Thursday, January 30, 2020

Heavy Mountain Rain, River Flooding, and Then a Major Cool-down

There will be plenty of action during the next week---more than I can possibly describe in this blog.

We start with a modest atmospheric river--a plume of enhanced low-level moisture--aimed at our area on Friday and early Saturday (see below), bringing substantial rain to the Olympics and north Cascades.

Atmospheric moisture early Friday evening, reds and white indicate high values--the 
atmospheric river

This atmospheric river will result in substantial rain over the next 48h, as shown by the figure below (accumulated precipitation through 4 PM Saturday).  Over 5 inches over the upper windward slopes of the Olympics and north Cascades.   Much less rain in the lowlands, with a dramatic rainshadow centered south of Port Townsend.  This is not a record-breaking rain event, but typical of the stronger ones we have several times a winter.


This rain is falling on saturated ground and flowing into rivers that are already high.  The past 72 hr have been quite wet over the southwest Olympics, mountains of Vancouver Island, and the north Cascades (see below), with many of these regions receiving 3-5 inches.


With wet ground, high river levels, and substantial rain, some flooding is inevitable, particularly since warm air and strong winds will accompany the heavy rain.  Such warmth will melt some of the lower-elevation snow, contributing to rising rivers.

 The latest forecasts of the Portland River Forecast Center predictions project major flooding (purple diamonds) on several rivers draining off the central and northern Cascades, and moderate or nominal flooding on several others (see below).

To further illustrate the flooding potential , here is the predicted river levels for the Snoqualmie River at Carnation.  A very rapid rise on Friday and Saturday to a peak level of roughly 58 ft, roughly ten feet above normal.  Followed by a rapid fall.


On late Saturday, cold air will flood into the region.  Trust me, you will notice it.  Not quite as cold as last time, but cold enough to bring large amounts of snow to the mountains, and a chance of lowland snow in some areas (particularly if a Puget Sound Convergence Zone forms on that day).

I will leave the snow and cold analysis to Saturday, when I can provide a more accurate forecast.  And that gives me enough time to pick up milk, eggs, and bread. 😊


11 comments:

  1. Milk, eggs and bread... that's French Toast shopping!

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  2. Do you think we will ever reach a climate where we will be faced with an atmospheric OCEAN?? Or worse...a lake?

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  3. Cliff,

    Thanks for all the time you invest regarding snow forecasts on our behalf!

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  4. Great weather for ducks and Sasquatch.

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  5. Pretty warm out tonight. Went for a walk 10 mins ago, and I felt hot (because I was jogging-) but still. Weather app said 59 degrees. Another one of those nights!

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  6. Cliff. Make it stop :)

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  7. Max wind gust in NW Bellingham today was 46MPH.

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  8. Tons of trees down from Port Angeles out to Kingston as we make our way back. Hood Canal closed yesterday and last night but was open at 7am this morning.

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  9. 1.51" of rain fell at my location in NW Bellingham between 5PM on 1/30 and 6:30AM on 2/1. I ended up with 6.09" of precip for January which is the second greatest monthly precip total in my period of record extending back to 10/1/15. Mount Baker Ski Area ended up with 294" of snowfall during January - possibly the snowiest January in its record.

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    1. Great reminder that recent rainfall amounts aren't really all that unusual, 2 times with 6" in 6 yrs, 1/3 of recent Januaries.

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    2. Not exactly. The other month in my POR with >6" of precip was December 2015. That's 2 months with >6" of precip out of the past 51 months, or ~4% of all months in my POR. However, it's most likely that monthly precip totals >6" would occur only during the wet season (October-April), as have the 2 months in question during my POR. So, I've measured 2 wet season months with >6" precip out of 32 total wet season months, so far (~6%). Or, alternately, months in which >6" of precip have fallen occurred during 2 wet seasons out of 5, so far (40%). That's 4% of all months, 6% of wet season months and 40% of wet seasons - unusual or not depends on the data resolution/time-scale you're referring to.

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