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Major weather organizations, The Weather Network included, have issued their seasonal forecasts for Summer 2015. Why are they so different? How are they made? And who does it better? Read on to find out more.
OUT OF THIS WORLD | Science Behind the Weather

Summer 2015: How our prediction stacks up against the rest


Scott Sutherland
Meteorologist/Science Writer

Sunday, July 5, 2015, 1:08 PM - Major weather organizations, The Weather Network included, have issued seasonal forecasts for Summer 2015. Why are they so different? How are they made? And who does it better? Read on to find out.

What everyone is saying

You can read all about The Weather Network's Summer Outlook here, including the regional breakdown, but the basic pattern is shown below:

Environment Canada's Seasonal Forecast

Environment Canada Forecasts - Temperatures (left) and Precipitation (right)

Temperature and precipitation forecasts from Environment Canada have two maps each. Whereas the "deterministic" forecast (pull slider to the right) predicts the expected conditions (above, below or near normal), the "probabilistic" forecast (pull slider to the left) gives the predicted likelihood that those conditions will occur, or in other words, the confidence level of the forecast.

AccuWeather's 2015

The Farmers' Almanac 2015 Summer Outlook for Canada

How each forecast is made

Some forecasters take a very hands-on approach, analyzing times in the past when there were similar patterns in weather, teleconnections and sea-surface temperatures (aka "analogue years"), and then taking into account how current differences from those past conditions will affect the outcome. Some run complex sets of computer models, generating an "ensemble" look at the future weather, which emphasizes the similarities between the various model results. Others take a combined approach that considers both analogue years and computer model results.

The Farmers' Almanac

The Farmers' Almanac has been around since 1818, and no one — except for their forecaster, Caleb Weatherbee (a pseudonym) — knows how their forecasts are produced.

As written on their website:

The Farmers’ Almanac weather predictions are based on a secret mathematical and astronomical formula. Developed in 1818 by David Young, the Almanac‘s first editor, this formula takes many factors into consideration, including sunspot activity, moon phases, tidal action, and more. This carefully guarded formula has been passed along from calculator to calculator and has never been revealed.

According to editor Peter Geiger, the Almanac draws their seasonal forecasts from its overall yearly forecasts, which are produced two years in advance. It's for this reason that their summer forecast was already pinned to their website as of April 20, 2015.

AccuWeather

AccuWeather declined to provide details about its methodology.

According to its corporate website: "Many industry leaders consider AccuWeather seasonal forecasts to be their best-kept strategic secret."

Environment Canada

Up until 15 years ago, Environment Canada forecasters had a very hands-on approach to their seasonal forecasts, adjusting computer model results after examining analogue years for similar weather patterns. However, the decision was made around the year 2000 to switch to a pure computer modelling approach.

According to the EC website, each forecast results from combination of 20 different model runs — 10 each from two different coupled atmosphere-ocean models (CanCM3 and CanCM4).

Environment Canada climatologist David Phillips said that forecasters meet to discuss the forecast before it is released, but no changes are made.

The reason for this? According to Phillips, it is to better evaluate how the models are performing. By removing the human influence in the results, it becomes easier to see how the model is handling various weather patterns, and thus where the model may need to be adjusted to produce better results.

However, call upon Phillips at any time during the season and he will give his view, drawing on his vast knowledge of Canada's weather history, and the latest update of the computer models — either the monthly update released on Environment Canada's website, or the daily model results.

The Weather Network

Here at The Weather Network, our team, led by Dr. Doug Gillham, produces our seasonal forecasts by taking a balanced approach. This team analyzes global weather and jet stream patterns, as well as global ocean water temperature patterns, and looks back through history for years that best match the current and projected patterns (aka "analogue years").

"While no two years are identical, we can learn a lot about upcoming seasons by looking back to see what similar patterns have produced in the past," Gillham says. "The biggest challenge is in correctly identifying the key factor that will drive the weather pattern during the upcoming season."

Our team also considers computer model guidance that is produced by weather services around the world.  These computer models assist us in determining to what extent the current pattern will persist versus how it will change during the weeks and months ahead. 

"Understanding the current pattern and how it should evolve is critical to being successful, as the models will often disagree with each other or come up with a forecast that does not make sense meteorologically," Gillham added.

Past performance

How the forecasts performed over the past year or two is no indication of how they will perform in the future, but it is worth seeing how the different methods compared against eachother.

Farmers' Almanac

Here's what Caleb Weatherbee had forecast for last summer and this past winter:


Credit: Farmers' Alamanac


Credit: Farmers' Alamanac

AccuWeather

AccuWeather forecasters produced the following outlooks for last summer and winter (click to enlarge):


Credit: AccuWeather


Credit: AccuWeather

Environment Canada

The computer model runs generated these seasonal forecasts for summer 2014 and winter 2014/15 (click to enlarge):


Credit: Environment Canada


Credit: Environment Canada

The Weather Network

Here are the outlooks for the past summer and winter seasons, produced by the forecasting team here at The Weather Network (click to enlarge):

What really happened last year?

When you boil it all down, this is what it's all about. How did the forecasts from last summer and winter compare with what really happened?

Summer 2014

A comparison between the four Summer 2014 forecasts and the actual observed surface temperature anomalies (departures from the 1981-2010 average, courtesy of WeatherBell), during Meteorological Summer — from June 1 to September 1, 2014. CLICK TO ENLARGE.

Winter 2014/15

A comparison between the four Winter 2014/15 forecasts and the actual observed surface temperature anomalies (departures from the 1981-2010 average, courtesy of WeatherBell), during Meteorological Winter — from December 1, 2014 to February 28, 2015. CLICK TO ENLARGE.

Whose Forecasts Came Out On Top?

Different forecast techniques certainly generate different results, as these comparisons clearly show.

AccuWeather and The Weather Network were the clear front-runners for Summer 2014, capturing the significantly cooler weather that was experienced through the Great Lakes area and into the southern Prairies, while also catching the warmth through British Columbia, northern regions of the country and in Atlantic Canada (although they caught different parts of the warmth in the east).

For Winter 2014/15, everyone saw what was coming in Atlantic Canada for precipitation (see previous page for the precipitation forecasts). Storm after storm dropped record levels of snowfall across that region of the country. As for temperatures, it seems like the everyone picked up the basic idea, but the details come out somewhat different. It was certainly not frigid in southern Alberta, nor was it above normal temperatures through the eastern Prairies. What’s particularly striking is how The Weather Network’s forecast almost exactly matches the pattern of the observed temperatures.

As for how seasonal forecasts perform, overall, it's helpful to remember that the forecast categories can be quite broad. While "near normal" is tied closely to the average conditions over the past 30 years or so, with some leeway (above and below) for variations, the "above normal" and "below normal" categories are completely open. So, for example, whether a season for any particular location finishes at 1 degree C or 30 degrees C above the "near normal" range, it would still be considered a "miss" for that location. Based on that, it only takes one particular storm - rain or snow — or one outbreak of extreme temperatures — to skew the observed conditions into a completely different category.

The mark of a successful forecast is to match the pattern of seasonal weather as closely as possible, without having wide misses, where locations forecast to have "below normal" end up with "above normal", or vice versa.

Sources: Environment Canada | AccuWeather | Farmers' Almanac

WATCH BELOW: With the look forward through summer, Chris Scott and Chris St. Clair look back at the conditions and forecast from this past winter

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