Whenever there's a crime wave, it's followed by weekend crime roundups, for obvious reasons: people have free time, a tendency and excuse to consume intoxicants, and homicides spike on Saturdays and Sundays. If it bleeds it leads, and it bleeds most on the weekends. By RedEye's count, Saturday and Sunday each have had about a third more murders than the third-place day (Monday); the ratio is similar in Los Angeles. So a regular feature of the Monday morning news is how many homicides there were over the weekend. If it's a few or more, it moves up the page and ahead in the broadcasts.

That got me wondering: what's an average weekend, as far as homicides, in Chicago? What's a "violent" weekend? Do we ever get weekends without any homicides at all?

Using RedEye's data, thoughtfully compiled by Tracy Swartz, I went through all the March-October weekends from 2007 through the beginning of June; five years' worth of data from the height of crime season seemed like a good sample. I strictly counted Friday-Sunday; no holidays are included—there were five murders on Memorial Day this year, for a total of 12 over Memorial Day weekend—or late murders on Thursday night or Monday morning.

The result? On average, there are 4.9 murders per weekend, with a median of five.

The most murders in a weekend? July 4th weekend of 2009, when there were 12 murders from 7/3-7/5 (with an additional five murders that Monday). The weather that weekend was good: cool (low of 61, high of 82) and dry (0.15 inches over three days).

The least? Zero, which happened three times out of 187 weekends:

* April 10-12, 2009 (a bit cold, temperature between 33-53 degrees)
* May 13-15, 2011 (that Friday was fine, in the 70s, until noon; then the temperature dropped almost 30 degrees and stayed below 51 all weekend)
* May 27-29, 2011 (cold and rainy)

The month with the most double-digit-homicide weekends in that time? October (three), followed by May and July (two). In 2008, there was a ten-homicide weekend in November (11/14-11/16, nothing particularly notable about the weather).

So from March through June 9-11, Chicago's had 85 weekend murders, for an average of 5.7 per weekend (an admittedly small sample size of 15 weekends), with one double-digit weekend. Here's what the distribution of murders per weekend looks like from 2007-2012.

Photograph: Chicago Tribune