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Old Jamestown, Missouri 7 Day Weather Forecast
Wx Forecast - Wx Discussion - Wx Aviation
NWS Forecast for 3 Miles NNW Black Jack MO
National Weather Service Forecast for: 3 Miles NNW Black Jack MO
Issued by: National Weather Service Saint Louis, MO
Updated: 1:26 am CDT Aug 21, 2026
 
Overnight

Overnight: Patchy fog after 4am.  Otherwise, mostly clear, with a low around 63. Calm wind.
Patchy Fog

Friday

Friday: Patchy fog before 8am.  Otherwise, sunny, with a high near 86. Calm wind becoming west around 5 mph in the afternoon.
Patchy Fog
then Sunny
Friday
Night
Friday Night: Clear during the early evening, then becoming mostly cloudy, with a low around 69. Light and variable wind.
Mostly Cloudy

Saturday

Saturday: Sunny, with a high near 86. North wind 5 to 9 mph.
Sunny

Saturday
Night
Saturday Night: Mostly clear, with a low around 65. North wind 3 to 7 mph.
Mostly Clear

Sunday

Sunday: Sunny, with a high near 82.
Sunny

Sunday
Night
Sunday Night: Mostly cloudy, with a low around 64.
Mostly Cloudy

Monday

Monday: A 30 percent chance of showers and thunderstorms after 1pm.  Partly sunny, with a high near 81.
Partly Sunny
then Chance
Showers
Monday
Night
Monday Night: A 20 percent chance of showers and thunderstorms.  Partly cloudy, with a low around 66.
Slight Chance
T-storms
Lo 63 °F Hi 86 °F Lo 69 °F Hi 86 °F Lo 65 °F Hi 82 °F Lo 64 °F Hi 81 °F Lo 66 °F

 

Overnight
 
Patchy fog after 4am. Otherwise, mostly clear, with a low around 63. Calm wind.
Friday
 
Patchy fog before 8am. Otherwise, sunny, with a high near 86. Calm wind becoming west around 5 mph in the afternoon.
Friday Night
 
Clear during the early evening, then becoming mostly cloudy, with a low around 69. Light and variable wind.
Saturday
 
Sunny, with a high near 86. North wind 5 to 9 mph.
Saturday Night
 
Mostly clear, with a low around 65. North wind 3 to 7 mph.
Sunday
 
Sunny, with a high near 82.
Sunday Night
 
Mostly cloudy, with a low around 64.
Monday
 
A 30 percent chance of showers and thunderstorms after 1pm. Partly sunny, with a high near 81.
Monday Night
 
A 20 percent chance of showers and thunderstorms. Partly cloudy, with a low around 66.
Tuesday
 
Mostly sunny, with a high near 85.
Tuesday Night
 
Partly cloudy, with a low around 69.
Wednesday
 
Partly sunny, with a high near 87.
Wednesday Night
 
Partly cloudy, with a low around 67.
Thursday
 
Sunny, with a high near 86.

 

Forecast from NOAA-NWS for 3 Miles NNW Black Jack MO.

Weather Forecast Discussion
777
FXUS63 KLSX 210335
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1035 PM CDT Thu Aug 20 2026

.KEY MESSAGES...

- Another round of fog (some potentially dense) is favored
  tonight/Friday morning, mainly in river valleys.

- Near to slightly below average temperatures will persist
  through the weekend into early next week.

- There is a low (20 percent) chance of showers and a few
  thunderstorms Friday night into early Saturday afternoon.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 225 PM CDT Thu Aug 20 2026

The passage of a subtle upper-level shortwave trough and a weak
boundary across southwestern IL/southeastern MO has been sufficient
for isolated showers to develop this afternoon, dissipating/drifting
southeastward of the CWA by this evening. Otherwise, a high pressure
center across the Midwest and Great Lakes will continue building
into the CWA tonight into Friday morning, contributing to conditions
favorable for efficient radiational cooling and fog with clearing
skies and residual moisture. Fog will be most widespread and dense
in river valleys with low temperatures around 60 F providing enough
air-water temperature difference for steam fog development in those
locations as well.

Fog will dissipate within an hour or two of sunrise Friday morning.
As the surface high pressure center begins retreat to the northeast,
weak low-level WAA and strong insolation will lead to warmer high
temperatures on Friday, closer to average in the mid to upper
80s F.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 225 PM CDT Thu Aug 20 2026

Late Friday evening into night, an upper-level trough entering the
Great Lakes will force a weak cold front into the CWA overnight that
slowly advances southward Friday night through early Saturday
afternoon. Showers and thunderstorms are expected to be ongoing
Friday evening along the front across IA into IL, but conditions
will be less favorable for precipitation along the front overnight
this far southwest with strong large-scale forcing passing to the
northeast, a weak capping inversion, and weak frontal convergence.
However, another opportunity for showers and thunderstorms comes
with weak mid-level FGEN and upper-level diffluence extending from
the Central Plains into MO later in the night into Friday morning.
Effective deep-layer wind shear of 35 to 50 kt, steep mid-level
lapse rates, and 1500 to 2500 J/kg MUCAPE suggest at least a low
threat of large hail could exist with these thunderstorms, but
significant questions regarding the coverage and large-scale forcing
mechanisms to support thunderstorms locally preclude any messaging
of threats at this point. With the front lingering near southeastern
MO into early Saturday afternoon, the potential for thunderstorms
also lingers across that area. However, CAMs have widely different
scenarios for the Friday evening-Saturday afternoon timeframe with
HREF probabilities of measurable rainfall mainly 25 percent or less.

Behind the cold front, anomalous upper-level longwave troughing
across the Great Lakes will facilitate arrival of a relatively more
substantial, seasonably cool and dry airmass into the Mid-
Mississippi River Valley Saturday into Monday with below average
high temperatures mainly in the upper 70s to low-80s F. By Monday
through mid-next week, global model guidance is in better agreement
that longwave troughing will loosen its hold on the Great Lakes
allowing a wavering front to lift northward toward the Mid-Missouri
River Valley. This front will be the favored corridor for rounds of
showers and thunderstorms around an upstream ridge in response to
passing shortwave troughs and/or nocturnal LLJs. There is an east-to-
west gradient in ensemble model probabilities of measurable rainfall
across MO through the period indicating uncertainties in the
northeastward progression of the front toward the CWA, which also
impacts how much temperatures warm next week. In the NBM, there is
at least an underlying warming trend toward average after Monday
with airmass modification.

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1028 PM CDT Thu Aug 20 2026

Fog is still expected across much of the area tonight, with the
worst of the impacts expected at river valley sites KJEF, KSUS,
and KCPS. There is a low chance for MVFR visibility reductions
at KSTL. Fog will dissipate by mid-morning, with confidence high
in VFR flight conditions then through the day. There is a very low
chance for isolated showers and thunderstorms tomorrow
afternoon.

&&

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

&&

$$

SHORT TERM...Pfahler
LONG TERM...Pfahler
AVIATION...Elmore
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Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather






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