April Flowers Bringing It

The Merced River approaches 'minor flood' stage tonight, with the previous two night's flows being near 5300 cfs, which is roughly double the average peak spring volume. Valley meadows are wet, some trails are under water, some campsites unusable, and it's a great time to be a duck. While exciting, this is the normal and predictable outcome from a winter that brought the Merced watershed 153% of average snowpack water content as of 1 April (and 176% in the Tuolumne watershed). The waterfalls are ripping right now. You may recall that (after vehicle accidents) swiftwater is the number one factor for visitor fatalities in Yosemite; respect the water. April has been warmer than usual (only one day of wist ice [frazil] in its typically most productive month) and we wonder if peak runoff has come 3-4 weeks earlier than the late May average.

There is still a huge quantity of snow at 7000' and above. While we did have some warm storms this winter that brought rain to high elevations, we had far more storms that delivered snow down to 2000'. Several recent SAR call-outs have resulted from people getting up into deep snow where they didn't expect it. Some have been getting their intel from various posts/photos about nice April hikes that others did last year - that was a very dry winter. The Fourmile Trail and the JMT below Nevada Fall (ice cut) are still closed and dangerous. The High Sierra Camps won't open this season. Expect stream crossings to be challenging and snow to persist well into mid-summer in the high country.

Dogwood flowers are at the puppy stage in Yosemite Valley. Tanagers, orioles and grosbeaks are singing and shining brightly. Peregrines are at their eyries. The green dragons are rolling. "This grand show is eternal..."

Post-winter Recovery

Springtime is making its way uphill in the Sierra with redbud peaking in El Portal now while unfathomable snow persists above 7000 feet. It can hardly be said enough: WHAT a winter we've had here! Storms were repeated with good frequency and lots of Pacific moisture, leaving us with a tremendous snowpack. The snowline was a bit higher than historical averages; not much accumulated in Yosemite Valley (though we had lots of rain runoff), but higher elevations have had fantastical quantities. The central Sierra has 175% of usual water content in the current snowpack. Picture the meadows and forests in the May Lake area buried by 6-7 feet of water (not 6' of snow, but 6' of standing water) - that's the nature of how much mature, dense snow is covering the tens of thousands of acres of Yosemite's upper elevations.

<-Bridalveil in flood.

Storm damage has been considerable in/near the park, with Hwy. 41 having been closed for a month by a washout, and crews working hard to repair slope movement on the Big Oak Flat Road below Crane Flat in hopes of getting it re-opened before Memorial Day. Trails at and above the Yosemite Valley level have a lot of downed trees; trail crew sawyers will be very busy for much of the summer to get those cleared. When you visit the Valley, check out the fragments of bark-less logs below Bridalveil or Yosemite Falls from trees that were uprooted and thrown over the falls this winter. Since December there's been a huge deposit of frazil (wist) ice below Yosemite Falls, and we're now in the month when one is most likely to be able to observe wist ice flowing.

The excitement isn't over. Because of the closure of the Big Oak Flat Road, Hwy. 140 has been handling much more traffic. This past Saturday, visitors were waiting over 2 hours in a 3.5 mile-long line of 800+ cars just to get through the stoplight at the Ferguson rockslide detour west of the park. (Easily avoided by coming in before 9am on weekends.) Because of the road construction in the Valley, the main parking at Yosemite Village will be closed for the next two months, and detours are confusing to both new and veteran visitors. It's going to be a very nice improvement once it's completed, but parking and navigating can be challenges on spring weekends now. Half Dome Village and the new lot by Camp Four are best bets. The road crew is already working to clear Glacier Point Road.

But, wait, there's more. The Merced is running almost 4x average flow today. All that snow in the high country seems likely to bring us some degree of 'high water incident' between now and mid-June (sure to cover some Valley trails at least), depending on how the warming progresses. Yosemite explorers should expect a delayed start to summer, with Tioga Road opening late, trails covered by snow and fallen trees, and creeks difficult to cross.

Ice, Ice, Maybe

There's an exceptional accumulation of waterfall slurry ice below Yosemite Falls right now, and the whole amphitheater is closed for safety reasons. The stream of 'frazil' flow meanders dynamically and it'd be possible for someone to get into real trouble with this unstable landscape. We know it's not really 'frazil ice' because this slurry is formed of frozen waterfall mist/droplets, but it's remarkable, whatever we call it.

There's frazil deposition in Royal Arch Creek and Steve B. says there's frazil in Bridalveil and Ribbon Creeks.

There's also a very healthy snowpack at higher elevations, well above average in depth and water content. The Valley has lots of water from recent storms; there's almost a foot of snow on the ground but running water in Sentinel, Eagle, Royal Arch, Ribbon and other creeks. This wet winter bodes well for summertime waterfalls, some groundwater recharge, and perhaps a more normally-timed start to the fire season. We'll have to wait a few months to fully assess the end of the drought.

Meanwhile at lower elevations flowers are blooming in the Merced River canyon: fiddleneck, baby blue eyes, and a galaxy of waterfall buttercups can be found.

Towhee and Frazil

Cold and snow chill Yosemite. We had frazil ice in Yosemite, Sentinel and Ribbon Creeks yesterday morning; a bit late in the season, but not unheard of. The Merced River has dropped just below the average flow rate for mid-May; it has been running at above-average volume since the big storms got started in November. Though average, the falls are still big, but they'll get bigger, and they'll still look good in July. Fire season gets delayed, though the moisture likely means more growth of small fuels like grasses.
A highlight on yesteday's birdwalk was seeing Superintendent Don Neubacher dash out of his office with binoculars in hand to stalk a seldom-seen green-tailed towhee outside the Administration building. He was accompanied by ace ranger-naturalist Karen Amstutz who spotted the unusual bird out her window and had the inspiration to pull the park's boss (a dedicated birder) away from his desk to see the towhee. I'm glad to know that our park is being looked after by such people. My group was surprised to see a second green-tailed towhee a short time later near Yosemite Creek.
Ranger JT reports snowplant emerging near Sentinel Bridge. I've seen a couple in the west end of the Valley, too. Along with new birds and plants, it's exciting to see the seasonal increase in park staffing as more interpretive rangers return to duty or start their first summer as seasonal rangers. Park visitors are lucky to have all these people leading walks and campfire programs, answering questions in the visitor centers, conducting tram tours and cultivating another 24,000+ Junior Rangers.
There is still room in the Yosemite Conservancy's 3-day "White Wolf Botany" course in early July. This is going to be some terrific field time for casual botanists in a special part of the park. We also have space for people to join us for the two "Family Camping Jamborees" in late-July in Tuolumne Meadows.

Warm then Storm

Last weekend's overcast and rain caused the Merced volume (and the tributary waterfalls) to drop back down to near average flow. One might think that rain would raise the river level, but, in fact, the cloud cover and cooler temperatures reduce the snow melting rate much more than a bit of rain can increase the runoff. Warm sun brought the flows up again through the week. Again this weekend we expect a cool storm to bring a bit of rain (and snow -which, of course, reduces the near-term runoff much more than rain does), so the waterfalls will be smaller at the start of next week than they are now.
On most days, the river (and tributary) volume exhibits a nice 24-hour cycle of rise and fall. The hottest part of the day is when the most snow melts up at 7-13,000'; this surge of melt doesn't reach the two Yosemite Valley river gauges until many hours later. It's odd that our highest water flows in the Valley happen after midnight - about 12 hours after the hottest part of the day. That's the lag time for high country runoff to make it down to 4000'.
It was cold enough in the Valley this past Tuesday morning (9 May) for people to observe frazil ice in Yosemite Creek and in Ribbon Creek. A deposit outside the eastern channel at Ribbon Creek persisted into the next day, looking like an anomalous patch of snow.
NPS road crews have reached Glacier Point, and they've reached the White Wolf area on Tioga Road, through average snow depths of 8' and 10' respectively.
The bizarre red snowplant is emerging from the ground in Yosemite Valley. Bracken fern is tall and unfolding its fiddlehead fronds. Dogwoods are fully alight now. Western Wood Pewees arrived this week in the Valley. The concentrations of yellow-rumped warblers and some other birds have dispersed from the Valley to higher elevations a bit. I've been seeing 1-2 bears a week in the Valley, more than has been my usual experience.
If you're up early and have a good eastern view, check out the concentration of planets in the east before dawn.

Wild, Wild Life

Black-headed grosbeaks are now singing in the Valley, there were more orioles on Thursday's birdwalk, and several dozen yellow-rumps encountered in 3 flocks -a tiny portion of them singing. Three Vaux's swifts patrolled over the Valley Visitor Center. Hummingbirds are doing display flights. About a month ago NPS volunteer interpreter Kirsten discovered a rare Virginia Rail near the boardwalk in Cook's Meadow.
On the mammal side, a dark brown bear has been grazing the Ahwahnee Meadow area lately. Two rescue helicopters there on Tuesday night didn't disturb its feeding. Biologists researching our fisher populations are delighted to have encountered a mother with young, moving them from place to place in the south area of the park. Good news for predators and general food web health; bad news for mice and squirrels.
Road crews are grinding away at the extra-deep snow on both Glacier Point and Tioga Roads, slowly making progress to open up the high country for our cars. Tomorrow morning might be cold enough for frazil production, but then it warms up for the early part of the week. There is still a chance for big frazil flows for another few weeks; just because April's over doesn't mean that we won't have some sub-freezing nights in Yosemite Valley.

Slow spring

Too warm for frazil ice, too cool for rapid snowmelt, our recent unsettled weather continues this week with a bit of cloudy damp. The weather forecast leads us to anticipate no frazil ice this week.
Black oak leaves are not quite starting to burst out of buds yet, though they have lower down. Cottonwood flowers are out along the river. Insectivorous orioles are in the Valley now, ahead of most insect food. Redwings are singing in Cook's Meadow, mallards swim in pairs, yellow-rumped warblers sing a bit on sunny days.
Former Yosemite employee Paul Keel, back for a visit, added a new species to the park's birdlist: our first ever white-faced ibis. Paul is a state park ranger now, down on the coast, and he got good photos of the ibis in El Capitan Meadow. You never know what you'll come across, if you're paying attention.
This morning we watched a male belted kingfisher working the oxbow lake in Cook's Meadow. Fun to see a fish predator well away from the river channel.
More predators will be on display in the Conservancy's "Hawks and Owls" field seminar the first weekend of June. Park ornithologist Sarah Stock and great grey owl specialist Joe Medley (yes, the son of Steve Medley) are the two instructors. We are delighted to have these two knowledgeable experts (and charming individuals) teaching this fun program. There's still space available; free camping and free park entry are part of the package. Raptors rule the skies...

National Parks Week

I am back in Yosemite after two weeks away, and what changes there are. The free entrance to Yosemite for National Parks Week, combined with some school spring breaks has meant a busy week in the park. The natural scene is busy, too.
Snow is gone from the Valley floor except in a few shady spots. Waterfalls are bigger than average, with the recent warmth getting a start on melting off our exceptional snowpack. Cooks, Leidig, El Capitan, Stoneman, Ahwahnee and Slaughterhouse (lovely, I know) Meadows all have standing and/or running water in them now; some paths are blocked, but none of the main ones yet. Table Rock, our local visual river gauge for Valley commuters, is underwater.
Frazil ice forecast for this weekend: POOR.
Yellow-rumped warblers are at their brightest in the black oak canopies, where tiny pink leaves are barely starting to emerge in the Valley. Black-throated gray warblers are doing their excited, buzzy call in the live oaks in the Valley now, too. A great gray owl was reported on its nest up near Crane Flat, though there's so much snow there still, their food is out of reach and it's hard to imagine successful breeding at this point.
Our "Moonbow Photography" Outdoor Adventures course was a success on Sunday night, with a bright bow visible for a couple hours in-between overcast periods. Next up is Ken Rockwell and Dave Wyman's "Spring Light Photography" course, and then an excellent "Hawks and Owls" program the first weekend of June.
Our regular public birdwalk will be seeking John Muir's favorite bird tomorrow, Cinclus mexicanus. Thursday is his 173rd birthday. Friday is Earth's birthday; stand up for what you stand on, as they say.

Yosemite Recovered

The storm of 20-21 March goes into the record books as one of the most significant in decades: over 12 feet of snow at the 7-8000' level, and 9 inches of heavy snow that broke down thousands of live oaks and other trees at the 2000' level. Electricity was restored after 6 days, and visitation has now picked up.
We've had very warm weather the past few days. Bird activity has increased, flowers are on the rebound, and the Merced River has doubled in volume and is really turbid. The river has gone over 1500 cfs at Pohono Bridge, more than twice the average flow for this date. Sierra-wide snow surveys show 165% of normal water content in the snowpack; our local results come out shortly and will surely be comparably abundant.
We all look ahead to the waterfall season of the next 3 months, hoping that all this snow runs off over a long span of summer, rather than all at once. Photographers Ken Rockwell and Dave Wyman have timed their "Spring Light Photography" course to coincide with predicted high volume, 19-22 May.
We're also coming into peak frazil season this month. The frazil ice forecast is poor for the next few days, as temperatures are mild. But the warmth makes more mist, which will produce more frazil particles when the temperature does drop again.
I'll be away from the park the next two weeks.

Wintery Equinox

Yosemite Valley's mostly bare ground got a few inches of snow overnight and it even accumulated as low as El Portal; most park roads are R2 this morning. Another wave of snow arrives early Sunday morning.
We had frazil ice in the Valley this week, with Yosemite Creek sending frazil into the Merced twice, and Ribbon Creek even fraziling all the way into the river on Thursday. The snow cone at Upper Yosemite Fall is as big as ever. Frazil forecast for the next several days: moderate, best on Monday morning.
Sentinel, Eagle and Horsetail Creeks flow to the river. Wosky Pond is very full.
Varied thrushes, which have not been very evident here this winter, were making their odd squeaks in Yosemite Village yesterday. Karen Amstutz and Michael Ross heard and saw a phainopepla in El Portal earlier. Karen noted a disoriented flock of Canada geese in the rainy nighttime of Badger Pass last weekend, likely drawn to the illuminated slopes.
Tonight's full moon coincides with perigee (the point in its elliptical orbit where it's closest to earth) so will appear a bit larger and about 15% brighter than an average full moon; this happens about every 20 years. Elsewhere in the sky this weekend: vernal equinox on Sunday when the sun rises due East and sets due West, and our day and night are about equal in time. Vernal means springtime, so Sunday is the first day of astronomical spring for the northern hemisphere. Vernal also is a big waterfall that will be running strong this season - given its current name by the first Euro-Americans in the Valley who saw its ferns and moss as springlike. Just upstream was a bigger, but somehow colder-looking waterfall that they named Nevada, meaning snowy.
This weekend is thus both 'vernal' in astronomy and 'nevada' in weather - Yosemite perfection.

The Wearing o' the Green

A lot of the recent snow is now gone from the floor of Yosemite Valley and run-off is picking up. The Merced River is now running at about twice its average volume for mid-March. We got a bit of rain last night and we expect more rain/snow off and on this week. It'll be a grand year for waterfalls with so much wet snowpack in our upper watersheds. Next weekend may also be stormy, with the snow level at or below Yosemite Valley. Frazil ice forecast: low-moderate probability for next weekend.
Meanwhile the foothills and Merced Canyon west of Yosemite are greener and greener with buckeye leaves still emerging. Redbuds are pinking, getting ready for their startling color show soon. Popcorn flower dominates at ground cover level, poppies are coming along, false goldfields and fiddlenecks are looking good. The Hites Cove Trail is well worth a stroll now - yes, even if it's on a rainy weekend; you'll see more newts and hear more chorus frogs singing love songs.
The Ahwahnee re-opens on Thursday, in time for St. Patrick's Day. Meanwhile, we send seismic sympathies to the people of Japan for the blow that the restless earth has dealt there.

Winter is Back

A more usual sequence of wintery storms has returned to the Sierra after so many weeks of dry, mild weather. Wildflowers in the lower Merced Canyon have had to endure extra-frosty mornings and a few doses of snow, even down to 2000.' Today we're in-between snows, with warm-ish, sunny conditions. A few inches of snow still cover the Valley floor, but creeks will come up as the sun converts the snow coverage to run-off. More snow and rain arrive tonight. We expect another set of high elevation snow survey data soon.
Frazil ice continues to appear in Valley locations, with our above average run-off and cold overnight lows. We don't generally see it this early in the season, but this year is different. Maybe its abundant apparitions are a result of the popularity of the video. As April draws closer, we may try to post frazil forecasts here. These can only work 2-3 days ahead, when we get good temperature forecasts from NWS.
Yosemite has come to life indoors, in the form of the Yosemite Renaissance art exhibit in the Museum Gallery, next to the Valley Visitor Center. There were 578 entries submitted, and just the best 42 qualified to be displayed for our enjoyment. Come see the varied pieces between now and early May; pretty inspiring.

More earth

The latest snow surveys show that the Merced watershed courses snowpack has 142% of average water content. Runoff in the Merced and its tributaries is still well above average flow for early February; all the waterfalls are looking robust.
This high flow combined with cold nights to give us frazil ice in Yosemite Creek on Monday and Tuesday nights (and probably others). This is earlier than usual, but not unprecedented. We know that California temperatures have risen by 1.5 degrees C since 1880; there must've been much more frazil through the season back in Muir's day. That may be one reason he abandoned his cabin along Yosemite Creek and moved into his 'hang-nest' up high on the eaves of Hutching's sawmill.
You saw Steve's frazil ice video in the Yosemite Nature Notes series (which is funded by Yosemite Conservancy). He's out with his camera each evening right now working on a 'firefall' film. Watch for that one soon, or come up to the park in the next 2-3 weeks and take your chances on seeing the shining glow of Horsetail Fall at sunset yourself. Get out with a pro photographer in next weekend's Outdoor Adventure course for an improved chance of capturing this phenomenon for yourself before you see Steve's version on-line.

Frazil Ice Planned for April

The NPS/YC Yosemite Nature Notes video on frazil ice has gotten remarkable viral traction on-line. We've received lots of messages lately about where/when people can see the stuff. As it says in the film, April is the best month for observing the ice flow in progress, but you have to either be lucky with timing, or come stay for the whole month so that you can go out before 8 every morning to see if it's there. If the night's temperature is well below freezing, you should see it. It doesn't generally happen in mid-winter because the water volume in the falls is too low to generate enough mist to form a lot of ice. (Though the conditions were right this year to form frazil in Bridalveil Creek in late December.) There's a decent likelihood that April visitors will at least see the remnant deposits of ice, which just look like snow lining the creek banks.
An earthquake near 1 a.m. Sunday morning was noted by some park locals, who heard it as much as felt it. It was a 2.2 magnitude, centered 14 km beneath the headwaters of the South Fork Merced River. The Clark Range has had a light series of small, deep quakes like this one over the past five years; this fits in with that movement under the batholith.
In more earth news, the Yosemite Conservancy has an Outdoor Adventure course February 18-19 seeking to photograph the elusive (almost mythical) 'firefall' effect that happens in Yosemite Valley for a couple weeks each year. Pro photographer John Senser has captured this transient phenomenon many times over the years and will be your best guide to find this glorious spectacle. Call Carolyn to sign up: 209/379-2646, extension 10.

Hecka Weather

We've had a terrific storm over the past few days, with more to come. It started raining Friday and has stayed wet since; Yosemite Valley has had more than 8 inches of precipitation (20% of the year's average total) in the past 4 days. Until this morning, it's all been rain, with high snowline; even Badger Pass got a soaking. This has brought up the waterfalls and flooded the Valley meadows. The gully below Cathedral Spires again surged out into Southside Drive. Sentinel, Ribbon, Eagle, Horsetail and Royal Arch Creeks (but not Indian Creek) are all flowing into the river. Wosky Pond is full and connected to the river. The river itself never approached flood stage, as had been threatened in earlier forecasts.
It was cold enough this morning to have frazil ice forming in Yosemite Creek; unusual for this point in the season. The Valley got over 6 inches of snow today, and Badger's gotten a lot more than that. The picture shown is from a walk up to the Vernal Fall Bridge this morning.
For more than a year I've been looking forward to tonight's astronomical coincidence of the winter solstice and a full moon - with that moon showing a total eclipse over North America. On top of that, the peak totality for our part of earth will be just after midnight, providing the potential for a nice long show. Now it appears that clouds over Yosemite will eclipse the dark orange midnight moon for us. As always, a lunar eclipse only happens with a full moon. A full moon always rises near sunset, is highest near midnight and sets around sunrise. That this full moon (and eclipse) happens during the longest night of the year and with totality close to midnight/overhead is just a happy accident. Whether we see the moon or not, winter solstice means that the days will start to lengthen toward summer - indeed an important date in the calendar.

Stormy Monday

More chilly weather lingers in our Sierra, with a winter storm warning starting tomorrow night, and several more inches of snow expected above 6000' again. The river has dropped to 1500 cfs at Pohono Bridge.
Highway 41 was closed for a time yesterday due to snow and vehicle accidents. A rockfall closed the Yosemite Falls Trail this morning. These are January scenarios, yet it'll be June next week.
Ribbon Creek carried frazil ice yesterday. Steve Bumgardner's terrific frazil ice video has been featured on the world's number one blog, boingboing: http://www.boingboing.net/2010/05/24/frazil-ice-fascinati.html#comments. Pete is honored.
Concentrated numbers of yellow-rumped warblers on this morning's birdwalk. Juncos were both flocking and singing.
Poison Oak on the Valley floor is about 50% leafed out, though it may have some frost damage. Yes, there is p.o. on the floor of Yosemite Valley, but you have to be remarkably unlucky to stumble into it. Farewell-to-spring (Clarkia) is blooming in El Portal now; given the conditions a little higher up it seems premature to bid farewell to a a season we've only glimpsed.

Crane Flat Bear Jam

A cinnamon sow has a nice pair of cubs of two different colors at Crane Flat. The family stopped a lot of traffic while they were grazing on new grass in the wet meadows there. Sad to think that so many bears are hit by cars each year; please drive with the wildlife in mind when you're in the park.
The Valley's dogwoods are maybe 90% emerged at this point; stormy weather today and yesterday further stalls their full brilliance. Cool, cloudy conditions dropped the river level down from 3000 to less than 2000 cfs at Pohono Bridge, below average for this date. But all the meadows are wet, some trails on the Valley floor have challenging creek crossings. There was a small quantity of frazil ice flowing this morning in Yosemite Creek and Ribbon Creek.
Juncos were back to winter flock behavior this morning. Chickadees were still observed in pairs, but no singing was heard. Tanagers and orioles were subdued by the cold. Snow coated the Valley rim this morning, but temperatures should be back up to the mid-70's by the end of the week.

Black and White TV

A turkey vulture flew over Yosemite Village, about 100 meters up, at 7:30 this morning. Especially on this cold, snowy sun-up, I take this to mean that the vulture roosted in Yosemite Valley rather than soaring upcanyon on thermals from lower elevation - something new for our neighborhood. Will condors be next?
More frazil ice formed up in Yosemite Creek this morning, covering all the channels and scouring more forest terrain of its natural duff. A good volume of slurry flowed into the Merced River. Frazil flowed in Ribbon Creek, too, and it went downstream of Northside Drive for the first time this season.
The handful of planted redbuds in Yosemite Valley are blooming; they endured a taste of snow overnight. Dogwoods are making progress, with some 'blossoms' up to 10 cm across and just starting to turn white.

New Arrivals

Michael Ross reports a western kingbird and an ash-throated flycatcher in El Portal, in the Merced Canyon. Black-throated gray warblers are working their way up from El Portal, through the extensive live oak canopy toward the Valley, singing their buzzy song for the past couple of weeks. It's still chilly and leafless in the Valley, so the caterpillars on which the arriving warblers feast haven't really emerged yet. Aside from the versatile yellow-rumps, other insectivores are holding off their arrivals here. It won't be long, though.
Steve Bumgardner reports that yesterday was our 8th day of good frazil ice flow in Yosemite Creek. Watch for his terrific footage of frazil in action to be posted in the 'Photos and Multimedia' section of www.nps.gov/yose early next week. His "Yosemite Nature Notes" videos are an excellent resource.

Yosemite's Curious Frazil Ice

2 April 2010

This is the month when locals look for frazil ice flows in Yosemite Valley. They can occur below any of our waterfalls, but are most often seen on large scale below Lower Yosemite Falls, when deposits can cover acres with what looks like snow, and can persist for months. We've had frazil forming on several recent mornings in Bridalveil and Yosemite Creeks.

It's hard to describe this material and its origin if you haven't seen it for yourself. Look at http://www.nps.gov/yose/photosmultimedia/ynn.htm in May for an NPS video that'll give you an idea. Imagine a creek turned into a slurry of suspended ice particles, or a lava flow made of ice, or spilling a million-gallon slushie drink into the forest.

It forms mostly in the spring when warm temperatures melt snow into high run-off and lots of mist in the waterfalls, then overnight freezing temperatures turn a portion of the spray into ice droplets, which flow along in the full creek. Because we get these conditions regularly, Yosemite is one of the best places to observe this 'waterfall spray ice' being created and then slowly melted away. There's a persistent myth that these deposits represent the sudden collapse of the Upper Yosemite Falls snow cone (a huge mound of ice that accumulates below the falls), but this is emphatically not the case. Frazil flows happen when it's quite cold, beneath falls with no snow cones, and they can happen repeatedly for weeks.

If you're lucky enough to be in the park this month, stroll by the base of the falls for a look.