It can be dependent on the day or hour, on a special event (the annual Northwest Washington Fair in Lynden attracted a lot of Canadians last week), on the currency exchange (the Canadian $ is still near a 30-year high, thus attracting Canadian shoppers and tourists to the US) and other factors.

The two main border crossings (at Peace Arch and the so-called Truck Crossing) are both undergoing renovations somewhat in preparation for the Winter Olympics in Vancouver/Whistler which is only adding to the delay.

So, to make a short story long your experience is not atypical and there have been much longer waiting times recently, even at the Aldergrove and Sumas crossings to the East.