RCNYILWX

Best quality snow of the season here, true fluff. Nice little overperformer event. Sent from my SM-G965U using Tapatalk

What's amazing is that the Euro is not quite as cold aloft as the GFS at peak magnitude but would still threaten to break the all time coldest 850 at ILX. Sent from my SM-G965U using Tapatalk

[emoji33] Sent from my SM-G965U using Tapatalk

Since the coldest temperature of the 2000s, -18 on 1/16/09, happened on a good radiational cooling night with only about -20 to -21 at 850 mb, have to account for that possibility. Sent from my SM-G965U using Tapatalk

The top 5 coldest temps at ORD all had 15+ mph winds so I think best shot is the peak advection Wednesday morning. Sent from my SM-G965U using Tapatalk

I think it includes today's event. Best way to compare is to check the map at weather.gov/lot/winter. We've been focusing on the Sunday night-Monday event in the storm total map there. Sent from my SM-G965U using Tapatalk

It's all about longitude it comes in at before it starts to track due east. I have my doubts it comes in notably farther north than GFS/NAM, though obviously can't fully rule it out. If it comes in farther west and makes it farther south before east turn, will help northern IL. As it is, GEM did shift back south and shows a solid event I-88 and north, with warning criteria northern tier, not too far off from last few runs of Euro. This is just a tough setup to model correctly and hinges upon the evolution described above. The models really aren't that far off at this point, kind of like hurricane track forecast errors a few days out, but the small differences matter for us. Sent from my SM-G965U using Tapatalk

12z GGEM Sent from my SM-G965U using Tapatalk

Even more of an impressive gradient between you and ARR, which was down to -24 last hour. Sent from my SM-G965U using Tapatalk

-28 at SQI. Sent from my SM-G965U using Tapatalk

Yep great point, yet another reason to take a step back from reading too much into every operational run. Sent from my SM-G965U using Tapatalk

Is it really a northern shift or just the majority of operational models favoring a more northerly track? They're on the northern end of the ensemble spread and could be outliers in their own right, we just don't know. Most important element is where the system enters the CONUS. Euro still has a strong surface low for a clipper/hybrid at 997 mb over southern IA then weakening a bit eastward, but most importantly it enters the CONUS farther west than the farther north op models. Hate to overuse the lack of sampling argument, but I really think the multiple moving parts, complex evolution, angle of approach, make it that we're unlikely to have consensus until we get more observed data on the important features. Chiefly the primary wave coming ashore into northern BC later tomorrow. I continue to think that I-80 and north in IL into southern WI will do well, with highest totals I-88 and north, and going to hold with that thinking until things become more clear. Sent from my SM-G965U using Tapatalk

Big hit I-80 and north. Good to see but also doesn't change the fact that nothing is set in stone with so many moving parts. Sent from my SM-G965U using Tapatalk

Good point. Spread actually increased on 12z GEFS vs 06z GEFS, showing the sensitive nature of the pattern evolution for this hybrid. We have 2 PV pieces dropping south over Canada that will play a role, another northern stream wave dropping southeast over Canada, and the parent short wave is well out over Pacific in the Gulf of AK. It won't be fully ashore into northern BC until tomorrow afternoon/evening. I think it is probably safe to say that areas south of I-80 are less likely to get into the potential 6"+ snow swath at this point but areas north still certainly in the game. Sent from my SM-G965U using Tapatalk

Still pretty sizable spread on the GEFS. The operational model trends except for UKMET are what they are today, though not gonna punt this for northern IL. This synoptic setup is a tough one for the models to nail and some of the important features are in a data void area. Sent from my SM-G965U using Tapatalk

What's your definition of DAB? Looks like 1-2" there, or right around 2" if you go by latest HRRR/RAP and Euro and GEMs. Toss the NAMs. Sent from my SM-G965U using Tapatalk

I don't buy the 00z NAM for tomorrow. Looks like classic NAM dry air issues with the unrealistic splotches of qpf/snow only where the model thinks saturation is sufficient. SREF only had one member with no measurable snow at ORD. Edit: Referring to 00z NAM12. 3km NAM looks much more realistic.

I think if trends hold tomorrow could be a sneaky disaster commute in the Chicago area. Bitterly cold temps and road treatments don't mix and fluffy arctic snow is already pretty slick. If today's dendrites are a sign of what tomorrow may be like, 20-25:1 ratios could fluff up to 1-3", maybe even a bit higher in spots. Wouldn't be surprised if a WWA is issued considering the timing coinciding with the PM commute. Sent from my SM-G965U using Tapatalk

The 06z GFS took the cake for most extreme solution for cold here. -41 at 850 at 12z Wednesday, with 500 mb heights touching 489 in far northeast IL and 1000-500 thicknesses in the 470s. We're at the point where moderation of what's being modeled will still give -30 or so at 850. Noon 2m temps over northern IL on Wednesday in the low-mid -20s on the 06z GFS, just incredible stuff.

Actually bottoms out at -34 at ORD Friday morning, insane. Sent from my SM-G965U using Tapatalk

Much better radiational cooling setup next Wednesday night/Thursday morning on this run of the Euro. Unbelievably cold min temps modeled in IA and IL. Looks like spots of -40ish in north central IA. Sent from my SM-G965U using Tapatalk

Still solid out here, but dampening eastward not good for farther east obviously. Everything still on the table with this. I do agree in leaning somewhat against the GFS op and ensemble members even stronger than the op for the reasons mentioned. Sent from my SM-G965U using Tapatalk

Agree. I remember being wowed by medium range projections of early January 2014 cold shot and it wasn't like this. Sent from my SM-G965U using Tapatalk

For reference, coldest 850 on record at INL is -42.1 and -39.5 at GRB, both on 1/16/82. Record low 850 for MPX is -39.3 on 1/9/82 (00z 1/10). Sent from my SM-G965U using Tapatalk

The duration of the well below zero cold is unreal on that run. Almost can't believe seeing that modeled when it's not in fantasy range. Edit: Below zero at the ORD point from 12z Tuesday until 21z Friday. Incredible.