509
FXUS63 KDMX 092104
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
304 PM CST Tue Dec 9 2025

.KEY MESSAGES...

- Strong, gusty winds developing tonight with wind gusts over
  50 to around 60 mph likely. High Wind Warning and Wind
  Advisory in effect.

- With reported snow pack character being generally wetter,
  blowing snow chances are lower, but not zero. Winter Weather
  Advisory covers blowing snow as well as the chance for narrow
  bands of snow, which are most likely over northern into
  eastern Iowa overnight.

- Active pattern continues through the rest of the week with
  additional snow chances and colder air returning.

&&

.DISCUSSION...
Issued at 304 PM CST Tue Dec 9 2025

While the forecast through the weekend remains active beneath
the northwesterly flow with plenty of shortwave energy, the next
18 hours or so will feature a plethora of sensible weather
conditions. The shortwave trough, or clipper, that will bring
these conditions is moving over North Dakota this afternoon
with a surface low pressure over eastern North Dakota. This has
led to strong low level warm air advection over our state,
which has lifted temperatures above freezing at all but our far
northeastern forecast area at this hour. This warming is
outpacing our forecast highs from yesterday afternoon and this
morning, which will be important to discuss later. Cross
sections show that the column is trying to saturate over
northern Iowa, and this is also apparent in the low dBZ radar
echoes there with no surface observed precipitation. There still
remains a low risk of freezing rain over far northern Iowa, but
temperatures will be warming into this evening so expect a
transition to rain. While road temperatures and surfaces are
below freezing, which may allow for a light glaze, again
temperatures should be rising above freezing mitigating
widespread impacts.

As the surface low moves to near the western shores of Lake
Michigan this evening, a cold front will plow through the state.
The low level cold air advection right behind this front along
with the stronger kinematics from the passing low will yield to
quickening winds this evening from northwest to southeast as
winds become from a northwesterly direction. Looking at a
variety of models, winds at 850mb do not look nearly as strong
as yesterday at this time so the ceiling of max winds is lower.
The 0z HREF 10m ensemble mean showed wind gusts of 50 to 55 mph
from roughly Highway 63 westward with the core of gusts of 55
to 60 mph west of Highway 71. A westward trend in the core of
the strongest winds did continue in the 12z HREF data. Further,
12z HREF showed a 12 hour probability of winds of 50 mph or
higher at 90 to 100% over almost our entire forecast area of
central Iowa with a probability of gusts of 58 mph or higher at
50% or higher north of roughly I-80 and generally along and
west of I-35. Given the location of the core of the strongest
winds and gusts, have issued a High Wind Warning for roughly the
same area with at least a few gusts over 60 mph expected. South
of the I-80 counties and near Highway 63 eastward, confidence
in wind gusts over 58 mph is lower, and have opted for a Wind
Advisory for those areas.

The concern yesterday and this morning on the forecast desk was to
what degree would these winds be able to unlock the snow pack
causing blowing snow and possible ground blizzard conditions.
As mentioned earlier, temperatures are higher than forecast and
with wet bulb temperatures above 32 degrees already from Algona
to Marshalltown and points southwest, this is changing the
character of the snow pack on the ground. With low level WAA
continuing into this evening, this should make it to maybe all
but the far north or northeast forecast area. So, how has the
snow pack changed? Yesterday, the snow was powdery at our
office, but at noon today, the 4" snow depth was overall wet
throughout and unlikely to blow. The Waterloo snow observer
stated the snow was sticker than yesterday. USGS field crews in
New Providence/Hardin County reported an 8" snow depth with a
`wet texture` and `firm when you step on it`. As they returned
to their office in Fort Dodge, the remarked that the fields are
a little barer and the snow has a `polished look to the top`.
At the USGS Fort Dodge field office, snow depth was 15" and a `lot
of it has melted and refroze on top...current conditions are
super wet feeling snow.` The emergency manager in Webster County
also stated that just below the wet layer it seemed `light and
fluffy`. In Crawford County, the emergency manager relayed from
their secondary roads that the snow is `wet and heavy due to
some melting` and thinks it will `crust over and not blow much`.
Now, farther north, the snow character seems a bit more
blowable. The Emmet County emergency manager report a 8" snow
depth with the snow character powdery. This is not surprising
given the warmer air is just starting to reach this area. Our
expectation is that with so many hours with temperatures and wet
bulbs above freezing, the depth of crust will largely keep the
snow pack locked in and/or too wet to be able to be lofted.
While some surface blowing or perhaps drifting snow is possible,
the chances are too low to raise a Blizzard Warning at this
time. There is a chance that a few areas may not have as deep
of a crust and may allow for the snow pack to be released. This
would most likely be in the deepest snow pack, which is roughly
along the Highway 20 corridor per NWS COOP observers and NOHRSC
snow analysis, or over far northern Iowa where the duration of
above freezing conditions will not be as long. This is roughly
the area highlighted by the Winter Weather Advisory. For the
Waterloo/Cedar Falls area, have grouped in wind advisory like
wording in collaboration with La Crosse and Quad Cities offices
to try to keep headlines simpler over that DMA.

The Winter Weather Advisory also covers the potential of
convectively driven snow showers. As the second push of cold air
advection arrives about 6 hours after the first - roughly after
midnight - along with a strong pressure rise couplet, low level
lapse rates will steepen. While models pushed the low level
instability and saturation into the dendritic growth zone (DGZ)
yesterday and last night, today`s data is less certain on how
widespread this potential will be. The NAM`s traditional snow
squall parameter is not pinging at all, which is in contrast to
yesterday, but does still shows potential in the 1km version.
The FV3 cores are more aggressive in the snow squall potential
farther south, but overall models point to northern into eastern
Iowa as the area if snow squalls are to occur.

As this clipper departs Wednesday, winds will diminish, but a stream
of energy in the northwesterly flow will reside over the area. Thus,
the next clipper will be approaching by the day Thursday with low
level thermodynamic forcing moving over the region. With the surface
low tracking over southwest Iowa, this will place Iowa on the cold
and snowier side of the clipper. Cross sections show moderate
lift up to and into the DGZ. This may bring a few inches of snow
to north central into eastern Iowa later Thursday into Thursday
night. Colder air will follow behind this clipper with yet
another clipper bringing accumulating snow into the state by
Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1148 AM CST Tue Dec 9 2025

VFR conditions are forecast to deteriorate later this afternoon
into this evening across the terminals. First, there is light
precipitation that may pass over northern Iowa with highest
chances at MCW, including a low chance of a short period of
freezing rain with temperatures rising causing a transition to
rain. At FOD and ALO, just light rain, if anything, is forecast.
As the precipitation slides out this evening, very strong and
gusty winds from the northwest will spread over the state along
with MVFR ceilings tonight. Wind gusts over 40 knots are likely
at all terminals and a few gusts to or a bit over 50 knots are
possible, especially over western and northern Iowa. Low level
wind shear may result and have left previous forecast LLWS;
however, the vector difference may not be great enough for true
LLWS and this may end up being more turbulence. With the strong
winds, visibility restrictions may occur if the snowpack on the
ground is able to be unlocked and blown and have this
advertised at MCW, FOD, and ALO to varying degrees. Narrow,
intense snow bands, or snow squalls, may develop after 6z until
around 12z, with this shown at PROB30 groups over northern
Iowa. Ceiling restrictions will persist through the end of the
period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 9 PM this evening to 9 AM CST Wednesday
for IAZ004>007-015>017-023>026-033>037-044>049-057>060.
Winter Weather Advisory from 9 PM this evening to 6 AM CST
Wednesday for IAZ004>007-015>017-023>028-034>039-048>050.
Wind Advisory from midnight tonight to 9 AM CST Wednesday for
IAZ061-062-070>075-081>086-092>097.

&&

$$

DISCUSSION...Ansorge
AVIATION...Ansorge