RCNYILWX

It's funny that the Euro, much more consistent than the other operational guidance so far, would have its first more noticeable shift closer in to the event when we're probably headed for watch issuances in the morning. Just to spice things up a bit lol. But in all seriousness, to your point, if you think of the operational models themselves as part of a super ensemble and also just one member among their own ensembles, the runs tonight are all well within the ensemble envelope. We have a pretty good general idea of the areas most likely to get hit hardest with some error bar padding either side. Even with the prior operational runs focusing more north of your area, you were still in the threat zone for the heavier snow, just like the northern tier is still in it despite what the 00z Euro just showed. Another thing to consider with tonight's runs is that unfortunately there were several missing RAOBs out in the southwest this evening, so maybe that's hindering getting a better consensus. Sent from my SM-G965U using Tapatalk

Yeah agree, that's why thinking closer to climo would work for the various negating factors including those you mentioned. I'm briefing the mid shift that I think our ratios are a bit low for Monday PM for the all snow areas. Sent from my SM-G965U using Tapatalk

So have been taking a closer look at BUFKIT soundings and Cobb output from PSU and starting to think the initial burst late afternoon into evening will have higher ratios than you'd think given the surface temps. Attached below is the 18z NAM BUFKIT sounding for ORD valid 03z Tuesday. GFS is similar but faster, implying heavy snow as early as 22z Monday. The white line to the left of the T/Td trace is omega and yellow line on the temp trace is the DGZ. We look for good alignment of strongest lift with the DGZ to feel confident about higher snowfall rates. In the case of this sounding, the omega is strong at greater than -20 ubar/sec and very well aligned with the DGZ. Another factor is the very steep mid upper lapse rates above 550 mb at near or over 8C/km, which is another favorable element for heavy convective snow rates. As mentioned above, the GFS is faster with this signature seen on NAM sounding and even a hair stronger omega between -25 and -30 ubar/sec. Given all these favorable factors, I think the Cobb ratio should be given consideration, because the Cobb takes into account favorable lift through DGZ. Output for 18z NAM and GFS is 13-15:1 for several hours after onset of initial burst of snow. I'm not sure I'd yet go 15:1 ratios, but I think these soundings and Cobb output make a good case to go with around climo (~12:1) and certainly no lower than 10:1 SLR late Monday afternoon through Monday evening. Edit: And forgot to add, the DGZ itself is pretty deep at about 3kft, which certainly doesn't hurt.

One aspect I'll be taking a closer look at tonight is the low and mid level frontogenesis progged. The models do a decent job of forecasting the existence of fgen, but much less good in placement and also maintenance, especially this far out. Even with a shearing h5 vort, you wouldn't expect the mesoscale banding to disintegrate because that's more driven by low-mid level thermal gradient, which will remain tight. That's a way that the big dog type totals could get farther east into the LOT CWA, with longer than forecast maintenance of intense fgen banding. It seems as if some of the guidance is starting to hint at that possibility. Sent from my SM-G965U using Tapatalk

I was briefed in on DVN's thought process today and I don't mind sharing some details: First off, they had to go into unplanned service backup, so ARX actually had to spin up and do all grids and products, except probably graphics. I think the word is that they felt they had time for the counties east of those they put in the watch to give next shift one more look. DVN has been aggressive in the past with watch issuance (they were very bullish with early watch for failed event last Feb), so I was personally surprised they didn't issue up to the LOT CWA. Our lead forecaster today would've been fine going with a watch into our CWA. Sent from my SM-G965U using Tapatalk

For those interested in the lake effect/lake enhancement, 18z GFS keeps it going on IL side into Wednesday lol. Sent from my SM-G965U using Tapatalk

Some Chicagoland/LOT northern IL specific comments re. 12z EPS: Looking at all 51 members, it's pretty clear a few outlier duds are skewing the mean a bit. A majority still bring 6+ at 10:1 across the whole metro. If we saw a lot more duds would be more concerning. The op seems to be leading the way toward prolonging snow on Tuesday with the 700 mb forcing hanging back. My guess is the duds don't have that and merely dampen eastward from shearing of 500 mb vort. If 18z op holds serve from 12z, we should see more EPS members hinting at prolonged snow on Tuesday for the 18z run. Sent from my SM-G965U using Tapatalk

Here you go Sent from my SM-G965U using Tapatalk

New EPS is more concerning for east of Chicago. A majority of members still keep the precip swath intact into Chicago proper, but also majority dampening quicker eastward. We'll have to watch that trend related to shearing of the h5 wave. Feel like at this longitude we'll be okay still, but a bit worried for posters to our east. Sent from my SM-G965U using Tapatalk

My polite suggestion moving forward is to try to not wear your emotions on your sleeves as much with every post. As red taggers in here, we can add to our credibility by posting in measured tones. Of course everyone in here loves snow, we wouldn't be posting in this thread otherwise, so nothing wrong with alluding to the desire of it to work out for ones area. Just to try to be more objective when discussing the meteorology, which also is to the benefit of everyone trying to learn. Sent from my SM-G965U using Tapatalk

I think we're still a bit far out to be concerned about the finer scale details of a particular operational run. There's a pretty good consensus developing on the big picture, which is I-80 and north favored and northern tier looking much better than it had been the previous few days. New ECMWF in a vacuum is less favorable with southward extent, though I'm sure when the ensembles roll we'll see wiggle room within the general consensus of the EPS, that's been rock solid consistent. Takeaway from the prolonged mid-level forcing on Tuesday is it would be a nice way to tack on higher ratio fluff with 850s down around -10C.

Secondary low forms with the 700 mb circulation and really keeps precip going for a while. Sent from my SM-G965U using Tapatalk

I think ratios will be too low overall for during the heaviest rates for true blizzard conditions out this way. We didn't verify in the November 2018 blizzard warning because the visibilities never tanked too low even though the winds were more than supportive. The magnitude of wind speeds and gusts progged should still increase the severity of the impacts. After starting out with 10:1 or less ratios, the snow later on should be more 12:1 and that would be on top of a more dense layer beneath so blowing and drifting probably becomes a bigger issue at that point.

It's looking decent on Tuesday. When I get to the office, will dig in more on BUFKIT. 850 mb temps still look on the marginal side for the bulk of Monday night from a thermodynamics perspective, but there's going to be good speed convergence and there's little shear. 850 mb temps on Tuesday cool to or just below -10C, which considering the well above normal lake sfc temps, seems like that would get it done with still supportive wind field. Sent from my SM-G965U using Tapatalk

12z UKMET in line with the consensus and not too much dampening into northern Illinois. Surface low track came in a bit farther south, which isn't a bad thing because 00z run was more concerning for mixing up to here for a time. Sent from my SM-G965U using Tapatalk

I could go either way, there's enough supporting evidence to issue today but sometimes it's not the worst to wait. My guess is DVN issues today. So it would be up to our forecasters whether to hoist a watch too because MKX would have too much uncertainty.

I could see waiting until tomorrow morning for the watch. Sent from my SM-G965U using Tapatalk

And the NAM is finally getting a clue. Sent from my SM-G965U using Tapatalk

I didn't want to be the first one to say it and I thought exactly the same thing when I saw where the max sleet amount is modeled lol. Glad I was able to get some sleet added into the forecast today. If that Euro output comes close to verifying that's a pretty significant amount of sleet. Sent from my SM-G965U using Tapatalk

The 00z Euro was the first run to hit the sleet threat harder. I was wondering if any of the models would pick up on this. It makes sense that there would be a sleet zone in between the snow and freezing rain zones, usually don't transition directly from freezing rain to snow in a system of this type. Sent from my SM-G965U using Tapatalk

Does anyone have any idea why WeatherBell's Kuchera output seemingly always bumps up totals to an unrealistic degree even in near freezing setups? Looking at the Pivotal Weather vs WxBell for 00z Euro it's a very noticeable difference that doesn't make sense since Kuchera is based off of MaxT from sfc to 500 mb. The WxBell Kuchera can rarely work out like with the clipper snow squall a few nights ago but otherwise always seems overdone. Sent from my SM-G965U using Tapatalk

That Ukie depiction of a 997 mb low just east of KC at hour 72 to 1000 mb near Cincy at hour 78 seems a bit far fetched even if you account for the good probability of the system occluding and weakening eastward. The UK has been very unstable leading up to this system so its hard to put a ton of stock into it for the forecast, even though (weenie goggles on) it is a nice run for the outcome we're hoping for. However, if we take the 00z Tuesday position off to the east of KC as a perfect prog, it becomes clear that the occlusion process aided by the confluence and shearing of the wave saves us from mixing or a rainer. That surface low position has me concerned anyway if it gets more guidance support for mixing getting farther north than the model depicts explicitly. Sent from my SM-G965U using Tapatalk

Yes, what I'm trying to convey below your post, but you in so many less words lol. Putting trust in the ECMWF because it's been the most consistent doesn't guarantee anything to the eventual outcome, but I think it being more stable and well within its ensemble envelope is useful confidence building information for the forecast process. Sent from my SM-G965U using Tapatalk

Very valid points you make aside, I'm struggling to come around to the idea that the precip shield of a well developed mid latitude cyclone is going to be that bullied by confluence from the north when the system had already established an expansive moderate to heavy precip shield. I think that it would be a more gradual process. An event that comes to my mind from growing up in NY is the Feb 5-6 2010 mid atlantic "snowmageddon" blizzard. That was probably the strongest west based -NAO on record amidst a record prolonged -AO. The confluence over the NYC metro was true buzzsaw stuff on the north edge. But yet the system itself didn't get shredded apart, it just led to one of the most extreme north side gradients you'll ever see (~30" in PHL and T at KNYC). As a snowlover, it was a nightmare scenario. But I think I go back to it because I want to believe a model like the GEM is depicting too rapid of destructive interference on the system. Itll happen eventually but I'd think longitude of my area has more wiggle room than points east. It's like a hurricane making landfall, it loses its heat source and eventually the whole system winds down but the precip doesn't fall apart immediately. If we're talking unimpeded Gulf trajectories, a well developed trowal and intense low and mid level f-gen into Iowa at our latitude, is the precip shield all of a sudden gonna dance southeast because of confluence? I'll end my rambling but that's my thought process on this. I buy the weakening eastward of the synoptic system because it makes sense but not such a rapid modulation of the precip swath. Sent from my SM-G965U using Tapatalk

I don't think even this version of the GFS has a great handle on boundary layer processes. My conceptual model is that unless the surface low tracks into our CWA, the strengthening northeast flow from lower dewpoint air to the east and northeast plus evaporative cooling as precip starts is going to make it tough to warm effectively. If anything, the later precip start could allow for maybe slightly more BL warming than if precip were starting earlier, but on the other hand, gonna be socked in with lowering and thickening overcast. The GFS is hard to trust in properly handling evaporative cooling in the boundary layer. Sent from my SM-G965U using Tapatalk