Western Washington winter outlook update based on La Nina

Scott Cronk n7fsp@linux.n7fsp.ampr.org
Thu, 15 Oct 1998 20:22:41 -0700 (PDT)

      The following statement is an updated outlook for this winter in
      Western Washington based on the latest NWS Climate Prediction Center
      La Nina long-lead forecast.  In response to the unfortunate
      misinformation concerning the outlook for this winter that has
      circulated in the last few weeks, we plan to issue a "local spin" of
      the CPC forecast to help better inform everyone of this winter's
      outlook.  The CPC issues their forecasts once a month in the middle of
      the month.  Please refer to our web site for more La Nina and weather
      information - http://www.seawfo.noaa.gov

      We tried to reach an initial set of e-mail addresses with this
      message.  Please feel free to forward this message to those you feel
      need to receive it.

      Ted Buehner
      NWS Seattle - Warning Coordination Meteorologist


 On 15 October 1998, NOAA's Climate Prediction Center (CPC) issued their monthly
 update to the long-lead forecasts for this coming winter.  The forecasts are
 based on current conditions, statistical trends, and computer forecasts.  The
 most important factor considered for this coming winter's forecast continues to
 be the developing La Nina.  Sea surface temperatures are colder than normal over
 much of the central tropical Pacific and trade winds are somewhat above normal.
 The combination of these conditions and computer forecasts allows the CPC to
 place a 90% confidence that the current La Nina will continue without
 interruption through mid spring.

 The updated forecast has only minimal changes to the one issued in
 mid-September.  For the United States, the forecast generally calls for drier
 and warmer than normal across the south, and wetter and somewhat colder than
 normal across the north.  CPC's overall confidence in this forecast remains
 quite high.

 The winter precipitation forecast for the Pacific Northwest continues to be wet.
 The period from November through March is anticipated to be wetter than
 normal with a good chance that this winter will be among the top one-third
 wettest winters.

 The winter temperature forecast remains somewhat less certain than the forecast
 for precipitation.  There continues to be some conflict in indicators and the
 CPCforecast remains "climatology."  A forecast of "climatology" places about
 equal probability (33.3%) that the average temperature will be below normal,
 normal, or above normal.  The conflict is between La Nina, which indicates a
 higher probability of colder than normal temperatures, and a long term warming
 trend in place over the Pacific Northwest.  It is uncertain as to which effect
 will dominate.

 It is important to note that La Nina winters are often characterized by strong
 fluctuations in temperature and precipitation.  As a result, it is reasonable to
 anticipate periods of cold winter weather and periods of mild weather, which
 average out over the course of the winter..  There is also an increased chance of
 low elevation snow events in western Washington, especially in the latter half
 of the winter.  Residents are encouraged to prepare for this increased
 possibility of cold winter weather.  For example, early preparations might
 include checking your antifreeze, mulching cold sensitive plants, and protecting
 exposed pipes.

 The CPC will issue their next update to this forecast on 19 November 1998.  For
 further details regarding the background of long-lead forecasts please refer to
 last month's discussion.

 Brad Colman
 Science and Operations Officer
 Seattle National Weather Service Office