Lagering is essentially the fermentation and conditioning of beer at temperatures around 40-50° F. Most homebrewers lager in an old refrigerator or modified freezer. I don't currently have that option. So, I attempted to do some lagering in the garage.
During this time of year in Minnesota, the average high is 58°F and the average low is 33°F. In a garage, the temperature should stay within a reasonable lagering range. Granted, this is NOT the best way to do this, but it is one way. In fact, one may argue it is a more traditional way. One that harks back to the pre-refrigeration days.
So, the time was right. Time to lager. The window was short. Do it now, or the garage will soon be at ale fermenting temperatures.
I brewed two batches, a pilsner and a Boston lager knock off of Sam Adams. I put them in the garage. The temp was a perfect 45° F. This was going to be perfect....
Then, the Minnesota climate kicked me in the groin.
The temperature plummeted and stayed plummeted for the last week. We spent a week without getting above freezing. The garage temperature dropped to fermentation-stopping temperatures. The warmest I observed was 38°. Usually, it was much worse than that. I had no choice but to bring the carboys inside. They have been on my concrete basement floor ever since. Fermenting at a nice cozy 60-64°F.
Is the beer ruined. Oh, absolutely not. I have no doubt, the result will be a very drinkable beer. However, it will be a far cry from what I was hoping to produce. The flavors will be different and the beer will not be as clear and crisp, but it will be good beer. I'm not worried about that.
The moral of the story: never, ever, ever, ever trust Minnesota weather. A few days before we dropped to our below freezing streak, it was 82°F. While the weather does annoy me, I revel in the fact that a 70° temperature difference during the course of a few days is not unusual for MN. Not many people have to regularly deal with this.
 There is of course a lot more to lagering than that, but I have a 2 inch stack of chemistry research papers to read. Most of my time right now is spent wondering why I assign assignments like this.
 Our deep freezer recently quit being a freezer due to a spent compressor. It gets cold, but doesn't freeze. It is in our garage right now. When it gets warm enough, I am going to try to convert it. 
 What a stupid sentence that was. It's like my freezer is a lager atheist and I want to convert it into a lager believer. "Do you believe in lagering as your personal savior?"
 OK, now I'm just procrastinating (see note 1)