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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: 3:11 am CDT Aug 8, 2026
 
Overnight

Overnight: Mostly clear, with a low around 72. West wind around 5 mph.
Mostly Clear
Saturday

Saturday: Sunny, with a high near 90. West wind 3 to 5 mph.
Sunny
Saturday
Night
Saturday Night: Mostly clear, with a low around 73. Light and variable wind.
Mostly Clear
Sunday

Sunday: Sunny, with a high near 93. Heat index values as high as 103. South wind 5 to 10 mph.
Sunny
Sunday
Night
Sunday Night: Mostly clear, with a low around 77. South wind 8 to 10 mph.
Mostly Clear
Monday

Monday: Sunny, with a high near 95.
Sunny
Monday
Night
Monday Night: Partly cloudy, with a low around 78.
Partly Cloudy
Tuesday

Tuesday: Mostly sunny, with a high near 94.
Mostly Sunny
Tuesday
Night
Tuesday Night: A 30 percent chance of showers and thunderstorms, mainly after 1am.  Partly cloudy, with a low around 76.
Chance
T-storms
Lo 72 °F Hi 90 °F Lo 73 °F Hi 93 °F Lo 77 °F Hi 95 °F Lo 78 °F Hi 94 °F Lo 76 °F

Extreme Heat Watch
 

Overnight
 
Mostly clear, with a low around 72. West wind around 5 mph.
Saturday
 
Sunny, with a high near 90. West wind 3 to 5 mph.
Saturday Night
 
Mostly clear, with a low around 73. Light and variable wind.
Sunday
 
Sunny, with a high near 93. Heat index values as high as 103. South wind 5 to 10 mph.
Sunday Night
 
Mostly clear, with a low around 77. South wind 8 to 10 mph.
Monday
 
Sunny, with a high near 95.
Monday Night
 
Partly cloudy, with a low around 78.
Tuesday
 
Mostly sunny, with a high near 94.
Tuesday Night
 
A 30 percent chance of showers and thunderstorms, mainly after 1am. Partly cloudy, with a low around 76.
Wednesday
 
A 30 percent chance of showers and thunderstorms. Mostly sunny, with a high near 92.
Wednesday Night
 
A 50 percent chance of showers and thunderstorms. Partly cloudy, with a low around 73.
Thursday
 
A 50 percent chance of showers and thunderstorms. Partly sunny, with a high near 86.
Thursday Night
 
Showers and thunderstorms likely. Mostly cloudy, with a low around 70. Chance of precipitation is 60%.
Friday
 
A 40 percent chance of showers and thunderstorms. Partly sunny, with a high near 83.

 

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

Weather Forecast Discussion
594
FXUS63 KLSX 080752
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
252 AM CDT Sat Aug 8 2026

.KEY MESSAGES...
- Hot and humid conditions are expected this weekend and through
  the middle of next week. Heat index readings in the 100 to
  108 range will start Sunday and persist into Wednesday.

- The heat breaks Thursday, with several rounds of showers and
  thunderstorms persisting through Friday.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 236 AM CDT Sat Aug 8 2026

Today: The radar is showing a decaying MCV from earlier
convection making its way across southern MO, and then there is
a cold front moving south from southern IA and into northern MO.
The MCV is expected to continue progressing to the east while
weakening, eventually getting sheared out by an approaching
shortwave over IL/WI. No showers or thunderstorms are expected
today due to the dry air aloft. Model guidance is also
indicating lack of forcing available in the region, with weak
subsidence caused by the convergence and negative vorticity
advection aloft. Meanwhile models are in consensus that the cold
front will stall out in central MO. Then late in the day, the
cold front will lift back to the north.

Moisture along the stalled front is expected to pool, with
dewpoints into the 70s during the day. This added moisture along
with air temperatures in the low to mid 90s will cause heat
index values to reach or exceed 100 F, particularly south of the
I-70 corridor. The retreating cold front will allow for higher
dewpoints and warmer temperatures to advance northward into the
region.

Sunday: An upper level low over the James Bay will remain quasi
stationary with several upper level disturbances heading east across
the Great Lakes region. A cold front will move south out of Canada
and then stall across southern Minnesota. Showers and thunderstorms
will likely develop over Iowa in response, but there will be a
southern extent to the precipitation as PWATs fall off from
around 2" in Iowa to 1.3" (just below the 50th percentile for
this time of year) over east/central Missouri. This means that
some storms will clip northern Missouri, but will likely not
have much of a southern push. Ahead of the cold front, dewpoints
will rapidly rise as low level moisture pools. 1000/ 850 mb
thicknesses also start to balloon due to compressional warming
with values approaching 1440 m. Given this, high temperatures
will likely be in the mid 90s with the latest run of NBM showing
only a two degree spread in the interquartile range (IQR). This
combined with dewpoints in the mid to upper 70s means that
triple digit heat index values will be widespread. Peak heat
index values will likely be located near and along the I-70
corridor where values could top out in the 105 to 110 degree F
range. These range of values could last until Wednesday. As
such, we have issued a Extreme Heat Watch starting Sunday and
persisting into Wednesday.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 236 AM CDT Sat Aug 8 2026

Monday through Wednesday: The overall upper level pattern remains
largely unchanged through Wednesday. Mid-level ridging across the
southwestern United States will remain elongated to the east while
multiple rounds of vorticity traverse east across the Dakotas and
Great Lakes region. Each day will feature highs in the mid 90s with
dewpoints in the mid to upper 70s. As such, the Extreme Heat Watch
is in effect through Wednesday. It should be noted that even though
IQRs are only a few degrees Monday and Tuesday, confidence rapidly
decreases starting Wednesday on the overall synoptic pattern. On
Wednesday, the IQR at STL from the NBM is six degrees while the IQR
by Friday and Saturday rises towards 15 degrees. Confidence is
also lower further north (e.g., Quincy, IL) due to the
possibility of showers and thunderstorms or convective cloud
debris starting Monday (IQRs 5 to 10 degrees).

Thursday and Friday: The rapidly falling confidence at the end of
the long term is due to the closed low that is currently over the
James Bay. This can be seen on the WPC Ensemble Sensitivity Analysis
(ESA) webpage which shows the variance in the extended coming
from how the closed low opens up and ejects east across Ontario
and Quebec. As the wave opens up, it is forecast to nudge south
and east shunting the ridging south. How far south is the main
question, as a multiple rounds of showers and thunderstorms
could form along a stationary boundary across the region.
However, where and when the wave ejects is still very uncertain.

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1234 AM CDT Sat Aug 8 2026

VFR through the issuance. Thunderstorms that were in Iowa
heading southeast have quickly weakened and dissipated, while
thunderstorms associated with the MCV over south/ central
Missouri will remain south of the terminals. This afternoon, no
showers and thunderstorms are expected as the MCV from Friday
pulls southeast of the region.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Extreme Heat Watch from Sunday afternoon through Wednesday
     evening for MOZ041-047>051-059>065.
IL...Extreme Heat Watch from Sunday afternoon through Wednesday
     evening for ILZ069-074-079-100>102.

&&

$$

SHORT TERM...Asel/BAH
LONG TERM...BAH
AVIATION...BAH
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Forecast Discussion from: NOAA-NWS Script developed by: El Dorado Weather






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