Forecasts and probabilities

Call me crazy, but I thought the forecast for Snowquester was pretty good, as total busts and epic fiascos go. The models in this case predicted serious snow in the I-95 corridor, but the storm “underperformed,” and didn’t drop snow intensely enough and consistently enough to cool down the warm layer of the atmosphere and the warm ground in the urban areas. For those of us in the city, Snowquester turned out to be the winter storm equivalent of Albert Haynesworth.

Still, I blame the storm more than I blame the computer models. The models are pretty good. It’s Nature that messed this up.

I don’t think the forecasters, from the National Weather Service to Bob Ryan to my colleagues at the Capital Weather Gang, have anything to apologize for. Seems to me they made clear in advance that this wasn’t a slam dunk (that’s why I decided to write a story about how squishy any snow forecast is for this part of the world in March). [Most prescient line in the story was the last one, as it turned out: “The snow will soon be gone, as if it never really happened.”] The forecasters correctly predicted that two low pressure systems would converge to form a winter cyclone over the metropolitan DC area. And they correctly said the snow would fall with a sharp geographical gradient, the west getting a lot and the east getting little. The gradient turned out to be much sharper than anticipated, as this graphic shows.

I am guessing the regulars on the weather blogs understand, and accept, the inherent uncertainties in weather forecasting. Here’s the key fact: The weather isn’t a machine. The weather isn’t the result of a deterministic process. No refinement of the models is ever going to result in a perfect forecast, because weather is chaotic, particularly stormy weather.

Now, here’s a nice ode to Snowquester, at the CWG blog.

Update: Here’s Jason Samenow’s postmortem on the forecast. “The best forecast for Snowquester was one we could not issue with a straight face, and one most Washingtonians would have ridiculed: Rain, sleet, and/or snow likely – heavy at times – with snow accumulations of 0-14 inches.”

Update 2: I’m told via Twitter that my chaos line is incorrect. Gavin Schmidt (@ClimateOfGavin) writes: “Chaos in weather systems is technically deterministic – it happens even without introducing random elements.”

Alvin Lee is gone. Loved that guitar solo at Woodstock.

Worth reading: Alexis Madrigal on being a digital journalist (doesn’t sound easy — man do I have it good!).

Joel Achenbach writes on science and politics for the Post's national desk and on the "Achenblog."

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Joel Achenbach · March 6, 2013

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