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If you're learning about this stuff, an easy way to see the important changes at 500 mb is looking at run to run trends of the h5 anomalies. Pivotal weather has a nice model trend loop tool that goes back 3 days worth of runs. Very easy to see the changes just from 06z to 12z run. The PV lobe over Hudson Bay being farther north allows the eastern positive height anomalies (ridging) downstream of trough to our southwest. These big picture changes are in addition to a much more favorable short-wave orientation and ejection described in some of the recent posts. And to top it all off as part of all the favorable changes for a stronger system, textbook right entrance region of an anti-cyclonically curved upper level jet streak that peaks at over 200 knots.

Noteworthy shift south. From a LOT CWA and my backyard (as a snow enthusiast like most on here lol) perspective though, we're in the threat zone. It's hard to tell if this particular run was under dispersive, though it kind of seems that way. Nonetheless, still several significant hits up into the metro and I think key takeaway is confidence continues to grow in a swath of impressive precip/snow, wherever it ultimately sets up. I wouldn't argue with feeling a bit worse about chances at this juncture in the far north CWA and northwest CWA and points west, though also still plenty of time. It was roughly around this lead time I believe from GHD II, that several guidance members shifted main axis south. This is not to imply that things will go a certain way because of how it went on some past occurrences, but that we're still pretty far out.

Excellent point. To see QPF output of that magnitude, have to assume a tremendous amount of latent heat release. With a juiced baroclinic zone to work with due to finally open Gulf trajectories advecting northward to it, you can get sufficient downstream height rises to counteract suppression from the TPV lobe over Hudson Bay. You don't want that feature to be overly suppressive, so the risk is dry Arctic air mass really sharpens cutoff, but without it, the background pattern could support a much farther north baroclinic zone. Sent from my SM-G998U using Tapatalk

The full operational ECMWF runs have actually had quite a bit of variability the past few days. Just last night had a similar situation. Changes aloft were overall fairly subtle from the 12z run that resulted in farther south orientation of the heaviest banding. We're still well far out enough that various aspects of this setup of far from being nailed down. You can point to a particular feature on the operational runs to be rightfully concerned about if that's how it plays out. We still have plenty of other data to say that this run and the other operational runs fall well within envelope of solutions that we've seen of the ensemble members. Sent from my SM-G998U using Tapatalk

I know the Canadian ensembles (GEPS) aren't nearly as commonly cited as the EPS and GEFS, but they too were more juiced with the 00z run than the 12z run. The operational run is not something that can be fully discounted, but viewed in the context of the ensemble shows that there's a majority of members with an evolution that results in main snow swath farther north. This is one of the reasons I don't really get too caught up in the UKMET. Without access to the ensemble, there's no way to know how it fits within the spread of the ensemble output.

00z GEFS members, mean (with sample points), 6"+ probs, and 12"+ probs. Hopefully 00z ECMWF and EPS hold serve if not improve. Sent from my SM-G998U using Tapatalk

Lurker on this thread (originally from College Point Queens) taking a short break on a busy day out here at NWS Chicago. Have been thinking that the snowfall distribution may end up somewhat similar to February 2013 and late January 2015 (hopefully a hair west of that one). The models have been consistent in depicting the 700 mb fronto bisecting Long Island. You'd expect the heavy snow band to set up just west of the modeled f-gen band on the cold side of the f-gen maxima. In events like this with a lot of wind, one of the impediments to getting widespread Kuchera ratios (among multiple flaws with the methodology) is fracturing of the dendrites. Also you'll have some subsidence either side of the heaviest band. But then within that band, the Kuchera ratios should be attainable despite the wind. Assuming the mid-level fronto does intersect Long Island, would expect beefy totals under the band with 18"+ certainly possible, especially if residence time of the most intense banding can be maximized. Elsewhere you should have ratios at or a bit above climo (so figure 11-13:1) or so.

And eastern region offices still do them. I think what we settled on (using winter storm watch and warning for higher end LES) is probably more confusing to some users. My preference would've been either to stick with status quo like eastern region went back to, or to simplify the name to a Winter Weather Watch, Warning, and Advisory, and specify the phenomena in the What bullet in the text. Storm implies a larger scale system, vs a mesoscale convective phenomena like LES. Sometimes it can be both, such as last Feb for Chicago and NW IN, so LES warning or advisory wouldn't have been ideal either. Sent from my SM-G998U using Tapatalk

It's not super practical from a going into an event time-frame to do that sort of consulting with other offices. More common would be to have webinar presentations where tips and suggestions for LES could be shared by forecasters in some of the more LES prone offices. Some of our forecasters also spent part of their careers at MQT, GRR, IWX, to name a few. So they bring that experience with them. Additionally, while big LES events are less common overall in our area, we do tend to get at least a few lower end to moderate events, so our forecasters with several to many years of experience have that in their mental database. We also have had some good west and south side of the lake events within the past 10 years to build from, of course including last February. Gino just shared a lake effect pointers presentation with the staff as a refresher for our experienced forecasters and to assist our newer forecasters. Just the near term changes with tonight's event show the challenges we face in forecasting and trying to message these events. Sent from my SM-G998U using Tapatalk

Fun/busy shift today. Had we not inherited a watch for Lake County Indiana, might have done things differently. Fresh in my mind, had the Sunday morning event that I worked during, that had warning type impacts into Lake County and probably an hour or two away from that south of downtown Chicago. Scenario of a more progressive band and/or earlier mesolow causing heaviest snow to slip back out over lake or band going nearly stationary for a few hours were all plausible scenarios. So with the watch already for Lake County, opted to expand into Central and South Cook zones and treat it more like a warm season convective watch. Lake effect is convection, so always higher uncertainty than synoptic at shorter lead times due to mesoscale uncertainties that can't be ironed out until some of the observational trends show the cards of how it may play out. Not too concerned about the HRRR/RAP trends yet until seeing the rest of the 00z CAMs. We did hint at higher impacts getting into northern Cook zone (north shore burbs) though decided to just keep watch for the zones we went with at noon and let the evening shift resolve the headlines. We have two of our better LES forecasters there (Gino, and Kluber, who made warning upgrade for Lake IN on Sunday), so we're in good hands this evening. Edit: In case anyone comes across this later, didn't want to mix messages with the updates done by the evening shift tonight. Great example of the nature of the beast that is LES forecasting. We trended toward the more western convergence placement on the day shift, but that still wasn't enough as it appears from latest guidance and upstream obs. We know these sorts of shifts are within the realm of possibility, but also still can only go by the guidance we have at hand to put out the forecast at the time.

With a super busy shift at LOT today dealing with LES threat, tried to do most I could to add some general details in extended. Asked neighboring offices if they'd consider tossing in some sleet and freezing rain chances and they opted against it, so I blanketed CWA with sleet/freezing rain chance late Tuesday night through Wednesday night. In reality obviously not the whole area would be in threat zone for icing on top of sig snow threat, but the surface and lower level pattern strongly supportive of a zone of sleet and freezing rain with cold drain from 1045 mb high to north. Hopefully most of the CWA ends up mostly snow and we get a big event (or an appetizer round) followed by the main course. Sent from my SM-G998U using Tapatalk

The EPS has been more unstable lately than I'm used to seeing it. GEFS has been more stable lately, but that doesn't mean it'll be right either. [mention=14]Hoosier[/mention] are we allowed to post the WxBell teleconnection charts on here? Large divergence of the EPS and GEFS becomes apparent by about 1/30-1/31. Prior to that they both show EPO popping back to positive around 1/27. This is only temporary on the GEFS as it goes back negative on the 31st and stays that way through the end of the run, while the EPS never gets back to a -EPO (though it's not strongly positive). PNA handling also quite different, with GEFS going -PNA by the 30th and then staying deeply negative, while EPS has only a temporary -PNA until 2/4 and then is neutral to slightly positive thereafter. The active period next week with deep southwest trough and downstream ridge amplification is pretty high confidence, though the details will be low confidence for a few more days. Beyond that, it'll probably be at least a few days until we see a decided jump toward one of the main ensemble suites or a relative compromise. For our purposes, would prefer the recent GEFS depictions later in the run to the EPS. 12z EPS runs have for whatever reason had a worse look than the 00z runs, though GEFS depiction still more favorable regardless with -EPO/-PNA/-WPO.

After my post late last week, there's certainly been more volatility out later in the ensemble runs, particularly on the EPS. Perhaps this is partially related to the MJO being stuck in the COD, reducing medium range predictability That would be due to several of the MJO phases (especially when MJO wave has higher amplitude) have well correlated mid level pattern configurations associated with them in DJF and JFM. Just the past two days, the EPS has alternated from a not great look late in the run, to serviceable/not bad last night, to objectively bad today. It's a note of caution about the lower predictability anyway that far out. Meanwhile the GEFS has seemingly been more stable later in the run and hasn't backed off -EPO/-WPO/-PNA. I know the EPS generally verifies better than the GEFS but I wonder if more stable/persistence is the way to go for a bit. The window of favorability is still there in the first week of February, but it's far from a sure thing to benefit any given part of the subforum. The nature of the pattern with a -PNA trough digging into the southwest and downstream ridge amplification could be overamped, but the hope is the heights could be suppressed enough by the TPV near Hudson Bay to avoid a warm cutter. There's been a signal on some of the operational runs out toward and beyond 10 days of larger storms that would fit the pattern thoughts, so I'd say give a few more days to monitor the signal on the ensembles before getting too concerned about what the op runs are showing. After the first week of February, it's really low confidence in the way things are headed since the ensemble means are quite divergent at the end of their ranges and the teleconnection forecasts are also quite divergent on the EPS and GEFS. Until our potential favorable window, looks like we'll be in a mostly quiet period away from the LES belts and watching that east coast beast late this week. I remain cautiously optimistic in getting a good storm during early Feb. Interested in seeing thoughts from other long range gurus/enthusiasts on here.

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