Annual and monthly tornado day averages by NWS forecast area

While we’re rapidly entering into the typical peak season for tornadoes across a whole, the actual peak largely depends on where you live. It can be in spring or summer, or perhaps even in the cold season.

The 122 forecast offices of the National Weather Service make a handy bucketing system to examine when and where tornadoes are most likely to be found in an average year.

To equalize the playing field a bit, we can look at tornado days rather than tornado numbers. Simply put, a tornado day has at least one tornado and as many as infinite tornadoes (though, probably not that many!).

Tornado days for all tornadoes

Most Central U.S. offices between the Mississippi River and the Continental Divide average about five to eight days a year with tornadoes in their warning area. Elevated numbers also include much of the South and parts of the Mid-Atlantic, as well as Ohio Valley.

The NWS Denver (BOU) office leads the pack for tornado days annually, with 11.4, per the current climate normals running 1991-2020. NWS Norman (OUN) in Oklahoma comes in second with 10.9 tornado days annually. NWS Jackson (JAN) and NWS Tampa Bay (TBW) also have tornado day averages of 10 or more days per year.

The following gallery includes maps of tornado days by month in the same format as above. Like with most severe weather indicators in the United States, a move north and west can be seen through spring and into summer before the main zone collapses back toward the warmer water of the Gulf in winter.

Looking at the top-five offices for tornado days, one notices many different patterns, despite peaks favoring spring.

Denver, Tampa Bay, and Grand Forks, ND all have versions of a normal histogram, with a peak in the middle and lower numbers at the edges. The offices on the Plains have a higher peak and no tornado average in winter. In Norman, Oklahoma, there’s a sharp rise from March to May and a sharp fall from May to July, then a small secondary bump in autumn. Jackson, Mississippi’s peak comes during April, but all months of the cool season are elevated, with a dip in the heart of summer.

By month, Jackson has the highest tornado day average in Jan., Feb. and March. In April, the Fort Worth office is tops. For May, it’s Norman and the highest peak of any office of any month with 4.2 tornado days. Denver is the top spot for June and Aug. July goes to Grand Forks. Sept. is Miami and Oct. is Houston, before Jackson returns to the top spot for Nov. and Dec.

In the searchable table below, you can take a look at monthly details for each office. To fit it all in there, I’ve included the NWS office ID rather than its full name. A map and list of those kinds of details can be found here.

Tornado days by month are shown to two decimal places so lower-end offices can be included. All maps show offices with 0.1 tornado days or more.

Tornado days for strong tornadoes

Strong tornado days are thankfully fewer given the propensity of strong tornadoes (F/EF2+) to substantially risk property and life. Compared to all tornado days there’s a general eastward bias to strong tornado days, with almost as many offices east of the Mississippi as west in the top ranks.

Notably, none of the high Plains offices with high tornado day counts have strong tornado day averages of 1 or above. In fact, many are well below that. For example, the Denver office goes from 11.4 tornado days per year to 0.6 strong tornado days per year.

NWS Jackson (JAN) sees the most strong tornado days per year, with an average of 3.4. NWS Paducah (PAH) and NWS Shreveport (SHV) are tied at 2.5 strong tornadoes per year. Then there’s NWS Norman (OUN), which averages 2.4 days, and NWS Little Rock (LZK) closing out the 2-plus pack at 2.1 days.

Given the comparatively small numbers, I have not included monthly maps for strong tornadoes. However, the data for them by office can be found in full below.

All offices in the top five for strong tornado days have a notable peak in those days. Only one peaks outside of April. In most cases, the top five have the least risk for strong tornadoes in the heart of summer thanks to a typically absent jet stream. As with the general tornado days, Jackson has a muted secondary peak in the cold season. It’s perhaps the office at the most risk for tornadoes throughout the year.

Two of the offices that made the top five for all tornadoes made the top five for strong tornadoes: Jackson and Norman.

As with tornado days, the Jackson (JAN) office owns the top spot in many months for strong tornado days, including: Jan., Feb., Nov. and Dec. In March, it’s NWS Birmingham (BMX) and by April it’s NWS Shreveport (SHV). NWS Norman (OUN) takes the top spot for May. June, July, and Aug. go to NWS Grand Forks (FGF). In September, NWS Minneapolis (MPX) tops the list. October is led by NWS Fort Worth (FWD).

Strong tornado days by month are shown to two decimal places so lower-end offices can be included. All maps show offices with 0.1 strong tornado days or greater.

Offices with an average of zero are not included in the tables.