TornadoAlleyForecast.com and Twisterforecast.com presents the following easy, accurate, and quantitation of damage for tornado activity and suspected tornadoes.

Step 1:

Consider and estimate the weight of the heaviest object, in pounds, which has been moved by the storm, suspected tornado or twister that you are observing; for example: 

A roof on a small home, would weigh about 200-300 lbs.

MASS OF COMMON ITEMS:

Aluminum chairs...............................................................................4.2 lbs

Tree 50’, 12” diam (small).............................................................2,000 lbs

Tree 80’, 24” diam (large)...........................................................20,000 lbs

Roof only

      Shingle................................................................................2.7 lbs/sq ft

      Slate...........................................................................(1/2”) 19 lbs/sq ft

Cars

      Small.............................................................................3,000-3,600 lbs

      Medium Compact............................................................3600-4200 lbs

      Large SUV, Hi Hummer..........................................................8,600 lbs

Bus

      School.......................................................................19,500-26,000 lbs

      City........................................................................................40,000 lbs

Tractor Trailer Rig...........................................................12,000-80,000 lbs

Homes

      Mobile...................................................................................12,000 lbs

      Small wood-frame.................................................................80,000 lbs

      Medium size brick...............................................................160,000 lbs

      Large steel reinforced......................................................1,500lbs/sq in

Schools

      Large steel reinforced.................................................2,000 lbs/sq inch

Factories and Commercial Structures

      Roof (metal) only.................................................................1.2 lbs/sq ft

      Everything roof to foundation..........................................3,000 lbs/sq in

Step 2:

Now estimate the volume of the object that you have just chosen: in length, width, and depth, which has been moved by the storm, suspected tornado or twister that you have just observed.

For example:  A roof on a small home, would have a volume of about 1 foot thick x 20 feet wide x 50 feet wide =  1000 cubic feet.

Step 3:

Divide the weight by the volume.  In the above situation, for example the weight/volume = density

Or, 200-300lbs/1000cu feet = 250lbs/1000 cu ft = 0.25 D

Step 4:

Now, estimate the time span in which the twister was on the ground doing the cumulative damage that you have observed.  Let’s say the whole time happened in 2-3 minutes.  So multiply the time value to get the time in seconds.

Time (seconds) = 2.5 min x 60 sec/minute = 150 seconds

Step 5:

Now, calculate the energy necessary to completely lift the roof off a small house.  Multiple the Density x Time, then take the log to base 10. 

In the above example to lift the roof off a small house:  log (0.25 x 150) = 1.57

To pick up a mobile home:  log (12,000/5’x15’x 8’) x (60sec/min x 5min) =  3.8

To destroy an entire school May 20, 2013, killing 24 children, for 47 min =  > 6

Formula for TORNADO and TWISTER Damage (proportional to energy) is:

Mary Ann Slaby’s Tornado (twister) DAMAGE Magnitude =

log10 [weight (largest structure damaged)/volume (largest damaged structure)] x time (in seconds twister was on the ground)