Wet weather expected later this week is likely part of a series of storms that could make this winter the wettest Arizona has seen in years, Valley meteorologists say.
"This year is the first year in a while that we could have above normal precipitation," said David Runyan, a meteorologist with the National Weather Service in Phoenix. "It’s very possible."
Runyan said the last time that the East Valley saw above average precipitation was 1998, after an El Niño season in 1997. Mesa, where the weather service tracks rainfall for the East Valley, received 11.06 inches of rain then — well above its 30-year average of 9.23 inches per year.
The 2003-04 weather cycle, also part of an El Niño year, could bring that level of rain in 2004-05, Runyan said. On Thursday, the East Valley should get about a half-inch of rain and temperatures should drop to the mid-60s, he said.
But weather experts say not to expect a drought buster.
Runyan said the Valley as a whole should average about 8 inches of rain per year. After several years of below average precipitation, the area is 14 to 16 inches in the red.
"It would take a good two to three years of not just normal precipitation, but abovenormal precipitation in order to return us back to adequate levels of groundwater," Runyan said.
Randy Cerveny, a meteorologist and Arizona State University professor of geography, said a drought buster would mean the desert soil was soaked through and runoff could reach water reservoirs.
Because of a weather phenomenon called the Pacific Decadal Oscillation, he said that soaking isn’t likely — maybe not even for a good 15 years.
The phenomenon refers to the way that temperatures in the Pacific Ocean affect the long-term frequency of rain in Arizona. With warmer temperatures, stronger and more frequent El Niño events are likely. When it’s cold in the Pacific, the desert usually sees less rain.
The temperatures oscillate over a period of a couple decades.
After a warm spell in the 1980s and 1990s, the Pacific Ocean has cooled. So, the first two decades of this century are likely to be dry, Cerveny said.
"There is good evidence that we are in the middle of a long-term drought," he said. "No one storm is going to be a drought buster."
Coping with what could be two decades of drought is the aim of the Drought Task Force appointed by Gov. Janet Napolitano in March 2003. The task force approved reports earlier this month addressing the drought and planning for the future.