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  • Tim McGill

Talking Severe Storms & Steamy Summer Weather

Severe Thunderstorm Warning Change

All severe storms are not the same so the National Weather Service is now adding a "damage threat" tag to severe thunderstorm warnings that are similar to the tags they already have been adding to both tornado and flash flood warnings. The goal is to better convey the impacts these storms can have based on their severity level.

The tags are broken up into three categories. The base category is the default that was routinely added to severe thunderstorm warnings before these changes were implemented. The considerable tag is for storms with winds of 70 mph and 1.75" diameter hail (golfball size). The destructive tag is for storms with winds of 80 mph and 2.75" diameter hail (baseball size).

Here's more from Chicago's National Weather Service Office:

On average, only 10 percent of all severe thunderstorms reach the destructive category each year, nationwide. Most of these storms are damaging wind events such as the August 10, 2020 derecho and some of the more intense rotating thunderstorms, called “Supercell” storms that can typically produce very large hail in their path, such as the Illinois record hail size in Minooka on June 10, 2015. The new destructive thunderstorm category conveys to the public urgent action is needed, a life-threatening event is occurring and may cause substantial damage to property. Storms categorized as destructive will trigger a WEA to your cell phone.

Learn how to stay safe in a severe thunderstorm. Knowing what to do before, during, and after severe weather can increase your chances of survival.

Here is an example of a considerable tag attached to a severe thunderstorm warning:

Heat & Humidity Will Surge Soon

Yesterday's high of 83° was the warmest high we have seen in five days. August has started out 5° below average but this relatively cool pattern will transition to a much hotter and more humid pattern by this weekend. A couple of seasonably warm and still relatively comfortable days first before that heat and humidity surge.

The HRRR Model has our highs today right around the average of 84° for today's date. A breeze off the lake will keep it cooler lakeside with highs there in the upper 70s.

The worst of this upcoming mini-heatwave will hit early next week. The combination of heat and humidity on Monday will make it feel like 95° to 102°. I expect similar heat index or apparent temperature values on Tuesday too.

Today and tomorrow will be more seasonably warm with fairly comfortable humidity levels. Highs both days will be in the middle 80s with dew points mostly in the middle 50s to near 60°. The lake breeze today will help keep it cooler lakeside but any lake breeze tomorrow will be limited to right along the shoreline as a stronger southwest wind develops.

There is a small chance of a spotty sprinkle or shower today but a slightly better chance for some Thursday afternoon. Most of today and tomorrow will be rain free.

Our dew points really jump on Friday and by the weekend they surge into the 70s. Dew points are the preferred measure of moisture in the atmosphere for meteorologists. A more southerly and southwesterly flow develops tomorrow and begins to transport more moisture up from the Gulf of Mexico.

The National Blend Of Models has highs jumping above average this weekend to near 90° and then hitting at least 90° on both Monday and Tuesday before falling a few degrees during the middle of next week.

More hazy in the air from wildfire smoke. The HRRR Model vertically integrated smoke forecast shows wildfire smoke from the west and Canada will waft into the sky across most of our country.

Here are some articles related to wildfire smoke that you may be interested in:

The signal remains fairly strong for the warmer than average pattern that starts later this week could linger well into the next one and even beyond. The 6-10 day forecast has outlooked Chicago for above average temperatures overall from August 9th through August 13th. The longer range 8-14 day forecast continues to favor us for above average temperatures overall from August 11th through August 17th. Average highs are in the lower to middle 80s for the start to August.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecasts keeps us warmer than average through nearly the end of August. The forecast for the week ending on August 20th has us outlooked for above average temperatures. The forecast for the week ending on August 27th favors us for above average temperatures overall too.

Northern Suburbs Drought Likely Deepening

Yesterday was the 5th straight day without any measurable rainfall. July ended up 1.81" of rain below average and we are now down 6.56" inches below average since the start of spring. August is running .44" below average.

Here is a recap of the latest drought analysis that I posted last Friday:

The latest analysis from the US Drought Monitor shows absolutely no change in drought conditions for northern Illinois from the previous analysis a week ago. The area of Illinois in a moderate drought (level 1 out of 4) remains unchanged at 7.17%. The area of the state in a severe drought (level 2 out of 4) remains unchanged at 2.31%.

It has been a fairly dry end to the month of July so far. Rainfall over a two week period that ended on July 28th shows the most parched portions of Illinois were out of luck when it came to rainfall. Parts of Lake and McHenry counties picked up just 10% to 25% of average rainfall during the period. Most of the northern third of the state was well below average in terms of rainfall.

The latest GFS model suggests a spotty shower or sprinkle possible today but better chances for scattered showers and thunderstorms coming Friday and over the weekend. I expect about 30% coverage on these storms so very hit or miss.

Even with several chances for rain in the coming days it doesn't look like it will amount to much rainfall overall. I ran the GFS model total rainfall forecast through Monday morning the range of rainfall is from as little as a tenth of an inch to as much as nearly three quarters of an inch. With all the moisture available to fuel weekend storms I expect some locally heavy rainfall amounts but the nature of these scattered storms means many areas will also receive little or no rainfall.

A glimmer of hope in the longer range rainfall forecasts for a more active pattern that could bring beneficial rainfall. The latest 6-10 day forecast has the Chicago area favored for above average precipitation overall from August 9th through August 13th. The longer range 8-14 day forecast also favors us for above average rainfall from August 11th through August 17th.

Here is my 7 day forecast:

Today: Partly to mostly sunny, isolated shower possible High: 85 (78 lakeside)

Thursday: Partly to mostly sunny Low: 64 High: 85

Friday: Partly/mostly cloudy, sct. t-storm possible Low: 67 High: 83

Saturday: Partly to mostly sunny, sct. shower/t-storm possible Low: 69 High: 87

Sunday: Partly to mostly sunny, sct. shower/t-storm possible Low: 69 High: 89

Monday: Partly to mostly sunny, sct. shower/t-storm possible Low: 72 High: 90

Tuesday: Partly to mostly sunny, sct. shower/t-storm possible Low: 73 High: 91


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