RCNYILWX

Northern IL/Chicago metro centric Wave 1: DAB, slight concern for freezing drizzle mixed with light snow/flurries after the initial fast moving snow band. Wave 2: Looks good with a currently favorable track for most except perhaps far northeast IL. Also favorable is the very deep DGZ with the moderate omega well aligned. Should be a fluffy, high ratio snow except on far northern fringe. Narrow enhanced f-gen band could put down a corridor of 3-4", outside shot at 4-5" if rates really max out and ratios are over 20:1. The main limiting factor is duration with only about 6 hours of solid snow to work with. Wave 3: Track has ticked south a bit, but still too far north for more than 2-3, maybe 4 hours of snow in the warm advection wing of the clipper. Any farther south we can get the track the better. Not uncommon to have brief heavy rates in these setups due to strong isentropic ascent from the warm advection and steep mid-upper level lapse rates. Sent from my SM-G998U using Tapatalk

End of January-First Week or Two of February Thoughts: The ensemble signal for an active and colder leaning pattern has not gone away. In fact, the signal has grown in recent days. Barring major changes, chances will be elevated for a regional winter storm (significant to major) or two during this stretch. Expecting a short period of moderation in the wake of the early-mid next week cold shot as the pattern reshuffles from persistent western ridging and eastern troughing, with positive height anomalies sliding east from the western ridge finally breaking down. Key Factors: - Very impressive poleward ridging in the western EPO and WPO domain (western half of Alaska and the Aleutians for a -EPO and a deeply -WPO): This will keep the tropospheric polar vortex (TPV) on our side of the pole, and a continuous stream of very cold air masses and Arctic highs from western and central Canada due to cross polar flow. This can be seen through: strongly positive height anomalies spiking northward over western AK and the Aleutians during the second half of the EPS and GEFS runs; modeled 1030-1035ish mb highs and consistently positive MSLP anomalies from western Canada into northern Plains; and sharply negative 850 mb anomalies locked in from western Canada to the northwestern parts of the sub-forum. This all signals very strong ensemble member agreement. - Increasingly -PNA in response to the strong upstream ridging: This will finally allow the return of short-wave troughs breaking underneath the EPO/WPO ridging and coming ashore on the west coast, along with the return of southeast ridging. The TPV staying on our side of the pole and migrating back southward in response to the north Pacific ridge spiking will keep the southeast ridge in check, with only modest positive height anomalies over the southern and eastern US. This will bring a favorable west-southwest flow pattern (storm track) and also lessen the risk for very warm cutters. 7 day precip anomalies poke back into the positive territory for the latter part of the EPS and GEFS runs over a good portion of the subforum. This will occur while large high pressures should be in place to the northwest for more classic synoptic surface patterns. NAO: Should average out positive, though with stable cross-polar flow regime, not seeing it playing a huge role. Main issue would be for any more amplified southwest flow systems not having an upstream block, so suppression would be less likely. While it's certainly been a very frustrating winter for many in the subforum, the upcoming pattern objectively offers reasons for optimism. Of course we can't quite lock this in yet, though the fact that the ensembles haven't backed off the favorable look at the end of January into February and this signal has grown as we inch closer is a good sign. So in sum, after the current clippers only aside from LES northwest flow pattern, signs continue to point toward a pattern change that will offer elevated chances for a regional winter storm or two. Beyond the potential favorable stretch seen on range of the 15-16 day ensembles, if the north Pacific ridging retrogrades farther west, that will allow the southeast ridge to flex more, though the poleward ridging is so strong that pattern shouldn't instantly go toward torchy, and is likely to stay active with high confidence in a -PNA. Here's hoping that we get a few events at least as good as late last January and February.

The New Year's Day snowfall record is 5". Don't screw up under pressure. Sent from my SM-G998U using Tapatalk

Jumping back in after a long hiatus... As long as the wave is not much more amped on Tuesday like the GEM/RGEM, I think ORD finally breaks the epic measurable snow drought (Edit: Getting 0.1" isn't a high bar to clear, right?? LOL). Support is there for a burst of heavy snow before the changeover to rain (see LOT AM Long Term AFD). Similar set-up to 12/29-30/20 with much milder antecedent air mass, but importantly, still very dry, leaving room for strong evaporative cooling before WAA overwhelms. Re. next weekend system, it was certainly eye catching to see such good op model agreement so far out. As you'd expect, tons of ensemble spread but still a good signal at this lead time for a system to affect the region. Belated Merry Christmas to everyone.

agree, and for the LOT CWA, the slower timing similar to the 12z Euro would up the ante. Sent from my SM-G998U using Tapatalk

Seriously, it's hard not to get lulled a bit. Thinking back to how things unfolded, it was a dead ringer for me to June 30th 2014, just shifted north. As it turned out, both that event and tonight had quite similar and extremely high end environments. I think we handled the event pretty well, but in hindsight, we could have/should have hit the strong tornado threat harder based on how the environment evolved. Going back to my first statement, I can absolutely say that the first round not producing like we thought it would be capable of changed expectations some for round 2. In that the data pointing to a higher end threat kind of sneaks up on us in a way. It happened with the 2nd derecho on 6/30/14 and in a way did tonight. We were thinking the same thing - we needed the rain, but didn't need *this* to get the much needed rain. Horrible situation, strong QLCS tornado at night in highly populated suburbs when a lot of people are already sleeping going into the work week.

That turned into a night I'll never forget at the weather office to say the least. The tornado tracked just north (less than a mile as the crow flies) from my house and then probably a quarter mile or less from my mother in law's house. A main west east street (Bailey Road) just north of my area has an entire row of powerpoles knocked over along with large trees blocking it. There's a large tree blocking the north south road (Coach Drive) through my subdivision (Naper Carriage Hill). My area was relatively unscathed just south of the tornado circulation where it appears we got the RFD like winds on the south part of the MV, leading to spotty tree damage, though relatively significant in spots. I spoke to someone with Naperville Electric when I was checking out the damage at Coach and Bailey and it sounds like the fairly bad damage goes back to just south of Bailey a bit to the west of Washington Street. Since I can basically roll out of bed to the damage, I might be helping out with the survey. Pretty shook and wired from this experience. It's kind of a helpless feeling when it hits so close to home. But also can say that these are the nights that make this job rewarding as we can literally save lives with the warnings we put out. Hope no one I know doesn't have any friends or family hit by the tornado and that there were no fatalities. I'm also saddened by parts of the town I've called home since I moved out here in July 2010 along with nearby suburbs being struck by terrible damage from this tornado. Sent from my SM-G998U using Tapatalk

We fixed it on Monday. Prior to that, it had been running noticeably warm even at night vs ORD and MDW. Sent from my SM-G998U using Tapatalk

The recorded length of the less than 1/2" precip streak at ORD may have been a bit misleading. Certainly possible one of Jan 30th or Jan 31st had 0.5" liquid equivalent. MDW 3sw COOP had 0.52" on 1/30 and 0.50" on 1/31. Then ORD just missed the higher totals and liquid amounts to its east in Feb. Still an impressively long dry/quiet stretch. We did correct the April CF6 to remove the erroneous TS occurrence on April 5th. Unsure why, but lightning distant in a few of the obs that day at ORD triggered the climate program to call it an on station TS occurrence. Based strictly off the Chicago obs we have, it shattered record for latest into year of a TS occurrence, with previous latest being May 3rd. I'm a bit leery of putting too much stock in it as a record because especially going back to when the official site was not an airport, we don't know what counted as a TS. Is it possible that lightning out over the open waters of the lake counted as a TS? Also even with airport observers, prior to modern remote sensing of lightning and ASOS in the mid 1990s, was there subjectivity in what counted as a TS observation? What we can safely say is that this year by far had the latest first TS at ORD in the ASOS era.

What's become clear is that the outdoor mask mandates were never needed, and likely relied on faulty guidance to justify them. At this point, most adults who wanted to be vaccinated have gotten at least their first dose and a majority of those who haven't probably are hesitant or are straight up anti-vaxxers. The CDC's new guidance finally recognized that we should no longer be tailoring society to protect people who largely don't want to be, or the hypercautious. Particularly outdoors, the vaccinated have essentially zero risk and the unvaccinated have extremely low risk, especially in the warmer months. I doubt many are going to continue to heed outdoor mask mandates and they're not usually enforceable anyway. Indoors will probably be a different story. There may be increased instances of people refusing to wear masks in stores, but I suspect for a while longer that most people will see it as a minor inconvenience not worth causing a fuss over. The indoor mask ordinances do need to be rolled back sooner rather than later though.

You never know with these intense f-gen bands. I think if it snows heavy enough for long enough, a couple sloppy inches on colder surfaces certainly possible. The most likely outcome probably still is mostly white rain aside from a sloppy coating here and there (similar to what 3km NAM has been showing), but will be interesting to see what we wake up to. Sent from my SM-G998U using Tapatalk

Revisiting this, for some reason we weren't included on the SPC collaboration call even though a few of our counties were in the MD. We probably would've been fine adding those few counties into the watch had we been included on the collab call. Sent from my SM-G998U using Tapatalk

The good news for this month vs what happened in 2012 is it'll be cool for the next week and pattern overall is forecast to be on the active side into the medium-long range. If this month doesn't come in at or above normal and the ridge starts to build in June, that would become more problematic. The rain we've gotten here in the southwest suburbs over the past week, while not a lot, has helped keep things pretty green. Sent from my SM-G998U using Tapatalk

June has historically been the most active month locally. Hopefully May picks up after next week and June is rocking. If you can go into June having already had an active season, that's a bonus. Sent from my SM-G998U using Tapatalk

I'll always regret not issuing an advisory on the day shift the afternoon before 4/14/19. Was strongly considering it, but with no buy in from the neighboring offices, opted against it. That was definitely a special case, as it turned out basically every box checked for heavy snow rates and overcoming the warm ground and high sun angle. I see it as a good mental check now when there's a possible solid late season snow event, knowing what went into that event helps the forecast at a challenging time of year to forecast snowfall. Sent from my SM-G998U using Tapatalk

Maybe for the southeast part of the CWA? The other aspect that's part of the headline decision in marginal situations is time of day. It's now after midnight down there, which means much less vehicles on the roads. With no impacts to this evening's commute and snow ending well before the morning commute, can't really justify putting an advisory out for that long. The potential for slick spots can certainly be messaged by various means, such as a Special Weather Statement, graphics, social media posts, retweeting INDOT, etc, without putting an advisory out.

If there were noteworthy road impacts, the case would be more defensible. Any snow higher than a trace today would technically be historic, no? The record for the date was T so if it merely set the new record at 0.1", that warrants an advisory? From the IND Evening Update AFD: "Road impacts appear to be minimal at this time, with the majority of the accumulations occurring on grassy areas." There's really no need for further debate on it, with no real travel impacts, advisories are typically not issued. Certainly some gray area and the product has been more commonly issued for sub-advisory criteria impact-based reasons in recent years, but this event doesn't hit that bar in the Indy area, regardless of the historic nature of the snowfall.

Liking the upstream satellite and radar trends across South Dakota w.r.t. tomorrow locally. Several CG strikes and GLM flashes, and Aberdeen, SD was reporting 1/4SM +SN a couple hours ago.

Really solid f-gen band, snowed hard enough here at LOT that we've been down around 1/2sm visibility and gotten a few tenths on the grass and car tops. Just wet roads and parking lot, though part of the sidewalk outside has a minor dusting. The meso models (aside from the RGEM) and the Euro certainly did best with band placement. Main issue will be that the band is too transient to support any legit accums and impacts. Sent from my SM-G998U using Tapatalk

We definitely got NAMmed by this event, and also the ECMWF being more bullish for several runs didn't help. I was never too excited about the heart of the metro and points west and northwest. But I was overly optimistic for the southeast 1/3 or so of the CWA while the NAM still had global guidance support from the Euro. I suppose some surprises are possible if rates end up heavier along the lines of some of the meso models. Failing that though, Wednesday now appears to have a higher chance of interesting weather. Sent from my SM-G998U using Tapatalk

Agree, shades of April 2, 2016. The NAMnest is modeling 45-50 dBZ cores on Wednesday, owing to those near dry adiabatic 0-3km lapse rates. One lacking aspect on Wednesday is the weaker wind fields, whereas April 2, 2016 had 45-60 mph wind gusts. Could envision 30-40 mph gusts on Wednesday in squalls. Sent from my SM-G998U using Tapatalk

I'm skeptical of how much falls during the day Tuesday if rates aren't heavy. And a majority of the guidance has the heavier snow toward and after sunset Tuesday evening mostly east of the CWA. I was thinking back to Feb 24 2016 when the northwest fringe just outside the heavy snow band that nailed the south burbs into northwest Indiana was essentially white rain despite coming down at a good clip at times. And that was in late February.

Completely agree, I think that it's gonna rip in that rapidly intensifying defo zone Tuesday evening, 1"+/hour type stuff. I currently like south burbs and south in LOT CWA into NW/N IN and lower MI for this event. Sent from my SM-G998U using Tapatalk

NAM fits my general idea for this system so I'll ride it lol. 850 mb front much quicker this run than 18z, so baroclinic zone sets up farther southeast and the top down and bottom up intensification of the synoptic system takes place just too late for most of the IL metro, on Tuesday evening. Looks like non efficient accums, mostly on colder surfaces, during the day on Tuesday over northern IL. Sent from my SM-G998U using Tapatalk

The ECMWF ensemble suite shifted a bit southeast vs 12z, but still a good hit of QPF across much of the Chicago metro. Agree on treating the UKMET as the outlier that it is for now. The Euro, GEM, and NAM all have initial f-gen driven banding starting Monday night over northern IL, that would probably be a narrower area of appreciable accums. Big question mark is when and where does the synoptic system really take off as mid-level wave goes neutral to near negative tilt, and allow a strong deformation axis to develop. The 12z operational ECMWF more or less is the middle ground between the farthest northwest NAM and farther southeast 12z GFS and GEM. At this point, seems more likely than not 1-3" amounts from the initial banding into the metro, with Tuesday PM the wild card. If the intense defo banding sets up just southeast, subsidence northwest of it would probably quickly shut off meaningful snow. Weighing probabilities at this still pretty early juncture, within LOT CWA, southeast of I-55 and particularly northwest Indiana probably have the best chance of a higher impact headline worthy event. Sent from my SM-G998U using Tapatalk