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  • Tim McGill

Cool Pattern Keeps On Coming

More Like Late March Than Early May

It was short sleeve shirts and shorts weather over the weekend when highs hit the 80s. Monday was mild with 70s but yesterday we fell into the 50s for highs. Jacket weather may stick around through at least the weekend depending on your tolerance for the unseasonably cool air that is coming.

We could remain cooler than average well into next week. There is even a chance for some light frost by Saturday morning More on the longer range forecast below.

O'Hare hit 58° for the official high on Tuesday and Northerly Isle only managed to make it to 52°. Today won't be quite as cool but will still remain at least a bit below average. Average highs for today's date are around 67°. We should see highs near 60° or a bit above away from the lake and only in the lower 50s lakeside.

One of the culprits for these cooler temperatures is a wind off of Lake Michigan. A brisk breeze at times off the lake will continue through Thursday and beyond. That means the closer you are to the lakefront the more likely you will fail to see highs warmer than the 50s.

The water temperatures in Lake Michigan vary from the lower 40s in the northern most reaches of the lake to the 50s at Chicago's beaches.

A closer look at the southern part of the lake shows 50s concentrated near our lakeshore but then surface water temperatures fall fairly quickly into the 40s not too far off shore. As long as there is a wind off of this chilly water it means we will be unseasonably cool.

The hourly temperature meteogram compares many different forecast models. The warmest we can hope for through the middle of next week is highs near 60° or just above. Most of the next seven days will feature highs only in the 50s. The coldest period will be early Saturday morning when lows could dip into the 30s away from the city.

The temperature anomaly forecast for Saturday morning shows northern Illinois having some of the biggest departures from average on the cool side compared to any other part of the country. Our lows Saturday morning may fall between 5° to nearly 15° below average. That means we could see lows dip down into the middle 30s in our colder spots north and west of the city.

This would not be a hard freeze but possibly cold enough for a little light frost. Our last freeze on average usually falls between April 21st and the 30th for most of us but even earlier (April 5th through the 15th) in the city.

Still Looking For Some Rain

We have a few chances for rain over the next ten days but it doesn't look substantial enough to put a significant dent in the drought. The GFS model shows at least four decent chances for rain through a week from Thursday. We have a good chance for rain late tonight into early Thursday with a few showers possibly redeveloping tomorrow afternoon. There may be a few spotty showers on Friday. There is another chance late Saturday night into early Sunday but the latest model runs have been suppressing the rain more and more south of the city.

The next round of rain in our forecast late Thursday into Friday may produce up to a third of an inch of rain for the city and our northern and western suburbs. South of the city the GFS model tapers off the rainfall totals to about a tenth of an inch. We will take anything we can get but we will need much more to help with the moderate drought much of the area is experiencing. We are now down almost 5" of rain below average since the start of spring on March 1st.

Four Downstate Tornadoes Confirmed On Tuesday

Four tornadoes hit central Illinois on Monday evening. This was confirmed by the National Weather Service on Tuesday. They were small tornadoes with most having a path width of 50 yards. The widest had a path width of about 100 yards. The tornadoes spun up in Cass and Sangamon counties. Their rank on Enhanced Fujita scale has yet to be determined.

Cool Middle Of May

The longer range temperature probability forecasts signal our relatively cooler pattern lasting into the middle of the month. The latest 6-10 day forecast has us outlooked for cooler than average temperatures overall from May 10th through May 14th. The 8-14 day temperature probability forecast has us favored for below average temperatures overall from May 12th through May 18th. Average highs for the middle of May are around 70°.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast is signaling a cooler than average pattern for the last two weeks of May. The temperature anomaly forecast for the week ending May 21st has us outlooked to be below average overall. The forecast for the following week ending on May 28th has Chicago below average overall too. Average highs for this period are in the lower to middle 70s.

Weak Long Range Precip Pattern Signal

The longer range precipitation probability forecasts take us from about average rainfall to above average as we move into the middle of May. The longest range of the two has us in the lowest probability range for above average precipitation.. The latest 6-10 day has Chicago favored for near normal precipitation from May 10th through May 14th. The longer range 8-14 day forecast though has us favored for above average precipitation overall from May 12th through May 18th.

Here is my 7 day forecast:

Today: Mostly sunny, cool & a bit breezy High: 60 (53 lakeside)

Thursday: Mostly cloudy, scattered showers early & late Low: 45 High: 57 (52 lakeside)

Friday: Partly/mostly sunny, spotty pm shower possible Low: 42 High: 59 (cooler lakeside)

Saturday: Partly to mostly sunny Low: 38 High: 59 (cooler lakeside)

Sunday: Mostly cloudy, scattered showers mainly south Low: 43 High: 58 (cooler lakeside)

Monday: Partly to mostly sunny Low: 41 High: 58 (cooler lakeside)

Tuesday: Partly to mostly cloudy Low: 42 High: 62 (52 lakeside)



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