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25089Weather Update. Weather Cafe By Rufus. Edging Toward Arctic Impact

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  • David Hoffman
    Nov 25, 2013
      Weather Update. Weather Cafe By Rufus. Edging Toward Arctic Impact

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      Edging Toward Arctic Impact

      Monday November 25

      There may be a snow flake in your future. Still iffy, yet consistently
      present on the charts. So, what does this mean? Got your morning beverage?

      Chilly, frosty mornings dry afternoons will continue around the region
      through Tuesday. Possible for a few extra mid-level clouds to stream by
      from the SW Tue Wed, although the system west of us will split into two
      pieces, one falls apart as it nears the PNW, the other will skid south just
      off the coast of California - providing some much needed precip to coastal
      zones of the golden state.

      Thanksgiving period still looks dry and slightly warmer. All the action
      will impact CA, as noted. The PNW will enjoy a calm period, with some
      sunshine, patches fog in places. Not too bad. As the extended weekend
      unfolds, though, a change will begin. Fri/Sat likely to see increasing
      clouds chance for some precip, esp north of Salem, by later on Saturday.
      Sunday travel home may be a bit dicey in places, esp north of Portland.
      Models are really holding together on the next major wx event for the PNW:
      bitter cold and snowy conditions. Dare we discuss?

      Transition from blah to burrr is modeled in the Sun-Tue period, Dec 1-3.
      Cold front dropping down from the north on the leading edge of Arctic Air
      will arrive Sunday. Rain/showers at first, but the air mass will rapidly
      chill down as the surface low tracks inland, drawing Arctic air well into
      position around the PNW for cold rain, turning to snow showers as the
      system exits to our east. The dry Arctic air will be the coldest of the
      season, and impact much of our region for several days. Will this verify?
      The scenario, with a few modifications, has been progged since last Friday
      evening, across many different models. Hence, this presentation of the
      event potential. Back to our story ---

      High pressure dome of Arctic Air (1040-1050 mb at times) will drive very
      cold air into the region after the Dec 1,2 front passes. Offshore blast of
      cold air out of the freezer through the Fraser Columbia outflows will set
      up dry overnight temps into single digits east (pushing to Zero in places)
      and teens west side. The first blast will begin to diminish when warmer
      moist air moves in from the west by Dec 6,7. If this solution holds, we'd
      likely see additional snow showers / freezing rain until the warm air
      scours out the cold air at the surface. You know the drill. However, some
      model solutions bring down yet another, even COLDER Arctic Blast in the Dec
      5-8 period for leading edge snow showers or freezing rain west before the
      colder shot of Arctic air settles in. This solution would hold precip in
      the southern OR region. Temps will drop lower than previous Arctic shot.
      (Let's hold on temp estimates until better confirmation of this second shot.)

      Either way, all indications are for a WINTER EVENT to develop around the
      PNW as the month of December gets under way. All of this is reminiscent of
      December 2008, although starting a bit earlier this time. Slight changes in
      the dynamics of these patterns have a big impact on duration or types of
      precip. For now, The WxCafe (TM) will suggest that the chance for snowfall
      -post-frontal passage, so not heavy - is probable during the early days of
      December.

      "The tree of liberty is one shrub that won't stand very much grafting."

      -Rufus

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