MYSTERY OF THE MONSOON
The 2017 monsoon could be a wet one for Phoenix. Or it could be dry. Or, perhaps most likely, it will be just about average. Take your pick. It’s that kind of year. As the Arizona monsoon season begins today, conditions are such that meteorologists can’t pin down what is expected to happen.
The possible development of weak El Niño conditions,
the abundance (or lack thereof) of Pacific cyclones and even the snowpack in the Sierra and Rocky mountains could have some impact on what happens here this summer.
Because of these factors and others, the Climate Prediction Center’s outlook for the summer calls for an equal chance for above average, below average or normal rainfall.
When it comes to heat, things are a bit more clear. The outlook calls for a 50 percent chance of above-normal temperatures.
El Niño is the climate phenomenon resulting in warmer-than-normal surface temperatures in the eastern Pacific Ocean near the equator. El Niño conditions are most likely to influence winter weather (they can cause warmer and wetter-than-normal weather in the southern United States), but there is a slim connection between it and what happens here during the monsoon.
When El Niño is present, our monsoon tends to be a little drier than normal. However, there isn’t a strong statistical connection between the two weather phenomena, National Weather Service meteorologist Chris Rasmussen said.
That’s especially true when El Niño conditions are weak.
“Because things are closer to the neutral conditions, its impact on our neck of the woods becomes a lot more murky, meaning that it could be the whole range of things,” Rasmussen said.
Conditions in the eastern Pacific are currently neutral, just below the El Niño threshold. But some meteorologists believe they may move toward weak El Niño levels. If that happens, they could play a role late in the monsoon season.
Glen Lader, meteorologist with the National Weather Service in Tucson, explained one impact El Niño could have in his presentation on the 2017 monsoon.
“Above-normal sea-surface temperatures are likely to result in more tropical cyclones, which means a greater chance for moisture reaching southeastern Arizona, especially late in the season,” Lader said.
If those storms are strong enough, they could inject more moisture into the atmosphere, which could make its way into northern Mexico and the Southwest to fuel monsoon storms.
The massive rains that caused flooding in the Valley on Sept. 8, 2014, were related to the remnants of a dying Pacific hurricane. More than 3 inches of rain fell that day, setting an all-time daily record. The normal total for the entire monsoon is just 2.71 inches.
Another factor feeding the uncertainty about the 2017 monsoon is something most people in the Phoenix area don’t think about when we’re sweating through the summer: mountain snow.
One of the things that has to happen for monsoon conditions to move in is a shift in a persistent area of high pressure that hangs around our region. Air circulates around areas of high pressure in a clockwise direction so, when that high is centered closer to the Four Corners area, it results in winds out of the south and southeast that tap into the monsoon moisture in northern Mexico. That moisture contributes to our summer storms.
That shift in winds from the usual dry, westerly direction is one of the defining features of the monsoon. According to Lader, that high-pressure area is just a dome of very warm air and, as such, it tends to hang out more in areas that are drier than others.
The Sierra Nevada and central Rocky Mountains had above-normal precipitation over the winter and have more snow remaining than usual. That could result in the area of high pressure spending more time in the hot, dry areas of southern Arizona, New Mexico and northern Mexico, which would be too far south to set up a flow of monsoonal moisture in the state.
“While the high doesn’t sit in the exact same location all summer long, it can favor one region over another for a number of weeks,” Lader said.
In addition to these and other factors, meteorologists rely on computer models that process loads of data to help make their forecasts. This season, even the computers aren’t painting a clear picture of the next few months.
So meteorologists are having a hard time predicting what kind of monsoon we can expect. People like Tony Esqueda will take the same approach to the monsoon as they always do: Be ready for anything that comes their way.
Esqueda is Tempe Section line maintenance supervisor for Salt River Project, the water and power utility company for about half of the metro area.
When storms blow through, it’s often Esqueda and his crews that have to repair the damage to power lines, transformers and other components of the electrical grid.
Even without the storms, summer can be a busy time for the linemen, as the area’s intense heat can tax the system. But the aftermath of microbursts, straight-line winds and other stormy weather really keep them hopping.
Esqueda isn’t waiting on the forecast to make sure they’re ready for whatever comes this year.
“I wish I could say if it’s going to be a busy season,” Esqueda said. “We haven’t been told it will be super-aggressive regarding storms. But we have to be ready regardless. We have to prepare the same way.”