Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

520
FXUS63 KLSX 261918
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
218 PM CDT Sun Apr 26 2026

.KEY MESSAGES...

- Moisture returns to the region tonight with multiple rounds of
  thunderstorms possible through Monday morning. There is a low
  severe weather risk with these storms.

- The greater risk of severe thunderstorms is Monday afternoon and
  evening ahead of a cold front. Large hail, damaging winds, and
  tornadoes are all possible.

- Our recent warm weather ends behind Monday night`s cold front
  with cooler and less stormy weather lasting through the
  weekend.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 217 PM CDT Sun Apr 26 2026

Moisture return continues across the Plains today to the east of the
lee trough. Dewpoints have already risen to summer-like levels in
Texas, in the 70s, with 60s pushing north into Kansas and western
Missouri. Thunderstorms are already ongoing across Kansas near the
leading edge of this moist advection, and additional thunderstorm
development is expected this afternoon and evening potentially even
further south ahead of the dryline in Oklahoma and Texas. Our area
currently remains under the influence of recirculated dry air around
surface high pressure now centered near New England. We`ve seen
continued warm temperatures due to warm air aloft within a mid level
ridge available through daytime mixing. Due to the dry air in place
locally, we do not expect thunderstorm development locally this
afternoon. Southwesterly steering flow will have a tendency to push
thunderstorms off to the ENE this evening into the overnight,
meaning that what happens upstream from Texas to Kansas will drive
the downstream impacts in our area overnight. The initial storms
will be outrunning the available instability and thus should be
weakening as they approach this evening.

A rather potent shortwave trough currently near Las Vegas will move
across the Rockies tonight and into the Central Plains on Monday.
This will shift the flow of Gulf moisture to the northeast out ahead
of a developing surface low and cold front. With the loss of heating
this afternoon, the moisture advecting into the region tonight will
be primarily occurring aloft, just above the surface, but as it does
so it is likely to trigger additional rounds of thunderstorms
tracking ENE across the region. We`re now within the range of many
of the high resolution, convective allowing models (CAMS) which we
often use to get an idea of how thunderstorms form, track, and
evolve. However, there`s very little consistency between the CAMs
and between runs of any one CAM. Thus if we were to base our entire
expectations off the latest CAM guidance, our expectations would
change as often as the new CAM guidance updates. What this tells us
instead is that this is more of a broad based thunderstorm threat
overnight into Monday morning, without a clear focus region to allow
us to pinpoint the track or timing. Some CAM guidance show the
development of one or more convective complexes. The environment
will be primarily based on elevated instability in the moist
advection above a stable boundary layer, so convective threats will
be focused on hail, locally damaging winds, and locally heavy
rainfall.

While precipitable water values will be well above normal for the
time of year, above the 90th percentile, it`s still only in the 1.3
to 1.4 inch range which does not suggest an immediate flash flooding
threat. That could change, though, if thunderstorms are able to
organize into a broader convective complex with the southern outflow
orienting itself perpendicular to the arriving moisture aloft, thus
creating rounds of training storms in one location. This is a rather
low probability of occurrence (less than 30 percent), so our
confidence in any flash flood impacts remains low. Northern parts of
the forecast area are favored for the most likely and most frequent
rounds of thunderstorms tonight, and thus the greatest total
rainfall potential.

Morning thunderstorms will have cascading impacts on the developing
greater severe weather threat Monday afternoon. While the increased
moisture leads to high confidence in enough instability for surface
based storms to redevelop along and ahead of the cold front Monday
afternoon; cloud cover, outflow boundaries, and lingering convection
will affect how extreme that instability becomes as well as the
location and timing of that threat. For example, CAM guidance which
shows more organized and long-lasting morning convection delays the
onset of storms in the afternoon to as late as 6PM. At that later
time, the frontal boundary will be further east, thus shifting the
greatest threat area further east. In addition, lingering outflow
boundaries from morning convection could further focus the threat in
the afternoon, even potentially enhancing the tornado threat near
that boundary. To shorten this long story, we still expect renewed
thunderstorm development during the afternoon and evening with
supercells and convective clusters the primary storm mode. The
availability of highly variable CAM guidance has actually lowered
our confidence in where the greatest threat will be, but the broader
enhanced threat remains for the entire region. Some greater
confidence in where the greatest threat develops can potentially be
gained after we`ve seen how this evening`s storms evolve, but more
likely after Monday morning`s convection.

Kimble

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 217 PM CDT Sun Apr 26 2026

Monday evening`s cold front brings a shift toward drier and cooler
weather that lasts largely through the end of the week. Another
shortwave trough treks east across the center of the country on
Tuesday, this time further south than Monday`s wave. The front will
also be further south, shifting the focus for the next day`s
convection further south with it. The frontal passage likely means
surface based convection stays south of our forecast area Tuesday
afternoon and evening, but we are likely to see elevated convection
or stratiform rain related to convection to our south affecting
southern portions of our forecast area. There is very limited threat
with this beyond lightning and heavy rainfall. After this ends
Tuesday evening it will be dry area wide for at least a few days,
with temperatures a few degrees below normal, mostly in the 60s for
highs.

Larger scale troughing takes hold of most of the continental US this
week, leading to the cooler weather. Within the broader trough, a
shortwave trough in the northwesterly flow moves through our region
on Thursday. This provides our next chance of rain, but Gulf
moisture remains unavailable with this, limiting the impact to some
light rain showers. This will initiate another surge of cooler air,
though, that will send temperatures even cooler for the end of the
week. Dewpoints in this air mass (in the 40s) suggest that even on
the coldest nights the temperature should stay above the level that
frost or freeze would be a concern.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1232 PM CDT Sun Apr 26 2026

VFR conditions continue this afternoon, but we`re entering a
period of unstable conditions with frequent chances for
thunderstorms. As moisture returns to the region tonight, areas of
thunderstorms are expected to track across the region. Timing
these storms as well as their location is very uncertain at this
point, but there is a general consensus on a decrease in activity
late Monday morning before one final round develops over the
center of the region Monday afternoon. This last round has the
best chance of being severe, and has greater confidence on the
timing especially at St Louis. Otherwise expect at least minimal
chances of thunderstorms anytime after 06Z tonight until a cold
front passes Monday afternoon and evening.

Kimble

&&

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

$$

WFO LSX