RCNYILWX

Our collaborated ratios were in the 7-9:1 range for the western and northwestern burbs during the day on Friday and I was good with those as a starting point. Temps are marginal so 10:1+ seems unlikely. South of I-80 and the city I had ratios as low as 5-6:1, so we certainly didn't go high with ratios. Then Friday night on the backside, they come up to 10-12:1 (highest inland) during the evening. Of course this is all contingent on keeping snow as the ptype. Sent from my SM-G998U using Tapatalk

Honestly, certainly couldn't discount a warmer outcome, but we were looking at a bit south of I-80 (aside from the very real lake influence) on too much uncertainty for a watch. I do think it's going to be white rain near the lake on Friday, but my thinking is that the 700 mb and 850 mb low tracks with this per the very consistent ECMWF and recently more consistent GFS are more favorable to keep things heavy wet snow away from the marine bubble on Friday. Definitely uncertain how far inland the lake influence on accums gets, but [mention=9209]mimillman[/mention] noting the difference between Wicker Park and the Loop yesterday afternoon swayed me to use the Dan Ryan as a rough demarcation zone. I was most on the fence about Livingston (not included), Kankakee (included), and Lake and Porter, but IWX wanted LaPorte in and I was fine to put them in the watch for collab purposes. WPC has an internal watch proposal that actually had the whole CWA in it. There was good agreement for the purpose of watch issuance in what we went with, and didn't consider not including central and southern Cook because of inland portions of those zones currently look good for warning level impacts per global consensus. Officially had about 5" along the Chicago shore, which very well could still be a bit high depending on how long temps take to cool Friday evening.

If anyone has specific LOT centric questions on forecast stuff from today, ask away and I'll try to reply a bit later. Apologies for the lack of a more in depth meteorological dissertation in the AFD lol - just less and less time available for us on days like this. Sent from my SM-G998U using Tapatalk

The second half had a much better air mass, but the front end Saturday night all the way into or through that Sunday morning was lower ratio with temps near freezing. This looks more marginal than that and the lake had some ice on it, or was near freezing at least. Main point about GHD II is that if we don't get dry slotted or too warm aloft, we can pick up a good amount of snow with more marginal temps. And in this case, there's been good agreement to this point on the deformation Friday night having a much better air mass coming in. Sent from my SM-G998U using Tapatalk

Plan is for me to do the forecast for the storm today. Definitely a risk with ptypes into the metro, though recall that GHD II started out pretty warm too. So hopefully we find a happy medium. The Chicago shore could be a bigger issue again. Sent from my SM-G998U using Tapatalk

Goes without saying but a really high end solution from the Euro. Powder keg of a setup if things break right.

Some would say the new hotness. Lol

Started snowing recently here in southeast/south central Naperville. Coming down at a decent clip but small flake size for now.

^Thanks! Feedback like that is helpful for us, as we constantly fine tune out graphics. We've gotten a lot of good feedback on the ptype timeline since we went to it over the past few years.

I think your latitude helps but if there's gonna be an issue in Lake County it'll be the southeast. Sent from my SM-G998U using Tapatalk

As you'd expect, crazy day at LOT today. Will try to chime in this evening and then try to sleep. Back in at 7am tomorrow as the shift supervisor. Roads should be fun lol.

I think it's a relative thing. The Euro is still the best model but the other models are better than they were due to computing power. Back when these forums got popular, the Euro was much better across the board, so even if it had similar or more fails, the other models had fewer successes. Another aspect I think of with modeling is the minor drawback of much higher resolution. In complex patterns with multiple moving parts, the error introduced by a higher resolution depictions can multiply in a way that may result in somewhat less stability run to run, such as what we were used to seeing with the Euro. Since the ensemble members themselves are higher resolution, they may be affected as well. I'm speculating, but perhaps this is an issue with the guidance being phase happy, or with handling convection at times?

The 03z RAP had a very impressive depiction of the front end WAA snow tomorrow night. It's a plausible solution, if not in the top end amounts but the idea of several inches, given PWATs nearing 0.7" (0.6" is considered very high for snow), steep mid-upper lapse rates, slantwise and at times upright instability, and strong lift. For the areas that max out, 1"/hour rates appear likely, and potential for 2"/hour is there. Was texting with our lead forecaster on midnights for the storm, Carlaw, and he thinks TSSN is a decent bet.

With the caveat that I've been off since Thursday and been more casually following than when I'm also working (I'll be back in tomorrow morning), I was a bit surprised how bullish they went with the snow forecast. You can tell it's an aggressive forecast on the probabilistic winter page, https://www.weather.gov/dvn/winter. Their expected forecast is not far off from the high end amounts, which are the 90th percentile of the distribution and are closer to the 90th percentile than the low end amounts, the 10th percentile. Ideally, we're probably closer to the middle (50th percentile) of the distribution at this range.

Easy to forget because we've been tracking so long, but a SLP pressure in the 980s is plenty strong for this area. If low-mid 980s means more snow for more of the metro, easy choice. Need the track to not be hard NNE from near STL to keep the dry slot and warmer temps aloft farther southeast. A slightly weaker system would help with that.

You're in the LOT CWA right? I can't see locations on Tapatalk. Would pass your report to the office if they could use a few. Sent from my SM-G998U using Tapatalk

Regardless of the exact outcome snow wise, this storm is a big win for the medium-long range guidance. The general idea of a deepening SLP track toward the western Great Lakes has been locked in at a well above average lead time.

And UKMET, if you want to hold out hope. I'm definitely less optimistic for this area but still going to give some time. Also, unlike some other misses in the past, we'll get in on the front end thump of snow.

I wouldn't be surprised at a similar snow distribution to 11/25/2018 if the track doesn't nudge back southeast. Don't discount the front end thump being productive though even into the city. Consider that a relatively modest upper wave produced localized 5" amounts with a similar thermal profile last night. Where you have strong lift well aligned with the DGZ, and steep lapse rates in the DGZ, you can get pockets of higher ratios even with temps around freezing. That's something the Kuchera maps won't pick up on.

Here's the depth change mean. The answer is probably somewhere between this and the Kuchera ratio stuff. 10:1 ens maps at least give a good idea of the heavier snow swath.

Every storm is different and you may very well be right, but the GFS/GEFS has been a bit too amped at this range with southwest type systems at this range over the past few winters. It's gonna be close and I feel better out here than I would in the city. The EPS mean SLP track has also jogged NW some vs. previous cycles.

24-hour 4"+ probs Sent from my SM-G998U using Tapatalk

You have competing factors - there is downstream -NAO blocking but it's in a bit of a low ebb as a 50N/50W low kicks out. Meanwhile, it's a dynamic, deepening system that wants to cut at least some due to height rises/latent heat release out ahead of it. I don't think it's going to go substantially NW bc of the downstream blocking but unfortunately we'll probably be riding the line due to the lack of an entrenched colder air mass that could have had the baroclinic zone farther southeast. We might have more wiggle room in the western suburbs than in the city and due south burbs. Sent from my SM-G998U using Tapatalk

Kuchera version, just for posterity First is run total and 2nd is 24 hour. Sent from my SM-G998U using Tapatalk

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?