RCNYILWX

Completely hypothetical... But if some location ever did receive 4 feet of snow in 36 hours, how high could a drift get? Real question for the pros though, how well can our weather models forecast an event on the leading edge of an arctic blast like what is shown? What do analogs show? The last one last year also was forecasting a decent snow at longer lead times (there were still blizzard warnings), but we mostly got an inch of dust with strong winds. 

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?

This GFS run is bonkers

All-timer save worthy

Gfs a bit juicier too. Guidance is really showing that def band cranking once it arrives. +SN and the winds could have us talking the B word. 
 

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.

That's not surprising. Lol. But definitely misleading the public. On a side note nam looking like it will be relatively north at end of its run. Probably near STL. Nice front end thump. If you can believe its temp profiles. 

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.

Did you see the 1000mb contour was inside the 996mb contour? Lol

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

Liking the look of that 12z EPS

The EPS has been very steady the last several runs.

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I'm just expecting slop here, much more interested in the following storm. I feel this will be Chicago's version of the heavy wet snow paste jobs Detroit got last January 25th and March 3rd.

Feel better about avoiding that insanely sharp cutoff March 3rd had.

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Noticeably with each run the low continues to shift west on the mean.


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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.

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going bullish with a DAB+ on the saturday mood flakes

Looks good for an inch to maybe two in spots.

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A number of the ensemble outliers have tightened up, starting to get some confidence in a good hit. 
 

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.

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The EPS looks better

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.

I would say these models now that they have gotten to such fine grid scale have done poorly on cold sector precip, I feel like this may be a situation like that as well.

Figure the amount of convection in the warm sector is something that may also contribute to struggles in handling the evolution of this system.

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Not at all a bad look. Lots of good members for a big Chi hit. 

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.

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Were you away for 2 years lol

2022 had good snows too in Kankakee County.

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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.

That's what I mean. I'd like to see better resolution. Just seems like connecting dots at mandatory levels. God forbid they offer that.

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

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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.

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the general agreement at 500 for a deep slp with a classic track looks great but I fear a lack of cold air and progressive nature are gonna keep this from being too interesting, ymmv and would love to be wrong
looks like actual cold available for whatever comes next which will be nice

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.

I’m def more in the camp that this is a mid Atlantic—>south snow storm at the moment. However there will be a significant longitudinal gradient. 
Where H5 closes off, in and away from the coast, sees the jack. 
The GFS track/evolution was near perfect for a significant mid Atlantic storm but look at the east surface winds ripping. And they never orient N/Northeast, instead to ENE. The surface high in reality extends from eastern Canada to Bermuda, and therefore maintains the surface wind direction off the Atlantic. This is being flagged on the ensembles, with +surface temp anomalies.
Model guidance has consistently been too cold with very short lead times this season. It’s ridiculous that GFS has LI in low mid 30’s with this wind and SST’s in upper 40’s. It’s a major issue for NYC metro. Hell even BOS will be 40F with this look.

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.

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The signal for a powerful storm is something else at this lead time. We received word that there will be Pacific recon flights this winter to help with upper air data for the models. Hopefully that helps make for a better forecast farther out.

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Per LOT extended range courtesy our very own:
Looking out beyond day 7, for multiple model cycles in a row, the ensemble means have consistently depicted the ejection of an anomalously deep western trough into the Midwest. The pieces could thus come together to support a strong synoptic system affecting the region (irrespective of precip. types) early in the first full work week of January. Medium-long range ensemble guidance also has been consistent in an active and colder pattern continuing through mid January, so there may eventually be some bonafide winter weather threats to track. Stay tuned.
Castro

For much of the LOT CWA, one of the more impressive EPS 10:1 snow means for our area in the day 8-15, with the 48 hour at about 5" valid ending Wednesday evening Jan 13th and about 6-8" across the Chicago metro for the 7 day period ending 00z 1/15.

Given the look at the end of both the EPS and GEFS, as discussed in the AFD, regardless of how the potential big storm plays out early in the week, barring major changes, we will have additional opportunities, perhaps several, and a good chunk of the sub-forum could get in on the fun.

The nice thing to see was the trend toward more of a -EPO with the continued -NAO/-AO that would keep a steady supply of cold air from our source region along with helping keep eastern mid-level heights in check amidst the continued active -PNA pattern.

Long long way off but the consistency for something big showing up in that time frame off the op GFS is interesting.  
End of the op Euro run, but has a nice look to it as well.  Certainly seems like a good chance we'll finally have something to track with this.
 

With a downstream -NAO, could see some modulation of the shortwave trajectory. Alternatively, even if the potential/probable system in the 9th-10th timeframe ends up a more wound up cutter, that could serve to shunt the baroclinic zone farther southeast.

Since western troughing will persist with the -PNA, we should see follow-up waves ejecting out and then the -NAO could stand to benefit us. Both the EPS and GEFS last night were strongly hinting at an active 2nd week of January, so there should be few chances to get something decent.

My best guess is maybe squalls that are stronger or last longer than normal?

It's not a Snow Squall Emergency, it's a Snow Squall Warning (SQW) with a 'significant' tag selected that will trigger the WEAs. Baseline SQWs will no longer get WEAs. I'm not sure how other offices are handling it but we're in disagreement with the policy and will not be issuing non WEA SQWs. We will only issue 'significant' SQWs that activate WEAs (between 5am and 10pm on weekdays and 7am and 10pm on weekends).

https://www.weather.gov/media/safety/Snow-Squall-IBW.pdf&ved=2ahUKEwjb3LmU4bODAxXcAHkGHTtqBzQQFnoECBsQAQ&usg=AOvVaw0Cpc_VkwVJaiOH4JJHj9VZ

Yes it does. Many are jaded from recent failures, GEFS not as good, and also that pattern can easily be great for the distant interior and bad for many on this subforum, time will tell. 

Understand the tendency to feel jaded by recent winters. We had a rough winter out here last year too. The 12z GEFS looks pretty similar to the EPS. From about 1/8-1/11 would be the concern for a more wrapped up cutter given the progged AN heights in that period. And on the GEFS, it verbatim gets the 850 0 line farther north.

On the other hand, with the NAO forecast to be solidly negative, also seems like a setup (should it come to fruition) that could be conducive to a SWFE. Then beyond that window, the pattern looks generally favorable with H5 heights trending to a bit below normal and a nice upper jet max focused over the southeast.