664
FXUS63 KLSX 230329
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1029 PM CDT Sun Jun 22 2025

.KEY MESSAGES...

- The Extreme Heat Warning and Heat Advisory continue in the
  forecast into Tuesday evening. Dangerous heat index values in
  excess of 100 degrees are expected.

- The weather pattern may not shift until later in the week which
  could extend this period of dangerous heat through Thursday or
  Friday.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 229 PM CDT Sun Jun 22 2025

Little change in thinking from previous forecasts this afternoon.  A
high amplitude pattern has been established over the CONUS with a
strong upper level ridge currently centered over the Ohio Valley,
and a long wave trough over the Rocky Mountains.  Dew point
temperatures are remaining in the low 70s so far this afternoon
despite soundings showing mixing up to 850mb.  Heat index values
reached the triple digits yesterday, and many locations are already
at or above 100 degrees already today.  The center of the upper high
will drift a bit eastward tonight and Monday, but not far enough to
make any difference in the sensible weather at the surface.  A few
models develop isolated convection over the eastern Ozarks during
the afternoon, which would certainly affect afternoon temperatures.
However, if storms develop they should be few and far between, and
most locations should see heat index values between 100 and 105
again Monday afternoon.  Heat headlines will therefore continue
unchanged for this update.

Carney

&&

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 229 PM CDT Sun Jun 22 2025

The pattern remains fairly stagnant at least through Wednesday with
the upper ridge locked in over the southeastern quarter of the CONUS
and a long wave trough over the Rockies. Temperatures/heat index
values will depend largely on if/where isolated-widely scattered
convection develops in the afternoon, and potentially any convective
debris that wanders into the area from overnight MCS activity that
would limit insolation.  With that said, the NBM`s interquartile
temperature range is only 2-3 degrees at most locations in the
forecast area through Thursday, indicating a high degree of
confidence.  Parts of southeast Missouri show a 3-5 degree range,
which is most likely due to afternoon convection over the eastern
Ozarks in some members of the ensemble.  All of the bias corrected
temperature guidance is cooler than the straight deterministic
guidance, which I think is dragging down the NBM mean temperatures.
Therefore I`m continuing to lean on the 75th percentile for
temperatures through Thursday which will keep highs in the mid to
upper 90s in most locations and heat index values around the century
mark.  Heat headlines may need to be extended in this case, but I
feel there`s enough uncertainty regarding the effects of
potential afternoon convection that I`m holding off at this time.

The GFS and ECMWF have consistently been showing a short wave moving
from the northern Plains Thursday into the Upper Midwest and
southeast Canada by Friday evening.  The wave attenuates the ridge
over the Mississippi Valley somewhat which could lower temperatures
a few degrees for Friday through Sunday, and increase the chance for
rain a bit. However, dewpoint temperatures should remain in the 70s
across most of the area which will produce heat index values in the
mid 90s to around 100.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1028 PM CDT Sun Jun 22 2025

Mostly clear skies are expected to persist through much of the
period. Clouds will slide from northwest to southeast Monday
afternoon/evening from unsettled weather well to the north.
Fortunately, only few mid/high clouds are forecast over metro
terminals, thickening to scattered/broken sky conditions from
central MO northeast through KUIN. VFR will persist through late
Monday evening.

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