RCNYILWX

Felt like this event exceeded our low expectations for northern Illinois. Some positive vibes as we kick off this active stretch. The higher ratios early this morning were interesting, because the snow definitely didn't feel light and fluffy when shoveling this morning. It also wasn't true cement though. We had strong omega well aligned with the DGZ, and steep lapse rates above the DGZ during the heaviest snowfall rates. The lift was associated with an upper jet streak and a mid-level fgen circulation. At onset last night, flake size was small, as the strongest lift was above the DGZ. A couple hours later, we had good alignment, and flake size improved, supporting the at or above climo ratios, despite surface temperatures hovering near freezing. This was yet another example of the challenge of snow ratio forecasting. Even if you have somewhat marginal temps, the sounding will often be a bigger driver of the ratios (Saturday night-Sunday was another example of higher than expected ratios). The Cobb output can help in these setups, vs. the Kuchera actually being too low. 10:1 maps appeared they did well enough for this event since they were higher than the Kuchera ratios. Of course once temps warmed and rates diminished late this morning and this afternoon, we've had essentially white rain, so the effective ratios are well below the Kuchera.

3" here in southeast/south central Naperville near the DuPage-Will Co. border. Picturesque paste. Edit: Checked a few other spots in the back yard and it might be more like 3.4".

Yep have been noting that on other guidance too. The Euro as you noted had kind of lost that look for a few cycles. It's going to snow over a large area due to that northern stream influence vs. the classic sharp cutoff northwest. Pretty interesting forecast in that the heaviest banding will be tucked in atypically close to the surface low while the lighter accumulating snows will expand well north and west. Also tricky from a headline perspective because I think the snow falling Wednesday beyond mid-late morning will be pretty low impact due to the temps at or above freezing. I think we're probably starting out with an advisory for the I-80 and south counties and then the day shift can make adjustments northward if needed. Some of the metro counties and into Chicago are a tougher call. The initial snow could come down at a decent clip, so if confidence grows in impacts to the commute, we may need an advisory for at least up to central Cook zone and probably DuPage. Sent from my SM-G998U using Tapatalk

The 18z Euro bumped north very slightly, but not in a meaningful way, and remains very different from the NCEP guidance. In fact, since temperatures will be around to even above freezing, could make a case using the Euro as a perfect prog that we wouldn't need an advisory for most of our counties. The places that have the snow start earlier tomorrow night are probably gonna have enough impacts Wednesday morning to justify an advisory though. While the latest ECMWF is generally a bit lower QPF wise farther north than the foreign guidance, it's probably not a meaningful difference. It's the NCEP guidance that stands out, particularly the NAMs. The GFS is not very different farther north, but it is farther north with the heavier banding across central IL and Indiana than the other globals. Sent from my SM-G998U using Tapatalk

I think another issue with this system is it's very compact. That sfc low track is normally good for much of the Chicago metro, but the 850 mb and 700 mb lows are tucked in closer to the surface low than typically occurs. Sent from my SM-G998U using Tapatalk

The 18z EPS only showed a slight downtick from 12z in its 10:1 mean snowfall output and that op run is not significantly different from the previous few runs aside from the lower QPF. Surface low track is almost identical to the 06z run. Concern shouldn't be based off that one run. Even though late January isn't sun angle season, our bigger issue is the lack of cold air going into the event plus temps near to even above freezing during the snow. This will limit accumulations unless the higher rates can get farther north. So we need to see support for better banding and higher QPF resulting from that farther north. Otherwise, the 1-3"/2-4" range from Gino's AFD is probably the ceiling in the metro (on colder surfaces).

Had forgotten to respond to @Hoosier a few nights ago about snow expectations for this mini event. I felt despite the guidance poorly handling things amidst a general downtick in QPF and snow that a corridor of 1-2" still looked good in northern IL and at the time favored north vs. south. Honestly had lost some confidence in the forecast and felt that localized 3" amounts were probably not happening anymore, but sure enough we had some 2"+ reports out in the northwest CWA and it looks like ORD will have over 1" for this event since they had 0.9" at 12z. RFD already had 1.3" so they should end up over 1.5" and may make a run to near 2". Also, it appeared at the time that some areas would have a dusting/coating at most, which looks to have been the case from the south suburbs and south and northwest Indiana. Tough forecast since the guidance struggled handling this one - the GEM and RGEM and HRDPS seemed to do probably best overall. Sent from my SM-G998U using Tapatalk

The track of the 00z run would probably result in better snow farther north than the verbatim output. Sent from my SM-G998U using Tapatalk

Because the GFS is more of an outlier now, I'm currently leaning toward the foreign guidance to be more likely on the right track. The warning type event is less likely, but that may not mean a whiff (maybe ALEK was onto something haha). Sent from my SM-G998U using Tapatalk

Still have to wait on the Euro for our final 12z operational data point, but did want to note that the foreign models (12z GEM and UKMET and 00z Euro) have a more expansive precip shield with light to moderate snow accums farther north. The GFS has the sharp NW cutoff that's seemingly more common in these setups. This is despite relatively similar surface low tracks and mid and upper level depictions. There's probably another physical reason beyond this, but simplest way to see the difference is that foreign models have much higher 850 mb RH farther north than the GFS. Sent from my SM-G998U using Tapatalk

That run was hurt by the h5 low digging a bit farther southwest, but even more so, comparing to 12z, positive tilt of the parent wave valid Tuesday night-early Wednesday vs neutral to negative tilt on the 12z run. The farther south h5 low path hopefully ticks back some on the next model cycles, though might very well be a meaningful data point, while the other element is much more uncertain. Any farther south with the parent wave definitely will make it tougher to get a far enough north surface low track because then you'd need to be more reliant on wave going full negative tilt. The 00z operational runs showed the caution flags in this setup - I think we'll have a decent idea by Sunday on which way things are leaning.

The GFS was a fast outlier with our main wave going back to the model runs 24-36 hours ago - it's now closer to the consensus, with main issue being how far south it digs the wave. Something to watch vs. getting overly concerned at this point. With the latest GEFS showing the spectrum of plausible outcomes better than it seems to do usually, the Euro suite should be a little more helpful given the sheer number of members, plus the better overall performing op model. RAOB sampling wise, should get partial sampling 00z Sunday and close to full 12z Sunday. The satellite derived stuff is so much better now, plus any over Pacific aircraft data can help, so this might be a more stable forecast (big picture) than some of our events.

Yep, this idea was already firmly in the realm of possibility per the ensemble members. It's a pretty fine line - was hoping to convey that to AFD readers today, in simplest terms, the surface low track with respect to the Ohio River will loom large in determining the haves and have nots. Unsurprisingly, the GEFS ticked slightly south vs. 18z, but honestly not bad at this range, with still a solid # of members with a good hit up into the metro. I don't feel any worse locally because of this run, other than that we remain in a precarious spot, and north metro even more so vs. my location on DuPage/Will border. The Canucks need to get their act together with the GEM running late, so us junkies have another data point for the 00z cycle lol.

00z GFS - not what you want to see in northern IL and points west. Short wave gets buried too far south in the desert southwest. It's also a hair less robust so it stays positively tilted for longer and results in a farther south low path that isn't able to track more sharply northeast. Still ends up good for farther south and east in the subforum, because other favorable aspects remain in play. The GFS isn't exactly a paragon of consistency, but it can be used to demonstrate what we don't want to see happen to get a good event up to Chicagoland. Sent from my SM-G998U using Tapatalk

Not to suggest that this event is going to be anything more than a DAB+ sort of deal, but think that the relative "dryness" of model runs and tick back up from 18z Euro is mostly related to guidance struggling with the rather nebulous forcing in this setup. Good proxy is 850 mb and 700 mb RH, which haven't changed much on the Euro and the global models in general. If you have saturation down to 850 mb and 700 mb is saturated with enough lift, it's usually gonna snow, putting amounts aside. I think the wonkiness of the NAM is two-fold: struggling like the other guidance with the forcing mechanisms and also having an issue related to its convective scheme parameterization that I think causes it to hold onto insignificant dry layers for too long. This will be the case more often in modest vs. strong forcing. And since the 3km NAMnest is run from NAM initialization, the dry air issue will carry over. This is probably the case too for the other CAMs running off the WRF core. Also, the RAP and CAMs are inherently less reliable farther out in their ranges. While it's quite possible/probable some areas only get a light dusting, I'd be surprised if there's areas that literally don't snow as implied by runs with 0 QPF response. Otherwise, for eastern IA and Northern IL, thinking 1-2" amounts still attainable, probably not localized up to 3" anymore though.

The ensembles have ticked northwest on the means if you go back several runs. Re. the seasonal trend to be weaker and farther southeast with systems, I think it is a climatological issue. The reason much of this subforum can give exact dates of memorable snowstorms is that we're in a less favored area for everything to come together just right air mass, and storm track and strength wise. It's why in a typical season, a majority of our events feature light to moderate accumulations. The recently concluded storm that nailed the upper MS Valley and northern Lakes didn't follow the seasonal trend after all. Big snowstorms are much more common with north and northwest extent in the Midwest, and of course are essentially a dime a dozen in the Northeast (though they're obviously having a terrible winter out there too). Thinking back to last season, GHD III (if you want to call it that) left potential on the table and had an even sharper NW cutoff because phasing that some earlier guidance (especially GFS) showed did not happen. In a fast flow La Niña pattern absent downstream blocking, that gives reason to be skeptical of the stronger and farther northwest solutions. Even without phasing issues, that could shunt the main shortwave (and surface low) far enough east to keep areas farther northwest out of the game. That being said, there are plausible reasons why this one can work out farther north and west related to the main wave likely being juiced, which can help with downstream height rises from latent heat release. It looks like upper jet dynamics should play a role as well. A lower likelihood of needing to rely on phasing means we're at the mercy of how much the main wave can do on its own. As things stand now, the chance of a mostly non event for the entire subforum has decreased (though is certainly not zero), but for those in the LOT CWA, we're unfortunately firmly in the cone of higher uncertainty, with more wiggle room with southeast extent and less with north and northwest extent.

That's mainly phantom dry air issues from a quick glance at stuff. If the Euro mostly holds, think 1-2" locally maybe 3" in highest swath. I had a point max of 2.2" in the CWA today near I-88 corridor. Sent from my SM-G998U using Tapatalk

If the pieces come together right, the air mass gives vibes of Feb 24, 2016 - think lower ratio and needing to be in the heaviest banding for good totals. Obviously don't want to repeat that nightmarish gradient in the Chicago metro, though for the areas affected, that was probably a top 10 event since 2010. Sent from my SM-G998U using Tapatalk

My personal favorites are Jan 4-5, 2014 and GHD II. I had an account during GHD I but definitely wasn't active in the storm threads for that, if I posted at all. Have read through the GHD I storm threads a few times though. Great stuff.

Best more recent examples of that probably Jan 30-31, 2021 with good near term trends for much of the CWA except far west and southwest, and Feb 14-16, 2021 for Chicago. Sent from my SM-G998U using Tapatalk

You would be incorrect for the EPS mean. I was actually surprised at how excited the Euro members are. A lot of spread, but less than the GEFS and GEPS. Sent from my SM-G998U using Tapatalk

Yep, that was the death knell. If we got a more classic synoptic evolution where the 850 mb low was associated with the eastern surface low, parts of northern IL would've been in the game. The fact that even with the unfavorable 850 mb low placement, we're getting some mixed ptypes this evening shows it wasn't too far off from a wet snow event in parts of the CWA.

The weekend deal is a step back from some of the GFS runs that had earlier phasing. That looks unlikely now. The southern wave gets embedded in the northern stream trough but not quite a full phase until later Sunday-Sunday night off to the east. Overall enough large scale ascent at the mid and upper levels plus saturation in the DGZ for light to moderate snow rates and accumulations. Current global and majority of ensemble guidance evolution would suggest that suppression by the northern stream is less likely but the ceiling for snow amounts is probably up to 3-4" if enhanced banding materializes and a general 1-3" otherwise. Suppression remains on the table if there's destructive interference between the northern stream and southern stream. Also some of the op models and ensemble members, most notably the GFS, are gapping some areas due to subsidence outside of banding.

I'm definitely not a fan of getting rid of advisories - supposedly surveys showed a majority were confused by them because to your point, what is a winter weather statement? What do the TV Mets message on their broadcasts - a winter weather statement is in effect? That is an interesting point though that getting rid of advisories may pave the way to issuing more purely impact driven warnings. Upcoming pattern continues to look solid for fairly regular chances - as long as the mean troughing stays biased west, but with TPV near Hudson Bay, it keeps everyone in the game. No guarantees, and this has certainly been a bad winter for snow enthusasiasts outside of MSP and the LES belts, but would be surprised if there's no widespread decent events in snow starved areas from this weekend through mid Feb. Sent from my SM-G998U using Tapatalk

We should start a movement on the sub forums to discourage posting of the Tropical Tidbits 10:1 snow/sleet maps. While there are flaws and some minor differences site to site with all the algorithm driven snow maps, at least the other sites are relatively similar in binning in QPF as snow. I prefer Pivotal Weather's maps overall, but COD maps are decent too. A few tips: - Algorithm snow maps are not the model producing that much snow - it's the specific algorithm ratio that converts snow QPF into snow accumulation. One of the few explicit model snow outputs is snow depth and then positive snow depth change utilizes the snow depth to give an idea on explicit accumulations. There is a total snowfall output available on Pivotal Weather (for RAP and HRRR) that uses a model parameterized snow ratio and is an explicit model snowfall output. The NCEP HRRR site has explicit model output snowfall as well. - Kuchera ratio is best used in below climo (wet/dense low ratio snow) to climo normal snow ratio scenarios, but is deeply flawed in very cold air masses. The ratio doesn't have an upper limit in extreme cold. - 10:1 ratio is not bad as a first guess in climo normal snow ratio scenarios and even colder air masses because outside of banding or absent strong omega perfectly aligned with a deep DGZ, the Kuchera ratios will often be overdone. 10:1 can give a rough idea and then adjust up where you think mesoscale banding will set up. - Positive snow depth change is a useful metric in low ratio to climo average ratios but will probably be a bit underdone in general. - Tropical Tidbits is much more liberal in QPF to snow so the footprint of snow accumulations in marginal to mixed p-type scenarios will almost always be overdone. It's probably okay when p-type isn't an issue. Sent from my SM-G998U using Tapatalk