Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

140
FXUS63 KLSX 231111
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
611 AM CDT Tue Jun 23 2026

.KEY MESSAGES...

- Seasonably cool conditions will continue through the work week.

- Showers and thunderstorms are forecast (70-80%) Thursday into
  Friday with the main concern being heavy rainfall potentially
  leading to flash flooding.

- A return to warm and humid summerlike conditions is anticipated
  late this weekend into the start of next week.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 214 AM CDT Tue Jun 23 2026

Recent surface analysis shows an elongated surface high working its
way into the region from the Upper Midwest. Both a clear sky and
very calm winds have settled into the area, promoting efficient
radiational cooling early this morning. These conditions overlaid
with a saturated near surface-layer is favoring the formation of
fog, which is becoming more noticeable on nighttime microphysics in
river valleys across the Ozarks as of 1am. Expansion of this patchy
fog is expected, with the better chances in river valleys/low-lying
areas, where pooling of cooler air and more consistent calm winds
will favor the conditions for fog. Any patchy fog will erode after
sunrise this morning. Northwesterly flow aloft maintains hold on the
area today, keeping temperatures seasonably cool, although, slightly
warmer than yesterday with highs in the upper 70s/lower 80s thanks
to more abundant sunshine today. The area is expected to remain
precipitation free through Tuesday night as a more active pattern
remains off to the southwest. Low chances (20-30%) for showers and
(weak) thunderstorms creep into the area on Wednesday, as some high-
resolution guidance progs the remnants from an MCS further
west/southwest falling apart as they move into the area. It is
possible that some of this activity becomes reinvigorated as it
moves into the area on Wednesday, especially if it is a time when
instability is maximized, during the afternoon/evening.

Peine

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 214 AM CDT Tue Jun 23 2026

By Thursday, regional mid-level quasi-zonal flow ensues, with long-
range deterministic guidance revealing a shortwave traversing into
the Great Plains towards the area. This feature is expected to
initiate an MCS/series of MCS`s out west, with confidence increasing
that these may impact the region Thursday into Friday. As of now,
the main concern with these systems for our area is the threat for
heavy rainfall leading to flash flooding. Normally, these systems
are fairly progressive which lowers the duration of rainfall, aside
from the poleward/equatorward ends where back-building and/or
training may be favored. However, with the potential for more than
one MCS or rounds of thunderstorms to impact similar locations, and
with PWATs progged to be near 2", the threat of locally heavy
rainfall is increasing for Thursday into Friday.

Into this weekend, a pattern flip is being revealed by long-range
guidance with longwave troughing out west and a ridge building
across the southeast. For the area, the most noticeable change is
expected to be a return of much warmer temperatures. This is
indicated well by LREF temperature IQRs that show a consistent
spread of only 3-5 degrees (high confidence) with means jumping from
the mid/upper 80s (late week) to the low/mid 90s (end of the
weekend/early next week). Analysis of the LREF mean 850mb
temperatures shows values near 23C across the area by late this
weekend, which is an airmass that would support highs in the mid 90s
given full mixing. Our chances for showers and thunderstorms, along
with how warm it gets, will rely upon the strength of the southern
ridge. A stronger ridge may work to push MCS tracks/more active
weather north of the area allowing for warmer temperatures, while a
weaker ridge may favor more precipitation chances and cooler
temperatures. Either way, with increasing surface moisture and temps
aloft, summerlike conditions are forecast to return including the
potential for heat indices >100F across the area.

Peine

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 608 AM CDT Tue Jun 23 2026

Overnight LIFR fog at a few low-lying terminals is already
dissipating at this hour thanks to the early sunrise. All
terminals will remain VFR through the valid TAF period, with a
light southerly wind prevailing this afternoon as a surface high
gradually departs the region.

MRB

&&

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

$$

WFO LSX