Johnston, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

857
FXUS63 KDMX 132043
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
243 PM CST Tue Jan 13 2026

.KEY MESSAGES...

- Becoming windy tonight and may approach Wind Advisory Criteria
  in a few areas late this evening and overnight.

- Colder Wednesday followed by light snow chances Thursday.

- Monitoring snow squall potential late Thursday night and
  Friday as a strong cold front arrives.

&&

.DISCUSSION...
Issued at 240 PM CST Tue Jan 13 2026

Hopefully everyone had an opportunity to enjoy the warm weather
today since we may not see these temperatures again in central Iowa
for awhile with a pattern change coming. Currently, there is a
ribbon of precipitation extending from southeast Nebraska to
southwest South Dakota along a thermal gradient aloft and fueled
further by a weak short wave passing over the gradient. This forcing
does extend into southwest Iowa but the airmass below the high cloud
bases (AOA 10 kft) remains quite dry therefore, not expecting much
more than sprinkles.

A strong area of low pressure is moving into southeast Quebec today
with mostly warm downslope flow from the west/west northwest in
the southwest quad of the system, including Iowa. The primary
cold front associated with the system is just now crossing the
International border into North Dakota and Minnesota with
temperatures in the single digits and teens along with dew point
values near to below zero. That airmass will be driven
southward and reach Iowa late tonight and into Wednesday, albeit
in a modified form as the airmass warms some with the lack of
snow cover across the state and into parts of Minnesota. The
pressure gradient across Iowa will increase ahead of the surface
boundary and mixing will increase due to differential cold
advection between the surface and the earlier arrival aloft.
Numerous deterministic models` soundings have mixed layer winds
at 40+ kts and upon initial review, would suggest the potential
for advisory criteria winds (sustained 30 mph/1 hr or gust to 45
mph). The modification of the airmass as it moves towards Iowa
will minimize the strength of the cold and thus the mixing
efficiency of these peak mixed layer winds to the surface. Since
it appears to be a marginal headline case and the uncertainty
of mixing efficiency and the lack of any headline criteria
observations upstream, will hold off on a Wind Advisory for now
and we will continue to monitor into this evening.

High pressure will drop into Iowa during the day on Wednesday and
should help scour the stratus out of the area, though some mid to
high level clouds may remain. The high pressure ridge will pass
across the state Wednesday night from northwest to southeast with
theta-e advection aloft commencing overnight that will lead to
increasing clouds and surface return flow beginning after midnight
over the west. Sounding profiles maintain some steeper lapse rates
just above the surface that will limit some of the potential
decoupling within the boundary layer. This all should prevent
temperatures from bottoming out and temperatures likely will become
steady or rising across the west late. After a brief passing of some
thermal ridging early on Thursday, another strong short wave will
descend south towards Iowa. This should lead to an area of light
snow developing over parts of central and eastern Iowa with some
accumulations possible.

Another strong surge of more Arctic type air arrives late Thursday
night into Friday morning. The NAM/GFS deterministic soundings are
showing a deep saturated layer with steep lapse rates that run from
the surface to near 700 mb, which runs through the dendritic growth
zone. Both models are also showing surface based instability up to
100 J/kg as strong frontogenetical forcing moves across the state.
This all points to the potential for impactful snow squalls
including strong and gusty winds. This is by far the deepest
saturation and instability potential that has shown up over Iowa
this winter season. We will continue to monitor this situation and
will also continue to allude to winter impacts with our message for
this time period. Wind headlines are possible should the winter
impacts not materialize on Friday.

The cold air will continue to settle south into Iowa through
Saturday with the chance for some warm advection on Sunday. The NBM
temperatures for Saturday and Saturday night continue to remain much
too warm as it tries to apply recent warm biases while trying to
play catchup to this cooling trend. Raw model guidance blends are 6 -
 8 degrees cooler and prefer those temperatures. Saturday will
remain blustery with gusty northwest winds persisting. Light snow
may be possible again on Sunday as the weak warm advection arrives
and the next short wave.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1139 AM CST Tue Jan 13 2026

A broad area of stratus over Minnesota will descend southeast
into parts of Iowa late this afternoon and overnight. At this
time, expecting mainly MVFR stratus at KMCW/KALO but there may
be more brief impacts at the other sites as well. The stratus
should begin to scatter Wednesday morning. Breezy west to
southwest wind this afternoon becoming gusty northwest mid to
late this evening with the arrival of a cold front. Gusts over
35 kts may occur. The wind will remain gusty into Wednesday
morning.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon