843
FXUS63 KDMX 191938
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
238 PM CDT Thu Sep 19 2024

.KEY MESSAGES...

- Scattered severe storms possible this afternoon and evening
  with large hail and damaging wind the main concerns. Strongest
  storms are expected across northern Iowa.

- Brief break form the rain on Friday with plenty of sunshine
  and temperatures in the mid to upper 80s.

- Widespread showers and storms across the area very late Friday
  and continuing through Saturday and Sunday. Rain totals
  through the weekend of 1 to 2 inches are expected.

&&

.DISCUSSION...
Issued at 238 PM CDT Thu Sep 19 2024

Benign showers and thunderstorms have persisted in the warm air
advection wing through the morning and early afternoon. These have
lingered longer than most CAMs would have suggested today but are
finally starting to exit into eastern Iowa. The cells have been
fairly efficient rain producers with isolated pockets of 1+"
today.

At the same time, cells have started to fire along a boundary draped
across northwest Iowa this afternoon. This is associated with a
shortwave across the northern plains that will swing east through
the evening and overnight. SPC mesoanalysis shows a window of 2000+
MLCAPE across western Iowa where clouds have cleared from morning
convection. CAMs agree and show 2000-2500 J/kg into the
afternoon/evening, though ECAPE is reduced by ~500 J/kg thanks
to dry air entrainment in the mid levels. Decent lapse rates of
6-7 C/km and some modest hodograph curvature support rotating
updrafts to produce large hail with stronger cells. While low-
level hodographs show some curvature in northern Iowa the
overall tornado threat is low with better chances further
north. Storms will sweep across the area this evening and exit
east after 06z, becoming weaker for southerly storms and as they
move east.

Friday will be a quieter day with plenty of sunshine as high
pressure builds behind the wave. With moisture in place from
evening storms and cooler temperatures overnight, some patchy
fog is possible in northern Iowa when skies clear out on Friday
morning. Warm air advection continues into the area and will
send temperatures into the mid to upper 80s yet again. Quickly
on its heels another trough will pass across the state as a
northern shortwave and southern stream closed low phase late
Friday evening. This will bring more widespread shower and
thunderstorm activity to the area Saturday and Sunday. Heaviest
rain looks to fall across central and southern Iowa where 1-2"
are possible. In fact, GFS and EC ensemble members show 70-80+
percent chance for at least 1" of rain through the weekend along
and south of roughly the highway 30 corridor. Severe chances
appear low at this time with less shear to help organize storms
and modest instability. Will monitor over the next few days for
changes that may impact evolution.

Temperatures on Sunday will be much cooler behind the front and
these cooler temperatures will linger through the upcoming week.
Expect to see highs in the 60s to low 70s with a few chances for
rain into next week

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1257 PM CDT Thu Sep 19 2024

Scattered showers and thunderstorms persist across central to
eastern Iowa early this afternoon and are expected to diminish
over the next few hours. Meanwhile, storms will develop across
northwest Iowa on a frontal boundary later this afternoon. This
will swing across the state through the evening and east of the
area after 06z. Behind this patchy fog is possible in northeast
iowa for a few hours with MVFR impacts possible at
KFOD/KMCW/KALO.

&&

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

&&

$$

DISCUSSION...Hagenhoff
AVIATION...Hagenhoff