Grimes, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

588
FXUS63 KDMX 232336
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
536 PM CST Tue Dec 23 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Patchy fog potential tonight, then more widespread again on
  Wednesday night into Thursday. Fog may be dense at times.

- Drizzle/light rain potential through mid-day Wednesday and
  again Thursday night into Friday. Some freezing drizzle may
  occur over snowpack on both days, generally in north central
  into northeastern Iowa.

- Mild, above normal temperatures continue through Saturday,
  followed by a cooldown Sunday into next week.

&&

.DISCUSSION...
Issued at 234 PM CST Tue Dec 23 2025

Light northerly flow, mild temperatures and mostly clear skies
characterize the conditions over Iowa today. Surface high pressure
has begun to fill in behind the cold front from earlier this
morning, and will dominate the pattern through the rest of today and
tonight. Tendrils of stratus clouds are beginning to reach southward
out of Minnesota and into far northern Iowa this afternoon, but have
been diminishing in coverage as they leak southward. Light winds and
partly cloudy skies tonight will bring potential for more efficient
radiational cooling and fog development into Wednesday morning,
especially near the snowpack in north central Iowa. Guidance is
fairly reserved with fog tonight, potentially due to infrequent
upper level cloud cover that will occasionally negate cooling.

As we get into Christmas Eve morning, we will start to see return
flow advect more low level moisture into the state on the backside
of the departing surface high. This moisture stream will first
arrive in southwestern Iowa tomorrow morning, before pivoting
northeastward through the state. Initially, this increasing low
level moisture will bring increasing fog potential and stratus
development over southwestern Iowa in the morning. However, as
deeper saturation is achieved, a transition to more of a light
rain/drizzle is looking increasingly likely. The lift is weak but
present in the saturated layer, as is some low level wind shear
which will produce more turbulence and help with droplet production
through collision coalescence. The extent of the drizzle through the
day Wednesday really depends on the model you look at. The colder,
more saturated NAM solution shows deep and persistent saturation
with drizzle occurring over much of southern, central and eastern
Iowa through the day tomorrow. Conversely, the more mixed and drier
GFS solution struggles to saturate down to the surface, keeping
conditions dry at the surface with stratus overhead. Expectation is
that the solution will fall somewhere between these two, likely
biased, outcomes. The highest likelihood for drizzle will be over
central into southeastern Iowa, with diminishing likelihood north
and west and farther from the main moisture stream. One important
consideration with the drizzle on Wednesday. Temperatures are
generally expected to warm above freezing as the moist air mass/
drizzle arrives. However, there may be a short period around late
morning to mid-day where drizzle is occurring and surface
temperatures are near to below freezing, resulting in a short period
of freezing drizzle. This is especially true in areas with remaining
snowpack along highway 20, as these areas won`t warm as easily. If
temperatures do warm slower than expected, ice accretion may occur
resulting in slippery travel conditions. Fortunately, temperatures
should continue to warm through the day.

The now increased low level moisture, light northerly winds and
clearing upper level clouds will then bring a more widespread
potential for fog overnight Christmas Eve into Christmas morning,
some of which may become dense. Pretty much any piece of guidance
you look at is keying on fog development throughout Iowa tomorrow
night into Christmas morning, and confidence for fog really doesn`t
get much better at this lead time. However, fog is fickle, so it`s
important to still acknowledge any failure modes. If there is
anything working against the fog tomorrow night, it would be the
potential for lingering stratus clouds that may inhibit radiational
cooling. But even then, with dewpoints in the mid 30s to low 40s,
temperatures really won`t need to cool much at all to reach
saturation. Therefore, if you have any travel plans or presents to
deliver Christmas Eve into Christmas Day, it will be important to
ensure your headlights and reindeer noses are working properly so
you can navigate safely to your destination(s).

The temperature forecast for Christmas Day has steadied itself over
the last 24 hours, as confidence increases in the cooler solution of
highs only reaching upper 30s north to low 50s south. The low levels
will remain saturated through much of Christmas morning with
overcast skies persisting all day, limiting insolation. Likewise,
southeast to easterly flow will limit warm air advection into the
region. Another weak wave looks to lift through the state later
Thursday night and into Friday, bringing more light rain/drizzle
chances to the eastern portions of the area overnight into Friday.
Again, will want to watch for near-freezing temperatures over the
snow pack in the event that some light freezing rain/drizzle
develops over northeastern Iowa. Will be watching this closely as we
get into the high resolution window.

Friday and Saturday look to warm a bit more as skies may finally
clear out and we get another shot of more southerly flow. However,
temperatures turn colder again as a stout cold front passes late
Saturday into Sunday. This frontal passage continues to look dry for
our area, but will likely be accompanied by breezy conditions as the
cold air advection barrels into the area. These colder temperatures
continue into Monday but may warm slightly again on Tuesday as 500
mb ridging builds to our west. There are some signs of another shot
of cold air as a system moves through around the New Year, but
reliability in forecasts beyond 7 days is quite low. Therefore, will
continue to monitor next weeks weather and message any potential
impacts as it draws nearer.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 527 PM CST Tue Dec 23 2025

In the immediate short term, monitoring the development of fog
in southern MN. It is advancing towards KMCW, which could mean
the terminal is affected for at least 2 hours. Fog will
eventually be shoved west as the winds become easterly,
affecting KFOD (less confidence further south). Southerly winds
pick up through the morning, bringing in drizzle and IFR cigs in
the process. Fog will then expand behind this initial cloud deck
late in the period, affecting especially the snow-packed sites
in the north.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Jimenez