Altoona, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

188
FXUS63 KDMX 231733
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1233 PM CDT Sun Aug 23 2026

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Quiet weather continues today with highs in upper 70s to lower
  80s. Areas of patchy morning fog remain possible.

- Rain chances return Sunday night into Monday morning (40-
50%), mainly across western Iowa. Severe weather is not anticipated.


- Early signs of a somewhat more active weather pattern next
  weekend, with a return of more persistent rain chances but any
  details still unclear at this range.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 218 AM CDT Sun Aug 23 2026

Saturday was arguably the best day in August so far! Highs climbed
into the upper 70s to lower 80s across the state with dew points
generally in the 50s and 60s making for a pleasant afternoon.
Surface high pressure remains in place across the Central Plains
this morning, keeping conditions calm across the Upper Midwest. With
the high ushering dry air across central iowa, skies remain mostly
clear tonight allowing for efficient radiational cooling. Lows
overnight are expected to drop into the upper 50s across southern
Iowa and lower 50s north. Given clear skies and calm winds, areas of
patchy fog remain possible overnight- primarily along low lying
river valleys, with minimal impacts as fog should remain fairly
wispy. As we head into late morning, fog will burn off and cloud
cover will increase from western Iowa ahead of our next incoming
disturbance.

The 500 MB trough centered over Ontario will begin shifting
eastward, flattening the northern edge of the Four Corners ridge
that has been anchored for past few days. Consequently, short range
guidance indicates a shortwave emerging off the Rockies, pushing
unsettled weather across the High Plains Sunday afternoon and
evening. This will allow rain chances to return to western and
central Iowa as early as Sunday night. The main forecast challenge
is the timing of initial rain onset, as forecast soundings show a
very dry layer in the lower to mid levels. While short range
guidance attempts to introduce showers into western Iowa as early as
Sunday afternoon, precipitation chances were kept out of the daytime
forecast due to the strong signal of dry air keeping initial returns
as virga. Overnight, a strengthening LLJ will push into western
iowa, enhancing low level moisture transport and saturating the
column top down. The highest precipitation chances (40-50%) will
align near the jet axis, with chances dropping of eastward toward
the Des Moines to Davenport corridor (30-10%) where the deep layer
saturation is harder to achieve. If the jet shifts further east,
rain chances will need to bumped up accordingly. Rain chances
gradually diminish into Monday afternoon. Severe Weather is not
anticipated with this round due to negligible instability, with
activity expected to remain mostly showers and an isolated storm or
two.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 1237 PM CDT Sat Aug 22 2026

By Monday night the eastern 500 MB trough will have shifted
over Quebec, while the western one crosses from Saskatchewan
into Manitoba, then subsequently shifts east southeastward into
the Lake Superior region by Wednesday. In Iowa this will be
concurrent with a very light surface pressure/flow pattern,
resulting in nebulous low rain chances at times from Monday
night into Wednesday. As the 500 MB trough moves over Lake
Superior, it will help push a large surface high pressure area
down the northern High Plains and Midwest during this time,
later bringing relatively comfortable and dry weather from
around Wednesday night through Friday. The onset of the
influence of this surface ridge will take the form of a modest
trough, pushing through ahead of the main mid-level shortwave
sometime around Tuesday night. Differences in timing and the
sharpness of the trough lead to a high variability in model
solutions, however, there does appear to be some potential for
good destabilization on Tuesday afternoon/evening and also
potential for moderate deep-layer (0-6 KM) shear of perhaps
30-35 KT or so. Again, there is significant variability in
these solutions and much will depend on diurnal timing, but it
is possible if the trough has enough low-level convergence and
comes through during peak diurnal heating time, there may be a
narrow window of opportunity for pulse storms with a severe
weather threat late Tuesday. A more likely scenario, however,
is that the trough comes through overnight with much less
instability and/or weaker shear, or that the trough is too weak
and low-level convergence is not sufficient to support stronger
updrafts, or both. By next weekend, the 500 MB pattern should
begin to shift just a bit, with the ridge flattening and
shifting a bit toward the southwestern U.S., while a more zonal
flow pattern sets up across the northern CONUS and Iowa. This
would favor a somewhat more active weather regime in our
region, with persistent rain chances likely returning. Of
course that is still a week-plus out, but something to keep an
eye on in the coming days.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 1233 AM CDT Sun Aug 23 2026

VFR conditions are forecast with no aviation impacts
anticipated. There is a very low (10-20%) chance of light rain
at FOD/DSM late tonight into Monday, but between the low
probability and the lack of notable impacts even if it were to
occur, have not mentioned in the 18Z TAFs.

&&

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

&&

$$

SHORT TERM...TDR
LONG TERM...Lee
AVIATION...Lee