772
FXUS63 KDMX 171757
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1257 PM CDT Mon Aug 17 2026

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Dry and pleasant during the daytime today!

- Thunderstorms return tonight into Tuesday. A few strong storms
  are possible along with locally heavy rainfall.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 305 AM CDT Mon Aug 17 2026

High pressure is centered over eastern Nebraska this morning with
the influence of the high pressure extending into Iowa. Very light
north winds to calm conditions extend across much of the state and
the only clouds over the state is shear anvil cirrus from storms
over southwest Kansas. The area of high pressure will move east
across Iowa today and for the first time in numerous days, the
forecast area will remain dry through the core daytime hours. High
temperatures will again be pleasant and in the upper 70s to low 80s
along with dew points in the 60s. Upper level low pressure will
descend into northern Ontario today and will swing a short wave into
the Northern Plains later today and towards Iowa tonight followed by
another short wave on Tuesday. The surface high pressure will begin
to become more positively tilted this afternoon and overnight and
that will allow for return flow and theta-e advection to reach
northwest Iowa. Thunderstorms are expected to develop over parts of
South Dakota and Minnesota this afternoon along a surface cold front
and attendant instability axis. These storms will track
east/southeast and should reach parts of northern Iowa overnight.
These storms will outrun the surface instability and will also run
into remnant dry air over central Iowa from the departing high.
While elevated instability will remain, the lack of the low level
jet (LLJ) focus weakening/diminishing storms as they move further
south into Iowa. The storms likely won`t be able to maintain balance
and will be trending outflow dominant as they arrive into Iowa.
While a damaging wind gust is possible over northwest Iowa, the
severe threat will continue to lessen deeper into the state.

Another area of storms to monitor will be the storms that will be
more closely associated with the LLJ that develop over western South
Dakota and Nebraska later in the night ahead of the 2nd short wave.
The kinematic forcing will move east and could maintain the storms
into Iowa late tonight and into Tuesday morning. These storms could
hold a damaging wind threat longer than the earlier mentioned
storms. The surface warm front should stay south of Iowa on Tuesday
due to the early morning storms and the area of low pressure across
eastern Colorado/western Kansas being suppressed further south during
the day. This should push the supercell tornadic potential south.
There is the potential for surface instability recovery by Tuesday
afternoon. Light surface flow is expected but good speed shear aloft
will exist which could promote organized convection. Low level
instability along with the light surface flow up to cloud bases
could promote horizontal vorticity stretching for landspout funnel
potential. Cannot discount a large hail and damaging wind threat
either. Moisture recovery will bring PWAT values back to near 2
inches over the southern half of Iowa and that may lead to locally
heavy rainfall, especially in areas with repeated storms.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 1249 PM CDT Sun Aug 16 2026

From Wednesday through Friday, Iowa will continue to reside
beneath northwesterly 500 MB steering flow, though which at
least two more shortwave impulses will travel overhead. At the
surface, however, the old decayed frontal zone should be pushed
to our south over Missouri by convective outflows from
Tuesday/Tuesday night storms. Additional showers may linger in
our southern counties Wednesday into Wednesday night, but then
decrease from Thursday onward with generally 10-30% POPs in the
extended. The quick passage of a surface ridge along with light
northwesterly flow should also allow for somewhat cooler
weather, with daily highs generally in the 70s to lower 80s,
though dewpoints will likely remain in the 60s to lower 70s.
There are some indications that next weekend a larger surface
high pressure system will build into the Upper Midwest and
Great Lakes region, which if this occurs, may provide more
tangible relief from the humidity that has persisted for the
past few weeks.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1246 PM CDT Mon Aug 17 2026

VFR conditions ongoing and expected to continue through the
daytime into the evening tonight. Some scattered cumulus has
begun to develop this afternoon as evidenced on satellite. Winds
out of the west today become out of the south tonight but will
largely stay light, under 10 knots before shifting back to out
of the west during the daytime tomorrow. Main aviation challenge
is the chance for showers and storms overnight through much of
the day Tuesday. Uncertainty in storm timing and evolution
remains on the higher side so only minor edits to previous prob
30 groups. There are at least shower if not thunderstorm chances
at all sites during the later portion of the TAF period but
coverage, intensity, and timing may all still change and the
coverage/intensity will affect the impacts at any one TAF site.
Expect updates in future issuances. Stronger storms could have
gusty winds and locally heavy rain at times which could lead to
lower visibilities and ceilings that may become at least
scattered MVFR.

&&

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

&&

$$

SHORT TERM...Donavon
LONG TERM...Lee
AVIATION...05