Seasonal Climate Forecast July – September 2016 Issued: June 16, 2016 Contact: ODF Meteorologist Pete Parsons or Oregon Department of Agriculture (ODA) - Oregon Department of Forestry (ODF) ODAProduction support from Diana Walker and Andy Zimmerman ODA Production support from Diana Walker and Andy Zimmerman Contact: ODF Meteorologist Pete Parsons or Oregon Department of Agriculture (ODA) - Oregon Department of Forestry (ODF) ODAProduction support from Diana Walker and Andy Zimmerman ODA Production support from Diana Walker and Andy Zimmerman

El Niño Southern Oscillation (ENSO) Current Status and Forecast El Niño has given way to ENSO-neutral conditions in the equatorial Pacific Ocean. Current sea-surface temperatures (SSTs) are near average across the east-central and eastern Pacific Ocean. El Niño has given way to ENSO-neutral conditions in the equatorial Pacific Ocean. Current sea-surface temperatures (SSTs) are near average across the east-central and eastern Pacific Ocean. The March – May 2016 Oceanic Niño Index (ONI) fell to +1.1°C. The Climate Prediction Center (CPC) thresholds for a weak, moderate, and strong El Niño are ONI values of +0.5°C, +1.0°C, and +1.5°C respectively. This index lags real-time SSTs, which have cooled into the ENSO-neutral range (near average). The March – May 2016 Oceanic Niño Index (ONI) fell to +1.1°C. The Climate Prediction Center (CPC) thresholds for a weak, moderate, and strong El Niño are ONI values of +0.5°C, +1.0°C, and +1.5°C respectively. This index lags real-time SSTs, which have cooled into the ENSO-neutral range (near average). CPC has issued a “La Niña Watch,” due to the likelihood of La Niña developing during the summer and continuing through the winter. The magnitude of the expected La Niña is less certain. CPC has issued a “La Niña Watch,” due to the likelihood of La Niña developing during the summer and continuing through the winter. The magnitude of the expected La Niña is less certain.

Forecast Overview The analog years used to generate this month’s forecast graphics are 1983, 1992, & ’s short-term verification has improved, so it replaces 1988 for this month’s forecast update. The analog years used to generate this month’s forecast graphics are 1983, 1992, & ’s short-term verification has improved, so it replaces 1988 for this month’s forecast update. The and El Niño winters were of similar strength to but were preceded by years with below-average ONI values. In contrast, the winter had above-average (≈ weak El Niño) ONI values. The El Niño events during the and winters were not quite as strong as the El Niño but were preceded by winters with positive ONI values, more closely matching The and El Niño winters were of similar strength to but were preceded by years with below-average ONI values. In contrast, the winter had above-average (≈ weak El Niño) ONI values. The El Niño events during the and winters were not quite as strong as the El Niño but were preceded by winters with positive ONI values, more closely matching It is important to mention the lack of close analogs to the period. That significantly hampers this forecast method* and may also help to explain the highly-unusual weather over the past year! It is important to mention the lack of close analogs to the period. That significantly hampers this forecast method* and may also help to explain the highly-unusual weather over the past year! *This forecast is based on historical weather data and does not use dynamic modeling (see Forecasting Methods). Forecasting MethodsForecasting Methods Dynamic CPC long-range forecasts already reflect potential La Niña development: (

Pacific Ocean Animated (PowerPoint only) SSTs (top) / Anomalies (bottom) Courtesy: SSTs have cooled to near average across the central and eastern tropical Pacific Ocean.

Tropical Pacific Ocean El Niño has transitioned to ENSO-neutral (cooling SSTs) Courtesy: Negative SST anomalies evident

ENSO-neutral Tropical Pacific Ocean El Niño La Niña ( ; ; ) Rapidly-rising SOI value is in-sync with top analog years

ENSO-neutral ONI value peaked last winter and is rapidly falling… El Niño Tropical Pacific Ocean ( ; ; ) La Niña Weak Strong Weak Moderate Strong ONIs of analog years all showed continued cooling with La Niña favored by autumn… Moderate

Neutral North Pacific Ocean Warm Cool ( ; ; ) Double-peak PDO structure common to all years Analogs support lower (cooler) PDO values by this autumn

Model forecasts favor ENSO-neutral conditions through spring 2014; followed by El Niño development. ENSO Predictive Models SSTs are expected cool to ENSO-neutral by this summer La Niña development likely by this autumn “Base” Graphic Courtesy: Graphic Courtesy: La Niña El Niño ENSO-neutral Wide spread in the magnitude of the cooling predicted by various computer models, ranging from cool ENSO-neutral to a strong La Niña, by this winter.

July 2016 Forecast Mean Upper-Air PatternUpper-Air Anomalies A wide range of weather patterns among the top analog years lowers forecast confidence. A wide range of weather patterns among the top analog years lowers forecast confidence. A slightly-enhanced jet stream, focused over California, may inject above-average moisture into southern and eastern Oregon. A slightly-enhanced jet stream, focused over California, may inject above-average moisture into southern and eastern Oregon.

July 2016 Forecast TemperaturesPrecipitation Near-average or slightly-above-average temperatures for the NW zones and north coast. Above-average shower activity may lead to slightly- below-average temperatures for southern and eastern zones. Near-average or slightly-above-average temperatures for the NW zones and north coast. Above-average shower activity may lead to slightly- below-average temperatures for southern and eastern zones. Since July is typically so dry, above-average rainfall is not saying much. Since July is typically so dry, above-average rainfall is not saying much.

August 2016 Forecast Mean Upper-Air PatternUpper-Air Anomalies Analog years become more in-sync during August, showing anomalous upper-level ridging centered over the Rockies. Analog years become more in-sync during August, showing anomalous upper-level ridging centered over the Rockies. Prevailing SW flow aloft favors generally dry weather but may also prevent any prolonged hot spells. Prevailing SW flow aloft favors generally dry weather but may also prevent any prolonged hot spells.

August 2016 Forecast TemperaturesPrecipitation Analog years are consistent in showing above-average temperatures but without any prolonged hot spells (lasting more than a couple of days). Analog years are consistent in showing above-average temperatures but without any prolonged hot spells (lasting more than a couple of days). Precipitation forecast is less certain, with analog years split between generally dry conditions and slightly-above-average rainfall. Precipitation forecast is less certain, with analog years split between generally dry conditions and slightly-above-average rainfall.

September 2016 Forecast Mean Upper-Air PatternUpper-Air Anomalies A blend of vastly differing analog solutions yields an average-looking upper-level pattern. A blend of vastly differing analog solutions yields an average-looking upper-level pattern. Forecast confidence is low, but there does appear to be a tendency for anomalous upper-level ridging to persist for much of the month. Forecast confidence is low, but there does appear to be a tendency for anomalous upper-level ridging to persist for much of the month.

September 2016 Forecast TemperaturesPrecipitation Lowered forecast confidence, due to a wide variety of weather patterns among the top analog years. Lowered forecast confidence, due to a wide variety of weather patterns among the top analog years. Splitting the difference yields near-average temperatures with rainfall ranging from below average west to above average east. Splitting the difference yields near-average temperatures with rainfall ranging from below average west to above average east.

July – September 2016 Forecast Mean Upper-Air PatternUpper-Air Anomalies El Niño has given way ENSO-neutral conditions and may transition to La Niña by the end of the forecast period. El Niño has given way ENSO-neutral conditions and may transition to La Niña by the end of the forecast period. The El Niño-enhanced jet stream, focused over California and southern Oregon, should relax over the summer. The El Niño-enhanced jet stream, focused over California and southern Oregon, should relax over the summer.

July – September 2016 Forecast TemperaturesPrecipitation While above-average temperatures are likely to continue, albeit to a lesser extent, the analog years did not feature prolonged heat-waves. While above-average temperatures are likely to continue, albeit to a lesser extent, the analog years did not feature prolonged heat-waves. Rainfall may be above average, especially east, but averages are quite low this time of year, so rainfall totals are still not likely to be impressive. Rainfall may be above average, especially east, but averages are quite low this time of year, so rainfall totals are still not likely to be impressive.

Forecast Resources CPC Official US Three-Month Forecasts (Graphics): CPC Official US Three-Month Forecasts (Graphics): h ttp:// 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: ODA Seasonal Climate Forecast Home: ODA Seasonal Climate Forecast Home:

Water Supply Information NDMC U.S. Drought Monitor: NDMC U.S. Drought Monitor: NIDIS North American Drought Portal: NIDIS North American Drought Portal: NRCS Snow Water Equivalent Oregon Map: NRCS Snow Water Equivalent Oregon Map: NRCS Snow Water Equivalent Products: NRCS Snow Water Equivalent Products: NRCS Weekly Water and Climate Update: NRCS Weekly Water and Climate Update: NRCS Western Snowpack Data & Water Supply Forecast: NRCS Western Snowpack Data & Water Supply Forecast: WRCC WestWideDroughtTracker: WRCC WestWideDroughtTracker:

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