Ottumwa, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

179
FXUS63 KDMX 050459
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1059 PM CST Thu Dec 4 2025

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

.KEY MESSAGES...

- Milder Friday with highs in the low 30s. Up to 40% chance of a
  dusting of snow over far northern Iowa Friday.

- Accumulating snowfall likely arriving later Saturday and
  moving out Sunday morning impacting travel. Current forecast
  has a band of snowfall of 3 up to 6 inches possible.

&&

.DISCUSSION...
Issued at 250 PM CST Thu Dec 4 2025

The overall weather theme for Iowa for the next week will be fast
moving, northwesterly flow that will bring multiple chances for
precipitation - mainly snow - to at least some portion of the state.
The most widespread accumulating snowfall for the state will be
centered on Saturday evening with more details about this below.

After the day started with a clear sky and record low temperatures
falling in multiple Iowa communities, have been watching GOES-East
Day Snow Fog RGB as an area of stratus slowly moves over the
northwestern quadrant of the state. In spite of the clouds over
those areas, temperatures statewide have risen above the zero degree
mark as of 2pm. With southerly flow of some kind into tonight,
conditions will not be as cold with lows above zero over central
Iowa.

The first fast moving shortwave trough, or clipper, is over the
Alberta province and will dive into the region Friday morning. The
stronger forcing will reside north of the state with cross sections
showing the depth of moisture and lift along the Iowa Minnesota
border more marginal. Still have continued to show low PoPs (around
30 to 40%) over the northern tier to two of counties. Accumulations
of a dusting are expected.

As this clipper exits, a stronger clipper will be coming down from
the Pacific Northwest. This clipper will bring strong low level
theta-e advection and frontogenetical forcing along with low and mid-
level QG convergence over the state. The track of the GFS has been
the outlier the last few days with a more southern track, but has
shown signs since last night of coming around to the consensus of
models bringing accumulating snowfall over much of Iowa. The
aforementioned forcing will help to bring snowfall into the state
from a general west to east fashion from sometime later Saturday
morning into Saturday evening. For QPF, have stuck with WPC this
cycle as they have nearly doubled the amount of QPF from the
previous cycle. While this could be increasing another 0.05 to 0.1",
will allow this upward trend to suffice for now. Of course, with the
increase of QPF means that snowfall amounts have also increased. NAM
and GFS cross sections show that moderate omega moves through the
dendritic growth zone (DGZ), though the DGZ is not exceptional in
its depth except over northern Iowa Saturday night, which may help
to enhance snow ratios for a period. For now, snow-liquid ratios on
the southern edge of this accumulating snowfall shield will be 10-
12:1, which is closer to climo for December, with ratios over
northern Iowa around 15:1 to perhaps as high as 20:1 towards the end
of the event. Thus, accumulations of at least 3 up to 6 inches are
possible in a northwest to southeast oriented band and would
necessitate an advisory. While this snowfall is shown in our
messaging, know that the forecast will change with snow totals
(monitoring QPF and snow ratio changes) and location of highest
snowfall (band placement). Winds continue to look below 15 mph and
thus blowing snow is not expected to be too much of a story after
the snow ends Sunday morning.

As we move into next week, another clipper will move into the region
later Tuesday into Wednesday. There remains a high degree of
uncertainty in placement with some models showing accumulating
snowfall over the state and others displaced to the northeast of
Iowa. Thus, won`t highlight much beyond the potential for a clipper
into the region with details still variable as they are at this time
range.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1057 PM CST Thu Dec 4 2025

LLWS at all sites at times tonight. Southwest winds persist with
some 20kt gusts possible after 18z. A front will bring snow
chances to KMCW but with minimal accumulations. Its main impact
to the rest of the sites is a wind shift and cig restricting
stratus, mainly after 00z.

&&

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

&&

$$

DISCUSSION...Ansorge
AVIATION...Jimenez