Transcript Teleconnections

Teleconnections
EPO, NAO, AND PNA (2006)
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. The recent EPO trend has shown a decline which
would probably favor a -EPO to be put into effect by the end of November.
The NAO was almost record negative in October. It was only the third time
in the last 58 years that the monthly NAO went below -2.0, the only two
other years to accomplish this are 2002 and 1968, with 2002 only being 0.04 away from the -2.24 in October 2006. Both of those years also saw
the NAO rise in November and then eventually fall again in December,
which is probably what could happen this year.
Teleconnections and
Favorable/Unfavorable Snow Patterns
I do expect to see some big storms out of this pattern
and in fact one can't get any better setup for the midAtlantic and Northeast. Consider... unbelievably
warm water offshore, a negative EPO,
southern stream coming along, cold, and yes
we can debate how cold, coming into the
picture. But as I was showing Elliot and Chris
Shabbot this morning, the Jan. 20, 1978, storm
up the East coast which was Boston's greatest
storm ever until the blizzard of 1978 a couple
of weeks later, had a strong positive NAO, a
positive EPO and AO and a subtropical
cyclone northeast of Puerto Rico that was not
named. Some you get the bear, sometime the bear
gets you. That was the anti-pattern for a big storm
with teleconnections but low-level cold air from the
cross polar flow got involved and built high pressure
and the rest is history, rather than mystery. I have
seen patterns work out the way I envisioned, but the
weather did not. -JB (Jan 2007)-
Note: Not snowstorms
for the I-95 corridor in
an unfavorable pattern
are rare. As DT has
stated they rarely stay
all snow and to get
mostly or all snow the
cold air has to be
formidable and holding
its own. -Hurm-
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…
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?
A+B+C+D= forecast
-DT (January 2007)-
Teleconnections and Favorable/Unfavorable Snow
Patterns (January 5, 2007)
El Nino is a naturally occurring cycle of warming in the Pacific
that has profound impacts on North America’s weather patterns.
The El Nino is marked by above normal seas surface
temperatures over the equatorial Pacific from off the coast of
South America westward to the International Dateline. This
particular El Nino event has been forecast since last summer
and we accurately forecast a warmer than normal November
and December throughout the Northeast – primarily as a result
of this El Nino. A typical El Nino is known to provide above
normal temperatures over much of North America – especially
Central and Western Canada (where our cold air typically
comes from) along with much of the northern portion of the
United States.
This particular El Nino event has been characterized as
“moderate”. This, coupled with a natural “warm climate” cycle
has combined to provide consistently above normal
temperatures throughout much of the country so far this winter
season. -Ross Murley-
Teleconnections and Favorable/Unfavorable Snow
Patterns (January 5, 2007)
The El Nino is showing signs of weakening – and more importantly, we are seeing a
significant change in the “MJO” or “Madden Julian Oscillation” – which has been
intensifying in the past few weeks. The “MJO” is another index that gages
fluctuations in pressure, winds, temperature and rainfall over the tropical Pacific. It
has been shown that the MJO can enhance or suppress the El Nino and have
marked impacts on the weather and general circulation over North America.
Additionally, one other intra-seasonal oscillation we keep an eye on, and perhaps the
most important one is the Eastern Pacific Oscillation. When this index is positive (as
it has been so far this winter), the influence of the Pacific tends to send a strong
zonal - or west to east jet stream across the country. This in essence, keeps all the
polar and Arctic air masses blocked up into Canada. This is perhaps one of the
strongest contributing influences to the extraordinary warmth thus far this winter.
This EPO is now forecast to turn negative – which will weaken the strong zonal (west
to east) jet stream across the lower 48, allow more of an “amplified” jet and help to
introduce progressively colder air masses.
Cumulatively, the strengthening MJO, an EPO going “negative” and a weakening El
Nino are all strong factors that point to a MUCH different pattern for the remainder of
the winter.