514
FXUS63 KDMX 041905
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
205 PM CDT Thu Sep 4 2025

.KEY MESSAGES...

- Breezy winds expected this afternoon through the overnight as
  low pressure and a cold front sweep into the area.

- Scattered showers and thunderstorms are possible this evening
  with the front, mainly over northern Iowa. Some storms could
  produce damaging winds.

- Cool and breezy conditions expected on Friday, then cool and
  dry into the weekend.

&&

.DISCUSSION...
Issued at 201 PM CDT Thu Sep 4 2025

Surface high pressure is quickly departing to the southeast today as
a fast-moving wave drops southward through the upper midwest and
toward Iowa this afternoon and evening. The deepening surface low
will increase pressure gradients overhead as it approaches,
resulting in breezy southwest winds with gusts around 20 to 25 mph
this afternoon. Wildfire smoke has also filled in ahead of the
approaching wave, with some visibility reductions around 8 to 10 SM
at the surface. This is expected to continue filling in through the
evening, but will be quickly pushed aside by the cold air mass
advecting southward with the surface low.

Pressure gradients will continue to strengthen as the wave
approaches the state this evening, with the strongest winds expected
in proximity to the surface low and along the cold front. Wind gusts
of 25 to 35 mph expected in northern Iowa in proximity to the low.
In addition to the gusty winds, strong lift and moisture pooling
along the front will produce scattered showers and thunderstorms
over northern Iowa as the system passes through. These will be most
likely near the surface low over northern and northeastern Iowa,
while area farther south and west will struggle with moisture
availability and weaker forcing. That said, although the
likelihood of showers/storms is lower, could still see a few
isolated showers or storms over central Iowa this evening as
well.

The potential for severe weather with these storms appears fairly
low for much of the area this evening, as instability will be quite
low (less than 500 J/kg) and shallow. Most of this instability will
be pooled right along the boundary, and will be dwindling after
sunset. That said, while the storms themselves may not be overly
rigorous, the wind fields within the environment surrounding them
will be quite strong. This of course suggests higher amounts of
shear for storm organization (0 to 6 km shear values will be over 70
kts), but moreso the potential for the strong winds aloft to be
mixed down to the surface through downward momentum transfer with
storms. Models indicate a roughly 45 to 55 kt jet aloft nosed into
the cold front, which could be transported to the surface by what
would otherwise be fairly shallow and relatively benign storms. For
this reason, an isolated wind threat will be in place with storms
this evening, especially around or slightly after sunrise. The storm
prediction center has issued a targeted marginal risk for severe
wind (level 1 of 5) over northwestern Iowa, where winds are most
likely to be mixed down to the surface. After sunset, the likelihood
for these strong winds with storms will diminish some, but the
possibility for an isolated gust to be mixed down will exist with
any storms tonight.

Once the front passes through, shower and storm chances will subside
but gradient winds will remain breezy through the night as cold air
advection fills in behind. The wave will depart to the east through
the night and the cold front begins to sputter over southern Iowa
toward Friday morning. Short range guidance is kicking out some
showers along the boundary as it slows and leaks south, introducing
rain chances to southern Iowa by Friday morning. However, lack of
forcing and very dry low levels should keep most of this
precipitation at bay, with only sprinkles or light rain
expected. The front then falls south of the state by mid-morning
on Friday.

Breezy conditions remain through Friday, but will diminish into the
afternoon and evening as pressure gradients weaken and high pressure
begins to fill in. Model soundings show a shallow layer of
instability developing as the boundary layer mixes out tomorrow
afternoon, suggesting afternoon cumulus is likely and even a few
sprinkles are possible, despite the extremely dry low levels. These
should dissipate after sunset.

Cool and dry conditions prevail through the weekend, with overnight
lows falling into the upper 30s to low 40s and daytime highs only in
the upper 60s to near 70. It`s possible elevated surfaces could see
some minor frost buildup in the mornings this weekend, but ground
temperatures and overnight lows should generally remain warm enough
to limit frost concerns. Rain chances return in the first half of
next week, so make sure to get out and enjoy the dry and pleasant
conditions this weekend!

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1225 PM CDT Thu Sep 4 2025

VFR conditions prevail through mid-day with winds increasing out
of the west southwest this afternoon and evening. Some
scattered cumulus around 3 to 4 kft have begun to develop over
portions of the area, as well as some VFR smoke at the surface.
Winds continue to increase this afternoon and evening as a cold
front approaches the area. Showers and isolated storms will
develop along the front, most likely impacting KFOD, KMCW, and
KALO. KDSM could see a shower but likelihood is lower. Gusty
winds will accompany the front, with a shift to more
northwesterly flow after it passes. Have maintained LLWS at KDSM
and KOTM where surface winds may be a bit weaker.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Dodson