A steady downpour Monday, more rain forecast today and another Pacific storm system due late this week will prompt Salt River Project to double the flow of water at the Granite Reef Dam east of Mesa today and keep it there for a day or two.
The bottom line: Get used to a rainswollen Salt River, a waterfall at Tempe Town Lake and road closures where McKellips and Gilbert roads cross the river.
The current storm is colder and less intense than last week’s deluge that flooded northern Arizona communities and stranded Valley motorists. It brought snow to higher elevations and is increasing the all-important snowpack for a still-droughtstricken state.
Charlie Ester, manager of water resource operations for SRP, said snowfall above 6,500 feet allowed SRP to delay increasing the water flow from Horseshoe Reservoir until today, to 30,000 from 17,000 cubic feet per second.
"It will be a longer duration this time. It could be 36 hours or so," Ester said. "In terms of volume, it’s five or six times" what was released during last week’s downpour.
Weather watchers, water management experts and creekside residents were keeping a careful eye on the north country Monday and were thrilled to see snow.
Clair Ketchum, a meteorologist with the National Weather Service in Flagstaff, said snow accumulations probably will exceed projections of one to three feet. The state has had 37 inches of snow this season, surpassing the normal level of about 31 inches.
Last week’s warmer storm system melted the snow and sent it cascading down river.
"We lost our whole back yard. . . . The water is right up to our building," said Anita Dalton, owner of the Center for the New Age in Sedona. "So we’re happy about the snow."
The Valley is expected to get up to three-quarters of an inch of rain from storms that began Monday morning and should fizzle out by Wednesday or Thursday, said Leslie Wanek, a meteorologist with the National Weather Service in Phoenix.
Two more weather systems will make their way into the state beginning Friday morning. A break is expected Saturday, but a chance of rain returns on Sunday.
Ester said he expects Roosevelt Lake, which makes up about 75 percent of the Valley’s total watershed, to rise to 40 percent of its 1.1 million acre-foot capacity after those storms clear out, up from about 30 percent before last week’s rain.
The Verde River watershed, composed of the smaller Horseshoe and Bartlett reservoirs, was at about 70 percent capacity Monday with releases into the Salt River increased from 12,000 cubic feet per second to 17,000 over the weekend to make room for this week’s storm runoff.
"We’ll store as much of it as we can," Ester said. "Right now our forecast is to receive about 70,000 cubic-feet-persecond into the Horseshoe Reservoir, but only have to release 30,000 from Bartlett."
By the time it reaches Tempe Town Lake, about half of that will have soaked in and helped replenish the groundwater supply, he said.
The prolonged water release of 30,000 cubic feet per second is unlikely to require Tempe Town Lake to lower the dam on its west side, said Basil Boyd, a water resource hydrologist for Tempe. The deflatable dams, located on the east and west ends of the lake, are able to withstand up to 30,000 cubic feet of water per second.
The east dam is completely down while the west dam has been deflated only about three feet since Friday, allowing about 17,000 cubic feet per second of water to flow over its brim.
Massive amounts of debris also are flowing over the downstream dam, including floating islands of palm fronds 60 to 80 feet wide, said Don Hawkes, deputy manager of Tempe’s water utilities department.
Tempe officials said a significant clean-up effort will be needed once the dams are back up and water stops flowing down the Salt River. Current flows, which equal about 132,000 gallons of water per second, are refilling the lake every three hours, said Kris Baxter, a Tempe Town Lake spokeswoman.
The Salt and Verde river watersheds encompass 13,000 square miles, larger than Maryland. Up until last month, however, the Verde River system had been receiving the lion’s share of rain.
Meteorologists said the current storms likely mean wetter-than-usual weather until March. The precipitation provides welcome relief, but it’s unlikely one wet year will overcome a nearly decadelong drought, said Tony Haffer, meteorologist in charge at the National Weather Service in Phoenix.
"It’s going to take a number of wet years to mitigate the drought," he said.
Snowfall this week is encouraging because it means water from snow runoff in the spring will be available at a slower pace, said Haffer. What’s needed for a good water supply this summer is more snowpack melting into the Salt River reservoir system, he said.
This week’s wet weather, he said, "may be a sign of things to come, but of course Mother Nature is the one that drives the ship."
The moisture also should help to lower fire danger this summer, weather experts said.
This soggy winter still presents some hope for drought relief. Last month, a federal weather researcher predicted that snowmelt in the Colorado River Basin could send twice as much water to Lake Powell this spring as it received last year. The snowpack above the watershed this week was reported to be more than 100 percent above average, which would increase the flow feeding the Central Arizona Project canal.