Why It’s Not Raining

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Sam Sweet
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Why It’s Not Raining

Post by Sam Sweet »

Just about everybody is sick of the lack of useful rainfall along the lower Pacific Coast this year (and last), and the projections are not very promising. Normally you make it rain by scheduling an outdoor event like a wedding or picnic, or by washing a car. I have heard that none of these things is working this year, so I thought maybe a post explaining why it isn’t raining would kickstart some storm activity. It’s worth a try, at least.

In recent years we have come to understand that atmospheric pressure and winds, and sea temperature and currents, are components of a global heat engine that is little affected by land and sea boundaries. Oceans and continents have their own unique effects, but there are many causal linkages tying together events between oceans, or across the equator.

Along the eastern edge of the Pacific Ocean the El Nino Southern Oscillation (ENSO) is a major player, alternating between El Nino and La Nina states on a cycle of about 5 (range of 2—7) years. Under El Nino conditions warm surface water spreads east along the equator from the coast of South America, with atmospheric circulation in the northern hemisphere bringing relatively warm, moisture-laden airflow to the west coast of the U.S. When this merges with cold fronts coming out of the north Pacific, abrupt uplift condenses large amounts of rain out of the southwestern flow. Under a La Nina regime cooler tropical surface waters in the eastern Pacific reduce the amount of subtropical air reaching the western U.S., and rainfall is accordingly less because northwest storms warm as they sweep south and display less condensation.

It is less well known that ENSO is subject to being overridden by a longer-period pattern termed the Pacific Decadal Oscillation (PDO). Recognized only in the mid 1990s, the PDO can enhance an El Nino event, but more often cancels its effects north of the equator. The cycle switches between high and low values roughly every 30 years (range of 20-50+ years), so it is in place for a very long time. It is the PDO that is driving present conditions along the west coast of the U.S.

The PDO consists of coordinated fluctuations between the Aleutian Low pressure system located in the Gulf of Alaska, and the North Pacific High pressure system located north or northeast of Hawaii. The PDO is a measure of sea surface temperature deviation from normal values off the coast of southeastern Alaska and adjoining British Columbia. It has been in a negative phase (low nearshore winter temperatures) almost continuously since 2000.

Image

ENSO and PDO have linked causes, but have different lag times and may also be separately affected by events outside of the Pacific (for example, North Atlantic cycles affect PDO but not ENSO). When you compare them as in the figure here the longer duration of the PDO cycle wins in counteracting El Nino events between 1950 and 1979, then becomes an enhancing factor from 1980-2000. Since then (as per figure above, but note the discrepancy in the number of positive monthly values) El Ninos have been dampened by a consistently negative PDO.

Image

What these two PDO states look like graphically (albeit crudely) is shown on the next two figures, first for a negative PDO. Here the Aleutian Low is small and shifted westward out of the Gulf of Alaska. This changes the amount of water entering the Alaska and California currents (not shown), and keeps nearshore surface waters cool.

Image

The North Pacific High is large and persistent, and acts to deflect storms from the northwest track and the moist air of the Subtropical jest stream. The northwest storms that do come down the coast are small and travelling quickly, being typically nothing more than a frontal band that produces an hour or so of rain followed immediately by a cold front and dry winds that evaporate much of the water before it gets into the ground.
Because these are cold storms warming as they come south rainfall tends to stop before dark as the dewpoint falls, and they do not exhibit much rainfall enhancement from passing over mountains. Small amounts of cold rain in daytime followed by freezing nights lead to significantly reduced aquatic breeding activity by salamanders and frogs.

A positive-phase PDO is in effect when the Aleutian Low is strong and centered in the Gulf of Alaska, leading to warmer nearshore waters and a stronger California current, with the North Pacific High reduced in size and shifted back toward Hawaii.

Image

This removes the blocking effect and allows a larger percentage of northwest track storms to follow the coast rather than being pushed inland. These storms tend to move more slowly, with rain falling over a day or two. The big change comes when a northwest storm runs into a heavy Subtropical jet stream moisture plume. This yields what is termed a “Pineapple Express” (not the movie) where warm, moisture-laden air is pushed upwards by the collision and by uplift in the coastal mountains, creating very high rainfall rates. Since the jet stream keeps feeding and the storm system keeps spinning in place, rain may continue for several days. Coastal mountains can get 20-30 inches of rain in 1-2 days, with rainfall rates above 16 inches/hour (Triple Divide Peak above Carpinteria, 2005). Pond-breeding amphibians obviously do well in such years, though the effects on streams can delay high reproductive success to following years.

It is very difficult, though not impossible, to get Pineapple Express storms during a PDO negative interval. The past 4 days (23-26 January 2014) are a case in point, where a very strong and wet Subtropical jet reached as far as Vancouver after lingering over southern California, yet there was no northwest storm to lift the clouds and cause condensation.


Where this goes from here is the $64 question. The PDO values are consistently negative, and we may be in for a 20+ year dry cycle onwards from 2014. Tree ring data have been used to examine rainfall patterns in the southwestern US back into the Middle Ages, and extended droughts are evident.

Image

The more recent pattern is for a dominantly wet phase since about 1500, so it may not be time to hang up your net just yet.
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PNWHerper
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Re: Why It’s Not Raining

Post by PNWHerper »

Awesome, Sam! Thank you for the great info and info graphics.

I especially like the very last one that shows patterns over the course of several hundred years. Wow, MEGA-droughts! :shock:
Richard F. Hoyer
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Re: Why It’s Not Raining

Post by Richard F. Hoyer »

SW:
Timely article as it started raining here in the western Oregon near the time you posted. pretty darn effective but simply displaced 800 - 1000 miles north.

Richard F. Hoyer
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sjfriend
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Re: Why It’s Not Raining

Post by sjfriend »

And here I thought it was congress all this time :? I guess this clears it all up. Now that we know what/why maybe Jerry can fix it. I sure wish some one would for both our sakes. Your bone dry and we're melting up here. No snow all year :cry: I've lived in CA during a long drought and it sucks!
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klawnskale
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Re: Why It’s Not Raining

Post by klawnskale »

Boo! Another dry, flowerless Spring in the western Mojave Desert. I will be witnessing the true tenacity and resourcefulness of desert torts on the DTRNA who chose to emerge. I fear we may lose some individuals with this third year of consecutive drought. I read that there were a number of notable tortoise deaths last year in the eastern Mojave. It was surmised it was due to drought. I actually saw mention of tree ring data on the local news to explain the drought cycles.
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monklet
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Re: Why It’s Not Raining

Post by monklet »

Thanks Sam for the highly informative post.
USA Today wrote:This image obtained from the National Oceanic and Atmospheric Administration shows snow and water equivalents in the Sierra Nevada mountain range in California abnormally low for January 2014 compared to the same time in 2013.(Photo: NASA/NOAA, AFP/Getty Images)
Image

From: http://www.usatoday.com/story/weather/2 ... y/4581761/

Uh oh, no good can come of this :( ...but then, water shortage may be the single most inhibitive factor against development. Stay thirsty my friends :)

Edit: Of course less development means less jobs:( ...such a pickle we've gotten ourselves into. :crazyeyes:
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Kelly Mc
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Re: Why It’s Not Raining

Post by Kelly Mc »

klawnskale wrote:Boo! Another dry, flowerless Spring in the western Mojave Desert. I will be witnessing the true tenacity and resourcefulness of desert torts on the DTRNA who chose to emerge. I fear we may lose some individuals with this third year of consecutive drought. I read that there were a number of notable tortoise deaths last year in the eastern Mojave. It was surmised it was due to drought. I actually saw mention of tree ring data on the local news to explain the drought cycles.

I hope your Spring goes well, nonetheless Klawnskale.

Tree Ring Data... Why is that profoundly beautiful? I can think of no other way truth could be better told than tree ring data.
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Bryan Hamilton
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Re: Why It’s Not Raining

Post by Bryan Hamilton »

Awesome post! Is this related to cold, wet winters in the east?
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sjfriend
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Re: Why It’s Not Raining

Post by sjfriend »

Bryan Hamilton wrote:Awesome post! Is this related to cold, wet winters in the east?
Short answer is 'mostly'.

With the high pressure over California it leads to storms going up north then diving south east of the hi. Its also causing us here in central Alaska to have warm winter as all the Hawaii moisture heads our way. We have no snow at all here.
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Sam Sweet
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Re: Why It’s Not Raining

Post by Sam Sweet »

"Mostly" is an excellent answer. A core fact about the weather is that you can describe exactly what happened, with thousands and thousands of data points on temperature, wind speed, humidity, air pressure, cloud heights, thermal, wind, and water vapor vertical profiles, radar and satellite images of great clarity and resolution, etc. Then you could take all that information and feed it back in at just the right places, and get a pretty different weather pattern out the back end. The local weatherman is not (only) a clown, it is truly almost impossible to predict weather in any detail.

Winter weather is especially sensitive to temperature differences, and especially anything that would raise cloud heights or increase rotational speed. There are usually two jet streams over North America, a polar jet that (when it behaves itself) enters the U.S. mostly in New England, and a subtropical jet that mostly stays over Mexico and the Gulf, but tends to turn northward east of the Rockies. The polar jet can bulge S, or the subtropical jet can swing N more or less anywhere across the U.S., frequently transporting an extensive band of warm, moist air. If this encounters a cold storm front traveling with the polar jet the storm's counterclockwise rotation digs into the moisture plume like a table saw, pushing clouds upward where they cool and condense.

Depending on where this happens we get Pineapple Express flooding on the west coast, blizzards on the high plains, tornado swarms in the Mississippi basin, or northeasters along the Atlantic coast. The ability of water to hold and release heat is remarkable, and it gives us almost all of our weather dramas.

Image

Depending on where this happens we get Pineapple Express flooding on the west coast, blizzards on the high plains, tornado swarms in the Mississippi basin, or northeasters along the Atlantic coast. The ability of water to hold and release heat is remarkable, and it gives us almost all of our weather dramas.
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Ameron
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Re: Why It’s Not Raining

Post by Ameron »

Great information & presentation, thanks very much. This sounds very logical, based on emprical evidence.

But wait! What if, as in so many other situations, things are not as they appear to be? What if there are silent Players behind the scenes manipulating events, unknown to Observers?

Two words: HAARP technology

Enlightened readers may also choose to reference these links & information. There may be more to this story than what meets the eye. There usually is, as most of us have learned…

Links
Cost of Chem Trails Program
http://www.infowars.com/cost-of-chemtra ... on-a-year/

Google search: Welsbach Refractory Seeding Agents, weather wars


YouTube video: What In The World Are They Spraying?

“What the military cannot control, it will destroy.”
Anonomous, high-ranking Air Force offical overheard by me years ago while I was enlisted in TX

1.0 Boa constrictor imperator (Hog Island)
1.0 Pantherophis guttatus (Miami)
1.0 Agrionemys horsfieldii kazakhstanica
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monklet
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Re: Why It’s Not Raining

Post by monklet »

Image
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Owen
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Re: Why It’s Not Raining

Post by Owen »

monklet wrote:Image
Baa Ram Ewe :lol:
hellihooks
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Re: Why It’s Not Raining

Post by hellihooks »

not bhaaaaaahd... :lol: :lol: :lol:
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chrish
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Re: Why It’s Not Raining

Post by chrish »

Ameron wrote: Enlightened readers may also choose to reference these links & information. There may be more to this story than what meets the eye. There usually is, as most of us have learned…

Links
Cost of Chem Trails Program
http://www.infowars.com/cost-of-chemtra ... on-a-year/

Google search: Welsbach Refractory Seeding Agents, weather wars


YouTube video: What In The World Are They Spraying?

“What the military cannot control, it will destroy.”
Anonomous, high-ranking Air Force offical overheard by me years ago while I was enlisted in TX
And here's a link you might find helpful. ;)
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todd battey
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Re: Why It’s Not Raining

Post by todd battey »

Another mind-expanding post from Dr. Sweet. Thanks, Sam! Great use of your graphics to explain the driving forces to our weather machine.

Why is it that in a positive PDO, with the shifting of the NP High and Aleutian Low (effects in the atmosphere), that the WATER temperature off the coast of CA gets WARMER? If positive PDO conditions lead to a stronger CA Current, wouldn't that bring more cold water down the CA coast?

Todd
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Sam Sweet
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Re: Why It’s Not Raining

Post by Sam Sweet »

The explanation that I've seen is that the predominant surface winds shift between NW and SW off the coast of British Columbia. Winds from the SW bring warmer surface water closer to shore (positive phase), while NW winds encourage upwelling of colder subsurface water. This is relative, it's still too frickin' cold.

The PDO was discovered by looking for physical reasons driving salmon cycles in the Pacific northwest -- upwelling brings nutrients, and generally beefs up the productivity of the affected patch of ocean. There is a good discussion at http://www.nwfsc.noaa.gov/research/divi ... ca-pdo.cfm.
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Jeff Lemm
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Re: Why It’s Not Raining

Post by Jeff Lemm »

It just rained so it must all be wrong - there's no global climate change, lol. Thanks Sam, always dig learning something new.
hellihooks
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Re: Why It’s Not Raining

Post by hellihooks »

What most folks don't realize is when the N Atlantic loses enough salinity, due to the influx of fresh water from melting Ice Caps... it will likely trigger the next 10,000 year Ice Age... :o jim
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Fieldnotes
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Re: Why It’s Not Raining

Post by Fieldnotes »

Obama tells Americans global warming is true. Knowing the fact that all things out of that man’s mouth are lies, makes the truth obvious. Only decades ago, they were blaming problems on global cooling.
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Sam Sweet
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Re: Why It’s Not Raining

Post by Sam Sweet »

Don't make me embarrassed to post here.
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crocdoc
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Re: Why It’s Not Raining

Post by crocdoc »

Too late.
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gbin
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Re: Why It’s Not Raining

Post by gbin »

Awesome thread, Sam. I learned quite a bit, and I appreciate it! :thumb:

Gerry
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chrish
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Re: Why It’s Not Raining

Post by chrish »

Fieldnotes wrote:Obama tells Americans global warming is true.
...as do almost 100% of the meteorologists, physicists, planetary geologists, and any other scientists with any credibility who have seen the data. Seems the president is in good company here.

It is a pity this sort of politics is infiltrating an otherwise very interesting and valuable thread, and an even bigger pity that I felt obliged to respond to it. :oops:
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Mark Brown
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Re: Why It’s Not Raining

Post by Mark Brown »

Thank you, Chris. There's a time and place for everything, and in my opinion, FHF is never the time and place for political discussions.

And just for the record, climate change did not originate with the current administration.

From 2007:

"By setting this goal, we acknowledge there is a problem, and by setting this goal, we commit ourselves to doing something about it," Bush said. "We share a common responsibility: to reduce greenhouse gas emissions while keeping our economies growing."
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Kelly Mc
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Re: Why It’s Not Raining

Post by Kelly Mc »

Still thinking the ability to analyze tree rings would be one of the greatest knowledges beyond the transience of human affairs.
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Nature Nate
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Re: Why It’s Not Raining

Post by Nature Nate »

Best news I've heard all day! A new algorithm that hasn't failed yet in it's predictions says we have a 75% chance of an el nino next season for the west coast:

http://www.utsandiego.com/news/2014/feb ... nce-of-el/

http://www.pnas.org/content/111/6/2064. ... 9ef831a672
hellihooks
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Re: Why It’s Not Raining

Post by hellihooks »

COOL!!! Till then, I've just about decided to take water with me, out in the field.. to give every herp I find a nice long drink... :crazyeyes: I went out yesterday and it was like herping in May, rather than Feb... :roll: jim
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Re: Why It’s Not Raining

Post by mwentz »

hellihooks wrote:COOL!!! Till then, I've just about decided to take water with me, out in the field.. to give every herp I find a nice long drink... :crazyeyes: I went out yesterday and it was like herping in May, rather than Feb... :roll: jim
Saint Helihooks - the patron saint of thirsty herps?

In my mind, I can see you gently cradling a fence lizards head, while it slowly drinks from your canteen.
hellihooks
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Re: Why It’s Not Raining

Post by hellihooks »

I'm thinking squirt gun... :crazyeyes: :lol: :lol: worked ok with my kids, when they were small... put their highchairs in a corner and fed them with a slingshot... :crazyeyes: :lol: :lol: :lol:
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