warning from noon today to 9 PM CDT Tuesday for 
     Jefferson MO-Saint Charles MO-Saint Louis City MO-Saint 
     Louis MO.

     Heat Advisory until 9 PM CDT Tuesday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Knox MO-Moniteau MO-Monroe MO-Osage MO-
     Shelby MO.

IL...Heat Advisory from noon today to 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 from noon today to 9 PM CDT Tuesday for 
     Jersey IL-Madison IL-Monroe IL-Saint Clair IL.

&&

$$

WFO LSX