Area Forecast Discussion

429
FXUS63 KLSX 070014
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
614 PM CST Tue Jan 6 2026

.KEY MESSAGES...

- Widespread rainfall is forecast on Thursday, though the axis of more
  significant rain (0.50"+) is now confined to parts of central
  and northeast Missouri as well as west-central Illinois.

- Unseasonably warm temperatures will continue through Thursday,
  with readings closer to normal for this upcoming weekend.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 222 PM CST Tue Jan 6 2026

Another day, another round of stratus for parts of the area, this
time across northeast Missouri and west-central Illinois. GOES-19
visible satellite imagery has shown continued westerly advection,
but also erosion on the southern side. However, this has been
confined to the southern flank whereas further west the stratus
has been more stubborn. The area that should clear last is our far
northern counties, likely around 2100 UTC. This is late in the
day, with not much in the way of warming/mixing before the sun
sets ~2 hours later. This raises the stakes for fog development,
with the most widespread (and possibly dense) fog most likely in a
northwest to southeast axis across central Iowa into parts of
northeast Missouri. Added fog here and have visibilities below
1SM, but it is possible that locally dense fog in our northeast
Missouri counties may be possible.

Any fog that does form likely will slowly lift into more pure
stratus Wednesday morning. With little/no advective flow, the
dissipation of the stratus will come down to how thick the stratus
is, solar heating, and any erosion. These are all difficult to
forecast 18-24 hours out, but stratus could at least impact high
temperatures in far northern sections of the forecast area on
Wednesday. Elsewhere, there is high confidence in plenty of
sunshine. Therefore, high temperatures in the low to mid 60s are
forecast. These readings would be nearly 25 degrees above normal for
the date.


Gosselin

&&

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 222 PM CST Tue Jan 6 2026

(Wednesday Night - Thursday Night)

Most of Wednesday night should be dry and mild, with low
temperatures only dropping back into the mid 40s. Chances of rain
ramp up after 0900 UTC Thursday, first in parts of central/southeast
Missouri as low-level warm/moist advection strengthens ahead of the
approaching midlevel shortwave trough. This aforementioned trough is
about 100-150 miles further northwest than it looked 24 hours ago.
Consequently, the focus for the most significant rainfall has also
shifted with this forecast package. Now the focus is across
central/northeast Missouri into west-central Illinois. LREF
probabilities remain high for at least 0.50" of rain, in the 60-80%
range. Further southeast, rainfall amounts drop gradually. Parts of
southeast Missouri are likely (60+%) chance to see at least a
quarter inch, but not much more.

By 0000 UTC Friday, a strong surface low is expected to be located
near the Quad cities, with an attendant cold front draped to its
southwest. This frontal boundary along with possibly a prefrontal
trough further to the east, could serve as foci for the
redevelopment of showers. Probabilities for 100+ J/kg of SBCAPE
remain very low (>snow) along/northwest of the track of a secondary midlevel
vorticity maxima. This area of precipitation may clip northern
sections of the area Friday night. The precipitation should start
off as rain, but may mix with or changeover to snow before ending.
Little/no accumulation is expected at this time. Even if the rain
were to change over to snow earlier than expected, rates should be
low enough to only accumulate on elevated/grassy surfaces. Marginal
(aka above freezing) surface temperatures and a warm ground should
make it very difficult for any impactful snow in our area.

Guidance still varies on how this secondary midlevel shortwave
trough interacts or phases with a closed low diving across the US-
Canadian border early Saturday. If this occurs far enough
west/south, we may see lingering chances of snow showers on Saturday
into Saturday night. Northern sections of the area have the best
chance currently (10-30%). Interestingly, the deterministic ECMWF has
on/off shown a true secondary cold frontal passage Saturday
afternoon/evening with light snow along/immediately behind this
boundary. There isn`t much support for this in ensemble guidance at
the moment, with the LREF only showing a 10-20% chance of measurable
snowfall. However, individual ensemble members are typically lower
resolution than their deterministic counterparts, so there may be
some merit to what the ECMWF is showing. At the very least, the
pattern with strongly cyclonic flow aloft does suggest at least the
possibility of on/off snow showers over much of the region Saturday
afternoon/evening.


(Sunday - Next Tuesday)

Ensemble guidance is largely in pretty good agreement to end the
weekend into early next week. The coldest day of the entire 7-day
period should be on Sunday as mean 850-hPa temperatures sliding
closer to -10C. Highs are expected to be mainly in the 30s, though
these values are more likely to come down a couple of degrees over
the next couple of days. The current forecast is very near the 75th
percentile of the NBM.

A quick warmup is expected early next week as mid/upper level
heights rise and return flow commences behind a departing surface
high. Readings are forecast to climb back above normal starting
Monday, with highs in the mid 40s to low 50s each day.


Gosselin

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 613 PM CST Tue Jan 6 2026

The low status deck that was over northeastern Missouri continues to
slowly advect to the east with light westerly flow across the
region. Areas where the low stratus cleared just hours before sunset
and where it is currently clearing will likely develop areas of fog,
some of which is expected to be IFR fog. Thus, the best fog setup
looks to remain over the KUIN terminal with IFR fog expected by
early Wednesday morning. However, some guidance indicates the
potential for fog to develop further south and east toward the STL
metro. Confidence in fog occurring around the metro terminals is
currently low (30-40%), but will continue to be monitored this
evening. Fog is expected to last until late morning with areas of
dense (

NWS LSX Office Area Forecast Discussion