Another winter, another predicted snowpocalypse that didn't happen. Does Les Schwab bribe the weatherman to forecast wintry doom in the hope we'll buy more snow tires and tire chains? —NOAA's Ark
The snow tire industry actually seems pretty free of weather-forecast-related corruption, Ark—it's Big Kale you need to watch out for. In any case, several factors conspire to make weather forecasts a bit more dire than the weather itself.
For starters, while it's certainly annoying when what was supposed to be 8 inches turns out to be more like one and a half (amirite, ladies? Ba-DUM-tsss!), it's better than expecting flurries and getting a blizzard.
If there's a chance of life-threatening weather, news outlets have a duty (and, of course, a financial incentive) to warn the public. The 40 percent or whatever chance everything will be boringly fine tends to be overlooked.
This is not unreasonable—if somebody told me there was an 80 percent chance my plane wouldn't crash, I'd tell him he buried the lead—but it does result in the occasional false positive.
There's also something called "wet bias," which is a measurable tendency on the part of forecasters to overstate the likelihood of precipitation.
For example, a 2002 study found that the Weather Channel routinely reported a 5 percent chance of rain as 20 percent. Apparently, people are too stupid to know the difference between 5 and 0 percent—they take 5 percent as a guarantee of fair weather, then blame TWC the one time in 20 it does rain.
This isn't the only fast one TWC pulls. You'll notice it never reports the chance of rain as 50 percent—to the aforementioned stupid people, that sounds like the forecaster is saying, "I don't know." Thus, it always rounds down to 40 percent or up to 60.
For what it's worth, the actual National Weather Service doesn't play these games—its website gives you its real best guess. Perhaps not coincidentally, the NWS predicted a modest 2 to 4 inches of snow on the eve of last week's storm. But how much kale can you sell with a weather report like that?