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Seasonal Climate Seasonal Climate Forecast (Forecast Forecast (Forecast
Method)Method) (Revised: May 26, 2012)(Revised: May 26, 2012)
This product is published by the OregonThis product is published by the OregonDepartment of Agriculture (ODA), in cooperationDepartment of Agriculture (ODA), in cooperationwith the Oregon Department of Forestry (ODF).with the Oregon Department of Forestry (ODF).
Contact: Pete Parsons, ODF Meteorologist503-945-7448 [email protected]
ODA Production support from Diana Walker and Mary Jane Schaffer
This product is published by the OregonThis product is published by the OregonDepartment of Agriculture (ODA), in cooperationDepartment of Agriculture (ODA), in cooperationwith the Oregon Department of Forestry (ODF).with the Oregon Department of Forestry (ODF).
Contact: Pete Parsons, ODF Meteorologist503-945-7448 [email protected]
ODA Production support from Diana Walker and Mary Jane Schaffer
Seasonal Climate Seasonal Climate Forecast (Forecast Forecast (Forecast
Method)Method) Find Past Years With Similar Find Past Years With Similar
Characteristics (Analog Years).Characteristics (Analog Years). Find Common Events or Trends Find Common Events or Trends
During Those During Those ““Analog Years.Analog Years.”” Use That Information to Predict Use That Information to Predict
Future Events and/or Trends.Future Events and/or Trends.
The assumption is made that no The assumption is made that no climate change has occurred from the climate change has occurred from the time of the analog years to present.time of the analog years to present.
Since the climate is constantly Since the climate is constantly changing, it is understood that this changing, it is understood that this assumption adds to forecast error.assumption adds to forecast error.
Forecast verification shows that this Forecast verification shows that this method still outperforms climatology.method still outperforms climatology.
What About Climate What About Climate Change?Change?
Top analog years are identified Top analog years are identified based based on sea-surface temperature (SST) on sea-surface temperature (SST) patterns across the Pacific Ocean.patterns across the Pacific Ocean.
Current and historical records of the Current and historical records of the Southern Oscillation Index Southern Oscillation Index (SOI)(SOI), , Oceanic Niño Index Oceanic Niño Index (ONI)(ONI), and Pacific , and Pacific Decadal Oscillation Decadal Oscillation (PDO) (PDO) are analyzed are analyzed to find past years with similar to find past years with similar characteristics to the current year.characteristics to the current year.
How Are How Are ““Analog YearsAnalog Years”” Picked?Picked?
Southern Oscillation Index Southern Oscillation Index (SOI)(SOI)
An index calculated based on the An index calculated based on the differences in air pressure differences in air pressure anomalyanomaly between Tahiti and between Tahiti and Darwin, Australia.Darwin, Australia.
Strongly related to temperature Strongly related to temperature changes in the tropical Pacific changes in the tropical Pacific Ocean.Ocean.
SOI is Based on PressureSOI is Based on Pressure Anomalies of Two Sites Anomalies of Two Sites
TahitiTahitiDarwinDarwin
Based on Based on SST departures SST departures from normalfrom normal in the Niño 3.4 in the Niño 3.4 regionregion
Defined as the three-month Defined as the three-month running-mean SST departure running-mean SST departure for normal.for normal.
Oceanic Niño Index (ONI)Oceanic Niño Index (ONI)
Areas Covered by Areas Covered by Various Niño Various Niño
Regions Regions
NOAA Operational NOAA Operational DefinitionsDefinitions
for El Niño and La Niña arefor El Niño and La Niña areBased on the ONIBased on the ONI
El Niño:El Niño: characterized by a characterized by a positivepositive ONI greater ONI greater than or equal to +0.5°C.than or equal to +0.5°C.
La Niña:La Niña: characterized by a characterized by a negativenegative ONI less than ONI less than or equal to -0.5°C.or equal to -0.5°C.
To be classified as a full-fledged El Niño or La Niña To be classified as a full-fledged El Niño or La Niña episode episode these thresholds must be exceeded for a these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month period of at least 5 consecutive overlapping 3-month seasons. seasons.
CPC considers El Niño or La Niña CPC considers El Niño or La Niña conditionsconditions to to occur when the monthly Niño3.4 SST departures occur when the monthly Niño3.4 SST departures meet or exceed +/- 0.5°C along with consistent meet or exceed +/- 0.5°C along with consistent atmospheric features.atmospheric features.
El Niño / Southern El Niño / Southern OscillationOscillation
(ENSO)(ENSO) Year-to-year variations in sea-Year-to-year variations in sea-surface temperatures, convective surface temperatures, convective rainfall, surface air pressure, and rainfall, surface air pressure, and atmospheric circulation across the atmospheric circulation across the equatorial Pacific Ocean.equatorial Pacific Ocean.
El Niño and La Niña represent El Niño and La Niña represent opposite extremes in the ENSO cycle.opposite extremes in the ENSO cycle.
Typical ENSO PatternsTypical ENSO Patterns
WarmWarmEventEvent
ColdColdEventEvent
Pacific Decadal Oscillation Pacific Decadal Oscillation (PDO)(PDO)
(Fluctuations in the Northern Pacific Ocean (Fluctuations in the Northern Pacific Ocean SSTs)SSTs)
Warm PhaseWarm Phase Cool PhaseCool Phase
Courtesy: http://jisao.washington.edu/pdo/Courtesy: http://jisao.washington.edu/pdo/
Pacific Decadal Oscillation Pacific Decadal Oscillation (PDO)(PDO)
(Highlights)(Highlights) More frequent and stronger El More frequent and stronger El
Niño events occur during periods Niño events occur during periods dominated by the dominated by the ““Warm Phase.Warm Phase.””
More frequent and stronger La More frequent and stronger La Niña events occur during periods Niña events occur during periods dominated by the dominated by the ““Cool Phase.Cool Phase.””
In 2007, we apparently transitioned In 2007, we apparently transitioned back into the back into the ““Cool Phase.Cool Phase.””
Pacific Decadal Oscillation Pacific Decadal Oscillation (PDO)(PDO)
(Each Phase Typically Lasts for 20-30 Years)(Each Phase Typically Lasts for 20-30 Years)
Cool PhaseCool Phase DominatesDominates(1890-1924)(1890-1924)
Cool PhaseCool Phase DominatesDominates(1947-1976)(1947-1976)
Warm PhaseWarm Phase DominatesDominates(1925-1946)(1925-1946)
Warm PhaseWarm Phase DominatesDominates(1977-2006)(1977-2006)
CoolCoolPhasePhase
(2007-?)(2007-?)
Data Courtesy: Data Courtesy: http://jisao.washington.edu/pdo/img/pdo_latest.jpeghttp://jisao.washington.edu/pdo/img/pdo_latest.jpeg
Seasonal Climate Seasonal Climate ForecastForecast
(Forecast Method)(Forecast Method)
Contact: ODF Meteorologist Pete ParsonsContact: ODF Meteorologist Pete Parsonsat 503-945-7448 [email protected] 503-945-7448 [email protected]: ODF Meteorologist Pete ParsonsContact: ODF Meteorologist Pete Parsonsat 503-945-7448 [email protected] 503-945-7448 [email protected]
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