Winter 2014-2015 is coming in with a vengeance,
the Green Mountains have been whitened and the mood is clearly appropriate for
some preseason prognosticating. This is year 10 of the SCWB. It started with
sporadic emails to Eric in 2004 and it continues now with blogspot, twitter and
our own urban dictionary of weather terminology designed specifically for the
avid New England powder hounds. The blog continues this year and will at least
start with plenty of anticipation. The pattern, currently anchored by a
magnificent looking positive PNA structure has delivered widespread cold to
eastern North America. But even more intriguing is the combination of what
appears to be at least a mild El Nino, a positive PDO and another
impressive expansion of snow/ice in the Northern Hemisphere. Are these the
ingredients for a round of 1977-1978 style fireworks ? Or will the welcomed
addition of the southern branch of the jet stream deliver all of its goodies to
Pennsylvania, New Jersey and points south like 2009-2010 or even worse, will
the winter STB like 1991-1992 after a chilly November. Worthy of some
discussion at the very least. I have added some links to further explain some
terminology. Most of them go to Wiki (And I encourage contributions to them).
After a 4-year hiatus, El Nino has returned,
and over recent weeks has been gathering strength. The state of the ENSO continues
to be one of the more reliable ways to predict behavioral patterns of weather
in a given season, particularly winter. It can be particularly useful when
trying to pinpoint the frequency of specific occurrences. And it is especially
relevant this year given its 4-year absence and the general presence of
La Nina at varying degrees of intensity over the past 4 years. The strength of
an El Nino is determined by the strength of positive sea surface
temperature anomalies in the equatorial Pacific Ocean. There has been much
discussion from the National
Weather Service's Climate Prediction Center about the potential ENSO
event this year and in spite of much discussion, El Nino, has
been slow to manifest. In the last 30 days however, sea surface
temperatures in key regions of the equatorial Pacific have warmed to about 1 C
above normal. Typically this is about the threshold where we see miner ENSO
impacts become more significant. These impacts include a suppressed and active
jet stream in the Pacific fueling a potent southern branch of the jet stream. A
jet stream capable of relieving California of its 2-year drought, bring
significant snows to the southern Rockies and heavy rainfall from Texas to the
southeastern states. Quite often, these many juicy weather systems culminate
their trip across North America by evolving into major East Coast weather
systems. Temperature impacts have also proven to be substantial, especially
during the bigger ENSO events. The persistent throng of energy in the Pacific
can counteract the southward advance of arctic air. Much of the Northern
Plains, Upper Midwest and most of the eastern two thirds of Canada typically
see above normal temperatures during a significant El Nino. The most
egregious example was 1998, where water temperatures warmed to over 2C above
average. Mad River enjoyed a fun-filled winter with plenty of juicy winter
storms, but it was warm and the season was interrupted by a damaging ice storm
in early January which required herculean efforts by many coop volunteers to
clean the woods of debris. This year's El Nino, like all the others
since, won't even be half the strength of 1998 and the result of this, we
hope, is that we see more of the typical impacts of precipitation as opposed to
temperature. I will point out that 1998 is often used as a reference point for
many global warming/climate change deniers. "We haven't globally warmed
since 1998 !" you will hear, or some version of that. Statistically that
is true when using 1998 as a reference point since the 3-Sigma El Nino of
that year provided for additional and significant temperatures perturbations
globally and thus many years since have been cooler than that globally.
Statistics have been and will continue to be manipulated to suit all sides of
every argument but that is one that has always bothered me. Back to our present
weather situation. Many might remember 2009-2010, the last El Nino winter
and the heart-ache in northern Vermont as the snow piled up well to our south
while General Stark enjoyed mostly dry weather for long stretches of
time. Yes that could happen again but the adverse storm track of
2009-2010 was primarily due to the extremely negative Arctic Oscillation that
accompanied that El Nino that year. We like negative AO's but not that
negative ! It is unlikely that combination will prevail again this year.
The PDO has earned its place in the
preseason discussion and like the ENSO, the index is defying the most recent 4
year history. The PDO (Pacific
Decadal Oscillation) describes the configuration of sea surface
temperatures in the mid-latitude Pacific, above the equator where we monitor
ENSO. Around the time of 2007, the PDO had its multi-decadal shift
going from an index that was mostly positive to an index mostly negative. It is
not a rule without exceptions, the PDO can be in a negative decadal
phase and have a positive year and vice-versa. It just has decadal tendencies,
which is how the phenomenon was discovered and although we are in a negative
tendency, it appears we will have a positive year. We went into last season
with a negative index but it turned in January and the index remained positive
through March. The index could switch this year but will at least start the
season positive. The sign of the index does have a tendency to be correlated
with the ENSO but not entirely. In the case of this year, the development of
the El Nino seems to have gone hand in hand with the evolving positive PDO.
Why is the positive PDO significant ? The long wave or jet stream
pattern can often have a difficult time locking in place with a negative PDO as
illustrated during the winters of 2011-2012 and 2012-2013. Often times, cold
and snowy weather can occur only to be abruptly interrupted by a intrusive
thaw. A positive PDO favors the ridge west/trough east regime and
these regimes can remain in place for longer periods uninterrupted.
I want to bring up an important side note related
somewhat to the PDO. I want to aknowledge an important driving force
behind last years cold weather, the repeated PV invasions and I also want to
aknowledge an individual who pointed this fact out on more than one occasion
last year. We mentioned the persistent Alaskan jet stream ridge as the catalyst
behind much of the cold, but an old colleague of mine, Joe Bastardi, referenced
that a driving force behind that particular weather feature was a large
area/bubble of warm water in the Gulf of Alaska. This very large bubble of
warmth blossomed in December of last year as the PDO switched from a
negative to a positive phase. Bastardi style of self-promotional forecasting is
something I take issue with at times and I particularly don't like his
invariable bashings of the National Weather Service, which employs many
talented meteorologists, who by law are not allowed to defend themselves
against his repeated attacks. That said, Bastardi did point out the importance
of this bubble of warmth in the Pacific and I think he's right, it was
significant. This large area of warmth remains positioned in the Gulf of Alaska
but it has shifted eastward slightly and the configuration of water
temperatures now resembles the classic "red-horseshoe" look of the
traditional positive PDO.
The real fun begins when we start talking about
the autumnal expansion of snow and ice in the Northern Hemisphere this year. It
wasn't going to be easy but it was achieved. We actually bested last year's
monster October snow cover number of 21.01 millions of square km and chimed in
this year with a 22.88 number
this year. The 2nd highest in the very brief 47-year history of recorded data.
Some of the recent November weeks are running almost 4 millions of square km
above last year according to our friends at the Rutgers
University Snow Lab - . Lets dumb this down a bit this year and
look at some big years in this 47 year history of recorded data. Here are a
list of big autumn snow cover years (at least 1 STDEV above normal) in
the Northern Hemisphere and the corresponding result in Vermont.
Year
Snowcover Temp Snow
1970 21.84
Cold Totally Epic
1971 21.53
Cold Snowy
1972 21.52
Mild Sucky
1976 25.72
Ext/Cold Snowy
2002 23.24
Cold Snowy
2009 21.01
Warm Normal
2013 21.01
Ext/Cold Slightly Snowy
By contrast here are some low snow cover years
and the corresponding result.
1979 14.68
Normal Sucky
1980 13.61
Cold Normal
1987 13.35
Warm Sucky
1988 12.78
Warm Beyond Sucky
1990 15.58
Warm 2x Beyond
Sucky
1994 14.23
Warm Sucky
There are a few exceptions on both sides of
course and it is hardly a perfect relationship. In fact, there are some recent
years where snow cover was within a standard deviation of normal (but still
above or below the normal) in the northern hemisphere and the weather in
Vermont did the opposite of what this illustration is trying to display. That
said, the 22.88 number is a strong signal and if past history is any
indication, the colder weather will win a majority of the battles this year as
it did last year.
In a poker game, players use the term
"tell" to describe a behavior or a demeanor that might give
competitors a clue as to the nature of a players hand. I look at the weather
the same way. By early November, it starts to exhibit a behavior that typically
foreshadows the nature of the winter. It doesn't work all the time but it earns
it's place as a contributing variable in the preseason discussion. This year it
is a pretty obvious one. We have just been slammed with the strongest attack of
November cold in more than a decade across the eastern half of North America.
Lake Effect snows totaling over 8 feet and temperatures that are as much as 25
below average all supported by a classic positive PNA
structure. It is a pattern I would expect we should see repeated a few
times this winter since it is one that we do typically see in
positive PDO years. What we need to really hope for is the support
from the active southern branch of the jet stream, which will be catalyst for
several monster east coast events 1978 and 1994 style.
Needless to say I am pretty stoked about the
upcoming winter. And yeah I am inherently stoked before every winter and I try
and provide that disclaimer to account for the bias, but this to me is the most
impressive collection of indicators we have seen in the last 10 years for a
cold and snowy winter. It will also likely be a collection of indicators
not surpassed in the 2nd 10 years of the SCWB, if we can achieve that
longevity. El Nino is providing us with some needed added southern stream
juice, PDO is having a counter-tendency positive year, there is a
mammoth amount of early Northern Hemispheric snow cover and the weather pattern
has already exhibited a need for a big positive PNA outburst. Could we crap out
like '91 ? Anything can happen and preseason forecasts can be inaccurate. I am
probably about 60 percent confident about this forecast as opposed to my normal
55 percent preseason confidence. 1991, by the way, was a stronger El Nino year
with a widespread and rather strong attack of November cold. The winter then
proceeded to fall completely flat and turned out to be quite warm with a
glaring lack of snow. The snow cover number that October though was 15.58
millions of square km. We were over 7 million square km above that this past October. With all that said, I expect, only for the 2nd time, for Vermont to see
a colder than average winter and I expect some above average snowfall along
with that. An additional shorter term update will follow in the coming days
which will include some snow around Thanksgiving and a temperature moderation
for the early part of December as we lose teleconnection support.
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