Precip. forecast is harder to call
The National Weather Service has released its winter weather outlook covering the months of December through February. Forecasters say it will be neither an El Niño year nor a La Niña year. Those are weather patterns dictated by warmer-than-usual or cooler-than-usual surface waters in the central Pacific Ocean, which tend to affect weather – especially precipitation – over the continental U.S.
The forecast models indicate a greater chance of warmer-than-normal temperatures in Arizona for the winter months than for average or below-average temperatures. The models indicate the warm weather is likely to extend into the spring. The greatest chance of warmer-than-normal temps is over northern Arizona.
The amount of precipitation is harder to predict. In "neutral" years – when the weather is not affected by El Niño or La Niña – precipitation can range from well above normal to well below.
Lead forecaster Mark O'Malley points out that last winter was much drier than normal over Arizona, while the winter before was wetter than normal. He says this winter is starting out with a near-record-low snowpack over the mountains in the northern part of the Colorado River basin, which feeds the rivers and reservoirs in Arizona. Without a generous amount of precipitation this winter, the reservoirs will be very low come spring.
The forecast models also predict that for the three-month February-through-April period, about 90% of the U.S. will be warmer than normal, with the greatest likelihood of higher-than-average temperatures over the southwestern states.