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.

ENSO NAO

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

Temperature Departure …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

Occurrence of Above Normal Temperatures is Related Weak El Nino Temperature Trends (Nov through March) 38% The data shows that the Occurrence of Above Normal Temperatures is Related To the Strength of the El Nino Episode. - + 62% Moderate El Nino Temperature Trends (Nov through March) - 20% + El Nino Exhibits a Moderate Statistical Correlation (.52) to Temperature. 80% Strong El Nino Temperature Trends (Nov through March) + 100%

Further Evidence That El Nino Strength is Important Nov Dec Jan Feb Mar Weak El Nino (-.34 deg F) Moderate El Nino (1.9 deg F) Strong El Nino (3.2 deg F)

Buffalo Toronto Detroit Weak El Nino -0.34 deg F Moderate El Nino 1.9 deg F Strong El Nino 3.2 deg F (F) Nov Dec Jan Feb Mar Toronto Weak El Nino -1.1 deg F Moderate El Nino 0.6 deg F Strong El Nino 2.4 deg F Nov Dec Jan Feb Mar Detroit Weak El Nino -0.1 deg F Moderate El Nino 1.6 deg F Strong El Nino 2.8 deg F Nov Dec Jan Feb Mar

Buffalo Temperature Departures During Moderate to Strong El Nino’s Deg F

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

(Nov-March) El Nino El Nino La Nina Deg F La Nina Weak Moderate Strong

(1 inch)

ENSO Advantages Drawbacks Moderate to strong events typically produce Positive Temperature Anomalies The stronger the ENSO....the higher the confidence level 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.

ENSO NAO

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).

The Two Phases of NAO Positive NAO Negative NAO

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

- NAO + NAO Looking at 500mb….. 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 Drawbacks 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!) 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? ENSO NAO

ENSO and NAO Do They Have a Combined Effect? Moderate Correlation ENSO + NAO Weak Correlation NAO Essentially No Correlation ENSO

ENSO and NAO Do They Have a Combined Effect? La Nina +2.34 El Nino +2.3 El Nino +1.4 La Nina +0.94 ENSO Component Only ENSO and +NAO Components

The cooling effects of a –NAO are clearly visible El Nino +1.4 La Nina +0.94 El Nino 0.3 La Nina -.82 ENSO Component Only ENSO and –NAO Component The cooling effects of a –NAO are clearly visible

Moderate to Strong El Nino Pattern 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

Warmest Averages Found During El Nino / + NAO 925 mb Temp Anomalies During Moderate to Strong El Nino Pattern EL Nino Alone EL Nino and +NAO EL Nino and –NAO Warmest Averages Found During El Nino / + NAO

El Nino/Positive NAO Polar Jet Sub-Tropical Jet

Broader Southwest Flow Trof Based Further East La Nina with Positive NAO La Nina with Negative NAO Higher Heights and Broader Southwest Flow Trof Based Further East

This begs the Question…… When does it get Cold in Buffalo?

Average Temperature Departures in Degrees F - NAO + NAO Strong La Nina 0.76 2.26 Moderate La Nina 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 Strong El Nino 2.04 3.23 18 of the top 20 warmest -NAO 0.46 +NAO 2.32 -0.73 1.50 1.11 3.13 Average Temperature Departures in Degrees F

Winter 1976-77 Neutral ENSO Strongly Negative NAO 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 Nov Dec Jan Feb 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

Average Snowfall from Past 50 Years in Buffalo Nov Dec Jan Feb 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 While snowfall during December El Nino events averages 36% below normal…. The 5 month winter average is only 7% below normal. Statistically….No Correlation Can Be Drawn Between ENSO and Snowfall. This was also found by a BGM NWS study for SE NY and NE PA, also by a BUF Student Intern Study on the Great Lakes Region. Only weak correlations have been found between La Nina and snowfall with Even less impressive statistics for El Nino.

Buffalo Temperature Departures During Moderate to Strong El Nino’s Deg F

No single month* or series total has a departure of more than 16% Toronto Nov Dec Jan Feb Mar Total La Nina 3.2 12.6 12.9 10.0 10.6 49.3 Neutral 3.3 9.9 13.4 8.3 45.0 El Nino 4.0 11.8 11.6 8.2 5.7 40.9 No single month* or series total has a departure of more than 16% from normal, but all sites show a trend to less snowfall during El Nino. Detroit Nov Dec Jan Feb Mar Total La Nina 2.6 11.9 10.8 9.4 8.0 42.7 Neutral 2.7 8.1 9.8 10.1 6.8 37.5 El Nino 8.2 11.2 6.7 6.2 34.9

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?

Average Temperature Departures in Degrees F - NAO + NAO Strong La Nina 0.76 2.26 Moderate La Nina 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 Strong El Nino 2.04 3.23 -NAO 0.46 +NAO 2.32 -0.73 1.50 1.11 3.13 Average Temperature Departures in Degrees F

Questions?