397
FXUS63 KDMX 050904
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
304 AM CST Wed Feb 5 2025

.KEY MESSAGES...

- Advisory for Freezing Drizzle/Slick Travel
- Quick Break & Windy Thursday with Saturday Mix System
- Return to seasonal winter temps Sunday into Tuesday with
  additional systems nearing Iowa Tuesday

&&

.DISCUSSION...
Issued at 304 AM CST Wed Feb 5 2025

Confidence: Medium to High

Surface high pressure continues over northern MN early this morning
and will gradually shift east. Strong low pressure in the Pacific
Northwest continues to shed a piece of energy toward the Central
Plains with a significant frontal boundary forming from the PAC NW
east across the Rockies, High Plains and then across Kansas to Iowa
at H850. Moisture has been gradually building north overnight ahead
of the trough, from the surface up through H850 with dewpoints in
the mid 20s to 30 over KS and MO. We remain quite dry at 0730z with
dewpoints near 0 in the north to the lower to mid teens in the far
south. As has been forecast with this event, the main moisture
channel will build into the Mid Mississippi River Valley and then be
forced east as the H850 trough swings east this afternoon. Although
we will be missing out on the deepest moisture, the first couple km
will become saturated with time as weaker surface flow pulls the
lower level moisture from KS and MO back into Iowa today into early
this evening. That sets the stage for saturation with freezing
drizzle becoming more widespread as we move into the mid to late
morning and afternoon hours. With the peak of the forcing and
warm air advection occurring this afternoon and early evening
over the south, the freezing drizzle will peak then and slowly
diminish into the evening hours. Forecast precip amounts have
been lowered by a couple hundredths over the area, but with a
slightly more efficient accretion rate due to the lighter winds
and drizzle vs freezing rain, we may still see amounts of 0.05
or higher in the southeast with lesser amounts elsewhere. As has
been alluded to in previous discussions, road treatments and
any road surface warming due to diurnal trends may help offset
impacts for some, but untreated and elevated surfaces will still
see some ice accretion leading to slick conditions whether on
roads or sidewalks. Highs today will creep back to the upper
20s to lower 30s with lows tonight falling to the upper teens
north to the upper 20s in the southeast. Tonight fog is expected
to form in the wake of the low. With temperatures below
freezing, some frost may form on any earlier untreated roads. As
the trough to our west tracks into the region tonight and
passes east of the area by early tomorrow, stronger H850 winds
of 40 to 50kts will begin to mix out as 4 to 5 mubar/s
subsidence works through the area. Though the cross gradient
flow is not perfect, soundings suggest that wind gusts may peak
out at 35 to maybe 45 mph over the north during the late morning
and afternoon hours tomorrow. Highs tomorrow top out in the
lower 30s north to the lower 40s south.

.Long Term /Thursday Night through Tuesday/...

Confidence: Medium

By late afternoon and early evening, winds will decouple with winds
dropping off overnight with lows in the teens north to the lower 20s
south by Friday morning. High pressure will continue on Friday with
the main storm over the Pacific Northwest now pulling east into the
Rockies. Trends remain consistent with previous packages and model
runs. The initially elongated low aloft at H850 will deepen as it
tracks east toward Iowa. Deterministic models are in good agreement
as well as the ensemble suite. There remain two distinct areas of
lift and likely precipitation; with the first area in the zone of
warm air advection along the warm front ahead of the southern stream
weak surface low in MO and another area over MN and far northern
Iowa where additional warm air advection is taking place in a weak
trowal/deformation axis backing into MN by midday Saturday. The
overall track and consolidation of the H850 low as it has nearly
exited Iowa will result in lesser precipitation over our area and
mostly in the far south/east and far north. Once again we will see
enough warming aloft to bring a mix to the south early Saturday with
areas north of US30 mostly light snow. Ensemble runs and various
deterministic output suggest about 0.20 of qpf over the north for
the weekend event with less than one tenth elsewhere. Snowfall
amounts will likely be limited to a lighter range of about 1 to 3
inches over the north third with most of this occurring in the
morning to late afternoon. With winds increasing behind the slightly
deepening system and a new cover of snow, some variety of headlines
may be needed for portions of the north. There is plenty of time to
work out the details in the next two days. Friday will remain just
above normal with highs in the upper 20s north to the upper 30s
south. Saturday will cool down as the low tracks over the region and
colder H850 temps filter into the area. Another weak area of high
pressure will build across the area Sunday. Monday into Tuesday
energy from a couple of systems nearing Iowa brings a chance of some
precipitation. With the current split flow continuing there is
sufficient uncertainty as to the extent and timing of any precipitation
those two days. With much colder air at H850 across the area, light
snow should be the predominant precipitation type.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1147 PM CST Tue Feb 4 2025

Overcast VFR conditions in mid and high level cloudiness
covered much of central IA at 06z, however MVFR stratus was just
beginning to enter far southern sections. This south to north
trend of lowering ceilings should continue into the morning with
IFR to MVFR ceilings central and south by 14z. Widespread
development of IFR to MVFR conditions south to north are
anticipated by afternoon with areas of -FZDZ and possibly some
-SN far north. Precipitation may end at western sites
 (KFOD/KDSM) toward the end of the period but IFR/LIFR stratus
 should persist through the end of the period (06z) area wide.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon today to 9 PM CST this
evening for IAZ034>039-044>050-057>062.
Winter Weather Advisory from 9 AM this morning to 9 PM CST
this evening for IAZ070>075-081>086-092>097.

&&

$$

DISCUSSION...REV
AVIATION...Small