Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

543
FXUS63 KLSX 212256
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
556 PM CDT Sat Mar 21 2026

.KEY MESSAGES...

- Very warm, near daily record high temperatures are expected in
  many areas again tomorrow, but a sharp cold front will bring
  more typical temperatures Monday (along with gusty winds late
  Sunday).

- Elevated Fire Danger for erratic fire behavior is expected
  Sunday afternoon in parts of the area, mostly across southeast
  MO and a limited portion of southwest Illinois.

- An isolated thunderstorm or two is possible in southwest
  Illinois late tomorrow afternoon and evening.

&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 142 PM CDT Sat Mar 21 2026

While we don`t anticipate major weather hazards during the short
term period, there are a few items to discuss, including near record
warmth and elevated fire weather this afternoon and again tomorrow,
followed by a sharp cold front and perhaps a few showers and
thunderstorms late in the afternoon and evening.

Before we get to tomorrow, we still have a few more hours of heating
left this afternoon, along with the potential for elevated fire
weather conditions. As of noon, temperatures have risen to within a
degree or two of where they were yesterday, and are on pace to reach
the upper 80s to near 90 degrees east of the Mississippi river. This
places all three climate locations (St. Louis, Columbia, Quincy)
within range of daily record high temperatures again today.
Meanwhile, relative humidity values have already dipped into the 30s
and 40s early this afternoon, and will likely bottom out between
roughly 25 to 35% in most areas, perhaps slightly lower in
central/northeast Missouri. While wind speeds have been very light
so far, areas of northeast Missouri and west-central Illinois may
see wind speeds reach 10-15 mph during the middle of the afternoon,
resulting in a brief period of elevated fire weather conditions.
While the overlap of breezy winds and low humidity will be brief and
limited in coverage, vegetation is currently very dry, which may
exacerbate the fire weather threat.

While quiet conditions are expected overnight, a persistent
southerly breeze is expected overnight thanks to an approaching low
pressure system and cold front from the northwest. This will
maintain persistent warm air advection aloft, and will set the stage
for yet another very warm afternoon tomorrow ahead of the advancing
front. In fact, in areas that remain south of the boundary during
the day, compressional warming may even add another few degrees to
the afternoon high temperatures, and we may see a few 90s during the
warmest part of the day. Not only this, but even though surface
dewpoints will be slightly higher than they were yesterday, these
very warm temperatures are still likely to result in minimum
humidity values reaching near 25 to 35% in the Ozarks. Between that
and a persistent 10-15 mph southwest breeze in these areas, along
with the previously mentioned dry vegetation, conditions will once
again support an elevated fire weather threat. While these
conditions are not extreme, we recommend leaving the outdoor burning
to land management agencies, as fires may behave erratically.

As the cold front moves through areas south of I-70 late in the
afternoon and evening, it will begin to interact with gradually
pooling low level moisture and modest instability (1000-1500 J/kg
MUCAPE). Model forecast soundings continue to indicate that the
warm sector will be characterized by both high LCLS and a very
stout layer of warm air aloft, and surface based initiation
remains much more likely to our east. However, there is a slightly
better chance for a few elevated showers and thunderstorms to
develop behind the front as it passes, although chances for this
activity are also slightly better across the Ohio River Valley.
Still, it won`t be out of the question to see an elevated shower
or brief thunderstorm considering the forecast instability, steep
lapse rates above the warm nose, and strong winds aloft. The most
likely hazards would be small hail and lightning, with better
chances for severe storms to our east.

Also, winds will become sharply northerly and increase behind the
cold front, with non-thunderstorm wind gusts very likely to reach 30
to 40 mph in many areas between late afternoon and late evening.
Wind fields within the mixed layer to not currently appear to be
strong enough to warrant a Wind Advisory at this time, but this will
need to be monitored.


19

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 142 PM CDT Sat Mar 21 2026

Behind Sunday`s cold front, an expansive area of surface high
pressure will settle into the Mississippi River Valley, bringing
with it a much more seasonable airmass and temperatures. While highs
are likely to be about 30 degrees cooler than the day prior, this
only will bring us down to near seasonal averages. While wind speeds
will be a limiting factor, humidity is also forecast to be low
enough that we will need to monitor the potential for some localized
elevated fire weather conditions as well. Otherwise though, Monday
is expected to be a generally comfortable and dry day.

This cooldown will be brief, though, as a broad upper ridge will
build again across the western and central CONUS during the mid-week
period. Once again, the core of the upper ridge will be located to
our west with northwest flow aloft overhead, building heights and
southerly low level winds will drive another warmup between Tuesday
and Thursday. This will be slow at first, as the northwesterly flow
aloft will leave the area exposed to a subtle clipper and weak cold
front Wednesday (along with a very modest chance for light rain),
but confidence is increasing that by Thursday temperatures will once
again climb well into the 80s. In fact, Thursday`s setup has a lot
of similarities to Sunday`s, as a cold front will likely approach
the area from the north, with persistent southwesterly low level
flow and warm advection ahead of it in the warm sector. Ensemble
mean 850 mb temperatures are once again forecast to reach or
exceed the 99th percentile, and unless the surface front arrives
slightly faster than expected, this will very likely result in
another very warm day.

Meanwhile, ensemble probabilities for precipitation are also
increasing in latest guidance as this cold front moves through the
area Thursday/Friday, albeit with some slight timing differences
among members. Ensemble mean PWAT forecasts have increased slightly
to near the 90th percentile of climatology, and we also note an
increase in instability projections as well. This appears to be
driving a modest signal for strong/severe thunderstorms in long
range CIPS/CSU output, and this trend will also need to be monitored
as we get closer to Thursday. At this time, confidence is low in the
quality of moisture and degree of instability that will be realized,
in addition to the typical timing concerns with frontal passages at
this distant time range.


19

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 544 PM CDT Sat Mar 21 2026

Dry, VFR conditions are forecast at the major terminals in the
region through the valid TAF period. Periods of low-level wind
shear are forecast at the central Missouri terminals through KUIN
overnight tonight with a strengthening LLJ overhead and light
winds near the surface. This threat abates by sunrise, when
surface winds should strengthen and the boundary layer mixes.

Southerly winds will prevail before a strong cold front advances
from north to south Sunday afternoon. While winds ahead of the
front will be largely near or below 10kts, they strengthen post-
frontal and remain strong through the evening. There is also a
chance for some showers and thunderstorms along the front,
primarily in far eastern Missouri and parts of Illinois. At this
time, all evidence suggests convection will initiate south and
east of the TAF sites, but this will be monitored.

MRB

&&

.CLIMATE...
Issued at 242 AM CDT Thu Mar 19 2026

Record Highs at STL/COU/UIN for 3/21-3/22
       STL        COU        UIN
3/21 90 (1907)  92 (1907)  88 (1907)
3/22 88 (1907)  90 (1910)  84 (1907)


&&

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

$$

WFO LSX