Tag: NOAA

Arizona’s Summer Monsoon Season Has Been A Lively One. But ‘Liveliest Ever?’

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After a so-so start to the southern Arizona summer “monsoon” season, storms pounded Tucson through early August with almost rhythmic frequency.

It was much the same in the metropolitan Phoenix area, which saw an unusual spate of strong storms moving through Arizona’s south-central Valley on five out of six days beginning on August 7.

This year’s summer storm activity has been widespread. Arizona’s eastern mountains saw almost daily rainfall from mid-July through early- to mid-August.  To the north, meanwhile, the strong storms started in earnest early.

Persistent, heavy rain battered the Flagstaff region commencing in mid-July, generating flash floods and localized flooding in many Flagstaff-area neighborhoods.

On July 18, a an estimated “1,000-year” storm dumped an astonishing six inches of rain on Flagstaff, with 4.5 inches of it pouring down in a span of just two hours.

The summer storm season has been so strong at times, in fact, that it has prompted some to ask: Is this the strongest monsoon-storm season ever for Arizona?

There’s no simple answer to that.

Arizona takes its summer monsoon season seriously. There is an extended web of agencies, including the Arizona Department of Water Resources, that performs a vast array of services tied to storm activity.

The National Weather Service, for example, monitors the conditions that may provoke Arizona storms. It reports both locally and from the service’s Climate Prediction Center (a function of the National Oceanic and Atmospheric Administration) in Maryland.

A complex, multi-agency system in Arizona, meanwhile, uses sophisticated land- and satellite-based technology to track storm production, including rain levels and flooding, and gets that information out to the public as soon as possible.

ADWR is the lead State agency for the Arizona Flood Warning System, or AFWS.

The AFWS is comprised of local, state and federal entities that collaborate on statewide strategies for flood management.

Podcast: Arizona Water Resources talks with Brian Cosson, Flood Warning Coordinator for ADWR

So, what is all that data telling us about the strength of the 2018 summer monsoon season thus far? It has set records in Flagstaff. But elsewhere?

Paul Iñiguez, a meteorologist with the NWS in Phoenix, recently told the Arizona Republic that from the standpoint of rainfall, the summer monsoons have been very productive in central Arizona, too.

“From June 15th through August 12th, this is the second most rain on average across (Phoenix) since 1990,” Iñiguez said. “It’s been wet.”

Some of the strength of the summer storms may be derived from “moisture surges” egged along by “tropical cyclones.”

Jon Gottschalck, chief of the Operational Prediction Branch at the Climate Prediction Center with the National Oceanic and Atmospheric Administration, told KJZZ recently about how “tropical cyclones” in the eastern Pacific basin are connected to Arizona’s monsoon storms.

Hurricanes, typhoons and other major Pacific storms all come under the general heading of tropical cyclones.

“Sea-surface temperatures, or ocean temperatures at the surface are strongly positive, meaning warmer than normal,” said Gottschalck. “And when those temperatures that are warmer than normal have been persisting for quite some time, there is more energy for tropical cyclones to develop.”

He said a spate of tropical cyclones in the eastern Pacific likely contributed to the moisture surges in Arizona and New Mexico that, among other things, produced the amazing string of consecutive stormy days in central Arizona.

Big Pacific storms, he said, do not have to  make direct hits on the Southwest to have an impact.

“The systems very often create moisture surges up the coast,” he said. “That very often tends to create stronger coverage of rainfall. In general, these storms don’t have to make direct hits on Arizona and New Mexico to do that.”

(For more on research into monsoon activity in Arizona, view the video below)

 

Attack of the Blob: How an enormous, persistent arctic low-pressure system is helping dry out the American Southwest

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It’s… the blob. It came from above. And it’s got the world in its grip.

And… it’s not going anywhere any time soon.

If that sounds like a trailer line for a low-budget sci-fi movie… well, it could be.

But it also fairly describes the powerful “Strong Hudson Bay Low” – an Arctic-spawned low-pressure systemthat locked in place over much of the Northern Hemisphere in mid-November. The strong, static “blocking” system is showing no sign of releasing its grip any time in the foreseeable future.

“WITH SNOW CONDITIONS IN THE UPPER COLORADO RIVER BASIN TRACKING AT JUST 31 PERCENT OF THE TOTAL AVERAGE SEASONAL ACCUMULATION AS OF MID-JANUARY, THE 2018 SEASON IS LOOKING DRYER THAN THE RECORD-DRY 2002 SEASON.”

And neither is one of the stronger regional effects of the huge low-pressure system:

An equally persistent, equally strong high-pressure ridge has locked into place beneath the blob. It sits in an equally unyielding “blocking” pattern over the eastern Pacific and the southwestern U.S., which is driving the west-east jet stream and its storms well to the north of the parched American Southwest.

That strong high-pressure system is proving to be a virtual mirror image of the Strong Hudson Bay Low, driving temperatures dramatically up and sapping the atmosphere of moisture.

“How strong and permanent it becomes depends on establishment of other high- and low-pressure systems as well as the amplitude of the jet stream around the globe,” explained Greg Smith, a senior hydrologist at the Colorado Basin River Forecast Center, a division of the National Weather Service and the National Oceanic and Atmospheric Administration.

Coming at the time of year when the western slopes of the Rocky Mountains typically build snowpack that, come spring, provides run-off into the Colorado River system, the moisture-robbing effects of this static high-pressure system may prove to be record-setting.

So too might the effects of the Artic blob.

On January 2 in the U.S., at least one location in all 50 states recorded temperatures below freezing. Yes, even in Hawaii.

Water fountains in Florida froze over. Off-shore, sharks swimming near Cape Cod froze to death. And all that occurred before the infamous “bomb cyclone” drove temperatures deeply negative on the entire East Coast for nearly a week.

On the opposite side of the globe, meanwhile, it’s the same deal. The Arctic blob has much of the eastern side of the Northern Hemisphere frozen and snow-bound, too.

In Yakutia, Siberia – 3,300 miles east of Moscow – residents reported their eyelashes freezing as temperatures dropped to an astonishing 88 degrees below zero Fahrenheit. In southwestern Scotland — typically cold and wet in the winter — blizzard conditions shut down highways. And shipping on the normally blue Danube – for now, icy gray – was halted because of ice.

All weather patterns being inter-related with all other weather patterns, the powerful high-pressure ridge sitting over much of the southwestern U.S. built up around the same time as the Strong Hudson Bay Low gathered its global steam – in mid-November.

And like its Hudson Bay “polar” opposite, there it has remained. And remained. Strong. Resolute. And dry.

While neither strong low-pressure systems that sweep down from the Arctic nor high-pressure ridges laying out over the western U.S. are unusual at this time of year, these systems are unique in one important respect: their persistence. They won’t quit.

The high-pressure ridge has proved so persistent – and the conditions it creates so dry – that hydrologists at the Forecast Center now are comparing this season’s snowpack in the Rockies (as well as in the Arizona mountains) to that of the infamously dry winter of 1976-1977, which produced one of the lowest inflows into Lake Powell on the Colorado River system on record.

How low did that inflow go?

The fall-winter “water year” season that ended in 1977 produced an unregulated Colorado River inflow into Lake Powell of roughly 5.8 million acre-feet. That is almost three million acre-feet less than the average river flow into Powell since 2000, a period when much of the Southwest, including Arizona, has been locked in chronic drought.

Measured against the historic average since 1964, the 1977 inflow into Powell was almost five million acre-feet below average. Since 1964, only three seasons have provided less runoff than 1977.

“What drew us to the comparison (with 1977) initially was the snow situation,” said Smith.

The Forecast Center’s highly advanced “SNOTEL” (for “snow telemetry”) network indicated that many of the Colorado River Basin’s snowpack areas, especially in the southern regions, were experiencing the “lowest snow on record,” according to Smith.

To Smith and other hydrologists, the atmospheric patterns prompting the weak snowpack seemed familiar:

“Some of us recall how poor conditions were in 1976-77. Then we noticed these large atmospheric features — strong low in the east and ridge in the west — were similar.”

Added Smith: “These are not uncommon features from year to year. But in both 1976-1977 and this year they were fairly strong, and the jet stream flow in the atmosphere similarly had a high amplitude. These strong low- and high-pressure systems, known as blocking features, or a blocking pattern, can be quite stubborn.”

As it stood in mid-January, the estimate for unregulated inflow into Lake Powell from the western slopes of the Rockies indicated the lake would receive 6.75 million acre-feet of runoff, or 62 percent of the historic, 30-year average. Not good, obviously. But not historically bad.

That estimate may be changing, however. And not for the better.

The lowest Colorado River inflow into Powell ever recorded was about 2.3 million acre-feet in 2002.

With snow conditions in the Upper Colorado River basin tracking at just 31 percent of the total average seasonal accumulation as of mid-January, the 2018 Water Year season – at this point in time — is looking dryer than the record-dry 2002 season.

A “snapshot” chart recently released by the federal Bureau of Reclamation compares the current water-year snow conditions with Water Year 2002. As of January 17, which is 57 percent through the snow-accumulation season, snow conditions were tracking well below conditions in 2001-2002.

Caveats apply, certainly.

Weather changes. The “blocking” low- and high-pressure systems could weaken and dissipate. And we are still relatively early in the snow-accumulation season. The very dry mid-January snapshot of conditions could look very different by mid-February.

As Smith notes, the 1976-1977 pattern finally broke down in March 1977, ushering in a much wetter late-winter period, especially in the northern Colorado and Great Basins.

As our days of unnervingly pleasant sunshine and annoyingly dry, easy breezes drone on – and on – the prospects for matching (or, gulp, “besting”) the Great Colorado River Dribble of 2002 increase.

But, again, as the forecasters well know, weather changes. Even the extraordinarily dry winter of 1977 ended pretty wet.

 

Arizona drought status summary, May 2017

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AZ drought image June 2017

Short-term Drought Status Summary for May 2017

While several storm systems passed through the state in May, the precipitation fell primarily across central and northern Arizona, leaving southern Arizona relatively dry.

The dry spring that followed the dry winter in southeastern Arizona led to deterioration in drought conditions in this area. Pima, Cochise, Santa Cruz, southern Maricopa, Pinal, Graham and Greenlee counties are now all in moderate drought (D1).

Until the monsoon activity begins, conditions are not likely to improve, and fire danger continues to be high in central and southern Arizona.

Long-term Drought Status Update: January – March 2017

The winter storms in January and February combined with the earlier storms in November and December brought significant rain and snow to northern and central Arizona.

The relatively heavy winter precipitation has finally improved many watersheds that were bordering an improvement over the past six months or longer.

Long-term drought and water supply conditions in northern Arizona and the Salt River watersheds are much better than they were over the past six to ten years. However, this winter was still not as wet as in late 1980s and early 1990s, before this drought began, and abnormally dry conditions still persist in many parts of the state.

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

 

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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.”