RCNYILWX

With officially 0 SD, it's only happened twice: 2/2/1996 (-5/-16) 2/3/1996 (-5/-19) I believe that -19 is the record low with no snow cover. With a T snow depth, it's happened 4 times: 2/23/1889 (-2/-11) 1/5/1912 (-5/-10) 1/6/1912 (-1/-11) 1/7/1942 (-4/-13) There's been 47 days total with sub-zero highs in the entire period of record. Sent from my Pixel 9 Pro using Tapatalk

Very good question - I will look that up. Sent from my Pixel 9 Pro using Tapatalk

You got it, impressive! I had forgotten that one. Sent from my Pixel 9 Pro using Tapatalk

Chicago posters, without looking it up, when was the most recent sub-zero low at ORD with 0 snow depth? Sent from my Pixel 9 Pro using Tapatalk

https://rapidrefresh.noaa.gov/ https://journals.ametsoc.org/view/journals/mwre/144/4/mwr-d-15-0242.1.xml The RAP is 13 km resolution, vs. 9km for the ECMWF, and 12km for the GFS and NAM, of the most commonly cited non-CAM guidance. The GDPS (GGEM) is run at 15km resolution and the RDPS (RGEM) is run at 10 km resolution. Finally, the UKMET is at 10 km resolution. What makes the extended RAP runs more prone to errors is that it's a hot start, hourly updating model with radar reflectivity as part of its data assimilation. This is just like the HRRR (which is initialized with RAP data) is more prone to errors in extended ranges. Think of the outer ranges of the RAP like days out on the ECMWF and GFS and beyond 24-36 hours out on the NAM. The RAP/HRRR can be right beyond 12 hours out, but in general they're more likely to be reliable within 12 hours, and even more so within 6 hours.

Should never have been issued so early, in hindsight.

I know you know that's overdone, but re. the LES, def a signal there for some accums, orientation and residence time of convergence TBD. Main limiting factor is lower inversion heights (around 850 mb), which would reduce flake size and snow ratios. Also the instability and lake to 850 delta Ts are on the modest side. The Canadians have higher inversion heights than the other guidance but not so much higher to explain the difference in QPF/snow amounts.

That plus the confluence from the upper low/PV lobe over eastern Canada and the northeast forced south by the NAO block.

Big drop in the 6"+ probs on the past few EPS and GEFS across our southern counties. 06z EPS only has 50-70% 6"+ probs roughly from STL to Lawrenceville. Barring a big change back in the other direction, we're not planning to hoist a watch this afternoon for the southern tier of counties in the LOT CWA.

The expected phase change back to a strong +PNA after the potential event next weekend caught my attention, thinking back to the Superbowl 2015 storm. It's not a perfect match but seeing some similar pieces in the Pacific pattern progression, when comparing the ECMWF ERA5 data on weather.us to the 500 mb anomaly forecast from the 00z EPS. A deep trough into the Aleutians forced a ridge spike off the west coast, dislodging what would become our main wave into the Rockies, while a deep trough also was in place over northeast NOAM and moving off the coast. This enabled height rises in between into the Midwest. Finally, a northern stream wave was able to dig in and at least partially phase in with the main wave for the deepening surface low we saw on 2/1-2. One of the biggest differences in the loading pattern was that the NAO was positive back in 2015 while it's forecast to be strongly negative in our timeframe of interest. That I think lends even moreso to the thread the needle aspect with the importance of a proper phase with the northern stream wave. If the phase is missed, the downstream blocking would suppress an overall weaker system. Back in 2015, the main wave being quite juiced and the lack of downstream blocking likely would've resulted in the good WAA thump that played out even without the phase for the prolonged high ratio deformation snow portion of that event. Overall, the analysis from [mention=525]Chicago Storm[/mention] and [mention=525]OHweather[/mention] is spot on in that the pieces could plausibly come together for a nice event, but with so many moving parts, things could certainly go wrong.

Decent looking snow squall setup on Wednesday on some of the guidance, 00z HRRR, past few NAM12 runs, and the 18z Euro. Sent from my SM-G998U using Tapatalk

Eric Webb's X feed (@webberweather) has been an interesting, good read lately. He's confident that this winter will have much more frequent -EPO episodes. Sent from my SM-G998U using Tapatalk

The potential has definitely upticked per the 12z cycle. Euro/EPS showed the most impressive bump but there's also a decent amount of spicy GEFS members. Not a huge fan of relying on phasing over the Rockies for the more juiced system given the confluence caused by the PV lobe over southeastern Canada. As a result, for interests in the northern half of DVN to LOT and points north, there may be a relative northward limit in the sfc low track in this sort of evolution even with phasing occurring. Obviously early enough in the game though for noteworthy changes in the whole setup still, for better or for worse. I wrote the long term AFD for LOT today, which also covered the cold shot beyond whatever happens Wednesday-Thursday. Chances have also upticked for WAA/fronto type snow late Tuesday night into Wednesday morning.

If you're a glutton for NAM punishment in its outer ranges, the 12z run took a pretty big step toward the global solutions for Thursday's first flakes.

Seems like a good time to make my annual return to discuss the pattern and winter events (with a general emphasis on the LOT CWA). First opportunity for wraparound snow looks like late next Wednesday into early Thursday on the early end of the spectrum, along the lines of the 12z GFS. The 00z ECMWF had a slower progression of the cutoff low, which would shift back the colder air and snow chances a couple days. We'll see shortly if that changes at all on the 12z Euro. Also found out the 06z and 18z operational ECMWF runs go out to 144 hours now.

Point well taken with respect to top end surge potential, but it would've needed to be a much larger shift to spare substantial impacts overall to the metro.

The NHC practically begs people to not pay any attention to plots of the center line of the cone, yet minute changes in the center line are treated like gospel. Sent from my SM-G998U using Tapatalk

We're watching on AWIPS at NWS Chicago and our educated guess has been the Anna Maria Island to Longboat Key corridor, seems like it would pass north of downtown Sarasota based on current radar extrapolation. Sent from my SM-G998U using Tapatalk

That's not a good sign to say the least. But certainly in line with the projections for the highest surge areas.

[mention=10150]bdgwx[/mention] Did you also happen to calculate the estimated IKE for Ian? Probably another good point of comparison there.

Thoughts with everyone down in the affected areas. As an NWS met (WFO Chicago), it always baffles me when I see coastal offices issuing special marine warnings during hurricane warnings. It's a waste of resources. Hoping at some point for a policy change to stop the silliness. We at the WFOs need to be focusing on tornado and flash flood warnings on land, and constant flow of information to emergency/public safety partners and the public via NWSChat and social media, not spending time issuing marine warnings for fishes. Just put waterspouts in the marine hurricane warning statements and in the gridded forecasts, and be done with it. If there's any boats out in a hurricane warning, that's on them.

I was the NWSChat/Slack person for the event, responsible for all of our main room chats and also a room we set up for city of Chicago support. Easily the most chat posts I've made in an event, just a total barrage at the height of the it. One of our radar operators recommended to post ~10 confirmed tornadoes' on there because that was about right. Almost every circulation had an at least brief TDS. Just hard to describe how crazy it was during that time, including briefly sheltering when we saw power flashes outside our window. Anyone on here who has pertinent damage information and photos for our survey teams tomorrow, please email [email protected]. Also you can let me know in a PM if you're trying to send information to one of our neighboring offices affected tonight. Sent from my SM-G998U using Tapatalk

That was mostly or entirely us because we were only in shelter for a few minutes. Had no choice but to go the carpet bomb route. When the entire line is spinning, go big lol. Sent from my SM-G998U using Tapatalk

NW Indiana would like to have a word with you lol Sent from my SM-G998U using Tapatalk

Nevermind discrete lol, it didn't have to be. Night of the QLCS twisters once the LLJ ramped up and low level shear increased markedly. One of the craziest nights in my now almost 14 years here. Sent from my SM-G998U using Tapatalk