Johnston, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

506
FXUS63 KDMX 051116
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
616 AM CDT Sun Apr 5 2026

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

.KEY MESSAGES...

- Milder today and less windy. Spotty rain shower chances
  northeastern Iowa late this afternoon into mid-evening.

- Cool Monday and Tuesday with increasing precipitation chances,
  especially late Monday night through Tuesday night.

- Breezy Wednesday with showers, a few storms along a cold front.

- Signal remains for a wet pattern and threat of heavy rainfall late
  this week into next weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 250 AM CDT Sun Apr 5 2026

The trough responsible for our active weather Friday and
Saturday is moving over Lake Superior early this morning. As it
has been departing, the stratus clouds associated with it having
been pulling away leaving a clear sky over central Iowa.
Surface high pressure will slip onto the central Plains and keep
a moderate pressure gradient between it and the departing
trough. This will keep breezy winds from the northwest over the
state, though not to the strength of Saturday`s wind speeds.
While the Lake Superior trough departs, northwesterly flow will
usher in a shortwave trough in its wake that will brush
northeastern Iowa and our northeastern service area with light
rain shower chances late this afternoon into mid-evening.
Forecast soundings show steep low level lapse rates fostering
some weak instability that will aid in the showery activity.
Also, won`t rule out a rumble of thunder.

As the work week begins, weak low level theta-e advection with some
contribution from a right entrance region of a passing jet to
our northeast will keep low, mainly rain chances over
southwestern Iowa. Forecast soundings show initially dry air in
the low levels, but point to saturation sufficient from west
central and southwest Iowa into some portion of south central
Iowa. The precipitation chances will spread gradually northward
Monday night through Tuesday night as the low level theta-e
advection strengthens. Temperatures in the column will be cold
enough per forecast soundings to support snow to start, though
the profile will be warming allowing for a rain snow mix and
then a change to rain Tuesday into Tuesday night. Before the
changeover, a light accumulation of snow may occur.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Issued at 250 AM CDT Sun Apr 5 2026

There will be a break in the precipitation at any given location in
Iowa later Tuesday into Wednesday as attention shifts to a shortwave
trough and associated surface low moving near the US/Canadian border
on Wednesday into Thursday. A cold front associated with this low
will slowly move into the state late Wednesday into Thursday
and be a focus for showers and storms. While kinematics and deep
layer shear are present, instability looks quite meager given
dewpoints in the 40s. Therefore, any widespread severe weather
looks unlikely. Much of Wednesday will also have breezy winds
ahead of this front.

An active and wet pattern still looks to set up late this week
into this weekend. Examination of ensemble trends show that the
heavy rainfall threat may now be slower to materialize. This is
due to the downstream ridge building back/trending westward,
which keeps a trough that yesterday would be over southern
California late this week now off the California coast and
limits the shortwave energy ejecting ahead of it into our
region. This wet pattern still looks to occur, just later now.
With the surface front settling over far southern Iowa if not
northern Missouri, still expect surges of theta-e advection and
shortwave pulses interacting with this boundary to aid in
several rounds of showers and storms as early as Thursday night
or Friday. Now, there will be intervals of dry conditions as
this pattern persists into next weekend. The multiple chances
for rainfall should result in at least renewed rises on some
area waterways per the National Water Model high magnitude flow
annual exceedance probabilities forced by the NBM and GFS. There
may also be a window for a chance of severe weather in this
period, but the more concerning signal remains the heavy
rainfall threat.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 615 AM CDT Sun Apr 5 2026

With the departing stratus, VFR conditions will prevail through the
TAF period. Showers in northern Iowa Sunday evening could bring MVFR
cigs, with confidence highest at KMCW. Winds will be gusty at points
during the day/evening depending on location, generally shifting
from NW to W around 23z and back to NW by 6z. Confidence and impacts
of showers at northern TAF sites will be monitored.

&&

.HYDROLOGY...
Issued at 250 AM CDT Sun Apr 5 2026

Widespread rainfall over the last couple of days has resulted in
responses across multiple area rivers. Most of these rivers are
forecast to reach and crest within action stage or below.
However, a few rivers farther north and east in the area are
seeing forecasts to near or just above minor flood stage within
the next couple of days. These include sites along the Cedar
and Iowa Rivers. The site of most immediate concern is the Cedar
River near Cedar Falls, where minor flood stage is forecast to
be reached late this morning or afternoon and a flood warning is
now in effect. The Iowa River near Tama is expected to near,
but stay just below minor flood stage early next week. Dry
conditions over the next few days should give rivers some time
to route water through the system and build some degree of
capacity in the soils, but likely won`t fully recover to
previous levels prior to additional rainfall later this week.
Therefore, rainfall amounts and placement will be important to
watch as we head into the second half of this week and more so
next weekend.

&&

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

&&

$$

SHORT TERM...Ansorge
LONG TERM...Ansorge
AVIATION...Ansorge/De Bruin
HYDROLOGY...Dodson