Should There Have Been a Severe Thunderstorm Warning Saturday? Are the Warnings Relevant?

Some residents, who were left without power for hours Saturday or experienced damage to their homes, might be surprised to find out there was no Severe Thunderstorm Warning in effect when storms rolled in about 1:50 p.m. Saturday, August 23, 2014. A large area of thunderstorms was visible on radar as a large broad line from Madison, Wisconsin to Champaign, Illinois.

An Areal Flood Warning was issued, but not until rain had already started falling. The storm caused flooding many areas, including streets and businesses. The Arlington Heights Chamber of Commerce office at 311 South Arlington Heights Road was flooded with about 4 inches of water.

On Tuesday, August 26, 2014 at 9:57 a.m. a Severe Thunderstorm was activated for Northwest Cook County, Northern Kane County, and all of Lake County, Illinois. Very little, if any damage occurred compared to the storm Saturday that was NOT accompanied by a Severe Thunderstorm Warning.

The main criteria for a Severe Thunderstorm Warning activation occurs when there is a radar indication or storm spotter report of hail one inch or larger in diameter or winds greater than or equal to 58 mph. Frequent lightning is NOT a criteria for a Severe Thunderstorm Warning activation, even though lightning can cause serious injury and death, property damage and power outages that can indirectly cause more property damage, especially when power outages are prolonged.

Did a 58 MPH or greater wind gust uproot this 60-foot pine tree at School Drive and Campbell Street in Rolling Meadows? Look at the length of the root (upper right) that was pulled out of the ground.

By the current NWS criteria, perhaps no Severe Thunderstorm Warning should have been issued Saturday, but by common sense and consideration of the resulting damage from Saturday’s storms, perhaps it is time the National Weather Service refine their definition of a Severe Thunderstorm Warning. A more relevant warning aligned with threat to life and property is possibly long overdue from the National Weather Service.

Saturday’s storm …

In Palatine, a house was struck by lightning at 961 West Wood Street, which caused a fire in the roof and attic of the two-story home. A neighbor saw large flames coming from the peak of the roof on the west side of the house. The top of the chimney at the house was also blown to pieces.

Numerous tree branches were reported down in Arlington Heights, Mount Prospect, Palatine, and Rolling Meadows.

A 60-foot tall pine tree was uprooted and fell on a vehicle parked in a driveway at School Drive and Campbell Street in Rolling Meadows.

Large branches were also reported down in Mount Prospect.

Parts of Arlington Heights were without power for more than six hours Saturday because of a thunderstorm. One area lost power for six hours, had restored power for about an hour, and then lost power for another two hours.

Weather Warning Definitions from the National Weather Service …

Severe Thunderstorm Warning
This is issued when either a severe thunderstorm is indicated by the WSR-88D radar or a spotter reports a thunderstorm producing hail one inch or larger in diameter and/or winds equal or exceed 58 miles an hour; therefore, people in the affected area should seek safe shelter immediately. Severe thunderstorms can produce tornadoes with little or no advance warning. Lightning frequency is not a criteria for issuing a severe thunderstorm warning. They are usually issued for a duration of one hour. They can be issued without a Severe Thunderstorm Watch being already in effect.

Like a Tornado Warning, the Severe Thunderstorm Warning is issued by your National Weather Service Forecast Office (NWFO). Severe Thunderstorm Warnings will include where the storm was located, what towns will be affected by the severe thunderstorm, and the primary threat associated with the severe thunderstorm warning. If the severe thunderstorm will affect the nearshore or coastal waters, it will be issued as the combined product–Severe Thunderstorm Warning and Special Marine Warning. If the severe thunderstorm is also causing torrential rains, this warning may also be combined with a Flash Flood Warning. If there is an ampersand (&) symbol at the bottom of the warning, it indicates that the warning was issued as a result of a severe weather report.

After it has been issued, the affected NWFO will follow it up periodically with Severe Weather Statements. These statements will contain updated information on the severe thunderstorm and they will also let the public know when the warning is no longer in effect.

Severe Thunderstorm Watch
This is issued by the National Weather Service when conditions are favorable for the development of severe thunderstorms in and close to the watch area. A severe thunderstorm by definition is a thunderstorm that produces one inch hail or larger in diameter and/or winds equal or exceed 58 miles an hour. The size of the watch can vary depending on the weather situation. They are usually issued for a duration of 4 to 8 hours. They are normally issued well in advance of the actual occurrence of severe weather. During the watch, people should review severe thunderstorm safety rules and be prepared to move a place of safety if threatening weather approaches.

A Severe Thunderstorm Watch is issued by the Storm Prediction Center in Norman, Oklahoma. Prior to the issuance of a Severe Thunderstorm Watch, SPC will usually contact the affected local National Weather Service Forecast Office (NWFO) and they will discuss what their current thinking is on the weather situation. Afterwards, SPC will issue a preliminary Severe Thunderstorm Watch and then the affected NWFO will then adjust the watch (adding or eliminating counties/parishes) and then issue it to the public by way of a Watch Redefining Statement. During the watch, the NWFO will keep the public informed on what is happening in the watch area and also let the public know when the watch has expired or been cancelled.

— National Weather Service

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