Area Forecast Discussion

323
FXUS63 KLSX 170827
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
227 AM CST Wed Dec 17 2025

.KEY MESSAGES...

- Mild weather for mid December continues today. After a brief
  cool down Thursday into Friday, the mild weather returns
  again.

- The only significant rain chances come Thursday morning with a
  frontal passage.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 225 AM CST Wed Dec 17 2025

Although a weak front has dropped into the northern part of the
forecast area this morning, it`s already quite diffuse and will
continue to lose its definition and influence over our weather this
morning. After light winds this morning, they`ll become southerly
later today with afternoon temperatures as warm or warmer than
yesterday for most.

A trough moving onshore in the Pacific Northwest this morning will
dig a sharp trough into the Central Plains tonight and head to the
Great Lakes on Thursday. The result will be a stronger cold front
which brings a brief shot of colder air to our area. Ahead of the
front, Gulf moisture surges northward late tonight leading to warm
advection showers developing ahead of the front and light rain along
and behind it Thursday morning. There`s even the potential for just
enough instability to develop for a rumble or two of thunder,
although instability will be too limited for a severe weather
threat. We continue to expect strong winds behind the front, but
cold advection comes in two waves: the first Thursday morning and
again Thursday evening. This results in two bursts of greater mixing
in the cold advection, but perhaps less intense winds overall.
Greatest gusts are north of the Missouri River where 40 mph gusts
are possible.

Kimble

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 225 AM CST Wed Dec 17 2025

The cold peaks Thursday night into early Friday as high pressure
crests over the region. As the high moves east we already see warm
advection beginning even on Friday, with the full warm up felt by
Saturday when temperatures reach the 50s again. The probabilistic
NBM actually has chances of 60 degree readings approaching 50
percent south of the Missouri River.

Another cold front moves through late Saturday, but the core of the
cold air is driven eastward through the Great Lakes. So we only get
a glancing blow of cold from this one, not as intense as Thursday.
So expect a little cool down Sunday going into Monday, but it will
still be near or even above average for late December, in the 40s.
The NBM interquartile range for highs Sunday continues to shrink
reflecting growing confidence in this glancing blow rather than a
full thrust of cold. Early next week the warmer weather returns with
ridging becoming dominant aloft through around Christmas.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1105 PM CST Tue Dec 16 2025

VFR flight conditions are expected to prevail at least into
Wednesday evening. Some lower ceilings may be building into parts
of southeast and central Missouri at the very end of the period,
however guidance isn`t very clear on heights that far out just
yet. A weak cold front will drift into the area, briefly shifting
the wind to the northwest along and north of I-70, but the wind
will quickly turn back to the southeast by Wednesday afternoon.
Low level wind shear is also a possibility Wednesday evening,
though conditions look marginal so have not included LLWS in the
terminal forecasts at this time

Carney

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion