Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

231
FXUS63 KLSX 281019
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
419 AM CST Sat Feb 28 2026

.KEY MESSAGES...

- Brief, localized elevated fire weather conditions may develop in
  parts of the area this afternoon due to breezy winds and low
  humidity.

- A round of accumulating snow remains likely (70-80%) in some
  areas between late Sunday and early Monday, with localized
  travel impacts wherever the heaviest band of snow falls.
  Confidence is low regarding exactly where the most significant
  snow will fall.

- Widespread, substantial rain remains likely (80+%) across
  multiple rounds from Tuesday through the end of the week, with
  the potential for a few thunderstorms as well.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 336 AM CST Sat Feb 28 2026

FIRE WEATHER TODAY:

While the more significant fire weather conditions occurred
yesterday and conditions have improved, we aren`t completely out of
the woods in that regard as we may still see some pockets of
elevated conditions lingering through this afternoon. As we approach
sunrise, a weak cold front has settled into the area and stalled,
and this feature is expected to remain roughly along the Missouri
river through the day today. Meanwhile, a surface low is expected to
slowly traverse this boundary today, and the associated pressure
gradient will maintain breezy surface winds ahead of it. North of
the front, these winds will be primarily easterly, while south of
the front they will be largely southerly. In any case, sustained
speeds of 10 to 12 mph with occasional gusts to 20 mph can be
expected for the most part. Meanwhile, humidity values on either
side of the boundary are likely to dip into the 25 to 35% range, in
spite of the arrival of mid level moisture and cloud cover. Along
the front itself humidity is likely to stay just a bit higher (and
the fire weather threat lower) thanks to moisture convergence, but
since this front may waver throughout the day, there aren`t many
areas that we can definitively say WONT see at least a brief
period if elevated conditions. Not everywhere will, but there is
at least a reasonable chance for this in all but perhaps a few
areas of southwest Illinois where lighter winds are more likely.

Meanwhile, due to the aforementioned mid-level moisture and forcing
from the surface low and subtle mid level shortwave, increasing
cloud cover and widespread virga can be expected during the day,
with perhaps a few pockets of light showers as well. The primary
limiting factor here will be the persistent and deep dry layer in
the lower levels, which will be difficult to erode (and also
responsible for the continuation of a marginal fire weather threat).
Even where rain reaches the surface, it likely won`t amount to much
more than a hundredth of an inch or two.

Overnight, a more substantial cold front will surge southward
through the area, along with a more seasonably cold airmass. While
initially this won`t have a significant impact aside from bringing
our temperatures back to more typical values Sunday, it will set the
stage for a late-season round of accumulating snow sometime Sunday
night through Monday morning.

ACCUMULATING SNOW LATE SUNDAY / EARLY MONDAY

Driving this event will be the arrival of a compact mid-level
shortwave along the leading edge of a southern stream jet streak,
which itself will begin to phase with the polar jet somewhere in our
vicinity. While the jet dynamics involved are somewhat complex and
partially obscured by blended ensemble guidance, deterministic
models reveal that this feature will generate some potentially
robust mid-level frontogenesis and omega (vertical motion) as it
arrives, which should drive rapid saturation and eventually drive
precipitation to the surface. Exactly how quickly this occurs is a
major forecast point, because as we have already established, very
dry low level air will need to be eroded first. Model guidance
remains somewhat split on how quickly this will occur, both due to
differences in the degree of dryness that will be present, and also
the strength of the forcing. However, while this may delay the onset
time, eventually precipitation will win out and reach the surface in
most areas, and likely by sometime Sunday night at the latest.

From here, the primary question will be the distribution of
precipitation types, including exactly where and how much
accumulating snow will fall. Before we get into what we don`t know,
we still expect that at least some areas will see accumulating snow,
and likely enough to cover roads and impact travel. While there
remains a lot of variability in this forecast, this aspect of the
forecast has remained relatively consistent.

However, confidence remains relatively low regarding exactly where
the heaviest snow will fall, and how much. This is due to a number
of factors, but we will start with uncertainty in precipitation
types and rates. Regarding the former, most forecast model soundings
continue to support snow as the dominant frozen precipitation type,
as we have not seen a significant warm nose aloft that would produce
much more than brief pockets of freezing rain or sleet. However,
this is not iron-clad, as many of these profiles remain near the
melting layer for a significant depth, even when the upper levels do
eventually cool into the dendritic growth zone. Meanwhile, some
deterministic soundings do show the loss of saturation in the colder
parts of the profile (-10 or lower), suggesting a possible
transition from snow to freezing drizzle. Likewise, non-trivial
ensemble probabilities for light freezing rain accumulations remain
(20-40%) in both the NBM and LREF, so it can`t be completely
discounted. However, even if that did occur, we have doubts that
road temperatures would be cold enough to support ice accumulations
of such light amounts. Meanwhile, the presence of dry air will
support wet-bulb cooling and a transition to snow, although this may
require more substantial rates in order to be fully realized.

As for precipitation rates, there remains some variability regarding
the strength of the forcing associated with the shortwave. However,
most models continue to produce enough lift to drive accumulating
snow to the surface, including potentially impactful amounts (75th
to 90th percentile amounts of 3 to 4 inches). If any locations reach
those higher amounts, it is likely to be within a relatively narrow
corridor where the strongest forcing exists. We do not expect that
these higher end amounts will be widespread, and there will likely
be a significant difference in impacts where these amounts fall and
where they don`t, due to the fact that warm pavement temperatures
are likely to quickly melt lighter snow amounts.

Finally, the last lingering source of uncertainty is simply the
track of the shortwave. Model guidance appears to be trending a bit
farther south with this system and likewise with the main corridor
of accumulating snow, although there is still a wide range among
both individual members and clusters. In general, global models and
ensembles remain a bit further north, although even these
(particularly the GEFS) have shown a slight southerly shift.
Meanwhile, early returns from some of the longer range CAMS have
been much farther south, bringing the corridor of accumulating snow
to right along I-70 and even further south. While we`re not
confident that these southern outlier solutions are valid just yet,
it does reduce our confidence in the location of heaviest snow.

Snow (and rain) are likely to wind down sometime Monday morning or
early afternoon, and attention then turns to the onset of an
extended period of wet weather.

BRC

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 336 AM CST Sat Feb 28 2026

While there will likely be a lull in precipitation sometime late
Monday, this is likely to be short lived as our active pattern
continues early Tuesday. On a synoptic scale, the upper flow
pattern is expected to transition from zonal to southwesterly,
which will put our region within an active storm track and
persistent warm air and moisture advection. This is likely to
produce multiple rounds of widespread rainfall from Tuesday
through the end of the work week, including potentially some
thunderstorms.

Between Tuesday and Wednesday, a potent shortwave will emerge from
the Rocky Mountains and drive lee-cyclogenesis, and the resulting
low pressure system will approach our area from the west. Ahead of
it, strong southerly return flow will drive the northward transport
of warmer air and rich moisture (95th+ percentile ensemble mean
PWAT), which will likely be concentrated along stationary/warm front
draped across our area. Due to the interaction of this moisture with
the stalled front and steadily increasing upper forcing, rain is
likely to steadily increase beginning early Tuesday and continue
until the surface low arrives Wednesday. Exactly where this initial
rain falls is somewhat uncertain and may depend largely on where the
surface front stalls, but this becomes less of a factor as the low
arrives and drives another round of rain. Meanwhile, ensemble
guidance does produce some modest instability during this period, so
at least a few thunderstorms will also be possible. The potential
for strong/severe storms remains somewhat limited by modest overall
CAPE values, but given the strong dynamics, this will need to be
monitored. In any case, the potential for substantial, drought
improving rain amounts exists in many areas Tuesday and Wednesday.
In fact, the ECMWF extreme forecast index output has begun to
highlight Tuesday with a modest potential for more impactful rain
amounts, adding more confidence to the potential for substantial
rain. This likely won`t be the last of it, either.

That`s because another similar trough is expected to follow right
behind the mid-week system, likely driving another round of
widespread rainfall later in the work week. While confidence in the
finer scale details is lower with the latter system, ensemble mean
PWAT values once again climb above the 90th percentile in all
available ensemble suites, and even to the 97th-99th percentile in
the LREF. All that said, confidence continues to grow that most of
the area will see substantial rainfall by the end of the week.

BRC

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 415 AM CST Sat Feb 28 2026

VFR conditions are expected throughout the 12Z TAF period. Winds
are expected to be highly variable today as a low pressure system
moves through the area, although speeds are generally expected to
remain below 20kt for the most part. Overcast mid-level cloud
cover is expected for most of the day today, with widespread virga
and perhaps some brief, very light showers. Confidence in rain
reaching the surface or causing visibility/ceiling reductions
remains too low to include in the TAF at this time. A cold front
will switch winds to north-northeasterly this evening and this
will persist through the end of the period.

BRC

&&

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

$$

WFO LSX