Signs of Summer

Cool, wet weather a week ago brought the river level down from above average to below average.  Now the unusual heat has brought it back toward a more typical volume again, a bit below 2000 cfs at Pohono Bridge.  I could be wrong, but the peak flow of the Merced and tributaries may have passed already - 3 weeks earlier than average.  We expect a long and active fire season this year.
The Valley has been humid and green lately.  Oaks and maples are all but fully leafed out.  Dogwood blooms light the forest from within. A cloudburst the afternoon of the 9th caused local flooding and felt like an August monsoon storm.

Otherwise the waters are retreating.  Sentinel and Ribbon Falls are noticably smaller than a week or two ago. Staircase, Horsetail and Royal Arch are just dribbles.  Eagle Creek and Horsetail Creek haven't flowed on the surface of the Valley floor at all this year.  Wosky Pond is no more than 15m across at any point. 
Orioles, vireos, warblers, tanagers, grosbeaks, peewees, and robins sing with energy in the mixed oak/conifer canopies throughout the Valley.  White-throated and Vaux's Swifts have been seen and heard on the Monday/Thursday Conservany birdwalks lately.  A rare yellow-headed blackbird has been observed calmly feeding in Yosemite Village for several days recently. 
Tioga Road opened this weekend; snow cover is obviously light in the high country.  There was a fatal accident at Vernal Fall last week.  Weekends in the Valley are busy now, but weekdays will be relatively calm until more schools get out.
Some of the Conservancy's upcoming courses are full, but there's still space in a one-day, mid-June geology adventure with the wonderful Greg Stock, our Park Geologist.  Some of our Half Dome trips still have space available this summer, too.  Summer seems to be upon us now.

It's not 'frazil ice'

Technically, frazil ice is a slurry of ice particles that forms at the supercooled surface of turbulent liquid water.  Frazil forms in rivers and in wind-blown lakes/reservoirs in cold places.  What we have in Yosemite is a slurry of ice particles that forms as liquid water is aerosolized in a waterfall descending through sub-freezing air.  The end product of each process looks similar, but the way the very different talus and till can look similar or the unrelated heron and a crane look similar, to be proper, frazil and the distinct Yosemite waterfall feature should be distinguished with a different label. 
We might shorthand this frozen waterfall mist as 'wist ice' or a 'wist slurry.'  Because its origin is distinct from true frazil ice, our phenomenon deserves it's own name, though I wouldn't really expect our established common usage of 'frazil' to change.
One line of evidence that tells us that this isn't frazil ice is that when the creek below the waterfall is filling with the slushy mass, there is no ice above the falls.  This photo shows Yosemite Creek just above Upper Yosemite Falls at 7:30a.m. on 16 April, when it was 24 degrees F there.

There are no ice particles above the waterfall, but a dense slurry flow below.  No supercooled liquid is involved.
We've had wist slurries flow in Yosemite Creek and Ribbon Creek the past couple of mornings when temperatures dropped into the 20's.  Near-term forecasts don't look cold enough to produce much wist for the next few days.
Yosemite Conservancy's Monday and Thursday 8 a.m. birdwalks in the Valley have resumed for the next two months.  Orioles and grosbeaks have arrived in Yosemite Valley; we eagerly await our first tanagers.  The first warbling vireo of the year was heard yesterday.
The Hetch Hetchy Road has re-opened after repairs.  Merced River Plan public comments are due April 30.  Tioga Road is melting out faster than usual.  River and stream run-off has been higher than usual for the past two weeks, but it's expected to taper off early.  Seasonal waterfalls should be quite small by mid-summer.
There's still space in Dave Wyman's 'Spring Light Photography' course in mid-May.  Dave is a charismatic teacher with years of experience in Yosemite, and Yosemite always has something to teach us.

Vernality

Thaw: It's really warm in the park this week.  The Merced River has increased its flow to well above average, but our runoff won't last very long this year.  The latest snowpack surveys indicate 68% of average water content for the Merced watershed.
Freeze: Despite the clear signs of spring, we are not beyond snow season yet. Vernal equinox is next Wednesday, but we still have two months of snowfall potential.   Frazil ice maximum in Yosemite Valley is still a month away.   Skiers have three more weekends to enjoy skiing at Badger Pass.
Thaw: In the lower canyon flowers grace the terrain with orange poppies, white popcorn flower, baby blue-eyes, and even the redbud are emerging in their unique purple.  Kinglets, flickers and Bewick's wrens are singing this morning, and three species of swallows have returned to El Portal.  Buckeyes are greening up.  Armadas of white-throated swifts are already sweeping the skies up to 5000'.
Freeze: Despite the scant snow, Tioga Road won't open any earlier this year.  To cut costs during the current federal cutbacks, NPS will delay the start of plowing.  XC skiers are still gliding at Crane Flat.


Lyell West Lobe

Thaw: I hope by now most of you have heard the news that higher up in the park our measurements of the Lyell Glacier indicate that it has stopped moving.  Technically speaking, a glacier is ice that moves.  Lyell had been the largest glacier on the west slope of the Sierra, but now that distinction falls to the adjacent Maclure Glacier.  The former Lyell Glacier might be properly called a glacieret or a glacial vestige.
Thaw/freeze: Comet Pan-STARRS is visible very low in the west after sunset.  It's not easy to get a low enough horizon in Yosemite to see this comet in the twilight.  Binoculars are key to spotting this comet, which will fade over the next couple of weeks. 
I'm excited about a special program on April 13 that brings together Muir's great-great-grandson and a Muir actor for a day of roaming John Muir's haunts in Yosemite Valley.  This will be a fun way to experience history in person.

Best Little Hoarfrost

The recent weeks of steady cold allowed the growth of terrific hoarfrost formations in Yosemite Valley. Spikes and florets and feathers of ice condensed out of the atmosphere onto the ground, river ice, and tree branches wherever moisture and cold combined. A bit of this happens every winter, but this season's displays are exceptional.
Late this week, conditions have thawed. The first Amsinckia (fiddleneck) of the season has bloomed outside the Conservancy office in El Portal. There's a sunny bank where they often show early, and here's our first contestant in this year's mating game. Wilhelm Amsinck never came to California, but was a patron of the Hamburg Botanical Garden and his philanthropy is still rewarded today with us exclaiming his name each spring. (The picture shows fiddlenecks last spring.)

In shady spots further down canyon, Kumlienia (waterfall buttercup) is blooming profusely now. Thure Kumlien was a Swedish naturalist who relocated to Wisconsin a few years before the Muir family arrived there. As John Muir did, he spent as much time in the woods as he could and later taught school for a time. Now his legacy lives on in this genus, the first flower we find each season.

The road into Hetch Hetchy has been closed until an eroding section can be safely stablized.
Steve B. has crafted his best video yet, "One Day in Yosemite." After you watch it, plan yourself several days in Yosemite.
The Conservancy's 'Yosemite Outdoor Adventures' are all on line for the whole year now. Don't miss out on a chance to get out on the trail with us and learn from the best in the field.

No Ahwahneechee Apocalypse

For what we call 2013 the world continues on its way, no matter our contrivances. The Ahwahneechee did not predict a global apocalypse for this recent solstice, and they were right! Our physical cliffs endure and are not something that needs to be averted. In Yosemite, neither Half Dome nor Yosemite Falls noticed when we replaced old calendars with new ones. The one real change that occurred during our holiday scurryings was that the sun is starting to inch northward in where it rises and sets, and that each new day is a litle bit longer. To be more accurate, the sun isn't doing anything; it's our spot on the world that faces toward and away from the sun at a slightly different angle each day. Solstice is real to Yosemite, our calendars perhaps less so.
It's been quite cold in the park for a few weeks; there's snow and lots of ice in the Valley. Frozen waterfalls like Widow's Tears and Silver Strand (on the south wall, between Bridalveil and Tunnel View)are extra prominent and solid now. If you're thinking about a closer look, KC and JT tell me that Widow's Tears is the longest ice climb in the US.

Feathery worlds of surface hoar can be found in shady meadows early in the day. Small amounts of frazil ice have formed on some creeks. The snow cone at Upper Yosemite Falls is building steadily.
Badger Pass and Crane Flat both have healthy snowpacks for snowshoers and XC skiers. No one is ice skating on Tenaya Lake this winter.
Some of the Summer Triangle asterism is visible over eastern Valley walls before sunup. As Muir wrote it: 'each in its turn as the round earth rolls.'

Physical Cliff

Our physical cliff is a combination of higher pitches and reduced horizontality...
A couple of inches of snow came to Yosemite Valley Wednesday night and it's staying on the ground, at least in the shady areas.
The skies are meant to be off and on cloudy/wet the next few days. This could make for a damp Christmas Bird Count this weekend, the 16th, but the birds aren't going anywhere so we'll count whatever we see. Contact our compiler at sarah_stock@nps.gov if you're interested in participating in this grand citizen science project. Yosemite's count has been tops in the nation more than once in recent years, for numbers of white-headed woodpeckers and Williamson's sapsuckers. We have superb woodpecker habitat in our diverse forests.

Light quantities of frazil ice have been observed flowing in Yosemite Creek the past couple of mornings. Overnight mist-ice accumulations on the wall of Upper Yosemite Fall has led to loud booms by mid-morning as huge flakes peel off in the sunshine and start accreting into the snowcone.
XC skiing at Badger Pass opens this weekend, on 12 inches of new snow. The slopes need a bit more depth, still. We've had plenty of storms but the snowline has been high, almost as if the climate were changing...

December Rains

Recent storms have ended our Indian Summer conditions here. The snowline remained high, and it's quite mild this week, but Glacier Point and Tioga Roads are closed to cars (probably until May).
The Merced River shot up from around 60 to just over 2000 cfs in Yosemite Valley during the latest wave of heavy precipitation. Our waterfalls have roared back to life after a long parched spell.

Leaves are off the deciduous trees now. At the same time, El Portal has a lush ground cover of brand new grass and forb growth. Newly sprouted lupines and cranesbill are already identifiable by their foliage, but we don't expect flowers for a few months.
I spent Saturday pursuing nothing but woodpeckers; we encountered six species between El Portal, Foresta and Crane Flat - a couple more hours of daylight might've turned up more of this interesting taxa. Acorn woodpeckers are very busy storing and sorting this year's crop. Did you know that they're in the same genus as the Lewis Woodpecker? The genus name Melanerpes translates as 'black creeper.'
The Conservancy's 2013 field institute courses are all now open for registration; you can find birding, wildflowers, geology, photography, family programs, art courses, backpack treks and no less than seven trips to Half Dome in the "Yosemite Outdoor Adventures" line-up. Yosemite has something to teach you...