FXUS63 KLSX 161950
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
250 PM CDT Fri Oct 16 2026

.KEY MESSAGES...
- Frost is expected north of I-70 late tonight into early
  tomorrow morning.

- Cooler temperatures are expected the next couple of days,
  followed by more seasonable temperatures next week.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 248 PM CDT Fri Oct 16 2026

Mesoanalysis shows that a sharp upper-level trough is over the
Midwest and Great Lakes region. The trough is a main driver for
the widespread cloud cover currently over the region. There are
embedded isolated showers within the cloud cover caused by weak
low and mid-level lapse rates combined with weak warm air
advection providing just enough lift to allow for sustainment of
these isolated showers. The trough also brought the cold front
through our region yesterday that introduced northwesterly flow
resulting in much cooler temperatures compared to the last
several days. This afternoon we are not expected to have
temperatures above the mid 50s, which is 20-30 degrees cooler
compared to yesterday. As this trough continues its trek to the
east, an upper-level ridge of high pressure will move in
covering the central CONUS. This evening, the approaching ridge
will result in gradually lowering wind speeds and clearing skies
from north to south. Radiative cooling will allow low
temperatures overnight in northeast MO and west-central IL to
drop into the mid-30s. With low wind, clear skies, and low
temperatures there is high confidence for frost development, so
the Front Advisory remains in effect for late tonight and into
early tomorrow morning. Southeastern MO and southwestern IL will
not experience any frost due to remaining cloud cover and
associated warmer temperatures as the clouds continue to scatter
out to clear skies Saturday morning.

Thanks to the approaching ridge, Saturday’s high temperatures
are expected to rebound to around 60 degrees, which is still
around 10 degrees below our seasonal normals. Cold and clear
conditions are expected Saturday night into Sunday morning as
well, creating another risk for frost development across the
region, but there still remains uncertainty with the exact
location of the surface high and subsequently surface winds. A
Frost Advisory is currently not in effect for tomorrow night,
but is not off the table if conditions allow. Sunday’s high
temperatures are expected to be slightly warmer (in the
mid-60s), as the ridge settles over the region.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 248 PM CDT Fri Oct 16 2026

There is a consensus among ensemble and deterministic guidance
that once the ridge moves over the region tomorrow, that it will
remain through the week. This leads to high confidence in a
relatively uneventful week. The ridge will be bookended by
troughing along the West and East Coasts causing weak low-level
southwesterly flow during the week. As a result, there exists
support for warm air advection, albeit subtly. This will result
in a gradual warming of temperatures through the week. The first
half of the week will see a return to near normal temperatures,
but how much we warm by the end of the week remains uncertain.
LREF guidance has Thursday’s high temperatures in the low to
mid-70s, while the NBM has upper-70s to low-80s. The NBM is
likely warmer due to it being composed of bias-corrected
guidance that is warmer than non-bias guidance. This warm bias
is likely a result of it currently being the cooling season
combined with recent unseasonably warm events. Given this
potential impact from the bias correction, the NBM is probably
too warm and confidence is low in its temperatures towards the
end of the week.

Confidence is high in dry conditions prevailing through the week
due to the presence of weakflow aloft and lack of any notable
disturbances in both deterministic and ensemble guidance.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1247 PM CDT Fri Oct 16 2026

Low stratus associated with an upper-level trough is impacting
the region creating MVFR ceilings. These MVFR ceilings are to
the northwest of the St. Louis metro terminals, but are moving
to the southeast and will impact the terminals this afternoon.
There are some isolated showers that could impact the St. Louis
metro terminals, but confidence is low that they will be
directly impacted. As a result, VCSH was included to account for
the possibility. Winds at all terminals are expected to remain
gusty through the day. As high pressure moves into the region
from the west overnight, winds will become calm and the ceilings
will rise to VFR eventually giving way to clear skies.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Frost Advisory from 1 AM to 9 AM CDT Saturday for MOZ018-019-
     026-027-034>036-042-052.
IL...Frost Advisory from 1 AM to 9 AM CDT Saturday for ILZ058>060-
     095>099.

&&

$$

SHORT TERM...Asel/BSH
LONG TERM...Asel/BSH
AVIATION...Asel/BSH