Norwalk, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

552
FXUS63 KDMX 180440
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1040 PM CST Fri Jan 17 2025

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Becoming windy with isolated snow showers possible north this
  evening

- Turning colder this weekend with bitter cold temps early next
  week. Cold Weather Advisory late Sat night though Sunday
  morning.

- More seasonal temps return Wed-Fri of next week

- Mainly dry this weekend and much of next week

&&

.DISCUSSION...
Issued at 324 PM CST Fri Jan 17 2025

Although isolated snow showers are possible north this evening,
the main weather story will most certainly been an extended
period of Arctic air and bitter cold temperatures from this
weekend through Tuesday. An elongated PV anomaly within the
maturing mean trough was noted from ID through the Dakotas into
MN this afternoon with the associated surface low over eastern
ON. The initial pressure trough/wind shift was through central
IA at 20z with gusty NW winds beginning to increase in its wake.
The airmass hasn`t changed much after its passage with
temperatures still quite mild for mid January, and even within
five degrees of records in a few spots. However the 6+ mb/3hr
isallobaric max was pushing through the Dakotas and MN helping
to increase winds upstream. The actual cold front was moving
through SD and MN ahead of this feature and its associated cold
advection and mixing, along with the isallobaric effects, will
create strong winds this evening with gusts 35-45 mph possible
as temperatures begin dropping.

Examination of forecast soundings show some interesting
features this evening as well. Although there is little
reflection in hi res model QPF or 1km reflectivity, the
soundings depict steep lapse rates to 750m with token SBCAPEs
and ceilings 2500-4000 ft. The top of this convection and cloud
layer are aligned with the dendritic growth zone (DGZ) with
super-saturation with respect to ice, so isolated weak
convective snow showers with stellar dendrite production are
possible later this evening as temp fall sufficiently. They
would be so shallow they would likely not show up on radar,
being below the 0.5 deg slice. The previous precip chances for
later this afternoon and shortly after sunset have been removed
from the forecast. Although there is a decent amount of
kinematic forcing and lift ahead of the aforementioned PV
anomaly, a noted dry layer around 1.5km should preclude anything
reaching the ground with ceilings still >=9K ft.

By the weekend and early next week a prolonged period of bitter
cold temperatures can be expected. With widespread lows below
zero Saturday through Monday nights. A sprawling long wave
trough will settle into the central CONUS with persistent
anomalously high surface pressure adjacent to the northern
Rockies whose associated northwest flow will continue to funnel
Arctic air into the region with reinforcing PV lobes cycling
through the trough and bringing an additional shots of Arctic
air late Saturday night and again late Monday. The coldest
night of the event appears to be late Monday night with lows in
the teens below zero north. 13Z NBM probabilities suggest temps
of -10F or less are likely/>60% across northern IA by 12z Tue.
Although the winds will not be too noteworthy later this
weekend, the combination of cold and wind will still be
sufficient to drop wind chills to advisory criteria (-20F
central & south, -25F north) at times during the late night and
morning hours Saturday night into Tuesday morning, especially
north. Have issued a Cold Weather Advisory for northern and much
of central IA 09-18z Sunday for starters, with additional
headlines possible into Monday and Tuesday mornings.

The long wave trough axis and surface ridge should both exit the
region by midday Tuesday with temperatures beginning to moderate
for the middle to latter portions of the next work week. Heights
will rise with a more tempered version of the mean trough still
in place across the Midwest. While the forecast is dry for the
time being, additional waves with preceding warm advection aloft
will continue to drop into the trough and may necessitate some
token precip chances once confidence in forcing and sufficient
moisture increases.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1040 PM CST Fri Jan 17 2025

A bit more pessimistic cig forecast this period as area of
shear driven snow showers/MVFR cigs advances south into the
area. Coverage of snow showers still not high enough to include
in terminals. Have prolonged the lower cigs until mid morning
(15-16z) with gradual improvement aft 16z. Low confidence
forecast, but with winds remaining strong, lower cigs more
probable. Winds remain strong from northwest with gusts 30 to
35kts through around 10z; then remaining 25 to 30 kts through
18z most locations. VFR conditions expected to return aft 18z.
/rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Cold Weather Advisory from 3 AM to noon CST Sunday for
IAZ004>007-015>017-023>028-033>039-044>050-057>062-070-071.

&&

$$

DISCUSSION...Small
AVIATION...REV