Marshalltown, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

995
FXUS63 KDMX 031159
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
559 AM CST Tue Dec 3 2024

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

.KEY MESSAGES...

- Strengthening and gusty winds from the northwest Wednesday
  through Wednesday night. Gusts approaching at least 45 mph
  over northern Iowa, with higher gusts possible.

- Some flurries/sprinkles may be possible Wednesday, but no
  widespread precipitation chances through the end of the week.

- Slight warm up today into Wednesday but breezy to windy
  conditions will not make it feel like much of a warm up.

- Very cold Thursday morning with feel-like temperatures near to
  below zero, but cold snap Thursday will be short-lived as
  temperatures moderate into the weekend.

&&

.DISCUSSION...
Issued at 359 AM CST Tue Dec 3 2024

The light snow of this time last night has been replaced by colder
temperatures as a high pressure crosses through the region today
before drifting off to the southeast U.S. tonight. Clear skies have
combined with the fresh snow and light winds to send temperatures
falling rapidly in some locations to the single digits while
lingering stratus in other areas has kept temperatures a tad warmer,
though in the teens. After the cold start, slightly warmer
temperatures are on tap today as mid-level flow out of the west
brings warm air advection into the area through the day. The thermal
ridge doesn`t arrive until tonight, however, so lows tonight will be
the larger benefactor with lows in the 20s, but high temperatures
today do look to reach into the 30s for all but the northeast who
don`t quite make it out of the upper 20s. The caveat is it may not
feel like a warmer day as winds increase into this afternoon
becoming breezy with gusts of 20-25 mph, a few gusts may reach
towards 30 mph in the north to northwest. If this isn`t enough wind
for you, just wait, there will be more on Wednesday!

Wednesday`s weather will feature a double cold front, the first
which moves through overnight into Wednesday morning shifting our
winds to be back out of the northwest and starting the process of
increasing our sustained winds and gusts. The strongest winds/gusts
will come a bit later in the day with the main front and stronger
cold air advection which is trending a bit faster than this time
yesterday. Temperatures will fall through the afternoon hours north
to south behind the passage of the surface front but the faster
progression means northern Iowa won`t have much of a chance to warm
up before temperatures start falling. Have backed off high
temperatures as a result with highs in the 30s to low 40s, but in
the grand scheme of things it won`t ever feel like a warm up anyway
with the windy conditions. As noted in the last several discussions,
a lot of boxes are being checked for very windy conditions to occur
from the cold air advection, strong subsidence, an increasing
pressure gradient, and steepening lapse rates as well. As a starting
point, have raised winds to the values seen in soundings at the
bottom of the mixed layer, but will likely still need to raise winds
more in the next few shifts as we are primed to reach gusts that
will be higher than those at the bottom of the mixed layer. Forecast
soundings are in fairly good agreement with 35 to 45 mph winds
at the bottom of the mixed layer, the strongest gusts in
portions of northern to northeastern Iowa. But, at the top of
the mixed layer winds max out closer to 45-55 mph+, so it is
certainly plausible to get some stronger gusts at times than the
35-45 mph currently advertised. Either way, a wind headline is
looking likely for Wednesday given the strong winds/gusts, which
will also last well into the night before decreasing into
Thursday morning.

With the steepening lapse rates, will also need to watch moisture
closely with a bit more moisture in soundings in this forecast
package, though admittedly for a very short window as the main front
moves through north to south. If everything comes together, could
see a quick burst of snow (flurries) or rain (sprinkles) depending
on how everything lines up. Models are starting to catch on to this
possibility with the north to northeast the most likely to see a
quick burst of precipitation at this point, though confidence in
location and time is low given the very small window of everything
lining up that would lead to such occurrence. Have at least started
with sprinkle or flurry mentions but will need to watch these
precipitation trends closely Wednesday.

Thursday will be much colder again with highs only in the teens to
20s behind this strong cold front, but the more notable weather may
be the morning lows in the single digits to low teens, but will feel
like zero in the south to 15+ below zero (-15 or colder) in the
north.

This second cold snap will be shorter lived as temperatures climb
again Friday into the weekend with a dry forecast prevailing through
at least the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 542 AM CST Tue Dec 3 2024

VFR stratus continues to linger early this morning impacting
portions of central Iowa and some TAF sites. Timing of its
dissipation is challenging given clearing on the backside
towards western Iowa, but additional cloud cover moving in from
the north. Overall trends suggest gradual improvements/clearing
over the next several hours with just high cirrus lingering
after about midday. KMCW may be the exception holding on to the
cloud cover longest. Winds out of the southwest will increase
into this afternoon with gusts near to exceeding 20 knots,
especially towards northern sites KMCW/KALO/KFOD. These winds
will decrease for a short time tonight before winds start to
increase again into Wednesday, becoming quite strong which will
be addressed in future issuances. Some LLWS remains possible in
the interim between gusts decreasing tonight and increasing
again Wednesday morning, but confidence remains too low to
include mentions at this time.


&&

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

&&

$$

DISCUSSION...KCM
AVIATION...KCM