The last couple months have been a precipitation roller-coaster around here. From early March to mid-April, we had rain on 30 of 45 days. Then we hit a stretch of a month when we couldn't buy a drop! That was followed by two weeks with more than five inches. Whenever we get in a persistent weather pattern, be it wet or dry, I'm always asked "Why are we stuck in this rut?"

The simplest answer is that the weather is naturally variable - it's normal to have periods of persistent wetness or dryness. More scientifically, you can always blame persistent weather on the jet stream, that fast river of air that blows about 25 to 30 thousand feet up. Sometimes the jet bends toward the south - dips that we call troughs. If one of these troughs sets up just to our west, we tend to have wet weather because upper-air winds here blow from moister southern latitudes. On the flip side, if the jet bulges toward the north - a bend we call a ridge - and that ridge sets up just to our west, dry weather is favored because that air tends to come from Canada. When either of these patterns locks in place for days and even weeks, we can settle into a period of persistent weather.

But what makes the jet stream lock into one of these patterns for long stretches? Here, there's no short answer - diverse influences from far away, such as El Nino, the amount of snowcover over the Arctic, or the temperature in the North Atlantic Ocean - can all nudge the jet stream one way or the other and keep it that way. But there are many such influences - some not known, all working together in very complicated ways - and a simple, tidy sound bite can't explain why the jet stream does what it does.