Mid Winter High Sierra Weather Transition Report of 2018

Alex Wierbinski's picture

By Alex Wierbinski - Posted on 14 January 2018


WINTER of 2018


Mid Winter Weather Transition Report


Let me explain how I look at Winter. The Sun just reached its most Southern Point, and is now moving Northward in the Sky, heating the Southern Hemisphere for the second time on its annual trip down to mid-Winter and back.

The Northern Hemisphere slowly cools as the Sun reaches its most Southern point. It's at or around mid-Winter this cooling deepens sufficiently to reveal the depth and character of each particular Northern Hemisphere Winter season. We observe this as the transition from the instability of the Fall-to-Winter storms to mid-Winter conditions at this time.

We've just watched that transition as the shift to mid-Winter conditions has knocked-out the persistant High that's been routing storms around the Sierra. Temps have also taken their next step down, and a Winter pattern begun to establish itself across the North Pacific and Arctic. The chilling will continue for the next month as the interactions of the momentum of cold deepening in the North and rising warmth in the South characterize this whole planet's North Hemispehere Winter season, not just the Winter of 2018 in the High Sierra.

We're just sitting under one small, dysfunctional weather component of this vast, destabilized, wounded planet.

Now the reheating of the Sun moving to the North is drawing a huge circular wave of heated air, water, and moisture North towards the already overheated Equator, which will begin pumping huge amounts of superheated tropical mositure Northward into the deepening Southbound ring of (not-so) cold air, water, and moisture wrapping around the Northern Hemisphere as the Sun drives North until Spring dawns up here. Or will it?

Watch Sea Surface Temps Shift with Season

How will the powerful La Nina affect the process?  On the other side of this flipping coin, the Arctic was warm this Fall coming into Winter. What configurations and relationships will the regional components of warm Arctic temps and cool La Nina waters take this year? These are crucial to storm creation and propagation, for exactly how our NE Pacific weather come together this Winter.

The temps and ice cover in the Arctic and the sea surface temps off the coast of Peru are both key players in determining each season's High Sierra Weather. Both are behaving abberently, one much warmer, the other much cooler.

The specifics of exactly how these bipolar forces interact, how they influence the chilled Northern Hemisphere absorbing, actually transporting and transforming the vast amounts of Southern Hemisphere tropical energy, moisture, into the Northern Hemisphere's regional storm seasons. This specifics of this annual process controls the unfolding character of the Winter of 2018 and ultimately will control its unique transition into just how and when the blooming life of the Northern Hemisphere "Springs" back to life. We're right in the middle of tracking those factors right now... to recap:

This season started with a heat wave through the end of a fiery Summer, had a near-record wet November followed by a near-record dry December driven by our old friend, the Persistant High. Last week we watched what I described above as, "the Winter Transition," break that Persistant High to finally re-establish a flow of Highs & Lows from West to East across the West Coast of the USA, rather than around it.

What's next? At this point the Persistent High has been pushed South, and its "chain of Highs" coming across the Southern North Pacific have dropped-down a bit further to the South, closer to the Equator. That looks to lower the likelyhood of a persistant High forming off the West Coast of California & Oregon, if not the whole N American Continent, as we've seen all December.

Latest Winter of 2018 Report


2018 Arctic temps compared to Average
Arctic Temps

October 2017 Report

December 2017


Latest News

National Snow and Ice Data Center News



La Nina: Looks powerful and persistent as of Jan 3, 2018



"Mechanics" of a Tropical Transport Mechanism


What this all means to me is that we're looking at good chances for tropical transport mechanisms to set up between stationary and slow moving Lows in Gulf Alaska and the lower position of our NE Pac High.
The Northern "component" of the TTM, a Low pressure zone in Gulf Alaska, would be allowed to sit there by the passivity of the warmer Arctic. The "Southern" component of the tropical transport mechanism being a lower-positioned, more Southerly position of the persistent High off the West Coast of California. How this Low-High configuration is situated determines if it would move tropical moisture to the Sierra, or around it.

We saw torrential TTMs routed around the Sierra by a Northern position of the High component all through 2015. Nonetheless, a Tropical Transport Mechanism can set up its Low-High configuration between each of the Low-Highs in any of the, "chains of Highs," coming across the Southern North Pacific, when there is a persistent Low in Gulf Alaska.

So, the warmer Arctic opens up one aspect of the tropical-transport mechanism, a stationary Low setting up in Gulf Alaska. The lower position of the Highs coming across the Southern North Pac opens up the Southern component of the tropical-transport mechanism configuration.

Yet the intensity of the La Nina rising off the Coast of Peru, and chilling-down the whole Southeastern portion of the North Pacific, tends to stifle tropical transport mechanisms at their source, by suppressing the intense tropical activity along the Equator running West to the NE shore of Indonesia. That's where the moisture for tropical transport mechanisms that hit the Sierra typically originate. La Nina can pee on that parade at its source, potentially creating clearer & colder skies in the Sierra Nevada by suppressing storm activity and cloud formation around Indonesia.

The "gun" of the TTM needs the "bullet" of superheated tropical moisture spewing out of the tropics, to get any year's "Pineapple Express" rolling.

The table is set for cooler and drier than "normal" conditions this Winter, with the chance of tropical downpours, of tropical transport mechanisms, forming occassionally.

That's how I see conditions, how I see the Northern Hemisphere's, "table being set," at the Mid-Winter Transition of 2018.

Unless the persistent High moves North, back into its blocking position. If so, the Sierra and the whole Southwest will go dry & cool. Not as cold as a typical La Nina, as everything nowadays is much warmer, but cool & dry nonetheless.


El Nino-La Nina Information & Measurements


Latest Winter of 2018 Report



Tracking Current Conditions

High Sierra Backpacker Calendar, January 2018

December 2017



High Sierra Snow Status

High Sierra Weather



WINTER of 2018


FALL 2017
Progress & Character




January 2018 News of Trail, Terran & Weather




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