Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

142
FXUS63 KLSX 191106
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
606 AM CDT Fri Jun 19 2026

.KEY MESSAGES...

- A subtle fluctuation between seasonably cool to near-average
  warmth and humidity will persist through next week.

- Widespread showers and thunderstorms are forecast from late
  Saturday night through early Monday afternoon with thunderstorms
  capable of locally heavy rainfall.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 212 AM CDT Fri Jun 19 2026

An area of surface high pressure that originated in Canada yesterday
has continued to slide southward and is now centered over the area.
Calm surface winds coupled with a mostly clear sky across most of
the area, aside from some higher clouds, has aided in modest
radiational cooling which has allowed most of the area to reach the
upper 50s to lower 60s early this morning. As a result some
locations, particularly in river valleys and low-lying areas, may
experience some patchy fog this morning that would begin to fade
shortly after sunrise today.

Precipitation wise, as of 2am (07z), there is currently some meager
scattered shower activity nudging its way east across southern MO.
This activity is tied to a southwest to northeast oriented band of
850mb frontogenesis, which model guidance shows will continue to
weaken throughout the early morning. This includes the CAMs, which
only resolve a few scattered showers or a stray weak thunderstorm
clipping Reynolds/Iron/Madison counties in southern MO just before
sunrise. As a result, a brief shower/weak storm cannot be ruled out
for portions of southern MO early this morning, but this scenario
remains unlikely (<15%) as subsidence associated with the surface
high continues to increase.

The aforementioned surface high is forecast to essentially come to a
halt and fan out across the Midwest. As a result, it will influence
our weather through Saturday in the form of light surface winds, low
cloud cover, low precipitation chances (<15%), and slightly below
normal temperatures. Quasi-zonal flow aloft will remain in place
during this timeframe with a general lack of mid/upper-level
features propagating within, favoring a quiet and tranquil pattern.
The only exception to this pattern is a few subtle pieces of mid-
level energy that long-range guidance resolves within the flow aloft
late tonight into early on Saturday. The best chances for showers
and a stray thunderstorm appear to remain just to our north across
Iowa/northern IL, where a better chance (20-30%) exists. As of now,
the ingredients are less favorable across our area, resulting in
spotty 20% chances across the area early on Saturday. Highs today
and Saturday will be very similar in the low/mid 80s with lows
tonight in the low/mid 60s across the area.

Peine

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 212 AM CDT Fri Jun 19 2026

At the start of the extended, the mid/upper-level quasi-zonal flow
pattern becomes increasingly active with several shortwave
disturbance progged to be traversing into the Great Plains. As these
features approach from the west, lee-side surface cyclogenesis
commences Saturday evening resulting in strengthening warm/moist
advection from the Gulf. By Sunday afternoon, the LREF mean reveals
precipitable water values near 2-2.1" across the area (95-99th
percentile), indicating the potential for heavy rainfall. With
several shortwaves lined up within the quasi-zonal flow, it appears
there will be about a 36 hour window from late Saturday night/early
Sunday morning into Monday afternoon, where heavy rainfall will be a
threat across the area. Coinciding with the abundant moisture will
be abundant instability, which is expected to be greatest across
western MO where the LREF indicates MUCAPE values ranging from 1,000-
2,000 J/kg across our area Sunday afternoon/evening. Forecast
soundings reveal that a warm cloud layer >12,000ft is certainly
possible, which increases the potential for warm rain processes that
normally lead to more efficient rainfall production. Lastly, model
guidance progs a strengthening LLJ on Sunday reaching 50+kts,
leading to abundant moisture transport that will feed and organize
ongoing thunderstorms and increase the potential for locally heavy
rainfall.

Analysis of deterministic long-range guidance reveals the potential
for an MCS to develop Saturday evening across NE/KS. It appears the
mid-level shortwave will work to trigger convective initiation near
the strengthening lee-side surface cyclone with eastward propagation
into western MO early Sunday morning. Once it nears the MO border,
guidance reveals a plethora of MCS evolutions, leading to low
confidence on where any threat for severe weather, mostly the
potential for damaging wind gusts, and heavy rainfall will be. As it
stands now, heavy rainfall is the primary threat as the atmosphere
will be primed to feed thunderstorms that will be capable of
producing efficient rainfall. Any thunderstorms within MCS`s or that
form along outflow boundaries and become oriented in a fashion to
support training or back building of storms will lead to an
increased risk for locally heavy rainfall and potentially flash
flooding.

Tuesday and into the middle of next week, northwesterly flow aloft
resumes behind a longwave trough that slides into the Great Lakes
region. A large-scale setup like this, with a lack of shortwave
features or southern stream influence, will work to cut off
precipitation chances for the area. The LREF probability for 6 hour
accumulating precipitation unveils this with less than 20% chances
across the entire area from Monday night into late Wednesday.
Additionally, seasonably cool to near normal temperatures are
forecast for the remainder of the extended also. Guidance is in good
agreement on this as LREF temperature IQRs are less than 7 degrees
through the end of next week.

Peine

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 605 AM CDT Fri Jun 19 2026

Dry and VFR conditions are expected through the period with light
and variable winds.

Britt

&&

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

$$

WFO LSX