Schaller, Iowa Weather Forecast Discussion

271
FXUS63 KDMX 151837
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
137 PM CDT Mon Sep 15 2025
.KEY MESSAGES...
- Still warm and humid today and tomorrow, and perhaps Wednesday
  before some relief arrives in the latter half of the week.
- Isolated to scattered showers and thunderstorms are forecast
  at times from this afternoon through Tuesday evening, with
  generally a 20-30% chance of rain at times.
- Persistent, higher (40-70%) rain chances are forecast from
  around Wednesday through Friday and may persist into Saturday.
  While rain will fall at intervals and not continuously, it is
  likely to fall each day in at least portions of our service
  area.
&&
.DISCUSSION...
Issued at 137 PM CDT Mon Sep 15 2025
At 500 MB, the large high pressure ridge that dominated the
Midwest over the weekend has been pushed a bit further eastward,
and now stretches from the southern High Plains northeastward
into the Great Lakes region. Iowa is still beneath the western
periphery of the ridge and temperatures remain well above
normal. However, a broad low pressure trough has carved out over
the northern High Plains and Rockies, with one lobe moving over
the Dakotas today. It was the approach of this trough that
shunted the ridge eastward and has provided a return of some
showers and thunderstorms today, as well as somewhat mitigating
the seasonally impressive heat of the past couple days.
As the 500 MB lobe of vorticity over the Dakotas today moves up
into Canada tonight, in its wake Iowa will lie beneath light
southwesterly flow between the larger trough well to our
northwest and the elongated ridge just to our southeast. The
result will be persistent, light southeasterly surface flow,
broad and nebulous forcing for ascent, ample available moisture,
and low coverage (20-30%) rain chances primarily tied to diurnal
heating with a maximum in the afternoon and evening today and
Tuesday. With very weak flow/shear and no strong forcing severe
weather is not anticipated, however, on Tuesday
afternoon/evening most model solutions depict strong 0-3 KM CAPE
of around 200-250 J/kg along with enhanced stretching
potential, signaling some potential for weak funnel clouds that
we will continue to assess tonight and tomorrow. Also, with the
main 500 MB ridge axis having moved east of us and some cloud
cover associated with scattered showers and storms, temperatures
will be held a bit more in check Tuesday with highs generally
ranging in the upper 80s and a few 90 degree readings very
similar to today. While this is below the levels seen last
weekend, it is still well above normal and combined with
dewpoints in the low to mid-60s, will still feel warm and humid
for most outdoor interests.
On Wednesday and Thursday the approaching 500 MB trough will
slow up and gradually close off, with the resulting low spinning
over the High Plains for a couple of days before finally pushing
across Iowa and Minnesota sometime roughly around Saturday. This
will bring several days of somewhat cooler, generally cloudy
weather in the latter half of the week, along with higher rain
and thunderstorm chances. Appropriately, PoPs steadily increase
from west to east around Wednesday with 40-70% rain chances in
parts of our forecast area between Wednesday and Friday or so.
The synoptic set-up does not favor significant severe weather
chances, however given the degree of atmospheric moisture and
weak steering flow/slow storm motions, locally heavy rainfall
will be possible. Very dry antecedent conditions are in place
which will mitigate any flooding concerns, however if high-
rainfall rate storms happen to affect a flood-prone area or any
location receives multiple rounds of heavy rainfall over those
few days, then some localized impacts could be possible. The
Weather Prediction Center has included a Marginal Risk of
flooding in Iowa accordingly.
The 500 MB trough will move off to our east around the latter
half of the weekend, but it appears another trough will deepen
over the central U.S. in the early part of next week. There is
considerable model variability in the solutions for that system,
but it is likely to result in continuing rain chances and a lack
of significant warming during that time.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1216 PM CDT Mon Sep 15 2025
Prevailing VFR conditions are forecast through the TAF period.
There will be isolated-to-scattered SHRA/TSRA at times, mainly
late this afternoon and evening, however the probability of
impacts at any given time and location is too low (generally
10-20%) to include in the outgoing TAFs. If any such impacts do
occur, then amendments will be considered.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
DISCUSSION...Lee
AVIATION...Lee

NWS DMX Office Area Forecast Discussion