February 11, 2014

Atmospheric Rivers Strike the Pacific Northwest

 Announcement:  The Northwest Weather Workshop will be on Feb 28th/March 1st in Seattle.

The NW Weather Workshop is the big annual gathering of those interested in the weather of the Pacific Northwest and everyone is welcome.  For more information, including the agenda and registration information, please check out: https://www.atmos.washington.edu/pnww/

During normal winters, the Pacific Northwest experiences several  atmospheric river events in which plumes of moisture surge into our area from the southwest.   This winter there has been a general absence of such features due to the persistent ridging over the eastern Pacific.

But things have changed, and this week we will have a persistent southwesterly flow that will produce heavy precipitation amounts from northern CA through British Columbia (see the upper level map below for 8 AM Wed morning-- a broad swath of southwest flow  is heading into the NW.   Winds are parallel to the lines).

 Our water supply is about to be greatly enhanced and the threat of a drought will recede.

It is pouring outside my house right now and the radar at 9:30 PM Tuesday shows both heavy rain and an amazingly distinct rain shadow to the NE of the Olympics.  It is hard to get over the fact there is no rain at all in that rain hole, but pouring a few dozen miles away.

Back to the atmospheric river.  Here is the predicted total amount of moisture in the vertical for 10 PM Tuesday night..  You see the plume of high moisture values (white and reds)?.  That is the atmospheric river.

Now it is time to impress you.  Here arethe 72 h precipitation totals encompassing the next 6 days. For the first three days (through Friday at 4 PM), many of the crests of NW mountain ranges will receive 5-10 inches of precipitation (in rain or snow, the value is the amount of liquid water in the precipitation).  Near the Oregon/CA border it is over 10 inches.

The next 72 hr is also very wet with a bit more emphasis over Washington and SW BC.  Add these totals together and plenty of mountain locations will get 15-20 inches.

 As of Wed morning, a number of NW rivers are at bankful and several are at flood stage including the Skokomish River of the SE Olympic Peninsula and a few over SW Oregon (see graphic from NW River Forecast Center)

 The precipitation near the CA/OR border is particularly welcome...this will help fill some of the big reservoirs in northern CA that are so critical for agriculture in the Central Valley.

And we had some strong winds (gusting to 30-60 mph)  Wednesday morning as a low center passed across southern BC (see map)
Here are some of the max gusts during the 24 h ending 7 AM on Wed.  Very windy in the Strait and along the coast, with several locations gusting above 50 mph.

The latest seasonal (Feb-March-April) outlook from the Climate Prediction Center is for normal precipitation over Oregon and Washington, but drier than normal over California.   We will see..


  1. Seems like this morning's windstorm took its time getting here. Peak gusts in the Duvall area seemed to hit after the advisories for SW WA and the NW interior had ended. Lost power around 4:45 am. Still off at 11:30 am.

  2. Thanks for yet another interesting and fact-filled post. Always a pleasure to learn what's up *up there*!

  3. Here in Eatonville we had a gust of 55 just before midnight, and another of 54 around 12:30 a.m. Crazy night! Looking forward to the next one! Love it!

  4. Yeah it's just pouring today! ;)

    No complaints about a surprise sun day at all.

  5. Cliff,
    Do you guys access mPing data at all? Meteorological Phenomena Identification Near the Ground (mPING)

    Friends back east are recommending it as a way to help forecasters with on-the-ground information about this snowstorm. We do that here in your blog for snow events (and others too) but it doesn't go anywhere beyond that, most of the time.

    Seems like this could be another useful tool in the hobbyist-assist area, along with Pressure.net which I've already got. :-)

  6. Is this what would be considered to be a "Pineapple Express?"


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

A Drier Than Normal Spring over the Pacific Northwest

I had to water some new plants today because the last few weeks have been relatively dry.   So I was curious.....how dry has it been in our ...