987
FXUS63 KDMX 060727
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
227 AM CDT Sat Sep 6 2025

.KEY MESSAGES...

- Forecast is dry through the weekend.

- Cool weather persists for a couple more days. Sunday morning
  low temperatures in the upper 30s across part of northern and
  western Iowa.

- Warming next week, with rain chances returning Monday into
  Tuesday.

&&

.UPDATE...
Issued at 227 AM CDT Sat Sep 6 2025

Tranquil conditions across Iowa on this early Saturday morning.
While a few low clouds are passing across the area, increasing high
pressure to the west and weak subsidence is helping to keep skies
mostly clear. Winds remain light at around 5 mph, however a few low
lying ares have gone calm this morning. In these areas patchy light
fog development is possible into the morning. Widespread fog
development is not anticipated. This afternoon another embedded lobe
of vorticity will round the low sitting to the northeast. This will
bring cloud cover to parts of northern to northeast Iowa, though
precipitation should be confined northeast of the area where better
forcing and moisture will be in place. Northwest flow will allow for
steady cold air advection through the day, keeping afternoon high
temperatures cool in the 60s.

By Sunday the low pressure begins to lift east with return
southerly flow filtering back into the area. This will bring
temperatures up a few degrees for Sunday, with a return to the
upper 70s to low to mid 80s Monday and into next week. Also
on the way for early next week is a return of precipitation
chances. A shortwave will move into Western Iowa later Monday,
but progress is slow from west to east and it looks to linger
slowly across the area perhaps into early Wednesday. Moisture is
lacking, so don`t expect a deluge with this slow moving wave.
Soundings show deep dry air to overcome and more spotty shower
and thunderstorm activity is more likely Monday and Tuesday.
Thunder chances are highest in western Iowa where a plume of
stability with around 500-1000 J/kg of MLCAPE will set up. But
with little shear to organize storms, the severe potential is
low at this time. Dry through the middle of the week with a
longwave trough that may reach the area late week into next
weekend.

&&

.DISCUSSION...
Issued at 138 PM CDT Fri Sep 5 2025

A large cyclone is currently parked over Ontario, with its
cyclonic flow extending down across the Upper Midwest. A lobe of
vorticity is evident in water vapor satellite imagery, crossing
South Dakota and headed toward northern Iowa this afternoon and
evening. Visible satellite imagery shows a large field of
diurnally generated stratocumulus clouds, covering much of the
region and enhanced by modest low-level cold air advection. As
the vorticity lobe swings overhead later today and provides some
mid-level lift, it may be sufficient to generate a few
sprinkles or light showers mainly in our northern counties.
However, forecast soundings illustrate most of the associated
lift will occur above the cloud layer, and the moisture is quite
shallow so any precipitation that does occur will likely be
very light and may not even reach the ground. Indeed, regional
radar imagery depicts a few light echoes approaching the
SD/MN/IA tri-state area, but so far no precipitation has
registered at surface observing sites beneath these returns.
Nevertheless, with the possibility of slight enhancement as the
afternoon progresses and in the interests of consistency, will
maintain the slight chance (20%) of showers forecast in our
north and northeast late this afternoon and evening. In any
event, no impacts are anticipated.

From tonight onward the Ontario gyre will begin to move off
slowly to the east, gradually weakening the cyclonic flow over
Iowa. Another lobe of vorticity will round the southwestern
periphery of the system again on Saturday, but farther northeast
than today with any associated showers more likely over
Wisconsin or far northeastern Iowa, so the forecast remains dry
for our service area. Concurrently, a ridge of surface high
pressure will build into Iowa from the northeast on Saturday
night and remain overhead on Sunday. This will result in light
winds and mostly clear skies, with temperatures falling to their
lowest point of the week on Sunday morning but then rebounding
by Sunday afternoon to levels higher than those seen the
preceding couple of days. The current forecast calls for lows in
the upper 30s across parts of northern and western Iowa Sunday
morning, with highs ranging in the mid 60s to lower 70s across
Iowa by Sunday afternoon.

From Monday through most of next week a synoptic pattern change
will occur, with roughly zonal 500 MB flow over Iowa on Monday
while a broad ridge develops over the Rockies. A weak trough
will dig over the Midwest around Monday night after which the
larger ridge will slowly traverse the central U.S. during the
latter half of the week. Long-range models show significant
variance in their depiction of the strength of the ridge, as
well as the timing and nature of various subtle impulses moving
through or over it during this time frame. The result is
intermittent, generally low (20-30%) rain chances next week, but
with little in the way of large or strong storm systems
foreseen at this range. The best chance for rain and
thunderstorms (40-60%) will come from around Monday night into
Tuesday in association with the aforementioned trough coming
overhead, but even then it appears instability and shear will be
modest. Temperatures will also be milder in this scenario, with
daily highs likely in the mid-70s to mid-80s for much of the
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1036 PM CDT Fri Sep 5 2025

Confidence remains high in VFR conditions prevailing through
the period at all terminals. Winds will be light from the west
overnight before becoming from the northwest at around 10 knots
by late Saturday morning through the afternoon hours. Cumulus
clouds with bases as low as FL050 will also develop by late
morning into the afternoon with coverage up to BKN over parts of
north central, northeast, and east central Iowa. These clouds
will dissipate and the winds will diminish around sunset.

&&

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

&&

$$

UPDATE...Hagenhoff
DISCUSSION...Lee
AVIATION...Ansorge