In June, forecast models and other analysis tools became strong enough to slightly nudge the optimism of CPC forecasters.

"Our main climate model has been doing very well in recent years and has shown some accuracy in forecasting the monsoon during the first month," said David Unger, a CPC meteorologist. "There is some indication that July will be above average, and even if the final two months are average, there is still a good chance for a wet monsoon."

It is still a cautious forecast; the odds are only slightly better than equal chances that about half of Arizona and New Mexico will get a healthy dousing. Also, the CPC model has shown little accuracy forecasting August and September with more than a 30-day lead time, and so these months remain a black box to the CPC.

"Monsoon forecasting over the season is so difficult," Gottschalck said. "July through September is a long period, and a lot can happen. Anything early on could be completely outweighed by the final two months."

Despite CPC uncertainty in much of the monsoon, a strong start favors an above average season. Another forecast, based on past summers that most resemble current and expected conditions, also bolsters this outlook.

"The bottom line is that when we look at our analog forecast, it is for a wet July, a so-so August and a wet September," said Art Douglass, professor and chair of the department of atmospheric sciences at Creighton University.

Douglass, who has been forecasting the monsoon since 1977, developed this outlook by analyzing 12 variables that span the Pacific and Atlantic oceans, including sea surface temperatures, sea level pressure, pressure levels in the atmosphere, and tropical convection.

Five summers on record –1984, 1986, 2001, 2006 and 2008 – had very similar conditions to those in June. When combined, most of Arizona and New Mexico received more than 110 percent of average during these summers.

"When you composite these years, it's a pretty optimistic forecast for rain," Douglass said.