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  • Tim McGill

Finally A Forecast With Some 70s

May Will Get Milder

It seems lately like we have been going backwards with this stretch of cool May days. Tuesday was the eighth straight day with below average temperatures. The last time we had that many cooler than average days in a row was the middle of February. Tuesday was also the fourth straight day with highs failing to get above the 50s at O'Hare.

Things are looking up beginning today. We should finally warm out of the 50s for most areas and hit 60° or more. Tomorrow's date is the first day in spring that we start to average a high of 70° and it only gets warmer from there. This forecast gets us back to about that average temperature by Friday with even a few spots close to 70° tomorrow.

Today will still be cooler than average despite plenty of sunshine. A breeze off the lake will keep us coolest along the lakefront with highs only in the upper 50s but most of us should make it into the lower 60s.

"Cooler near the lake" is an expression we know all to well here. It will apply through the weekend. O'Hare is far enough inland though that highs by Thursday should get close to 70°.

The remote sensing of southern Lake Michigan's surface water temperatures was obscured by some clouds earlier in the week but a more clear picture of the cool water emerged yesterday. The latest remote sensing plot below shows lower 40s near the center of the lake but lower 50s along the shoreline here. Buoys and other observations indicated lower to middle 50s right along the lakefront. Any breeze off of this chilly water will keep things cooler this time of the year.

We will slowly but surely get back to about average over the next few days but the longer range forecasts continue to suggest a surge of even milder air coming towards the end of next week. The temperature anomaly forecast for a week from Thursday shows a lot of brown where there used to be blue. In other words, above average temperatures will be replacing the cooler than average temperatures that have been so common lately. The forecast below shows us about 5° to 10° above average by May 20th. That would mean highs in the middle 70s to around 80°.

The slow but sure warm up is reflected in the hourly temperature forecast for the next seven days A few models have us falling back to near 60° for a high by Sunday but overall the temperature trend is onward and upward.

It's About To Get Loud

The notorious "Brood X" cicadas are beginning to make some noise in about a dozen states including Illinois. They may only hang around for a few weeks but they will make their presence known. Their combined chorus can be as loud as 100 decibels or about the equivalent of turning your car stereo up as loud as it can go.

This particular brood will stay south of the city and show up in east-central Illinois and several other states in the Ohio Valley and out to the east coast. These Brood X buggers impacts one of the largest geographical areas of all 17-year periodical cicadas. Their numbers are huge and can peak at about 1.5 million per acre.

Their emergence in the spring is tied to ground temperatures. Their sweet spot is about 64°.

Climate change means those temperatures are now reached earlier in the year. A study by Climate Central calculated the 10-day average temperature in the region Brood X is found is now running 8° warmer compared to 1970. The emergence Chicago's variety of cicadas is now about four days earlier compared to a half century ago.

Bring On The Rain

There are still some parched portions of northern Illinois in a moderate drought that could use some rain. O'Hare is 1.27" of rain below average for the month so far and down 5.51" since March 1st. The GFS model suggests an unsettled pattern starting late Saturday into Sunday with some hope for showers and then another stretch of rain in the form of showers and thunderstorms about a week from today into the following Friday.

The GFS model spits out about a half inch of rain or a bit more here in total by Monday morning. This would definitely put a dent in the ongoing drought in portions of northern Illinois but even more rain would be needed.

Signal Still Strong For Warmer Pattern

Our return back to a more mild May pattern by the weekend could be a sign of things to come. Both longer range temperature probability forecast favor us for above average temperatures overall. The latest 6-10 day forecast still has us outlooked for above average temperatures overall from May 17th through May 21st with the highest probabilities reaching into northern Illinois. The 8-14 day temperature probability forecast keeps us above average overall from May 19th through May 25th. 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.

Mixed Bag For May Moisture

The longer range precipitation probability forecasts favor us first for above average precipitation then drop us to near normal. The latest 6-10 day forecast has Chicago favored for above average precipitation from May 17th through May 21st. The longer range 8-14 day forecast also has us favored for about average precipitation overall from May 19th through May 25th. I will have an update on our drought situation later this week.

Here is my 7 day forecast:

Today: Sunny & not quite as cool High: 62 (55 lakeside)

Thursday: Mostly sunny & milder Low: 44 High: 66 (58 lakeside)

Friday: Partly to mostly sunny Low: 46 High: 69 (cooler lakeside)

Saturday: Partly to mostly sunny, shower possible late Low: 49 High: 69 (cooler lakeside)

Sunday: Mostly cloudy, on & off showers Low: 50 High: 68 (cooler lakeside)

Monday: Mostly cloudy, scattered showers mainly early Low: 55 High: 72

Tuesday: Partly to mostly sunny Low: 56 High: 73 (cooler lakeside)



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