One of the go-to "fun facts" of the weather so far this year is that tornado activity is well below average, with this year's preliminary tornado reports clocking in nearly 400 below normal. This week, though, proves more than ever that it only takes one tornado to make it a bad year.

In the past week, we've seen at least four EF-4 tornadoes, three EF-3 tornadoes, and more than two dozen weaker tornadoes. The number of violent EF-4 (and possibly one EF-5) twisters surpasses the tornadoes seen in late April as the strongest outbreak so far this year.

Stanton-Pilger-Wakefield Tornado Family

Ground zero for tornado activity this week was northeastern Nebraska, where no fewer than six tornadoes touched down and tore up several small communities. The worst storm in the outbreak occurred on Monday, June 16 when one supercell produced five tornadoes — two of them at the same time (pictured above) — in what's known as a "tornado family."

On the Enhanced Fujita Scale, which estimates the tornado's winds based on the damage the produce, four of the five tornadoes clocked in at the second-highest rating of an EF-4 (166-200 MPH), with surveyors leaving the door open for the possibility of the Pilger tornado receiving an EF-5 (201+ MPH) rating when they conclude their study of the damage. The fifth tornado near Stanton, not included on the map above, was a weak EF-0 (65-85 MPH).

The worst of the five tornadoes was westernmost of the twin twisters that hit Pilger, which destroyed more than 75% of the town, killed two people, and injured nearly two dozen more. One of the victims was five-year-old Calista Dixon, who was at home with her family when the tornado hit. She passed away as a result of her injuries. Her mother is still in a medically-induced coma, and her brother was seriously injured. The second fatality in the storm was a gentleman in his 70s who was involved in a weather-related traffic accident, according to CNN.

If the Pilger tornado is ultimately rated an EF-5, it will be the first top-of-the-scale twister since the devastating storm that hit Moore, Oklahoma back in May 2013, and only the 11th since 2000.

The Coleridge, Nebraska Tornado

One day later, a similar scenario played out when a solitary supercell formed over northeastern Nebraska. The storm took full advantage of the unstable air around it and produce at least two large tornadoes which barely moved while they scoured the earth near the small town of Coleridge.

The tornado destroyed several buildings but thankfully left behind no casualties. One of the tornadoes was at least an EF-3, but the NWS in Omaha is still investigating the damage it left behind before it releases its report.

Wessington Springs, South Dakota Tornado

On Wednesday, June 18, yet another strong tornado touched down, this time in the small town of Wessington Springs, South Dakota. The tornado had an incredible structure to it, with up to five suction vortices — smaller, intense whirlwinds within the rotation of the tornado — seen dancing around in the fields as the storm moved through the area. These suction vortices are the reason why tornadoes can destroy one house and seemingly "skip" the house next door.

More than three dozen homes were either damaged or destroyed by the storm, including one home where a group of storm chasers were able to pull a family out of the rubble. The chasers aided the family before taking the above picture of the battered neighborhood, complete with a rope tornado in the background. An excerpt of the story Chad Cowan posted on his Facebook page tells the scene they encountered while trying to help the victims:

As I was about to move on to the next house, I heard a muffled woman's voice yelling from near the front door. I had to climb over a bass boat to get to where I could hear her, and she was in the basement talking through a small window in the foundation that was covered in debris. I asked how many people were down there and if there were any injuries.. she said there were 6 of them, 4 adults and 2 little girls and everyone was okay but debris was blocking the stairway and they couldn't get out. I promised her I would get them out and ran around looking for a way in the house but saw no way of getting to the stairway through the thick debris piles. Looking around and seeing all of the damaged houses and feeling helpless, I tweeted "People trapped please send help". Then I saw a neighbor who had just emerged from his slightly damaged house, and called out and waved him over. He asked if I had tried the front door, and I told him it was locked to which he replied "not anymore" and kicked it in. There was a refrigerator that had somehow ended up on the other side so the door wouldn't open more than 6 inches. The back door was unidentifiable among the wreckage so the garage was the only possible entrance and exit.

Carter County, Montana Tornado

A strong EF-3 tornado touched down in southeastern Montana on the evening of Tuesday, June 17, destroying numerous structures and tossing around cars like toys. This was the strongest tornado ever recorded in southeastern Montana, according to the National Weather Service, and it dispels the myth that tornadoes — strong ones, at that — cannot cross mountains.

Madison, Wisconsin Area Tornado

Yet another EF-3 tornado touched down very early in the morning on June 17, this one threatening downtown Madison, Wisconsin. The storm produced two tornadoes; the first, an EF-3 that produced heavy damage in Verona, Wisconsin, and the second touching down ten minutes later in Madison proper, producing EF-2 damage.

The storm was incredible to watch on weather radar, pictured above. The tornado occurred in the "comma head" of a squall line, which forms when the northern end of a squall line curls back like a comma head and develops a fairly pronounced spin on radar imagery. Tornadoes can form in these comma heads, and that's exactly what happened around Madison on Tuesday morning.

As the Storm Prediction Center's data shows, we are still 30% below the 8-year average for tornado activity as of yesterday, with only 682 reports of tornadoes (note that reports of tornadoes are different from documented tornadoes) so far this year.

Even if it's been a slow year and we're still below average, it only takes one tornado hitting one populated area to make it a bad year.

[Images via StormChasingVideo / NWS / Gibson Ridge / Chad Cowan / via NWS by Meagan Reedy / Gibson Ridge/ SPC]

You can follow the author on Twitter and send him an email here.