Altoona, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

411
FXUS63 KDMX 261139
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
639 AM CDT Sat Jul 26 2025

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Showers and thunderstorms continue across southern Iowa this
  morning, tapering off by midday. Heavy rain with pockets of
  3+" possible.

- Becoming hot and humid Sunday and Monday. Heat index of 105+
  expected for much of the area both days.

&&

.UPDATE...
Issued at 234 AM CDT Sat Jul 26 2025

Showers and thunderstorms across northern Missouri have started to
fill in early this morning and expand into southern Iowa along the
plume of moisture and on the nose of the increasing LLJ. The severe
threat remains quite low with very little available shear. And while
a stronger gust might be possible from collapsing cores, with deep
warm cloud layers the temperature differential is likely not going
to be enough for anything substantial. Of greater concern is the
heavy rain threat across southern Iowa with PWATs of 2-2.5" through
this morning. 1-3" with pockets of 3-5+" are certainly possible,
especially towards southeast Iowa. Activity tapers off towards
midday with the rest of the afternoon mainly dry across the
area. Some afternoon redevelopment is possible, but at this time
this looks most likely just southeast of the area.

By Sunday high pressure, and therefore heat, begin to build across
the area. There is more than sufficient moisture in place with
dewpoints of 75-80F likely, coincident with afternoon
temperatures in the low 90s. This will send the heat index into
the 100-105+ range across much of the area, prompting an
extreme heat watch. Monday looks even warmer with the heat index
reach 105-110+ and expansion of heat watches/other headlines
are likely. The main area of uncertainty in temperatures is the
possibility for convection with a shortwave passing across
northern to central Iowa. Associated cloud cover may dampen
temperatures a bit, however timing also looks to be later in
the evening per recent guidance which may reduce any impacts.
With this uncertainty, will reevaluate on the day shift. In any
case, the heat Sunday and Monday will be some of the warmest of
the season and care should be taken to keep cool and safe.

&&

.DISCUSSION...
Issued at 247 PM CDT Fri Jul 25 2025

Showers and isolated thunder over southern Iowa are the first of
what will be intermittent shower and thunderstorm chances lasting
through the evening. These chances will spread northeastward through
the evening bringing the potential for more heavy rainfall to the
area. Fortunately most of the rain last evening stayed outside the
forecast area so soils aren`t as primed as what was anticipated this
time yesterday. However, still anticipating some potential for flash
flood impacts over southern Iowa, primarily in urban areas should
prolonged heavy rain occur over the same area. Rainfall amounts will
generally be around 1 to 3 inches, with isolated pockets of 4 inches
or more certainly possible in some locations over southern into
southeastern Iowa.

Of similar concern will be a lower confidence but potentially
impactful secondary band that develops slightly farther north in a
few of the short range models. This would put a line of slow moving,
training storms over central into north central Iowa, which is an
area that received heavy rainfall earlier in the week. Likewise,
rivers in these areas are already running at increased flows as
water continues to route southward from rain this week. Should this
band of 1 to 3 inch rain fall over one of these basins, the
additional runoff could exacerbate conditions on the rivers, as well
as lead to localized flash flooding as the water works it`s way
through the system. Similarly, any heavy rainfall over urban areas
could cause flash flooding and ponding on roadways. Again, this is a
lower confidence scenario as most of guidance keeps the heaviest
rain over southern Iowa where rivers are less aggravated, but
certainly something to keep a close eye on. If this band displaces
even farther north where flood warnings and watches are already
ongoing, particularly on the Iowa and Cedar Rivers. The Des Moines
River basin is also running at increased flow and could be impacted.

Beyond the heavy rainfall and flash flooding risk, there remains a
low chance for a few stronger storms, particularly in southern Iowa.
The main threat with these storms will be strong winds as rain falls
and the downward mass flux produces increased outflow from the
storms. The storm prediction center currently has a marginal
risk for severe weather just south of the forecast area and
barely clipping our southeastern counties, but gusty winds are
possible farther north of this area as well. Precipitation
lingers into Saturday morning but should mostly wrap up through
mid-day. Some guidance suggests isolated redevelopment in the
southeast Saturday afternoon, but this will be fairly sporadic.

The next hazard on deck is the hot and humid conditions that develop
Sunday into Monday as thermal ridging/warm temperatures aloft leak
eastward into the forecast area. Highs Sunday and Monday will be in
the low to mid 90s, with dewpoints pushing the upper 70s to near 80
in some locations. This would push heat indices into the 105 to 110
range, likely warranting heat headlines on Sunday and Monday. Monday
is currently forecast to be the warmest day, however, guidance has
begun to key in on a shortwave dropping southward into the forecast
which could impact high temperatures on Monday. This wave may also
bring some severe potential to the area, with SPC pulling the
marginal risk for severe weather.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 639 AM CDT Sat Jul 26 2025

Patchy fog has developed across northern Iowa, bringing IFR to
LIFR impacts to northern sites KFOD/KALO with recent
improvement at KMCW. This is expected to diminish in the next
1-2 hours. Meanwhile showers and thunderstorms have expanded
across southern to central Iowa with impacts at KOTM and nearing
KDSM. These will taper off through the morning with improvement
to VFR conditions by midday.


&&

.HYDROLOGY...
Issued at 247 PM CDT Fri Jul 25 2025

With upcoming heavy rainfall in the south this evening, and the
potential for a secondary band of heavier rainfall slightly farther
north in the area, there will be a risk for additional impacts on
area rivers this evening into Saturday. Basins of greatest concern
will be the Iowa and Cedar River basins, which already have multiple
sites approaching minor flood stage. Additional heavy rainfall of 1
to 3 inches within these basins could compound with the already
elevated river levels and exacerbate flood concerns. Similarly, the
Des Moines River basin is running at elevated levels, although no
sites are currently expected to approach flood. This could change if
the heavier band occurs. The Cedar River basin is at a lower risk of
being directly impacted by this band, but is only slightly displaced
from the expected area. The Iowa River basin and Des Moines River
basins being farther south will be at a greater risk for being
impacted by this band, which could push sites into flood stage that
weren`t previously expected, especially those between the Highway 30
and Interstate 80 corridors. Urban areas will also be at risk for
flash flooding, especially as runoff routes into already elevated
streams. &&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Saturday morning for IAZ059>062-071>075-
081>086-092>097.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Watch from Sunday afternoon through Sunday
evening for IAZ004>007-015>017-023>026-033>037-044>049-057>062-
070>075-081>086-092>097.
Flood Watch until noon CDT today for IAZ059>062-071>075-
081>086-092>097.

&&

$$

UPDATE...Hagenhoff
DISCUSSION...Dodson
AVIATION...Hagenhoff
HYDROLOGY...Dodson