Hoosier

00z Euro looks a little south, fwiw.

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 905 PM CDT Fri Apr 26 2019 .UPDATE... 826 PM CDT Main forecast update this evening was to upgrade the far northern tier of counties along the WI/IL border to a Winter Storm Warning, with confidence growing for mainly all snow and high totals for these areas Saturday morning into Saturday evening. Have maintained the Winter Storm Watch for the I-88 corridor in northern IL, with lower confidence on rain/snow trends remaining. Guidance still indicating a period of strong forcing is likely on Saturday, associated with approaching mid/upper level trough and surface low along with persistent and strong FGEN. While the area may remain in a warmer air mass at the start of Saturday, guidance pretty consistent with a colder pocket of air moving across southern WI and northern IL during the morning. Although boundary layer conditions may initially be on the warmer side to offset snow, the arrival of this colder air and strong forcing with dynamic cooling should help any rain moving across far northern IL to transition over to a rain/snow mix by mid/late morning, and then soon after all snow. Do think a cooler trend with temps seems more probable for areas in the Warning in far northern IL given the setup, and have trended the forecast this way. This has provided a slightly quicker transition through midday, with all snow then expected in the afternoon through the evening. The arrival of steeper lapse rates and instability aloft is still appearing likely in the afternoon, and have continued slight chance thunder. This all will support a band of heavy wet snow to fall in the afternoon, with hourly rates of 1-2 inches still possible within the main band. Expect snow totals within the warning to be around 5 to 8 inches. Snow may initially take some time to accumulate on pavements, however, this heavy snow will soon quickly overcome the warmer temps. Snow accumulating on the pavements, greatly reduced visibility along with winds gusting to around 40 mph will support hazardous travel Saturday afternoon. Further to the south, along the I-88 corridor, confidence still remains on the lower side with rain/snow trends. This lower confidence includes where a likely very sharp snow gradient will setup. Still tough to say how this system and precip trends will evolve along this corridor, however, it`s possible that a southward trend with this snow could continue. Nonetheless, with this lower confidence, have continued the Winter Storm Watch for this corridor. Further to the south, mainly rain is still appearing likely with a chance of showers and thunderstorms in the afternoon. The warm sector of this system is appearing to stay south of the CWA on Saturday at this time, but it`s possible it could clip locations south of the Kankakee river valley. If this were to occur, will need to monitor the slight possibility for an isolated stronger storm. Rodriguez

The northern tier seems pretty locked in for a warning criteria snowfall... or at least close enough to warning criteria. Could make a solid argument to upgrade that tier below that is still currently in the watch. Unfortunately for LOT it pretty much bisects the metro area, so the ramifications of handling it wrong would be magnified.

A nice thing about a storm at this time of year is the late sunset. You don't get frequent chances to watch it rip in daylight after 7 pm central/8 pm eastern.

00z HRRR is taking the surface low fairly solidly into Missouri... not just ride the border.

Today's high at ORD was 63. I searched and could not find an instance of a 60+ degree high on the day prior to a 6"+ snow in Chicago, so that could be interesting to monitor. There have been a few instances of highs in the mid/upper 50s on the day before a 6"+ snow. Some may recall that it was warm right before the big snow in January 1967. It was warm but not 60+ on the day before: 1/24/1967: 65 1/25/1967: 54 1/26/1967: 32... 16.4" snow 1/27/1967: 31... 6.6" snow

Don't have the link handy but if you google iem archive you might be able to find it. They have an archive of past watches/warnings though the data is incomplete the farther back you go. I'd bet money that LOT has never issued a warning this late.

As far as leaf out, is this about what it looks like for you folks up north? Obviously not a uniform process, but I'd say this is fairly representative of the landscape locally.

I am sold on some accumulation around here but not buying into the heavy amounts on the GEM and a couple of the hires models. I think a couple inches is a good guess with some potential for more. The thermal profiles are really teetering in the afternoon so can't rule out a snowier surprise.

Euro Kuchera basically has 10:1 in the main band, when comparing that map to this

Indeed. The mid month storm was unusual enough and now we are looking at a potentially unprecedented occurrence in Chicago metro, at least in the past 135 years or so.

Lake temps are generally a couple degrees warmer than the mid April snow, so for areas around northeast IL I would expect similar influence to a couple weeks ago (which wasn't that much away from areas right near the shore), maybe just a tad more pronounced.

Northern burbs are basically a lock. Question is farther south.

Kind of a substantial difference between the NAM and RGEM.

Euro suggests high end advisory snows for Chicago... maybe flirting with warning criteria especially toward ORD.

0z Euro continues south.

850 mb and 925 mb

The 03z RAP is fairly cold aloft... actually would even be a threat to mix in snow around here if it weren't for the warmth in the lowest couple thousand feet.

1"+ calendar day snows at Rockford, Milwaukee and Madison on/after April 27. The Rockford record book in particular looks like it could get slapped silly. Rockford: May 1, 1940: 1.5" April 30, 1907: 1.5" April 27, 1979: 1.0" May 11, 1966: 1.0" Milwaukee: April 30, 1907: 5.0" May 10, 1990: 3.2" May 3, 1935: 3.2" April 30, 1994: 2.8" May 10, 1902: 2.0" April 30, 1888: 2.0" May 1, 1909: 1.9" May 9, 1923: 1.2" April 28, 1909: 1.0" April 29, 1907: 1.0" Madison: April 30, 1994: 7.8" May 3, 1935: 4.8" May 10, 1990: 3.0" May 2, 1945: 1.9" May 2, 2004: 1.2" April 29, 1996: 1.0" April 27, 1988: 1.0"

At this point I am thinking about 6-10" in the heavy band. Weekend timing is better than weekday but the roads should pretty much become a disaster for anybody out in it. Am concerned about the impact to power lines and the leafing out trees with those amounts plus gusty winds.

Hopefully the title change doesn't jinx the storm.

Agree with your thoughts. Generally about 6-8:1 but perhaps locally/transiently higher.

Will have a lot of RAOB sampling on the 12z Friday cycle. The system moving through the region today/tomorrow should stop this from shifting too far north.

Rates should be pretty good, so I would expect it to stick on the pavement.

Still some time to back down a bit but overall to me this is shaping up to be every bit as significant as the mid April storm. You could argue maybe more... if not from an amounts perspective then just because it's a couple weeks later.