610
FXUS63 KLSX 061134
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
534 AM CST Thu Nov 6 2025

.KEY MESSAGES...

- Mild weather continues through at least Friday, but a strong
  cold front late Saturday brings a dramatic temperature plunge
  headed into the new week.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 232 AM CST Thu Nov 6 2025

Relatively fast zonal flow aloft continues across the region with
nearly daily frontal passages. These fronts have had little effect
on daytime temperatures, but low level moisture continues to slosh
back and forth with each frontal passage. Yesterday a cold front
moved through and brought drier air, but as high pressure moves east
today the winds turn southerly and bring the moisture back in. All
areas warm up into the 60s today, potentially near 70 in central
Missouri. But the moisture will be slowest to arrive in parts of
Illinois where low humidity and increasing winds will bring
conditions close to elevated fire danger, though the trend will be
for improving humidity as moisture arrives. After discussing with
neighboring offices, we have opted not to message elevated fire
danger today.

Low level moist advection continues this evening as the next cold
front approaches from the northwest. This time there`s better jet
dynamics with it and we`re expecting scattered showers and perhaps
an elevated thunderstorm to develop during the overnight hours as
moist advection on the low level jet produces modest instability
mainly over northern MO into central IL. This activity moves off to
the northeast by morning on Friday. The cold front itself is a bit
slower to move through, with winds behind this front turning more
westerly this time. Once again we don`t see a big difference in
daytime temperatures after the front moves through. In fact we`re
likely to be a few degrees warmer on Friday as deeper mixing in the
westerly flow behind the front allows for more areas to reach the
70s. However, the front is effective at pushing the low level
moisture aside, this time for good.

Kimble

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 232 AM CST Thu Nov 6 2025

The big story continues to be one final cold front, this one with
quite a stark temperature drop behind it. It drops south into Iowa
and northern Missouri Friday night before the next wave of low
pressure tracks eastward along it on Saturday. With low level
moisture scoured out ahead of this low by Friday`s front, there`s
not a lot to work with in terms of generating precipitation.
However, the deepening surface low will aid in pulling some of the
limited remaining moisture up and over the front into the frigid
Arctic air, allowing for some post frontal precipitation. This is
most likely across Iowa into northern Illinois Saturday and Saturday
night where temperatures may be cold enough for some snow. However,
some of this may also wrap around further southwest into parts of
our area as the low heads east and the Arctic air plunges southward
Saturday night. Among the long range ensemble guidance, 50 to 70
percent of members now produce precipitation across our forecast
area, but those that do remain light. Less than 40 percent produce
0.1 inch or more. Although temperatures do plunge, we expect that
the limited moisture pulls away to the east before temperatures fall
cold enough for snow in our area.

Cold surface high pressure dives southward through the Plains
Saturday night into Sunday with strong cold advection across
Missouri and Illinois. While temperatures ahead of the front
Saturday reach the 60s and possibly low 70s, Sunday will only see
upper 30s to low 40s during the daytime hours with a stiff northwest
wind making it feel even colder. For the first time this season we
actually get to talk about the Wind Chill which will be in the teens
and 20s by Sunday morning. There continues to be high confidence in
a hard freeze across the entire region Sunday night and Monday
night. Just how cold will depend on whether we can get clear, calm
conditions one of those nights. Sunday night seems likely to keep
some of the elevated northwesterly winds to prevent strong
radiational cooling, but cold advection alone will still be enough
for a widespread hard freeze. As the surface high pressure axis
crosses the region Monday night we stand a better chance of seeing a
period of clear and calm conditions, but at the moment it`s unclear
how soon winds pick back up out of the south/southwest. If we do
hang on to clear, calm conditions most of the night, then low
temperatures may be significantly colder than the currently
forecast, with teens more widespread in the cold spots.

This brief early season cold punch ends on Tuesday. After a cold
morning, southwest winds push warmer air back into the region. Just
24 hours ago, the NBM interquartile range (IQR) for high
temperatures on Tuesday was 12 to 14 degrees indicating a lot of
uncertainty on just how quick this warm up would be. Now, though,
the IQR has fallen to only 6 or 7 degrees, cutting that spread in
half compared to yesterday. That gives us even greater confidence in
the warm up with a return to the 60s becoming increasingly likely.
This warm air is not accompanied by return moisture, so this will be
a dry warm up. Southwesterly flow and a rapid warm up coming out of
an Arctic air mass is a classic set up for elevated fire danger
conditions, and we continue to see this as the greatest day of
concern from a fire weather perspective. NBM guidance increases
dewpoints by about 15 degrees on Tuesday compared to Monday,
although we don`t see much physical support for this kind of an
increase without a notable source of moisture upstream. There`s
strong potential for actual humidity values to end up lower than
currently forecast. In addition to the low humidity, wind forecasts
have nudged upward as well, as a cold front approaching from the
northwest helps increase the pressure gradient between it and the
surface high over the Southeast US. The probabilistic NBM is now
advertising 60 to 90 percent probability for sustained winds greater
than 10 mph Tuesday afternoon. Finally, there will be several days
of low humidity between now and Tuesday, including multiple hard
freezes to kill any remaining green vegetation making local
vegetation more susceptible to fire spread should fires start. It`s
a little early to start messaging this fire danger more broadly, but
we will continue to watch this and discuss it in the Fire Weather
Forecast.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 526 AM CST Thu Nov 6 2025

TAFs are similar to the last forecast package, focusing on gusty
winds today. These winds will shift from southeasterly to
westerly/southwesterly by the end of the period with the arrival
of a cold front. Light rain is likely at KUIN tonight as the front
passes, so added mention in the TAFs. Flight restrictions are not
expected. Guidance has let up some on MVFR ceilings lining the
front, so maintained VFR conditions at all terminals.

Soundings again show marginal low-level wind shear for tonight,
with the highest chance of this occurring at KUIN. With chances
lying on the brink of being impactful and with LLWS wavering
beyond that threshold or below depending on the model, decided to
hold off on adding it to the TAFs for now.

Jaja

&&

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

$$

WFO LSX