What Can We Expect From El Niño This Winter?

Transcription

1 What Can We Expect From El Niño This Winter? Water Forum September 8, 2015 Pete Fickenscher Senior Hydrologist NOAA / National Weather Service California-Nevada River Forecast Center Sacramento, CA

2 What is El Niño? What is the outlook regarding the current El Niño? What impacts can we expect in Northern California from El Niño?

3 not a storm El Niño is Not. El Niño is a ocean-atmosphere pattern in the tropics. Inaccurate to say about extra-tropical weather: El Niño systems or El Niño storms Fictional monster character

4 Oceanic Niño Index (ONI) Based on SST departures from average in the Niño 3.4 region of the eastcentral equatorial Pacific. El Niño: characterized by a positive ONI greater than or equal to +0.5ºC. Extra-Tropics An El Niño or La Niña episode requires at least 5 consecutive overlapping 3- month seasons. Based on a set of improved homogeneous historical SST analyses produced at NOAA NCEI: Extended Reconstructed SST or ERSST. We have recently upgraded to ERSSTv4 from ERSSTv3b.

5 ENSO : El Niño Southern Oscillation ENSO Neutral ENSO Positive (El Niño)

6 Current Conditions & Forecast the blob El Niño

7 cool phase warm phase

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10 Average all years La Niña Events Mean = 52.7 in. All El Niño Events Mean = 53.4 in. Strongest Events Mean = 59.2 in.

11 La Niña Events Mean = 102% All El Niño Events Mean = 107% Strongest Events Mean = 120%

12 La Niña Events El Niño Events

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15 Summary Currently : strong El Niño conditions are present An El Niño is extremely likely this winter (95% chance) Big Question: Will a strong El Niño continue through this winter? Potential Impacts in Northern California Rainfall : Snowpack : Flooding : slightly higher probability of above normal precipitation slightly higher probability of above normal snowpack lower probability of major flooding Because Northern California represents the main water supply region for California, El Niño is not a reliable factor in predicting an easing of the drought

16 Extra Slides

17 El Niño likely coming, but will it make a difference? (Sacramento Bee Headline July 20, 2015) What is wrong with this picture? In January 1997, a swollen American River surges under the Rainbow Bridge in Folsom. Owen Brewer Sacramento Bee file

18 winter

19 ONI (ERSSTv4) data going back to 1950

20 Sub-Surface Temperature Departures in the Equatorial Pacific During the last two months, positive subsurface temperature anomalies were observed across most of the equatorial Pacific Most recent pentad analysis Recently, negative anomalies at depth remained in the western Pacific, while positive anomalies have persisted across the central and eastern Pacific.

21 Low-level (850-hPa) Zonal (east-west) Wind Anomalies (m s -1 ) During early March, early May, late June/early July, and early August, westerly wind bursts were observed between 140ºE and 180º. In the last week, westerly wind anomalies remained strongest over the east-central equatorial Pacific. Westerly Wind Anomalies (orange/red shading) Easterly Wind Anomalies (blue shading)

22 850-hPa Zonal Wind Indices over the equatorial Pacific Ocean Western Pacific Central Pacific Eastern Pacific

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24 Precipitation impacts are not identical even with a Strong El Niño Strong El Niño DJF (peak ONI 2.1ºC ) Strong El Niño DJF (peak ONI 1.8ºC )

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26 Uncertainty in forecasting Impacts Though scientists have a wealth of data on El Niño patterns and powerful prediction models, the weather phenomenon's effects on the Northern Hemisphere are still unclear because Arctic warming is also affecting the Atlantic jet stream. "The truth is, we don't know what will happen. Will the two patterns reinforce each other? Will they cancel each other? Are they going to act in sequence? Are they going to be regional? We really don't know." (David Carlson, director of the World Climate Research Programme) (quoted by Tom Miles, Reuters, Sept. 1)

27 California-Nevada River Forecast Center Pete Fickenscher Senior Hydrologist National Oceanic & Atmospheric Administration National Weather Service 3310 El Camino Ave., Suite 227 Sacramento, CA (916) Tel.: (916) ext. 339 Fax.: (916) Website: