RCNYILWX

I'm doing the winds, and another thing that is extremely concerning given the lake levels is the lakeshore flood threat. But as for the rest of the elements, it'll be Carlaw again. Our last mid of 7. New crew tomorrow night, both good forecasters, MTF and Kluber. Sent from my SM-G965U using Tapatalk

Starting to wonder if this event will have similarities to the 12/28/15 major sleet event. The cold press from the north will be similar and in that event we were coming off an incredibly torchy month. We were more concerned about icing threat and sleet became the much bigger deal except near and south of I-80.

Might be the NAM being the NAM until the main wave gets into its grid domain tomorrow. Sent from my SM-G965U using Tapatalk

Hopefully with the addition of RAOB sampling of the southern wave we get some clarity with the 12z cycle tomorrow.

The coarse 850 mb maps on meteocentre unfortunately only go out to 72 hours. It shows >=0C for the entire CWA still at 12z Saturday but would think the CAA would kick in after in earnest based off the surface low track this run has. Clicking back through the 2m temp progs from weather.us would suggest ice/sleet in the northwest 1/3 of the CWA on Friday night into early Saturday. That timeframe early Saturday could corelate to what you mentioned about icing threat extending into Saturday morning prior to sufficient cooling aloft.

12z UKMET looks good for backside snow in northern IL and possibly far NW IN. Only basing off surface temps and surface low track from weather.us so someone would have to confirm if that's accurate. 12z run is slightly east of 00z. Sent from my SM-G965U using Tapatalk

Some good hits in the members for the LOT CWA. Sent from my SM-G965U using Tapatalk

12z Canadian significantly backed off with cold side precip. Barely advisory level snows in the deformation area. And not much ice either it appears.

While a primarily rain event is very much in the cards with a painful miss just north/northwest, it's still well within the envelope of possibility for the deformation snows to nail much of the Chicago metro at this range, particularly I-55 and northwest. As has already been mentioned, there have been important changes in the handling of the southern wave. Also, convection has been known to mess with mass fields of systems, along with the possibility of robbing some of the moisture transport. And there will be a ton of convection south of here with this system. There very well could be an area of warning criteria ice somewhere in interior northern Illinois. However, as laid out in Carlaw's AFD, there are so many points of uncertainty with that aspect of forecast 3 days out. There's reason to doubt huge ice accums with very heavy precip rates forecast, and possibility convection causes more sleet. That said, with the strengthening northerly winds Friday night into Saturday, it won't take huge ice accums to cause significant issues with falling tree limbs and power outages.

[emoji817] What a tough forecast. So many intricacies to it that we won't have a really good handle on probably til Thursday. I'm not doing the grids and AFD for the storm tonight but we're in good hands with my colleague who is taking it on. Sent from my SM-G965U using Tapatalk

The assumptions being made when there's still so little we know about the key mid-level features. Amped/NW of course is on the table, but then we have the 12z operational GFS to demonstrate how that northern stream wave could still suppress height fields and compress the flow enough to keep the southern wave farther southeast. We won't have higher confidence on the track and strength of the southern wave itself yet either for a few days. The GEFS has tended to be more amped than the operational, which we'll see shortly if that continues with the 12z. The EPS mean has been pretty close to the op, but that's with a member spread has left room for the amped/northwest track, weaker/southeast and in between. The 06z members had several that were quite similar to the 00z operational snow swath. For the Chicago area, I think a mostly rain miss NW, a good snow (maybe front end ice Friday night for parts) and a miss southeast with the main wave are all still plausible.

I'd use caution with verbatim surface temps from the GFS. New version hasn't proven yet it properly handles evaporative cooling. That was a chronic bias of the previous GFS, not saturating and cooling the boundary layer properly in heavy precip. Air mass flowing in from the surface high is cold and most importantly very dry (see dew points just northwest of us). That's why it's showing sig icing, due to wet bulbing. Given the amount of precip it's showing with dew points in the 20s, 2m temps would likely verify colder in scenario. Another aspect is the antecedent air mass. I think it's okay out this way and not that marginal at the surface due to that strong high pressure off to the northwest. Recall, to name one example, that GHD II started off with marginal surface temps with a rain/snow mix. Aloft is where the issue lies and why this will all come down to track and strength of the southern wave and the surface low, to state the obvious. As things stand now, Friday night has noteworthy icing potential somewhere in the region.

Beat me to it. Here's the h5 look at the end of the run. Sent from my SM-G965U using Tapatalk

Here are the member snow totals Sent from my SM-G965U using Tapatalk

18z EPS (ECMWF Ensemble) Sent from my SM-G965U using Tapatalk

The tight baroclinic zone over the region indicates potential for strong low and mid level f-gen and associated banding. Don't need a wrapped up system to get good precip amounts in cold sector with that as the mid December event along I-70 corridor showed, along with some of the events in recent winters (Feb 8-9 2018 comes to mind up here). Also, there's good agreement in strong upper jet divergence for large scale ascent. There's lots of ways this could go and it could certainly be a minimal event, but also counter reasons why it could work out. Sent from my SM-G965U using Tapatalk

Although it's not registering as a -EPO on the teleconnection charts because of the strong negative height anomalies along the Pac NW coast, the mid week ridge spike over Alaska due to a deep ULL over the Bering Sea functions as a temporary -EPO to dislodge that very cold air and send it southeastward. Then it looks like another ridge spike over Alaska Friday into Saturday that's trended stronger on the EPS vs yesterday.

That's actually incorrect. Look at the GEFS and EPS ensemble mean 2m temps over the northern Plains and northern Lakes next Friday and Saturday. There's pretty high confidence in a cold surface high being draped north of us based off MSLP anomalies in both ensembles.

Strong ensemble support for that long of a lead time. Both 00z EPS and GEFS ensemble means have a surface low tracking up the Ohio Valley and expansive high pressure off to the north/northwest. Next weekend could be a window for snow for some of us, along with an icing zone in between as you mentioned, in an otherwise fairly hostile pattern. Friday's cold front would temporarily shunt the low level baroclinic zone farther southeast and then the question is what comes of the southwest trough after it ejects. One way to avoid the phasing issues we've been having is to allow the southern stream wave to come up on its own and deepen due to the tight thermal gradient. Just to use the operational runs to illustrate the point, the 00z Euro kept the northern stream wave much farther north, allowing the southern stream wave to come farther north. On the other hand the 00z and 06z GFS brought northern wave much farther south, compressing flow between it and southern wave, which flattens heights and keeps the southern wave moving quicker and farther south. At the very least, some possibility of having more interesting weather to track. Sent from my SM-G965U using Tapatalk

Agree on Morch. The most anomalous weather event on record should be 1 or 2. I think GHD is fine as #1 ultimately because it's the most intense blizzard for the area in modern history so it really stands out to people. As for #3, I'd still keep that as the entire 2013-14 winter because of its place among the coldest and snowiest on record (coldest Dec-March) period and should be at least #2 for snow if not for the ORD measuring debacle on 1/1/14. Would agree with summer 2012 being higher. GHD II we perhaps could've grouped it in with the extreme cold the rest of February. Also I'd have Rochelle ranked higher than 11/17/13 for tornado events in the CWA. Could make a case that 6/22/15 or 6/5/10 are more deserving to be in top 10 for the CWA, but I understand why it stands out to people because of the time of year and the Washington supercell. Finally, I'd swap out the April 2019 snowstorms for the April 17-18 2013 flooding, which was the worst flooding event of the 2010s for the CWA as a whole.

Big news...Pivotal weather now has forecast soundings from the Euro. Sent from my SM-G965U using Tapatalk

Sign me up Sent from my SM-G965U using Tapatalk

Painful miss east Sent from my SM-G965U using Tapatalk

Written by my good friend and one of our lead forecasters at NWS Chicago. Have a happy and healthy 2020 everyone and here's to a fun year of weather. Sent from my SM-G965U using Tapatalk

Cross posting from January thread: Can say with reasonable confidence that January will be active. The big question is how persistently amplified the southeast ridging is and the placement of Aleutian/AK ridging. Getting the ridging farther east into the EPO domain could make for a more than serviceable month for central, western and northern portions of the sub. Farther south and east could certainly be dicey if this weekend and next week's possible window is not cashed in on. The January-February 2019 500 mb composite anomaly below and sensible weather results shows that the general idea being forecast by the longer ranges of the ensembles and Euro weeklies can work out really well for portions of the sub. On the other hand, a too amplified southeast ridge and Aleutian ridging too far west could make for a warm/rainy active month for much of the sub and congrats MSP and north/northwest. I don't think we can say yet for sure that the MJO being forecast to go with amplitude into the warm phases makes it a lock that it'll be a trash pattern even central and west, just that the warm risk is certainly there. If I'm recalling correctly, a good chunk of last January and February was spent in the warmer MJO phases. This shows it can work out for some of us, but did also make for the bad winter farther east and southeast in the sub and points east. Also, I'd much rather have an active month biased warm that at least gives a chance for things to break right for a good event than endless cold and dry. Experience shows us that for a big dog we need at least some southeast ridging. The oscillating going on in later ranges of the EPS shows that we'll be on the edge so we'll have to wait and see which way things are leaning. Finally, with the likelihood of stout low level cold air masses northwest of here and warm press from SE ridge, we'll also have to watch for sig icing events in the battleground zone, similar to last February. Sent from my SM-G965U using Tapatalk