January 26, 2016

Major Atmospheric River Period for the West Coast

The weather action is about to move from the eastern U.S. to the western U.S. as strong atmospheric rivers pummel the West Coast with heavy precipitation, with the potential for a major cyclone to strike California later on the weekend.

One of the best ways to see plumes of moisture associated with atmospheric rivers is to view the integrated water vapor forecasts:  predictions of the total water vapor in a column.  Atmospheric rivers are generally warm and juicy....lots of water in the column.  And when these rivers hit the western U.S. terrain, heavy rain or snow (at high elevations) can occur.

The water vapor image for Wednesday evening shows an atmospheric river reaching the Northwest.

A day later  (4PM Thursday) it aims for northern California.

Friday at 10 AM, it is still directed into central/northern CA.

This atmospheric river is going to have important implications for California, some good (filling reservoirs big time) and some not so good (potential for flooding).

Now let's look at the forecast precipitation from the UW WRF model (12km grid spacing).  For the next 72h, the NW gets the brunt of the atmospheric river, with 5-10 inches in the Olympics, Vancouver Is., and north Cascades.  Northern CA starts to feel the impacts.

Expect some flooding on rivers flowing out of the North Cascades.

During the next 72h the atmospheric river aims directly at CA and the Sierra gets the hardest hit of the past few years, with the model going for 5-10 inches of precipitation on that range.

How much snow in the mountains you ask?  For the first 72h, not much snow over the Northwest because the atmospheric river will be quite warm.  Sorry. BC does better being farther north.

But snow lovers should not be too concerned.  During the next 72h, as the atmospheric river and its associated warmth slide southward, cooler temperatures and substantial snow extend over the Washington Cascades.    Importantly, the Sierra, being of higher elevation, gets feet of snow.   

The total precipitation from the NOAA/NWS GFS model from now through Tuesday at 10 AM PST?  Very wet, with 5-10 inches over the Sierra, Cascades, and coastal mountains.

In short, a water bonanza for the western U.S., topping off Pacific Northwest reservoirs and snowpack and proving a huge influx of water for California. Expect to see major reservoirs, like Shasta, at 80%  of normal within a week.

And then there is the potential for a major windstorm.  The European Center model brings one into the Northwest in a few days, while the U.S. GFS has a big storm predicted for California on Sunday (see below).  Too much uncertainty at this point, so stay tuned.  This might not happen.


  1. My rain gauge has collected 5.82 inches for January. The coming AR will push it over normal January rainfall. This will be the third consecutive month of above normal rainfall. A little different from past strong El Nino's.

    For those of us who served in the Southeast Asian war (Vietnam, Cambodia, Laos and Thailand), a round of record cold air hit the jungles and paddies. A few excerpts from Bob Henson's blog:
    "Northern Thailand’s largest city, Chiang Mai, located at latitude 18.8°N and an elevation of 1020 feet. The average high and low for January 26 in Chiang Mai are 87°F and 60°F. “It is the daytime cold temperatures here that are probably unprecedented, not the daily low temps,” he told me. “We went from a monthly record high of 36°C [96.8°F] on Saturday to 90°F at noon on Sunday to 55°F with rain at noon on Monday, an amazing drop in 24 hours for this neck of the woods. Today [Tuesday] it was 52°F and drizzling at noon. Our high for the day was 54°F, the coldest daily max in memory for the area. It seems virtually certain that snow must have been falling in the mountains of northern Thailand above the 1500-1800 m level [around 5000-6000 feet].” Herrera noted: “On Tuesday the max temperature was higher at Tafjord, Norway, than in Chiang Mai, Thailand…in January!”

    The mountains of Laos have never officially reported snow cover. Brief flurries were reported in Laos on Tuesday down to elevations below 1000 meters (3300 feet), according to Herrera. Both Thailand and Laos might have received accumulating snow at high elevation on Tuesday--although if the snowfall were brief and limited to sparsely populated areas, it might have gone undocumented even if it did occur. Temperatures across Southeast Asia should be rising dramatically over the next couple of days, as the air mass aloft is already warming."

    Thanks Bob.

    Most of these people don't own a sweater, a warm blanket or a space heater. A cold wind will literally blow right through most homes. Your body is accustomed to 90F and it drops to the 50s and there is no place to warm-up, brrr. Come March it will be in the 100s, the paddies will almost dry-up, the people scoop up the fish from the nearly dry paddies using hand-made nets. Come May, the monsoon rains re-fill the rice paddies. A cycle that has reliably repeated for several thousand years.

  2. That last graphic is Fraser Valley Outflow writ large.

  3. That appears to be a ten foot plus or minus rise at Shasta Reservoir which is currently at 71% historical average of 3e6 acre feet so a 10% rise to 80% normal is 3e5 acre feet and the reservoir has 3e4 acres (at max pool (whatever that is)) so 3e5 / 3e4 = 10 foot rise.


    Hope so and hope the Sierras get what they need.

  4. A pleasant 62 degrees on the central Oregon coast today so the warmth is already here, but without the rain.

  5. .. Five or six days of stronger and steadier movement and spread of colder air mass more southward, with main colder air also at the same time both slowing its main movement and progress more longitudinally east while additionally appearing to be losing strength where considering its more over-all force of movement. .. A general situation where looking at these ideas main colder air related and focused all together, very similar to that having been in place and the case leading up to the main stronger period of precipitation where considering the 1996-7 El Nino if a full month earlier, more from Dec. 26th of 1996 through to Jan. 3rd 1997.

  6. Is this event unexpected in terms of the long term seasonal forecast? I vaguely recall a prediction that the rest of the winter would be rather dry.

  7. Strangely, the NOAA forecast for us here in central CA (monterey bay) is fairly muted over the next week, with some uncertainty expressed due to varying models. But there is no hint of big rains for the upcoming week for the greater SF bay area.

    I'm surely hoping you are the shining beacon on this one Cliff. So far, our precipitation in California this water year is just average.

    Thanks for the great blog- Cliff.

  8. Mark, my wife has family in Bangkok. They said it was very cold (by their standards) recently. We've been there several times, and high temperatures in the 60s in Bangkok are virtual unheard of! Sounds... pleasant to us, though.

  9. The top picture--if my calculations are correct Gene Simmons would be located around 150W.

  10. I live in San Rafael, CA, just 15 mi north of San Francisco, and while we have received 14.3 inches of rain so far in January at our home rain gauge ("average" is 10), little in my opinion has been El Nino influenced. The atmospheric river shown here looks impressive but it seems directed at far Northern CA near the Oregon border. I believe there are other forces at work like an unusually persistent high pressure system that is knocking storms away from most of southern and central CA. We are not seeing any river here. Appreciate any insights as my perspective is El Nino is a bust so far.


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