FXUS63 KLSX 111723

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1123 AM CST Mon Dec 11 2023


- Temperatures vary little through the week with highs and lows
  near or slightly above seasonal norms.

- Dry conditions are favored with less than 20 percent of the
  ensemble members supporting measurable rainfall next weekend.


.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 310 AM CST Mon Dec 11 2023

Regional analysis (09z) shows a weak surface low over southeast
Nebraska tracking east-southeast into northwest Missouri this
morning. IR satellite shows broken mid/high clouds (12k feet)
extending from north-central Missouri southeast along and west of
the Mississippi River. Clouds are in response to a wing of weak warm
air advection that will have a modest impact on temperatures today.
A nearly stationary boundary extends southeast of the surface low
and bisect Missouri. Light/variable winds running ahead of the
boundary, eventually turn out of the south over the southwest third
of the state.

The features will gradually translate east/southeast today, drawing
in slightly milder temperatures this afternoon. Clouds will clear
out as the features continue to translate east/southeast through the
morning. Mostly sunny skies and strengthening southerly surface flow
will allow for a modest boost in temperatures with highs about 5
degrees warmer than Sunday. Conditions remain stable through the
short term period with mainly clear skies allowing temperatures to
fall back into the mid-20s/low-30s tonight.

A cold front pushes into the region late tonight into Tuesday, which
has a greater impact on northeast Missouri and west-central
Illinois. The front lacks moisture with mostly clear skies
persisting into Tuesday, but does have a sensible impact on
temperatures over northeast Missouri and west-central Illinois.
Highs will top out in the low-40s in these locations, while southern
sections of the forecast area warm closer to 50 degrees. The front
is expected to clear most areas by Tuesday night. However, mid to
high clouds are sent into the region from west to east as an upper
closed low positions over the southwest CONUS. This should help keep
temperatures from falling too much despite the cold front. Lows are
similar to Monday night - mid-20s/low-30s.


.LONG TERM...  (Tuesday Night through Sunday)
Issued at 310 AM CST Mon Dec 11 2023

NBM ensemble data shows exceptionally tight clustering with 25th-
75th percentile temperature ranges of 3-5 degrees (at most) through
Friday. Even heading into next weekend, when spread slightly
increases, temperature ranges are only 5-7 degrees. The only
precipitation probabilities are introduced late Friday into Saturday
with less than 10 percent of the members supporting measurable
rainfall (0.01" or greater) across any portion of the CWA. This
being said, there is higher than average confidence that current
forecasts through the period will play out close to reality with a
few minor notes.

A strong surface high (near 1040mb) traverses the Upper Midwest into
the Ohio Valley through midweek as a cold front slips south of the
forecast area. Cooler air will be fed into the region on the light
east and northeast surface flow that works around the eastern and
southern periphery of the surface high. Meanwhile, medium and long
range guidance shows high RH values (70-90 percent) ejecting
eastward from the closed low out of the southwest CONUS, signaling
mid/high level cloud cover impeding sunshine through much of the
day. With temperatures starting out in the mid-20s to low-30s, lack
of sunshine and passage of the front will keep temperatures from
moving much with highs more in line with December norms (40s).

Temperatures climb slightly Thursday into Friday on southerly return
flow as the high shifts east. The main question has been related to
rainfall potential, which continues to look low, but non-zero. NBM
remains below 10 percent on precipitation chances through the
weekend, along with LREF ensembles showing less than 20 percent
supporting measurable rainfall. GFS deterministic guidance shows a
northern stream closed low passing overhead from northwest to
southeast, while the ECM has the system moving well to the north.
This gives little confidence that any meaningful rainfall will come
to fruition with dry and mild conditions through the end of the



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1122 AM CST Mon Dec 11 2023

Dry and VFR conditions will prevail through the TAF period.
Southerly winds today will continue to increase through the
afternoon and diminish around sunset. A dry cold front will move
through the region Tuesday morning and veer southerly winds to



Issued at 536AM CST Sun Dec 10 2023

The early morning's light and variable surface flow will turn out
of the south through mid/late morning. Sustained surface winds
increase to around 10 knots this afternoon with an occasional
gust possible, especially over northeast Missouri and west-central
Illinois. Temperatures are expected to warm into the low-50s over
southeast Missouri today, while dewpoints remain in the 20s. This
results in minimum RH values around and just below 30 percent
around peak heating. Though winds increase and temperatures warm,
overlap of conditions result in a short-lived, limited area to
support marginal/borderline elevated fire conditions. If elevated
fire criteria is met, it would most likely occur between 18z and
22z in a general area south of Jefferson City, along and west of
highway 63.