1. El Nino and La Nina
An important atmospheric variation that has an average period of three to seven years.
Goes between El Nino, Neutral, and La Nina (ENSO cycle, El Nino Southern Oscillation)
Has large influence both in the tropics and midlatitudes.
Main source of forecast skill beyond a few weeks.

5. An Important Measure is the Temperature in the Tropical Pacific

6. Niño Region SST Departures (oC) Recent Evolution
The latest weekly SST departures are:
Niño 4
-0.1ºC
Niño 3.4
-0.8ºC
Niño 3
-1.1ºC
Niño 1+2
-1.2ºC

7. Central and Eastern Pacific Upper-Ocean (0-300 m) Weekly Average Temperature Anomalies
Negative subsurface temperature anomalies were present through December Positive anomalies with large fluctuations in amplitude were present from mid-January through mid-July Since mid-July, anomalies decreased and have remained negative.

8. Sub-Surface Temperature Departures in the Equatorial Pacific
In the last two months, negative subsurface temperature anomalies have persisted across the central and eastern Pacific Ocean.
This figure cannot be updated at this time.
Most recent pentad analysis
Recently, the strongest negative anomalies are between 160ºW-80ºW.

9. Why do we care?
The circulations in the midlatitudes are substantially different in El Nino, Neutral, and La Nina years.
Since the temperature of the tropical Pacific changes relatively slowly, this gives some meteorologist some insights into the weather over the next several months.

10. El Nino – weak Aleutian High

11. La Nina – strong Aleutian High

12. CPC/IRI Probabilistic ENSO Outlook
Updated: 9 November 2017
La Niña conditions are predicted to continue (~65%-75% chance) at least through the Northern Hemisphere winter , with a 51% chance of continuation through February-April 2018.

13. IRI/CPC Pacific Niño 3.4 SST Model Outlook
The multi-model averages predict La Niña to persist into early 2018.
Figure provided by the International Research Institute (IRI) for Climate and Society (updated 17 November 2017).

14. SST Outlook: NCEP CFS.v2 Forecast (PDF corrected)
Issued: 26 November 2017
The CFS.v2 ensemble mean (black dashed line) favors La Niña through March-May 2018.

15. Snow and La Nina
Typically more snow in La Nina years--but no guarantees. This is a statistical relationship.
Major impact after January 1

18. Implication for this year: higher than normal probability for lowland snow in Seattle

19. U. S. Seasonal Outlooks December 2017– February 2018
The seasonal outlooks combine the effects of long-term trends, soil moisture, and, when appropriate, ENSO.
Precipitation
Temperature