November 29, 2012

Heavy Rain and Massive Snow

It was a warm, cloudy day here in the Northwest with large contrasts of rain (see figure below of the observed 24-h precipitation ending 7 PM Thursday): over 3 inches in the Olympics, but only light rain over the lowlands, and a few sprinkles across the basin of eastern WA.   Why so little over the Cascades but lots over the southern slopes of the Olympics?  The key reason is that the flow aloft was southerly (from the south) and you can't get good upslope on the Cascades from the direction.  But you can get good upslope over the south-facing slopes of the Olympics.

But the real precipitation story is to our south, over southern Oregon and northern CA, where some locations got over four inches (pink color) and over two inches was commonplace.  But this is just the beginning.

 With a large low center center over the NE Pacific and persistent strong flow pushing eastward to our south, northern CA is going to get hammered during the next several days.
Flooding is inevitable.

Take a look at the latest UW WRF model precipitation forecast for the next 72 h:  huge amounts, including over 10 inches in "favored" upslope locations.  The Olympics and north Cascades are also wet.

 From weather satellites that measure atmospheric moisture, we can see the narrow plume of water atmospheric river..that has been feeding the California rainfall.

 Tonight I will premiere a new figure created by UW WRF modeler Dave Ovens:  72hr snowfall!  Lots (feet) of snow over the mountains of BC, and the higher elevations in the Cascades do very well indeed (foot or more).  Most of the accumulation at pass and ski area elevation will occur later in the weekend as the freezing level drops and the wind direction becomes more westerly.   The Sierra Nevada range goes to white (literally)--more than 45 inches of snow at higher elevations!  The folks at Tahoe must be salivating. 

Here is a close up of the 72h snowfall ending on Monday at 4PM for Washington.  Baker and Rainier will be buried.  Stevens, at least a foot.   Snoqualmie will pick up a half-foot or so.  Not sure whether it will be enough to allow them to open.


  1. I had to come point this out. I know you deal with a lot of rain shadow in Washington, especially around the Olympias and the Puget Sound so I thought you might appreciate another example of rain shadow.

    The 24 hour rain totals for Medford, OR was >2 inches, while Klamath Falls on the other side of the mountain from Medford had .19.

    Looking at the Mesonet it the totals went from amounts in the 2-3 inches west of the cascades to amounts less than 3/4 of an inch on the east side. Thought it was worth bringing to your attention.

  2. The upper-air cyclone covering the entire NE Pacific is of some note, yes?

    I've been observing weather in the Northwest since 1963, and I cannot recall ever having seen one of this broad areal coverage.

    Perhaps, Professor, you could discuss the levels of energy in such systems, and whether, in your opinion, those systemic energy levels have changed with the advent of a warming globe.

  3. Can someone point me to the map in the first image of this post? The one with tags indicating local rainfall pinned to a google map. Thanks

  4. Eric,

    Its the NWS Mesnonet

    Its a great tool, but can be hard to find if you don't know you're way around the NWS website. The easiest way I know is to choose any WFO's webpage and click on Observations in the left-hand sidebar.

    The above URL is from Weather Forecast Office in Portland, OR. But once in the mesonet you can scroll and zoom and lick at any region you want.

  5. Rivrdog: What warming globe? It appears that the Pacific coast weather is the outlier.

    The there is this news article about the nature of the relationship between extreme weather and climate change:

    I hope Dr Mass will comment upon these matters.

  6. As a mountain person who happens to love the weather, the new snow map is amazing. However why cut off just the WA detail? As a new resident of Portland, I want to know about Mt Hood!

  7. Cliff,

    What are your thoughts on the possibility of "mega floods" caused by atmospheric rivers as proposed in the recent SciAm article? The article is focused on California, but it seems to indicate that this is a possibility for any west coast state including Washington.


  8. Eric, if you like to bookmark the Seattle Area it's

  9. Paddy,
    that article repeats the standard obfuscation of equating local weather with global climate. Consider the global temperature pattern for the past year compared to the long-term average (also known as the temperature anomaly):

    The past year has been one of the top 10 warmest on record (just go to the NASA GISS web page)


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

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