April 07, 2018

A Record-Breaking Atmospheric River Hits California and Strong Marine Cyclone Offshore of Washington

A lot to talk about.   It is pouring outside as I write this....really coming down

The forecasts of an extreme atmospheric river hitting California proved highly accurate.   To start, here is a water vapor satellite image (the satellite sensor observes a wavelength for which water vapor is a very good absorber and emitter) for 5 AM this morning.

You can see the very long plume of moisture stretching from Hawaii to the central WA coast.   A very large cyclone (the swirl) is directly west of Washington State (more on that later!)

The moisture content of this atmospheric river is extraordinarily unusual, unprecedented in many ways.  To prove this to you, here is the climatology of precipitable water (PW) at Oakland, California and the value of PW  observed this morning from the twice-daily radiosonde weather balloon ascent.  Precipitable water is the sum of the water vapor in a vertical column of air.

The value (1.69 inches) blows away the daily record (the thin red line).  It is higher than any day from late September through early July.  This is huge. 

The highest value observed at this location during the wet season of the year.

And note that this is the time of the year when atmospheric moisture at Oakland is generally lowest.

With such large values of moisture heading into California, rainfall totals have been large.  As shown below (click to enlarge), a number of locations over the western sides of the coastal mountains and the Sierra Nevada have received 4-6 inches of rain over the past 48 hours--several more than 6 inches.  They would have gotten much, much more if the incoming winds had been stronger.

Some rivers in the region are already at flood stage (red circles in plot below) and CA reservoir operators are releasing substantial amounts of water to ensure to safety of their dams, especially the heavily damaged Oroville Dam.

And the rain is not over for California. ANOTHER system is expected next week, with substantial rains from northern CA into the Northwest (see 72h total ending 5 AM next Saturday).

Here in the Northwest, heavy rain is falling over Washington State as a frontal band associated with a very strong Pacific cyclone moves through (see infrared satellite image at 7 AM this--Saturday--morning).   Beautiful, large storm with the clouds swirling into the low center.

The 3-h forecast for this time suggests we are dealing with a 972 hPa low center, with an intense pressure gradient (change of pressure with distance) around the storm.  That means strong winds.

 In fact, the forecast wind gusts  for 11 AM predict 60-65 kt gusts reaching the Oregon and Washington coasts.

The maximum gusts for the 24-h ending 7 AM show strong winds already, with some favored locations in the coastal mountains getting to 70 mph, with 40-50 mph gusts at some places along the coast (click to expand map).

The low is going to slowly drift our way as it fills (decreases in strength) as shown by the forecast map at 5 AM tomorrow morning.

By 2 PM today, winds will be really cranking along the Washington coast and over NW Washington (e.g., San Juans), as shown by the forecast winds at that time.  50 kt gusts will be common in those areas.  That means some power outages.

Winds over Puget Sound should increase today as the low approaches, perhaps to 30-40 mph, later today and Sunday morning.  Not enough for major impacts.  And showers will continue until mid-day Sunday for most folks on the western sides of the Cascades.


  1. Cliff: am I misunderstanding the predictions, or Are we expecting a series of relatively deep low-pressure systems rolling out of the gulf of Alaska over the next ten days to two weeks?

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  3. Here in Bellingham, it all seems to have kind of fizzled. Very little precipitation and not much wind. Wind at the airport, which tends to be higher due to its exposure, was only 43 mph around noon, which is not unusual at all. It's about 7:30 pm and the wind advisory continues until midnight, but I would be very surprised if it picked up as it has been declining since noon.

  4. Probably should have used the Blended Total Precipitable Water loop at:http://www.ospo.noaa.gov/Products/bTPW/TPW_Animation.html?fromDate=20180404&fromHour=0&endDate=20180407&endHour=6&product=EAST_PACIFIC_TPW&interval=3hours GOES water vapor channel is fine for identifying moisture centered at 700-300 hPa, while microwave showing total pecipitable water moisture on loop would give better representation of the low level moisture.

  5. Live from Whiskey Ceek Beach, WA.... 15 miles of Port Angles.
    Dead calm all day Saturday with steady rain.
    Rarely is the Strait this calm.... 2 foot waves working their way in from the ocean.
    We must be full in the lee of the Olympics...
    Skier Jay

  6. It's interesting to watch the widespread effects of these rivers. I often look at the webcams on the top of Mauna Kea on the Big Island, and it seems like these rivers often coincide with snow on Mauna Kea - happened today: http://www.cfht.hawaii.edu/en/gallery/webcams.php

  7. Showers early Saturday morning in north Whatcom County, and dry throughout the rest of the day. Some wind, but nothing noteworthy. No weather event in this region.

  8. Just another overhyped storm here in Portland. Maximum wind not much more than 35 mph and not a deluge of rain (only about an inch and a quarter.)). Can’t tell you how many times these things have not lived up to the dire forecasts. Why not just say there is potential for a major storm rather than getting all breathless about it?

  9. Looking at flights to and from SeaTac yesterday morning (Satuday), I saw that the 7 a.m. flight to San Luis Obispo landed instead at the Fresno airport and the return flight from San Luis Obispo was cancelled. I then checked and flights by other airlines to San Luis Obispo ran two to three hours late in the morning.

  10. Following this fizzle non-event here in Bellingham, I see the NWS is taking to posting a nearly worthless "Special Statement" non-forecast. I think comments like the following have little value:

    "April can be wet and blustery. If you`re planning on outdoor activities, be prepared with rain gear. Mariners can expect frequent changes in the wind as springtime can be blustery at times in Western Washington."


    It appears to me like they really have very little idea of what is going to occur.

  11. Odd thing is, here in Medford (SW OR), we've got almost nothing out of the whole storm.

  12. Can someone please explain what happened to the Record-Breaking Storm of All-Time? Thanks.

  13. Unknown,

    The Wind Advisory for Western Whatcom County called for gusts up to 45 mph so the figure from the airport was just about spot on. In fact, "they" clearly had a very good idea of what was, and did, occur. "They" have the most difficulty pinpointing precisely when and where weather impacts will occur but "they" most certainly have a pretty good idea what will occur most of the time and when "they" don't "they" make it clear that "they" don't because, assuming "they" is the NWS, they're a public service organization and it's in their mandate to do so.

  14. The highest wind at the Bellingham Airport was a single gust of 43 mph, but overall this was very tame and really not much of an event an all. A single gust barely over 40 mph with moderate sustained wind and everything else well below 40 mph is not much at all, particularly for this exposed location. This certainly was not any kind of record breaking event, either for wind or precip. This turned out not to be something to get worked up about. I think many of the comments here reflect that Cliff was well off the mark, regardless of what the NWS said.

  15. I see again this morning inconsistencies in the NWS forecast for Whatcom County. The forecast page states:

    "Breezy, with a light south southeast wind becoming south 21 to 26 mph in the morning. Winds could gust as high as 38 mph."

    However, on the same page there is a link to a wind advisory for the area that states:

    "WIND...South to southeast 20 to 35 mph with gusts 45 to 50 mph."

    I see these inconsistencies and conflicts all the time from the NWS. It is like no one is really reading what they are posting. These are major differences in the forecast. I will say that since moving to Bellingham from Seattle, I have gotten used to gusts in the mid-50's at the airport, so I don't get as concerned as I used. But, I think the NWS could do a much better job in terms of what it posts.

  16. NWS forecasts may seem inscrutable at times to the layperson. Perhaps you should stick with the weather channel...

  17. Not sure what the wise crack about the weather channel is supposed to mean. I can read and what I read is not very predictive. By the way, today's wind advisory ending at 3 pm did not materialize at all. Almost no wind by noon. One gust of 36 mph at 11 am at the airport. So, the wind advisory was a flop and another big miss by the NWS.

  18. It's really not accurate to call Oroville dam heavily damaged at this point (and even last year I'd quibble about degree of damage to the spillway versus the dam as whole). The roller compacted concrete exposed on large portions of the spillway for the repairs is not suited for long term erosion resistance, but the main concern at this point seems to be minimizing the additional repairs necessary next summer to the RCC before it is finished up with a smooth, hard layer of structural concrete.

    Between that and the huge amount of storage capacity they're preserving in the reservoir specifically for big storms like this, there's not much reason to worry about Oroville this year.

    So far, the reservoir doesn't seem to have come within 30 feet of their planned elevation for using the spillway, and that level is itself a long ways below the full reservoir capacity.

  19. Looking like a third time in a row for a bust on a wind advisory for Bellingham. The advisory expires today at 3pm. So far, a single gust of 35 mph at around 11am with sustained winds mostly in the teens and low 20's. Advisory stated:

    "WIND...Southerly winds will increase to 20 to 35 mph with gusts
    as high as 50 mph this afternoon."

    All the usual warnings about trees limbs and power outages. Again, all of this seems way off the mark. Maybe things will increase before 3pm, but the numbers show everything decreasing at this point.


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