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  • Tim McGill

More April Showers For Chicago

Mostly Dry Friday, Rain Returns This Weekend

Just some spotty showers or sprinkles possible early today but more April showers in the forecast this weekend. We saw the first significant rain here yesterday in two weeks. It may help diminish a drought that was beginning to develop. More on that below.

After a cloudy start to Friday we should see some sunshine emerge this afternoon. Our northern suburbs will be last to see some clearing so it will be cooler there compared to areas south of the city. Highs today should range from the middle to upper 50s near the Wisconsin state line to near 70° well south of Chicago.

It will remain breezy at times today with winds diminishing a bit on Saturday. Gusts today should approach 30 mph.

The threat of rain drops off sharply this afternoon and then jumps back up for Saturday.

Wet At Times This Weekend

Keep the umbrella handy this weekend. The GFS model shows the best chances for rain will be Saturday and later Sunday into early Monday morning. There may be a few thunderstorms later Saturday too. Rainfall amounts may be heavier Saturday compared to Sunday. Most of next week should be dry.

The GFS model squeezes out an additional three quarters of an inch to nearly an inch of rain in total from today through Monday morning.

O'Hare reported .36" of rain on Thursday. It was the first significant rain there in two weeks. We are still running nearly a half inch below average for rainfall this month and nearly two inches below average since March 1st.

Yesterday's rain was especially appreciated in Lake and McHenry counties. According to the latest update from the U.S. Drought Monitor, some of our far northern suburbs were in a moderate drought before the rain fell on Thursday. There is also an expanding are of northern Illinois that is considered "abnormally dry" and one step away from entering a drought.

The majority of Midwest wildfires come in March, April and May. The dry start to spring is cause for concern after recent wildfires lead the governor of Wisconsin to declare a state of emergency. Our recent rain has helped but as I discuss below, the longer range forecasts are calling for a drier than average pattern.

Northern Indiana held steady compared to last week's update from the U.S. Drought Monitor. A little over 2% of the state remains in a moderate drought with nearly a quarter of the state abnormally dry.

The drought has deepened a bit out west. Nearly two-thirds of that region is in at least a moderate drought and almost 60% in a severe drought or worse. This too is cause for concern after last year's record breaking wildfire season out west.

Dropping From Above Average To Below

The hourly temperature meteogram compares many different forecast models. Our highs will remain above average today and tomorrow. Average highs this time of the year are in the middle to upper 50s. We drop back below average for the middle of next week. Highs Tuesday through Thursday will be in the middle 50s but only 40s along the lakefront.

The GFS model's temperature anomaly forecast has Illinois covered in blue Wednesday morning. Our temperatures early that day will be around 2° to 7° below average. That means lows by Wednesday morning may dip down into the 30s.

Strong Cool Pattern Signal

April is still running 12° above average even after cooling off by nearly 15° Thursday compared to Wednesday . The longer range forecasts continue to hint strongly at a cooler pattern though coming for the middle of the month. The latest 6-10 day temperature probability forecast has us outlooked for below average temperatures overall from April 14th through April 18th. The 8-14 day temperature probability forecast has us favored for below average temperatures overall from April 16th through April 22nd too. Average highs in Chicago move from the upper 50s to near 60° during this period.

The even longer range Subseasonal Experiment (SubX) forecast is signaling a warmer than average end to April. The temperature anomaly forecast for the week ending April 23rd has us outlooked to be above average for the period. The forecast for the following week ending on April 23rd has us outlooked to stay above average overall. Average highs for the end of April are in the middle 60s.

Will Drought Deepen Here?

The longer range precipitation probability forecasts still signal a drier than average pattern into the middle of the month. Rain this week will help but if the forecasts verify, more of the Midwest might develop drought conditions. The latest 6-10 day forecast has Chicago favored for below average precipitation from April 14th through April 18th. The longer range 8-14 day forecast has us outlooked for below average precipitation overall from April 16th through April 22nd too. The risk for spring flooding is above average for many area rivers. More on that below.

Spring Flood Risk Forecast

The National Weather Service considers many risk factors for spring flooding. They include snow cover, soil moisture, and current river conditions.

"A significant snow cover with high water content can increase the chances of flooding once warmer weather melts the snow. Elevated soil moisture conditions reduce the amount of rainfall that is soaked up by the ground and increase the amount of water that then runs off into area streams. Above average river levels reduce the river rise required to reach flood stage, while below average river levels would require an increased amount of river rise to reach flood stage."

The map shows the locations where there is a greater than 50% chance of moderate or minor flooding during March through May 2021.

Their latest forecast suggests the flood risk is above average for many of our area rivers. The Des Plaines and Fox rivers in particular need to be watched closely.

Here is my 7 day forecast:

Today: Spotty showers early, becoming partly sunny pm, breezy High: 63

Saturday: Cloudy, rain likely, isolated t-storm possible Low: 47 High: 62 (cooler lakeside)

Sunday: Mostly cloudy, showers likely, breezy & cooler Low: 46 High: 58

Monday: Partly to mostly sunny Low: 45 High: 62 (cooler lakeside)

Tuesday: Partly to mostly sunny Low: 40 High: 56 (cooler lakeside)

Wednesday: Partly to mostly sunny Low: 38 High: 58 (cooler lakeside)

Thursday: Mostly cloudy, scattered showers, breezy Low: 49 High: 63



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