We continue this week's blog series to help you get prepared for severe weather season. Today's topics will focus on hail, damaging thunderstorm winds, and the Storm Prediction Center severe weather outlook categories.
While severe weather can happen just about any time of year in Wisconsin, severe storms most often occur between April and August. Additionally, severe storms can happen any time of day, but occur most often in the late afternoon and evening. On average, there are between 30 and 40 thunderstorms days each year in the state.
Do you know the most common severe weather threat in Wisconsin? Damaging winds. Fifty-four percent of severe weather events in Wisconsin are damaging wind events.
One criterion for severe thunderstorms is winds of 58 mph or stronger. These may be estimated, based on radar and velocity returns, or observed. Straight-line winds can, and do, produce significant damage every year. There are multiple storm modes that can produce damaging winds. Squall lines, pulse storms, supercells, quasi-linear convective systems, bow echoes, and downbursts are a few. Some of these wind events can produce hurricane-force winds!
Another storm type that can produce very strong winds are derechos. These are convective wind events with a width usually greater than 40 miles. They travel long distances and last many hours. According to the Milwaukee National Weather Service, Southern Wisconsin and Southern Minnesota have the greatest number of derechos in the country. You may recall the derecho that caused significant damage across Iowa in August of 2020. SE Wisconsin was on the edge of this storm, which produced two tornadoes, damaging winds, and heavy rainfall.
Severe thunderstorm winds can knock down trees, bring down power lines, loft trampolines, tear shingles from roofs, the list goes on. Because of the damage that strong winds can cause, remain indoors during a severe thunderstorm warning, and stay away from windows. If you are in an area with vulnerable trees that could fall onto your home, take shelter in a basement or the lowest level of your home.
Hail is another threat during severe weather season. A severe thunderstorm warning will be issued if a storm is estimated, or observed, to be producing 1" or larger hailstones. In Wisconsin, 34% of severe weather events are from hail that is one inch in diameter (or larger). The southern half of Wisconsin has historically experienced more hail events compared to the northern half of the state. On average, there are about 15 days each summer that thunderstorms produce hail 1.5-inches or larger across Wisconsin. If hail is expected, park your car in the garage or under a carport. Also, stay indoors and stay away from windows in case of damage.
In Wisconsin, the largest hailstone on record fell nearly 100 years ago. The record hailstone was recorded on May 22, 1921 in Wausau and measured 5.7". The second largest on record was more recently, on June 7th, 2007 in Port Edwards, measuring 5.5".
Learn more about how hail forms here.
Before any of these thunderstorms occur, Storm Team 4 has likely been telling you that there is an upcoming risk for severe weather. You may see us show a Severe Outlook map, similar to the one below.
This data is coming from the Storm Prediction Center (SPC). The SPC is a branch of NOAA, and their primary job is to forecast locations in the country with the highest risk of severe storms. They issue outlooks about a week into the future. The day 1 and 2 outlooks have a higher level of detail regarding storm mode and specific weather threats. Depending on the amount of storm coverage expected, and forecast confidence, the SPC gives locations an outlook risk. It's a 1-5 scale, with 1 being a low-end risk for a few strong storms, and 5 being a very high risk of widespread and intense storms.
On days when Wisconsin is included in the SPC risk area, it's important to pay attention to the forecast and weather conditions. Storm Team 4 will always do our best to keep you informed ahead of the storm.
Don't put off getting ready for severe weather season. Be sure to look for tomorrow's weather blog, where we will discuss the dangers of flash flooding and lightning, and how to stay safe from these threats.
Also, join us on Facebook Live all week at 10 am and 7 pm for the opportunity to chat about severe weather with Storm Team 4.
In case you missed Monday's blog - find out how to know when severe weather is headed in, and what action to take.