Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

398
FXUS63 KLSX 221925
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
225 PM CDT Mon Jun 22 2026

.KEY MESSAGES...

- Seasonably cool temperatures will continue through the work week.

- Chances of showers and thunderstorms increase later this week
  with the best chances (60-80%) Thursday night - Friday.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 220 PM CDT Mon Jun 22 2026

Anomalously strong surface high pressure (~1018 hPa; >90th
percentile of climatology) currently over the Upper Midwest is
expected to slide east/southeast through Tuesday. This strong high
pressure will continue to yield seasonably cool temperatures and
dry weather at least through Tuesday. Exact low temperatures
tonight will depend on how quickly it clears out from north to
south. Given the continued advective component and the stratus
becoming more cumuliform throughout the day today, it does appear
likely that most of the area should clear out. This would help
allow for a seasonably cool night with lows in the mid to upper
50s. Highs on Tuesday are expected to moderate back into the upper
70s to low 80s, mainly due to increased sunshine. Those readings
would still be 3-4 degrees below normal though for the date.


Gosselin

&&

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 220 PM CDT Mon Jun 22 2026

(Tuesday Night - Wednesday Night)

The first of what may be several MCSs is expected Tuesday night into
Wednesday morning, though this cluster of thunderstorms should focus
more over the south-central Plains and into the mid south. Our rain
chances (30-60%) are mainly associated with a cold frontal passage
Wednesday afternoon/evening. Moisture return looks to be an issue
ahead of this front, and the MCS to our southwest will not help
things. In addition, we could get some debris clouds in southwestern
counties, which could help limit instability. Weak surface
convergence is also expected along the frontal boundary, so mainly
scattered showers and (weak) thunderstorms are expected.


(Thursday - Saturday)

The MCS train will continue Thursday morning as another complex
should move east/southeast out of the central Plains. This MCS
may have a better chance of impacting our region, but I would not
be surprised to see that one also focus more to our southwest. Model
guidance tends to have a distinct north bias with MCS tracks,
especially when there are antecedent rounds of convection. That is
why the Thursday night - Friday time period looks to be our best
chance (60-80%) of seeing widespread showers and thunderstorms. That
is when the mid/upper level ridge begins to build northward enough
to help shift the track of the MCSs more toward the mid-Mississippi
Valley. All that being said, it is very difficult to pin down the
exact timing/track of any of these MCSs multiple days away. Due to
these factors, it is too early to say how much of a hydrological or
severe threat there will or will not be in our area. That being
said, any area that does get hit by multiple MCSs likely would be
more prone to flash flooding. Each MCS/complex should be fairly
progressive and precipitable water values are high, but not
extremely high (just above 90th percentile). Possible
preconditioning of the soils though from an prior MCS though could
mean there is an increasing flash flood threat for Thursday night
into Friday. Timing is also critical for any severe threat. Late
night/morning activity likely would stay sub severe, but an MCS
could become reinvigorated during the afternoon as diurnal
instability increases ahead of any complex.

Temperature trends during this period are a bit tricky. While
nighttime lows will assuredly be on the increase, daytime highs will
depend heavily on the track/timing of each MCS. Friday is likely to
be cooler than Thursday given this is our best chance of seeing
widespread thunderstorms and cloud debris, but the inter-quartile
range on high temperatures does increase to about 5-9 degrees.
Therefore, confidence is not high with respect to high
temperatures.


(Saturday Night - Next Monday)

Ensemble guidance is in very good agreement that mid/upper level
ridging will amplify over the central CONUS late this weekend into
early next week. This should mean a turn more toward pure summer,
with increasing heat/humidity likely. There is however some
differences with the strength of the ridge, with one of the four
clusters (~21% of LREF members) showing weaker ridging and having
our area more susceptible to "ridge-running" shortwaves/MCSs.
This is not the likely scenario by any means, but sometimes
anticipated heat events do get knocked back by nocturnal
convection. In the absence of any convection/clouds, the incoming
air mass should support highs in the mid 90s starting Sunday.
These temperatures combined with increasing humidity could mean at
least a few days with heat index values of 100-105 plus as we look
to close out the month of June.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1200 PM CDT Mon Jun 22 2026

Stratus/stratocumulus will continue to slowly lift through the day
and eventually scatter out from north to south. Dry/VFR conditions
are forecast thereafter along with decreasing wind speeds. Some
river valley fog is possible tonight, but confidence is too low
currently to add into KSUS/KJEF/KCPS.

Gosselin

&&

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

$$

WFO LSX