DENVER (CBS4) – Hail is virtually guaranteed in Colorado in May and June. But something has been different this year. There have been no large, costly hailstorms like in previous years and tornadoes have also been infrequent. Why?
While severe weather is possible in any month, Colorado’s severe weather season usually ramps up in May, peaks in the third week in June, and then quickly decreases in July.
CBS4 spoke with Dr. Samuel Childs from the Department of Atmospheric Science at Colorado State University who explained a mostly persistent ridge of high pressure that has been over Colorado in recent months has helped deter the develop of large hail and tornadoes. The ridge creates a west or southwest flow in the upper atmosphere which does not typically bring the moisture and instability necessary for damaging hail or destructive tornadoes. However, what this flow can help develop in the spring and summer months is wind. Lots of wind!
Let’s take a look at the numbers.
Through June 23, Colorado has experienced a total of 14 tornadoes spread over 5 days. And most of those tornadoes were small, relatively weak “EF-0” landspouts that touched down in rural Weld County on May 20.
That means Colorado is currently about 15 tornadoes and 4 tornado days below normal. Typically by June 23 that state reports an average of 26 tornadoes spread over 9 days.
The last two severe weather seasons have been very close to average with 26 tornadoes reported in 2018 and again in 2019. So with the severe weather season about to start winding down for 2020, it would seem Colorado will end up with far fewer tornadoes compared to normal.
It has also been a relatively quiet year so far for large hail. Through June 23, there has been a mere 10 reports of severe hail which is defined a hail at least 1 inch in diameter.
June is typically the most active month for hail in Colorado with an average of 98 reports – just in June!
But while tornadoes and large hail have occurred far less often than usual, severe wind has been off the charts. In fact, Dr. Childs at CSU calls Colorado’s 2020 wind reports “unprecedented”.
On average, the state gets 90 reports each year of wind from thunderstorms reaching 60 mph or stronger. So far this year, the total is more than twice the average with 151 severe wind reports. The vast majority of these reports occurred on a single day. On June 6, 2020 an unusual “derecho” wind event crossed Colorado and caused 91 reports of wind reaching at least 60 mph. There were also 17 reports of wind reaching at least 75 mph. Both of these counts set new daily records for the state.
The presence of more severe wind rather than severe hail or tornadoes is unusual for Colorado. But severe wind is always a threat when thunderstorms “collapse” due to dry air in the lowest level of the atmosphere. So the same persistent ridge of high pressure that has helped deter large hail and tornadoes has also helped promote the development of severe wind.