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..."

Wet Spring

After another very dry winter, Yosemite has had a bit of recovery with a wet spring. We had warm storms in March and April and are now enjoying a string of about 10 days of cool, cloudy afternoons. The first weekend of April we had the markedly unusual experience of a very late, warm, winter-scale storm. This atmospheric river brought high elevation rain instead of snow, a flood forecast, and a successful pre-emptive evacuation of Yosemite Valley. Sure enough, the Merced River came up through the campgrounds, over the roads, through Housekeeping Camp, and filled the meadows. NPS has nice footage online. There's a persistent myth that these 'Pineapple Express' storms melt a lot of snow, but they really don't. It's the high elevation rain over thousands of acres of bare rock and thin soils that fills the river. This flood event wasn't from a 'monster' rainstorm, just a pretty big storm up high. Lower elevation side streams barely rose, compared to what the river did.

Because of the poor winter and the late-season rains, our springtime runoff peaked a month ahead of normal. The Merced and the waterfalls are already declining in volume, especially with the cloudy conditions we've been having. The clouds are delaying our minimal runoff a bit, which will help waterfalls last and forests to stay watered a bit further into the summer.

The park is still busy felling hazard trees, the small portion of our dead trees that might fall on people/roads/infrastructure. This year's below-average precipitation and above-average warmth will continue to stress Sierra forests (over-thick with trees due to decades of fire suppression) and we'll see more of the weak trees succumb to native bark beetles. Despite changes in Washington, D.C., the NPS in Yosemite is sticking with science and is not dodging the reality of climate change in its training of new rangers. The climate IS changing, it's changing NOW, in ways more rapid than ever, it is because of OUR hydrocarbon use, and it'll have serious consequences for US. It's disappointing that some political leaders think they know more than NASA or the National Academies of Science. Among other things, our fire season is longer, more severe and is costing us all more money to deal with. I'll be heading up to Lyell and Maclure Glaciers with Yosemite Conservancy groups in August and I expect to see those small ice bodies closer to leaving Yosemite entirely glacier-less.

Luckily, because we are causing the current rapid changes in climate, we should have some influence over it. Let's work to reduce our mistake and bring back snowy winters.

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.

High Water 2017

I am quite impressed with NPS preparations for anticipated flooding in the next couple of days; this is much different from the surprises of 1997's flood. Forecasting has been honed and there's institutional memory of the last big one.

As of last evening, all visitors have been evacuated from the Valley. Staff housing in the Half Dome Village area has been evacuated and all other locals are being told to stay put as of tonight. Peak flow is expected late in the day on Sunday. Projections are for about 17,000 cfs at Pohono Bridge, where the Merced exits the Valley. Average river flow for this time of year is about 100 cfs, and because of this week's rain the river is carrying 572 cfs right now. Again, that projection is for the river to increase to 30 times the current flow by tomorrow evening. We had a flood warning in mid-December but the river didn't quite reach 5000 cfs; it needs to get to about 7000 cfs before the water comes up on to a road in the Valley. The river would first gently back up on to pavement at Wosky Pond on Northside Drive.

If we do get to 17,000, this'd make it the 6th biggest recorded volume for the Pohono gauging station. The bigger events were the floods of 1937, 1950, 1955, 1964 and 1997. Five 'big' floods in a century averages to every other decade or so. What some locals parochially call 'The Flood' of twenty years ago was only a little bit bigger than those other four were, and such floods affect far more than just Yosemite. There was no gauging station in 1862, when the Merced surely exceeded its 1997 size in a mega-flood that wrecked the whole state.

All these high water events happen December-February and are due to warm storms, which bring rain to high elevation instead of snow. There's a persistent myth that the 1997 flood was due to rain melting recent snows, but the science says that rain doesn't melt very much snow. The floods happen simply by high snowline causing tens of thousands more acres of watershed to receive rain. Especially in higher terrain with thinner soils and vast expanses of bare granite, that rain just runs off right away and swells the rivers downstream.

I share Muir's enthusiasm for such events; he witnessed and wrote about the flood of December 1871. While I shelter in place, I look forward to seeing the video record collected by the professionals.

June Skiing

Tioga Road has opened, but summer has not really arrived in the park's high country yet. Tuolumne Meadows is a lake, Tenaya Lake is mostly iced over (with renewed freezing and new ice last night), snow covers a good portion of the terrain above 6000' (north-facing slopes are mostly snow) and meltwater is filling every trail. Skiers still have time to enjoy the slopes near Ellery Lake, False White, Mt. Conness, Mt. Hoffmann, Mt. Dana and more. Backpackers are going to struggle for a while to find trails, to make distance over snow, to avoid wet feet in all the runoff. No facilities are yet open along the Tioga corridor, including TPR, Saddlebag Lake road, White Wolf or anything in Tuolumne Meadows.
Half Dome cables go up this week for those with permits. Walked the west valley loop on Saturday; flowers are looking good: iris in El Cap and Bridalveil Meadows, yellow violets, white Nemophila, Arnica, Senecio, Alumroot, thimbleberry, Linanthus, larkspur near the base of Bridalveil Fall, creek dogwood, Azalea (smells SO good), globe gilia, blue dicks, golden brodeia, silverleaf lotus, Indian paintbrush, pussypaws, catchfly, and more. We saw no snowplants on the loop. One sow bear with two cubs near El Cap's Nose. Slackliners working their art over the icy Merced at El Cap Bridge. Ribbon Creek is running very high in several channels. Birdsong is still plenty active: grosbeak, tanager, Wilsons and yellow warbler, Cassins and warbling vireo, creeper, song sparrow, spotted towhee, etc.
Hotter days are coming this week and the river may hit another peak above flood stage. It is unusual to have such a late peak, such a high peak, and for the river to hover close to the flood level for two weeks like this. What next in this atypical spring/summer transition?

High Water is Here

The river gauge at Pohono Bridge is just about tapping the formal 'flood' stage this morning, at 6300 cfs, or a hair under the 10' mark. This is a little lower than the forecasted overnight peak. Tonight's projection is to go over 11' or perhaps 9000 cfs. If it gets that high, the river will be up on parts of Valley roads, not to mention flowing into two campgrounds and Housekeeping Camp. Rangers have been preparing for days for this surge of meltwater, to evacuate people ahead of nighttime peaks as needed and to implement area closures for safety.
There have been lots of cyclists enjoying the delight of pedalling on the Tioga Road without cars for the past couple of weeks; no noise but birds, running water and the whisper of gumwalls. There is still snow at Crane Flat, and lots of deep snow higher up. The avalanche zone at Olmsted Point has been a lingering concern, so that part of the road is closed to cyclists and pedestrians. Road/trail crew personnel have been working on that spot and with this week's heat and clear skies, there is a fair bit of buzz about the road opening this weekend. Nothing is official and the high country route may not be safe enough to open until next week.
From Olmsted Point we can see that Tenaya Lake is still frozen over. Today's San Francisco Chronicle has an item about the park's Tenaya Lake Area Plan, in which the Conservancy is involved for funding.
Tenaya's ice is melting quickly, and washing down-canyon to fill Yosemite Valley with its own transient lakes.

Yosemite Flood Watch

NWS has issued a Flood Watch for our part of the Sierra starting Friday evening. We are getting warmer weather this week and the Merced River has started rising again, reaching 4000 cubic feet per second (cfs) at Pohono Bridge (the west/downstream end of Yosemite Valley) last night. The average annual high water flow for the Pohono gauge is just 2500 cfs.
As has been said elsewhere, on top of our tremendous snowpack, it's been an unusually cool and wet spring. The normal warming (and therefore snowmelt) trajectory has not happened; there is still a huge quantity of snow in our higher elevations. We have just a little less snow now than what we usually have in April; the combination of June heat and April snowpack suggests powerful possibilities. The rate of Merced runoff may get interesting in the next few days.
We had two spikes of just under 5000 cfs in early May. Then we had another cool stretch and on the typical annual highest water date of May 20, the river was running only about 1800 cfs, 72% of average volume.
NBC Nightly News aired a feature last week about Yosemite's big waterfalls during a period when they were running right about average for springtime. The exceptional flows may have already happened, or may be coming within this next week. Though we're now 3 weeks past the usual highest flow date, we may not yet have seen our biggest water volume for the season. In 2010 we topped out at near 8000 cfs; if it stays warm (like June usually does; our forecast continues warming for the next 5 days) we may surpass that and see the Merced back up through Wosky Pond on to Northside Drive.

The burst of spring

I encountered my first Western Tanager of the year on Monday's Conservancy bird walk - just moments after a participant asked about them. It was a stunning, bright male in the black oaks in front of the visitor center - lots of exclamations from all present. Since then, more males have arrived and are singing in Yosemite Valley. This morning we had the triple feature of the bright neo-tropicals when within a short time we also saw the male Black-headed Grosbeak and Bullock's Oriole. Surprises on Monday were the Lark Sparrow feeding on the gravel trail along Cook's Meadow and the Western Kingbird sallying out from the black oak canopy over the meadow. This morning we had a decent look at Vaux's Swifts.
Those black oaks are pale green with dangling flowers now and a few leaves are starting to emerge. The early dogwood below the former diversion dam site, along 140 has 'blooms' almost 3 inches across which are almost fully white. Most Valley dogwoods are still pale green - they're more than a week behind an average spring schedule.
The Merced River has leapt in volume with the warm weather this week; it's doubled in volume in the past five days. This morning it had already exceeded the average springtime peak - and there are still a few weeks of potential increase to the average high flow date. Low-lying Valley trails are starting to get wet, but there's no real flooding yet. (Last year peak flow reached 2.5 times what it is now!)

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.

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.