Cranes make annual return to San Luis Valley; Monte Vista Crane Festival, March 6-8, 2020

The sandhill cranes are back in the San Luis Valley on their spring migration. Photo credit: Colorado Parks & Wildlife

Here’s the release from Colorado Parks & Wildlife (Joe Lewandowski):

Cranes make annual return to the San Luis Valley

In the San Luis Valley nature is again putting on one of its most memorable displays: the spring migration of greater sandhill cranes. In appreciation of this wildlife spectacle, area organizations, businesses and wildlife agencies are holding the 37th Annual Monte Vista Crane Festival, March 6-8.

“Everyone who lives in Colorado should take the time to see this ancient and magnificent migration,” said Joe Lewandowski, public information officer for the Southwest Region of Colorado Parks and Wildlife. “This is one of only a few great wildlife migrations in the United States that people can easily see. The sights and sounds are amazing.”

The cranes started arriving in mid-February, flying from their winter nesting grounds to the south, primarily in New Mexico. The large wetland areas, wildlife refuges and grain fields in the San Luis Valley draw in about 25,000 birds. The cranes stop in the valley to rest-up and re-fuel for their trip north to their summer nesting and breeding grounds in Idaho, Montana and Wyoming.

Even if you can’t travel to the San Luis Valley during the weekend of the festival, there is still plenty of time to see the birds. The cranes usually stay in the valley for most of March.

Cranes are among the oldest living species on the planet: Fossil records for cranes date back 9 million years. The birds that migrate through Colorado are the largest of the North American sandhill subspecies standing 4-feet tall with a wing-span of up to 7 feet and weighing in at 11 pounds. Besides their imposing size, the birds issue a continuous and distinctive call. At this time of year cranes are engaged in their mating ritual and the birds perform an elegant hopping dance to gain the attention of other birds.

The birds are abundant in areas near the town of Monte Vista. They can be seen most readily in the Monte Vista National Wildlife Refuge, about five miles south of town of Colorado Highway 15. Birds also gather at the Alamosa National Wildlife Refuge, southeast of the town of Alamosa, and at that Rio Grande, Higel and Russell Lakes state wildlife areas.

The cranes are most active at dawn and at dusk when they’re moving from their nighttime roosting areas to fields where they feed. In the middle of the day, they “loaf” and eat in the grain fields of the Monte Vista refuge.

Be sure to dress warm, as winter still reigns in the valley.

During the three days of the festival, free tours are offered at 7 a.m. and 4 p.m. when the birds are most active. Visitors ride buses to various spots on the wildlife refuge and U.S. Fish and Wildlife Service staffers talk about the migration and the refuge. If you want to take a tour, be on time because the buses leave promptly.

Birdwatchers who travel on their own should be cautious when parking, getting out of vehicles and walking along roads. View birds from a distance with binoculars and spotting scopes, and observe trail signs and closure notices.

Many other bird species – including eagles, turkeys, and a variety of raptors and waterfowl – can also be seen throughout the San Luis Valley. Look in the many cottonwood trees for owl nests.

The festival headquarters and starting point for the tours is the Ski Hi Park building located near U.S. Highway 160 on Sherman Avenue on the east side of Monte Vista. Visitors can pick up maps, schedules and information at the headquarters.

Besides the tours, a variety of workshops are put on by bird, wildlife and photography experts. An arts and crafts fair continues through the weekend at the headquarters building.

Approximate distances to Monte Vista: Denver, 220 miles; Colorado Springs, 182 miles; Salida, 85 miles; Vail, 175 miles; Durango, 135 miles; Grand Junction, 230 miles.

For more information on the Monte Vista Crane Festival, see:; or For more information on State Wildlife Areas in the San Luis Valley, go to:

Sandhill Crane via Colorado Parks & Wildlife

Stanford researchers develop a better way to detect underground water leaks

Here’s the release from Stanford University (Danielle Torrent Tucker):

Stanford researchers propose a new way to locate water leaks within the tangle of aging pipes found beneath many cities. The improvement could save time, money and billions of gallons of water.

You can delay irrigating the lawn or washing the car all you want, but to really make a big dent in water savings we need to stop water waste long before the precious resource ever reaches our taps.

A new way to detect leaks in aging pipes underground could save save money and billions of gallons of water. (Image credit: HiddenCatch / iStock)

An estimated 20 to 50 percent of water is lost to leaks in North America’s supply system – a major issue as utilities contend with how to sustain a growing population in an era of water scarcity.

“People talk about reducing the time you take showers, but if you think about 50 percent of water flowing through the system being lost, it’s another magnitude,” said study author Daniel Tartakovsky, a professor of energy resources engineering in Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth).

In a move that could potentially save money and billions of gallons of water, Tartakovsky, along with Abdulrahman Alawadhi from the University of California, San Diego, have proposed a new way to swiftly and accurately interpret data from pressure sensors commonly used to detect leaks.

In addition to water utilities, Tartakovsky said the method could also be applied to other industries that use pressure sensors for leak detection, such as in oil and natural gas transmission networks that run under the sea and pose additional environmental hazards.

The research was published online Feb. 12 in the journal Water Resources Research.

Water hammer

The new method targets water leaks in transmission mains, which are typically routed out of sight underground. Water transmission networks in North America and much of Europe are fitted with sensors that measure pressure to gauge flow.

The researchers built upon a technique known as the water hammer test – the industry standard for predicting the location of leaks. The test involves suddenly shutting off flow through a pipe and using sensors to gather data about how the resulting shock wave, or “water hammer,” propagates. Tartakovsky and Alawadhi propose a new way to assimilate this data into a mathematical model to narrow down the location of a leak.

The current method for detecting leaks is computationally expensive; to reduce the cost, analysts need to make a lot of simplifying assumptions, according to Tartakovsky.

“We proposed a method that is fast enough that you don’t need to make these assumptions, and so it’s more accurate – you could do it in real time on a laptop,” Tartakovsky said. “It’s something utilities can use with existing computational resources and the models they already have.”

By improving speed and accuracy, the researchers’ method saves money, both in terms of time and labor and the cost of wasted water. For example, if you wanted to find a leak in a football field–length pipe, you could dig up the whole field until you hit wet soil, or you could use the new method to constrain the location of the leak to a 10-meter section of the pipe.

“In cities, it’s harder because pipes are under buildings and you have to break asphalt and things like that, so the more accurate your prediction of the location, the better,” Tartakovsky said.

Cities have the most potential for major water leaks – and the older the urban areas, the bigger the problems, with their complex networks of aging pipes.

“For operators who routinely use water hammer tests, the cost of this is zero – this is just a better way of interpreting these tests,” Tartakovsky said. “We are not selling it or patenting it, so people could just use it and see whether they get better predictions.”

Fremont County OKs expansion of gold exploration — The Pueblo Chieftain

Gold seam via ZME Science.

From The Pueblo Chieftain (Tracy Harmon):

The Fremont County Commission on Tuesday unanimously approved a conditional use permit request from Zephyr Minerals Ltd. to expand its gold exploration area southwest of here…

Among the 24 conditions of the approval require Zephyr to get sufficient water to the drill site and avoid disturbance of ground within 500 feet of Grape Creek, Bell said.

The company would expand the current 593 exploration area by 1,169 acres for a total of 1,762 acres. The Colorado State Land Trust board last April OK’d exploration on a parcel in the Grape Creek/Horseshoe Mountain area, just southwest of Canon City’s Temple Canyon Park.

“I feel like they (Colorado State Land Board) made it pretty tough on them. They have to helicopter water in,” Tim Payne, commissioner, said.

Commissioner Dwayne McFall said land use issues are the hardest for the commission to address because there are residents who are both for and against them.

Zephyr currently is conducting exploration just west of the Dawson Ranch neighborhood in the Dawson Peak area. The new exploration area would be to the west of that —on U.S. Bureau of Land Management Land — and Zephyr has another application pending with that agency.

Exploration would impact less than 2% of the permitted area, according to the application. The disturbance area would be about 3 acres.

Exploration would be done in two phases, including an airborne magnetic and electromagnetic geophysical survey. The second phase would be “traditional core drilling to test targets generated by the airborne survey,” according to the application.

From The Cañon City Daily Record (Carrie Canterbury):

The expansion will add acreage to the west of the current boundary of the CUP. The application was approved by a majority vote by the Fremont County Planning Commission in January and was tabled by the county commissioners Feb. 11 to allow the board more time to compile findings…

During the February meeting, Will Felderhof, the executive chairman and director for Zephyr Minerals, said his company has demonstrated during the last eight years that they’ve been doing everything correctly, that they are committed to doing things properly and they are committed to following all of the rules and regulations.

The board heard from 13 people during a public hearing Feb. 11. Of those, 10 were against the expansion, two were neutral and one was in favor.

Gary Peterson, the chairman of the Royal Gorge Preservation Project, said the CUP expansion request “is an operational part of the process that leads to the development of a full-blown mining operation that has the potential to propel our community into just another dirty little mining community … ”

Others speaking in opposition shared concerns about water, noise, access and imposition the expansion could have on wildlife.

Findings presented Tuesday state that the Colorado Parks and Wildlife and the Bureau of Land Management have expertise regarding the potential disruption of wildlife in the area and the lighting proposed for the drill site is minimal and does not exceed the amount that is necessary for the operations.

The board prohibits the applicant from conducting drill operations without a source of water to use in the process, which may require the use of a helicopter or other means without the use of roadways or other vehicular traffic.

San Luis Valley: Local leaders dispute [Renewable Water Resources] survey’s false claims — The Valley Courier

Pond on the Garcia Ranch via Rio Grande Headwaters Land Trust

From the Rio Grande Water Conservation District, San Luis Valley Water Conservancy District, and Conejos Water Conservancy District via The Valley Courier:

Many San Luis Valley residents recently received a phone survey inquiring about support for a proposal to export 20,000 acre-feet annually from the Valley to the Front Range.

The project proponents, Renewable Water Resources (RWR), have stated their intent to pump deep groundwater from the confined aquifer over Poncha Pass and Trout Creek Pass to the South Platte River.

RWR’s website is fraught with misinformation regarding the water supplies, hydrology, and legal obligations of the Valley.

The phone survey was no different. The call included approximately 20 questions, many with significant factual inaccuracies. It is important that community members have an understanding of the truth about their water resources.

The proponents would not provide a list of the survey questions. Therefore, the following account of key questions may not be exact.

Survey Question: “Did you know there are 2 billion acre-feet of water within the Valley aquifer system?”

Fact: This figure is false and has long been quoted by tycoons looking to get rich by exploiting the Valley’s water resources. The origin of the claim that there are 2 billion acre-feet stored in the deposits underlying the Valley is a USGS report from 1971 where geologist Phil Emery took a stab at estimating the contents of the aquifers. During the trial for the American Water Development Incorporated (AWDI) water export proposal, another ill-advised effort to take water from the Valley, Emery noted he had miscalculated his estimate. Further court decisions, studies, and the State of Colorado’s groundwater model, the Rio Grande Decision Support System, have shown there is no unappropriated water in the basin. Meaning, all of the surface and groundwater has been spoken for by existing water users. In fact, there are more claims to water than can be satisfied and the Valley’s water supplies are over appropriated.

Survey Question: “Do you realize this proposal will withdraw water from 3,000 feet below the surface and will have no environmental impacts?”

Fact: Pumping from 3,000 feet impacts the confined aquifer, which is the deeper of the Valley’s two aquifers. The confined aquifer is connected to the unconfined (shallow) aquifer and surface flows to some degree. RWR has expressed intent to pump from a series of deep wells in the north end of the Valley. Extensive pumping in this area could have great impacts to surface and groundwater, which supply the Great Sand Dunes National Park and Preserve, Baca National Wildlife Refuge, and numerous important ecosystems on public and privately owned lands.

Survey Question: “Are you aware of the pending action by the State Engineer to shut off irrigation wells in Subdistrict 1 with no compensation?”

Fact: There is no pending action by the State Engineer to shut off irrigation wells in Subdistrict 1. In response to the recognition by local water users and State officials that groundwater use in certain parts of the basin is unsustainable, local leaders worked to pass legislation that allows communities within the Valley to create plans to balance water use and supply. The Rio Grande Water Conservation District (RGWCD) then formed Groundwater Management Subdistricts (Subdistricts) to create and implement plans of water management. These actions allow the Valley water users to work together to recover aquifers themselves, rather than facing sweeping orders from the State Engineer to shut down or curtail wells. Subdistrict 1 has been in operation for ten years and has until 2030 to recover the groundwater to levels identified as the sustainability targets in the legislation that enabled Subdistricts. The State Engineer and staff of the Colorado Division of Water Resources have provided critical support and are working closely with local water managers to ensure implementation of the plans of water management is successful.

Survey Question: Did you know there have been pipelines exporting water out of the San Luis Valley for the last 100 years?

Fact: There are no existing pipelines out of the Valley. There are two ditches that take water across the Sangre de Cristo mountains from Medano Creek to a ranch in the Wet Mountain Valley. These diversions occur pursuant to a 1914 court ruling and divert a combined total of 15 cfs from May 15-July 15 of each year. The cumulative diversions total an average of 1,063 acre-feet per year, a far cry from the 20,000 acre-feet proposed by RWR.

The RGWCD, San Luis Valley Water Conservancy District, and Conejos Water Conservancy District urge residents to take action by seeking out the facts of the Valley’s water resources and advocating for the truth. Please see for information about current aquifer levels and the Subdistricts’ efforts to manage our groundwater.

New study predicts less water in #ColoradoRiver as #Utah considers its #LakePowell Pipeline — The St. George Spectrum #COriver #aridification

This $2+ billion project would pump 28 billion gallons of water 2,000 feet uphill across 140 miles of desert to provide just 160,000 residents in Southwest Utah with more water. Graphic credit: Utah Rivers Council

From The St. George Spectrum (Lexi Peery):

Climate change is increasing the variability of the Colorado River so much so that the river could lose one-fourth of its flow by 2050, according to a new government study.

As plans for the 140-mile Lake Powell Pipeline — which would divert over 86,000 acre-feet annually from the reservoir to southwestern Utah — are under review by the Bureau of Reclamation, what does the Colorado River’s diminishing flows mean for the project?

The new report, produced by the U.S. Geological Survey and published in Science, attributes a 16% decline in the river’s flow from 2000-2017 to rising temperatures. The Colorado River hydrates seven downstream states, storing water in shrinking Lake Powell and Lake Mead reservoirs.

Washington County Water Conservancy District Manager Zach Renstrom said he thinks the variability of climate change provides even more reason for the county to pursue the pipeline.

“Climate change is a big deal to us, we are very concerned about it, and specifically how it’s going to affect our watershed,” Renstrom said. “When we look at these dynamics, they’re one of the strong arguments for the Lake Powell Pipeline because we need to make sure to have a robust infrastructure in place so we can adjust for (climate change).”

Rising temperatures, less snow

Seen from the air, Glen Canyon Dam holds back the Colorado River to form Lake Powell. The state of Colorado is looking into how to fund a program that would pay irrigators to reduce their consumptive use in order to send water downstream to a savings account in Lake Powell. Photo credit: Brent Gardner-Smith/Aspen Journalism

USGS scientists considered two scenarios of climate change in the Colorado River study. In one, warmer temperatures by 2050 would reduce the amount of water flowing in the river by 14-26%. In the other scenario, warming would take away 19-31% of the river’s flow…

Milly and fellow USGS scientist Krista Dunne focused on the reflectivity of snow, known as albedo, as a key element in the river’s sensitivity to warming. They zeroed in on the role of snow cover as a “protective shield” for water in the river basin.

Milly likened the flowing river to the leftovers of the “meal” of snow and rain that falls across the basin after evaporation has “eaten” its share…

And the amount consumed by evaporation is driven by how much energy the basin absorbs in the form of sunlight. The snow cover in the Rocky Mountains reflects back to the sky and space a significant fraction of the sunlight.

As the world gets hotter with the burning of fossil fuels, more of the precipitation falls as rain instead of snow. And the snow melts away earlier in the year. As the snow cover in the mountains is progressively lost, the river basin absorbs more energy…

“When we talk about structural deficits and overuse of the Colorado River system, it’s exclusive to the lower basin,” WCWCD spokesperson Karry Rathje said.

Washington County’s population is projected to grow 229% by 2050, but Renstrom says he’s worried that growth may come sooner than expected. He’s pushing to get the pipeline going in the next 10 years in order to diversify the county’s water supply.

“Even when we look at reduced flows … the water in the Lake Powell Pipeline should be available for us to withdraw,” Renstrom said. “As the guy who has to worry about where water is coming from in 30 years if some of the higher-end climate models come to pass, and the Virgin River is dried up, it makes me feel very secure that we’ll have another tool in that toolbox.”

Utah Rivers map via

Cloud seeding study validates ski industry staple — @AspenJournalism

Scenes from the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) project, which was undertaken in Idaho’s Payette Basin in winter 2017. Credit: Joshua Aikins via Aspen Journalism

From Aspen Journalism (David O. Williams):

n innovative new study conducted in Idaho and published on Monday seems to confirm what Vail and other Colorado ski resorts have believed for decades — that “cloud seeding can boost snowfall across a wide area if the atmospheric conditions are favorable.”

“This is a revelation. We can definitely say that cloud seeding enhances snowfall under the right conditions,” said Sarah Tessendorf, a scientist at the National Center for Atmospheric Research in Boulder and co-author of a new paper on the research conducted by scientists from the University of Colorado Boulder and University of Wyoming, among others.

Cloud seeding uses ground-based generators to disperse dust-sized silver iodide particles into clouds so that ice crystals can form on those particles and fall to the ground in the form of snow. Scientists, water managers and ski industry executives say it’s precipitation that would otherwise stay in the clouds, so cloud seeding is an environmentally safe way to enhance snowfall.

But the efficiency of cloud seeding has so far been hard to prove. Tessendorf said previous cloud seeding studies were unable to achieve statistically significant results because the natural variability of the weather was too great and demanded a larger sample size than could be reasonably obtained, for financial reasons.

In winter 2017, the National Science Foundation, which sponsors NCAR, teamed up with the Idaho Power Company to conduct a field study called SNOWIE (Seeded and Natural Orographic Wintertime Clouds — the Idaho Experiment).

SNOWIE used supercomputing technology to develop a new computer model to simulate cloud seeding, as well as new measurement capabilities, such as a high-resolution cloud radar on a Wyoming research aircraft that can see previously invisible cloud features. Researchers also located mobile radars on mountain ridges north of Boise to see clouds not visible to stationary National Weather Service radars that are blocked by the mountains themselves.

The scientists then used airborne seeding instead of ground-based generators because the silver iodide dispersed downwind from the aircraft in a zig-zag pattern, which is a very unnatural pattern for precipitation to form.

That allowed the scientists “to unambiguously detect the impact of cloud seeding in these clouds using the mobile and airborne radars,” Tessendorf said. “This had never been done before. In the three cases we report on, there was negligible natural snow falling, so the zig-zag pattern was able to be detected very clearly and tracked to the ground to quantify the snow reaching the ground due to seeding.”

One of the examples cited in a press release accompanying the study was a cloud-seeding flight on Jan. 19, 2017, that generated snow for 67 minutes, dusting about 900 square miles with a tenth of a millimeter of snow beyond what was falling naturally.

“This was barely enough snow to cling to the researchers’ eyelashes,” the release reads, ‘but it would have stayed in the air if not for cloud seeding.”

“We tracked the seeding plume from the time we put it into the cloud until it generated snow that actually fell onto the ground,” said Katja Friedrich, a University of Colorado Boulder professor and lead author of the new study.

Scenes from the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) project, which was undertaken in Idaho’s Payette Basin in winter 2017. Credit: Joshua Aikins via Aspen Journalism

Finding the ideal storms

Dave Kanzer, deputy chief engineer for the Colorado River District, helps oversee a system of 25 ground-based cloud-seeding generators in the central Colorado region that includes Grand, Summit, Eagle and parts of Pitkin County. Nearby generators include one atop Arrowhead and another above Camp Hale.

Kanzer said storms from the north and northwest, which tend to be colder, are ideal for cloud seeding, with temperatures in the clouds no higher than 21 degrees Fahrenheit and no lower than 5 degrees Fahrenheit. If the clouds have the right temperature range and the right moisture levels but lack sufficient particles for ice crystals to form, that’s where cloud seeding comes in.

“We take advantage of the first two and we add the proper amount of particulate matter to enhance the snowfall and precipitation … and that accumulates in the snowpack somewhere in the range of between 5 and 15% on a per storm basis when those conditions are met,” Kanzer said. “And that helps to increase the water yield of the snow sheds in the range of 1 to, 4% of water on a seasonal basis.”

Scenes from the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) project, which was undertaken in Idaho’s Payette Basin in winter 2017. Credit: Joshua Aikins via Aspen Journalism

A tool to maintain snowpack

The Colorado Department of Natural Resources regulates cloud seeding, permitting operations in nine different parts of the state. The operations in the central zone, at the headwaters of the Colorado River, are funded by a wide range of groups, including Front Range utilities and water districts that divert Western Slope water, including Denver Water and Northern Water.

The Colorado River District spends around a $150,000 a year contracting with Western Weather Group to run the program, which Kanzer said is about the same amount Vail Resorts spends on the program for its four Colorado ski areas – Vail, Beaver Creek, Breckenridge and Keystone.

Vail Resorts declined to comment for this story.

Kanzer presented on cloud seeding at a November Eagle River Watershed Council meeting in Avon, where a few of the 50 or so participants got heated in their questioning of the environmental safety of the process.

Kanzer said cloud seeding is safe, using inert silver iodide that cannot be detected in the environment after it’s released into clouds. He added the process could become increasingly critical to maintaining mountain snowpack as the climate changes.

“It’s one tool that we can use to mitigate or adapt to the changes that we have not only predicted but are starting to experience with shorter snow-covered seasons,” Kanzer said. “And so (cloud seeding) helps us extend that time or at least forestall the reduction.”

Aspen Journalism collaborates with The Vail Daily and other Swift Communications newspapers on coverage of water and rivers. This story ran in the Feb. 25 edition of The Vail Daily.

Cloud-seeding graphic via Science Matters

New Lead Reduction Program underway — News on TAP

In March, Denver Water is launching a major initiative to protect customers from lead in their homes. The post New Lead Reduction Program underway appeared first on News on TAP.

via New Lead Reduction Program underway — News on TAP

Westminster to raise water and sewer rates for next two years — The #Denver Post

Water infrastructure as sidewalk art

From The Denver Post (Megan Webber):

Westminster’s city leaders want to replace aging water tanks and a water main and keep up with environmental regulations, and they are asking residents to fork out an extra $7 a month in their water and sewer bills to pay for it.

City Council is hosting public meetings to explain the needs and why it wants to increase rates in 2021 and 2022 for the projects. Under the proposal, the average customer will be billed an extra $4 for drinking water and $3 for sewer each month in 2021, and then again in 2022. That equates to about $168 per customer over the next two years.

The exact rate increase depends on each customer’s usage and varying usage year-round, said Westminster Public Works Director Max Kirschbaum…

The projects on the table include $16 million to replace deteriorating storage tanks for drinking water, $11.5 million to replace a water main on Lowell Boulevard and $4.6 million to meet new environmental regulations for the Big Dry Creek Wastewater Treatment Facility, according to the city’s website.

The city’s water is filtered in a plant that was built in 1970, Tom Scribner, water treatment plant superintendent, said. Age and everyday wear and tear has chipped away at the concrete and pipes. The plant still works and is expected to last another 20 years before it needs to be shut down…

The city is working on repairing infrastructure at several sites throughout Westminster, including a $16 million underground pipe project on 112th Avenue and Huron Street and a waste-water pump on Zuni Street between 84th and 88th Avenues…

For the past decade, the department has been spending about $30 million a year on maintaining infrastructure, Kirschbaum said…

The Public Works department is hosting a series of open houses to inform Westminster residents about the bill increases and changing infrastructure. The first was on Feb. 26 at City Park Recreation Center, and a second is scheduled for March 18 at the same location at 6 p.m. Refreshments will be provided.

#ClimateChange Is Coming for Your Powder Stash — Outside Magazine

Powdery run in Breckenridge, CO. By Dusty Wright – Imported from 500px (archived version) by the Archive Team. (detail page), CC BY 3.0,

From Outside Magazine (Katarina Zimmer):

As the climate warms, Colorado may see fewer days of this light powder and more of the heavy, moist stuff, according to Noah Molotch, a professor of snow hydrology who directs the Center for Water, Earth Science, and Technology at the University of Colorado, Boulder. “One of the first signals that I think we’ll see related to climate change in Colorado is an increase in snowfall density,” Molotch says. “As it gets warmer, that snow will be less fluffy and heavier.”

The reason lies in how snowflakes form, thousands of feet above the ground. Each snowflake begins when water vapor in clouds condenses around particulates—like pollen or dust—creating ice crystals, which begin to grow outward. Because of the unique features of water vapor movement at icy temperatures, vapor will condense only onto the very tips of the crystals, forming six arms, each splitting into many branches—ultimately, a snowflake. True to the cliché, each one is indeed unique.

For the quintessential, picture-book snowflake to form, the temperature must be between minus 8 and 15 degrees Fahrenheit, with a relatively high level of moisture in the air. Different shapes arise at temperatures slightly warmer than 15 degrees but still below freezing: columns, prisms, and needles that don’t look anything like traditional snowflakes. “If one were to cast judgment on the beauty of snowflakes, these would not win the beauty contest,” Molotch says.

When the air is warmer, the movement of water vapor inside clouds will slow down. Instead of condensing onto the outermost tips of ice crystals, water vapor will build all around it, rendering its nascent six-sided structure indistinguishable. Ultimately, this creates thick blobs that often collide with water droplets and other flakes in the air and reach the ground as dense, heavy snow. David Robinson, a snow scientist at New Jersey’s Rutgers University, calls it “packing snow,” which is great for crushing into snowballs and snowmen but makes for a more arduous skiing experience.

No studies have attempted to document an increase in snow density over time, Molotch says. Gathering that data isn’t something scientists can easily determine from satellites or airplanes and would therefore require a lot of work on a large scale. But based on well-understood physical principles about how snow forms under different temperatures in the atmosphere, it’s likely that Colorado skiers may gradually see less light powder as the climate warms—although, Molotch adds, the state’s snow still has a way to go until it becomes as heavy as snow in the Sierra.