Seasonal Climate Forecast April – June 2015 Issued: March 23, 2015 This Product is Published by the Oregon Department of Agriculture (ODA), in Cooperation with the Oregon Department of Forestry (ODF). Contact: ODF Meteorologist Pete Parsons at or Get related Seasonal Climate Forecast information at: This Product is Published by the Oregon Department of Agriculture (ODA), in Cooperation with the Oregon Department of Forestry (ODF). Contact: ODF Meteorologist Pete Parsons at or Get related Seasonal Climate Forecast information at:

Forecast Method Notes… This forecast is generated by utilizing weather records from previous years (analogs) with similar oceanic and atmospheric indices, as compared to the current year. This forecast is generated by utilizing weather records from previous years (analogs) with similar oceanic and atmospheric indices, as compared to the current year. Only “cool phase” PDO years were used to create the forecasts issued this past autumn and winter. However, the real-time PDO index is highly positive, which may help to explain the recent significant increase in forecast error. Only “cool phase” PDO years were used to create the forecasts issued this past autumn and winter. However, the real-time PDO index is highly positive, which may help to explain the recent significant increase in forecast error. Current analog year selection gives priority to years that most closely match both real-time Pacific Ocean sea-surface temperature (SST) profiles and predominant North American jet stream circulation patterns (see Forecasting Methods). Current analog year selection gives priority to years that most closely match both real-time Pacific Ocean sea-surface temperature (SST) profiles and predominant North American jet stream circulation patterns (see Forecasting Methods).Forecasting MethodsForecasting Methods The top analog years used to create this forecast (1977; 2005; 2007) are unchanged from last month. The top analog years used to create this forecast (1977; 2005; 2007) are unchanged from last month.

El Niño Southern Oscillation (ENSO) Current Status and Forecast SSTs are above average across the central and western equatorial Pacific Ocean and cooler east. This SST pattern is representative of El Niño Modoki conditions ( ref: ). SSTs are above average across the central and western equatorial Pacific Ocean and cooler east. This SST pattern is representative of El Niño Modoki conditions ( ref: ). The Oceanic Niño Index (ONI) remains greater than +0.5 ºC, which is indicative of weak El Niño conditions. The Oceanic Niño Index (ONI) remains greater than +0.5 ºC, which is indicative of weak El Niño conditions. The Climate Prediction Center (CPC) slightly favors the continuation of El Niño through this summer. The Climate Prediction Center (CPC) slightly favors the continuation of El Niño through this summer. The “analog years” used to create this forecast all showed weak El Niño conditions (some of Modoki type). The “analog years” used to create this forecast all showed weak El Niño conditions (some of Modoki type).

Pacific Ocean Animated (in PowerPoint only) SSTs (top) / Anomalies (bottom) Courtesy:

Tropical Pacific Ocean SSTs above average west and central; near-to-below average east. Courtesy:

ENSO Indices El Niño La Niña ( ; ; ) ENSO-Neutral

El Niño El Niño peaked at weak strength in all 3 top analog winters. El Niño ENSO Indices ( ; ; ) ENSO-Neutral La Niña El Niño “Modoki” conditions have existed for the past 4 months.

Model forecasts favor ENSO-neutral conditions through spring 2014; followed by El Niño development. ENSO Predictive Models Borderline El Niño conditions will likely continue through spring “Base” Graphic Courtesy: La Niña El Niño ENSO-neutral

April 2015 Forecast Mean Upper-Air PatternUpper-Air Anomalies A “split-flow” jet stream pattern will continue to direct weather systems onshore this spring (typical during El Niño). A “split-flow” jet stream pattern will continue to direct weather systems onshore this spring (typical during El Niño). The “split” in the jet stream will likely weaken incoming weather systems, with considerable energy heading into California. The “split” in the jet stream will likely weaken incoming weather systems, with considerable energy heading into California.

April 2015 Forecast TemperaturesPrecipitation The “signal” for warmer-and-drier-than-average weather weakens. The “signal” for warmer-and-drier-than-average weather weakens. Mountain snowpacks may show some minor early-spring recovery from their near-record late-winter levels. Mountain snowpacks may show some minor early-spring recovery from their near-record late-winter levels.

May 2015 Forecast Mean Upper-Air PatternUpper-Air Anomalies Analog years begin to exhibit more diverse weather, but a “split-flow” jet stream pattern should continue to bring weather systems onshore. Analog years begin to exhibit more diverse weather, but a “split-flow” jet stream pattern should continue to bring weather systems onshore. Storm strength, across Oregon, is the big question, with considerable energy likely being directed more into SW Canada and California. Storm strength, across Oregon, is the big question, with considerable energy likely being directed more into SW Canada and California.

May 2015 Forecast TemperaturesPrecipitation Lowered forecast confidence due to wide-ranging analog solutions. Lowered forecast confidence due to wide-ranging analog solutions. An exceptionally cool and wet 1977 skews the forecast graphics, which may be overstated and 2007 had above average temperatures was wetter than average and 2007 was drier than average. An exceptionally cool and wet 1977 skews the forecast graphics, which may be overstated and 2007 had above average temperatures was wetter than average and 2007 was drier than average.

June 2015 Forecast Mean Upper-Air PatternUpper-Air Anomalies An “enhanced” but continued “spit-flow” jet stream pattern is likely to affect our region. This “springtime” pattern is typical during El Niño and will likely result in no major monthly departures from average in either temperature or precipitation. An “enhanced” but continued “spit-flow” jet stream pattern is likely to affect our region. This “springtime” pattern is typical during El Niño and will likely result in no major monthly departures from average in either temperature or precipitation.

June 2015 Forecast TemperaturesPrecipitation Slightly enhanced westerly flow aloft would have a tendency to keep western zones a touch cooler than average, with the opposite effect east of the Cascades. Slightly enhanced westerly flow aloft would have a tendency to keep western zones a touch cooler than average, with the opposite effect east of the Cascades. No significant departures from average precipitation are indicated. No significant departures from average precipitation are indicated.

April – June 2015 Forecast Mean Upper-Air PatternUpper-Air Anomalies During El Niño, it is common to see a wintertime upper-level ridge, along the west coast, much like we saw this winter. During El Niño, it is common to see a wintertime upper-level ridge, along the west coast, much like we saw this winter. In the spring, this typically gives way to a “split-flow” jet stream pattern, with increased storm activity making it onshore. In the spring, this typically gives way to a “split-flow” jet stream pattern, with increased storm activity making it onshore.

April – June 2015 Forecast TemperaturesPrecipitation A transition away from much warmer-and-drier-than-average weather, to something closer to “average,” is likely (typical of spring with El Niño). A transition away from much warmer-and-drier-than-average weather, to something closer to “average,” is likely (typical of spring with El Niño). Mountains may get above-average spring snow, but that won’t alleviate water concerns due to near-record low late-winter snowpacks. Mountains may get above-average spring snow, but that won’t alleviate water concerns due to near-record low late-winter snowpacks.

Helpful Resources CPC Official US Three-Month Forecasts (Graphics): CPC Official US Three-Month Forecasts (Graphics): CPC US 30-Day & 90-Day Forecasts (Discussions): CPC US 30-Day & 90-Day Forecasts (Discussions): CPC Weekly & Monthly ENSO Discussions: CPC Weekly & Monthly ENSO Discussions: Australian Government Weekly Tropical Climate Note: Australian Government Weekly Tropical Climate Note: Australian Government ENSO Wrap-Up: Australian Government ENSO Wrap-Up: IRI ENSO Quick Look: IRI ENSO Quick Look: NRCS Western Snowpack Data & Water Supply Forecast: NRCS Western Snowpack Data & Water Supply Forecast:

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