FV-Mike

Excited for N IL first bigger storm of the year. Neb and S IA looks golden. Interesting note from LOT on ratios in this morning afd

Forecast soundings indicate a bit better spatiotemporal overlap of
the deeper ascent within the DGZ on Monday afternoon/evening than
previous iterations. The result was a jump in Cobb ratio output
towards 13-15:1. At the same time, though, thermal profiles will
still be rather warm, with a deep saturated layer hugging -1 to -8
C which tends to support a larger degree of riming which would cut
down on ratios. Did nudge our ratios up a smidge for Monday
afternoon/evening closer to 11-12:1

LOT's afternoon AFD starting to get me excited. Here is a little portion. 

The main message we`d like to convey is that while there is
uncertainty inherent to this particular forecast and generally all
winter system forecasts at this time range, confidence continues
to increase in a potential winter storm impacting the area. This
includes an increasing chance for a swath of several inches of
snow, with distinct potential for 6"+ of snow, and certainly not
out of the realm for well over 6" if ingredients come together to
support heavy mesoscale f-gen driven banding, considering that
well above normal moisture content (unseasonably high PWAT/mixing
ratios for a winter system). Snow forecast was leaned toward the
thus far quite consistent ECMWF suite and also accounted for a
large northward jump in the 12z GEFS mean and many of its members.

Regarding our snowfall forecast, we feel that the chance that our
entire CWA is missed by moderate to significant snowfall amounts
is decreasing. That said, there are multiple competing factors to
this forecast, with subtle changes of key players ultimately
modulating where the highest snowfall amounts occur in a north to
south range and peak snowfall amounts. Our current thinking
regarding the broader area in which narrower east to west banding
is liable to set up with several to 6+" of snow is fairly close in
line with WPC`s Day 4 Snow/Sleet outlook and placement of 30-50%
and 50-70% contours, which will help drive our snow forecast
message.

DMX thoughts on the bigger system.

Some light wintry precip may linger into Sunday, but then the atmosphere
quickly reloads as a lead shortwave ejects from the mean western
conus trough. There remains significant differences between the
latest deterministic Euro and GFS both in track and intensity.
GEFS mean leans more toward the more northerly and robust Euro.
PoPs were boosted above the NBM output for Sunday night into
Monday across southern into central Iowa to reflect increasing
confidence in another round of snow moving through. The
significant model spread hinders confidence in possible snowfall
amounts, but moderate to heavy snow is not out of the question.

Nice to see areas in the GL that have been missed in the range for this storm

Maybe a couple on inches for us N IL folks from Saturday through Sunday

Wasn't expecting much for the CHI area but LOT's update is saying its warmer than expected. 

Snow trends have changed slightly for this present system.
Observations and initial soundings show a warmer atmosphere than
originally indicated, and model soundings continue this trend. We
have bumped our surface temperatures upward somewhat to reflect
these slightly warmer conditions. With warmer temperatures in our
column and at the surface, the transition from rain to snow will
occur later, and confidence that some areas further southeast will
turn to snow at all is not high. With these changes, expected
snow accumulations are lower, and primarily limited to our
northwestern counties, with up to 1 to 1.5 inches the expected
amounts. Future messaging will reflect these changes, which will
also include the likelihood that impacts are minimal to the
commute for most of if not the entire area.

Pretty detailed thoughts from LOT for the long range. 

Looking beyond day 7, pattern across north America continues to
appear on very consistent run to run trends of ensemble forecasts
that it will become more favorable for more sizable precipitation
and snow producers. Driving force will be a spiking poleward
ridge in the vicinity of Alaska (negative East Pacific Oscillation
(-EPO)), downstream troughing onto the west coast (negative
Pacific North American pattern (-PNA)), and quite notably, a very
impressive signal for a deeply negative North Atlantic
Oscillation (-NAO), marked by closed contour ridging over southern
Greenland on the ensemble means. Typically, strong negative
height anomalies onto the west coast portend milder Pacific driven
patterns. However, in this case, should medium range guidance be
on the right track, the high amplitude ridging to and north of
Alaska will set up cross polar flow into our source region and the
-NAO would act as a roadblock from systems cutting very far
north. So, in sum, the relatively active pattern over the next
several days could become quite active with more regular plowable
snow threats at least through the end of January.

Accuweather going all in for the late Jan cold

Been under a heavy band fo last 30 mins. Best snow of the day so far. Think we get to 2 inches out here

went sledding with the kids. Good sized flakes coming down now. Hoping for 2-3 inches by the end of the day

visibility dropped quickly. grass is almost covered

My county, Kane  (IL), added to WSW.  nice suprise

22 minutes ago, Grizzcoat said:

2" hour rates at DSM!!

KDSM 291854Z 10009KT 1/8SM R31/1400V1600FT SN FZFG VV004 M05/M07 A3013 RMK AO2 SFC VIS 1/4 PRESFR SLP217 SNINCR 2/3 P0019 T10501067

Have a friend flying from O'hare to DSM today at 2:30. Flight is still on. I told him this morning there was no way it would be getting out

1 minute ago, bud2380 said:

Massive shift south on the NAM, LOL.  This is why we know not to trust it.  It does this ALL the time.  Never gets its act together until within 36 hours, and even then sometimes. 

Wow NAM now looks like the Canadian. 

I like what the HRRR is showing. Anything to end the rut the Chicago area and points east. 

LOT leaning towards the Euro

the ECMWF and CMC global have
favored the southern energy rounding the trough to help with a
modestly deepening surface low in the frontal trough much closer
to our latitude. This sort of setup would slow down the cold air
mass by several hours, but more importantly allow for the
blossoming of cold sector precip on the 700 mb trough axis.

With overall a bit better operational and ensemble support for
this idea, including roughly half of ECMWF ensemble members and an
uptick in support from the GEFS, have similarly to previous shift
trended the grids in favor of this. Should subsequent trends
continue down this general path, at least some snow accumulation
would be possible later Wednesday night into Thursday morning in
the deformation axis.

Tom Skilling posted this over the weekend. Shows the lack of snow for the Chi area in December over the last 10 years. Also of note is how the total seasonal snowfall ended. 

Got no snow here but it looked great on TV during the Hawkeye game! Go Hawks!

Nice looking storm. Hoping this bumps a little SE. Happy with a couple inches 

Starting to get interesting around the 12th

32 degrees while a small band is pushing through Chi suburbs. Grass and cars starting to get covered

Snowing harder here than I anticipated. Grass is lightly covered

What are we thinking for Chicagoland fellas - yet another grass whitener/ground wetter?

Still think 3-6 is a good bet. Not sure if your trolling though...….

Skilling's FB update moments ago

A little geek stuff now---so fair warning, tune this out if this sort of material is not your "cup of tea". 45 model forecasts have been analyzed for this prediction and model generated snowfalls among them centered on the city ranging from as little as 3.4" to as much as 16.6". Either of these two totals sits at the most extreme ends of extrem the forecast spectrum. These have a lower likelihood of actually occurrin--but should either of them actually occur, totals like these are likely to impact a limited portion of the Chicago area.
If one averages all 45 snow forecasts centered on Chicago, the total which emerges is roughly 9". Taking this figure and the accumulation estimates which sit in the middle of the pack as well as other variables we weather types look over, a predicted snowfall range of 6 to 12" range makes the most sense at this time.
I'm posting a set of varied model snowfall forecasts for you to check out yourself. It is always fascinating to watch how complex situations like the one coming together is handled by these incredibly sophisticated models.
What's been interesting--and I noted it in my posts Sunday--is how the the axis of heaviest snowfall as predicted by has been sinking southward. It started yesterday in southern Wisconsin-----it's now down across the Chicago area. Interestingly, the vaunted European Center model and its ensembles place the axis of heaviest snowfall just south of Chicago--still producing a respectable 7-8" snowfall city with as 4.5" near the Cook County/Lake county, IL line and totals as high as 11" on the Indiana line and into Lake CiLke County, IN. It's also interesting that our 4km RPM model is producing a snowfall in the 6" range through the heart of the city building to 10" toward the Illinois/Indiana line at Lake County, N. The suggesting of both these models as well as the UK Met center's models is that accumulation tallies will ease heading north into northern counties an toward the Wisconsin line and just north where 3-4" would be most common.
I'll keep your posted on updates as this winter storm and new data important to it and its impact come in..

Nws and skilling seem to be going with the northern track around here. Following the last run of the gfs.

LOT keeping with the northern track but Skilling has mentioned numerous south runs. Quote from his FB Page

" Southward shifting model guidance on potentially significant snow accumulations in that time frame, as covered in our earlier discussion, suggests other sections of the Chicago area may need to be included in future WINTER STORM WATCH issuances should that forecast trend continue. Stay tuned!"