Is it Summer Yet?

This year, we didn't get a chance to see Erik's parents at Christmas. So, Sven started asking when we were going to see FaFa and Granma. I told him that FaFa and Granma were going to visit Seattle this Summer. When Sven asked when Summer was going to arrive, I explained that when the days are sunnier and longer, that's Summer.

One morning, in the middle of the wettest January in history (January 2006 had 28 straight days of rain) Sven said to me "Its a sunny day today. FaFa and Granma and coming." Looking out the window at the cold wet weather, I had to explain that Summer was still a few months away.

How does one explain seasons to a child?