RCNYILWX

For the benefit of the board, a visual of our grand total snowfall forecast tonight-Sat AM snowfall from the LOT dayshift (MTF through 12z Thursday portion and myself the rest of the event). This ended up falling out pretty close to the internal graphics WPC shares with the WFOs for collaboration purposes and I think looks pretty reasonable based on all the available data. We've been breaking the forecast into two separate "events" in graphics and only going with the first part on the probablistic snowfall page. That's because we feel that putting out the grand total snowfall forecast in a public facing graphic on the web and especially social media would make the event seem more impactful than it will likely end up being. Plus, as has been discussed, the net snowfall will end up some percentage lower than this grand total when accounting for melting and compaction. Will post additional thoughts later.

Honestly don't know what's going on at this point, why I said hopefully they do a case study and can attempt to address the issue if it ends up being wrong as seems likely. I wish I could give a better explanation. The divergence crops up on Thursday morning and then it's a strong outlier until Friday night. I think one of the best timestamps to compare is 12z Friday. One of these things is not like the other (00z GFS, 00z NAM, 00Z GGEM, 12Z ECMWF, 00z GEFS ptype as proxy).

100% agree. I was looking more closely at the various model depictions and the GFS doesn't make much physical sense. Particularly Thursday night into Friday, there's barely any thermal gradient with a developing and strengthening 925 mb low and it keeps doing this run after run. Regardless of ultimately how things turn out, the 00z NAM depiction makes sense as a direct point of comparison. It has the warmer air on the east and southeast side of the low wrapping back into the colder air on the north and northwest side of the low. The GFS has most of the 925 mb low uniformly from 0 to +1C until Friday evening, like it's wrapping that air in and locking it in place. If the GFS ends up wrong as we expect, would hope the modelers at NCEP will investigate what went wrong. Based on WPC's internal collaboration graphics this afternoon, they completely tossed the operational GFS thermal profiles as well. Sent from my SM-G965U using Tapatalk

Agree that better dynamics could be at play later on in the event. Also it's late January and not late March or April, that helps. I was thinking about the daytime vs nighttime issue and even though it's not worry about sun angle season yet, would think with such marginal BL temps, daytime might hurt if rates are too low vs same conditions at night. Sent from my SM-G965U using Tapatalk

If anyone is looking closely at point and click or hourly weather graphs for this event we do have a fair amount of rain and snow mention during the day on Friday because of surface temps being as marginal as they are. Would think that at periods of lower precip rates that we could mix or flip to rain, or falling snow would not accumulate and essentially function as white rain. Sent from my SM-G965U using Tapatalk

Exact details of the setup are certainly still subject to change, especially farther out in time, but I have a hard time believing all the other models and ensembles are wrong on 925 mb temps. Sent from my SM-G965U using Tapatalk

I think we can safely toss the operational GFS 925 mb temps. That doesn't detract from the concern about how marginal the surface temperatures are for accumulation efficiency. Ratios would also be below 10:1 much of the time, so accumulated liquid precip as snow at an average 8:1 ratio might be the way to go. Not sure why the Kuchera map on WxBell has higher snow amounts than 10:1, since Kuchera method is supposed to account for more marginal setups to give lower than 10:1 ratios. The 12z Euro favored time windows for the LOT CWA/Chicago metro would be later Wednesday night into Thursday morning, Thursday night into Friday morning and then later Friday afternoon-Friday night. There would likely be lulls in between these windows. Sent from my SM-G965U using Tapatalk

Looking at ptype progs from individual members, such as on COD, the ensembles are still nothing like the operational. Sent from my SM-G965U using Tapatalk

The GFS stubbornly keeping 925 between 0 and +1C is really what it comes down to. The other models aren't doing that. On the midnight shift last night, the forecasters considered the GFS thermal profiles to be an outlier. That said, the combination of weak and disjointed forcing and marginal BL conditions means that accumulations tomorrow night through much of Thursday night will likely be inefficient (lots of white rain). Would look to Friday and Friday night as the upper low gets closer while slowly deepening and the system develops better deformation precip for a bulk of the snow accumulation, wherever that max axis ends up. Sent from my SM-G965U using Tapatalk

I find it interesting that the GEFS has consistently been hitting this harder than the operational GFS. Perhaps different physics packages helps explain, but also, in an inherently complex and odd setup like this, the higher vertical resolution of the op vs the ensembles might be of detriment. The lower vertical resolution of the ensemble can help smooth out features as opposed to what at times can be garbage in garbage out with the operational models. We haven't really seen this behavior with the ECMWF suite for this potential event but it can be an issue at times. My inclination now would be to lean toward the GEFS and ECMWF suite since those have been more consistent. Outer ranges of NAM have pointed more toward the latter. As things stand right now, this doesn't look like an exciting event (aside from a interesting analog mentioned in previous posts), but with such a long duration, could add up to respectable totals on colder surfaces if things break right. In a mild hemispheric pattern, I'd take that as a win. Since I like to think of local events that may have some similarities, off the top of my head came up with January 14-15, 2018. That was a long duration 3-6" snow due to a slow moving ULL, though it was much colder aloft. Parts of DeKalb, Kane, and DuPage had a jackpot zone of 6-7". https://www.weather.gov/lot/2018Jan15_snowfall Sent from my SM-G965U using Tapatalk

Would suggest posting Midwest view Sent from my SM-G965U using Tapatalk

GEFS did once again. Ride the ensembles. Sent from my SM-G965U using Tapatalk

WWA for Porter County. Still a good amount of uncertainty close in, as latest HRRR is earlier to focus the convergence into Lake County, and actually has slightly higher amounts in eastern Lake than within Porter County. It then goes onto scrape the Cook County shore with the band. NAMnest on other hand primarily focuses on Porter County much of the time and never gets the heart of the banding over Lake County and misses Cook County altogether. Sent from my SM-G965U using Tapatalk

Every state has their own Alek [emoji38] Sent from my SM-G965U using Tapatalk

Need a halfway decent lake effect event. Even in the worst winters, usually get at least one. As an example, 2011-2012 had a short but intense LES event for NW IN in Feb, for which we issued a Blizzard Warning. 10" of snow in spots in 4-6 hours with 40-50 mph wind gusts. Sent from my SM-G965U using Tapatalk

I'm guessing closing in on 3 if not there yet. Haven't measured. Borderline +SN now. Sent from my SM-G965U using Tapatalk

I should've known from your username lol. I think I did and momentarily blanked out Sent from my SM-G965U using Tapatalk

Are you in McHenry County too? I was gonna relay some reports to the office Sent from my SM-G965U using Tapatalk

How much snow there? Sent from my SM-G965U using Tapatalk

A rough estimate from DVN correlation coefficient mixing line would bring that through the Chicago metro in about 4 to 5 hours from west-southwest to east-northeast.

Highlighting the importance of starting the snow earlier. Sent from my SM-G965U using Tapatalk

Daylight snow, congrats Sent from my SM-G965U using Tapatalk

In it here, surrounded by good snow Edit: Getting going now quickly

Most of the county still in 3-4" range on our graphic with part of south in 2-3". I'm not sure I would've lowered totals based on trends but it was only a small adjustment and with the WWA out at this point it is what it is. Sent from my SM-G965U using Tapatalk

Steady -SN just got going here in southeast/south central Naperville. Sent from my SM-G965U using Tapatalk