The North American monsoon season officially began on June 15 and so did the Southwest Monsoon Fantasy Forecasts, a community game hosted by the Arizona Institute for Resilience at the University of Arizona.

Returning for its sixth consecutive year, the much-anticipated game invites the public and weather enthusiasts to forecast the monsoon season and compete for points with friendly rivalry. 

Zack Guido, the principal investigator of the fantasy forecasts project and an associate professor at the Arizona Institute for Resilience, said that monsoon is a season that captivates people's imagination, excites them and gets them thinking about what the upcoming months are going to be like.

"Predicting rainfall for the next two or three days is itself a significant challenge in the monsoon. Predicting a full season? We don't have good answers and so we decided to turn the question around to the people who live in the region," Guido said. "We turned that into a game."

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Each year, participants predict rainfall in five major cities: Tucson, Phoenix, Flagstaff, Albuquerque and El Paso, with about 400 participants playing on average. But this year, Guido's team has introduced several new features that allows players to take their forecasting game a step further.

In the long-running seasonal challenge, players make monthly forecasts for July, August and September in each of the five cities for a total of 15 forecasts. Players earn points at each station based on accuracy. A "risk multiplier" lets players bet that rainfall will land well above or below average. The further from the norm, the bigger the multiplier if they are right. 

Now, Guido's team is ramping up the weather enthusiasm by introducing a weekly tournament. The weekly forecasts don't have to cover all five stations; players can enter any number of them. This means, the weekly competition plays out station by station. It works more like a sports ladder than a pure accuracy contest.

"It's just like how the USTA tennis works – you get points if you win your matches, and then you go up in the rankings," Guido said.

Running across the 13 weeks of the season, every player starts with the ranking of 1000. Players are paired at random in week one. After that, the system matches people of similar standing, much as tennis ladders do. If you win your weekly matchup, points are added to your ranking. If you lose, points come off. Within a few weeks, a clear order emerges, and the highest-ranked players tend to have a face-off by the final week. Whoever ranks highest after week 13 wins. 

Two things drive the weekly score. Winning a matchup is worth 32 points. On top of that, accuracy also has rewards: a perfect call earns up to 32 bonus points, with the bonus shrinking as the forecast drifts from the actual rainfall. Players can win a matchup even with a weak forecast by simply beating their opponents, but only sharp forecasts collect the full 64 points each week. 

Sign-up is open now, and the two games run independently. In the seasonal challenge, each monthly forecast is due just before the month starts – July by 11:59 p.m. on June 30, August by 11:59 p.m. on July 31 and September by 11:59 p.m. on Aug. 31. The weekly tournament happens each Tuesday through Monday, with forecasts due by 11:59 p.m. the Monday before. 

There is one other additional feature this year. Guido's team wants to learn how players gather information for forecasting – which tools they turn to, from National Weather Service forecasts to the products that professional forecasters use – and whether playing the fantasy forecast game changes those habits.

What the season might bring

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As for the monsoon itself, Michael Crimmins, a climate extension specialist and a professor at the Department of Environmental Science, said the dominant factor this year is a strong El Niño that became official unusually early and is already shaping the atmosphere across the Northern Hemisphere.

In the past, during El Niño events this strong, the monsoon tended to start slow, arriving late and weak through early summer, picking up only by mid-season. The late stretch, from the end of August into September, often used to turn wet as tropical storms push moisture in from the eastern Pacific.

This year carries a twist, Crimmins said. Climate models have leaned the other way, hinting July could be wetter than usual.

"That leaves me a little bit confused. Models are leaning one way, but history suggests a different path, so we'll just have to wait and see," Crimmins said.

What Crimmins is watching most closely is the chance of several tropical storms reaching the Southwest, most likely in late August and September – the activity that could give this monsoon its peak moments.