958
FXUS63 KDMX 190818
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
318 AM CDT Sun Jul 19 2026

.KEY MESSAGES...

- Hot and humid today and tomorrow. Heat peaks on Monday, but
  could be tempered by storms and/or smoke aloft.

- Two rounds of storms are possible on Monday. Severe storms are
  expected and may produce damaging winds, along with hail and
  heavy rain. There is also a low tornado threat in northern
  Iowa.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 318 AM CDT Sun Jul 19 2026

The cool front that sank south across Iowa through the day on
Saturday is draped across northern Missouri early this morning.
In the wake, temperatures overnight have been much cooler than
recent nights. Most areas are in the low 60s, though southern
Iowa still sits in the low to mid 70s nearer the boundary.
Patchy fog has developed in a few places early this morning and
may expand through sunrise, though widespread dense fog is not
anticipated. Despite the cooler morning temperatures, the
thermal ridge will rebuild through the day with afternoon highs
back into the upper 80s and low 90s. The rebuilding ridge will
result in an instability axis setting up across western to
southern Iowa this afternoon. There is little forcing in place
today, however an isolated thunderstorm could develop there.

Our attention then turns to the pattern shift that is expected to
result in two rounds of thunderstorms: overnight tonight into early
Monday morning and again Monday evening. Strong theta e advection is
anticipated into the area during the daytime which may result
in the warmest day of this hot stretch. Forecast highs, for now,
are in the mid to upper 90s. At the same time, convection
chances in the morning could temper afternoon warming potential
depending on how quickly things can recover. Smoke overhead is
also possible and could also influence daytime temperatures.
Given the uncertainty here, no heat advisory has been issued,
but one may be needed if confidence in convective evolution and
subsequent impacts to temperatures increases. If recovery
occurs as currently forecast, heat indices in the afternoon
could exceed 100-105 for much of the area.

Round 1: Overnight and early Monday morning. A shortwave trough will
ride across Montana and the Dakotas Sunday, reaching the upper
midwest overnight. Convection from this wave is expected to track
across South Dakota overnight, decaying as it reaches Iowa with
remnants moving across the state through the early morning. Most of
this should be sub-severe by the time it reaches the state, however
a few stronger cores may persist and could result in hail or a
stronger gust.

Round 2: Monday evening. The atmosphere is expected to recover
behind the early morning decaying convection with strong theta e
advection into the area and an airmass that becomes deeply
unstable by afternoon as the upper level shortwave tracks north
of the state. Recovery in the warm sector of the associated
surface low will result in 4000+ J/kg of MLCAPE across the area.
The jet is robust as well, inducing 50-60 kts of 0-6 km shear.
This shear will be more than sufficient for organized convection
with well maintained and longer lived updrafts. As such,
evening convection is expected to be much more vigorous than
the decaying convection of the morning, and this is the primary
window for severe storms. Storms are expected to develop along a
cold front that will push across the state in the evening,
though airmass thunderstorms ahead of the front are possible in
afternoon especially on any lingering outflow boundaries from
morning convection. By late afternoon convection is expected to
initialize. It is possible that two areas of convection develop,
as hinted at in recent CAM guidance. The first area would be
near the surface low cutting across Minnesota into Wisconsin and
northwest Iowa with the second along the trailing cold front
with best convection west near the edge of the thermal ridge on
the instability axis. As the cold front pushes across Iowa
through the evening, convection is expected to become more
widespread along the entire front trailing across Iowa. As it
grows upscale into an MCS overnight expect that wind will be
the primary hazard. Large hail is also a concern, especially
with initial updrafts with steep mid and low level lapse rates
of 7-8 C/km. Hodographs are fairly straight, but a tornado
cannot be ruled out mainly near the surface low in northwest
Iowa with enhanced stretching and a little better low level
curvature. There is also plenty of moisture in place with PWATs
around 2" with warm cloud depths exceeding 4000 m, which will
allow for efficient rainfall. Progressive storm motions and dry
antecedent conditions (along with mature crops) should mitigate
most hydro concerns.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 243 PM CDT Sat Jul 18 2026

Showers and storms are expected to taper off after sunrise Tuesday,
with surface winds shifting northwest as the mid-level trough and
associated deepening low pressure system departs the region. A
tightened pressure gradient on the backside of this system will
bring breezy conditions through the day, with gusts up to 20-30 mph.
Highs as a result will also be ``cooler`` with values in the 80s,
and dewpoints in the upper 50s to low 60s. The pattern through
midweek generally remains the same as the ridge remains west of the
region and upper level northwest flow continues to bring slightly
cooler and less humid conditions overhead, as highs generally top
out in the 80s and dewpoints reach into the upper 50s to low 60s.
Subtle waves riding the larger scale flow with periods of some level
of moisture return though could bring additional chances of showers
and possible storms to Iowa later Wednesday through Friday, though
details are not as clear on exact timing and coverage details of
this activity and will be refined in the coming days. More summer
like conditions are expected to return near the end of the work week
as temperatures gradually return into at least the low 90s as the
ridge strengthens once again.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1055 PM CDT Sat Jul 18 2026

VFR conditions ongoing and largely expected to continue through
the TAF period. The exceptions to this are any patchy fog that
can develop into Sunday morning and any smoke impacts with
wildfire smoke moving into the area. Confidence remains too low
in impacts at any TAF site for fog, and in visibility reductions
from the smoke at KALO/KOTM/KMCW. Will continue to monitor
trends and amend as needed. Light and variable winds overnight
settle out of the east to southeast on Sunday.

&&

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

&&

$$

SHORT TERM...Hagenhoff
LONG TERM...Bury
AVIATION...05