641
FXUS63 KLSX 240301
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1001 PM CDT Sun Aug 23 2026

.KEY MESSAGES...

- Seasonable temperatures in the 80s continue this week with
  mostly dry weather expected.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 230 PM CDT Sun Aug 23 2026

A ridge of high pressure in the Southwest US and a trough over
the Great Lakes has led to a subsident upper level flow through
our area. That promotes high pressure and dry weather. At the
surface, broad high pressure extends from western Ontario south
into northern Missouri this afternoon with this high gradually
nudging east over the next couple days. Tonight we`ll see winds
go light and temperatures drop into the low 60s and upper 50s.
For some this will be the first time we`ve seen 50s since June.
Clouds have the potential to complicate the cooling forecast
tonight, especially in central Missouri. A limited attempt at
moisture return northward through the Plains tonight may trigger
an area of convection in Nebraska, tracking southeast into
western Missouri. The rain from this likely stays west of our
forecast area, but clouds have a better potential to spread into
central Missouri, potentially holding temperatures a bit warmer
overnight, in the low 60s. Tomorrow will be a very similar day
to today, though perhaps a few degrees warmer. The high slides
east allowing winds to turn southeasterly. Another day of sun
will help to modify the air mass back into the low to mid 80s.

&&

.LONG TERM /MONDAY THROUGH SUNDAY/...
Issued at 230 PM CDT Sun Aug 23 2026

The trough in the east sees some reorientation this week. The
initial trough lifts northeast out of New England and into the
Canadian Maritimes while another trough arrives from the west
and digs into the Great Lakes to replace it. Meanwhile, the
Southwest Ridge remains largely in the same location with some
daily wobbles. For us locally we`ll maintain the persistent
northwest flow aloft with richer moisture remaining suppressed
to the south and west. Temperatures continue to gradually
rebound through the mid and even upper 80s by Wednesday.

The next trough arriving in the Great Lakes pushes a cold front
southward through our forecast area Wednesday into Wednesday
night. This represents our next best chance for rain, but those
chances remain fairly limited locally. The better forcing with
the trough passes by to our north, while the richer moisture
remains suppressed to our south. The low resolution ensemble
(LREF) guidance remains more ambitious with rain chances than
the NBM. Of the LREF guidance, 60 to 70 percent of members
produce rain across our forecast area in the 24 hours ending
Wednesday night, up 10 percent from yesterday. Meanwhile, NBM
12hour PoP remains in the 10 to 20 percent range. This
discrepancy is partially a result of timing variance in the
guidance, but also uncertainty in the development of another
convective complex to our west over the Plains linking up with
the better moisture. The LREF may also be overestimating the
rain chances a bit due to the lower resolution of this guidance,
something NBM is tuned to adjust for with low QPF events. If we
look deeper in the LREF we see the percentage of members that
produce 0.05 inch or greater rainfall is only 30 to 40 percent
over that same time period. This gives credence to the idea that
the low resolution guidance may be indicating more widespread
light rain amounts than should be expected as precipitation in
this time period should be convective in nature.

The air mass behind Wednesday`s front is not as cool and dry as
the last one, and we only get a small taste of it. So we do see
the high temperature forecast for Thursday and Friday a few
degrees lower than Wednesday, but still near normal for this
time of year, in the mid 80s. Guidance is in good agreement that
the western ridge flattens and spreads out across the southern
tier of the country this weekend into the following week. This
reduces the extremity of the heat within the ridge, but also
broadens that warmth back into our area. By Saturday the NBM
probability of 90 degrees creeps back up into the 20 to 40
percent range. Mercifully, the humidity remains limited at least
initially, with NBM probability of 70 dewpoint only up to about
40 percent by the same time frame.

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 957 PM CDT Sun Aug 23 2026

Cool overnight temperatures and light winds will provide ideal
conditions for fog, particularly in river vallies. This will
lead to a high chance for impacts at KJEF, KSUS, and KCPS. The
threat of fog outside of river vallies is greatest across
portions of central Illinois, leading to a threat of reduced
visibilities at KUIN. Any fog that develops will dissipate
shortly after sunrise, with VFR flight conditions then expected
through the day. While winds have been forecast to prevail out
the east, they may remain variable through the day.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.

&&

$$

SHORT TERM...Kimble
LONG TERM...Kimble
AVIATION...Elmore