My friend John Feldt is a Certified Consulting Meteorologist who provides weather and climate information to producers across the country. He posted this great summary of this year’s severe weather season on his site at http://www.bluewateroutlook.com/. He gave me permission to reproduce it here.
The jet stream weakens and pushes north approaching July. This usually reduces the number of major severe storm, including tornado, outbreaks.
The core of the traditional tornado alley extends from Texas northward into the Plains states of Oklahoma, Kansas, and Nebraska.
However, take a look at reported tornadoes so far this year. Note the relative lack of tornado touchdowns in the traditional tornado alley.
There has been much more tornado activity across the South Central and Southeast U.S.
May is typically the most active tornado month for Kansas and Oklahoma tornadoes.
Note the lack of tornado activity across Kansas and Oklahoma this past May — only a handful of touchdowns.
Here is a plot of tornadoes for the entire year to date. Note that the year started off with above-normal activity. However, the month of May (the most typically-active month) lagged. The total number of tornadoes so far this year (812-Mid June) lags the normal of 974.
In fact, the number of May tornadoes (59) this year was the lowest in the past 50 years.The last time May had fewer than 100 tornadoes was in 1970 when 88 touched down in the U.S.,
Additionally, NOAA’s Storm Prediction Center did not issue any moderate (level 4) or high (level 5) risks of severe weather in May 2020, a first in records dating to 2002.
Source: Storm Prediction Center
You can more clearly see the active start of the severe weather season in April followed by a unusually-quiet May and June in this plot of storm reports.
Why was there a lack of May tornadoes across the U.S. tornado alley? To a large degree, conditions need an active jet stream to produce wind shear conducive to tornado development. The jet stream was active across the southern tier of the nation early this spring but jumped unusually-far north in May.
A Shift in Tornado Alley?
Here is an image showing the average path length of tornadoes within 25 miles of a point. Note that while the greatest density of tornadoes occurs in Oklahoma, tornadoes in Mississippi carve longer tracks, and the risk of being impacted there is greater.
Researchers at Fort Hays State University in Kansas found that the Deep South is in essence a continuation of the more traditionally recognized Tornado Alley.Mississippi and Alabama have been especially hard-hit by long-track tornadoes.
2020 tornadoes have clearly followed the trend towards the southern-tier U.S. tornado track.
Tornadoes in the so-called Dixie Alley (portions of eastern Texas, Louisiana, Arkansas, Tennessee, Mississippi, Alabama, and Georgia) can be particularly dangerous. In addition to remaining on the ground for longer times, these tornadoes often occur at night and can be hidden in heavy rainfall making them harder to see.
Despite the quiet spring, Kansas supercells over the open prairie of western Kansas are always an impressive sight. Here are two supercells (rotating thunderstorm) from May 21st.