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  • Tim McGill

Severe Storms Possible Late Today

Large Hail & Damaging Winds Main Threat

We had a rather warm and windy weekend. There were wind gusts up to 60 mph on Saturday. The high at O'Hare hit 85° on both Saturday and Sunday. That made it the warmest weekend in eight months.

We start the week off about 10° above average today. Highs should reach into the lower to middle 70s.

We have our first real organized threat of severe weather for 2021 today. The main threat from any strong storms that fire up on this Monday is damaging winds or large hail. An isolated tornado can't be ruled out. The best timing for strong storms would be between 5 pm to 10 pm.

Most of the area is under a marginal risk for severe weather. The marginal risk category is the lowest on the scale of risk levels issued by the Storm Prediction Center. South of I-80 there is a slight risk for severe weather today. That is level two out of the five possible categories of severe risk. The ingredients are present for an Mesoscale Convective Vortex to develop to our west this afternoon and then sweep through here late today. An MCV is an organized low pressure-center that is typically 30 to 60 miles wide and 1 to 3 miles deep that is capable of producing strong to severe thunderstorms. The National Weather Service has some excellent tips on how to be prepared for any possible severe weather.

It's hard to get severe weather without any rain. This April was the 6th driest April on record with just .71" of rain. We are down more than four inches of rain below average since the start of spring. Through April 28th there were no reports of severe weather in the Chicago area and all of northern Illinois.

So Long 70s After Today

Today will be the warmest day of the week by far. Highs will climb into the lower to middle 70s before a cold front comes through tonight. Our highs will fall into the 50s Tuesday and we won't see any more 70s at least through the weekend.

Lows for Wednesday, Thursday and Friday morning will fall into the lower 40s. If you did some spring planting this weekend your plants should be safe this week. We will have some chilly mornings but no risk of a freeze this week. We have now moved beyond the average dates for our normal last freeze in northern Illinois. It is unlikely we will see another freeze this spring but the risk is non-zero. The latest freeze on record for Chicago is May 25th.

While we won't see a freeze this week it will feel quite a bit cooler tomorrow compared to today. The temperature anomaly forecast for Tuesday afternoon has temperatures here around 5° to 10° below average. Tomorrow afternoon will be at least 10° to 15° cooler than today. The most dramatic drop will be along the lakefront where it will be nearly 20° cooler Tuesday compared to this afternoon.

Putting A Dent In The Drought?

After a round of possible strong storms late today there are at least three more decent chances of rain over the next ten days. The GFS model suggests at least scattered showers on Thursday with another round of rain late Saturday into Sunday. The last chance of rain in this forecast is a week from Wednesday.

The GFS model precipitation accumulation forecast through Tuesday morning spits out about a half inch to nearly three quarters of an inch of rain in total. Some stronger storms may produce locally heavier amounts of rain though. Any rain is welcomed considering the moderate drought that much of northeast Illinois is now in.

Cool Pattern Sticking Around?

The longer range temperature probability forecasts keep us cooler than average at first and then back to about average. The latest 6-10 day forecast has us outlooked for cooler than average temperatures overall from May 8th through May 12th. The 8-14 day temperature probability forecast has us favored for about average temperatures overall from May 10th through May 16th. 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.

Hopes In Longer Range For More Rain

The longer range precipitation probability forecasts offer hope for more rainfall to put a dent in our drought. Both forecasts favor a more active pattern as we move into the middle of May. The latest 6-10 day has Chicago favored for above average precipitation from May 8th through May 13th. The longer range 8-14 day forecast though has us favored for above average precipitation overall from May 10th through May 16th too.

Here is my 7 day forecast:

Today: Cloudy, spotty showers early, showers & possible strong thunderstorms late High: 74

Tuesday: Mostly cloudy & cooler, scattered showers Low: 51 High: 58 (53 lakeside)

Wednesday: Mostly sunny Low: 42 High: 59 (cooler lakeside)

Thursday: Mostly cloudy, scattered showers Low: 45 High: 58 (cooler lakeside)

Friday: Partly to mostly sunny Low: 42 High: 60 (cooler lakeside)

Saturday: Mostly cloudy, shower possible late Low: 44 High: 63 (cooler lakeside)

Sunday: Mostly cloudy, scattered showers Low: 48 High: 62 (cooler lakeside)



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