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December 2014

On Cue?

Posted: December 1st, 2014


via Climate Prediction Center

NOAA Climate Prediction Center


It’s December 1st and meteorological winter has begun. Astronomical winter begins on the Solstice, of course, but we creatures of the water cycle might be excused for focusing on another moment–the meaningful period in which the jet stream tends to settle into place for about three dark, wet months.


At the moment the jet stream is split out over the Pacific, with moisture going either to Alaska or California. That’s about how the atmosphere is supposed to be behaving as we start this winter, too. Recall that we are amidst a weak El Niño event in which we’re expected to remain warm and dry. Typically El Niño doesn’t become evident until December; this one appears to be starting on cue.



Given the offshre jet stream split, it’ll be a quiet week with moderating temperatures and scattered, light rainfall later this week.


The latest National Weather Service forecast for Seattle has no rainfall until 0.02″ late Wednesday, followed by 0.07″ Thursday, 0.10″ Friday, 0.05″ Saturday, and 0.20″ Sunday. The UW WRF-GFS and ECMWF each have no rain until late Thursday and little thereafter.


Over SPU’s mountain reservoirs, the NWS forecast shows under 0.50″ Wed-Fri, and again less than 0.50″ Sat-Sun. By the time precipitation arrives, snow levels will have likely climbed well above 4000 feet, so only peaks will get dusted. As usual with arctic outbreaks, this latest one–the second of the season–will feature somewhat strong easterly mountain gaps winds. The latest forecast indicates sustained 20- to 30-mph easterlies late tomorrow through early Thursday.


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