167
FXUS63 KDMX 291957
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
257 PM CDT Mon Jun 29 2026

.KEY MESSAGES...

- A prolonged period of hot and humid conditions will continue through
  the coming week and potentially the Fourth of July weekend.
  An Extreme Heat Warning is in effect for the entire area.

- Severe thunderstorms are possible this evening into the
  overnight in northwest Iowa, with damaging winds being the
  primary threat. However, there is uncertainty in how far into
  our warning area these storms may advance.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 256 PM CDT Mon Jun 29 2026

The heat wave is in full swing across the state today as heat
indices are already topping 100F this afternoon and may continue to
climb a few degrees further, while perhaps being just a couple
degrees behind schedule with the presence of cumulus possibly
limiting sunshine. Dewpoints are well into the mid 70s and may
continue reaching towards the upper 70s through the rest of the
afternoon and evening. Immense amounts of instability is being built
beneath a stout cap, now over 6000 J/kg in a large part of the
state. Remarkably strong synoptic winds for this time of year are
being mixed down from 850 mb, caused by the low to our north,
causing wind gusts on the order of 30 knots across a good part of
the state. As we head into the evening, a slight risk is in place
across our far northwest, with multiple chances at storms tonight.
700mb temps will be 15C across most of the state this evening,
keeping us clear of any storm chances, but towards 03z the cold
front approaches our far NW counties, and 700 mb temps cool in a
narrow zone ahead of the cold front. CAMs are split about 70/30 in
favor of storms briefly trying to form early evening and eventually
being capped off before making it into our CWA. However, some
solutions have convection robust enough to build up a cold pool that
continues into a few counties of our area and trudges through that
very unstable and very capped airmass sitting across the warm
sector. These storms would pose mainly a damaging wind threat by the
time they get to our CWA, but large hail and even a tornado is
possible if a storm complex can take advantage of the strong 0-1km
shear.

Assuming a large cold pool doesn`t develop during the mid evening
and exhaust the environment, another shot at severe storms across
our NW will happen towards 7-9z. The nocturnal LLJ surges with a new
shortwave over the central plains tonight. Elevated convection will
likely develop at the nose of the LLJ and in the post frontal zone
of the slowing cold front over central Nebraska near 4-6z. As the
front reorients tonight, this elevated convection will try to ride
the theta-e gradient from central NE to far NW IA. As it does, it`s
cold pool may attempt to nudge further into the highly unstable
airmass across our NW CWA. The uncertainty lies in how effective
this cold pool can be at lifting capped parcels to their LFC to take
advantage of the instability. Given strong capping, and mediocre mid
level shear, but strong instability, the most likely solution is the
overnight MCS with some damaging wind potential impacts far
northwest IA, perhaps including a couple of our counties, but is
unable to advance further southeast away from the frontal boundary.

On Tuesday, a similar pattern is in place, with ridging to the
southeast, ample sunshine, and mid-70s dewpoints causing extreme
heat. Headlines last through all of Tuesday to account for yet
another day of 100+ degree heat indices and lack of any relief from
limited cooling overnight. Overnight cold pools may perhaps keep
temps a tick lower across NW Iowa on Tuesday, but there is still
high confidence in extreme heat across the rest of the state.
Renewed chances for storms exist again in the evening and overnight
Tuesday as the nocturnal LLJ surges again to the west and perhaps
initiates storms that run across the theta-e gradient once again.
However, storms are possible earlier in the evening for central and
northern Iowa as CAMs are hinting at some convection along the wind
shift boundary as we reach peak instability.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 256 PM CDT Mon Jun 29 2026

A similar pattern remains in place through Saturday. High pressure
to our southeast will keep the heat and humidity in place,
especially across the central and southeast part of the state. Heat
indices may drop a tad, but the danger may lie more in the continued
days of heat, and the lack of overnight relief with lows in the
upper 70s. Therefore, the extreme heat warning has been extended for
a large part of the state through at least Wednesday with
anticipation of possible further extension in the coming days. As
has been talked about the last few days, the heat is expected to
continue through the 4th of July weekend, where heat indices on the
order of 100 are still being forecast. Storm chances will continue
each day, particularly in the western and northern part of the
state, as the ring of fire pattern continues. The usual pattern will
continue to be large instability built up during the day, LLJ surges
at night, and initiates storms overnight that attempt to push east
through the highly capped environment over our CWA. Though marginal,
it is also worth mentioning the excessive rainfall outlooks across
Iowa. With large PWAT and storm chances, chances for flash flooding
can`t be ruled out on any given day. Per the usual for this time of
year, these storm chances will be highly uncertain in their exact
timing and intensity.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1247 PM CDT Mon Jun 29 2026

Scattered to broken cumulus across the terminals are causing
occasional MVFR conditions this afternoon, particularly at KMCW, but
all sites should maintain VFR conditions by mid afternoon through
the end of the TAF period. Confidence is high in LLWS at all sites
beginning late evening through the overnight as surface winds begin
to calm, though there is a chance LLWS begins earlier than what is
included in this issuance. Additionally, there is a low (~20%)
chance for thunderstorms at KFOD and KMCW through the
evening/overnight but confidence is too low to include in this
issuance.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Warning until 9 PM CDT Tuesday for IAZ004>007-
015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097.

&&

$$

SHORT TERM...De Bruin
LONG TERM...De Bruin
AVIATION...De Bruin