The Effects of Climate
Variability on Buffalo, NY
Winters
Robert Hamilton
National Weather Service
Buffalo, NY
Climate Variability

…variations in the mean state of the climate on
all temporal and spatial scales beyond that of
individual weather events. The variability may be
due to natural internal processes within the
climate system, or to variations in natural or
anthropogenic external forcing.

…a fluctuation in climate, which could last for a
specified period of time, usually of the order of
seasons to years to decades.

…changes in the long-term characteristics of
weather.
Methodology
CPC’s Oceanic Nino
Index (ONI) based on 3
month running mean of
Equatorial Pacific SST
 Threshold of +/- 0.5C
for a Minimum of 5
Consecutive months
 Used Winter Values of
ONI from 1950 through
last winter (2003-2004)

Methodology…..

NAO Index Based on Difference in MSLP Anomaly
between Iceland and Gibraltar.
 Used Winter Values of this Index...1950 to Present
 Unlike ENSO….no real defined ‘Neutral Phase’
Methodology….

Buffalo Temperature and Snowfall Departures
Since 1950 Were Averaged…Then Grouped
With Various ENSO and NAO phases.
 The Resulting Temperature and Snowfall Trends
Will Be Discussed.
NAO
ENSO
Mod-Strong El Nino
Mod-Strong La Nina
El Niño:
•Extended Jet Stream
•More zonal flow over U.S.
•South shift of storm track
•Weaker Hudson Bay Low
•Fewer arctic outbreaks
La Niña:
•Retracted Jet Stream
•More meridional flow
•Blocking over N. Pac
•Stronger Hudson Bay Low
•More arctic outbreaks
El Nino
El Nino
…For Buffalo…
+1.5 F Average Monthly
Temperature Departure
For All El Nino*
66% of Dec-February
Months Have Had Above
Normal Temperatures…
….The majority of
the Remaining Months
Featured Weak El Ninos
And/Or -NAO’s.
* Dec-Feb
38%
Weak El Nino Temperature Trends
(Nov through March)
-
+
62%
Moderate El Nino Temperature Trends
(Nov through March)
20%
The data shows that the
Occurrence of Above Normal
Temperatures is Related
To the Strength of the
El Nino Episode.
+
80%
Strong El Nino Temperature Trends
(Nov through March)
+
100%
El Nino Exhibits a
Moderate Statistical
Correlation (.52) to
Temperature.
Further Evidence That El Nino
Strength is Important
6
5
4
3
Temp
2
Departure
1
(F)
0
-1
-2
Nov
Dec
Jan
Feb
Weak El Nino (-.34 deg F)
Moderate El Nino (1.9 deg F)
Strong El Nino (3.2 deg F)
Mar
6
5
Buffalo
Weak El Nino -0.34 deg F
Moderate El Nino 1.9 deg F
Strong El Nino 3.2 deg F
4
3
Temp
Departure
(F)
2
1
0
-1
-2
Nov
Dec
Jan
Feb
Mar
4
Toronto
Weak El Nino -1.1 deg F
Moderate El Nino 0.6 deg F
Strong El Nino 2.4 deg F
3
2
Temp
1
Departure (F)
0
-1
-2
Nov
Dec
Jan
Feb
Mar
6
5
Detroit
Weak El Nino -0.1 deg F
Moderate El Nino 1.6 deg F
Strong El Nino 2.8 deg F
4
3
Temp
2
Departure (F)
1
0
-1
-2
Nov
Dec
Jan
Feb
Mar
Buffalo Temperature Departures
During Moderate to Strong El Nino’s
5
4
3
Deg F
2
1
0
Nov
Dec
Jan
Feb
Mar
El Niño:
•Extended Jet Stream
•More zonal flow over U.S.
•South shift of storm track
•Weaker Hudson Bay Low
•Fewer arctic outbreaks
La Niña:
•Retracted Jet Stream
•More meridional flow
•Blocking over N. Pac
•Stronger Hudson Bay Low
•More arctic outbreaks
Interesting La Nina Statistics
 56%
of La Nina Winter Months Exhibit
Above Normal Temperatures for Buffalo
 Above Normal Temperature Departures
can be Just as Significant as those from
El Nino
 La Nina often produces ‘mild winters’ for
Buffalo….but helps to provide some of the
coldest months.
La Nina
La Nina
Buffalo Temperature Departures
During Moderate to Strong La Nina’s
3.5
3
2.5
2
1.5
1
0.5
0
Nov
Dec
Jan
Feb
Mar
Temp Departure per ENSO Strength
(Nov-March)
3
El
Nino
2.5
2
Deg F
El
Nino
1.5
La
Nina
1
La
Nina
0.5
0
-0.5
Weak
Moderate
Strong
Average Snowcover Days Per ENSO (1 inch)
100
80
60
Days
40
20
0
C+
C
C-
N
W-
ENSO Event
W
W+
ENSO
Advantages

Moderate to strong
events typically produce
Positive Temperature
Anomalies
 The stronger the
ENSO....the higher the
confidence level
Drawbacks

Weak ENSO events
reveal no statistical
correlations/trends.
 Statistical Correlations
using ALL ENSO events
are not significant.
 Very weak correlations
to snowfall. Slightly
higher correlations found
with La Nina.
NAO
ENSO
What is the North Atlantic
Oscillation?




Difference of normalized sea
level pressure between Iceland
and the Azores.
Highly variable occurrence
with little variation in mean
structure from month to month.
Corresponding index fluctuates
from month to month and
week to week. El Nino can
persist for 2-3 years.
NAO is most noticeable during
the winter (November - April).
Positive NAO

A stronger than usual
Subtropical High and
a deeper than normal
Icelandic Low.
 Strong North Atlantic
Jet Drains Arctic Air
Away from N.America
 Eastern U.S. receives
“mild and wet” winter
conditions.**
** M. Visbeck Feb 2000 (Columbia University)
J. Hurrell 1995 (NCAR)
Positive NAO
Negative NAO



Weak Subtropical High
and Weak Icelandic Polar
Low.
Arctic Air Pools Over Nrn
Canada and Settles
Southward Due to
Reduced North Atlantic
Flow.
U.S. East Coast receives
more cold air outbreaks
and hence snowy
weather conditions.**
** M. Visbeck Feb 2000 (Columbia University)
J. Hurrell 1995 (NCAR)
Negative NAO
Looking at 500mb…..
+ NAO
- NAO
The Positive NAO 500mb Chart Features a Strong
Zonal Flow….while the Negative NAO Chart Shows
Increased Amplitude with a Greenland Block in Place.
925 mb Temps
+ NAO
-NAO
Colder Boundary Layer Conditions During a Negatively Phased
NAO with Temperatures Averaging About 5 deg Celsius Lower.
NAO
Advantages

Moderate Temperature
Correlation For
Significant Events
 Strongest Temperature
Correlations Found Over
the Western Great Lakes
 Most Significant Snow
Correlations Found in
the Lake Effect Snowbelt
areas (Buffalo!)
Drawbacks

Very weak month to
month temperature
correlation
 Only a ‘hint’ of a month
to month correlation
found for snow
(less than 0.30).
 Only weak correlation
for snow found away
from the LES Belts.
What Are The Combined Effects?
NAO
ENSO
ENSO and NAO
Do They Have a Combined Effect?
Correlation to Temperature
Moderate
Correlation
0.45
ENSO
+ NAO
0.4
0.35
Weak
Correlation
0.3
NAO
0.25
0.2
0.15
0.1
Essentially
No Correlation 0.05
0
ENSO
ENSO and NAO
Do They Have a Combined Effect?
Monthly Temp Departure Deg F
2.5
2
1.5
La Nina
+2.34
1
0.5
0
El Nino
+2.3
El Nino
+1.4
La Nina
+0.94
ENSO Component Only
ENSO and +NAO Components
Montly Temp Departure Deg F
2
1.5
1
0.5
El Nino
La Nina +1.4
+0.94
El Nino 0.3
0
La Nina
-.82
-0.5
-1
ENSO Component Only
ENSO and –NAO Component
The cooling effects of a –NAO are clearly visible
El Nino
El Nino, +NAO
+45m
+70m
El Nino, -NAO
500 mb Anomalies During
Moderate to Strong El Nino Pattern
EL Nino Alone
EL Nino and +NAO
EL Nino and -NAO
El Nino/Positive NAO
Polar
Jet
Sub-Tropical
Jet
La Nina with
Positive NAO
Higher Heights and
Broader Southwest Flow
La Nina with
Negative NAO
Trof Based Further East
This begs the
Question……
When does it get
Cold in Buffalo?
- NAO
Strong La Nina
Moderate La Nina
0.76
+ NAO
2.26
0.16
2.38
Weak La Nina
-2.06
2.32
Neutral ENSO
-0.73
1.44
Weak El Nino
0.61
0.74
Moderate El Nino
0.18
3.03
2.04
3.23
Strong El Nino
-NAO +NAO
Average Temperature Departures in Degrees F
0.46
2.32
-0.73
1.50
1.11
3.13
18 of the top 20 warmest
January 500mb Composite
Neutral ENSO…Negative NAO
Winter 1976-77
Neutral ENSO
Strongly Negative NAO
Jan 500mb Hgt Anomaly Comp.
Neutral ENSO…Negative NAO
925mb Temp Anomaly During a Combined
Neutral ENSO and Negative NAO
What about Snowfall??
Unfortunately,
ENSO and the NAO do not
correlate well to snowfall
5
4
3
2
1
0
Nov
Nov
Dec
Dec
Jan
Jan
Feb
Feb
Mar
Mar
Total
La Nina
10.8
26.3
24.2
16.2
15.7
93.2
Neutral
10.9
28.9
25.9
17.9
10.7
94.2
El Nino
12.8
16.3
25.5
18.7
13.4
86.7
Results of Combined
ENSO / NAO Events
 Gains
Generally in Temp Arena Only
 Much Improved Temperature Correlations
 Certain Combinations Provided Evidence
for More Dramatic and Conclusive
Temperature Anomalies
 Still No Help with Snowfall Prediction
(Lake Effect and Number of Synoptic Storms Likely a
Contributor to this)
Who Benefits?
 Utility
Companies…
Particularly Gas Related
 Winter Recreational
Sites….Ski Resorts
 General Public Via CPC
What About This Winter??
 Mark
Rodwell...Researcher for Met Office U.K.
has 67% Accuracy Forecasting Predominant
Phase of the NAO.
 Forecast for This Winter is a POSITIVE NAO.
 Given CPC’s Indication of a Weak EL Nino….
What Can Buffalo Expect This Winter?
- NAO
Strong La Nina
Moderate La Nina
0.76
+ NAO
2.26
0.16
2.38
Weak La Nina
-2.06
2.32
Neutral ENSO
-0.73
1.44
Weak El Nino
0.61
0.74
Moderate El Nino
0.18
3.03
2.04
3.23
Strong El Nino
-NAO +NAO
Average Temperature Departures in Degrees F
0.46
2.32
-0.73
1.50
1.11
3.13
Questions?