2018 Wisconsin Storm Season Weakest in 26 years
If the season ended today, the 210 storm reports in 2018 would be the lowest since 1992. 26 years!
There are many months left in the year. We could have multiple more days with severe weather. Anything could happen yet. And now that I've pointed it out mother nature will probably change her mood. This story is not an excuse for you to let your guard down, just hoping to give you some perspective.
FACT - Severe thunderstorms are becoming less frequent in Wisconsin
"Storm Reports" consist of tornado, wind gust (or damage), and large hail reports across Wisconsin. As an example of how much we've changed in just 20 years, there were 955 storm reports in 2006 compared with 210 (so far) in 2018. You can argue that heavy rainfall, heat waves, and cold outbreaks are getting more or less intense but we don't report these events the same way. In the context of damaging tornadoes, widespread wind storms, and massive hail; there is no question our thunderstorms are getting less frequent/weaker.
- The average tornado count per year has decreased by 50%, from 33 in 2007 to 16.
- The total report count average has decreased from 727 in 2008 to 461.
- I predict another 2006 or 2011 within the next 1-3 years simply looking at the trends above. Minima have been followed by maxima since 2003.
The fact storm reports are decreasing long term is interesting because of the world we live in.
Each year we become more efficient with communication of storm reports. Each year the number of storm reports should increase due to societal awareness, social media, and overall sensitivity. Each year it becomes harder to compare historically. Even the 1990's are debatable now. When I say weakest since 1992, what do we really know about 1992? If 1992 was today, how many storm reports would there be? Today we have drones, phones, and radar technology that didn't exist back then.
The next question is how severe? Are we talking 10 EF0 tornadoes OR 5 EF2 and 5 EF3? I will let you research that for yourself. The last F4-F5 tornado was Oakfield in 1996.
What's driving it?
Proof of big picture causation for a random process like severe thunderstorms is not possible.
Severe storm reports are driven by thunderstorms which occur randomly on a small scale. Indiviual thunderstorm severity depends on atmospheric relationships; the more balanced and organized updraft the stronger the storm will be. They are often a reflection of change with the strongest storms usually coming with the strongest cold fronts or low pressure systems.
Thunderstorms are driven by low pressure systems, boundaries, and fronts. Low pressure systems are driven by large scale weather patterns. Large scale weather patterns are driven by ocean, sun and earth interaction. Yes, "2018 favored riding in the west. 2017 favored storms over the great lakes." Okay great, meteorologists can consider that causation on month to month or year over year resolution. But what about causation over the last 20 years? What drives the 20 year trend? What is the big picture?
The most similar year to 2018 recently would be 2009 with 279 storm reports. 2009 was coincident with our last total solar irradiance (TSI) minima. Key word: COINCIDENT.
Is there a direct correlation between total solar irradiance max/min and severe weather trends in Wisconsin? Over the last two cycles yes, but before that NO. Same with sunspots. I believe when ocean sun and earth interactions are coincident it can lead to extreme weather. They force weather collectively, not just one or the other. This should be expected with a complex system like the atmosphere. I often find that it's the flux between weather regimes that energizes the atmosphere; the actual moment of change.
Recently our spring season has been slightly cooler with fewer severe storms. This should not "break the season" because the majority of reports come in June and July.
The big picture 20 year relationship between storm reports and solar activity is very good. Both decreasing. This leads me to believe that as we continue to descend into grand solar minimum, our long term in storm report trend with decrease as well. I predict there will be big years like 2005, 2011, and 2017 sprinkled in there but the white noise will continue to decrease.
I don't have a 30 page research paper or PHD to support it; but one possible connection between thunderstorms and the sun is that a weakening sun will force the jet stream to become longer, more amplified, and therefore weaker. If the jet stream is weaker, then the low pressure systems are weaker. The weakening trickles down to the thunderstorm. Everything slows down. There are other high resolution considerations such as upper level temperature, surface instability, and wind shear regimes. For example; relatively cold upper air increases the energy level in the lowest layers of the atmosphere.
The data will not show direct correlation because the oceans or earth could be out-of-phase in a manner that cancels out or distorts solar forcing on the yearly resolution... but the long term (20 year) trend remains.