U.S. Likely to Finish 2018 With Its Fewest Severe Weather Watches in More Than a Decade

Through Nov. 28, NOAA's Storm Prediction Center (SPC) had issued 428 severe thunderstorm watches or tornado watches in 2018, according to Sam Lillo, a meteorology Ph.D. student at the University of Oklahoma. That's far less than 2016, which had 517 watches, the fewest in 11 years of compiled records. It's likely 2018 will surpass that number.

Severe thunderstorm and tornado watches are issued by SPC for a period of several hours when atmospheric conditions are conducive to the development of thunderstorms capable of producing destructive straight-line winds, large hail and sometimes tornadoes. They can encompass a part of one state or parts of several states in a region of the country, most often east of the Rockies.

Lillo noted that of the 428 total watches issued so far this year, 308 were severe thunderstorm watches and 120 were tornado watches.

When breaking it down further, it's likely 2018 will have the fewest severe thunderstorm watches since at least 2007. Just 308 have been issued through Nov. 28, safely below the current lowest total for a year which is 347 in 2017.

The number of tornado watches issued by SPC in 2018 would also be at a 12-year low if the year had already ended. An additional nine tornado watches will have to be issued by the end of the year in order to draw even with 2016 which had the fewest of those from 2007 to 2017.

Severe weather reports, including tornadoes, damaging winds and large hail, have also been tracking below average as we head into the final month of the year.

The fewest severe weather reports in a year dating to 2000 will likely remain 2014 which had 18,580. That said, this year could finish with the second or third-fewest number of severe weather reports since 2000 held by 2015 (19,172 reports) and 2013 (19,345 reports), respectively.

Preliminary SPC reports show that damaging wind gusts in 2018 have been close to the 2005-2015 average of 13,061 through Nov. 28.

Occurrences of large hail through Nov. 28 were just 74 percent of the 10-year average of 6,179.

A slow spring season contributed to 2018's preliminary tornado reports being 81 percent of the average to date.

The reason for the dearth of tornadic activity in spring 2018 was an unfavorable jet stream pattern, which persisted through most of March and April, when the ingredients for severe weather typically begin to come together. A southward dip in the jet stream, or upper-level trough of low pressure, persistently set up across the central and eastern states and dug all the way into the Deep South.

Moisture was trapped near the Gulf Coast in that setup, unable to surge northward into the Midwest and Plains. Additionally, that pattern prevented jet stream disturbances from punching out of the Rockies and into the Plains – a common severe weather setup in the spring months.

While that pattern wasn't as dominant in May, it was still present at times, keeping the month's tornado count far below average.