Monday, May 2, 2016

No, AccuWeather Can't Really Forecast 90 Days In Advance And Nobody Else Can, Either

AccuWeather thinks it can correctly forecast
your daily weather for each of the next 90 days.
Don't buy it. Can't happen 
Here at my weather perch in St. Albans, Vermont, it rained most of Sunday and high temperatures were about 10 degrees cooler than average.

I knew the day before this kind of weather would happen.

The National Weather Service, AccuWeather, the Weather Channel and most other meteorologists are pretty damn good at telling us what's going to happen the next day.

However, back on February 1, I had no idea what the weather would be like on May 1. Oh sure, I knew it would be warmer than winter, snow was unlikely, but specifics? Nah.

Nobody did. Not even the best meteorologist in the world.

Still, AccuWeather has gone ahead with the launch in April of their forecasts for the next 90 days for where you live.

Just type in the city nearest you and away you go.

The forecasts are specific for each day. I randomly selected July 24 in Burlington, Vermont, AccuWeather tells me the high temperature will be 84, and the low 57 with "some sun, a t-storm, warmer."

If you click on that date, the forecast gets insanely specific. Much more so than what a normal National Weather Service (and responsible) forecast for the very next day would be.

For instance, we learn from AccuWeather that on July 24 in Burlington, the wind will blow from the west, northwest at 7 mph with gusts to 13 mph. It will rain for 1.5 hours and the total precipitation that day will be 0.14 inches.


As good as AccuWeather's forecasts almost always are for each of the next three or four days from now, don't believe the hype. It's still impossible to know exactly what the weather is going to be one, two or three months from now, no matter what AccuWeather says.

Oh sure, you can get a vague idea. I know that temperatures in Burlington, Vermont during early July are normally in the low 80s during the day and around 60 at night.  That gives me a baseline of what to expect that time of year.

Long range forecasts hint at a possible warmer than normal July because of a fading El Nino and a possible resurgent La Nina, but even that vague hot summer forecast is really iffy.

In their breathless announcement about the 90 forecasts, AccuWeather said:

"'AccuWeather continues to be a pioneer in providing users with industry-leading weather innovation, helping them to better plan their lives and stay safe,' said Steven Smith, President of Digital Media at AccuWeather. 

'Every day, we challenge ourselves to provide our users with the world's best and most impactful forecasts available worldwide. Driven by customer demand, the Day By Day 90 Day Forecast was developed to provide our users the same intuitive trend tool they rely on with AccuWeather's Day By Day 45 Day Forecast, now showing expected weather conditions three months in advance."

Well, yeah, customers demand the service. People often ask me what the weather is going to be like on a specific day two months from now. Just because people want it doesn't mean they can get it.

In 2014, when AccuWeather started issuing forecasts for 45 days out, people legitimately criticized that, too. The fact is, take any weather forecast for more than a week from now with an enormous grain of salt.

Still, as the Washington Post Capital Weather Gang notes, AccuWeather defended the 45 day forecasts then, as they are defending the 90 day forecasts.

In December, 2014, AccuWeather founder Joel Myers told Capital Weather Gang: "We're a very scientifically-based company....We wouldn't issue something that didn't have a scientific basis. People accept the fact a forecast is not perfect, but they want the best estimate the science will allow."

Myers also said computer models are a lot better these days, despite what the naysayers claim. "People always stand in the way of progress, limited by what they believe and what they've seen."

Yes, computer weather forecasting models have gotten better and people should strive to advance science, and forecasting and skill in that forecasting.

But I'm concerned about overselling forecasts to the public. There's already a persistent and vocal drumbeat that meteorologists are "always" wrong and it's the only job you can repeatedly screw up at and still stay employed.

These long range forecasts like AccuWeather's are "not only undermining their reputations but are diminishing the credibility of the weather forecasting profession," wrote University of Washington meteorologist Cliff Mass in his blog more than a year ago.

Mass went on: "Is providing forecasts you know to be inaccurate any different than selling magical elixirs that you know can't provide the promised cure? I will let you decide."  

Though AccuWeather forecast is specific, if you look closely, they subtely keep things vague by not departing much from what conditions are "normal" for that time of year.

 In their May forecast for most of July, the chilliest high temperature of the period is expected to be 78, while the warmest will be 87, for a range of just nine degrees.  Low temperatures in the AccuWeather forecast range very narrowly between 56 and 65 degrees

In reality, there's almost always a much greater range of temperatures over a three and a half week period. For instance, last summer, daily high temperatures between July 1 and 29 ranged from 71 to 93  degrees. Overnight lows were between 49 and 71 degrees.

Those 2015 temperature ranges of 22 degrees over the course of four summer weeks are pretty typical for a Burlington, Vermont July.

I've decided to do a little experiment.  I copied down on Sunday, May 1, what AccuWeather says the weather will be like in Burlington, Vermont daily between June 26 and July 29, the last day of their extended 90 day forecast.

Then on July 30, I'll compare the AccuWeather forecast to reality, using stats from the National Weather Service office in South Burlington, Vermont.

(For the record, the National Weather Service does not offer specific daily forecasts beyond seven days out.)

I bet most of the May 1 AccuWeather forecasts for late June and most of July will be off.  They'll get a few of them, because, well, a clock reads the correct time twice a day, right?

AccuWeather tells me the weather in Vermont is going to be gorgeous over the Fourth of July weekend, with sunny skies and temperatures in the mid-80s.

I'm still going to wait, though to decide whether to go to the beach, and what to wear when I go to the fireworks displays.

1 comment:

  1. Ha! I suppose "some sun, 80s, chance of a thunderstorm" has a 50% verification for Burlington in July anyhow since "chance of a thunderstorm" is super vague and true most July days. Accu weather is dumb.