Asteroid Fun

Space.com has a link to a Catastrophe Calculator. Hee! I've been playing with it for a bit. It takes a little set up, but it sure is fun. First you must set a distance between impact site and observation point. I set it for 850 miles; the rough distance between St. Louis and a festival I'll be attending in August. Since that's well over the horizon, I wouldn't see squat; so I'm not mentioning thermal radiation.
I tested the impact results of a porous asteroid striking St. Louis type land. I set the parameters of a 40 degree angle and a velocity of 22 km/hr. The results for a rock the size of a:

car: hits every other month - leaves a 105 m crater - no seismic effects would be felt
house: hits every 5.9 years - 307 m crater - no seismic effects would be felt - generates a 0.1 mph wind
1 acre field: (rare) hits every 1.1 x 10(to the fourth power)years - 2.79 km crater - has a Richter Scale Magnitude of 6.3, but I still wouldn't feel it at the festival - almost no ejecta would fall on us nekkid pagans - but we would hear it at a decibel level of 55 dB (as loud as heavy traffic)
St. Louis City (roughly 17 miles in diameter): City sized rocks don't hit very often, the frequency is about every 8.9 x 10 (to the eighth power) years - it would leave a complex crater 210.73 km across (From St. Louis to the Lake Of The Ozarks) - I would still miss out on the spectacular fireball, but the thermal radiation would get me anyway. My sarong would catch fire, much of my body would suffer 3rd degree burns; but that wouldn't matter because the festival site is always under a fire watch or fire ban in August, and the trees would ignite. As if flaming clothes, 3rd degree burns and a forest fire weren't enough; 273.7 seconds after impact, the campsite would shake. - 597.7 seconds after the impact, ejecta would start raining down on us. (remember, we're 850 miles away from the strike) the rest is yoinked wholesale from the site: The air blast will arrive at approximately 4561.7 seconds.
Peak Overpressure: 231761.5 Pa = 2.3176 bars = 32.9101 psi
Max wind velocity: 287.4 m/s = 642.8 mph
Sound Intensity: 107 dB (May cause ear pain)
Damage Description:


Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

Highway truss bridges will collapse.

Glass windows will shatter.

Cars and trucks will be overturned and displaced, requiring major repairs.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.