RCNYILWX

If we're to get a closed off low lifting close to due north like the Euro run will also have to watch for the magnitude of the high pressure to the north. The setup offered by the Euro is somewhat similar to 12/28/15 (Edit: the event referenced by@WI_SNOWSTORM), though that one had a stronger HP to the north/northeast. Should the surface ridging extending back west across the northern Lakes trend stronger, that could play a big role in sleet vs freezing rain distribution. 12z run verbatim looks icier farther north than 00z run did without looking at the ice accum output, still borderline IP vs ZR for a time around 12z north of I-80 using 925 mb temps and winds as a proxy. You could also keep the surface (away from Lake Michigan) at or below freezing for a longer duration with that odd due north track because that would prolong the period of northeasterly sfc winds and associated evaporative cooling. Would be an impactful mixed precip event for the LOT CWA as modeled on the Euro, especially north half and away from Chicago shore. Lots of time to go on this one and pretty much a wide variety of outcomes on the table.

Red flag for me was seeing 925 mb wind speeds being at 40-50 out of the east-northeast. When combined with the progged h8 and h9 temps, that's a strong signal for cold/dry air damming. Sleet will be something to watch for in this setup if we get a wound up low like on the 00z ECMWF. Sent from my SM-G965U using Tapatalk

Just with respect to the 00z ECMWF operational run, I think there would probably be a much larger zone of sleet. Valid 12z Friday when both Pivotal and WeatherBell algorithms are showing primarily freezing rain, I'd guess those 925 mb and 850 mb temps would be supportive of sleet, especially north of I-80. Don't have access to forecast soundings to confirm though. Also looked at the GEM for Tuesday night into early Wednesday and it appears the algorithm is accumulating ice when the soundings for at least a portion of the icing zone with northward extent would favor sleet. Does appear there would be a freezing rain zone south of the sleet zone. Regarding the overall 00z suite, focusing on wave 2 alone, all we can say is that the potential for a high impact event is there, but lots of moving parts. Going to take a while to sort this one out. Wave 1 looks to produce a swath of advisory to low to mid range warning snows, with a mixing zone south, and even wave 1 has a good deal of uncertainty associated with it. Sent from my SM-G965U using Tapatalk

Yeah, can't blame the sentiment. But now that the secondary low/southern wave is slowing to not coming up until Friday, that's an eternity in model land, and clearly not the final solution. Sent from my SM-G965U using Tapatalk

Fwiw, the 18z EPS doesn't have a lot of east outliers with the secondary low, has more tracks that would be too far west for much snow here, with a slight westward adjustment of the mean. It would be nice to get some of the front end snow, but failing that, I think overall best chance (not necessarily a good one yet) to get a 6"+ snow is with the secondary low/wave 2. While there's been a tendency for weaker/sheared/more east with secondary development, the magnitude of the eastern ridging makes a case for Alek and Hoosier's worry of a more amplified nw track cutter/rainer. I'd still lean toward miss east being a bigger worry, but miss NW is not too far off. I think we're in the game here, but as always need a lot to work out right to get a good event locally. Sent from my SM-G965U using Tapatalk

That pattern could produce snow events because of the assistance of the strong -NAO to modulate the +EPO some. It's certainly not a cold pattern. I'm not on the optimism train, just saying that's not a lock to be snowless like this month has been. The 850 mb positive anomalies are not obscene and the mean 850 mb 0C line is near or south of I-70. If we get a lower amplitude wave, could snow here with that. Sent from my SM-G965U using Tapatalk

To your point, here are the low locations on Wednesday and Thursday night into Friday for the 12z EPS, followed by individual member total snowfall. Good support for a weaker primary and a stronger secondary, so I agree that we're in the envelope. Unfortunately it's another pretty much thread the needle setup. Sent from my SM-G965U using Tapatalk

Well, the UKMET is something... One thing we can say for sure is it's not even close to the 00z GFS aloft. Other than that, much different evolution than we've seen on the other operational runs. Sent from my SM-G965U using Tapatalk

Yep just noticed the same thing and edited my post to reflect that. The GEFS still appears to follow the op more than the EPS does, 30 members vs 51 on the EPS may have something to do with that. That said, seeing a few members go toward a strong secondary might be a sign. Sent from my SM-G965U using Tapatalk

We'll see here shortly with the UKMET and then the Euro which way things are leaning. This past setup, I think the GFS having the support of the UKMET was key. It can be prone to some big swings but it's a solid model per verification stats, we just have less data available from it. If UKMET supports a GEM-like solution like the 12z run did and the ECMWF and EPS bumps again, we might be seeing a trend toward a GEM-like outcome. Edit: and vice versa could be true too. Did notice that the spread of the GEFS members increased, which despite the op-like solution being still more favored could be a sign of lowering confidence in which scenario is more probable.

Even though it was warmer than normal, January 2012 happened to be the best month of that winter, two decent storms and the only AN snow month of the cool season. The second event in January 2012 had nice high ratio fluff with the longest duration of 1/4 mile visibility in snow at ORD and MDW since GHD I and caused nightmare travel on a Friday afternoon commute. Sent from my SM-G965U using Tapatalk

It appears to have some better front end snow, but wouldn't think in reality the sfc low track on that run would be supportive of it. Sent from my SM-G965U using Tapatalk

Probably...so far UKMET is a no Sent from my SM-G965U using Tapatalk

GFS performed best with the current setup, way north with the primary and better east for secondary, but it's been spotty at best otherwise (by far the worst for the big dog in the east). I'd say overall the modeling has been poor, it seems to struggle in fast flow patterns. Hopefully with the big time -NAO signal coming up that can help slow things down and improve the modeling. Sent from my SM-G965U using Tapatalk

Not gonna get sucked back in yet, but the 00z GEM came way back south on the 30th-31st, bringing warning level snows into northern IL, including QCA and much of the Chicago metro (which right there probably means it's wrong [emoji38]) except for the far south. We'll see if the UKMET and ECMWF shift at all tonight toward a more favorable evolution, like what the GEM depicted.

Not at the office so I'm not sure what went on with that. Seems like there's another chance to get on the board tonight if any of the occasional more robust snow showers move over ORD. This holiday mood dust is better than nothing. Did a lights tour around Naperville and the snow falling made for a nice vibe. Sent from my SM-G965U using Tapatalk

Both winter 2009-10 and 2010-11 had deeply -NAOs, 09-10 pretty much wire to wire, and were good winters for Chicago. The blocking in 2011 eroded in time for GHD I. That's not a statement about how things may go here the next few weeks, but just a note to point out a -NAO can be good here. With respect to moving forward, the ensembles also show a +EPO look with the big NAO block (backed up by the forecast teleconnection indices), so that could help prevent it from being more torchy and *maybe* assist in keeping some systems farther south. The deep blocking may come too late to help us next week though.

Certainly could, as the passage of the vort will be accompanied by a reinforcing surge of cold advection. At least according to the NAM depiction, with the lake effect + synoptic enhancement could see squally type stuff swing out your way during the day on Friday. Sent from my SM-G965U using Tapatalk

I had noticed the 12z RGEM brought in some light (around 1") accums to parts of northern IL late Thursday night into Friday morning. The models have been very consistent in a strong 700 mb vort wrapping around the stacked upper low, but main question has appeared to be available moisture. Tonight's 00z NAM showing some light QPF with this feature, so things might be trending toward getting a DAB+ down for Christmas morning. Sent from my SM-G965U using Tapatalk

Glass half empty view... It just doesn't want to snow here and we're a lock for BN snowfall. This week is very frustrating. Aside from a few model runs that drew everyone in, was never really that excited about big snow for the Christmas Eve threat, just as something thread the needle that could work out if everything came together right. Figured that we could meh our way to an inch or two but that's seemingly impossible now. Even the clipper warm advection wing this morning was a total fail. Glass half full view... Still have plenty of time left and that example of 1998-99 and a few other examples on Hoosier's list. 2012-13 was an interesting one too, because we had several near misses that winter that could've resulted in a much different outcome. The northern tier counties actually ended up rallying for a well AN snowfall winter. Another example not on Hoosier's list: 2014-15. November was cold and had some snow but only a T in December, tied with 2 other winters for least snowy December. Seemed like getting to AN that year was less likely but of course GHD II happened. Ya never know. Sent from my SM-G965U using Tapatalk

Aside from the derecho, which I say thankfully wasn't bad at all where l live, definitely a more boring year weather wise. Noteworthy events in the LOT CWA in chronological order: January 10-11 significant lakeshore flooding. The winter side of that system was a big old bust, but the lakeshore flood certainly wasn't, as it was the most significant episode since Halloween 2014 and perhaps since the February 1987 event. - April 7th wind blown sig severe hail in far northern Illinois, some up to 3" in diameter, which is really impressive for an April event. The event was also noteworthy for the SPC handling it quite poorly in the outlooks (removal of general thunder in the day 2 update from some of the areas that had sig severe hail yikes), while it was a pretty synoptically evident good early season severe setup for days. - May 14th and 17th flooding events in the metro. The 17th was the most widespread flash flooding in the metro I think since the April 2013 flood and locally the most sig flooding I had seen where I live in Naperville. We issued our first (and warranted) considerable tag FFW on the 17th. The footage of the Chicago River flooding in the South Loop in particular was pretty nuts. - June 9th Cristobal remnants, more for the novelty of that setup. - June 26th severe event, with some sig severe wind reports. It was actually a pretty respectably widespread event by recent standards and it and April 7th are the most notable severe episodes of the year aside from August 10th. - June 27th flooding. A lot less fanfare than the May flooding because the rural southeast CWA was hardest hit, with actual observed rainfall of over 8" in southern Newton County and radar estimates up to 10". Had this rain occurred over the metro, we would've had a high end flash flood event. It was also my first issuance of a considerable tag FFW. - August 10th derecho and QLCS tornado outbreak, with the strongest tornado in the Chicago city limits since 1976. - Persistent summer warmth, including Chicago setting its warmest summer on record. It loses significance for me because we believe the ORD ASOS site has been affected by local construction to skew temps warmer there, including August being first summer month in our entire dataset in which ORD finished warmer than MDW. Summer 2012 stands out as much more noteworthy and memorable than summer 2020. - November 3-10 warm wave. Up there with mid to late February 2017 as the most impressive stretch of out of season warmth in recent history aside from Morch 2012.

The GFS hasn't caved yet, but I would be surprised if it ends up being more correct on the setup. It's on its own with the early development of a deep surface low way up in the northern Plains from a completely different handling of the northeast Pac wave. Edit: Unfortunately, the 12z GEFS doesn't tell us much because it appears that ensemble remains too non-dispersive with the operational. Meanwhile, the GEM is pretty similar to its previous runs, just on the deeper more phased side of the spectrum, so in that sense would not be good for the LOT CWA but a good event in MN, northern IA and WI. The NAM at the end of the run looked interesting and pointed toward a phased solution, though caution advised in trying to extrapolate out from the end of NAM runs. Either way, it's certainly more in the Euro and GEM camp.

IDK, I'm not trying to be overly optimistic, but I don't think the most recent Euro weeklies and GEFS extended (I don't really look at the CFS and it's probably getting discontinued anyway at some point) look terrible for January. It appears the EPO will average positive but it doesn't look to be due to a black hole over Alaska but northeastern Pacific and northwestern North America troughing that's pretty common in La Nina's. The -NAO signal is still there to mute heights some in the east. If there's enough dateline ridging (-WPO) and a huge vortex doesn't set up over AK, that typically provides good cold air discharge that can bleed from western and central Canada into the northern Plains and northern Lakes. I see there being opportunities and probably averaging near to above normal temps but potential for some decent cold shots assuming cold does build into the Plains. Don't get me wrong, it's not screaming great pattern or anything, but it looks more serviceable than the dumpster fire that has been December, except for a few lucky spots.

Those coarse resolution CFS maps don't make any sense. Even if you account for background climate signals, there's no mid and upper pattern configuration that would torch the entire continent. If Alaska is torching that extreme, then there's gonna be a trough over at least the eastern half of North America. If a good chunk of the CONUS is torching, Alaska will be cold due to ++EPO from the TPV parking nearby, like in 2011-12.

I think there's a decent enough chance at this range to get some modest accums but certainly lean against the fun phased outcome from the 00z Euro two nights ago. Overall there's been a slight uptick in ensemble probabilities of light (1"+) accums. With the cold air mass coming in for Christmas, will take what we can get for the holiday mood and to get on the board if tomorrow morning doesn't produce measurable at ORD. Edit: Re. IWX's tweet, a little surprised at the 'significant rain and snow' wording because that would require the phased solution. Otherwise, best chance for a significant precip event looks to be in the eastern Lakes and points east, probably east of their CWA. Edit 2: Just saw 06z Euro, and it looked potentially more interesting extrapolating out from hour 90 than the 00z run ended up being. On the Euro ensemble though, currently very little member support for a heavy snow swath in the western and central sub, though a rough estimate is about half of members have light to moderate snow swaths nearby.