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BACKPACKER ALERT: February 20, 2017
Alex here, from Tahoe to Whitney.
Sorry about the delay contacting you. I have had a series of distracting personal events while Nature has cut loose. Nonetheless, I have been tracking the wild weather across the Backpacker News Pages on the Forum and the Backpacker's Calendar on the Trail Guide. I hope you've checked them out and found them useful and informative.
Recent Backpacker News
First, we've been tracking the Oroville Dam Crisis, which you can review through the News link above. But, we've also been tracking the evolution of this crazy tropical Winter that triggered this crisis, which brings the first "catch up" item: Backpacker Alerts.
We first observed rain across the Sierra Crest on Jan 6, turning this into a BAD SNOW BACKPACKER ALERT on Jan 20. The snow pack is shattered with bad layering caused by rain between snow storms. We've documented these events in Jan entries of the 2017 Backpacker's Calendar:
Layers of bad snow weaken this year's snow pack from bottom to top. This will present dangerous avalanche conditions until the snow pack melts. Beware!
We had a BACKPACKER ALERT for cold conditions on Jan 24 and 25 as temps went down to -15 at Charlotte Lake. Below zero temps were recorded up and down the Sierra Crest.
CURRENT BACKPACKER ALERT
Today we face a series of Short, Medium, and Long threats associated with the long series of tropical flows out of the Southwest that have composed this most remarkable Winter of 2016-17.
This year's crazy season is reaching a pivotal point, a moment of decision! The ground is saturated. The rivers and creeks are running high to flood stages. The reservoirs are all full, while the Sierra holds record snow. We face imminent flooding dangers across the state. All of this is happening under a record-level snow pack.
A warm and wet tropical Spring will bring widespread disaster and destruction to California during the Spring Thaw, if we even get to that point without experiencing widespread Winter flooding.
Check out this current RADAR, as it illustrates our situation:
Watch Oroville get pounded via US NWS RADAR:
(2-20-17, 15:05 PST)
This RADAR is instructive, particularly because its, "line of flow," the direction of frontal winds out of the Southwest it represents have been dominating our weather pattern since November.
These tropical rains speak to, and are products of low pressure zones in the Gulf Alaska, persistent Lows sitting or forming up, then just sitting there, or wandering leisurely East, if not just bumbling around the Gulf Alaska. These persistent & stationary Lows have been setting up these tropical storm tracks out of the Southwest that the NW of the US has experienced this Fall and Winter.
The vast High that has been sitting off the West Coast of California for the past five Winters has dropped South this year. Too far South. This has set up tropical flows between the persistent Low in Gulf Alaska and our now transient Highs that have dropped down to the Latitude of LA, or even lower than that...
Click the graphic linked to below to see the animation tracking Pacific Pressure Zones. Set it for "14 Days," and whichever player you prefer:
Let it run through once quickly, to load up, then stop it to click through day by day to watch the current patterns playing out in a digestible manner.
The pattern of persistent & stationary lows in Gulf Alaska this Fall and Winter has been very interesting, and only yesterday and today are we getting signs that this pattern is weakening, and could be breaking up. I doubt it.
The real factor driving our fate will be the effect when the rising trajectory of the Sun begins moving tropical ocean heat North. That belt of tropical heat moving North will be like loading a bullet into a rifle, if this year's pattern of persistent lows in Gulf Alaska continues drawing tropical moisture into the Northwestern US. We will see epic flooding.
Click the graphic to see a cool animation of how much heat is in the Pacific Ocean, and how it is moving:
Right now Pacific Heat is still dropping to the South, but at a pace grinding to a halt. It will soon turnaround!
Let's see (referring to our calendar), Last year the Northward movement of Pacific Ocean tropical waters began happening on FEB 29:
Check out this year's calendar:
(Check Jan of this year and Dec of last to see this season's amazing precip.)
These tropical flows bringing us tropical moisture out of Hawaiian Latitudes all Winter long have been relatively weak so far. VERY Persistent, but generally weak.
The storm track directing tropical flows out of the Southwest in our direction will really start moving some water once the rising Sun of Spring starts moving warm tropical ocean waters North, where these tropical flows can suck their tropical moisture up, and move it to us. That's due to start becoming possible in the next ten days or so.
Get ready to rumble!?
Well, get ready for more record-level rain, snow, and flooding if this pattern of Low Pressure Zones in Gulf Alaska holds up, which looks likely through Spring by my observations and interpretations, even with its recent weakening. We'll see!
Great for snow campers. Not so good for PCT Hikers who want to hit the trail and cross the Sierra as early as possible. The line of the JMT-PCT could well be obscured by snow all Summer long.
1> Not an early start year for PCT-JMT hikers.
2> Potentially dangerous fording and trail conditions early in Summer.
3> Moist conditions all Summer long feeding mosquitoes all Summer long.
At this point who knows when the Spring Thaw will come, but I can tell you it will be huge and likely very destructive in many locations, if not all. Timing and intensity of the Spring Thaw depends on how this mass of snow heats up through Spring, and if these torrential tropical flows turn into heavy Spring rains across the Sierra Crest.
I am betting on a warm and wet Spring, as that's been the increasingly powerful emerging trend/pattern over the last 20+ years...
We are currently and in the medium-term looking at the potential for catastrophic dam failure and Wintertime flooding. In the longer term, we are facing a series of serious dam failures and floods during Spring if water managers cannot empty their reservoirs before this massive snow pack turns into a raging Spring Thaw.
I put the chances of a long, slow and mellow Spring Thaw at ZERO.
There may not be anything anyone can do if torrential Spring rains scour a massive snow pack while the ground is already saturated, the rivers already running into already full reservoirs. Everything will break or be overwhelmed.
These magnitudes of flows have happened before, and will happen again. I am not saying this will or will not happen, only that all the cards making widespread, disastrous flooding possible are still on the table.
I generally sign-off my letters to hikes with "Happy Trails," but in this case I say,
"Keep Your Eyes on the Skies!"
And the lakes, rivers, and especially our snow-covered mountains,
Winter Backpacker Alert