198
FXUS63 KDMX 130824
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
324 AM CDT Thu Aug 13 2026

.KEY MESSAGES...

- Early morning thunderstorms, some severe, are expected this
  morning, then scattered thunderstorm chances last through this
  afternoon and evening. Damaging winds are the primary threat
  with isolated large hail, locally heavy rain, and a tornado or
  two also possible this morning.

- Additional thunderstorms are possible overnight and early
  Friday morning with some amount of uncertainty due to the
  evolution of this morning`s storms. These storms could be
  severe with pockets of heavy rain as well.

- The pattern remains active with storms chances through the
  weekend and early next week.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 302 AM CDT Thu Aug 13 2026

Thunderstorms are expected yet again this morning, once again with
severe potential. Compared to the past several nights, this looks
like the `best` setup for severe thunderstorms across western and
central Iowa. Storms have formed driven by pronounced shortwave
energy that has been notably lacking the past several mornings and
are making their way east across Nebraska. Mesoanalysis suggests a
strong cape gradient across the state which the line which the line
will ride on. At the same time, there is ample shear across the
state. One of the failure modes for previous nights would be the low
level jet (LLJ) being farther to the south than guidance suggested.
Given the better synoptic forcing, there is less reliance on the LLJ
for this round of storms. There are still some questions about the
strength of the MCS as it moves across the state. Radar trends show
new updrafts forming in front of the main MCS and the 05z HRRR shows
a `one-two punch` with these updrafts growing upscale quickly before
being overrun by the main MCS. If the updrafts out ahead do form
into another line, this will lessen the blow of the MCS as it moves
into the area and gets overrun. However, if these updrafts prove to
be transient and we only see the main MCS, the potential ceiling is
much higher in terms of our severe weather threat. Damaging winds
are the primary threat once again, as with isolated instances of
large hail and locally heavy rainfall, especially over any built up
cities or towns. There is also a low QLCS tornado potential, though
there is high uncertainty on the location of where the QLCS tornado
threat is highest and this is further complicated by the potential
for two lines. Should this MCS take a classic bowing shape, the
northern side of the bow would be favored for QLCS spinups given the
orientation of bulk shear vectors relative to the MCS itself.
Otherwise, the threat will remain lower pending storm
interactions. As for the heavy rainfall threat, this line
should be fairly progressive through the morning hours. Locally
heavy rainfall is still possible and flash flooding would become
a concern over cities and towns where drainage is not as good.

Once the MCS clears our area which looks to be around the early
afternoon hours, most areas should remain dry, although some
guidance hints at lingering showers and storms in north central
Iowa on the warm air advection wing, which leads us into tonight.
Guidance is still rather split on how everything is handled Thursday
night into Friday. Compared to previous runs, guidance is starting
to trend later with with warm air advection precipitation. Some
guidance suggests more robust convection earlier on, while other
solutions are more showery through part of the night. A lot of this
hinges on what our MCS does with the boundary currently analyzed
across Missouri. There is a solution where the outflow from this
morning`s MCS will counteract that boundary moving north into Iowa,
which would have further implications on convection overnight. If
the boundary remains farther to the south, anything that forms over
Iowa would be more stable and the severe threat would be rather low.
There are other solutions where the boundary could make it into Iowa
and, paired with better forcing, some level of severe potential
would exist. We are expecting showers and storms even if they
are not severe and rain amounts could start to add up, making
flash flooding a concern. See the HYDROLOGY section for a few
more details.

Following this warm air advection today, highs will once again
poke up a bit - into the mid to upper 80s across southern and
central Iowa (pending cloud cover clearing) with the mid to
upper 70s farther north where scattered precipitation is
expected throughout the day.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 142 PM CDT Wed Aug 12 2026

Overnight convection lingers into Friday morning with continued
hydro concerns into the day. The pattern remains active through the
weekend and upcoming week as wave continue to ride across the
thermal ridge in this "ring of fire" set up. Repeated rounds of
convection will rely on earlier rounds for both placement and
strength. A few lulls in convection are possible next week, but
timing out which days this may occur is difficult at this time
range.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1133 PM CDT Wed Aug 12 2026

Primarily VFR conditions prevail this evening, although sporadic
MVFR ceilings have occurred with patchy stratus. These
conditions will generally persist through the morning, although
a shallow fog may also develop at times. As we get closer to day
break, there is high confidence that a thunderstorm complex
will pass through the area, potentially impacting all sites.
All sites may be impacted, but KDSM has the highest confidence
with an arrival around 12z for that terminal. Strong winds and heavy
rain may accompany the main line of storms. The rest of the
sites remain on the fringes, but will likely see rain or storms
as well. Low clouds then follow this system, keeping at least
MVFR conditions over Iowa through the day Thursday. More
scattered showers and storms are possible Thursday afternoon.

&&

.HYDROLOGY...
Issued at 302 AM CDT Thu Aug 13 2026

Pwats of 1.5 to 2" today become largely over 2" on Friday,
peaking near 2.5" by Friday evening. These will be paired with
warm cloud depths, several rounds of rain, and the potential for
training storms, and 1-2" per hour rain rates or more with
thunderstorms. Although there remains some uncertainty with the
corridor of highest rain amounts today through Friday, west
central Iowa in particular has the potential to see some
excessive rainfall where rainfall amounts may start to reach
towards 3-5" or more. Similar rain amounts may start to add up
through portions of central and then east central Iowa into
Friday morning and then evening with subsequent rounds of rain
and many models are hinting at some localized amounts even
higher. A Flood Watch for Flash Flooding was hoisted that may
have a wider coverage area than needed, but with some lingering
uncertainty in the exact placement of highest rain amounts,
wanted to make sure the watch covered the potential different
threat areas which range from southern to central Iowa to
central to north central Iowa. Central Iowa does appear the most
likely regardless from around the I-80 to Highway 20 corridors.
The main concerns with the excessive rain amounts are flash
flooding, especially in urban and poor drainage areas, though
some rises on area rivers and streams is likely.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday afternoon for IAZ023>028-033>039-
044>050-057>062-070>075-081>086-097.

&&

$$

SHORT TERM...67
LONG TERM...Hagenhoff
AVIATION...Dodson
HYDROLOGY...05