Although the weather has/had been fairly constant in much of the region during
the early 2004 season (i.e. unusually cool and wet, particulary in Iowa,
Minnesota, Wisconsin, and the eastern Dakotas), the AI values plotted over
time for the cool/wet areas initially decrease and then increase.  The reason
for this is that weeks 11, 12, and 13 have negative weighting and weeks 14,
15, 16.... have positive weighting.  The weighting is according to the
definition of AI on the main page and usually doesn't produce drastic swings
early in the season because early in the season the weights are slight.