774
FXUS63 KLSX 202059
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
259 PM CST Thu Nov 20 2025

.KEY MESSAGES...

- Another round of rainfall is expected tonight into Friday. A few
  thunderstorms are also possible. Rainfall amounts will range
  from around 0.50 inches to about 1.50 inches. Higher amounts are
  possible with thunderstorms.

- Dry and mild weather is expected this weekend.

- Another round of rain will affect the area on Monday into Monday
  night ahead of a cold front. This front will eventually bring
  much colder air to the Mid Mississippi Valley for Wednesday and
  Thursday.

&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 254 PM CST Thu Nov 20 2025

Wet weather will continue through at least Friday and probably the
first part of Friday night.  A warm front which is currently over
southern Missouri will drift north tonight to near the I-70
corridor.  Continuing low level moisture convergence in the vicinity
of the front will produce widespread rain and a few thunderstorms
into Friday evening.  Short range guidance shows the low associated
with this warm front moving through Missouri into Illinois late
Friday afternoon into the evening.  Somewhat drier air will spill
into the Mid Mississippi Valley behind the low and eventually shut
the precipitation off.  However this may take longer than earlier
forecast.  Many short-range models show precipitation continuing
behind the surface low as the mid/upper level short wave passes
through the region.  The RAP is showing some low level frontogenesis
in the wake of the low which is probably what`s forcing the
continuing precip in the models.  Have therefore bumped PoPs up over
the NBM Friday evening to likely and categorical across much of the
area, and lingered chance PoPs after midnight.  HREF storm total QPF
LPMM shows a few spots with 2+ inches of rain, but this should fall
over an extended period, not just an hour or two so am still not too
concerned with flooding.  Temperatures through Friday night remain
mild with highs mainly in the 50s to low 60s.  Low temps tonight
will only dip into the low to mid 50s for most locations, but it
will be cooler behind the low Friday night with lows ranging from
the mid 30s to mid 40s.

Carney

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 254 PM CST Thu Nov 20 2025

This weekend continues to look quiet with mild temperatures as high
pressure builds across the Mississippi Valley.  The next upstream
short wave is currently digging into the eastern Pacific just off
the California coast.  It will move across the Rockies and move into
the Central Plains by 12Z Monday.  Medium range deterministic
guidance continues to be in very good agreement with the speed and
strength of the wave.  It looks like the GFS is still a little
faster than the ECMWF as the wave moves through the Mid Mississippi
Valley Monday night, but the timing is closer than yesterday`s runs
were.  The NBM and LREF temperature IQRs on Monday and Tuesday are
in the 3-6 degree range for most locations, which is very good
agreement for a period with a frontal passage.  All guidance is
still advertising a good chance (60-80 percent) for rain ahead of
the front on Monday, though it doesn`t look like we`ll get as much
as we are with the short-range system.  Low level ridging will
linger along the Gulf Coast ahead of the front which will limit
moisture return, and the heaviest precip should be across the lower
Mississippi Valley.

Medium range guidance also remains very consistent in handling the
next upstream short wave which drives the secondary (and much
stronger) cold front through Missouri and Illinois late Tuesday into
Wednesday morning.  There are timing differences between the GFS and
ECMWF, with the ECMWF being faster.  It amplifies the wave more
quickly than the GFS and pushes the nose of the Arctic airmass
behind the front into Missouri and Illinois by 06Z Wednesday while
the GFS is about 6 hours slower.  The GFS also develops post-frontal
precip while the EC is dry.  Even with those differences, LREF
temperature IQRs on Wednesday and Thursday remain pretty tight at 4-6
degrees which lends high confidence to the advertised cool down
Wednesday and Thanksgiving.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1139 AM CST Thu Nov 20 2025

IFR flight conditions are expected to prevail through the period.
A warm front will drift north from southern Missouri to near the
I-70 corridor by late tonight. The front will produce more
widespread rain and possibly a few thunderstorms tonight into
Friday. Rain and fog will reduce the visibility to 3-5SM and
occasionally below through much of the night. There may be some
improvement to ceilings this afternoon, but not likely to get
above 900ft, and then ceilings will drop again with the rain
tonight.

Carney

&&

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

$$

WFO LSX