Chicago Storm

+TSFZRA here.

It's like a tropical downpour right now, and still only 31. Rain is way too heavy to have much, if any, accum though. With heavy rates like this you need temps in the mid-20's or lower. So looks like QPF amounts will work out, but ice accrual amounts will under-perform due to high rates in a more marginal temp environment.

Solid FZRA right now, sitting at 29.

Widespread thunderstorms from the Quad Cities down into W. Illinois.

Pea size hail report in QC area.

You should do well up there with the ice. Temps still in the upper 20's there currently, and might not go above 32 the whole event.

Yea, we're definitely in disagreement lol.

Suburbs to me go out to DKB-Morris-IKK. Those areas on in to the main metro are out of the equation for decent icing.

There's no way they would downgrade at this point...but it's pretty clear a significant ice threat is not happening in the metro, or even the suburbs at this point. I-39 area on towards the QC has the best chance for highest amounts.

Decent amount of TS in SE. Iowa right now.

ARR 35 and JOT 36. This one might be over before it starts for some areas under headlines.

A lot of the higher end guidance from last evening has come in warmer and a bit north this morning. One thing that hurts is that the SFC flow becomes more easterly, instead of being more northerly...which will help bring in more modified air. So there is high bust potential today...and at this point I'd say its more likely than not.

The RAP, and some other guidance, is ice storm warning worthy for the heart of the axis. .

Did I mention, lol? .

lol is lol. .

Indeed "warmer" and north. If that trend continues, likely can write this one off for much of the area.

Tue-Wed looks fairly good, and I could see an axis of ≥0.25" ice accrual across portions of the area. Wed-Fri is much more iffy...Could be snow, ice or rain.

The presence of CAPE on some guidance suggest TSFZRA being quite possible.

In addition to the above, ORD tied the record low max temp yesterday of 1 (1971).

1.7" at ORD and 1.9" here from yesterday and last nights clipper.

Other Chicago cold stats... Coldest Windchills: 1. -60 1/10/1982 2. -59 12/24/1953 3. -58 1/20/1985 4. -53 1/17/1982 5. -52 1/30/2019 5. -52 2/9/1933 7. -50 1/18/1994 8. -48 1/16/1977 9. -48 1/18/1930 10. -44 1/15/1994 Coldest Noon Temps: 1. -21 1/10/1982 2. -18 1/30/2019 3. -17 1/20/1985 4. -16 12/24/1985 5. -15 2/9/1933 5. -15 1/22/1936 5. -15 1/16/1982 8. -14 1/18/1994 8. -14 1/6/2014 10. -13 1/16/1977 Coldest Low Temps On Record: -27 1/20/1985 -26 1/10/1982 -25 12/24/1983 -25 1/16/1982 -23 1/30/2019 -23 1/19/1985 -23 1/17/1982 -23 12/24/1872 -22 1/21/1984 -21 1/31/2019 -21 1/18/1994 -21 12/23/1983 -21 12/22/1872 -21 2/9/1899 Coldest High Temps On Record: -11 1/18/1994 -11 12/24/1983 -10 1/30/2019 -10 1/25/1897 -8 2/9/1899 -7 1/16/1977 -6 12/23/1983 -6 1/29/1966 -6 2/9/1933 -6 1/4/1884

ORD is back up to 0, which ends the streak at 53 consecutive hours below freezing (If I counted correctly.) This makes it the 4th longest such streak on record. Most Consecutive Hours Below 0: 1. 98 Ending 12/26/1983 11AM 2. 66 Ending 2/4/1996 2PM 3. 60 Ending 1/11/1982 8AM 4. 52 Ending 1/31/2019 11PM 5. 48 Ending 1/21/1985 8AM 6. 45 Ending 1/19/1994 2PM 7. 44 Ending 1/6/1988 1PM 7. 44 Ending 1/16/1994 12PM 9. 43 Ending 1/17/1977 1PM 10. 42 Ending 1/17/1982 11PM

No doubt the winds were the issue. ORD had winds of 5-15mph all night, as did other metro OBS sites, which kept temps from dropping much. As you said, with no CAA associated with the winds, there was nothing to significantly drop the temp. Out west, the wind situation was much better...though there were still issues. You would see temps drop quickly with calm winds, only to have winds kick up to 5mph and temps rise...with that progression having occurred for a while at many OBS sites. There was just enough gradient on the northeast side of the ridge, preventing winds from totally going calm out west, and be much lower in to metro...which would have lead to much colder temps everywhere with perfect radiational cooling conditions. Probably would have seen sites like SQI/RPJ/FEP/ARR/DPA end up near -40.

DPA and ORD can't really be compared, even when removing the newer development around ORD. It is very developed around ORD overall, with dense business parks and dense suburban areas surrounding, and ORD is also much larger overall. With DPA it's a small airport...It has a "large" rural like area just to the north heading towards Wayne, and then also south with Fermilab, and also to the east in less populated northern portions of West Chicago. If anything, PWK is a much better comparison to ORD. PWK has dense suburban area and dense business parks to the north, east and south. Only real difference is the narrow forest-like area along the Des Plaines river just west. This is why PWK and ORD often have similar temps on the hotter days in the warm season and colder days in the cold season.

Have had light snow here for the past several hours.