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  • Tim McGill

From Flirting With Frost To 70s In Six Days

Updated: May 11, 2021

Slow But Steady Warm Up

It was almost a wintry end to our weekend. A gusty northeast wind combined with unseasonably cool temperatures to make it feel like the 30s much of Sunday. Valparaiso even reported some wet snow early in the day. While it is unusual to get snow this late into spring it certainly isn't out of the question.

Here are some important dates when it comes to late season snow in Chicago:

  • Latest last date of a trace of snow or more of snow: May 25, 1924

  • Latest date of measurable snow (.01" or more): May 11, 1966

  • Latest date of 1" of snow or more: May 3-4, 1907

No snow in sight but it could be cold enough for frost tonight away from the city and yet another chance for frost comes Tuesday night into Wednesday morning.

First we have to deal with more 50s for highs today. This will be the third straight day O'Hare has failed to warm above the 50s. Highs should top out in the lower to middle 50s for most of us today with only upper 40s lakeside. These are typical temperatures for late March. After our warm start to May with back to back 80s we have now slipped to about 1.3° below average overall for the month.

A cool breeze will keep coming off the lake through most of this week. Highs will be stuck in the 50s today and tomorrow before finally climbing into the 60s by Wednesday.

After a mix of sun & clouds today with a few spotty showers our skies should clear out tonight and allow for temperatures to tumble into the lower to middle 30s north and west of the city. This sets the stage for some light frost again tonight into tomorrow morning.

A slow but steady warm up is coming though that will take our highs to near 70° by Saturday. 70s are more likely Sunday and into at least early next week.

Average highs climb to 70° or more by May 15th. We could climb to nearly 10° above average by a week from Tuesday with highs near 80°.

It won't exactly be "weather whiplash" but there will be a big but gradual swing in temperatures between tomorrow and the following Tuesday. We will wake up to temperatures around 10° to 15° below average Tuesday morning (lower left image) and by next Tuesday temperatures will bounce back to around 10° above average (lower right image).

Rain Still Needed North

Areas south of the city got soaked with more than two inches of rain on Sunday but north of the city remained mostly dry. The GFS model suggests it should stay mostly dry here through at least Friday. There may be a few spotty showers today especially south of I-80. There is even the potential for some rumbles of thunder and gusty winds with a few cells. Tuesday through Friday should be dry.

The forecast for precipitation from the GFS model through the weekend is fairly sparse. The range of rainfall in total is from as little as a few hundredths of an inch to about a quarter of an inch. If this forecast verifies it means the ongoing drought from near and then north and west of the city will deepen. O'Hare picked up a paltry .12" of rain on Sunday and is now an inch below average this month and down over five inches of rain since March 1st.

Milder May Pattern In Long Range Forecasts

After our cool and even cold at times weekend we can now look forward to a return to milder May weather. The long range temperature probability forecast both favor us for a warmer than average pattern. The latest 6-10 day forecast still has us outlooked for above average temperatures overall from May 15th through May 19th but the probabilities are low. The 8-14 day temperature probability forecast keeps above average overall from May 17th through May 23rd. Average highs for this period are in the lower 70s.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast has been consistently calling for a cooler pattern recently but the latest forecasts now favor the Chicago area for near normal temperatures for the end of May and start of June. The average highs for this period are in the middle 70s. The temperature anomaly forecast for the week ending May 28th has us outlooked to be about average overall. The forecast for the following week ending on June 4th has Chicago about average overall too.

More Moist Middle & End To May?

The longer range precipitation probability forecasts continue to favor us for a more active pattern that could help alleviate the drought in portions of the Chicago area. Both forecasts have the Midwest and most of the middle of the country outlooked for above average precipitation. The latest 6-10 day forecast has Chicago favored for above average precipitation from May 15th through May 19th. The longer range 8-14 day forecast also has us favored for above average precipitation overall from May 17th through May 23rd.

Here is my 7 day forecast:

Today: Partly to mostly sunny, spotty showers High: 54 (48 lakeside)

Tuesday: Mostly sunny Low: 37 High: 56 (50 lakeside)

Wednesday: Sunny skies Low: 39 High: 62 (cooler lakeside)

Thursday: Partly to mostly sunny Low: 44 High: 66 (cooler lakeside)

Friday: Mostly sunny Low: 47 High: 68 (cooler lakeside)

Saturday: Partly to mostly sunny Low: 50 High: 70 (cooler lakeside)

Sunday: Partly to mostly sunny Low: 51 High: 73 (cooler lakeside)



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