Wednesday, April 04, 2012

25 Day Forecast? Will It Be Better Than A Crystal Ball?

Gotta give them credit for trying.  AccuWeather is going out beyond the limb, out beyond the edge of the leaf even, to predict weather.  They are launching the 25 day forecast today, which means they will be predicting weather out past three weeks.

Mark your calendar, if AccuWeather is right, for 0.71" of rain on Monday, April 23rd (click on the image on the left for their "full" forecast).  Accu is not only predicting rainfall for more than two weeks out but they are taking a stab at "how much" as well as wind trajectory and speed.

Keep in mind that April is one of the more meteorologically volatile months on the's certainly not July and the biggest threat is heat and thunderstorms.  You can have anything from nor'easters to 90 degree weather in the span of a few weeks around here!

“The AccuWeather 25-Day Forecast is a scientific and meteorological breakthrough,” said Dr. Joel N. Myers, AccuWeather Founder and President in a press release. “It is a revolutionary, innovative tool that you can use to make your personal and business plans anywhere you live or travel. For events already scheduled, such as weddings or sporting events, it gives you the best available, most accurate, detailed advance guidance on how to plan, given the weather forecast. It is truly one-of-a-kind.”

The full 25 day outlook for Philly as of this afternoon is below.

In my dialogue with AccuWeather's PR guys, I asked them specifically the following which I didn't get a response.

"Many times there is a significant amount of spread in computer modeling in the longer range (10-15 day) between each model run, which can yield quite a lot of change in the longer range forecasts that we're accustomed to seeing.  How are the 15-25 day "trend" forecasts going to account for those potential volatile spreads between runs of a particular model so the forecasts are somewhat consistent from day to day or evening to morning?"

The closest response I've seen so far is that "While day 20 and 25 is not going to be the exact temperature… you’re going to be able to see we’re going into colder [or warmer] weather pattern,” according to Henry Margusity in an interview with Capital Weather.

The kicker is that sometimes those patterns can alternate (colder, warmer, etc.)  in each run of a computer model, especially the farther out in the future one goes.

The methods are proprietary...the rumor mill suggests a blend of European weekly modeling along with a filtering through algorithms to come up with hard data.  

Forecasts typically lose accuracy past seven days -- so it will be interesting to see how this 25 day outlook will pan out...and yes, we will keep track of it occasionally as well!