The Absurdity of Weather Forecasts Beyond 10 Days

Editor’s Note: This is a weekly column written by Meteorologist Joel Gratz that will take you “behind the scenes” of the typical weather forecast. Joel is the founder of ColoradoPowderForecast.com, where you can sign up for his email alerts.

Boulder, CO - You’re addicted to powder, and like most skiers and riders with this ailment you check the weather constantly. And not only do you check for the latest update on the storm coming up in a few days, but you’re also constantly wanting the long-range predictions, trying to get a handle of what’s coming up next week or even the week after. Well, I have news for you: stop looking at the long-range forecast. If you want to get a feel for the next seven days, go ahead. But if you’re trying to key in on a storm that’s eight, 10, or 15 days away, just forget about it.

Ok, I know. You’re skeptical of my pessimism about long-range forecasts. After all, when you head to The Weather Channel you have access to 10-day forecasts. When you head to Accuweather they provide 15-day forecasts. So, do they know something about long range forecasting that I don’t?

No. They just don’t care about being accurate and would rather give you an inaccurate
forecast than no forecast at all. In my experience predicting powder, I have pretty good confidence in the forecast three days before a storm, and I have decent confidence in making very general predictions about five to seven days out. Beyond that, there is almost no reason to trust a weather forecast.

Case in point, the 10 day forecast for Jan. 22, made on Jan. 11. The image below shows the range of possible outcomes of the computer models. In a perfect world with a perfect forecast, all of the colored lines will fall exactly under each of the four white lines (the purple under the furthest north white line, then all the blue lines under the next white line, then the green lines, then the red lines).

The Jan. 22 long-range forecast modeled on Jan. 11.

The Jan. 22 long-range forecast modeled on Jan. 11.

If you’re confused, don’t worry. The point of the image below is that in this 10 day forecast the “best guess” of the computer models is represented by the white lines, which show a trough, or dip, in
the East. This would mean stormy weather in the East and clear, dry weather in the West. However, looking at the average of the colored lines which represent other possible weather scenarios, it looks more likely that the trough could be further west, providing snow to at least Montana, Wyoming, and Colorado during this time.

So, what is the 10 day forecast? Snow in the East and dry in the West? Or powder in Colorado? The answer is, of course, to ignore this 10 day forecast in favor of checking back in about five days. There is just too much variability with this length of forecast to have any confidence in the outcome.

Sorry for being such a downer, but it’s the best science we have right now, and I’d rather give no forecast than a wild 10-day guess!

 

Joel first fell in love with weather and skiing at age four, and this passion for snow has not faded with age. After earning his Meteorology degree from Penn State in 2003 and a Masters from the University of Colorado in 2006, Joel started Colorado Powder Forecast out of Boulder, Colo., to help fellow snow lovers with accurate and entertaining weather forecasts. 

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