RCNYILWX

Trust in the pattern moving forward. May not cash in immediately but think we'll get at least a solid event or two. It hasn't been what some earlier model runs showed yet, though the amount of cold air and chance for decent baroclinicity should win out eventually. And at the least, the chances of lighter snow we're getting for now are better than the nothingness we had for 2 weeks to start January remember. Sent from my SM-G965U using Tapatalk

Revisiting this, some of the early HRRR/RAP runs and to a bit lesser extent the NAMs and HRWs clearly were far too aggressive. Had thought 2-4" was attainable across a good chunk of the CWA in expectation that the ratios could perform even outside banding. This was before it started to become more clear that this would be one of those fairly common setups where only in the banding would ratios perform to their capability and the CAMs were overdoing QPF. It appears that the CAMs were reacting to mesoscale banding and distributing this QPF over much too widespread an area and were in general too wet. These are tough forecasts because the globals don't necessarily do as good a job picking up on the f-gen banding, while the CAMs do but might be too aggressive in doing so. Plus the ratio question really takes being precise in ascertaining where banding will set up to forecast the localized 15-20:1 ratios while the rest of the area comes in close to 10:1.

The band from BRL to VYS is where it's at for getting the high ratio dendrites. It looks like that should slide across the southwest burbs and then probably south of downtown Chicago. Might be close to getting clipped by the band at my location. Sent from my SM-G965U using Tapatalk

Ratios in these situations are always tied to how well the omega is aligned with the DGZ. If there's a mismatch, you get pixies, no matter how deep the DGZ is. Today is conditionally favorable for 20:1+ ratios because of the deep DGZ but it looks like it will be temporary and tied to the somewhat transient f-gen banding. Wherever ratios end more around 10:1 today is a good case study for the flaw of the Kuchera method (and also underscores how ridiculous the WeenieBell maps are). Because it's based off the MaxT from the surface to 500 mb, and the whole column is very cold, there's no way for the Kuchera ratios to not be high today and in other events with cold sfc temps, which means caution is advised for all events moving forward with snow maps. The Cobb ratios found on PSU BUFKIT site are better for a day like today because the Cobb ratios are based off how strong the lift is and how well aligned it is with the DGZ. Kuchera is better for more marginal thermals or when it looks like climo ratios are better than 10:1 for a given event.

Both the HRRR and NAM place the banding signature a bit north of where the low-mid level f-gen has been maximized on recent model runs, which is where you'd expect it. Sent from my SM-G965U using Tapatalk

I'm surprised they didn't go into Indiana with it, which may have had to do with IWX and IND not issuing for any of their counties. Haven't seen that quick of dampening eastward within the CWA on the guidance. There's a little bit of good and a little bit of less good from what we know so far. Clearly they didn't rely solely upon global guidance and ensembles for QPF and snow output. On the other hand, there's support for going farther north and east with the headline. My guess, if the AVN AFD is a clue, is that we wanted to go farther north but DVN didn't even want to issue anything. The map looks weird enough with LaSalle in and not Bureau and Putnam and points west. Imo having included LaSalle could also have included some counties farther north and east in the metro without yet putting Lee County in. Sent from my SM-G965U using Tapatalk

The truthers would say this is a combination of a massive uptick in suicide and a bunch of older people with co-morbidities all decided to die in one year Sent from my SM-G965U using Tapatalk

12z NAM valid 22z 800-600 mb 2D f-gen from FSU site http://moe.met.fsu.edu/banding/ Sent from my SM-G965U using Tapatalk

No because that's a common NAM problem in Arctic air masses. The GFS has a much lower QPF output but it's completely saturated through the DGZ. Sent from my SM-G965U using Tapatalk

Pivotal Kuchera Sent from my SM-G965U using Tapatalk

Yep, guaranteed based on the Aviation AFD that they'll be taking them up. Sent from my SM-G965U using Tapatalk

Nice tidbit here from our 18z TAF Aviation AFD Sent from my SM-G965U using Tapatalk

I'm liking a 2-4" range for the LOT CWA. Sent from my SM-G965U using Tapatalk

While it's possible that the northern tier ends up with somewhat less snow, I doubt anywhere in the CWA gets shut out tomorrow. Sent from my SM-G965U using Tapatalk

Award for most weenie 12z run goes to the WRF-ARW Sent from my SM-G965U using Tapatalk

I think there's upside potential above our official 1-2, locally 3" forecast, for reasons that have been discussed (high SLR, steep lapse rates, low and mid-level f-gen). Now that the HRRR has gotten more realistic, the 06z NAM runs probably represent a reasonable best case scenario for now. Good to hear the Euro bumped QPF on 06z run. Sent from my SM-G965U using Tapatalk

WeatherBell weenie vision still fluffs it up to 1-3", looks like that's still doable as long as we get snow out of this wave and the DGZ is very deep. If the meso models hold with a better event through tomorrow, then can put more stock in them. Sent from my SM-G965U using Tapatalk

Solid event around here today. Unfortunately missed the first round of ++SN but woke up in time for next round, then the backside snow and wind this evening has been solid. Considering much of the modeling had this as a rainer a week ago, no complaints even though I bought into that for a bit (was just trying to jinx it [emoji38]). Regarding headlines for this event, without a true impact based winter storm criteria, we're kind of just left to wing it and decide on a case by case basis. The WSW we issued for the NW CWA was definitely for impacts and largely to match up DVN and MKX (they ended up going with a WWA). As it turned out, and probably not too surprisingly, open areas outside of the warning had some legit winter storm impacts this evening and of course when the heavy snow came through it was briefly extremely low visibility. It's a tough call on these since you'll have a good amount of time with WWA impacts and the more sustained winter storm type impacts. I was also surprised DVN never upgraded any part of their CWA to a BZ.W, as they we're strongly considering one. Not always true but my perception is that they generally prefer to have the same winter headline for their whole CWA, eastern IA posters can confirm. Sent from my SM-G965U using Tapatalk

New Euro and EPS will be key tonight. UKMET not a total dud like other globals with implied 1-3" from just under 1/10" to some spots a bit over 1/10" liquid equivalent across the CWA. Figure ratios of at least 15:1 are attainable with a very deep DGZ and previous NAM runs also had steep mid-upper lapse rates. Even though the 12km NAM backed off on QPF, its simulated reflectivity still looked pretty good. Sent from my SM-G965U using Tapatalk

+SN BLSN, visibility under 1/4 here, can tell because it's tough to see across the park from my backyard and that's no more than 1/8 mile away to houses on other side. Sent from my SM-G965U using Tapatalk

AO and NAO negative through the end of the run, just less negative after day 10 than they'll be through day 10. All in all, not really disagreeing, will probably be last week to 10 days of the month before there's much change. By then, some huge negative departures will have been built up and snow pack should also too, which could also help serve to delay a noteworthy pattern change. Sent from my SM-G965U using Tapatalk

Depends which ensemble you're looking at too, new 12z GEFS looks very cold through beyond d10 and the 06z run only hinted at possible relaxation at the end which takes us almost out to the last week of the month. 00z EPS showed an easing out in the day 10-15 but it too hinting at higher heights near Greenland all the way through day 15. At some point figure this has to end, though the polar blocking has been way more persistent than anyone expected going into this winter, so that probably remains a wildcard. If the past is any guide, the 09-10 block actually lasted into March but by the cold air was gone. I'm not sure how much influence the MJO is having as most phase diagrams have it looping around in 7, with only CFS trying to send it into p8. Sent from my SM-G965U using Tapatalk

In this sort of a pattern, each operational run needs to be treated similarly to an ensemble member. A good way to tell a pattern is active and also prone to less lead time for higher predictability is looping 6-hour QPF or snow on the ens. Starting Saturday there's members that have action every 6-hour block, with certain time periods a bit more favored than others. With multiple lower amplitude short-waves it adds a lot of chaos to the modelling. Sent from my SM-G965U using Tapatalk

Since I think it's meant to be for this thread, the 12z GEM has a really nice event starting Sunday evening and continuing through Monday. Probably would've been better to group together the 7th through 9th because there's a way you can get a longer duration round out of this setup, such as shown by the GEM. The ECMWF runs I cited in medium long range thread had some wave spacing between Sunday and Monday, though it's too soon to tell if we could get one longer event or two shorter events or specifically most favored areas. All we can say is that multiple short-waves that won't be sampled for a couple days lends to lower predictability than last weekend's event. Don't think the threat has really trended downward, gotta take a wait and see approach. The pieces are there for a nice event because of the tight baroclinic zone expected to be in place. Sent from my SM-G965U using Tapatalk

You wrote that before the 12z GEM rolled out haha. Looks really nice for Sunday evening/night through Monday. I think ultimately the later Sunday-Monday period has a decent chance to work out for a solid event. Saturday PM should snow in most of the CWA but needs work to be anything more than a 1-3" type event. Sent from my SM-G965U using Tapatalk