Then there's the cultural reality that, regardless of the economic situation, people spend money on holidays even if it means cutting back elsewhere.

FORBES: Mother's Day By The Numbers

Joe Sobel, a meteorologist for Accuweather, says the company's policy is to not change the percentages outputted by its models, but to modify how it presents those numbers for instance, by emphasizing chances of precipitation, even when they are low, on weekends and holidays, when precipitation can be particularly annoying.

WSJ: Some Percentages Are Just Fair-Weather Friends