693
FXUS63 KLSX 212308
AFDLSX

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

.KEY MESSAGES...

- Dangerous heat will continue Sunday through at least Tuesday.
  Heat index values of 100+ are expected each afternoon.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 218 PM CDT Sat Jun 21 2025

A strong upper level ridge is moving across the Mississippi Valley
today.  The ridge will settle over the eastern United States by
early Sunday morning and remain nearly stationary into next week.
Low level southwest flow continues to funnel 70+ degree dew point
air from the southern Plans and Gulf Coast up into the Lower
Missouri and Mid Mississippi Valley.  This pattern will persist
tomorrow, and Sunday looks like a near carbon copy of today.
Forecast soundings are showing deep mixing into a relatively dry
layer aloft, so afternoon dew point temperatures may be a couple
of degrees lower. However, dangerous heat index values in excess
of 100 degrees continue to be likely Sunday afternoon and the
Extreme Heat Warning and Heat Advisories will continue unchanged
at this time.

Carney

&&

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 226 PM CDT Sat Jun 21 2025

...Corrected...

The primary concern moving into the medium range remains excessive
heat.  The upper level ridge remains over eastern U.S through much
of the week, although it is forecast to weaken slowly in the
Wednesday through Saturday time frame.  LREF mean and GFS/ECMWF
deterministic models show 594+ dam heights at 500mb locked in over
the Mid Mississippi Valley through at least Tuesday, so the
atmosphere will have the potential to be just as warm through
Tuesday as it is today and Sunday.  With that said, there is some
question about how high the heat index will get both days as
forecast soundings show deep mixing which could cause surface dew
point temperatures to drop several degrees during the afternoon.
There`s also the possibility of some afternoon thunderstorms,
primarily on Tuesday which could also break the heat.  While some
deterministic models, most notably the GFS, do print out QPF Tuesday
afternoon over our area, I find it difficult to imagine there will
be as much convection as advertised under the influence of the
ridge.  While I cannot totally rule out precip on Tuesday, I think
the wetter members of the NBM are influencing the deterministic PoPs
and temperatures causing them to be too high and too low
respectively. Have therefore cut PoPs to no higher than 20% on
Tuesday, and leaned on the 75th percentile for highs on both Monday
and Tuesday.  This will bump heat index values up a little from
previous forecast and lends a little more confidence in continuing
the heat headlines. The potential for precip and cloud cover
increases as the ridge breaks down during the latter half of the
week, so will stick with the NBM`s deterministic mean highs and PoPs
through the end of the period.

Carney

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 604 PM CDT Sat Jun 21 2025

Southwesterly winds will continue to draw hot and humid conditions
into the region with few mid/high clouds on occasion. Gust subside
tonight before returning over central MO and west-central IL. For
metro terminals, KSTL was the only site including a prevailing
group for gusts, largely accounting for the broader, open
airfield. While surrounding sites may push 20 knots, the stronger
winds will remain west and slightly lower than today`s winds.

Maples

&&

.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 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