RCNYILWX

Those coarse resolution CFS maps don't make any sense. Even if you account for background climate signals, there's no mid and upper pattern configuration that would torch the entire continent. If Alaska is torching that extreme, then there's gonna be a trough over at least the eastern half of North America. If a good chunk of the CONUS is torching, Alaska will be cold due to ++EPO from the TPV parking nearby, like in 2011-12.

I think there's a decent enough chance at this range to get some modest accums but certainly lean against the fun phased outcome from the 00z Euro two nights ago. Overall there's been a slight uptick in ensemble probabilities of light (1"+) accums. With the cold air mass coming in for Christmas, will take what we can get for the holiday mood and to get on the board if tomorrow morning doesn't produce measurable at ORD. Edit: Re. IWX's tweet, a little surprised at the 'significant rain and snow' wording because that would require the phased solution. Otherwise, best chance for a significant precip event looks to be in the eastern Lakes and points east, probably east of their CWA. Edit 2: Just saw 06z Euro, and it looked potentially more interesting extrapolating out from hour 90 than the 00z run ended up being. On the Euro ensemble though, currently very little member support for a heavy snow swath in the western and central sub, though a rough estimate is about half of members have light to moderate snow swaths nearby.

The GEM was much more 00z Euro-like but also emphasizes the thread the needle nature of the setup. The southern wave goes neutral to negative tilt on its own and the system takes off but cuts too far northwest, followed by full phasing of northern and southern waves. From a big picture perspective, it's a step in the right direction. Edit: The 12z GEFS was also another step in the right direction.

FWIW, the NAM wiped the floor with the current GFS from 84 hours out to verification on the east coast storm. Should keep an eye on how the parallel GFS is handling things because it performed much better than the operational with that system. Sent from my SM-G965U using Tapatalk

06z GEFS was a step in the right direction, pretty easy to see just by looking at height anomaly run to run comparison with the 00z. Sent from my SM-G965U using Tapatalk

Need this post on the potential event thread. Sent from my SM-G965U using Tapatalk

Re. Euro op, the 00z run wasn't a huge difference from the 12z run conceptually, just shifted farther south with the surface low. Key thing is the wave rounding the trough being allowed to come up and have a chance to phase in with the northern wave. Member spread increased between the 00z and the 06z EPS, so we might be reshuffling the deck, and need to see the clustering lean more toward the southern solutions on the 12z run and the other ensemble systems as well moving forward. As is seemingly always the case, we have pieces of energy coming from two data sparse regions plus the reliance on a phase to play out in a way that results in a favorable outcome for our area. With the very mild air mass out ahead of the possible system and owing to this strong positive mid-level height anomalies to the east, we also can't rule out a farther northwest rainer cutter. I think chances of a decent event somewhere in the sub have increased a bit, but still need a lot to happen just right for the Chicago metro snow hole.

Added more stronger SLP members farther south than 18z EPS so roughly 2 clusters within that increasingly large spread. The northern cluster is still favored slightly more, probably tied to the key question of the northern stream short-wave. Due to the difficulty of getting a proper phase like depicted on the 00z Euro and some of the EPS members, think it's a lower probability outcome but still worth tracking because it's all we got. Sent from my SM-G965U using Tapatalk

It remains a thread the needle setup. It's the old need a phase to work out sort of deal, which as we all know went great last winter. That said, the last two runs have had important changes toward increasing potential for a solid event. Most importantly, the northern stream wave is slower and not as strong, which allows the southern stream wave to come up and eventually phase in. 00z EPS is rolling out, so we'll see shortly how much ensemble member support the operational has. Sent from my SM-G965U using Tapatalk

Euro showing the setup we need for Wednesday night into Thursday to work out. Long way to go but nice to see it on this run. Sent from my SM-G965U using Tapatalk

The IT side of the agency is a running joke. We always talk about what we should have but don't. When we got AWIPS2 5 years ago or whatever it was, it was okay for 2010. Anyone seen the Sportsmax skit from SNL? 'I have 500 sworn affidavits that our IT is the best in the world!' lol Sent from my SM-G965U using Tapatalk

The NWS way. And they didn't even put correlation coefficient on there, only the most useful dual pol product. Can't wait until the next new page comes out in 15 years. Sent from my SM-G965U using Tapatalk

Just one run but the 00z GFS is interesting for December 23rd. Shades of January 29, 2008 with a sharp Arctic front and rain to 1-3" of snow, wind, and a flash freeze. Would sign up for that. Sent from my SM-G965U using Tapatalk

Chicago hasn't had a 6"+ calendar day snowfall since 2/9/18. The last 6"+ snowstorm was 11/26-27/18. Was thinking about that in context of how NYC didn't get as much as some of the earlier model progs, but Central Park still got 10.5", which was their largest December storm since Boxing Day 2010. The last double digit snowfall at ORD was 11/20-21/15 and the last double digit snowfall during met winter was GHD II. Obviously major events are a lot less common out here than the east coast but we're seriously overdue. December has become a feast or famine month locally, mostly famine since 2010, with only 2010, 2013, and 2016 featuring above normal snow. The prior decade on the other hand had some very big Decembers (with also a few lean years), none more so than 2000. We won't be able to finalize what the December normal will be for the '90-'20 climate normal period until this month ends but prelim data is the December average/normal will drop to 7.5" from 8.2".

How was 95-96 in SE MI? That's the only recent low snowfall Nina that was colder than normal here. Even though Nina's don't have the reputation of big east coast winters, 95-96 is snowiest all time for NYC and 10-11 was on track to threaten that had it not stopped snowing in February. The ensembles continue with a not terrible look to close out 2020. Not cold, but not a blowtorch, and near average heading into the coldest time of the winter isn't a bad thing for snow prospects. Sent from my SM-G965U using Tapatalk

It's not the big storm we all want, but the Euro showing a decent Pac hybrid clipper on the 22nd into the 23rd and then a follow up weaker wave into the morning of the 24th not far from here keeps some hope alive of getting snow cover down for Christmas. The ensembles also have a decent look toward the end of the run with a -EPO, -PNA, -NAO, -AO. May make for an active and not too mild stretch into January if that comes to fruition. Sent from my SM-G965U using Tapatalk

That's the one! I'll fix my original comment. Definitely a good cautionary system with respect to mid level warmth. I remember watching the mixing line surge northward on correlation coefficient on OKX and DIX during that event. You made a comment later that the models often underdo the warming aloft and that's absolutely right. It's tough to say yet that the NAM is handling it perfectly because even at this range it can be too amplified with key mass fields. That said, have seen it perform better than the globals several times out here re. warm nose aloft. Hopefully the Euro is capturing things well enough and a good chunk of the city and interior LI can manage to get several hours of heavy snow rates before mixing/dryslot.

Not gonna pretend that I'm optimistic for next week. It looks as usual too progressive on the operational modeling in that timeframe. The trend on the EPS last 2 runs to become much more northern stream dominant, which was the more likely outcome anyway, really diminishes the chances for anything to work out for us out here. All I can say is that it's far enough out for changes to occur from the current look. The cold looks like it'll be legit not very modified Arctic air, so all we can do at this point is hope that somehow we can get some snow down for what looks like it could be a very cold Christmas period. CAD for Christmas would certainly be a nice cherry on top of 2020 lol.

Only wraparound/CCB that I can remember really working out for a storm that didn't have a good track overall for the city and western and central LI was the Christmas 2002 noreaster. I guess you could kind of group in the late Feb 2010 Snowicane but that was an odd beast of a storm. Sent from my SM-G965U using Tapatalk

The NAM was actually supposed to be replaced this past summer as part of replacing the entire modeling infrastructure with the GFS's FV3 core. This is the setup the ECMWF and UKMET have, with all their modeling under the same core, from global to meso to ensemble and weekly/seasonal. Taking the NAM off line was pushed back because better verification needed to be seen of the GFS/FV3 doing the things the NAM does well as well as the NAM. The coming upgrade of the GFS, if it is a marked improvement, and that's obviously the goal of the effort, will eventually result in that timeline of the NAM being discontinued into focus. In addition, this newest upgrade of the HRRR may be the last significant one until the high res suite gets fully moved over to the FV3 as well. Sent from my SM-G965U using Tapatalk

Plot twist, Alek's backyard as the snow capital of the Chicago metro. Edit: In all seriousness though, the LES parameters aren't terrible tomorrow from a thermodynamics perspective and duration as well. When I looked yesterday, lake induced ELs were peaking on the forecast soundings at 6k-7k feet, which is a bit better than marginal. The problem is the possibility as partial ice loss as we lose saturation in a portion of the DGZ. Overall DGZ saturation won't be great and lift peaks below it, so flake size should be pixies. Hoping the FZDZ monster is avoided.

For winter weather headlines, the winds typically get grouped into the WSW. You wouldn't issue a HWW on top of a WSW, similarly wouldn't issue a Wind Advisory on top of a WWA. In our bulleted current text products, an extra bullet for additional details might be included that mentions the 45-60 mph wind gust potential. The one location it's probably tricky is out east on Long Island where changeover should occur quicker and amounts might not reach warning criteria but the winds do. My guess is because the snow/mix would be impactful enough plus the damaging winds, might do a WSW for simplicity. Not speaking for OKX though, just speculating based on how my office and surrounding offices typically handle multi faceted winter events.

The current ECMWF is 9 or 10km resolution. The parent NAM is 12km and NAM nest is 3km. The HRWs (ARW, NMM and NSSL) are 4km. Sent from my SM-G965U using Tapatalk

Lurker on this thread, originally from College Point Queens, been working at NWS Chicago since 2010. Jealous of this storm, as it's been exceptionally boring out here and big snowstorms like Superstorm 93, Blizzard of 96 etc drove my passion for the weather. Anyway, certainly can't discount the depictions of the NAM and the RGEM in this timeframe. It was comforting to see the Euro with an all/mostly snow solution for the city. That said, think big picture old school meteorology before we had access to this firehose of data. The parent mid-level low has trended stronger and farther run over run (looks like we'll even get fringed by light snow out here which was very low probability just a few days ago). With the pretty far north and west mid-level low center tracks, this seems to be a setup that favors a very intense front end thump with very strong large scale and mesoscale ascent (low level f-gen and steep lapse rates) in the warm conveyor belt. Hopefully not like the [Edit: March 4 2017] storm that got flooded with warm air and caused a mix much quicker. Recall the 93 Superstorm had a terrible track for the coast but we still got 10-14" on the front end because the warm advection thump was that intense. For the city and a good chunk of Long Island, you could see most of your liquid equivalent QPF as snow but then dry slot and mix with the 700 mb deformation zone displaced well to the north and northwest. Good luck to everyone that's been tracking this storm! Wish I was heading up to the Catskills to ski on Thursday lol.

Thanks for posting those, never got around to it yesterday. 12z run today looks better than yesterday anyway. Sent from my SM-G965U using Tapatalk