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  • Tim McGill

Slow Start To Severe Weather Season

Cool Means Quiet

So far, so good for severe weather season. The peak months in Chicago are May, June and July but severe weather can, and has occurred every month of the year in the past. There have been zero reports of severe weather in our area since the start of the year. In a typical year there will be around 32 days with reports of severe weather. It hasn't been this quiet since 1987. The National Weather Service office in Romeoville has a great summary of the lack of sever weather thus far in 2021.

The National Weather Service doesn't want us to let our guard down. They have excellent advice for handling all types of severe weather.

Even though this year is the 7th slowest start for severe weather on record in Chicago, a slow start does not always correlate with a quiet year overall. We still have plenty of the peak months for severe weather to get through.

Reports of severe weather can include damaging winds of 58 mph or stronger, and/or 1" diameter hail or larger, and/or tornadoes. All severe weather reports so far in Illinois during 2021 have been well south of the city.

It only takes one event on one day to bring our severe weather reports tally quickly back to about average. The derecho that struck in August last year is a good reminder. Nearly every county in the Chicago area on August 10th last year had a tornado warning at some point that night. There were over 200 reports of severe weather in northern Illinois and northwest Indiana. There was a total of 15 confirmed tornadoes in the area.

Our pattern turns cooler the next few days which should keep the threat of severe weather at a minimum through at least the weekend. Thunderstorms thrive on at least some heat, moisture, instability and a way to lift the unstable air. We will be lacking those ingredients for the next several days.

Today should feature quite a bit of sunshine but that won't help warm us up much. Highs today should be in the middle 50s.

Gusty winds are expected again today. Those strong west winds combined with 50s will feel a lot colder than yesterday's 60s. Highs tomorrow for at least portions of the area may fail to climb out of the 40s.

Umbrellas Get A Break

The GFS model keeps us mainly dry through the weekend. There could be a few spotty sprinkles Wednesday afternoon but most of the day and most areas should be dry. The next decent chance of rain doesn't arrive until late next Monday into Tuesday.

So Long 60s Until Sunday

The hourly temperature meteogram compares many different forecast models. Monday's high of 62° at O'Hare will be the warmest day of this week. The next time we might hit 60° isn't until Sunday.

The GFS model's temperature anomaly forecast suggests there could be a reinforcing shot of cool air coming early next week. The forecast for next Tuesday afternoon keeps us around at least 5° to 10° below average. Average highs by then are around 61°.

Cool Long Term Signal Gets Stronger

The longer range temperature probability forecast is showing a strong signal for a cooler than average pattern for the last part of this month. The latest 6-10 day forecast has us outlooked for below average temperatures overall from April 18th through April 22nd. The 8-14 day temperature probability forecast has us favored for below average temperatures overall from April 20th through April 26th too. Both forecasts have higher probabilities in favor of a cooler pattern than yesterday's forecasts. Average highs in Chicago move from the upper 50s to lower 60s during this period.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast is signaling a cooler than average end to April and a return to around average for the start of May. The temperature anomaly forecast for the week ending April 30th has us outlooked to be a bit below average overall. The forecast for the following week ending on May 7th has Chicago bouncing back to about average overall. Average highs by the start of May are in the lower 60s.

Drier Long Range Forecast Signal Stronger Too

The probabilities have increased for us to have a drier than average pattern overall for the end of this month. The latest 6-10 day forecast has Chicago favored for below average precipitation from April 18th through April 22nd. The longer range 8-14 day forecast has us outlooked for below average precipitation overall from April 20th through April 26th too.

Here is my 7 day forecast:

Today: Partly to mostly sunny, breezy (gusts to near 30 mph) High: 57

Wednesday: Partly to mostly cloudy, spotty pm sprinkles possible Low: 37 High: 50

Thursday: Partly to mostly sunny Low: 38 High: 54 (cooler lakeside)

Friday: Partly to mostly sunny Low: 39 High: 57 (cooler lakeside)

Saturday: Partly to mostly cloudy Low: 39 High: 57 (cooler lakeside)

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

Monday: Becoming cloudy, chance of rain late Low: 42 High: 61 (cooler lakeside)



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