Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

232
FXUS63 KLSX 201712
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1112 AM CST Sat Dec 20 2025

.KEY MESSAGES...

- While we have another brief cooldown to get through tomorrow, a
  significant warmup is nearly certain Monday through Thursday.
  Daily record high temperatures will be within reach Christmas
  Eve and especially Christmas Day.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 159 AM CST Sat Dec 20 2025

While we still have one brief cooldown on the way tomorrow, the main
story for the next week continues to be the expectation of
unseasonable warmth heading into mid week, with near-record highs
possible on Christmas Day. Before we get there, though, we have one
more cold front to discuss in the short term.

Early this morning, breezy southerly winds have developed in
response to a surface low moving along the U.S./Canadian border. As
a result, warm air advection has kept temperatures about 10-15
degrees warmer than they were at the same time last night, and this
warming trend will continue into the afternoon as well. Highs across
the Ozarks and southwest Illinois are likely to climb will into the
50s today, perhaps even to near 60 in a few spots, which amounts to
an even greater departure than yesterday`s highs (about 20 degrees).
While areas farther north will also be warmer than yesterday, a cold
front is expected to reach our northern areas before peak heating,
which will cap our temperatures here to somewhere in the mid to
upper 40s. Still above average and noticeably warmer than yesterday,
but not quite as comfortable as areas farther south.

This front will push through the area late in the afternoon and
evening, and will bring another brief round of colder air. Still,
"colder" in this case will actually be close to seasonal averages,
if not still a few degrees above average by tomorrow afternoon when
temperatures are likely to rise into the 40s. Meanwhile, this cold
front will also be a dry one, and no precipitation is expected.

From Sunday night onward, attention then turns to our much
anticipated warmup, which will be discussed in greater detail in the
long term section below.

BRC

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 159 AM CST Sat Dec 20 2025

Between Sunday night and Thursday (Christmas Day), a broad upper
level trough is expected to gradually build across the central U.S.,
eventually reaching exceptional heights for this time of year. In
fact, ensemble mean 500mb geopotential heights reach near
climatological maximums by Thursday across a large portion of the
southern and central plains. Meanwhile, a series of ridge running
troughs will drive increasing southwesterly flow across the plains
and Mississippi Valley, with an initial surge Monday followed by
another round Wednesday through Thursday. The combination of these
features will drive a steady warmup across our area, culminating in
near record warmth on Christmas Eve and Christmas Day. At this
point, it is a near certainty that afternoon temperatures will climb
to at least 25 degrees above average on both days, and the only
question now is whether or not we will set daily
records...particularly on Christmas Day itself.

In addition to the exceptional 500mb heights, there is a long list
of indices that suggest daily records will be achievable Christmas
Day. For starters, ensemble mean 850 mb temperatures are forecast to
reach or exceed the 99th percentile on both days area-wide, in all
of the major ensemble suites. Meanwhile, the ECMWF Extreme Forecast
Index product strongly suggests that temperatures will reach
"extreme" levels for this time of year, which adds more confidence
to the going forecast. Meanwhile, ensemble temperature spreads are
also quite narrow, with interquartile ranges of only a few degrees,
and median values in the low 70s Christmas Eve and Christmas Day
(per the LREF and NBM).

It should be noted, though, that while records will be within reach,
the operational NBM output is actually the warmest available
deterministic forecast we could find. For instance, the latest NBM
forecast for Thursday`s high temperature in St. Louis is now 75
degrees, which would break the daily record of 71 degrees easily.
While that is possible, the NBM may also be a bit too bullish, in
spite of the evidence above that suggests that this is at least
plausible. Since we`re only talking about a difference of a few
degrees at temperature ranges that likely won`t cause immediate
impacts, regardless of how unusual these temperatures are, we
opted not to deviate from the NBM for now.

From Friday onward, a cooling trend appears increasingly likely as
the upper ridge flattens and cold fronts return to the area.
However, temperature spreads do increase considerably during this
timeframe, and in spite of the trend, the forecast continues to
favor slightly above average temperatures through the weekend.

Finally, precipitation chances remain rather low for the next week.
The only noteworthy opportunity for such will be across our
southeastern areas, mainly the Ozarks and southwest Illinois, where
some light rain and/or drizzle may periodically develop between
Monday and Wednesday. This appears to be largely driven by warm air
advection overrunning lingering cool surface air, with model
soundings that feature ample low-level saturation and little, if
any, instability. While we will likely see persistent cloud cover
early in the week that might take a couple degrees off of high
temperatures during the initial stages of the warmup, we don`t
expect meaningful precipitation accumulations.

BRC

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1109 AM CST Sat Dec 20 2025

Confidence is high in dry and VFR flight conditions through the
TAF period at all local terminals. Winds will quickly become
north-northwestelry this afternoon as a front passes over the
region, then becoming variable overnight as high pressure moves
through.

Elmore

&&

.CLIMATE...
Issued at 200 AM CST Thu Dec 19 2025

Well above normal temperatures are forecast around Christmas,
with record temperatures within reach. Records for our three
climate sites and the years that they occurred are listed below.

   KSTL  KCOU  KUIN
12/2473(2021)74(2021)69(2021)
12/2571(1889)74(1889)66(2019)


&&

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

$$

WFO LSX