590
FXUS63 KDMX 131130
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
630 AM CDT Sun Sep 13 2026

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Scattered to widespread shower and storm chances will increase
  this morning. Locally heavy rainfall amounts may lead to
  ponding water or minor flash flooding.

- Heavy rain and thunderstorms possible Monday. Some may be
  severe, especially in the afternoon. Heavy rainfall and
  training storms may result in flash flooding.

- Heavy rain and storm chances persist through at least mid-
  week. River flooding and flash flooding is possible.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 400 AM CDT Sun Sep 13 2026

Overnight surface analysis shows widespread high pressure centered
over northern Montana into southern Canada. This 1022 mb surface
high is exerting its influence across much of the northern CONUS, as
evidenced by mostly clear skies and temperatures ranging from the
upper 40s in the far northwest to the upper 50s in the far
southeast. To the south, lingering convective activity persists
along a stationary boundary draped across Missouri and Kansas.
Locally, temperatures are in the mid-50s under mostly clear skies.

EARLY MORNING THROUGH SUNDAY EVENING:

While surface high pressure remains to the northwest, the region is
sandwiched between two upper-level troughs. The first trough is
centered over Hudson Bay and is pivoting southeast toward the Great
Lakes, while the second sits over the Pacific Northwest, leaving
weak ridging in between. Overnight model guidance pushes a 110 to
120 kt jet streak through the Hudson Bay trough. Although the core
remains north, its right entrance region will cross the Central
Plains and Mid-Mississippi Valley through the morning, supporting
convective development. High-resolution CAMs and deterministic
models show PoPs increasing around 09Z and progressing rapidly
across the area today. A strengthening LLJ will further support
convection by advecting rich Gulf moisture northward. Forecast
soundings for later this morning indicate deep saturation from the
surface to 500 mb alongside PW values exceeding 1.50 inches, which
sits near the 90th percentile for this time of year. This moisture
profile will promote efficient, heavy rainfall today. Fortunately,
the system remains progressive, keeping the overall flooding threat
relatively low; however, the WPC has placed southwestern portions of
the CWA in a Day 1 Slight Risk for excessive rainfall to account for
localized minor flash flooding. As the main trough pulls east,
rising geopotential heights will yield a lull in convective activity
later this evening into the night.

MONDAY:

Overnight tonight into Monday, the Pacific Northwest trough
will cross the Rockies into the High Plains. Model consensus tracks
this negatively tilted trough out of Wyoming toward the lakes of
central Manitoba, drawing its associated surface low into the
Dakotas and pulling a warm front northward through the day.
Consequently, the potential for strong to severe thunderstorms will
increase Monday afternoon and evening. Forecast soundings and
hodographs reveal a strong veering wind profile enhanced by an
accelerating afternoon LLJ. Curving hodographs alongside elevated
ESRH and bulk shear values favor damaging winds and tornadoes. CAMs
suggest convection may initiate as discrete supercells before
growing upscale into a severe convective system aligned with the
advancing warm front. The primary limiting factor remains the degree
of boundary-layer destabilization achievable Monday afternoon.
Nevertheless, the SPC has outlined southwestern portions of the area
in a Day 2 Slight Risk, with all hazards possible. In addition to
severe weather, heavy rainfall remains a major concern as the LLJ
once again advects moisture into the region. Soundings depict PW
values reaching 1.80 to 1.90 inches which is the 99th percentile,
deep saturation up to 500 mb, and skinny CAPE profiles. Furthermore,
NAEFS ensemble anomalies place Iowa in the bullseye for 99th
percentile PWs, with integrated water vapor transport (IWVT) values
maxed out relative to climatology. These factors will elevate flash
flooding potential Monday into Tuesday, prompting the WPC to issue a
Day 2 Slight Risk for excessive rainfall across the entire forecast
area.

A surface high pressure center will maintain quiet conditions short-
term before an upper-level trough and strong jet dynamics trigger
widespread heavy rain today, prompting a Day 1 Slight Risk for
excessive rainfall in southwestern areas. Following a brief evening
lull, a negatively tilted trough and warm front will move into the
region on Monday. This second system brings a dual threat of severe
weather (including damaging winds and isolated tornadoes) and
potential flash flooding driven by near-climatological maximum
moisture levels, placing the area under Day 2 Slight Risks for both
severe weather and excessive rainfall.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 254 PM CDT Sat Sep 12 2026

By Monday afternoon, better instability (~1500 J/kg) will begin to
develop in the warm sector along with 50+ kts of deep layer shear.
The limiting factor will be warm low- to mid-level temperatures
leading to a notable amount of convective inhibition. Therefore, any
thunderstorms that occur will need to overcome this cap, which will
be most likely along the southwest to northeast oriented boundary
from western into northern Iowa. This boundary is expected to be the
focal point for thunderstorm activity through the afternoon and
overnight into Tuesday. Monday afternoon, some strong to severe
storms will certainly be possible along the boundary, with hail and
wind being the primary concerns. A tornado threat does exist as
well, thanks to a healthy amount of low level turning, but would be
contingent on storms becoming rooted at the surface. This
conditional risk has prompted the storm prediction center to issue a
Day 3 slight risk focused on western into central Iowa for Monday
afternoon.

Along this boundary will also be a quite moist environment with
PWATs pushing 2" or higher, which would put them at the high end of
climatological PWATs for this time of year, suggesting efficient
rainfall production. Likewise, storm motions parallel to the
boundary will lead to training storms and a heavy rain and flash
flooding threat Monday afternoon through the overnight. The highest
amounts are currently being modeled over northern Iowa, with 24 hour
QPF amounts of 3 to 5" being depicted by 18z Tuesday. The location
of course will be dependent on where the boundary sets up, so it`s
likely this area will shift through the coming days. However, the
signal is certainly there for a heavy rain threat Monday night
through Tuesday. Should these amounts be realized, flash flooding is
possible if not likely, especially if it occurs in any urban areas.
The weather prediction center rightfully has slight risks for
excessive rainfall over Iowa every day starting tomorrow through
Wednesday.


>> FLOODING CONCERNS INTO THE MIDDLE OF NEXT WEEK

The aforementioned surface boundary continues to produce storms
Tuesday into Wednesday as well. Breaks will likely occur between
pockets of forcing, but heavy rain and storms persist each day
through Wednesday and potentially beyond. The weather prediction
center rightfully has slight risks for excessive rainfall over
Iowa every day starting tomorrow through Wednesday. In addition
to the flash flooding concerns, we may see rivers beginning to
respond as well. GEFS-induced hydrologic ensemble forecasts
suggest many of the rivers over north central into southern and
eastern Iowa could be pushing into action or flood stage by the
second half of next week. Unfortunately, the active pattern
really doesn`t look to let up through the second half of the
work week and into next weekend, but solutions diverge at that
point.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 625 AM CDT Sun Sep 13 2026

Showers have developed this morning and are slowly working
eastward. Fortunately, showers have stayed away from terminals,
however, that won`t be the case as showers and storms increase
in coverage throughout the day. Terminals KDSM and KOTM have
the best chances of seeing precipitation but did add PROB30s to
the remaining sites for the shower potential through the
afternoon. Once showers dissipate this afternoon, a lull in
activity is expected overnight before showers and storms return
after 10Z/Monday. Winds are forecast to be easterly throughout
the day around 10 knots but thunderstorms could bring gusty and
erratic winds this afternoon.

&&

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

&&

$$

SHORT TERM...Vorst
LONG TERM...Dodson
AVIATION...Vorst