Tag: atmospheric rivers

Weather and climate in the Southwest: Part Two

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This is the second part of a discussion with Arizona’s top weather climatologists about drought, rainy winters and why California gets so much more of those “atmospheric rivers” than we do

storm over monument valley

In this discussion with Arizona’s top weather climatologists about the long (and continuing) drought in the Southwest, we talk about the reasons behind the abundant moisture during the 2016-2017 winter and expectations for the future (cross your fingers!).

Today’s talk features Mark O’Malley, forecaster and Climate Science Program manager for the National Weather Service.

Published on March 8, Part One featured an interview with Arizona State Climatologist Nancy Selover. Dr. Selover is the Julie Ann Wrigley Global Institute of Sustainability Research Professor at Arizona State University’s School of Geographical Sciences and Urban Planning in the College of Liberal Arts & Sciences.

Selover and O’Malley are the co-chairs of the State Drought Monitoring Technical Committee, which is responsible for gathering and analyzing data regarding Arizona drought, climate and weather.

The information they provide is used by the Governor’s Interagency Coordination Group, which makes an annual recommendation to the Arizona Governor about whether the state’s long-running state of drought should be extended. Or… not. Arizona Department of Water Resources Director Tom Buschatzke co-chairs the ICG.

Climate science – a field of study that has evolved rapidly in this century – examines a phenomenon like “drought” from an increasing number of factors.

For one thing, it makes the recommendation to the governor on whether to continue the drought declaration more precise.

Drought impacts can range from a lack of soil moisture, affecting range land and farming, to water levels in the state’s reservoirs. And all of the factors that climatologists weigh when deciding whether drought exists can vary widely in time and scale. But all the drought factors taken together make it more difficult to establish with certainty when a drought may begin or end.

“I think it’s generally accepted that Arizona is in a standing, long-term drought since 1999,” said Mark O’Malley of the National Weather Service.

“But clearly there are years and parts of years in the past 17 years where drought has been less expansive and less intense. There really is no good way to say drought in Arizona started on ‘x’ day in 1999.”

Like State Climatologist Nancy Selover – O’Malley’s co-chair on the State Drought Monitoring Technical Committee – O’Malley sees the effects of the very wet 2016-2017 winter as a real positive for most of Arizona. But the slowly improving drought conditions locally are impacted by the summer monsoons, too, he notes.

“We have experienced three to four excellent summer monsoon seasons where thunderstorms and rainfall across the state have been quite good, but we’ve also had five consecutive winters with below average snow in the mountains,” said O’Malley. And it is that snowpack in the mountains that is important for the state’s water supply.

“This winter has been good — especially around the Flagstaff area — but doesn’t totally compensate for the five previous dry winters.”

In terms of moisture, “good” in Arizona consistently is less good than on the California coast, where unprecedented winter moisture largely has ended that state’s drought. There are a number of reasons for that phenomenon, says O’Malley. Some are atmospheric. Some are geographic.

For one, he notes, central and northern California are at higher latitudes than Arizona, and so more commonly fall under the jet stream – which also explains why even during the sodden 2016-2017 winter, Los Angeles and San Diego are getting less moisture than, say, Sacramento.

Then there is the effect of those mountains separating the coastal cities from Phoenix, which, among other things, tends to wring out moisture from those Pacific storms as they sweep inland.

“Moisture from the Pacific streams unencumbered into the coastal cities with lift provided by air flowing over the mountains providing even more rain and snow,” said O’Malley.

“As the air flows over the mountains into far southeastern California and Arizona, it sinks. And you generally need air rising to produce precipitation.”

Often, he notes, there is “nothing left over for Arizona” in those storms. “This is why the deserts from Yuma through Death Valley, Calif., are the driest places in the United States.”

With California reservoirs literally overflowing and with Los Angeles Mayor Eric Garcetti calling for a state of emergency as a result of the melting snowpack in the eastern Sierra Nevada, California is confident – for now, at least – that it is nearly free of drought.

What about Arizona?

“By both objective measures and impacts, drought in Arizona is certainly better  — which is to say, we have less drought — than last year at this time, and substantially better than two to three years ago,” said O’Malley.

“I wouldn’t go as far as using the term ‘waning’ — that word infers a resolution or termination in the immediate future.”

It doesn’t take much for an arid state to slip back into serious, widespread drought conditions.

“Bottom line, because of our location, growing population, and demand for water, Arizona will always be susceptible to drought.”

 

Seriously? Yes, seriously: Drought-busting moisture levels in parts of the state don’t mean the Arizona drought is done

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Record snowfall in the Sierra Nevada…double the average snow in parts of the Rockies… one “atmospheric river” after the next hitting the coast…and enough snowpack in the eastern Arizona mountains to give Lake Roosevelt an outside chance of filling up this spring…yet Arizona remains in drought? Yep

 

The news is abundant in the West about all the moisture abundance occurring nearly – accent, nearly – everywhere.

Western saturation is the biggest story of the winter in the U.S.

In some areas of northern California, rain totals reached 400 percent of normal in December.  January snowpack in the Sierra Nevada mountains stood at 173 percent of normal, the equivalent of 5.7 trillion gallons of water.

It wasn’t just California experiencing all those remarkably wet atmospheric rivers. As early as mid-January, the Colorado River snowpack stood at 57 percent above the long-term median for that time of year and that was before the big storms of early and late February swept through the Rockies.

Westwide SNOTEL Current Snow Water Equivalent (SWE) Percentage of Normal

The U.S. Department of Agriculture’s latest “Westwide SNOTEL Current Snow Water Equivalent Percentage of Normal” maps of the western mountains are more purple than a ripe eggplant, indicating vast swatches of the region with snowpack deeper than 150 percent of average.

All of which sounds splendid, seemingly alive with drought-busting possibilities… until you have a look at the sobering reality on display in the U.S. Drought Monitor short-term report for February in Arizona.

The February Drought Monitor report may provide the best evidence of the 2016-2017 winter in the Western U.S. for three consistent climate truisms:

  • “Weather” is not the same as “climate,” and
  • Drought is more closely aligned with climate than with weather; and,
  • Drought may come and go in a region, but it comes and goes at different paces in different parts of the same region

The February report concluded: “February was a relatively dry month across parts of the state bringing less than 50 percent of normal precipitation over the eastern third of Arizona and a few spots in northwest Arizona.”

U.S. Drought Monitor – Arizona (February 28, 2017)

 

Relatively… dry?

This may come as a huge surprise to residents of Maricopa, Yavapai, Coconino, Yuma and La Paz counties, where “much wetter than normal conditions” prevailed. But, then, central Arizona is where most of the residents of the state are too. Most Arizonans were getting wet from the same rainstorm.

It’s a big state. As State Climatologist Nancy Selover notes, the big storms brought plenty of cold air and snow to the northern and western parts of the state, but tended to short-shrift the eastern-mountain watersheds: “They have tended to miss the southeast and many of them have missed the White Mountains as well.”

The headwaters of the Salt and Gila rivers are “below average in snowpack for this time of year,” she said. “Though the Verde is above normal.”

That, Selover observed, is “all short-term drought.”

“We have not had the type of precipitation that will replenish our water resources, so we are not anywhere near being over the drought for long-term water resource concerns.”

Still, said Selover, February overall was “a helpful month” in terms of contributing to the 2017 Water Year profile, which depicts healthy moisture levels since October.

The National Weather Service map of Arizona depicting “Seasonal Precipitation, October 2016 – February 2017” may not  have quite the “ripe eggplant” look as the Western snowpack map, but it’s not far off.

A map of the whole Colorado River Basin rainfall for February and the 2017 Water Year through February map

So where does this mostly-better-than-average winter leave Arizona?

As a part of the Southwestern region? Great: “The Upper Colorado Basin is in great shape this year so far, but we need three or four more consecutive years like this to make up for the deficits,” said the State Climatologist.

But Arizona, specifically? Good, sure. But not great:

“For my money, we are entering the 23rd year (of drought) now,” said Selover.

“I think it started in 1994 after the very wet 1993.”

 

SNOWPACK IN THE ROCKIES: Hey, it’s not ALL about California!

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It’s still early, but much of Arizona’s watershed, as well as the western face of the Rockies, is experiencing higher-than-normal precipitation, too

 

rocky-mountains-in-winter

Nothing against California, you understand. We’re all delighted to hear about this winter’s bounty of rain and snow, especially as it piles high in the Sierra Nevada.

Love all those “atmospheric rivers.”

It is great to hear of expert-level debates over whether the Golden State’s drought designations should be eased — or even lifted entirely — especially in the north of the state.

There are parts of the mountains immediately east of Sacramento and San Francisco that have experienced well over 200 percent of the official average precipitation. As they say in southern Cal: Whoa!

But, well… it’s not all about California, you know.

According to data compiled and analyzed by the National Water and Climate Center, precipitation thus far in the “water year” – that is, the period beginning October 1, 2016 – has been predominately “near to well above average” almost everywhere in the West, except Alaska.

Meanwhile, the snowpack in the southern regions of the Western U.S. – the areas of the West most seriously impacted by record and near-record drought – is being judged “well above average,” according to the results reported in the Water and Climate Center’s Snow Telemetry (SNOTEL) summaries.

That snowpack translates, ultimately, into the statistics that matter most to the 35 million-odd people living in the Colorado River basin: the streamflow forecasts and the expectations for reservoir storage levels. And those are looking better than they have in a long time too:

The SNOTEL measurements depict “well above average streamflow in the middle and southern parts of the West,” and reservoir storage amounts that should be “above average in Montana and Wyoming, near average in Colorado and Nevada.”

As of February 1, the Center is forecasting inflows into Lake Powell at 147 percent of the 30-year average for April through July, a critical streamflow period.

Almost… California-esque.

For Arizona specifically, the precipitation picture has brightened considerably this winter.

“We have to go all the way back to 2010 the last time we filled the reservoirs,” said Salt River Project water operations manager Charlie Ester to 12News on February 2.

“In the seven years since then, we have progressively lowered the reservoirs to the current conditions.”

With much of Arizona’s water supply beginning its annual journey on the western slopes of the Colorado Rockies, the Water and Climate Center’s early February report is promising. January produced 217 percent of normal precipitation in Colorado, and the February 1 snowpack is at 156 percent of normal, up 43 percent from January.

As a result, streamflow forecasts “are nearly all above normal with the western basin projections providing the highest forecasts,” according to the Water and Climate Center report.

Even in the best of times, precipitation never distributes evenly.

As of February 1, the “snow-water equivalent levels” – that is, the amount of liquid, flowing water expected to be produced from a region’s snowpack – range from 88 percent of median in the San Francisco-Upper Gila River Basin to 166 percent of median in the Verde River Basin.

Still: “Cumulative precipitation since October 1 is now well above normal in all major river basins for the water year.”

Precipitation disclaimers in the arid Southwest are always lit bright, however. The remarkable measurements of the winter to date are entirely capable of petering out to nil. Which is a pretty good summary of how last winter went.

A winter’s precipitation is the result of weather. And while drought is a function of weather over time, it isn’t something that disappears in a single, wet season.

The effects of drought, for example, can be cumulative. The volume of Southwestern desert dust that blows east onto the western slopes of the Rockies has been shown to have a cumulative effect on the duration of the winter season.

NOAA’s Cooperative Institute for Research and Environmental Sciences at the University of Colorado Boulder, for example, reported in late 2013 that the snowpack of the Rockies “is melting out as many as six weeks earlier than it did in the 1800s,” as a result of a thick layer of desert dust.

It’s not just drought that impacts Colorado River streamflow, in other words.

Moisture at these levels in the West can make people forget quickly the long-term issues the region faces. Already, Californians are in a fierce debate over whether to extend Gov. Jerry Brown’s emergency drought declaration and whether or not to ease up on other water-conservation efforts.

“Most water agencies have yet to adjust to this ‘new normal’ and are operating on outmoded assumptions and practices that place the state at risk of water shortages and worse,” argued climate-change expert Alex Hall of UCLA in a commentary that appeared February 5 in the Los Angeles Times.

Hall’s concern – that the recent snow and rain will blunt efforts to improve water-use efficiencies in southern California – is a concern for the entire Southwest.

Could this one year’s abundance blunt efforts to resolve the systemic over-allocation of Colorado River water, for example?

If there is a downside to the current – and literal – flood of moisture into the region, it is that.

“While I’m happy about all the snow,” said Water Resources Director Tom Buschatzke, “we don’t have enough certainty about what Mother Nature is going to send us.

“We have to focus on what we have control of.”