RCNYILWX

If you don't want ice in the LOT CWA, a southward trend won't help us, as it would just shift the sleet and icing zones farther south across more of the metro and surrounding areas. Need a substantial jump south to get significant snow into the CWA, which seems rather unlikely at this point. Still certainly enough time for adjustments north and south in the "wintry mess" zone though. The 12z EPS for instance did nudge south on Wednesday-Wednesday evening with the 850 mb warmth, plus the surface low/trough and front position, while the GEFS nudged slightly north. These 12z changes notwithstanding, I'd hedge south with the frontal position on Wednesday, as long as the lead surface wave remains flatter. The warm sector will be potent for this time of year, but plenty of precip in the vicinity of the front, plus the cooler dense air north of the front often wins out even in spring setups, while in this case the air mass north will be supplied by 1035+ mb high pressure to the north.

I'd recommend grabbing the winter sounding from COD (just have to select winter and generate new sounding) or go to Pivotal Weather which automatically will give a winter sounding. On the bottom right of the winter soundings, you'll see layer energy information, which is the Bourgoin method to determine precipitation types. It's analogous to CAPE and DCAPE, positive energy aloft and negative energy low level. The precip. type tab in BUFKIT uses the Bourgoin method. Any positive energy of 25+ J/kg represents full melting, while sleet probabilities increase at -75 J/kg and below. Even with high positive energies (near or above 100 J/kg), negative energies of -100 J/kg or lower tend to allow for sleet to at least mix in and the higher magnitude negative energies can overcome high positive energies to result in primarily sleet. The preferred profile to use is the wet bulb vs. solely temperature based profile. Two examples of this from the 12z ECMWF below, first from interior far northeast IL and the other from near the state line on WI side of the border. Sent from my SM-G998U using Tapatalk

Yep was going to make that point regarding Alek's post, would have to be a much colder air mass to overcome a milder boundary layer from flow off the lake and get any noteworthy ice in Chicago. Still think there's a scenario in which sleet is higher end in this setup farther south into the metro. Probably tougher for that as currently modeled with the magnitude of the warm nose though, would need stronger low level CAD to refreeze into sleet, while southern WI looks more favored at the moment.

The FRAM (freezing rain accumulation model) estimate output. Ice Accumulation Reference - Forecasting https://training.weather.gov/wdtd/courses/woc/winter/fcst-hzds/ice-storm-accum/presentation_content/external_files/Ice%20Reference%20v1.pdf

December 28, 2015 if the low manages to take a more southerly path toward the area. Sent from my SM-G998U using Tapatalk

A zone of significant icing and sleet to its north certainly plausible in this setup, and severe weather in the warm sector. The sharp baroclinic zone and juiced air mass would still be in play with a weaker system, so given the 1035-1040 mb high pressure sandwiched to the north and northeast, that would bring the freezing rain and sleet zones farther south. As it stands, the 12z ECMWF verbatim showing ice storm criteria ice amounts (including with FRAM estimate) and 1-2" of sleet north of I-88 and into southern Wisconsin even with a fairly deep surface low is a red flag for what could happen with a slightly weaker and farther south low pressure track.

Snowing at ORD and MDW now due to low level lake effect, despite being under the dry slot at the moment. Can best see the echoes streaming in on the terminal dopplers. Edit: Joe/Chicago Storm beat me to it

The HRRR stays deeply saturated enough (-10C or colder) for longer, through about 18 or 19z that would hold onto poorer quality snow. But mid-late afternoon, the cloud temps warm up and then have to wait until toward 00z and beyond to flip back to low quality snow. It's a very tough forecast. Sent from my SM-G998U using Tapatalk

The most recent guidance brings a pronounced dry slot centered around 500 mb pretty far north. If you're in the Chicago area and were excited by the 18z NAM kuchera algorithm output, it's definitely overdone based off what's shown on the forecast soundings. There's still uncertainty with how much of the warm conveyor belt (warm advection) precip gets up into northern IL tomorrow morning, with the NCEP guidance more bullish on that note. After that, the models are in good agreement in loss of cloud ice due to the dry slot and this possibly even causing ptype issues up near the WI border (I'm leaning toward there being just enough saturation to stay as a poor quality snow up there). For much of the Chicago metro and points south, some of the guidance brings the warm nose in, and some is colder, but it's kind of immaterial with the cloud temps around -6C. I'd think we'd still have sleet with the low level wedging and steep lapse rates possibly yielding a convective effect driven flip to sleet at times. However, if the WCB precip misses us, concerned that most of the precip tomorrow is a liquid and some sleet mix, with rain/drizzle vs freezing rain/FZDZ dependent upon surface temps. Eventually, the cloud temps cool off to the -10 to -13C range late afternoon and onward, which would shift ptype to mainly low quality snow through Thursday evening. Lake enhancement prospects also seem likely to be affected by the dry air issues aloft. The snow amounts, even in the WSW within LOT CWA, might be overdone due to the mid-level dry air issues. Roads are probably still gonna be shitty for the Thursday PM commute though.

I'm here this evening - not sure if we'll be able to make any changes this shift, but wouldn't be surprised if there's an expansion by the midnight shift. Sent from my SM-G998U using Tapatalk

They didn't have to issue a warning this morning. Could have waited to make the call on the day shift today. My observation is that they as an office feel like they have to make decisions earlier than they need to and sometimes unnecessarily lock themselves into these situations. Hopefully it works out. Sent from my SM-G998U using Tapatalk

You're better than that.

I buy decent sleet accums on the north end of the warm nose aloft. Good signal for a low level cold wedge and the incoming air mass with this system is legit wintry. The exact location of the heavy snow band remains a challenge because the differences are being driven by variance in the fgen circulation response. Sent from my SM-G998U using Tapatalk

The benchmark for a February torch until it's surpassed is February 2017. 6 days in a row of highs from the mid 60s to around 70 at ORD on 2/17-2/22 and then 2/23 hit 59.

2012-13 is another analog to the current season in terms of low snow to this point. That season ended up with an AN Feb and March to salvage merely slightly below normal for the season at ORD. It also had near misses to prevent an AN seasonal total, and far northern IL did finish above to well above normal. If we don't get a solid event or two the rest of this month, having to rely on March to escape 2011-12 like futility will be a taller order, but not unheard of. 2001-02 is another somewhat recent example that had just under 20" going into March, but had 11.2" in March to finish slightly below normal on the season (I consider ~30" slightly below normal given the year to year volatility of snowfall). Ultimately, ORD often finds a way to get to 30"+, though this season does look to be a challenge to do so.

That Euro run is basically textbook on how it can work and is the probable best case scenario. Mild antecedent air mass and a ~980 mb low taking a favorable track for us are a precarious position to be in. I buy the signal at this point (997 mb low over IND on the EPS mean) that there's more likely than not to be a follow up system to the Tuesday rainer and it's probably our only chance until the last week of February. Sent from my SM-G998U using Tapatalk

Beavis is next level lol. Would probably find a way to complain if he lived in the mountains in Utah where one of the ski resorts has had almost 500" this winter already. Sent from my SM-G998U using Tapatalk

The CFS stuff on their crappy in house site never looks like the output on WxBell and Tropical Tidbits. Progression on that output looks pretty similar to the other ensemble data. Not sure why there's such a large discrepancy. Might be worth emailing CPC. I will say that I personally rarely go to the CPC page for the CFSv2, and don't really look at it much even on the other sites.

Looking at the upcoming pattern, given the MJO influence likely playing a role in flexing the SE ridge, certainly not a cold look and some outright torch days will be in play. That said, the fact that there will be cold air into Canada, northern Plains, northern Lakes, means it's not a pattern not necessarily devoid of snow threats farther south (still would be better farther west you go given the southeast ridge). While the favored corridor overall should be similar to what we've seen this winter, shorter wavelengths this time of year with an already active wave train is how it can work. There have been some operational runs showing this, with a lead warmer cutter and then follow up wave interacting with a temporarily shunted baroclinic zone post fro-pa. It's thread the needle amidst more wet than white threats, but not zero (though pessimism is not unreasonable). After the mild and wet southeast ridge regime, still looking at a possible transition to a better pattern beyond mid month with positive height anomalies in the western part of the EPO domain and potentially -WPO as well forcing the TPV a bit farther south. This may be related to MJO wave propagation and stratospheric evolution. In the last few runs, the EPS has been a bit quicker to go into a colder look, so certainly not a lock yet. Sent from my SM-G998U using Tapatalk

The zonal winds becoming negative are indicative of a SSW, though tropospheric coupling and/or the split or displacement causing effects like 2018 (2013 another somewhat recent example) are far from a given. My post was a little tongue in cheek because of our luck in springs being the one thing we're good at ruining haha.

This is not what you want to see if you want a warm March-April. Sent from my SM-G998U using Tapatalk

The outcome of that run was actually a pretty sizable shift south in the (more meh) snow swath, though to your point, another example of a system with a decent track and much less cold air to work with for the time of year than there typically would be. It's going to be another thread the needle situation where it can work out in a narrow swath if the system is deep enough. Sent from my SM-G998U using Tapatalk

I look at that snow season as one that wasn't far off from a big total at ORD (ended up just slightly below the current normal). Had the big February stretch, but didn't get into the max swath in any of the events in that stretch. Also had several near misses, including the December clippers that favored WI to lower MI, a whiff west and south with the big late March event, and a miss north with the April blizzard. Sent from my SM-G998U using Tapatalk

By February, the pattern finally resembled a more classic La Niña look with amplifying southeastern ridging. It was decidedly un Niña-like most of the time prior to that. I believe the SSW and subsequent blocking disrupted what might have been a mild and active spring. The SPV has had times of being strong this winter, but lack of NAO and AO blocking hasn't been the main driver of the warmth since January. I wouldn't rule out stratospheric effects causing issues in March-April this year because January was warm. This December had a period of pretty strong NAO blocking. 2011-2012 isn't a good analog either because it had a huge PV lobe parked on top of Alaska November onward. Sent from my SM-G998U using Tapatalk

Out here, we had by far our snowiest month of that winter in February and a record tying 9 days in a row of measurable snow. The 2nd half of the month was mild and wet (with a big river flooding event in Indiana and east central IL), but finished exactly normal at ORD following the cold and snowy start. Biggest factor in the cold March-April 2018 was a poorly timed SSW event in the latter part of February that set up an extended period of deep -NAO blocking. April was particularly brutal because it was essentially another month of winter when almost everyone but beavis are craving warmer temps by then. If you want something to ruin spring, a prolonged late season blocking episode is one of the common ways to do it. Sent from my SM-G998U using Tapatalk