May 12 2015 BACKPACKER ALERT: El Nino Seasonal Update & MJO Information

Alex Wierbinski's picture

By Alex Wierbinski - Posted on 12 May 2015


Tahoe to Whitney
Seasonal Update

Weather Trend Change

Recent developments in the central Pacific are of vital importance to the legions of backpackers planning early season High Sierra backpacking trips.

Another cell of warm water has developed in the West-Central Pacific this year, almost exactly like last year’s failed El Nino.

On Thursday, March 5 the Climate Prediction Center declared an

El Nino Advisory


Quoting the CPC
“There is an approximately 70% chance that El Nino will continue through Northern Hemisphere summer 2015, and a greater than 60% chance it will last through autumn.
By the end of March 2015, weak El Nino conditions were reflected by above-average sea surface temperatures (SST) across the equatorial Pacific and by the expected tropical atmospheric response.”

The result of this hot water persisting, moving West, and forming a fully-fledged El Nino could be tropical flows bringing prodigious precipitation to the Pacific Northwest this Spring.

We are not at that point yet. But it has moved into the realm of possibility.

During this time of year it would not be atypical for storms out of the Northwest to deliver massive amounts of snow.
Though long term warming trends and severe drought conditions have reduced the risk of severe late Spring storms out of the Northwest, they are a possibility that must always be accounted for in our planning and preparation.

Spring snowfall is still very possible due to the current early date in the season, and the continued possibility of low temperatures at high altitudes, regardless of the source of the moisture..

Three feet of snow can fall overnight if a tropical flow develops and delivers a load of precipitation under the proper cold-temp conditions.

Normal early season weather threats are now significantly deepened by the formation of an El Nino.

It is still early enough in the season that a significant flow of El Nino inspired tropical moisture could fill the Sierra with a load of snow.
Powder conditions would hinder trail location and locomotion for a day or two. Current melt rates are at least an inch a day, so compression and melting will be rapid.

The temperatures are on average too high and increasing too quickly to hold snow for long.

On the other hand, a too warm tropical flow could bring heavy rains across the Sierra Crest to scour the remaining snow off the Sierra Crest.

If El Nino conditions do continue to evolve and produce heavy precipitation at this late date it is more likely to produce rain than snow.
The specific conditions will determine the outcome of any weather event, and our crystal ball looks like it might be filling up with tropical clouds right now. Or maybe not…

Time will tell, and we are observing.

Independent of what does happen, the chances of encountering heavy weather this Spring have just significantly increased with the evolution of a mass of hot water in the Central Pacific triggering the release of this El Nino Advisory.

This warning must be factored into trip planning, gear selection, and our monitoring of the evolution of weather conditions preceding our trip must move up to the next level.

Keep your eyes open!

We must watch the evolution of the specific conditions contributing to the development of this El Nino carefully, even anticipating an alteration in our current dry pattern towards potentially increased precipitation, even if this blob of Hot Water dissipates as did last year’s.

Independent of what happens next, more heat has already been injected into the system than anticipated by forecasters and indicated by current patterns and trends. This heat is going to affect the trajectory of Spring weather transitioning into the Summer pattern.
The question now is, “Will it get hotter, or go away?”

There will be more precipitation now, even if the El Nino does go away, and possibly a whole lot more precip if this El Nino establishes itself, or persists before dissipating.

  MAY 14 As of this instant we are experiencing a typically unsettled transition from Spring to Summer, but atypical as this transition is occurring without the series of warm and mixed weakening cold storms that are typical of this time of year.

We are undergoing an unsettled transition from Spring to Summer within a set of unusual drought conditions.

We are currently getting no indications of El Nino or tropically sourced weather across California or the High Sierra at this time.

But this situation could change rapidly. The water temperature signals from the Central Pacific indicate a 70% chance of and El Nino developing this Spring, and less that it persists through Summer.

IRI ENSO Forecast

None of these trends point to a known, assured outcome. The weather system has changed, and is behaving in very unusual ways.
The development of an El Nino during Spring is weird in itself, and this warming pattern has displayed numerous “anomalies” in its development and distribution.

It is apparent that new weather global and regional patterns and behaviors are emerging. These new patterns have made predicting the trajectory of weather difficult everywhere.

The ability to track sea surface and sub-surface water temperatures, to observe and track persistent anomalous tropical storms, divergent winds, and the rhythmic patterns of short-lived anomalies in the tropical atmosphere has not just given meteorologists the ability to sharpen their El Nino-La Nina, Pacific Oscillation, and Decadal Pacific Oscillation observations, but they can now articulate the most subtle factors affecting the development, evolution, and final expression of the weather patterns headed our way.

The HIgh Sierra Backpacking Weather page is adding the data presented by the 
El Nino – Southern Oscillation Team so we can watch the heating and cooling of the
The knowledge that heat is building or dissipating in the Central Pacific can set the framework for our accurately anticipating our potential best and worse case scenarios for a given set of weather predictions.

El Nino – Southern Oscillation

Studying this information gives us insight to better understand the underlying trends influencing weather.

Below the great swings in temperature across the Pacific Ocean of El Nino and the Southern Oscillation there are a host of contributing factors and related patterns feeding or dependent on the ENSO.

These subtle contributing factors determine the fate of a weather system’s evolution, if hurricanes form up or fail, and if storms follow typical tracks or get deflected.

We are falling through the looking glass of Meteorology now:

Climate Prediction Center
Monitoring Intraseasonal Oscillations

Read their fascinating expert account of the art and subtleties of the operation of our delightfully complex weather system:

Tropical Interseasonal  Oscillation Concepts and Relationships  

Background Information

How an El Nino works

What the El Nino Advisory Means

Slate Article
El Niño Has Arrived, and It Could Produce the Warmest Year on Record

Best Article
Incredibly strong El Niño still developing, bringing surge of winter warmth,
 Many large US cities recorded record-warm temperatures this fall
December 2nd, Ars Technica.

 El Ni​ño will last through summer, says US climate center,
Guardian, May 14, 2015.

My hats off to the National Weather Service and the National Oceanic and Atmospheric Administration. Those folks do amazing work. That’s US Citizen’s money very well spent.

Happy Trails,


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