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November 2014

Taste of Winter

Posted: November 10th, 2014


The culprit: ex-Super Typhoon Nuri (via Jeff Masters)

The culprit: Ex-Super Typhoon Nuri (via Jeff Masters)


An arctic air mass well to our northeast will provide strong Cascade gap winds, subfreezing temps, and a little mountain snow this week. This early taste of winter is being brought about by one of the strongest Pacific Ocean storms ever recorded. Ex-Super-Typhoon Nuri, which struck Japan last week, deepened so rapidly over the Bering Sea that it forced cold air southward thousand of miles away downstream.


Impacts to SPU systems and services are expected to be minor as the amplified pattern begins to modify. Snow in our watersheds is generally a good thing, scattered icing may slightly delay solid waste collection, and our deciduous tress have probably now shed the majority of their leaves. That said, strong easterly mountain gap winds mid-week are likely to cause a few power outages and the like in the lower watersheds. A National Weather Service Special Weather Statement issued earlier for the foothills has been removed, however.


A weak frontal system will bring light rain (and the slightest chance of frozen precipitation regionally) on Thursday and Friday, otherwise dry weather is expected to persist into next week.


NWS Area Forecast Discussion
NWS Watches, Warnings, Advisories
SPU My Services
SPU Water Supply Outlook



Out of the red.

Out of the red.


After two weeks of near-saturation, we have slipped below the USGS landslide threshold, and based on the forecast should remain below beyond the forecast period.


USGS Landslide Information



masonry pool

Last snow-free reservoir shot this season? Masonry Pool (image: Mark Hopf).



No precipitation is expected until Thursday and Friday when a total of 0.48″ is predicted citywide by the NWS. The latest UW WRF-GFS and ECMWF model runs generally concur. Temperatures are expected to drop below freezing around midnight and bottom around 30°F shortly after sunrise on Wednesday, and again on Thursday.


In SPU’s mountain watersheds, snow levels will drop from 3000-4000′ to 1000-0′ on Monday and Tuesday, then gradually rise to above 2000′ by Friday. 1-3″ of snow (~0.80″ liquid equivalent) is expected at reservoir level on Thursday and Friday. Mountain gap easterly winds will increase early Tuesday, sustain at around 25-30mph early Wednesday, and gradually decrease on Thursday.


NWS Forecast Table Interface—Seattle
NWS Forecast Table Interface—Tolt Reservoir
NWS Forecast Table Interface—Chester Morse Lake