OK, you're going to have to see this yourselves. There may be an asteroid on the way, impact 4/13/2029. Got to wonder if that is a Friday.
First, go here. Dr. Jerry Pournelle is a smart and well-educated fellow, and he is interpreting the data as saying there is a 1-in-63 chance of this asteroid will impact with a yield of 2200 megatons. Data is early now; this is based on 101 observations. There is a link to the actual JPL data on that page, you can see what you make of it.
One thing I see, and this might be nothing but data changes since he posted, is that the yield is down to 1570 megatons, if I'm doing the math correctly.
JPL also notes on their "Impact Probability":
The probability that the tabulated impact will occur. The probability computation is complex and depends on a number of assumptions that are difficult to verify. For these reasons the stated probability can easily be inaccurate by a factor of a few, and occasionally by a factor of ten or more.
Using one of the Internet nuclear weapon effects calculators and the 2200 megaton figure, within a radius of 21.6 miles, nearly everyone will be killed. Widespread damage will occur out to 56.9 miles. (Link to calculator here; I've converted from metric to English units.
Using the Asteroid Impact Effects Calculator and making some assumptions, we have the asteroid breaking up during its passage to earth, but not dispersing much. The final crater will be 4.5 miles across and 1/3 mile deep. At 62 miles (100 kilometers), the impact will feel like a 6.9 earthquake. The blast wave will be a wind of 72 MPH and windows will shatter.
No need to panic yet, as pleasant as this all sounds. Every time I've seen one of these, further data has shown that the initial impact probability was overstated. Then again, I've never seen the initial probability this high. This will bear watching--as far as I can see, the mainstream media has not picked up on this yet.. Let's hope that complex computation and difficult to verify assumptions work in our favor.