Affton, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

988
FXUS63 KLSX 132030
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
230 PM CST Tue Jan 13 2026

.KEY MESSAGES...

- Light rain is expected this evening, mainly south of I-70. The
  next chance of precipitation is Thursday night/early Friday
  morning with a 40 to 60 percent chance of light snow in west-
  central/south-central IL.

- Multiple cold fronts are expected to move through over the next
  4-5 days, with temperatures getting progressively colder behind
  each front. The coldest temperatures will be Saturday into
  Sunday morning.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 223 PM CST Tue Jan 13 2026

Strong west-southwesterly surface winds today have allowed
temperatures to quickly climb into the low 50s (north) to mid 60s
(south) across the area. The warmer temperatures (S of I-70), have
been aided by downsloping winds off the Ozark Plateau. Throughout
the day, mid-level stratocumulus clouds have been on the increase
due to falling heights aloft associated with an approaching
upper- level trough. These clouds have limited the rate of
warming slightly, particularly in the northern half of the area,
where these clouds have been more persistent since sunrise.
Surface winds will slacken and veer to the west this evening ahead
of the aforementioned upper-level trough and its attendant cold
front(s).



Some model guidance is indicating a `double barrel` cold front setup
with this system. It appears that the first FROPA (overnight) brings
a notable wind shift to the northwest and a round of light rain to
locations mainly along and south of I-70. High-res guidance has been
consistent, with the 50th percentile for accumulated precipitation
staying around 0.02" for the STL metro and up to 0.06" for points
south. Even the HREF 90th percentile has only a few pockets with
up to 0.10", mainly to the southwest across the Ozarks. With the
deep westerly/northwesterly flow ahead of this system and very dry
low- level air in place, there is not a sufficient amount of
moisture being advected into the region, thus increasing
confidence that rainfall amounts will be very light. The second
FROPA, marked by an increase in surface winds, looks to bring a
reinforcing shot of low- level CAA around sunrise tomorrow. This
reinforcing shot of CAA could lead to some saturation of the lower
levels along with steeper low-level lapse rates, indicating the
potential for some sprinkles or flurries tomorrow morning, mainly
along and east of the Mississippi River. The period for sprinkles
or flurries will be brief (2-3hrs) as dry air wins out, likely
leading to a clearing sky by the late morning hours.

With continued CAA tomorrow afternoon under deep northwesterly flow,
temperatures will struggle to moderate from the morning despite an
expected clearing trend by the afternoon. At most, temperatures may
flatten out during the afternoon with peak solar insolation, before
quickly falling again tomorrow after sunset. Tomorrow night, a
surface high will be sliding to the south across the Central Plains
placing the region under light northerly flow, resulting in a good
setup for radiational cooling. As a result, lows Thursday morning
will reach the low to mid teens across the area.

Peine/Pfahler

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 223 PM CST Tue Jan 13 2026

Through the end of the week and the weekend, upper-level longwave
troughing will persist across Ontario, Canada and the Great Lakes,
leading to northwesterly flow prevailing over the Mid-Mississippi
River Valley through most of the period. Brief ridging will allow
temperatures to recover somewhat with low-level WAA taking place
from Thursday into Friday; however, additional upper-level shortwave
troughs will pass Friday into the weekend, providing multiple cold
frontal passages accompanied by increasingly cold air infiltrating
the region. An arctic airmass is finally anticipated to be in place
Saturday into Sunday morning with 850-hPa temperatures cooling to
near the 2.5th climatological percentile. The NBM interquartile
temperature range (IQR) is generally in the 20s to around 30 F for
high temperatures on Saturday, but low temperatures Sunday morning
are uncertain due to whether or not a low-level arctic anticyclone
is positioned favorably close and there will be any light snow
cover. This uncertainty results in a 10 F-IQR spread between
slightly below 0 F to the low teens F. The coldest temperatures are
at least expected along/north of I-70, where ensemble model
probabilities of below 0 F wind chill values are 40 to 60 percent at
this point with persisting light winds.

Ahead of a passing cold front Thursday night/early Friday morning,
model guidance is signaling a transient band of light snow
developing within a corridor of mid-level isentropic ascent/WAA and
moisture. Ensemble model 24-hour probabilities of measurable
snowfall centered on that time period are highest at 60 to 80
percent across west-central/south-central IL, with 1" probabilities
20 percent or less. These probabilities assume 10:1 SLR and are
likely underdone (higher SLRs favored), and with snow falling
overnight and the antecedent cold airmass, minor impacts are
possible in those areas. It is worth noting that the PoPs in our
official forecast are lower and still increasing as timing
differences are gradually resolved. Elsewhere, confidence is lower
that accumulating snowfall will occur with the potential for more of
the snow to go toward sufficiently saturating the atmosphere. The
pattern will remain favorable for episodic flurries and light snow
showers Friday evening through Saturday evening with multiple
passing shortwave troughs and accompanying cold fronts amid deep
northwesterly and cyclonic flow persisting.

Forecast uncertainty increases Sunday into early next week, with
global model guidance spread on if the upper-level longwave trough
downstream shifts enough to provide a break from northwesterly,
cyclonic flow in lieu of low-level southwesterly flow/WAA. As such,
the NBM IQR of temperatures is spread around 10 to 15 F, ranging
from temperatures moderating toward average to cold, below-average
temperatures persisting.

Pfahler

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1159 AM CST Tue Jan 13 2026

Increasing mid-level clouds will continue to move in from north to
south today with gusty west-southwesterly surface winds relaxing
shortly after sunset this evening. The low chance (30%) for light
rain tonight remains over the central Missouri and STL metro
terminals with no VIS reductions expected. A strong cold front drops
in from the north tonight, bringing lower stratus (3-5kft) and
strong northwesterly winds gusting to 20-28kts by the morning. Some
of the lower stratus may briefly reach MVFR but confidence in these
lower ceilings is not high at this time. Clouds will eventually
clear by tomorrow afternoon.

Peine/Pfahler

&&

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

$$

WFO LSX