RCNYILWX

Here's the depth change mean. The answer is probably somewhere between this and the Kuchera ratio stuff. 10:1 ens maps at least give a good idea of the heavier snow swath.

Every storm is different and you may very well be right, but the GFS/GEFS has been a bit too amped at this range with southwest type systems at this range over the past few winters. It's gonna be close and I feel better out here than I would in the city. The EPS mean SLP track has also jogged NW some vs. previous cycles.

24-hour 4"+ probs Sent from my SM-G998U using Tapatalk

You have competing factors - there is downstream -NAO blocking but it's in a bit of a low ebb as a 50N/50W low kicks out. Meanwhile, it's a dynamic, deepening system that wants to cut at least some due to height rises/latent heat release out ahead of it. I don't think it's going to go substantially NW bc of the downstream blocking but unfortunately we'll probably be riding the line due to the lack of an entrenched colder air mass that could have had the baroclinic zone farther southeast. We might have more wiggle room in the western suburbs than in the city and due south burbs. Sent from my SM-G998U using Tapatalk

Kuchera version, just for posterity First is run total and 2nd is 24 hour. Sent from my SM-G998U using Tapatalk

The CIPS analogs start at hour 132, so the best we can do is CPC 6-10 day analogs. The December 1978 analog had 13" in Chicago the last 4 days of the month. Edit: Aside from some of the obvious greats, my knowledge of Midwest snowstorms prior to my time here (started in summer 2010) isn't the best. Any other dates stick out on the analog list?

All-timer save worthy

24-hour captures the defo for northern IL but misses the front end snow Monday night into Tuesday morning.

12z EPS modeled pattern for next weekend vs. December 2009 H5 composite anomaly. Deeper -PNA forecast but otherwise pretty good match with 2009.

Not surprised at all to see the NAM that amped at this range. Front end thump with the WAA has looked decent for a while - the air mass isn't cold but cold enough.

Unfortunately ILX has been using these maps in their graphics too.

The EPS has been very steady the last several runs. Sent from my SM-G998U using Tapatalk

Feel better about avoiding that insanely sharp cutoff March 3rd had. Sent from my SM-G998U using Tapatalk

The GEFS mean has had a gradual tick west, agree, while the EPS mean has generally been pretty consistent with the SLP track. With a good antecedent cold air mass, we'd have a little more wiggle room on the track. Sent from my SM-G998U using Tapatalk

Looks good for an inch to maybe two in spots. Sent from my SM-G998U using Tapatalk

The GEFS actually likes interior northern Illinois down to west central IL more - definitely been consistently west of the op. Should see a tightening of the spread the next couple cycles. Sent from my SM-G998U using Tapatalk

Another example of the importance of the ensembles at this range. The east coast system this weekend is a good case in point - there's still been noteworthy run to run swings by the operational runs in the last few model cycles.

Figure the amount of convection in the warm sector is something that may also contribute to struggles in handling the evolution of this system. Sent from my SM-G998U using Tapatalk

Yep, based off that, no real changes in thinking. It's good to see the ensemble not hugging the operational with plenty of members still supporting a good outcome here as you noted. The obvious caveat is there's members also similar to the operational, so that solution remains plausible, though the majority are west of the operational. The mean was actually a tick west and stronger from the 06z run. Sent from my SM-G998U using Tapatalk

2022 had good snows too in Kankakee County. Sent from my SM-G998U using Tapatalk

Will be interesting to see the 12z GEFS, starting to roll out now. The 06z operational was similar to the 12z, but the 06z GEFS still had a majority of members northwest of the op. We're still at the phase of the forecast where these operational solutions fit within the ensemble spectrum. The snow enthusiast in me would be lying if I said seeing sharp cutoffs like that in the modeling don't make me nervous (shades of 2/24/16, also in a strong Niño) but in this case there really is plenty of time left.

The weathernerds site has sounding data out to 240 hours for the 00z and 12z ECMWF runs. Here's an example from a random point I picked in New England at hour 90 of the 06z run. It looks like a bit better resolution than on WxBell and there's also a data readout from any pressure level you pick on the sounding. https://www.weathernerds.org/models/ecfull.html?&inittype=zoom&initfield=Get_Skewt&initcycle=determine&initfhour=090&initimdimx=1050&initimdimy=630&initrange=55.000000000000:230.000000000000:20.000000000000:300.000000000000&initcx1=0&initcy1=0&initcx2=0&initcy2=0&initcross=False&initsound=True&initsoundx=847&initsoundy=196&initloop=False&initoverlay=False&initlstart=000&initlend=240&initlint=3&initol1=Get_Skewt&initol2=null&initol3=null&initol4=null&initol5=null&initcities=On&inithgwys=On&initunits=On&initlatlon=Off Sent from my SM-G998U using Tapatalk

If you treat the operational runs as essentially ensemble members in their own right, especially at this range of the forecast, it makes sense to see blips like the 12z Euro operational, since there had already been ensemble solutions similar to that. A wide range of outcomes remain on the table while the big picture idea of a strong/deepening SLP tracking over the region still holds. Assuming the Pacific recon flights are happening, that may help narrow the goalposts some by later in the work week. Sent from my SM-G998U using Tapatalk

A paste bomb with wind could be very high impact if the SLP comes in anywhere close to as deep as recent Euro and GFS op runs and many ensemble members. The system doesn't look all that progressive to me as modeled relative to other past higher end synoptic systems. Your point about lack of cold air is certainly valid though. With the south buoy still 43 degrees, and unlikely to cool off more than a couple degrees over the next week, could make for white rain on the lakeshore and a few to several miles inland until winds turn offshore. Think the November 25-26, 2018 snowstorm.

You're not wrong that in the GFS depiction, it would start out mild due to the easterly fetch off the mild ocean. Except the flow does turn northeasterly enough to cool things off. It doesn't have to go due north to funnel colder and drier air southward. Look at the lower dew points to the north of NYC/LI during the day. Once the surface low tracks far enough east, the subtle shift to more NE from E and ENE to start the day plus the air mass being cold enough aloft and higher precip rates amidst lower dew point air being advected southwest helps cool the boundary layer via dynamical and evaporative cooling. It might take longer in reality than the model shows to cool off because of how warm the marine layer is over the well above normal SSTs, but the process the 06z GFS shows is still physically valid with the track it depicts. Sent from my SM-G998U using Tapatalk