Warm Atmospheric River Aims Parade of Storms at U.S. West During La Nina Year of 2017

A river of moisture arises from the Pacific Ocean and links up with a procession of enormous storms that bring heavy surf, flooding rains, and mountain snows to the U.S. West. It’s a weather narrative that one usually associates with a strong El Nino during winter time. But the powerful El Nino ended last year and it failed to bring the expected rains. Meanwhile, in early 2017, during a La Nina year in which typical trends would tend to point to drier conditions for the U.S. West, a procession of severe storms is now slamming into California.

El Nino Pattern During a La Nina Year

So what the heck happened? What could possibly cause such a crazy weather flip-flop in which record drought conditions extend through a time of El Nino but severe and extreme rains come with the onset of La Nina?

The answer appears to be that a record warm ocean combined with a strongly positive Pacific Decadal Oscillation to produce a powerful river of moisture aimed directly at California. And when the associated storms arrived it was with an extreme intensity — setting off numerous flash flood events.

atmospheric-river-pacific

(Water vapor models show an atmospheric river running out of the Western Pacific — crossing that vast ocean before engorging storms slamming into the U.S. West Coast on January 17 of 2017. This is a severe weather feature more typical of an El Nino year that is now occurring during a period of weak La Nina conditions. The difference being that rivers of moisture running into California typically issue over Hawaii. The present ‘Pineapple Express’ is coming all the way from the Philippines. Image source: Earth Nullschool.)

An almost continuous spate of heavy downpours since the first week of January has now unloaded enough moisture to fully slake severe drought conditions over Northern California and to considerably reduce the drought in the south. Overall, precipitation totals for the past 30 days have been as much as 2.5 times above the normal amount for California.

Another Batch of Heavy Rain on the Way

This week, NOAA expects another batch of powerful storms to come blasting out of the Pacific. Sections of Southern California are predicted to get hit with around 9-13 inches of rain over the next seven days while the north receives another 10 to 15 inches. These are notably severe rainfall totals for California. And NOAA model predictions have tended to range higher over the past 24 hours.

 

noaa-extremely-heavy-precipitation

(NOAA 7-day precipitation forecast indicates a severe rainfall event for the U.S. West Coast with heaviest amounts hitting parts of Northern California. Image source: NOAA.)

According to Accuweather, the heavy rains are expected to spur flash flooding, increase the risk of mudslides and to possibly push some rivers over their banks. However, since many rivers are still at low levels following persistent drought during the last five years, over-topping is less of a risk than it otherwise would have been.

Storms tend to bring cooler weather to this region and the Western U.S. has cooled somewhat during 2017 compared to past years. However, the conditions in which these storms are firing are warmer than they have been in the past. As a result, mountain snowfall has occurred higher up on the slopes. Consistent with the warmer than normal storms, Accuweather predicts this week’s storm system will not produce big snowfall totals for the Cascades as snow levels are driven above 7,000 feet by the warmer than usual temperatures.

Very Warm, Moist Pacific; Positive Pacific Decadal Oscillation

There’s been very little weather and climate discussion as to why heavy rains are falling in California during a year when the odds stacked against such an event would tend to be higher due to La Nina. The elephant in the room at this time is a major excursion of global surface temperatures in the range of 1.2 C above normal during 2016. A notably severe climate change related insult to the Earth system. Such extreme atmospheric warmth will tend to hold more water vapor aloft in suspension. As a result, when the rains do fall, they will tend to be heavier and come more in the form of downpours and deluges than as moderate or lighter precipitation.

sea-surface-temperature-anomalies-pacific

(This sea surface temperature anomaly map shows that despite La Nina, the Pacific Ocean, on balance, is much warmer than normal. These warmer than normal sea surfaces are pumping out a considerable amount of moisture — which is helping to feed the powerful storm systems running into the U.S. West Coast. Image source: Earth Nullschool.)

To this point, despite a La Nina blanketing the Pacific’s central Equatorial region in cooler than normal waters, most of the Northern Pacific is considerably warmer than normal. And all this extra warmth is helping to pump a lot of water vapor into the atmosphere above the ocean zone. A feature that is not typically consistent with La Nina, but one that is consistent with a considerably positive Pacific Decadal Oscillation acting in conjunction with overall global warming. Positive Pacific Decadal Oscillation (PDO) values are associated with above normal sea surface temperatures in the Eastern and South-Central Pacific. Positive PDO tends to produce longer and strong El Nino events. And it is also associated with strong storm tracks running from west to east along the 40 N latitude line.

Storm Track Runs All the Way to U.S. West Coast

To this  point, it’s worth noting that PDO has been in a positive range for the past three years running. But it wasn’t until recently that a persistently strong storm track stretching all the way to the U.S. West Coast has developed. During past years, strong storms veered north into Alaska and Canada, deflected by powerful ridges over the U.S. West.

crazy-wavy-jet-stream-u-s-canada

(The crazy, wavy jet stream with a strong storm track hitting California and a ridge riding up into Central Canada is rather changed from the Ridiculously Resilient Ridge blocking pattern that helped to spark severe droughts along the U.S. West Coast during 2013-2015. Now, severe flooding rains are the rule of the day. Under human-caused climate change, we can expect weather patterns to tend more toward extremes. For the U.S. West Coast extreme drought has been replaced by heavy rains. Image source: Climate Reanalyzer.)

Assisting the process of storms running toward the U.S. West Coast was the removal of a hot blob of water off coastal Washington and Oregon as a zone of somewhat cooler than normal waters formed. These cooler waters extended from just off Northern Japan to south of the Aleutians and on toward the U.S. West Coast. This zone is providing a dipole temperature anomaly between the cooler than normal surface waters in the north and the warmer than normal waters in the south. As a result, the Jet Stream has a nice slot along which to produce a powerful, flat storm track. These two features — a strong temperature dipole between the 40 and 50 degree latitude lines and a very warm Pacific producing copious amounts of moisture south of the 40 degree latitude line — are the key ingredients that appear to be fueling the powerful West Coast storms in a counter-La Nina fashion.

In contrast to the 2013 to 2015 period, high pressure ridging along the U.S. West Coast is not now strong enough to deflect the storms running across the Northern Pacific. In other words, it appears that the influence of the Ridiculously Resilient Ridge and hot Ocean blobs off Washington and Oregon during 2013 to 2015 is has now faded out. However, the new climate and weather trends driving this most recent influx of heavy rainfall to the U.S. West Coast are almost as odd and notable.

Links:

Threat of Flooding For U.S. West Coast

West Coast Storms Cause Dangerous Flooding in California

U.S. Drought Monitor

Climate Reanalyzer

GISS Temperature Data

Climate Reanalyzer

Pacific Decadal Oscillation

Hat tip to Colorado Bob

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Bad Climate Outcomes — Atmospheric Warming to Ramp up as PDO Swings Strongly Positive?

Last year, quietly and without much fanfare from the mainstream press, the Pacific Ocean underwent a powerful shift. A shift from a state in which cooler surface waters absorbed atmospheric heat, to a phase in which surface water warming caused ocean heat to be transferred to the world’s already warming airs.

The shift was heralded by a powerful oceanic Kelvin Wave. One that brought warm water up from the depths and spread them across the Pacific Ocean surface. Ever since that time, warm Kelvin Waves have continued to refresh this surface water heat pool.

monster-el-nino

(Major Kelvin Wave that heralded a switch to strongly positive PDO values for the Pacific. Image source: NOAA/ESRL)

And so the Pacific Ocean surface warming continued throughout 2014.

By December, Pacific Decadal Oscillation (PDO) values, a measure directly tied to this warming, hit a new all-time record level of +2.51. That’s the highest and hottest PDO value since record-keeping began in 1900. One that only backed off slightly into January at +2.45 in the preliminary measure.

It’s a major swing in Pacific Ocean surface temperatures to a phase where more heat is dumped into the atmosphere. One that is causing some scientists to warn that a new period of rapid atmospheric warming may just be getting started.

image

(Sea surface temperature anomaly map shows very warm surface waters dominate much of the equatorial, eastern and northern Pacific in a signature that is strongly characteristic of a powerfully positive PDO on Thursday, February 26 2015. Image source: Earth Nullschool. Data Source: Global Forecast Systems Model.)

PDO and The Multi-Decadal Heat Pump

Pacific Decadal Oscillation (PDO) is a periodic change in sea surface temperature states in the Pacific. One that is thought by many oceanic and atmospheric researchers to have a strong influence on global weather and temperature variability.

In the negative state, PDO tends to encourage La Nina events which also coincide with a downswing in global temperatures as the vast Pacific waters take in more heat. In the positive state, PDO tends to encourage El Nino events which result in the great ocean belching heat into the air on a grand scale — pushing atmospheric temperatures higher.

All things being equal, this natural variability would pan out — marking upswings and downswings in a global average. However, human fossil fuel burning and related greenhouse gas emissions have bent this curve upward by trapping more and more heat in the lower atmosphere. So the case is now that during positive PDO phases, in which more El Ninos occur, atmospheric warming has tended to ramp drastically higher. And, consequently, during negative PDO phases, atmospheric warming has tended to merely slow down even as oceanic warming sped up.

You can see this speeding up and slowing down in the below graphic provided  by Weather Underground:

PDO vs global temperature change Weather Underground

(Global temperature change since 1900 vs phases of positive PDO [1925 to 1945 and 1975 to 1998] and negative PDO [1945 to 1975 and 1998 to 2014]. Image source: Weather Underground. Data Source: NOAA.)

In the era during which global temperatures have been increasingly driven by human greenhouse gas emissions, four phases of PDO have been recorded. Two were positive, two were negative.

In the first positive PDO phase during 1925 through 1945, global average temperatures jumped upward by about 0.5 degrees F (+0.25 F per decade). This initial surge in atmospheric warming abated as global temperatures remained roughly steady during the negative PDO period of 1945 to 1975 (+/- 0 F per decade). But by 1975, PDO values were positive again and the period through 1998 showed a rapid warming of about 0.8 F over 23 years (+0.4 F per decade). After the super El Nino of 1998, PDO values again trended negative as atmospheric warming continued at a somewhat slower pace of about +0.15 F per decade.

Global Warming and Related Ills to Ramp Up?

This underlying trend should be cause for serious concern.

The first issue is that we see warming now during negative PDO decades where we only saw cooling or zero warming before. Given the present rate of warming in the range of +0.15 F per decade during periods in which the Pacific Ocean is taking on atmospheric heat, one could expect the next positive PDO phase to see decadal warming in the range of +0.55 F or higher (or by about 1 C in 20-30 years).

Such a rapid pace of warming could challenge the fabled 2 C ‘point of no return’ before 2050 (for reference, we are at about +0.85 C above 1880s values now). And it is for this reason that some scientists are now starting to sound alarm bells.

In the recent Weather Underground commentary penned by Jeff Masters, Kevin Trenberth, an NCAR scientist and one of the world’s foremost experts on ocean temperature dynamics, noted:

“I am inclined to think the hiatus [in global temperature increases] is over, mainly based on the PDO index change. If one takes the global mean temperature from 1970 on, everything fits a linear trend quite well except 1998.”

NOAA global surface temperature anomalies

(Global surface temperature anomalies. Image source: NOAA.)

Though Trenberth does not explicitly spell out the potential for an overall warming acceleration, he does point toward a return to the +0.29 F per decade trend line seen since 1970. Meanwhile, Matthew England of the University of South Wales warned in the same Weather Underground commentary that any post ‘hiatus’ warming would be likely to be very rapid.

Dr. Michael Mann, a climate scientist of considerable fame both due to his Hockey Stick tree ring study and due to his ongoing success fighting off smear campaigns launched by climate change deniers, recently put together climate model assessments that showed world temperatures exceeding the 2 C threshold by 2036 under business as usual greenhouse gas emissions. To reach such a high reading so soon would require in excess of 1 degree Fahrenheit warming over each of the next two decades. And such a rate of warming would be very rapid indeed, unprecedentedly rapid and well outside the linear trend line from 1970.

Michael Mann today made related comments at Realclimate on the more recent oscillations in Pacific Ocean sea surface temperature:

There is the possibility that internal, natural oscillations in temperature may have masked some surface warming in recent decades, much as an outbreak of Arctic air can mask the seasonal warming of spring during a late season cold snap. One could call it a global warming “speed bump”. In fact, I have… Given the pattern of past historical variation, this trend will likely reverse with internal variability, instead adding to anthropogenic warming in the coming decades. That is perhaps the most worrying implication of our study, for it implies that the “false pause” may simply have been a cause for false complacency, when it comes to averting dangerous climate change.

To these points, it is worth noting that any rate of warming above 0.3 F (0.2 C) per decade is extraordinary and terrifying. Such a rate is enough to achieve post ice age warming of 4 C in merely 2 centuries where it took 10,000 years to achieve such warming before. Warming at 0.4, 0.6 or 1 F per decade would be both drastic and devastating to current climates, geophysical stability, weather stability, glacial stability, water security, food security, and ocean health. In the current world, already warmed by about 0.85 C above 1880s levels any acceleration to current warming is a rather bad outcome on top of an already dangerous situation.

Links:

Are We Entering a New Period of Rapid Global Warming?

Climate Oscillations and the Global Warming Faux Pause

NOAA’s National Climate Data Center

NOAA’s Earth Systems Research Lab

Monster El Nino Emerging From the Depths?

Far Worse Than Being Beaten With a Hockey Stick: Michael Mann Climate Model Shows 2 C Warming by 2036

Global Warming Speed Bump? The Answer May be Blowing in the Wind.

Earth Nullschool

Global Forecast Systems Model

Hat Tip to Colorado Bob

Hat Tip to Bassman

May Likely to Break Global High Temperature Record as El Nino Conditions Strengthen in Pacific

The human warming-riled monster weather event that is El Nino continued to advance over the Equatorial Pacific this week. Ocean surface temperatures throughout the basin from north and east of New Guinea and along a broad stretch of thousands of miles of ocean climbed. Sporadic west winds and an overall weakness in the trades extended the expansion of warm surface waters along the serpentine back of the El Nino pattern from west-to-east even as a high heat content Kelvin Wave kept conditions below surface much warmer than normal.

sstaanim

(Pacific Ocean sea surface temperature anomalies from 2 April to 28 May. Animation source: NOAA)

Large and growing regions of 1 to 2 C warmer than normal surface temperatures expanded in broad, 1,000 + mile stretches near the date line and ranged out from the west coast of South America. An impressive region of, very hot, 2-3 C positive anomalies grew through an ever-larger span from Santa Cruz Island to coastal Ecuador and Peru. Though the above graphic is not granular enough to catch it, daily anomalies in this hot pool exceeded extremely intense +3.5 to +4 C readings.

Readings in the range of +0.5 to +1 C invaded regions north to south, east to west, joining in an extraordinary zone stretching from the Philippines to South America, and from Baja to Hawaii to the Solomon Islands. A separate pool of very hot water north of New Guinea and near the Philippines is likely to play a further role in El Nino development throughout this year should weak trades and anomalous west winds persist. Then, a second and reinforcing pulse of warm water is predicted to push the entire Equatorial Pacific Basin well above a +1 C positive anomaly by late Summer through Fall.

Weekly Anomalies

(Sea surface temperature anomalies in the four key Nino regions all show continued warming through the end of May. Image source: NOAA.)

The tightening grip of El Nino is plainly visible with each of the four key Nino zones showing ongoing temperature increases in what is now a 3-4 month long event. Meanwhile, the key Nino 3.4 zone closed its 4th straight period above the +0.5 C Nino threshold even as it jumped to +0.6 C above average this week. Notably, the Nino 1+2 zone off South America hit a very warm +1.6 C average positive anomaly this week, showing additional warming from strong late April values.

Together, these values all show very solid continued progress toward El Nino.

image

(Map of geographical Niño zones provided by NOAA.)

Conditions in Context: May 2014 Likely Hottest on Record Amidst Ongoing Extreme Weather

Overall, Equatorial Pacific ocean surface temperatures continued their advancement from May 27 to June 2, rising from +0.59 to +0.68 C above the 1979 to 2000 average throughout the week. Global sea surface temperatures have remained in an exceptionally hot and likely global record range between +1 and +1.25 C above 1979 to 2000 averages throughout the month of May and into early June. These extraordinary readings likely combined with very high atmospheric values to put May of 2014 in the range of hottest on record. It is worth noting that, according to NOAA, April of 2014 was also the hottest in the 134 years since global temperature measurements began.

El Nino tends to spike atmospheric heat and, when combined with a brutal human greenhouse gas forcing, greatly increases the likelihood that a given year will reach new global heat extremes.

For 2014, El Nino and global warming related weather disruptions already appear to be taking hold with the Indian Monsoon appearing weak and delayed, a summer heat dome building over Europe and Western Russia, with Southeast China experiencing record floods even as northern and western China and Japan experience record heat. Ongoing droughts and crop disruptions in Brazil, building heat and drought in Indonesia, and Australia experiencing two back to back hottest years on record is also indicative of the screaming global heating that typically comes when El Nino gives human-caused warming an explosive boost.

Links:

NOAA

Indian Monsoon Disrupted

Monsoon Misses Date With India, Onset Delayed

Monster El Nino Emerging From the Depths

 

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