RCNYILWX

I think that, however much one wants to ascribe CC to things, the reality of the winter climate on the west side of the lake at this latitude (Chicago area and west) is one of volatility. These forums became really popular back in the late 2000s and early 2010s. 07-08 through 10-11 happened to be the best 4 year stretch for winter enthusiasts in this area since the late 1970s. Since that stretch, it's been much more mixed. The highs of the highs (13-14 and GHD II) and the lows of the lows (11-12 and 16-17) and a lot in between. Last year was extremely cold and active just west and north of here through Feb after a break in December-early January and we had a good stretch of winter from mid January through beginning of Feb. 17-18 had fairly lengthy doldrums but also had a memorable stretch of 9 straight days of measurable snow and the bitter cold of late December-early January. This really isn't unusual for our winter climo. Think back prior to the 4 year run, the 00s were not great until then. 00-01 had one great month, 01-02 was one of the worst winters until March 02 (which still sucks when you think about it), 02-03 was only good east and southeast of here and 03-04 was also not good here. 04-05 had one good month in January and 05-06 was torchy with only 26" at ORD. The 90s also were very mixed, with the best event of the decade being of course the 99 blizzard. The 80s were mixed for snow as well, 81-82 the big snow season of a decade otherwise known more for its extreme cold shots. So I understand why there's a lot of complaints about this winter, it hasn't been good for winter interests after the early start. If it doesn't turn around in the snow department, then it would rightfully deserve a low grade, but it wouldn't be unusual in the context of winter climatology. Stringing together good stretches and getting things to break our way with storm tracks or not is what separates the good from the mediocre winters and often one or two events separate good/mediocre from bad. It's the winters like 13-14 and the late 70s are the exception to the rule and are once a decade or every couple decades type phenomena. Having 4 consecutive good winters like 07-08 through 10-11 is also rare on the climo spectrum, but a lot of us are constantly hoping for a stretch like that.

Kuchera totals Sent from my SM-G965U using Tapatalk

That is odd. 00z GEM looks close to what the general guidance consensus has been and nothing like the 00z GFS. If the GEFS (different physics package from op and all) diverges significantly from the operational, may have to chalk up the op to being an outlier if ECMWF is close to previous runs at 00z. Overall, it's hard to ascribe much to one of the models handling a feature differently as being anything but something that can happen in this range. And With the main wave still well out over the Pacific, we'll have to wait and see. But want to see more support for an operational GFS like outcome before getting too concerned by it. Sent from my SM-G965U using Tapatalk

00z GFS is not what you want to see for a good event...except for MN, central and northern WI, the UP and northern Lower MI. Sent from my SM-G965U using Tapatalk

Yep just looked, ticked north slightly, but can tell it also lost some of the beefier members, as the 24 hour mean came down over WI and far northern IL. At this point, can be considered noise level changes. Sent from my SM-G965U using Tapatalk

To go back to this and your original post, I don't think surface low track is that important early on. Barring major changes, with the air mass we'll have in place, evaporative cooling will further knock down temps aloft so that we'll start as snow. But if you're trying to denote the areas favored to stay snow the entire event, then that's fair to start from the IL-WI border. Given latest data, I'd be surprised if most places, except maybe far southern CWA, don't start as snow and easily accumulate. The question becomes how quickly temps warm aloft with stout southerly flow and how much resistance is given by evaporative cooling. That's where the models rarely ever overestimate and often underestimate WAA. But even in this case, a solid front end thump can bring a few to several inches of snow prior to changeover. That's what WPC is favoring in their day 5 outlook, with most of the CWA in 70-90% probs for 0.25"+ liquid equivalent in snow/sleet accums, supported by the GEFS and EPS. In fact, the 12z EPS (haven't looked at 18z yet) had 80+% probs for 24 hour 10:1 snow accums of 3"+ for I-80 and north.

Do you mean rain including freezing rain or just plain rain and snow line? You're ignoring the strength of the departing surface high. My biggest concern is WAA resulting in a quicker flip to an icy mix but I'm not concerned about temps below freezing in the metro until later Friday night, surface low track dependent. The surface low being well southwest of us, with the surface warm front well south and the high slowly shifting east puts us in a good spot to start as snow everywhere with questions on duration. Sent from my SM-G965U using Tapatalk

I don't trust how long into Friday evening the 12z Euro verbatim keeps 850 mb temps Conceptually with a setup close to as depicted would favor 3-6 hours of snow thump then mix/change to sleet then freezing rain and then plain rain, maybe flip back to snow on back side. Looks like a mess for the Friday PM commute as things stand now.

Good to see the Euro come in colder aloft. It looks like the 500 mb wave is less amped than the previous run and eventually the surface low comes out farther south. It's a solid antecedent air mass with the cold dry high pressure influence slower to depart and 850 mb level starts out quite dry and doesn't moisten as much as 12z run. But still odd to see the 850 mb level staying that cold due to evaporative cooling alone with straight southerly flow of 30-40 + kt. The southerly flow aloft is weaker than the 12z run, but still plenty for strong isentropic lift. Sent from my SM-G965U using Tapatalk

Recall that's essentially what the non NAM guidance was showing for Feb 12, 2019 ice event. Sent from my SM-G965U using Tapatalk

Looks like a decent icing setup for a time because of the position of the high pressure off to the east and warm front stays south. Your east southeast wind trajectories are pulling from lower dew point air off to the east which would help with evaporative/wet bulb cooling. I do wonder if with that exact setup shown on GFS the surface warming would occur quicker once wind goes more southeast due to lack of any snow cover over the region. Sent from my SM-G965U using Tapatalk

Even though the GFS is showing it staying snow for a decent amount of time, I don't like that setup to stay snow as long with southerly flow at 850 mb for a while. Would think the thermal profiles would verify warmer than modeled in medium range and it would be more of brief snow to sleet and freezing rain here. The surface may be more conducive to staying colder with the departing Arctic high influence and winds more east southeast. Need changes in the mid-level pattern to feel better about a snowier outcome locally.

00z EPS (ECMWF ensemble) has continued theme of last few days of going to a very cold pattern look out in the day 10-15. MJO is at a very high amplitude phase 4 crossing into 5, warm phases for the winter explaining the very pronounced east/southeast ridge currently. According to information posted on other subs by Don S, this progression has historically supported the MJO wave keeping enough amplitude to progress into the colder phases. Assuming this holds, the idea of a sustained colder pattern unfolding later in January and beyond holds merit. The GEFS has also basically gone over to the EPS idea out in the extended. I still think our best chance for a more significant spread the wealth type of event would be prior to the pattern going in the direction of the EPS, if it's on the right track. Thereafter, the exact position and orientation of mean western and Alaskan ridging and downstream trough over will determine whether we go to a very cold and dry clipper type pattern (ex. Feb 2015 after GHD II) or a more active but just as cold pattern (ex. January-February 2014). Sent from my SM-G965U using Tapatalk

Since UKMET has seemingly performed very well with this event based off 00z consensus of the surface low track and deformation axis orientation being close to what it's consistently shown the past few days of runs, I'm inclined to buy it. We do have to account for the risk that the moisture transport gets robbed into the defo zone as cyclone alluded to. Hopefully the high res models that explicitly forecast convection have a clue on that. It appears the higher resolution guidance is also trying to resolve mesoscale banding due to strengthening low and mid level frontogenesis over the area later in the afternoon into the evening, especially at the 850 mb level. So some of the irregularity to the QPF field may be related to trying to resolve areas of subsidence outside the banding. Assuming things don't fall apart, which is possible, there could be a 3-5/4-6 hour period of legit winter conditions with mod-heavy snow and blowing snow centered on the evening. Wouldn't be surprised to have near blizzard conditions in open areas. Sent from my SM-G965U using Tapatalk

UKMET came out late tonight, looks like with a fairly similar track and getting northern Illinois into the deformation precip Saturday PM. Sent from my SM-G965U using Tapatalk

Alek to Geos bullseye in IL. Lock it in. Sent from my SM-G965U using Tapatalk

Agree there I've been thinking farther south in the area showing freezing rain. Would think with westward extent too where you have a higher chance of staying below freezing deeper into the cold air. This is all obviously dependent on the exact sfc low track which we haven't completely nailed down yet. Bringing up the 2015 event again, what I found really impressive with it is that the mesoanalysis at the time and reanalysis indicated that the 850 mb temps south of I-80 got as high as +8 to +10 but yet that's where the most significant ice accums were in the CWA. Sent from my SM-G965U using Tapatalk

This sounding over northern IL from the 12z Euro illustrates the point I've made about the model ptype algorithm potentially overforecasting freezing rain and underforecasting sleet. In the lower right of the pivotalwx soundings, they have temperature and wet bulb profile information. The positive and negative energies in J/kg are from the Bourgoin layer energy ptype technique. When there is a warm layer aloft sufficient for full melting, whether ptype is sleet or freezing rain depends on the negative energy below it. Two of my co-workers have done extensive work on modifying the Bourgoin method based off observed soundings and ptype observations from the events used and they're getting a paper published in AMS. Many of the NWS offices in the area use this method for ptype derivation. In it, the studies done show that when negative energies get greater than -100 J/kg, sleet probs steadily increase and -125 J/kg or more is 100% sleet probs with lower freezing rain probs even if there is more positive energy aloft. Based off the wet bulb profile showing -156 I think that sounding would support sleet more than freezing rain even though best guess precip type is listed as freezing rain. Sent from my SM-G965U using Tapatalk

Maybe it's to the point where the GFS is overcompensating for the effects of the high pressure to the north? That's a bit of a wild card. I do think with the angle of approach of the surface low, it will favor areas west of the lake staying below freezing because you don't lose the northerly component to the wind and that's pulling from very cold and dry air to the north. That said, GFS seems too cold. The ECMWF tends to do pretty well with temps so would have to lean towards what it's showing with the tracks being very similar. It'll be an interesting test case for the new version of the GFS. Sent from my SM-G965U using Tapatalk

I think they're using 48 hours but I could be wrong on that. Sent from my SM-G965U using Tapatalk

The 00z EPS, in a big change in recent days, went to a broad west coast ridging and Alaska ridging out in day 10-15. PNA trended back to neutral on the teleconnection charts. So the hope there would be to not have an amplified western PNA ridge. If that sort of look verified as shown on the EPS it might be an active clipper/hybrid pattern versus the true dreaded CAD when the PNA ridging becomes more amplified and east based. Also that sort of pattern would be good for the lake effect belts. I've read some LR gurus wondering if EPS is rushing pattern change some, but it's done pretty well thus far this season. Edit: As posted above, that look would more likely favor the east coast for larger synoptic systems but still no signs of a -NAO. Sent from my SM-G965U using Tapatalk

January 12, 1960 The precip will bridge Friday and Saturday so it may be tough to do the daily record but maybe a decent chance to set an unofficial record for 2-day total for the month of January. The calendar day precip record for meteorological winter is *probably* safe lol. 4.47" on December 2, 1982. Here's the link to the attached Chicago's daily record listings for January and then you can access the other months from there: https://www.weather.gov/lot/January_Daily_Records_Chicago Sent from my SM-G965U using Tapatalk

We're thinking sleet will be a much bigger issue in our area. The surface pattern and progged 925 mb cold drain are eerily similar to 12/28/15. Check out the reanalysis page on weather.us to compare to the model consensus for this event. Due to the warm start to the season, the lake is fairly mild for this time of year, so maybe the lakeshore struggles more with p-type. But west of the city, selling the huge ice totals on the verbatim web based outputs. With the surface low strengthening to sub 1000 mb well south of us and nearly 1040 mb high to the north that's an ideal setup to drive the low level cold wedge southward on strong northeasterly flow aloft. Depending on the exact track of the surface low, there could be a potent WAA surge toward Saturday evening that may flip areas back to ZR or even plain rain. Sent from my SM-G965U using Tapatalk

Just took a look at 00z NAM and it would suggest big time sleet on Saturday roughly from ORD southwest to about VYS. I took a photo of one of our internal ptype derivation grids, negative energy low level, from the modified Bourgoin energy technique, which the original can be found on BUFKIT and pivotalwx soundings (lower right). All the areas in the dark blue would be sleet, with the white/pink area in between a transition IP/ZR zone depending on sfc T. This is valid 21z Saturday. Sent from my SM-G965U using Tapatalk

Some tonight in northwest LOT CWA is a decent possibility I think. Sent from my SM-G965U using Tapatalk