Nov 28-30th Post Turkey Day Winter Storm

[frostfern]

3 hours ago, A-L-E-K said:

Radar looks good, early weenie waa will make or break

Long duration WAA can’t fail too bad.  It’s not one of those quick hitting systems that depend entirely on heavy rates.

[jlauderdal]

Has anyone seen any flakes flying from this system yet?

[Baum]

2 minutes ago, jlauderdal said:

Has anyone seen any flakes flying from this system yet?

Nebraska vs Iowa game.

[wegoweather]

 

[Chinook]

This one is going to come close to giving me rain, but the models say it will be snow at just over 32 degrees

[Chicago Storm]

5 minutes ago, wegoweather said:

 

bah, let them play.

snow football is the best football, and it definitely was as a kid.

[ChiTownSnow]

What are your thoughts on this @Chicago Storm low or high end? 

[Jebman]

This out of Des Moines AFD

393
FXUS63 KDMX 282347
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
547 PM CST Fri Nov 28 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Prolonged snowfall through Saturday has begun in the west
  early this afternoon. Significant snowfall amounts of 8 to 12"
  are expected through Saturday evening, with some locally
  higher amounts possible.

- Gusty winds behind the snowfall may lead to blowing and
  drifting of fresh snowpack on Saturday night.

- Much colder temperatures move in on Sunday, with wind chills
  in the single digits above and below zero.

&&

.DISCUSSION...
Issued at 250 PM CST Fri Nov 28 2025

The well-advertised winter storm for this weekend is now knocking on
our doorstep early this afternoon. The responsible wave is now
making it`s way over the Rockies, with surface low pressure building
over the plains. Pressure gradients are tightening in response to
this, increasing southerly flow and beginning to stream gulf
moisture northward. Weak frontogenesis on the periphery of the
building low pressure is currently producing radar returns
(snow) over eastern Nebraska, western Iowa and up into the
Dakotas where a lobe of better upper level moisture is also
present. This precipitation is combating some drier air below
and struggling to reach the ground, although surface
observations and MPING reports are already beginning to report
snow over the western portions of Iowa.

As we progress through this afternoon, this precipitation aloft will
slowly drift east and continue to saturate down through the dry
layer beneath. At the same time, increasing low level moisture
transport and theta-e advection will begin to lift northward ahead
of the building surface low, giving this area of precipitation the
extra push it needs to reach the surface. This will mark the
beginning of our prolonged period of snowfall over the state.
Precipitation coverage will initially be focused under this
initial lobe of weak frontogenesis and theta-e advection.
However, as the 500 mb wave continues toward the central CONUS,
and deepens into a pronounced trough, the building surface low
pressure will close off and lift toward the state. This will
bring strong isentropic lift up into Iowa, causing the
precipitation to expand over the entirety of the state
throughout the day Saturday.

Snowfall amounts have continued the upward trend this shift, now
increasing southward and slightly eastward. The expectation is still
that most of the area will see amounts in the 8 to 12" range, with a
band of higher amounts up to 15". This heavier band likely won`t be
widespread, but instead in the "Venn diagram" where the heavier
snow from the theta-e wing tonight meets with the heaviest
rates from the actual low pressure passage tomorrow. This area
of higher (13"+) amounts varies somewhat from run-to-run and
model-to-model, causing NBM to produce a fairly large area of
13"+ values in the forecast. Generally, the expectation is still
for these higher amounts to be along interstate 80 and north,
favoring the eastern portions of the forecast area. Of course,
once you reach a certain point with snow amounts, it becomes
more nitpicky than impact-driven. This prolonged snowfall is
going to create travel impacts for most of the area on Saturday,
whether your location ends up on the higher or lower end of
that spread. Likewise, areas that only briefly cross through the
heavier bands will still see periods of 1"/hr rates or higher,
which will lead to visibility reductions.

Farther south in the state, there is still some question on snowfall
amounts as warmer surface temperatures attempt mix rain with the
snow. However, with the slight southwestward trend in higher
amounts, have seen an increase in forecasted snow totals over
southwestern Iowa. For this reason, have upgraded a few counties in
southwestern Iowa from the advisory to a winter storm warning. It`s
still possible the warm air wins out in these areas, but model
soundings indicate the surface warm layer will be extremely shallow
and wetbulb temperatures only around 33 to 34 F at their warmest. It
stands to reason that heavier rates will be able to overcome this
shallow warm layer, and snow through it. Dynamic cooling of the
layer may occur as well, as snow falls an melts (removing heat from
the air) but southerly flow/warm air advection will work to negate
this cooling. Given this delicate balance, this area definitely has
the most uncertainty in snow amounts. In addition to this rain/snow
mix, there may also be a brief period early Saturday morning where
ice introduction is lost and freezing rain/drizzle develops. This
seems to be a fleeting threat and significant accumulations aren`t
expected. However, be on the lookout for isolated patches of ice in
southwestern Iowa.

The heaviest snowfall rates should be wrapping up around the early
evening in our forecast area with lingering light snow lasting till
about 10 pm to midnight. While the falling snow should be improving
through this timeframe, there is a growing signal for wind gusts
increasing to around 25 to 35 mph behind the cold front late
Saturday afternoon and evening. These winds should primarily be
displaced from the heavier snowfall rate that are associated with
the warmer portion of the system, but a brief phasing of falling
snow and increasing winds could lead to reduced visibilities into
Saturday evening. Likewise, fresh snowpack/loose snow on the ground
will be susceptible to blowing/drifting around. This blowing snow,
in conjunction with snow still on the ground, will prolong travel
impacts into Saturday night and early Sunday morning. Winds/gusts
will then diminish through Sunday morning.

High pressure and colder air fills in behind the system on Sunday,
dropping temperatures over the area. Wind chills on Sunday morning
will be near and below zero, making for quite chilly conditions for
anyone getting up to move snow on Sunday morning. These cold
temperatures and wind chills continue through the first part of the
week, with highs on Sunday and Monday only reaching the upper teens
to low 20s and overnight lows falling into the single digits Monday
and Tuesday mornings. Wind chills through this same time will be
quite cool in the single digits above and below zero. Of note,
another system looks to clip the state on Monday into Tuesday,
bringing additional snow chances to the area. Fortunately, amounts
look marginal compared to this weekend`s system, with ensemble
probabilities showing a roughly 50 to 60% chance for an inch or
more of snow in southern Iowa and only a 30 to 40% chance for
two inches or more. Additional details on the early week system
will be provided in the coming days.

[Weather Mike]

11 minutes ago, ChiTownSnow said:

What are your thoughts on this @Chicago Storm low or high end? 

Agree what do you think. LOT has reduced downtown Chicago amounts despite some recent model runs showing a good >9 inch dump. It’s like they are assuming the worst is going to happen so don’t get too excited in the city. 

[Harry Perry]

0z NAM is doing NAM things… drying out quite a bit in some of the expected higher-end areas in eastern Iowa/western Illinois. DVN goes from over a foot down to 9” this run. 

[Chicago Storm]

13 minutes ago, ChiTownSnow said:

What are your thoughts on this @Chicago Storm low or high end? 

I don't think it will be high end around our area (probably no widespread 12"+ totals that is, unless ratios surprise, which seems doubtful at this time). The metro region as a whole will likely see a general 6-10" overall (locally higher), though. Highest totals will likely be western areas, with the overall setup peaking west and slowly dampening out as it heads east.

[Radtechwxman]

6 minutes ago, Harry Perry said:

0z NAM is doing NAM things… drying out quite a bit in some of the expected higher-end areas in eastern Iowa/western Illinois. DVN goes from over a foot down to 9” this run. 

Watch it be right. Lol. I hope this precip shield fills in south like hrrr shows later. Right now main waa band setting up pretty north in Iowa. Always nail biting watching these evolve. 

[Chicago Storm]

5 minutes ago, Harry Perry said:

0z NAM is doing NAM things… drying out quite a bit in some of the expected higher-end areas in eastern Iowa/western Illinois. DVN goes from over a foot down to 9” this run. 

Has to do with placement/handling of heavier and more convective precip, not actual drying per-se.

[cyclone77]

10 minutes ago, Harry Perry said:

0z NAM is doing NAM things… drying out quite a bit in some of the expected higher-end areas in eastern Iowa/western Illinois. DVN goes from over a foot down to 9” this run. 

Probably backing down more towards reality.  Still high-end event nonetheless.

[TheNiño]

What are the thoughts on lake enhancement? MKE is mentioning it will increase totals but LOT seems to disagree.

[homedis]

What are the thoughts on lake enhancement? MKE is mentioning it will increase totals but LOT seems to disagree.

From what I see on most guidance, it’ll increase QPF but will also reduce the ratios due to the warmer lake waters, so it’s almost a net zero. Not sure what will actually happen

[ChiTownSnow]

5 minutes ago, TheNiño said:

What are the thoughts on lake enhancement? MKE is mentioning it will increase totals but LOT seems to disagree.

IMO the low placement favors Wisconsin shore more than Illinois.  Between mke and Sheboygan in WI look money with those SE winds

[Harry Perry]

9 hours ago, WxMatt21 said:

Yeah, I noticed IWX has been pretty hesitant to use their NDFD output until recently! 

And wouldn't you know it, 12 ECMWF came in wetter/snowier, and in better alignment with the rest. Right now, I'm going to wait for the 18z NAM/HRRR to come in before making drastic changes, but my team is struggling with whether we want to keep things the same or up the totals since the consensus has been overwhelmingly snowy for most. My argument against is compaction, which could give off the impression we were dead wrong lol! 

Also, I'll be curious to know how well the NBM does when all is said and done. It has hardly budged over the past 48 hours

 

 

[Jackstraw]

55 minutes ago, Jebman said:

..."It`s still possible the warm air wins out in these areas, but model soundings indicate the surface warm layer will be extremely shallow and wetbulb temperatures only around 33 to 34 F at their warmest. It stands to reason that heavier rates will be able to overcome this shallow warm layer, and snow through it. Dynamic cooling of the layer may occur as well, as snow falls an melts (removing heat from the air) but southerly flow/warm air advection will work to negate this cooling. Given this delicate balance, this area definitely has the most uncertainty in snow amounts."

Best disco for those of us on the southern edge. Shallow warm layers in these setups tend to produce little liquid. Takes a little more umph/depth in temp rise right along the transition to produce more robust liquid, especially with a fresh snow pack preceding. I've rarely seen more than light drizzle in setups like these, better chances of a full light or heavier rain switch with temps above 34 and at least a +freezing 850 nose to help. Not saying it cant but this setup is half my winters lately. Now where and how long does it last?

Starting to call my area Kitchen Sink Canyon lol

[Baum]

Looks like it could happen based on radar

[cyclone77]

Top down saturation almost complete.  Should be seeing the first flakes before long.

[Radtechwxman]

I hope the radar really blossoms and fills in like models are suggesting. Trough seems to be approaching western NE. Isentropric lift should start increasing next few hours.