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upcoming California weather, potentially severe statewide

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  • Gjon_Hazard@fws.gov
    This is about California weather, not California birds. Given that weather can affect birding and bird movements, however, I thought it would be apropos to
    Message 1 of 1 , Jan 15, 2010
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      This is about California weather, not California birds. Given that weather
      can affect birding and bird movements, however, I thought it would be
      apropos to spread the word (although further general discussion on CALBIRDS
      would probably be frowned upon).

      Below is a forward of a forward. I'm not sure of its source, but it is
      generally corroborated by National Weather Service forecasts.

      Cheers,
      -Gj

      Gjon Hazard, Encinitas/Carlsbad, CA

      (not an official post by the USFWS)


      ----begin forward----

      Get ready. This is what the emergency response community is saying:

      Currently, the strong El Nino is reaching its peak in the Eastern Pacific,
      and now finally appears to be exerting an influence on our weather. The
      strong jet has been apparent for quite some time out over the open water,
      but the persistent block had prevented it from reaching the coast. Now that
      the block has dissolved completely, a 200+ kt jet is barreling towards us.
      Multiple large and powerful storm systems are expected to slam into CA from
      the west and northwest over the coming two weeks, all riding this extremely
      powerful jet stream directly into the state. The jet will itself provide
      tremendous dynamic lift, in addition to directing numerous disturbances
      right at the state and supplying them with an ample oceanic moisture
      source. The jet will be at quite a low latitude over much of the Pacific,
      so these storms will be quite cold, at least initially. Very heavy rainfall
      and strong to potentially very strong winds will impact the lower
      elevations beginning late Sunday and continuing through at least the
      following Sunday. This will be the case for the entire state, from (and
      south of) the Mexican border all the way up to Oregon. Above 3000-4000
      feet, precipitation will be all snow, and since temperatures will be
      unusually cold for a precipitation event of this magnitude, a truly
      prodigious amount of snowfall is likely to occur in the mountains, possibly
      measured in the tens of feet in the Sierra after it's all said and done.
      But there's a big and rather threatening caveat to that (discussed
      below).Individual storm events are going to be hard to time for at least
      few more days, since this jet is just about as powerful as they come (on
      this planet, anyway). Between this Sunday and the following Sunday, I
      expect categorical statewide rainfall totals in excess of 3-4 inches. That
      is likely to be a huge underestimate for most areas. Much of NorCal is
      likely to see 5-10 inches in the lowlands, with 10-20 inches in
      orographically-favored areas. Most of SoCal will see 3-6 inches at lower
      elevations, with perhaps triple that amount in favored areas.

      This is where things get even more interesting, though. The models are
      virtually unanimous in "reloading" the powerful jet stream and forming an
      additional persistent kink 2000-3000 miles to our southwest after next
      Sunday. This is a truly ominous pattern, because it implies the potential
      for a strong Pineapple-type connection to develop. Indeed, the 12z GFS now
      shows copious warm rains falling between days 12 and 16 across the entire
      state. Normally, such as scenario out beyond day seven would be dubious at
      best. Since the models are in such truly remarkable agreement, however, and
      because of the extremely high potential impact of such an event, it's worth
      mentioning now. Since there will be a massive volume of freshly-fallen snow
      (even at relatively low elevations between 3000-5000 feet), even a
      moderately warm storm event would cause very serious flooding. This
      situation will have to monitored closely. Even if the tropical connection
      does not develop, expected rains in the coming 7-10 days will likely be
      sufficient to cause flooding in and of themselves (even in spite of dry
      antecedent conditions).

      In addition to very heavy precipitation, powerful winds may result from
      very steep pressure gradients associated with the large and deep low
      pressure centers expected to begin approaching the coast by early next
      week. Though it's not clear at the moment just how powerful these winds may
      be, there is certainly the potential for a widespread damaging wind event
      at some point, and the high Sierra peaks are likely to see gusts in the
      100-200 mph range (since the 200kt jet at 200-300 mb will essentially run
      directly into the mountains at some point). The details of this will have
      to be hashed out as the event(s) draw closer.

      In short, the next 2-3 weeks (at least) are likely to be more active across
      California than any other 2-3 week period in recent memory. The potential
      exists for a dangerous flood scenario to arise at some point during this
      interval, especially with the possibility of a heavy rain-on-snow event
      during late week 2. In some parts of Southern California, a whole season's
      worth of rain could fall over the course of 5-10 days. This is likely to be
      a rather memorable event. Stay tuned.
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