628
FXUS63 KDMX 140357
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1057 PM CDT Thu Aug 13 2026

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Storms are expected particularly across the central part of
  the state this evening through the overnight and again
  tomorrow afternoon into Saturday morning.

- Storms that occur tonight and tomorrow pose a threat for large
  hail and damaging wind, and perhaps an isolated tornado. The
  larger impact will be large rainfall amounts. There is a Flood
  Watch issued for most of the state for potential for flash
  flooding in urban areas as well as stream and river flooding.

- The pattern remains active with storm chances through the
  weekend and mid next week.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 252 PM CDT Thu Aug 13 2026

Lingering subsevere storms and anvil shield are in the process of
clearing the CWA this afternoon as the morning MCS has dissipated
and moved east. Our active weather pattern continues on through the
short term with a ridge over the south central US and ridge-riding
shortwaves continuing to be directed across Iowa. The outflow
boundary was pushed into Missouri this morning but has begun
recovering instability into southern Iowa. A conditional storm
threat exists towards southern to central Iowa along the instability
gradient. If surface based convection can develop on this boundary
before dark, it will be in an environment with decent low level
shear given surface easterlies. This could support a brief window
for supercells, however, any surface based convection will be
opposing poor low level lapse rates and subsidence.

Because the low has developed eastward, the main storm development
region tonight will be focused more over Iowa rather than
development over the high plains and MCS maturing off to our west
like has been the case the last several nights. The next round of
storms tonight may be less organized and will be primarily driven by
the LLJ exit region convergence. Convection is expected to develop
generally after 2z tonight on the gradient of better lapse rates and
MUCAPE. Instability should certainly be sufficient for support
widespread convection, though shear will be limited above 3km. 1-3km
shear on the order of 30-40 knots may be favorable for some brief
bowing segments, but this effect may be offset by largely saturated
profiles and limited DCAPE, so cold pools may struggle to get
organized. All things considered the threat still remains for some
large hail or damaging winds. The larger impact will likely be
rainfall amounts and hydrology impacts, so see the updated hydrology
section below. A swath of 1-3" will be common especially where
continued storm development occurs around the LLJ nose.

By Friday morning, rain clears out in the morning once again and
reloads for an afternoon and evening round of storms. An MCV rides
the western fringe of the ridge and will provide the forcing needed
for afternoon storm development. A weak surface low associated with
the MCV meanders across the central part of the state through the
afternoon and evening. Beginning with afternoon severe threats. CAMs
are notoriously bad at handling the low level wind fields in these
types of environments. Mid and upper level flow will be weak, so
long duration storms are less likely. However, the strengthening LLJ
through the afternoon could lead to some enhanced low level shear.
The most likely environment tomorrow is one with some pockets of
enhanced CAPE and perhaps 0-3 CAPE, overlapping with mainly some low
level shear. This could support some transient supercell or bowing
segments for some isolated large hail and gusty winds with perhaps a
tornado if everything comes together. Again the larger impact will
be hydro concerns. Weak flow and PWATS over 2" will result in slow
moving or training storms with efficient rainfall production through
a large portion of the Friday overnight period. HREF guidance shows
widespread 1-3" of rain through Friday night with the main
swath setting up over central to eastern Iowa. However, a few
members show precip amounts over 5 inches over some very
localized areas. Again, CAMs frequently don`t handle convective
coverage well from MCV setups so there is still large
uncertainty in rain totals tomorrow.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 252 PM CDT Thu Aug 13 2026

The ring of fire pattern continues through Saturday night. PWATs
over 2" linger until a cold front sweeps through Sunday morning.
GEFS/EPS guidance highlights Saturday into Sunday morning as another
period of storm chances, with similar potential for marginal severe
chances and flash flooding as we have seen most of this week. High
pressure and drier canadian air may bring a brief break from any
rain chances before the ridge breaks down a bit and shortwaves and
enhanced flow return to our part of Midwest by midweek. This will
need to be monitored for renewed severe weather and heavy rain
concerns.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1038 PM CDT Thu Aug 13 2026

Storms lifting northward out of Kansas, along with additional
t-storm development associated with the low level jet, will
begin to impact the KDSM/KOTM terminals after 08Z tonight.
Storms will then continue to lift n/newd and impact KFOD/KALO
and possibly KMCW between Expect decreasing CIGs to MVFR to IFR,
with occasional lower VSBYs with heavier thunderstorms. After
the initial round of storms, persistent MVFR to IFR may linger
through the day, especially in the north through the afternoon.
There is a chance for additional thunderstorm development
tomorrow afternoon and into tomorrow tonight.

&&

.HYDROLOGY...
Issued at 252 PM CDT Thu Aug 13 2026

Active weather with periods of moderate to heavy rain are expected
through at least Friday night. Main questions are location and
amounts, which may significantly impact hydrologic responses.

WPC plans to upgrade their Day 2 excessive rainfall outlook (ERO)
to moderate risk for much of our CWA south of US Hwy 20. A Day 2
moderate risk ERO is rare for our area, averaging once every 2+
years, which highlights the potential significance. Locally
significant flash flooding is possible in urban areas or other areas
that receive the heaviest rain. We typically have decent capacity
this time of year for heavy rainfall in the rural areas, however,
the recent bouts of moderate to heavy rain have reduced
that capacity. Additional heavy rain especially with current QPF
values would produce more significant responses than typical.

In terms of river flooding, significant within-bank rises are
expected on many streams. At least isolated to scattered minor river
flooding is possible, with more significant flooding possible as
well. Since QPF will be around rainfall-runoff inflection point,
just a little more QPF than forecast may produce more significant
flooding. For example, if QPF averages around 0.5 to 1 inch more
than forecast, then widespread minor river flooding with multiple
locations seeing moderate or possibly major flooding may occur.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Saturday morning for IAZ023>028-033>039-
044>050-057>062-070>075-081>086-092>097.

&&

$$

SHORT TERM...De Bruin
LONG TERM...De Bruin
AVIATION...Fowle
HYDROLOGY...Zogg