Weather Blog

Long range model chaos: 55 degrees? Or -2?

Long range model chaos: 55 degrees? Or -2?

Back in the day, long range forecast models used to be sent out via glorfied fax machines -- a printer would sit in the weather center and churn away a bunch of boring-looking black-and-white charts. And you paid through the nose to get access to them.

These days, forecast models easily available online in full color -- and free. And in doing so, has opened up what used to be a somewhat secretive world of weather forecasting to anyone with the right URL.

Social media has taken it a step further and now it makes it very easy to share forecast thoughts with forecasters and weather fanatics.

And it also brings several more pairs of eyes to what can be some amusing forecasts some of the models can put out from time to time, especially in winter when the lookout for snow is heightened.

More than a few people have caught an eye-popping forecast that one model run from late Monday night had for the Northwest. Here is what the model translated into forecasts for Seattle for the week of Thanksgiving:

Hah! A temp of 12 degrees after a morning low of -2 on the morning of Wednesday, November 23! That would shatter all sorts of all-time records around here.

Oh, but what the model giveth, the model taketh away.

Here are the comparison charts forecasting the same period, but successive model runs (the one in the left was the overnight chill-out scenario, the one on the right is the later Tuesday morning forecast run.)

For those who don't speak weather forecast-chart-ese, the one on the left shows a big arctic high poised right over B.C. that has blasted arctic air into Western Washington (and really, the entire West Coast). The chart on the right shows a rather warm rain storm heading into Seattle with a high likely in the mid 50s and even rain at Snoqualmie Pass.

And that's just one forecast model running the same computations just 6 hours apart.

Now, long range forecast models run in a lower- resolution mode once they get to Day 7 so it can hurry up and compute days 8-16 before the entire forecast gets obsolete, so mountains and other important features get glossed over, so that too affects reliability.

But overall, it just goes to show how super long range forecasts are just not very reliable yet. But they sure can be fun to dream about!

(P.S. - If you want to see some real winter excitement -- check out this forecast for western Alaska from Tuesday morning)