Other Factors: Teleconnections

1
Other Factors Teleconnections

• Its not one teleconnection (indices etc.), it
  is all the players on the field that count (Joe
  Bastardi of Accu-Weather).
• For it drives home a point about broad brushing
  ideas. The negative NAO is a signal for cold, but
  unless everything is just right, it is something
  that drives storms south (Joe Bastardi of
  Accu-Weather on March 22, 2006).

2
Other Factors Teleconnections

• In other words, a negative NAO does not make a
  snowstorm. A positive PNA does not make a
  snowstorm. A negative NAO and a positive PNA
  together do not make a snowstorm. Patterns make
  snowstorms. A conglomeration of indices create
  the framework on which a pattern can be built.

3
Other Factors Teleconnections

• All you snow lovers should know that the most
  favorable pattern for a snowstorm on the east
  coast (between the EPO, NAO, and PNA) is a -EPO,
  -NAO, and PNA. Rapid changes from negative to
  positive of the NAO can cause major east coast
  snowstorms. Recently, we have been seeing pretty
  much the opposite of all of those, hence the warm
  conditions. A -EPO favors cold conditions across
  the east, while a EPO does the opposite.

4
Teleconnections and Pattern Change (January 2007)

• WHY has the last two months of this winter-- all
  of NOV nearly all of DEC and the first 10 days of
  Jan --been so warm?You could argue it was the
  moderate El Niño. I sytated earlier that when the
  El Niño was weak we were cold and September
  October... when it reached moderate intensity the
  pattern turned mild.You could argue it was the
  developmental large vortex over the Bering Sea
  flooded western Canada with a fairly strong
  Pacific Jet that prevented any sort of
  amplification in the northern branch of the Jet
  stream. Of course such a vortex in THAT location
  is common during moderate El Niño events.You
  could argue that the Pacific Ocean -- the PDO --
  was in the Negative Phase which means a lot of
  cold water over the eastern Pacific / West coast
  which supports a trough of the West Coast and
  therefore Ridge in the East.You could argue
  that one reason was the lack of any High latitude
  blocking over eastern Canada Greenland because of
  the very bad unfavorable sea surface temperature
  configurations in the Northwest Atlantic.
• Continued

5
Teleconnections and Pattern Change (January 2007)

• You could argue that since the Polar Vortex was
  on the other side of hemisphere ---that is to say
  over Asia it has been impossible to get any sort
  sustained cold pattern in North America since the
  heart of the cold air is on the other side of the
  world.You could argue that is because the EPO
  has been a positive phase for most of November
  December and the first 10 days of January there
  cannot be any sustained Ridge on the West
  coast.Pick your reason. You may pick or select
  several of them. I would. Some of the above
  stated reasons are interrelated.SO.... If you a
  forecaster that is still arguing that the pattern
  shift is not really a big deal.... and it's just
  a cold weather interval... then you have a
  serious problem.If your reasons for issuing a
  warm forecast and a continuation of the more
  pattern over North America to all November all
  the semblance first 10 days of January... how do
  you STILL make that forecast since almost ALL of
  those item / facts I listed above have
  changed?ABCD forecast
• -DT (January 2007)-

6
Teleconnections (NWS December 2006)

• The teleconnection indices that help us sort the
  larger overall show us over the Pacific Ocean are
  FCSTG conditions that favor warmer weather (POS
  EPO WPO). Closer to NOAM though the PNA which
  is positive is FCSTD to become negative this week
  making it a threesome for a milder regime. Toward
  the first day of winter its (PNA) FCSTD to become
  positive again which would bring some Canadian
  shots of cold air our way. This is depicted in
  the far away land on the GFS right now FCSTG a
  colder shot to arrive around then. In the other
  pond (Atlantic), the NAO which has been strongly
  positive (The last cold shot did not linger too
  long) is forecasted to get closer to neutral.
  This might keep some of these colder blasts
  lingering longer than the last one.

7
Other Factors Index Combination

• The NAO, AO, and PNA are all important indices
  when it comes to forecasting a large scale snow
  event. Some professionals say that a negative
  NAO, negative AO, and neutral PNA are very
  favorable for mid-Atlantic snows because the
  storms crash into the Pacific coast, come east
  and hit a block, which in turn slows them down
  with cold air in place, making it favorable for
  snow. However, I feel the best situation for a
  large snowstorm in the PHL area is the following
  
• 1. Negative NAO trending positive or trending
  negative (very steep slope)
• 2. PNA trending positive (very steep slope)
• 3. AO negative

8
Other Factors Index Combination

• 1. Negative NAO trending positive (very steep
  slope)
• http//www.cpc.ncep.noaa.gov/products/precip/CWli
  nk/pna/new.nao_index_ensm.html
• 2. PNA trending positive (very steep slope)
• http//www.cpc.ncep.noaa.gov/products/precip/CWli
  nk/pna/new.pna_index_ensm.html
• 3. AO negative
• http//www.cpc.ncep.noaa.gov/products/precip/CWli
  nk/daily_ao_index/ao_index_ensm.shtml
• According to a senior forecaster at NOAA,
  negative AO and NAO favor big snowstorms
  somewhere in or near the eastern U.S. but the
  chances at a given location are still rather
  small."