520
FXUS63 KDMX 010352
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1052 PM CDT Sun Aug 31 2025

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Shower and thunderstorm chances (30-60%) will increase into
tonight, continue into Monday, before decreasing Monday afternoon.

- Thunderstorm hazards today will be lightning and localized heavy
rain. Funnel clouds will be a possibility as well thru early evening
as well, although they will be weak and NOT expected to touch the
ground.

- Strong cold frontal passage on Wednesday morning will bring with a
fall-like air mass for the Wed-Sat. High temperatures are expected
to only reach the 60s, with overnight lows in the 40s (maybe even
some upper 30s in areas across the far north!).

&&

.DISCUSSION...
Issued at 251 PM CDT Sun Aug 31 2025

The blocking pattern and resultant stagnant progression remains
locked in across the CONUS as a broad ribbon of nearly stationary
shortwave energy extends NW-SE from the Dakotas thru the mid-
Mississippi River Valley. It`s here that a broad area of moist
ascent is contributing to intermittent rain showers and embedded
thunderstorm chances that will persist thru midday Monday mainly
central and west. Similar to yesterday, short-range CAM guidance
points to a NW-SE oriented convective band forming north and east of
DSM this afternoon along the differential heating boundary. Rainfall
has been highly localized as slow motions and training
showers/storms resulted in large gradients over short distances,
which will likely persist with tonight and early Monday`s activity.
Like last night, some areas may pick a quick several inches of rain.
However, do not anticipate any widespread flooding concerns given
recent run of dry weather.

The shortwave finally begins to depart on Monday as the downstream
Rex Block finally breaks, allowing the pattern to become progressive
once again. Rainfall chances will remain during the morning hours,
however will see a general decrease by Monday afternoon as the
system departs. High temperatures Monday look very similar to today,
reaching into the 70s for most locales.

Tuesday will be a transitional day as we await the arrival of the mid-
week cold front. Well upstream, the stationary low over the eastern
Pacific retrogrades, amplifying the ridging across western NOAM and
steepening the meridional flow into the center part of the country.
By Wednesday morning, this will bring a strong cold front
strengthening winds, turning them northwesterly, and advecting a
cooler air mass into the state. There will be no shortage of forcing
along the front, so rain chances will increase in proximity of the
cold front moves through. Behind the front, 850mb temperatures are
progd to fall to 0 to 2C across northern sections of the state. This
means high temperatures will generally only warm into the 60s during
the afternoon; with overnight lows falling into the 40s. There are
some indications that upper 30s will be a possibilitiy across the far
north as well.

A second cold front appears to pass through Thursday night
reinforcing the cool air mass while bringing the possibility of
another quick shot of rain. Otherwise, expect dry conditions through
the remainder of the period.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1052 PM CDT Sun Aug 31 2025

Scattered showers and isolated thunderstorms will linger through
Monday, but mainly across western and southwestern Iowa with
probability significantly lower (20% or less) at our TAF sites.
Therefore, there is no mention in the outgoing 06Z TAFs. Areas
of fog will likely develop late tonight/early Monday morning as
well, but again will primarily be west of the terminals with
some impact possible at MCW/FOD but more unlikely at
ALO/DSM/OTM. Will advertise MVFR at the former two sites, but
amendments may be needed overnight based on short-
term/observational trends.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...Hahn
AVIATION...Lee