RCNYILWX

Pretty sure you're overstating futility there. Midway 3SW had 39.1" last year (more than ORD's 36.1) and will finish above normal for this season too with 38.3" so far, vs. 41.2" at ORD. Even if you're lower than MDW 3SW, I'd bet you're over 30" for this season, which is still near normal to date. Sent from my SM-G965U using Tapatalk

Comment I made wasn't about expecting more of a snow threat anywhere in CWA on the front end of the system, need very significant changes for that to happen. Wouldn't be surprised if it verifies weaker on approach and thus tracks more overhead before strengthening vs. cutting to our west. A majority of 00z European ensemble members had the low tracking over northern Illinois. Sent from my SM-G965U using Tapatalk

Wouldn't be too surprised if it bumped more southeast, seems like a majority of the decent surface lows this winter have ended up southeast of the medium range operational model consensus. Sent from my SM-G965U using Tapatalk

Up to 41" on the season. With the pattern looking cold and active to close out the month and into March, a good chance to get to 50+ at ORD. Sent from my SM-G965U using Tapatalk

ILX advisory for their northeastern counties is for inclusion of freezing drizzle on top of snow accums up to 2". Without that, they probably wouldn't have issued. If freezing drizzle looks more likely to occur down in southern LOT CWA, we may need to expand the advisory and perhaps include the Chicago metro counties not in headline for map purposes. Agree that a long duration 2-3/2-4" snowfall on a Sunday otherwise probably doesn't need one. Sent from my SM-G965U using Tapatalk

I believe the NAM12 is suffering from unrealistic dry air issues that cause that splotchiness to the output. Have seen this issue several times the past few winters. Best way to compare is how you did with the simulated reflectivity vs the QPF/snow output. Other models look much more realistic as you said, including RAP/HRRR. Sent from my SM-G965U using Tapatalk

Looks like it's playing catchup. 12z run bumped up from 06z run pretty significantly. Sent from my SM-G965U using Tapatalk

I'm in same boat as you. Pass on nonsense of last March-April unless we get a big dog locally. Sent from my SM-G965U using Tapatalk

Models have come into good agreement on a long duration 2-4" event for much of northern IL, with possibility of some minor additional LES accums late Sunday night into Monday morning. Looks good for 3-6" in eastern IA/QCA. Hopefully as cyclone mentioned the long duration can help this to be an overperformer. Sent from my SM-G965U using Tapatalk

Nice improvement by the NAM tonight, especially in eastern IA/QCA. Would be cool if the blind GFS/FV3 squirrel finally found a nut. Sent from my SM-G965U using Tapatalk

Very good assessment. I think a big challenge in these situations other than making the assumption that the warm nose push will be at least as aggressive as the most aggressive model (NAM) is that we don't have any real time analysis of the warm layer. Aircraft soundings help but they're essentially point based so you can't track the trends and most of the soundings are from the larger airports. When the RAP/HRRR is underdoing the northward push and magnitude of the warm layer, it's a big hindrance. That's because the closest we have to real time analysis is the SPC mesoanalysis using the RAP as a background field, so it can definitely throw off even the best forecasters, and played a role in the lack of a lead time to warnings. As to the point about the southern CWA counties, the points you made are very fair. Being off duty for the event and an outside observer but certainly watching things closely, I think the signs were there that temps would mostly be AOB freezing for much longer than expected. Just by tracking the surface wet bulb zero line on mesoanalysis, it wasn't budging and didn't make any northward movement until the late evening. That would also play a role in reaching the warning criteria ice accums farther north. With the surface low well south and east-northeast winds locking in temps mostly 32 or less and pulling from dews in the low-mid 20s over southern lower MI and northeast IN, that argued for multiple hours of flatlining temps. In addition, the sensitivity of even a glaze of ice accums w.r.t. road conditions is something that most of the time we err on the side of caution for and issue an advisory. Certainly a very tough forecast and often times we do perform internal assessments about what went well and what could've been done better in cases like these. Sent from my SM-G965U using Tapatalk

Ensembles still look active with a -EPO/-PNA most of the time and I'll take my chances with that. If it doesn't work out, that's how it goes with weather, but I'd be surprised if we get to the end of February without having at least one decent snow event. The operational models 4-5+ days out are typically prone to big swings, but it seems like the very active Pacific jet/fast flow pattern this season has added more chaos than usual to the modeling, making them less stable and at times unusable in the medium range and beyond. Best advice is patience and hope we score some good snow events. Sent from my SM-G965U using Tapatalk

Where in DeKalb County are you? I can forward your report to the office for an LSR if you haven't yet. Sent from my SM-G965U using Tapatalk

My office started with just metro counties and west in an advisory, then expanded 1 tier south earlier today, then eventually CWA wide with 2 updates this evening. Finally we upgraded to warnings in part of the CWA then just a little while ago expanded the ice storm warnings we had issued late evening to now include most of Chicago metro except far north/northwest. We have the same issue out here with the snow ratio grids used to derive the snow output. It's been less of an issue in this area this winter from what I've seen but last year we had several events with low snow ratios despite cold temps due to the lift being above the DGZ and over forecast snow amounts as a result of ratios being too high. We try to account for the ptypes in the snow amount forecast with the prob of weather type (powt) methodology (using modified bourgoin energy technique), so that when there's low hourly snow probs and/or 2m temps AOA 35, we don't accumulate snow that hour and it subtracts it out of the 6 hour snow grid. Sent from my SM-G965U using Tapatalk

I put together some select total ice accums as of 06z from regional ASOS sites (by adding up I6 groups in metars). Most impressive widespread ice storm in years in this area. MLI: 0.47 DVN: 0.41 ARR: 0.32 VPZ: 0.30 DPA: 0.27 ORD: 0.22 RFD: 0.19 CID: 0.18 MDW: 0.15 PIA: 0.14 PWK: 0.09 Sent from my SM-G965U using Tapatalk

Was a red flag when we started off where I live in western Chicago metro as ZR/IP and not snow with SPC mesoanalysis off because of using RAP background which was too cold. Places well west and north in DVN CWA that were supposed to stay snow like CID and DBQ went over to ZR. Could see the mix line surging north on CC and knew it was all over. Good lesson today to err on the side of the warmth aloft being at least as aggressive as the most aggressive model. Sent from my SM-G965U using Tapatalk

Some select ASOS ice accums as of 06z (by adding up I6 groups in METARs): MLI: 0.47 DVN: 0.41 ARR: 0.32 VPZ: 0.30 DPA: 0.27 ORD: 0.22 RFD: 0.19 CID: 0.18 MDW: 0.15 PIA: 0.14 PWK: 0.09 Sent from my SM-G965U using Tapatalk

I'm an off-duty met from NWS LOT (Chicago). Haven't been following closely enough to know how the models have been depicting things over there, but just wanted to note that the NAM did by far the best with the warm nose here in northern IL and into eastern IA. The other models, including RAP/HRRR, were too cold aloft and not aggressive enough in pushing the warm nose steadily northward. We're now in a full on ice storm out here (I had close to 0.2" as of an hour ago where I live) and 2m temps flatlining around 31-32 with several more hours of steady precip to go. Sent from my SM-G965U using Tapatalk

The piece of guidance that had this scenario depicted pretty close to how it's unfolded is the NAM. I think the challenge in this setup is that you can think of a physical reason why a blend of the guidance would work out and how heavy rates could slow or even stall the advance of a warm nose. Today we had our hourly update guidance suite (RAP/HRRR) with the fake out colder trend, and since the background field for SPC mesoanalysis uses that, it also had 850 temps colder than reality. Unfortunately there's no public access to aircraft soundings that would give non NWS/FAA a better idea of trends. It's tough to throw all the eggs into the basket of one model, but a good lesson to err on the side of a more aggressive push of the warm nose aloft. In hindsight, it all seems simpler and makes sense. Sent from my SM-G965U using Tapatalk

Thanks, will pass your report on too. How are roads around there? Sent from my SM-G965U using Tapatalk

I relayed your report to the office. Did you happen to measure or estimate how much ice you've gotten? Edit: Also, where about are you in Kankakee?

Yup, what makes this such a tough call. 18z NAM didn't back down and has a big ice storm for much of the CWA. Comparing initialization and 21z to most recent mesoanalysis depiction of 850 0 line, it appears it'll be a bit farther north, though that doesn't mean it'll be wrong this evening. With earlier precip onset, we should at least start as snow. Certainly have seen NAM be right on the warm nose before, though often in those cases it has support of RAP/HRRR, which instead this time have been generally ticking colder aloft. Maybe a blend is ultimately the way to go. Such a tough forecast and gonna come down to real time/nowcast. Sent from my SM-G965U using Tapatalk

This is a very tough ptype forecast, especially between the I-80 and I-88 corridors and about 10-15 miles either side. Despite what I posted earlier, having looked more at the soundings, I'm not buying sleet being much of an issue other than mixing in at times. It should be primarily either snow or freezing rain. The big question is the northern extent of the warm nose and if it's enough to get full melting or do heavier rates keep it more as snow. The NAM and RGEM are by far more aggressive with the magnitude and northern extent of the warm nose around 850 mb, with the other guidance much more muted and farther south. Given lack of stout low level cold wedge around 925 mb, it doesn't appear there will be enough refreezing energy for widespread full freezing of melted hydrometeors into sleet, except maybe far north for a time if warm nose does get that far north. The pivotal weather soundings show this better with the temperature and wet bulb profile positive and negative energies. A modified version of the wet bulb is what we're using for ptype derivation in our grids, rule of thumb is negative energy of 100 j/kg or more gives 100% sleet probability and less than 50 gives 0% sleet, while for positive energy, I believe 20 j/kg gives full melting. So the big thing to watch on mesoanalysis this evening is the 850 mb zero line. Within the vicinity of that will be transition zone likely driven by rates to go over to all snow and far enough south will be solidly freezing rain.

Unless the short range guidance 2m and sfc wet bulb temps are too cold this evening into tonight, would think we have to extend headlines south at least to I-80 corridor counties. With brisk east-northeast surface winds coming from the cool dry high pressure to the east, doesn't look good for temps warming rapidly above freezing. NAM12 verbatim has warning criteria ice all the way to 2 tiers south of the current advisory. Even if that's too far south and overdone with the ice accums, latest HRRR has headline worthy ice accums in the I-80 counties not currently in the advisory. The other challenging aspect is exact p-type. Most recent RAP/HRRR are colder and have mainly sleet for I-88 counties and snow for WI border counties. From what I recall, RAP/HRRR did a good job picking up on the more stout low level cold wedge for our pinger fest on 12/28/2015. Sent from my SM-G965U using Tapatalk

Pivotal and COD 24 hour kuchera snow algorithm output from 12z GFS. Sent from my SM-G965U using Tapatalk