You probably went to bed on the 26th hearing that New York City was going to get buried in snow.
You probably woke up on the 27th and learned that it was Boston and New England east of New York that got buried.
One problem is that forecasters went with what they were comfortable with rather than what was most probable.
There was plenty of evidence the #blizzardof2015 wouldn’t be record-setting in New York. http://t.co/ovoCRvn6aa pic.twitter.com/eLNllFx4HHAdditionally, lots of computing power goes into weather forecasting, and even 24- and 12-hours in advance of events, there are still very meaningful error bars on predictions. Uncertainty
— FiveThirtyEight (@FiveThirtyEight) January 28, 2015
has been a problem for media forecasters who have historically been too confident in predicting precipitation events. A study of TV meteorologists in Kansas City found that when they predicted with 100 percent certainty that it would rain, it didn’t one-third of the time. Forecasters typically communicate margin of error by giving a range of outcomes (10 to 12 inches of snow, for example). In this instance, I don’t think the range adequately showed the disagreement among the models. Perhaps a probabilistic forecast is better.We have our own local problem with forecasting. And here too forecasters are riding what's comfortable rather than what's probable.
|Have we exaggerated likely traffic in 2031?|
Planners, policy makers, and electeds are all making decisions on a single traffic forecast pushed very far out into the future. We should know more about how reliable it is likely to be.
|Trend-line mania: 61 out of 61 projections were too high.|
Also, the same slope on the trend line always!
Planners may think the perspective here is equally wrong in the other direction. Fine. But they must admit that their modeling inputs now assume a high level of growth in driving.
And it is no longer reasonable to assume only this; and conversely it is no longer unreasonable to perform similar modeling with assumptions for low and even declining levels of driving.
Washington State is in fact making their primary forecast with a declining level, and the Feds have revised theirs and moved to a forecast with low growth instead of higher growth.
We are out of step with our neighbors to the north, and we are out of step with the Federal Highway Administration. Shouldn't we get with the program?
|via Washington State Ferries|
Transportation Revenue Forecast, October 2014
(Sightline link broken)
Even if you think the low projection is unlikely, any statistician would tell you now that it has a substantial non-zero chance of being closer to reality than the high projection.
Don't be like bad weather forecasters, ok?