186
FXUS63 KDMX 160409
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1109 PM CDT Sat Aug 15 2026

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

.KEY MESSAGES...

- Scattered shower and thunderstorm chances this afternoon into
  the early evening. Severe risk is low, but isolated gusty
  winds and heavy rainfall are possible, mainly in southern
  Iowa.

- Drier conditions for most on Sunday with low chance (less
  than 20%) for scattered showers/storms in far southern Iowa.

- Dry conditions continue during the day Monday, thunderstorm
  chances returning northwest on Monday then area-wide on
  Tuesday.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 246 PM CDT Sat Aug 15 2026

Low stratus continues to span much of the forecast area early this
afternoon. This cloud deck has limited sunshine over the northern
two thirds of the area, keeping temperatures relatively cooler
compared to southern Iowa where skies are clearer. As of 2 pm,
temperatures are only in the upper 70s over northern Iowa, but
nearing 90 in far southern Iowa. The clearing in southern Iowa is
notable not only for temperatures, but also for thunderstorm
potential as a subtle shortwave and associated boundary tracks
through Iowa today.

Weak radar returns are already being detected by the KDMX radar,
albeit mostly showers at this time. Through the afternoon, mixing of
the boundary layer will allow for destabilization and surface-based
convection to develop, mainly over southern Iowa. Mixed layer CAPE
values are expected to exceed 3000 J/kg, providing plenty of energy
for displaced parcels. There will be no shortage of moisture around
this afternoon, as indicated by the sultry upper 70 to near 80
surface dewpoints and precipitable water values of 2 to 2.1". This
will make for rather efficient rainfall rates with any storm that
develops. Isolated flash flooding could occur, but the sporadic
storm coverage and progressive storm motions should limit the
overall risk, so have therefore opted to hold off on another flash
flood watch for this evening. With the efficient rain production,
gusty winds could become a concern as updrafts go up and collapse
into a well-mixed boundary layer boasting DCAPE values of 1500 to
1900 J/kg. This threat will also be fairly isolated and most likely
over the southern portions of the area where sun has been more
prevalent today.

While there are isolated risks with storms this evening, those
mentioned above are generally the only things the storms have going
for them. Mid-level lapse rates overhead are quite poor (around 6 to
7 C/km) and will actually be diminishing to under 6 C/km through the
afternoon. The kinematics will also be fairly poor and storms will
struggle to organize with deep layer shear values mostly under 30
kts. The low level kinematics are also unimpressive given the weak
low level flow. Therefore, the risk for severe hail or tornadoes is
low, leaving isolated gusty winds and heavy rainfall as the main
concerns this evening. The storm prediction center`s (SPC)
marginal risk for severe weather (level 1 of 5) over southern
Iowa seems appropriate for this afternoon. If any gusty wind
risk exists, it will be with storms in this area with
diminishing threat farther north. On the rainfall side of
things, the weather prediction center has trimmed up the slight
risk (level 1 of 4) for excessive rainfall to only include
eastern and southeastern Iowa and a marginal risk (level 1 of 4)
of excessive rainfall for the rest of the area.

Most of guidance pushes the boundary south of Iowa this afternoon,
taking most of the remaining instability and overnight shower or
thunderstorm potential with it. There is still a chance (~20% or
less) for some showers or storms to scrape along the Iowa/Missouri
border tonight into early Sunday, but most solutions keep this south
of Iowa and over northern Missouri. For most, if not all of the
area, Sunday looks like it will be a nice reprieve from the
onslaught of shower and thunderstorm chances we`ve seen over the
last week.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 246 PM CDT Sat Aug 15 2026

Our lull in precipitation chances will continue into the day
Monday but our break is short-lived as shower and thunderstorm
potential returns to northwest Iowa Monday night, and area-wide
again Tuesday into Wednesday. Given this will be another
northwest flow regime, it`s tough to get too involved in the
details. That said, the Tuesday storms do seem to have a rather
healthy environment with increasing instability and modest deep
layer shear supportive of more organized convection. SPC does
have a day 4 15% risk for most of Iowa and WPC has put out a
slight risk for excessive rainfall for Tuesday. The pattern
remains relatively active through mid-week and then ridging
begins to build through the second half of this week.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1110 PM CDT Sat Aug 15 2026

Main aviation challenges will be low ceilings overnight and
patchy fog development. Most sites will see some degree of MVFR
or low end VFR ceilings before these lift or scatter into VFR
by mid morning. In addition, recent rainfall and light winds may
allow patchy light fog to develop, especially at ALO and OTM
with MVFR restrictions shown. Winds from the north-northwest
will be increasing towards 10 knots around sunrise over northern
Iowa, which may limit the fog potential in these locations.
Those winds from the north-northwest will reach 8 to 12 knots
around midday with VFR conditions prevailing through the end of
the period.


&&

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

&&

$$

SHORT TERM...Dodson
LONG TERM...Dodson
AVIATION...Ansorge