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  • Tim McGill

More Details On Sunday's Strongest Tornado

Lofted Debris Was A Sobering Sign

My post on Tuesday described Eric Lenning's process of surveying the damage from the Naperville to Willow Springs tornado. He's the Meteorologist-in-Charge of Chicago's National Weather Service office in Romeoville. Eric and his colleagues saw a sobering sign that this storm would produce some serious damage when he viewed the storm on radar Sunday night as it struck. Forecasters saw a "tornado debris signature" on doppler radar Sunday night. A TDS is sometimes referred to as a "debris ball". The image above shows the doppler radar signature they saw that indicates debris being lofted into the air from a tornado. In this case, the debris was lofted to around 20K feet.

Eric and National Weather Service released more preliminary information on this tornado. The Naperville/Willow Springs tornado was a powerful EF-3 on the Enhanced Fujita Scale with winds up to 145 mph. An EF-3 tornado produces "severe damage". The path length was a bit more than 16 miles with a maximum width of 600 yards. This is the first significant (EF-2+) tornado to impact the Chicago Metropolitan Area since an EF3 tornado hit Coal City in 2015. It was also the strongest tornado to impact DuPage County in 45 years.

Notice the description of the damage this type of tornado can bring includes heavy cars not just being lifted off the ground but also thrown:

Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations are badly damaged.

The survey teams have now completed the preliminary assessments of the three tornadoes that impacted northern Illinois and Indiana Sunday night.

Aside from the Naperville to Willow Springs tornado there was an EF-0 tornado on the Enhanced Fujita Scale that struck the Plainfield to Romeoville area (maximum winds of 85 mph) and and another EF-0 tornado that hit South Haven, Indiana (maximum winds of 75 mph).

Back To More Seasonable Summer Warmth

Tuesday's high of 73° at O'Hare marked just the 5th day this month to come in below average. So far June is running just under 5° above average. Average highs for today's date are around 83°. We will be warming back to and even above average the next couple of days. The HRRR model has our highs today topping out in the middle to upper 70s today.

Our dew points will climb along with our temperatures. Dew points are the preferred measurement of moisture for meteorologists. The climbed from the 40s to the 50s yesterday and are set to climb into the 60s by Thursday afternoon. It will make it feel more muggy the next several days. More importantly, it suggests more moisture in the air to fuel potential showers and thunderstorms.

It was a bit breezy yesterday but expect stronger winds on this Wednesday. Gusts will approach 30 mph today and through Thursday afternoon.

Our threat of rain diminishes around the middle of the day. So after some morning showers mainly south of the city, expect some sunshine to break through the clouds during the afternoon. Rain chances ramp back up though for Thursday afternoon and night.

The National Blend Of Models has highs warming from the 70s again today to 80° or above tomorrow through Friday of next week.

The long range temperature probability forecasts favors us a seasonably warm end to June and start of July. It keeps it cooler south of here and warmer north and west of Chicago. The 6-10 day forecast has outlooked us for about average temperatures overall from June 28th through July 2nd. The longer range 8-14 day forecast also favors us for near normal temperatures overall from June 30th through July 6th.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast favors us for above average temperatures overall for the first half of July. The average highs for this period are in the lower to middle 80s. The temperature anomaly forecast for the week ending July 9th has us outlooked for above average temperatures overall. The forecast for the following week ending on July 16th also has Chicago outlooked for above average temperatures overall too. It takes a close look at this second map to see we are the exception for Illinois. Most of the state is outlooked for about average or below average temperatures.

A Dent In The Drought Coming

We are now up .53" above average for June rainfall. Recent rain has brought some drought relief. The rainfall deficit since March 1st is still near 6 inches below average.

I'll have an update on our drought and the latest analysis from the U.S. Drought Monitor in this Friday's post.

Here is a recap of my post from last week with details on our drought that does not include our recent rain:

Our ongoing drought in northern Illinois has both deepened and expanded according to the latest analysis from the US Drought Monitor. Almost 3% of the region is now in an extreme drought for the first time this year. That's the third of four levels of drought with "exceptional" being the fourth or worst level. 6.43% of Illinois is now in a severe drought (up from 4.58% last week). 9.18% of the state is in a moderate drought (up from 8.52% last week). The worst of the drought is centered in the northeast corner of the state and includes most of Lake County, all of McHenry county and portions of Cook, Kane, DeKalb and Boone counties. This does not take into consideration the rain that fell Thursday night into Friday morning.

Last Friday's post also included a look at Wisconsin, the Midwest and where the drought is hitting hardest, the western states.

The GFS model suggests a more active period coming tomorrow afternoon and lasting through a good portion of Saturday. There will be periods of showers and thunderstorms but most days will not be washouts. Friday should see the most significant rainfall with locally heavy amounts possible.

The HRRR model total precipitation forecast through most of today shows the areas favored for some rain (mainly early today) are from Chicago and on into our western suburbs and also south of city. The range of rainfall is around a tenth of an inch to under a half inch of rain in total.

Some of the storms later Thursday and Thursday night could be strong to severe. The Storm Prediction Center has placed us in a marginal risk area for severe weather during that period. A marginal risk means isolated severe thunderstorms possible that would be limited in duration and/or coverage and/or intensity. Large hail and damaging winds are the biggest threat from possible severe storms Thursday. The early outlook for Friday/Friday night has also us in a marginal risk area for severe weather.

The GFS model total rainfall forecast through Sunday gives us hope for some significant drought relief. It squeezes out a range of rainfall from a half inch northwest of the city to nearly four inches in northern Indiana. Most of us would receive an inch or two of rain if this forecast verifies.

The long range precipitation probability forecasts are trending the Chicago area towards a more active pattern. The signal isn't that strong but it is still encouraging in light of the drought. The latest 6-10 day forecast has the Chicago area outlooked for around average precipitation overall from June 28th through July 2nd. The longer range 8-14 day forecast also favors us (slightly) for above average precipitation overall from June 30th through July 6th.

Here is my 7 day forecast:

Today: Sct. showers mainly early then mostly cloudy, breezy High: 78

Thursday: Mostly cloudy, mainly pm sct. showers/t-storms, breezy Low: 67 High: 83

Friday: Periods of showers & thunderstorms, heavy rain possible Low: 71 High: 82

Saturday: Mostly cloudy, periods of showers & thunderstorms Low: 68 High: 80 (cooler lakeside)

Sunday: Partly/mostly sunny, a few showers possible Low: 66 High: 80 (cooler lakeside)

Monday: Partly to mostly sunny Low: 65 High: 81

Tuesday: Partly to mostly sunny, sct. shower/t-storm possible Low: 64 High: 83



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