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New Measure of Strength and Impacts of Atmospheric River Storms

New Measure of Strength and Impacts of Atmospheric River Storms

Alex Wierbinski's picture

By Alex Wierbinski - Posted on 26 February 2019


 "Atmospheric River" Smacking California
Atmospheric river hits California, more precisely, a Tropical Transport Mechanism. Credit to Jesse Allen, NASA Earth Observatory/ VIIRS satellite
Fantastic Shot by Jesse Allen, NASA Earth Observatory/ VIIRS satellite.


Tropical Transport Mechanism Quantification

CW3E Research Notice

CW3E Releases New Scale to Characterize Strength and Impacts of Atmospheric Rivers,
CW3E, February 5, 2019.


New scale to characterize strength and impacts of atmospheric river storms,
University of California - San Diego, February 5, 2019.



All CW3E AR Forecast Tools

All NOA-ESRL AR Forecast Tools



Precip & AR Toos on the Weather Page

Selected AR Measurements

Current Total Precipable Water

All Precip Forecasts & Models



Words Matter
First, a few words about words.

Tropical Transport Mechanism
Since the name of this Tropical Transport Mechanism always seems to be changing, from the, “Pineapple Express,” of my childhood, to the era of, "Tropospheric Rivers," and now today, finally, to, “atmospheric river,” I long ago decided to maintain my most basic descriptive term for this weather phenomenon of, “Tropical Transport Mechanisms,” calling them the, Tropical Transport Mechanisms, that they are.

I would rather call a natural phenomenon words that describe what they are, and what they are doing, rather than what they are, “like.”

To me, the conditions that create the reality of the vast transportation of tropical moisture that we experience are a, “Tropical Transport Mechanism,” and have absolutely nothing to do with rivers.

“They are prevalent over the Pacific Ocean and can deliver to the Western United States much of its precipitation during just a few individual winter storms.

The New TTM Scale
Five Levels
“...assigns five categories to atmospheric rivers...using as criteria the amount of water vapor they carry and their duration in a given location.”

"weak," "moderate," "strong," "extreme," and "exceptional."

Created By
Director of Center For Western Weather and Water Extremes (CW3E), of the Scripps Institution of Oceanography.

“...lasts in an area for less than 24 hours, it is demoted by one category, but if it lingers for more than 48 hours, it is promoted.”

Highest Impact TTMs
Duration Important
“...is based on research showing that a combination of strong water vapor transport with long duration over a location, is what causes the greatest impacts.”

The Scale
The first three levels are described as being decreasingly, “beneficial,” as duration and intensity increases.

AR Cat 1 (Weak) “...24 hours at the coast, and produced modest rainfall. ”


AR Cat 2 (Moderate) “...lasted 42 hours at the coast, and produced several inches of rain”


AR Cat 3 (Strong) “...36 hours at the coast, produced 5-10 inches of rain...”


AR Cat 4 (Extreme) “...36 hours produced up to 14 inches of rain in the Sierra Nevada...”

AR Cat 5 (Exceptional) “...lasted over 100 hours at the Central California coast.”


Extreme Events Necessary
“...come to understand how these events frequently make the difference between flood and drought years in key coastal regions around the world such as California.”

"The scale recognizes that weak ARs are often mostly beneficial because they can enhance water supply and snow pack, while stronger ARs can become mostly hazardous...“

Leaders and Averages
One Per Year
“Previous analysis has shown that on the West Coast, the Oregon coast receives the most atmospheric rivers in the "extreme" range (AR Cat 4), averaging about one per year. ”

(Note 45 TTMs during 2017, and that 2019 has already seen a series of TTMs.)

Forecasting Power
”...the atmospheric river scale is intended as a tool to increase situational awareness ahead of a major storm in a way that reflects conditions broadly in a region of roughly 50 km size.”



A few Hints about

Formation and Tracking
Powerful storms North of the Equator, NE of Indonesia, are typically where vast  cells and huge streams of superheated tropical moisture, that make up TTMs, are lofted high into the atmosphere. From this location the spin of our planet puts them on a trajectory towards the West Coast of the USA.

Tropical storms and mositure rising from positions further to the East of the NE coast of Indonesia, North of the Equator, typically move NE towards Northern Mexico.

Tropical Storms off the NE coast of Indonesia are set up to travel towards the West Coast of the US, while storms further to the West typically climb North up the East Coast of Asia.

The hot seas off the NE corner of Indonesia are the, "sweet spot," for beginning vast flows of tropical moisture across the N Pacific to California and the High Sierra.

We use this tool to track the tropical super-storms that loft such vast volumes of super-heated and saturated airs, paying special attention to the seas off the NE coast of Indonesia.

 Global IR Temps


The ability of the ocean and atmosphere to work together like this, to loft fantastic amounts of super-heated moisture high into the troposphere, is very dependent on hot water.
Specifically, the sea surface temperatures off the Northeast coast of Indonesia. The temperature status of that region is heavily influenced by the cycle of El Ninos and La Ninas. We track ocean heat, and its anomolies, here:

How Hot’s That Water?


Weird Hot Water

A New, Seasonal,  "Northern" El Nino?

A Regular Event in Our Future?

New Norhern El Nino, AKA, "The Blob?"


History of The Blob

2018 NOAA WEST COAST FISHERIES REPORT, & History of the Blob

What Happened? Retrospective View of The Blob


Future of The Blob

October 2018: The Blob is Back?



The Big One

Hints of Things to Come

2015 Huge El Nino: Shifted Global Temps into New Gear


Favorable TTM Conditions
Once we get hot sea surface temperatures driving the formation of massive tropical storms, watch out! After that, we just need a favorable disposition of the NE Pac High, to bring it flowing across California and the Sierra. Or, on the other hand, a properly-situated persistant High can deflect the most powerful Tropical Transport Mechanisms around California & The Sierra.

Freak Weather Express
Biggest Drought During Biggest El Nino
We had the biggest El Nino in recorded history during the driest Winter in Sierra/California history, with both happening simultanously in 2015. A huge, persistant , blocking High Pressure zone anchored off the West Coast of the USA conducted the vast majority of that season's El Nino-driven super-powerful Tropical Transport Mechanisms around California and the Sierra.

Climate Change News: The Big Blocking Ridge an Existential Threat



What Are Tropical Transport Mechanisms?

What is the Pineapple Express?


Tropical Transport Mechanisms

Center For Western Weather and Water Extremes (CW3E)


All NOAA ESRL AR Forecast Tools


Tracking Extreme West Coast Weather: The Weather Page




The Weather Page
Precipitation Forecasting

The Weather Page
Tracking El Nino-La Nina, Hot Tropical Waters


All the Pieces…
"Mechanics" of a Tropical Transport Mechanism




WEATHER NEWS, Recent Record Rainfall, April 7-8 Tropical Transport Mechanisms

 45 TTMs During 2017 !!

"Last year’s wet season (from October 2016 to March 2017) had 45 atmospheric rivers, one-third of which were ranked as “strong” or “extreme” by the Center for Western Weather and Water Extremes at Scripps Institution..."



April 7 High Sierra Calendar: Inches Fell in one Day





Jan 2018

Mid Winter High Sierra Weather Transition Report of 2018



March 2018

Risks and Rewards: Tropical Transport Mechanism Targets So California





March 2018
TTMs of Climate Death
Tropical Transport Mechanisms Operating Directly from Tropics to Arctic,
Signaling the End of our Ancient Global Weather Patterns.








Trail News Forum

Feb 2019 Trails, Weather, Terrain News





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new, measurement, scale, tropical transport mechanism, atmospheric river, vapor, duration, weather, information, links, storms, tropospheric rivers, Pineapple Express


Originally Published
2019-02-06 15:30:52

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