Marshalltown, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

722
FXUS63 KDMX 290354
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1054 PM CDT Sun Jun 28 2026

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

.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, except in northeastern Iowa where it begins on Monday.

- Additional storm chances are possible Monday evening into
  Tuesday and again at times midweek.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 312 PM CDT Sun Jun 28 2026

Quite the eventful morning unfolded as a Mesoscale Convective System
(MCS) that was over the Dakotas last night made its way eastward
across the northern to north-central portions of Iowa, which lead to
some severe wind reports in Hancock county (Britt and Garner in
particular at 58mph), along with hail reports that were small in
size and more sparse. Otherwise, a much needed dose of rainfall was
received across northern and north central Iowa, with a nice swath
of 1-2 inches that should provide at least a little relief given the
ongoing drought conditions over these areas. Lingering storms from
this decaying complex continue to move over far eastern Iowa along
the instability gradient, which is expected to further weaken given
the decrease in upper level support as it moves out of Iowa through
the rest of the afternoon. Otherwise, a broader look at the upper
level synoptic features today shows the large trough covering much
of the western half of the CONUS, while broad ridging slowly
intensifies over the central and southeastern parts of the country.
Increasing southwesterly flow will continue to lift a much warmer
and humid airmass over the region today, which marks the beginning
of the well known heatwave that will impact the area over the next
several days. Temperatures have been steadily increasing so far for
most areas with values through the 70s in the northeast half of
Iowa, and even warmer through the 80s in the southwest half where
breaks in the clouds have been occurring per satellite imagery. The
trend in decreasing cloud cover is expected to continue further east
and north with time for the rest of today, which should allow for
temperatures to increase even further. Given the lingering clouds
though, and especially the coverage of storms in northern Iowa this
morning, have bumped down forecast highs a few degrees over much of
the area, with highs expected to top out in the upper 80s to low 90s
across the area, warmest west and south. High dewpoints through the
70s are common across the area, which should allow heat index values
to top out above 100 degrees over much of the forecast area. The
Extreme Heat Warning remains unchanged as a result across the
southwestern two-thirds of the state today. Please make sure to
practice appropriate safety measures to avoid heat-related illnesses.

Dry conditions are expected to continue across the forecast area
through Monday, starting out the day with minimum temperatures prior
to sunrise in the mid to upper 70s. The warm and humid airmass will
continue to lift north and east as the Upper Ridge ascends across
the southeastern CONUS and portions of the Great Lakes, with mostly
sunny skies and strong southwesterly low level flow. This will allow
for temperatures to quickly climb through the 90s across
Central Iowa, paired with heat indices up to 110 degrees and
breezy surface southerly winds. The Excessive Heat Warning will
continue for the southwestern two thirds of the forecast area,
but also the remaining northeast counties given the higher
confidence setup. By the evening into Monday morning, a defined
shortwave within the western trough is expected to lift across
the Dakotas and into Minnesota, with a trailing cold front
expected to arrive into northwestern Iowa. Deterministic models
generally indicate the development of showers and storms after
00z in northwestern Iowa, with this activity generally variable
in evolution between various members. The elevated warm layer
will likely be somewhat of a limiting factor in storm
development, along with limited moisture aloft, given the drier
profile above the cap. If elevated convection is able to
develop, the main concern would be large hail given more than
favorable MUCAPE values over 4000 J/kg and steep lapse rates
around 8km, paired with effective shear values around 30-35
knots that should allow for longer hail residence times. The SPC
Slight Risk area remains over this area and will need to
continue to be closely monitored over the next 24 hours. PWATS
near 2 inches and warm cloud depths will also allow for heavy
rain with this activity, though given the capacity soils across
the north, concerns are minimal for a flooding risk at this
time.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 312 PM CDT Sun Jun 28 2026

There remains the signal for another period of showers and storms as
another wave within the larger scale trough lifts near Iowa Tuesday
evening into Wednesday, along with an increasing low level jet
overhead. Showers and storms are suggested to develop across
portions of northern and western Iowa per Euro, while the GFS and
NAM are on the drier side as any activity is further north into
Minnesota closer to the warm front. These details are more on the
uncertain side at this time, so will need to monitor this over the
next few days. A Marginal Risk covers this area per SPC, with hail
and gusty winds the main hazards where storms do develop and grow
upscale. Otherwise, the main story will continue to be the long
stretch of extreme heat as the upper ridge moves very little through
the mid to late week period, including the 4th of July holiday.
General highs are expected through the 90s each day, with heat
indices above 100 degrees for much of the area, while overnight lows
generally ``bottom out`` in the mid to upper 70s, providing little
relief from the heat. Additional heat headlines are certainly
possible in the coming days, but will need to monitor potential
limiting factor such as overnight storm activity prior to each day,
which models indicate are certainly possible over parts of Iowa.
Specific details regarding coverage and intensity of these periods
of active weather will be better known in the coming days.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1048 PM CDT Sun Jun 28 2026

Removed gusts in the short term due to lack of observations. Stratus
has formed over the northeast part of the state, affecting KMCW
and KALO the most. Currently expecting these to remain VFR.
LLWS common overnight. VFR conditions with gusty winds during
the day with gusts over 30kts common after 18z, easing winds
after 00z. Have reflected chances for stratus with a FEW deck
in the north in this same timeframe.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Warning until 9 PM CDT Tuesday for IAZ004-005-015-
023>025-033>037-044>050-057>062-070>075-081>086-092>097.
Extreme Heat Warning from noon Monday to 9 PM CDT Tuesday for
IAZ006-007-016-017-026>028-038-039.

&&

$$

SHORT TERM...Bury
LONG TERM...Bury
AVIATION...Jimenez