Why Are We So Bad at Predicting How Much Snow We’ll Get?

Slate ^ | JAN. 3 2018 | Geoff Fox

[nickcarraway]

We’ve gotten better, but there are still a lot of calculations at play.

How much is it going to snow Thursday? As a meteorologist, the bane of my existence is predicting snow. It is the most difficult forecast I make with dozens of different ways it can go wrong. More troubling, it’s probably the forecast most scrutinized before and after the fact.

But why? What is it about snow that makes it so tough to pin down?

Though temperatures at ground level are important, the critical numbers for assessing snowfall are much higher up in the atmosphere. We’re looking for ice crystal growth, which happens when the air is wet enough and cold enough—sometimes down to -20° Fahrenheit, though the biggest snow growth happens at somewhat warmer temperatures.

The ice crystals start small, but as they collide, they grow, until finally they’re large enough and heavy enough to fall to Earth. Snow is water plus air—air being very important. It’s the fluff factor, the reason an inch of water can be 5 inches of snow or 30 inches or something in between. The snow liquid ratio, or SLR, is different for every storm (high SLRs are good for skiing, bad for snowballs). And that’s what we’re trying to predict—how much liquid is going to produce how much snow.

Most snowstorms are driven by low pressure systems hundreds of miles across. Around the low, warm air rises and cools. That causes water vapor in the air to condense and form clouds. Liquid droplets come next until gravity and temperature begin to dominate. For those who live in snow belts there’s a second method to produce snow, the lake effect. Assessing these two methods of snow production should allow you to get a good idea of how much snow to expect, but often

[<1/1,000,000th%]

It doesn’t snow anymore.

[OrangeHoof]

Meteorology....The only profession where you still get paid when wrong.

Not true or almost every pollster and political pundit would be unemployed beginning 2017.

[bruin66]

The “Never-ending drought” in California never-ended last year.

[Southside_Chicago_Republican]

My wife like to look at the extended forecast to see what the weather will be like a week from now. I look at it too, to see how often the forecast changes in the course of the week. The weather forecasters are at their best when they are tracking a storm on the ground. When they say the thunderstorm is going to hit my area at 8:31, I can pretty much count on it. Otherwise, not so much.