St. Peters, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

190
FXUS63 KLSX 041755
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1255 PM CDT Mon May 4 2026

.KEY MESSAGES...

- A storm or two will be capable of primarily large hail for areas north
  of I-70 this evening.

- Periods of rain are expected (100% chance) tonight through Tuesday
  night. The threat of flooding is very low.

- Below normal temperatures are expected Tuesday through Thursday.


&&

.SHORT TERM... (Through Tuesday Night)
Issued at 235 AM CDT Mon May 4 2026

The cold front responsible for the convection last evening and
overnight will wash out this morning, with another day of breezy
southwesterly winds pushing temperatures to around 80 degrees this
afternoon. The front washing out will also allow for Gulf moisture
to stream into the area, raising dew points by about 10 degrees
compared to yesterday. This will yield an unstable airmass over the
CWA ahead of yet another cold front sagging southward through the
Midwest as an upper-level trough deepens over the central CONUS.

Model soundings continue to show the warm sector remaining capped
through the daylight hours, with CI being confined to along and
immediately ahead of the front this evening. Guidance has converged
on this occurring either in or in close proximity to northeastern
Missouri and west-central Illinois during the evening hours. This is
when storms will have the best chance at remaining discrete and when
their greatest potential for producing severe weather will be. Bulk
shear will be around 30 kts, supporting a multicellular storm mode.
MUCAPE ranging from 1,500-2,000 J/kg will lead to strong updrafts
capable of large hail, and while damaging wind gusts can not be
ruled out, a near-surface stable layer is expected to mostly
mitigate this threat. As the number of updrafts along the front
increases, updrafts congeal thanks to the low-level jet nosing up to
and running parallel to the front, and instability decreases, storm
intensity will weaken during the early overnight hours as they
approach the I-70 corridor.

The low level jet and disturbances within the southwesterly flow
aloft will lead to rain chances continuing along and behind the
front through Tuesday morning and into the evening hours. While this
prolonged period of rain may raise concerns for flooding, the amount
of QPF over the duration it is expected to fall over does not
support flooding. The 00z HREF shows a corridor of around 2" falling
south of I-70 by Tuesday evening. At worst, this amount of rain may
exacerbate ongoing minor flooding or push smaller streams back to
minor flood if it falls within sensitive basins.

Guidance consensus is that rain will slowly end from northwest to
southeast Tuesday evening into the overnight hours, though exactly
when will depend on the speed of the cold front. A faster front
supports rain shutting down by midnight Tuesday night, while slower
solutions have rain lingering into Wednesday morning. A majority of
guidance favors the former, which is reflected in the current
forecast.

Elmore

&&

.LONG TERM... (Wednesday through Sunday)
Issued at 235 AM CDT Mon May 4 2026

Both deterministic and ensemble clusters show that on Wednesday, the
axis of the upper-level trough will be pivoting through the Great
Plains and entering the Midwest. While confidence is high that the
front responsible for Tuesday`s rain will be well south of the area,
there is a low chance (20-30%) that residual low-level moisture may
yield light rain along an axis of weak convergence as the trough
axis approaches. Otherwise, cloud cover and deep northwesterly flow
will keep temperatures running well below seasonal normals. While
this does elevate the concern for frost during the overnight hours,
the prospect of cloud cover and the core of the post-frontal airmass
passing well away from the CWA yields high confidence in this impact
not occurring. The 25th percentile of ensemble guidance also keeps
lows in the upper 30s, boosting confidence in lack of impacts.

The upper-level trough pulls northward to end the week, allowing for
low-level ridging to build into the Middle Mississippi Valley. As a
result, winds will become south-southwesterly and support
temperatures returning to around seasonal normals.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1247 PM CDT Mon May 4 2026

Scattered showers and thunderstorms will continue this afternoon
and into the evening, mainly across parts of eastern Missouri and
southwest Illinois. The storms will be capable of brief heavy rain
which could lower the visibility to 3 miles or less. The strongest
storms may also produce small hail. Additional thunderstorm
development is expected this evening ahead of a cold front across
northeast and central Missouri. Isolated storms could produce 1
inch or larger diameter hail and wind gusts to 50kts, mainly along
and north of I-70. Widespread showers will continue on Tuesday
morning behind the cold front with ceilings falling low MVFR along
and south of I-70, and IFR across the eastern Ozarks.

Carney

&&

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

$$

WFO LSX