ENSO Background
"El-Niño" is named after a Peruvian Christmas
festival where the warming of the waters off Peru
is said to occur near the birthday of "The Boy" (El
Niño), or the Christ child. Meteorologists thus
named the phenomenon the "El-Niño Southern
Oscillation", or ENSO for short. The reverse
phenomenon, the cooling of the eastern Pacific
waters, was at first called "Anti-El-Niño", until it
was realised that this literally meant the AntiChrist ! To avoid this unfortunate connotation, it
was renamed "La-Niña" (or "The Girl").
Current SOI Data (CPC)
ENSO and SOI
• The El-Niño Southern Oscillation is the result of a
cyclic warming and cooling of the surface ocean of the
central and eastern Pacific. This region of the ocean is
normally colder than it's equatorial location would
suggest, mainly due to the influence of northeasterly
trade winds, a cold ocean current flowing up the coast
of Chile, and to the upwelling of cold deep water off
the coast of Peru.
• At times, the influence of these cold water sources
wane, causing the surface of the eastern and central
Pacific to warm up under the tropical sun - this is an
EL-NIÑO event. This results in heavy rainfall in South
America, but severe droughts in eastern Australia. The
more intense the El-Niño, the
Great ENSO and Southern Oscillation Site
ENSO and SOI
• It has been found that the cyclic warming and cooling of the
eastern and central Pacific leaves it's distinctive fingerprint on
sea level pressure. In particular, when the pressure measured
at Darwin is compared with that measured at Tahiti, the
difference between the two can be used to generate an "index"
number. When there is a positive number, we have a La-Niña
(or ocean cooling), but when the number is negative we have
an El-Niño (or ocean warming).
Great ENSO and
Southern Oscillation
Site
SOI
The 2006 El Nino
“It is important to keep in mind 2 salient points
regarding this El Niño event. First we have never
seen a El Niño event develop in the month of
August. Not once as it ever happened. Second ...last
winter...2005-06 featured a weak La Nina event. If you
take a look at the history of the El Niño events in the
Winter which have occurred after a weak La Nina the
previous Winter we find a very significant fact in the
database.
Which is this... Most of the El Nino events that have
occurred after a WEAK La Nina the previous
Winter has NOT reached Moderate El Nino criteria
for more a than a few weeks. (DT)
The 2007 La Nina (Fall) –SSC-
La Nina in 2007 –SSCPacific Pattern Conclusion
Based on everything mentioned, I give the following odds for a DJF ENSO event per
my index:
- 15% of a Weak La Nina (-0.5c to -0.9c)
- 70% chance of Moderate La Nina (-1.0c to -1.5c)
- 15% chance of Strong La Nina (below -1.6c)
There is a good chance that the La Nina will sustain itself, or weaken at a very slow
rate throughout the Winter. Based on this, here is my predicted range for the months
of Nov - Feb.
- November: -1.0c to -1.4c
- December: -1.1c to -1.5c
- January: -1.1c to -1.5c
- February: -0.9c to -1.3c
A Winter time Moderate La Nina favors persistent ridging south of the Aleutian
islands, with a trough in the Gulf of Alaska and sometimes Alaska. The downstream
effect of this pattern over the USA is for above average temperatures and below
average precipitation over the South, and Eastern US. Below average temperatures
and above average precipitation is favored over the Upper Midwest and Northwest,
US. The Pacific signal expected is almost as bad as it gets for the East.
Local Climatology and ENSO
El Nino good, La Nina bad for the Mid Atlantic. Baltimore
average seasonal total overall=20.58"
ENSO Neutral average=24.29"
El Nino years average=22.84"
weak Nino average=21.56"
mod Nino average=28.06"
strong Nino=19.98"
La Nina years average=17.0"
weak Nina average=22.5"
mod Nina average=11.74"
strong Nina average=13.15
The data suggests that an El Nino on average is favorable for
slightly above average snow for Baltimore, with a moderate El
Nino the jackpot!!! La Nina on average favors significantly less
than average snow for Baltimore! The most unfavorable ENSO
condition for snow in Baltimore appears to be a moderate La
Nina.
ENSO and Philadelphia Snowfall
Climatology
On average, weak El Nino winters rank #1 when it comes to Philadelphia
having its snowiest winters relative to average (average = 19.3 inches).
However, seasonal totals may vary greatly among weak El Nino winters.
Moderate El Nino winters also favor seasonal snowfall totals that are above
average. Strong El Nino winters strongly favor below normal seasonal
snowfall totals as do Strong La Nina winters.
Of the 14 El Nino winters that were either weak or moderate:
– 9 had above normal snowfall
– 5 had below normal snowfall
– average snowfall + 23.4 inches
– snowiest winter = 2002-03 (46.3 inches)
– least snowiest = 1918-19 (4.5 inches)
Note: Baltimore, Maryland experiences its largest average seasonal snowfall
total during moderate El Nino winters. Moderate El Nino winters favor much
above normal snowfall to our south and southwest.
El Nino and Local Climatology
• El Nino’s tend to favor colder than normal
February.
• Large scale snowstorms are more likely in
El Nino years.
• Weak El Nino’s tend to be colder than
moderate El Nino’s along the Eastern
seaboard.
Importance of ENSO
“Although there is little doubt that the El Nino
events are somewhat is over hyped... the fact of
the matter is that El Nino and La Nina events are
major players and MUST be considered in any
attempt to make a seasonal forecast. The
technical name for the El Nino and La
Nina event is ENSO. The warm water events
popularly called El Nino can also
be referred to as warm ENSO
while the cold water events La Nina
is referred to as cold ENSO events.” (DT)
Weak Versus Moderate/Strong El Nino Events
These next four images will clearly show differing
impacts between a weak El Niño and a moderate or
strong one with respect to temperatures and
precipitation. As you can clearly see there is a very
strong correlation between a weak El Niño event and
colder than normal temperatures over much of the
central and especially eastern US. Taking a look at the
precipitation patterns we see that in the period of
OCT- NOV- DEC there is a strong bias of Much Below
Normal rainfall over the lower Plains during the weak
El Niño event that is not their during a moderate or
strong El Niño. Not surprisingly the drought they have
been having over the lower Plains strongly matches
the warm El Niño scenario with regard to rainfall. DT
Weak Versus Moderate/Strong El Nino Events
You see, in a strong El Nino year, so much warm air keeps
getting pumped northeastward that the jet never has the
chance top come down over the smaller continent of North
America. The air only marginally cold over North America on its
own; it must be seeded and grow colder on its way into cause
the severe cold weather we see sometimes. In the strong El
Nino seasons, the southern jet is so pronounced is pumps
warm air all the way through North America and it keep the jet
tight, the vortex feeding back so when it does come south it
often does with limited quick shots and its main residue is over
Greenland and Iceland.
ENSO and Temperature and Precipitation
U.S. Climate Data: Put
Patterns
December 2006 Precipitation
Map Here for true el Nino
conditions.
• El Nino Link
El Nino
El Nino
El Nino
500mb Heights/
Anomalies for
December 23, 2006.
Note: The entire 2nd
half of December was
much above normal
temperature wise for
Philadelphia. There
was also no reported
snow in PHL or NYC
during this time
frame. In fact, NYC
had a snow-less
December in 2006.
El Nino Data
Click here for current El Nino Data
1925-26: ?
26-27: ?
39-40: ?
40-41: ?
51-52: NEUTRAL/
WEAK
53-54: NEUTRAL
WEAK
Previous ENSO Years (1951 to present)
57-58: Nino maxed out at
+1.6 making it a
MODERATE/STRONG Nino
58-59:
63-64: (Weakened quickly
by February)
65-66: Nino maxed out at
+1.6 making it a
MODERATE/STRONG Nino
69-70:
72-73: Nino maxed out at
+2.1 making it a STRONG
Nino and the 3rd biggest on
record
76-77:
77-78: (MODERATE EL
NINO)
79-80:
82-83: Nino maxed out at +2.3
making it a STRONG Nino and
the 2nd biggest on record
86-87: Nino maxed out at +1.6
making it a STRONG Nino
1987-88: (MODERATE EL
NINO). Weakened rapidly in
Feb/Mar)
1991-92: STONG Nino from Jan
through March
92-93: MODERATE EL NINO
1994-95: (MODERATE EL
NINO)
97-98: Nino maxed out at +2.5
making it a STRONG Nino and
the largest on record
02-03: Nino maxed out at +1.5
making it a MODERATE Nino
2004-05
JB on El Nino, SOI, Ridging, Jet Streams, and
Storms (Jan 2007)
“In fact if one researches the el nino winters, many of the
storms one sees are with active branches of the southern jet
and un-phased with the northern branch, though one or two
"blockbusters" ( blizzard of 1958, March 1958, blizzard of 1966,
twins, Ohio valley and New England of 1978) do love to show
up in weakening el nino's.
Major warmth that has been beaten back close by, cross polar
flow and here comes the southern jet with the negative SOI
pulse of the MJO. What happens in such cases is a battle that
leads to plenty of snow and ice nationwide with southern
stream storms, and at first no big wind up storms, but as the
pattern matures, that is when you have to worry about the
extreme. The big key here is the visible fall of the height field
east of the date line over the coming weeks, and the
development of a ridge northeast of the Caspian and the major
Alaskan ridge,. Those two ridges can lock hands over the top,
and force the low height field to develop with cross polar flow
coming into it, from Hudson bay to the gulf.” JB post in January
2007
More JB on Weakening El Nino’s and Cold
Outbreaks
“I am more convinced than ever about what we are
facing here as far as cold goes and feel that the period
Feb 1-15 has a good chance to be a top 10- to 15-day
period of ANY 15 DAY PERIOD of cold for the nation as
a whole. Yes, this is a step even deeper into the
freezer, but there is almost unanimous model
consensus on a pattern that fits very closely with
previous severe cold outbreaks in weakening El Nino
seasons. Certainly, the ensembles have not thrown any
cold water on this, and operational runs of all the models
I have seen say the same thing, that the cold is
expanding with time and that what we are seeing now is
not as cold as what is coming.” - JB on January 19,
2007-
Transition into El Nino (Summer 2006 into Winter
2006) and Forecasting the Trend During the
Winter
The turning of the SOI (Southern Oscillation Index) to
a prolonged negative phase beginning in May and
continuing through to the present also sounded alarm
bells, that a warm phase of the ENSO, or an El Nino
was coming. The MEI (Multivariate ENSO Index)
began to rise in mid-Spring and has continued since,
exceeding the El Nino MEI threshold (>= 0.5) in July
and recorded a value of 0.892 as of September. By
mid-August equatorial SST anomalies had risen above
0.5 degrees C in all 4 ENSO regions in the equatorial
Pacific indicating that in deed we have transitioned
into an El Nino this Fall.
Transition into El Nino (Summer 2006 into Winter
2006) and Forecasting the Trend During the
Winter
A key assumption a seasonal forecaster must make this winter
is if this current warm phase is going to be a weak, moderate,
or strong episode. My arbitrary definition is a DJF (DecemberFebruary) MEI average value of 0.5 to 1.0 for weak, 1.0 to 1.5
for moderate, and > 1.5 strong. This is of course arbitrary and
may or may not be true but is what I will use for my evaluation.
In looking at computer model forecasts of ENSO, the behavior
of the SOI, equatorial Pacific sub-surface temperatures, and my
own reasoning, I believe that this ENSO warm episode will
peak in the moderate classification I have designated above,
probably somewhere between 1.0 and 1.25 from an MEI
perspective, and that the meteorological winter (DJF) 06-07
MEI average value will be somewhere in that range. So what
this all means is that I favor an ENSO state that is in the
moderate category. (Raleigh Wx)
The 2006 El Nino
“It is important to keep in mind 2 salient points
regarding this El Niño event. First we have never
seen a El Niño event develop in the month of
August. Not once as it ever happened. Second ...last
winter...2005-06 featured a weak La Nina event. If you
take a look at the history of the El Niño events in the
Winter which have occurred after a weak La Nina the
previous Winter we find a very significant fact in the
database.
Which is this... Most of the El Nino events that have
occurred after a WEAK La Nina the previous
Winter has NOT reached Moderate El Nino criteria
for more a than a few weeks. (DT)
DT on El Nino and QBO (January
2007)
• The QBO dropped DRAMATICALLY in DEC to well
under +10 to a value of +6.10... this combined with
a weakening El Nino (+0.9) during the week of
January 1, 2006 tells me the 2nd of the winter will
be impressively cold and stormy for much of the
US as it has been warm and dry. The combination
of weakening moderate El Nino and near neutral
QBO winters are a LOCK -- as much as one can
have such thing in seasonal forecasting for a
Good if not GREAT 2nd half of winter and a
delayed spring. (DT)
El Nino and Temperature Anomalies
(DT)
Weak El Nino’s
Moderate El Nino’s
Strong El Nino’s
El Nino (Strong and Moderate)
October and El Nino
El Nino and NAO (October 2006)
El Nino Regions (DT)
El Nino Data (October 2006)
Note the trend of a
strengthening El
Nino to
Moderate/Strong
values with a
gradual weakening
after reaching a
peak in
DEC06/JAN07.
• Nino3.4 SST Anomalies
• ENSO Model Forecasts
• ENSO Model Forecasts
El Nino Data (January 2007)
Note the
trend of a
weakening
El Nino
El Nino (Digging a Little Deeper)
Seasonal Snowfall Estimates for 2006-2007
“Based on snowfall tendencies during weak to
moderate El Niño events coupled with a warm
anomaly in ENSO Region 1+2, odds favor lesser
snowfall amounts in some of the cities that have
fared very well in recent years in the northern MidAtlantic region. Eastern New England seems poised
for average to above average snowfall.” Don S.
TAKE NOTE:
Thus it is important to note the exact nature of the El Nino
relative to the specific regions of the Pacific Ocean.
(HURM)
The Peaking of El Nino
“In terms of years that
saw a weak to
moderate El Niño
peak no later than
NovemberDecember-January,
the East tended to be
cool while the central
and southern Plains
tended to be warm.”
Don S.
El Nino Trends (November 2006)
Climatology says that a +1.5 peak suggests that the trimonthly El Nino will most likely max out in the +1.4 to +1.8
range, with a 3 month average El Nino max being in the +1.3
to +1.5 range. The recent trends alone suggest that we have
a near 100% chance of seeing a Mod-Nino for DJF, and there
is now an increasing chance that we could actually see a
Strong Nino peak sometime in the DJF time frame.
Chance of a Mod-Nino dominated winter: 80%
Chance of a Strong-Nino dominated winter: 20%
-SSC(2006)Note: Philadelphia climatology varies greatly between
moderate El Nino winters and strong El Nino winters, as it
does for the weak and moderate El Nino comparison.
How strong this El Nino becomes is KEY to our overall
winter temperatures and snowfall. Hurm (2006)
El Nino and MJO
Watch out
during phase
7 and 8 of the
MJO. The
“Pineapple
Express” and
the “Southern
Jet
Impulse(s)”
can BOTH
play into a
major east
coast
snowstorm.
El Nino and PDO
Typically weak to moderate El Nino events support a
positive Pacific Decadal Oscillation (PDO) and thus a
ridge in the west and a trough in the east with cooler
than average temperatures especially in
January/February) and more precipitation/snow than
normal with an active subtropical jet. In addition to the
Equatorial Pacific, the North Pacific has an effect on our
weather. Currently there is an expanding cool pool of
water in the Gulf of Alaska. The water profile can change
very quickly, but if this cool pool should grow stronger,
this suggests that when the North Atlantic Oscillation
(NAO, see discussion below) is positive that warmer air
would be able to make it into our region more easily as
the amplitude of the ridge/trough axis would be flatter.
(Capital Weather 2006-07 forecast)
EPO and El Nino
During El Nino's, the effects of the EPO are little to
none. This is shown in great lengths by winters 91-92
and 94-95. During these winters, the EPO was
severely negative, but the Pacific flow across the
northern US and Canada was too powerful to allow for
the EPO to have any impact. The El Nino acts as a
block in that regard. Because of this, I can say with
high confidence that the EPO will be a non-factor this
winter. Since it will have little to no impact, it isn't
worth predicting for, although an El Nino does favor a EPO. (Posted by met on easternuswx.com for winter
of 2006-07))
El Nino and Computer Forecasting Models
(Winter of 2006-07)
 Many of the weather models beyond Day 5 or 6 will be
depicting a biased to the WARM side throughout most of this
winter. This warm bias will exist because many of the weather
models are going to be over depicting the troughs coming in
from the eastern Pacific into the Western portions of North
America. And if the model over does the deep trough on the
West Coast... the Ridge over the central and eastern US will of
course also be overdone
This will be especially true when we have a -NAO in place. This
is a very common model characteristic of weak and moderate
El Niño winters.... and it is imperative that weather forecasters
keep this in mind. As a result we will see a consistent tendency
of the warm air to be over forecasted at Day 7 or let's say
Day10 only to see each subsequent model run showing the
warm air backing off a little more. DT