Affton, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

892
FXUS63 KLSX 090943
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
443 AM CDT Sat May 9 2026

.KEY MESSAGES...

- Widespread dense fog will continue to impact parts of the area
  early this morning.

- A cold front is expected to bring scattered showers tonight and possibly
  a rumble of thunder, mainly north of I-70. A cool down is
  expected behind this front for Sunday and Monday.

- Another cold front is expected to move through the region
  Tuesday night, but there is a lot of uncertainty with
  temperatures mid-late week behind this boundary.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 231 AM CDT Sat May 9 2026

GOES-19 nighttime microphysics RGB imagery and surface
observations show widespread dense fog across parts of central,
east central, and northeast Missouri. The expectation over the
next couple of hours is for further expansion to the east as
higher clouds exit. Some weak advection to the northeast is also
expected. Have therefore expanded the dense fog advisory and it
now covers much of the CWA.

After sunrise, the fog should lift more into a low stratus layer and
eventually advect more to the east/northeast as low-level winds pick
up. The stratus is likely to fairly quickly lift/scatter out
completely by late morning as the GOES-19 cloud thickness product
shows most of the fog to be less than 800 feet thick. However, there
are a few pockets > 1000 feet AGL which may take longer to
completely scatter out. Regardless, the expectation at this time is
for this fog/stratus to have very little to no impact on daytime
high temperatures. Speaking of which, increasing low-level
southwesterly flow along with at least partial sunshine should allow
for temperatures to climb well into the 70s to near the 80 degree
mark across much of the area. Those readings would be several
degrees above normal for the date and the warmest day so far during
the month of May for many locations.

Another cold front is expected to approach from the northwest early
this evening as a more potent midlevel shortwave trough digs into
the Great Lakes. At least scattered showers are expected with this
cold front due to increasing low-level moisture advection and ascent
downstream of an approaching midlevel impulse. The coverage of
showers should be highest north of I-70 this evening. Overnight, the
forcing for ascent abates, so chances of rain decreases. A few
rumbles of thunder are also possible this evening due to the
presence of weak instability. Moderate low/mid level frontogenesis
is forecast behind the front overnight tonight into Sunday morning,
which could help linger some light rain showers well behind the
surface boundary. How quickly these showers depart along with some
low clouds behind the boundary will be important for high
temperatures on Sunday. If lower clouds are able to linger into mid
afternoon, that would likely keep highs more in the low to mid 60s.
Otherwise, the expectation is for mostly upper 60s.


Gosselin

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 231 AM CDT Sat May 9 2026

(Sunday Night - Monday)

Seasonably cool and dry conditions are expected Sunday night into
Monday as a strong (1024+ hPa; >95th percentile of climatology)
surface ridge of high pressure is draped across the mid-Mississippi
Valley. Lows Sunday night are expected to be seasonably cool,
dropping back into the low to mid 40s. Those readings would be about
10 degrees below normal for the middle of May. Some slight
modification in temperatures is expected on Monday due to plentiful
sunshine. Highs in the upper 60s to low 70s are forecast from east
to west across the area.


(Monday Night - Tuesday)

Models are in good agreement that the surface ridge will move
eastward into the Ohio Valley Monday night, with southerly return
flow commencing in its wake. Temperatures will rebound as a result,
with lows in the mid 40s to low 50s Monday night and highs back near
80 degrees on Tuesday.


(Tuesday Night - Friday)

Ensemble guidance continues to show another midlevel shortwave
trough digging into the Upper Midwest/Great Lakes Tuesday night into
Wednesday, sending another cold front through our neck of the woods.
Uncertainty with the location/strength of midlevel troughing and the
strength of the air mass behind the front remains high at this time.
The spread between the 25th/75th percentiles from the LREF for 850-
hPa temperatures is about 5C Wednesday evening. For reference, that
would likely equate to a range from temperatures returning to well-
below normal levels to near/slightly above normal. Both the GEFS/EPS
had trended cooler for several consecutive runs, but those ensemble
suites seem to have converged a bit toward the middle. The EPS had
been quite a bit cooler than the GEFS, but those differences are
more muted tonight.

Forecast uncertainty (with respect to temperatures) continues into
Friday. While three of the four clusters of the 500-hPa height
pattern show a building mid/upper level ridge into the middle of the
country, the one that does not does have nearly half of the total
membership (45%) of the LREF. This cluster still has pronounced
mid/upper level northwest flow across our area to the west of
troughing across the northeastern CONUS. So while a warming trend is
expected heading toward the end of the work week, how warm is an
open question.

In terms of rain chances, a chance (20-30%) of showers and maybe a
few thunderstorms are possible late Tuesday/Tuesday night with the
cold frontal passage. Another chance (20-30%) for showers and
thunderstorms exists Thursday night into Friday. All in all though,
a mostly dry pattern is expected to continue with little/no signal
for any widespread, significant rainfall.


Gosselin

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 439 AM CDT Sat May 9 2026

The ongoing fog/stratus will continue early this morning, but it
is expected to quickly lift and scatter out within a few hours
after sunrise. Thereafter, VFR conditions are expected. A cold
front may bring some scattered showers to the area, but the
probability was too low to add PROB30s attm. Winds are expected to
veer from the southwest to the north/northeast behind the front.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 8 AM CDT this morning for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Dense Fog Advisory until 8 AM CDT this morning for Adams IL-
     Brown IL-Calhoun IL-Greene IL-Jersey IL-Macoupin IL-Madison
     IL-Monroe IL-Pike IL-Saint Clair IL.

&&

$$

WFO LSX