983
FXUS63 KDMX 170440
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1040 PM CST Thu Jan 16 2025

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

.KEY MESSAGES...

- Continued warm into Friday, but turning windy and colder
  Friday night

- Most significant Arctic air of the season coming with
  prolonged bitter cold this weekend through Tuesday

- <=30% chance of measurable light rain or light snow Friday
  afternoon and evening, otherwise mainly dry through the period
  (Thu 23rd).

&&

.DISCUSSION...
Issued at 342 PM CST Thu Jan 16 2025

Mild, zonal flow was in place across the Midwest but that will
turn to a cold, expansive central CONUS mean trough with H5
heights down to 516 dam or less by late the weekend. The
introductory mechanism will be an elongated PV anomaly across
the southwestern Canadian provinces this afternoon with an
associated surface low just ahead. By midday tomorrow the
surface low should be over southern Ontario with its attendant
surface trough and wind shift passing through Iowa. Temps today
were toward the extreme high end of the guidance envelop and
expect similar conditions Friday with highs well into the 40s.
The true cold front will arrive across northern Iowa by sunset
however ushering in much colder temperatures and gusty northwest
winds. The cold advection and steep low level lapse rates may
trigger some weak convection with either light snow or rain
showers depending on temps, which may linger into the evening
south in the form of flurries or light snow showers. Winds may
gust to 35 mph or more north Friday night.

The main weather story of the period, a prolonged period of
Arctic air, will becoming entrenched across Iowa and the Midwest
this weekend through Tuesday, driven by anomalously high
northern Rockies/Canadian surface high pressure and an extended
period of reinforcing northwest flow at low levels. Widespread
below zero lows are expected for three nights (Sat night-Mon
night) with highs no better than the single digits above zero
Sun and Mon. Cold Weather Advisories (replacement of Wind Chill
Advisories) will likely be needed at least off and on through
this period.

The pattern should begin to modify heading into Tuesday when the
last short wave enters the base of the long wave trough followed
by rising heights into midweek. Confidence in how this evolves
is not great with cluster analysis showing a fairly even
distribution among members, however most solutions suggest a
milder trend back toward normal temps. With no great feel on
short wave track or strength, the forecast remains dry for the
moment. However one window to watch is Wed night into Thu. 12Z
EPS and GEFS probabilities for measurable precipitation are
around 40% north, so this would be a window to monitor if those
trends persist through future model cycles.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1040 PM CST Thu Jan 16 2025

Pressure gradient increases overnight with strengthening surface
winds from the south. Non-convective low level wind shear is
expected overnight into Friday morning as the low level jet
intensifies ahead of an approaching cold front. VFR conditions
are forecast for the overnight as well into midday Friday. The
front passes through the state through the day with winds
veering gradually through the day from south to northwest as the
boundary slides across Iowa. VFR conditions persist for much of
the day as well with MVFR ceilings becoming more likely across
northern Iowa by the end of the period. Winds from the northwest
are also likely to become quite strong by the end of the period
as cold advection intensifies.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Cogil