1. La Niña and The U. S. Winter Outlook Mike Halpert, Deputy Director Climate Prediction Center / NCEP December, 2011

2. Review of 2010-11 Forecasts/Verification Potential Climate Features impacting U. S. Winter 2011-12 U. S. Outlooks Outline

3. 3 December 2010 - February 2011 Heidke = 41 Coverage = 57% Heidke = -16.8 Coverage = 56%

4. NH Winter Arctic Oscillation (AO)

5. Arctic Oscillation (AO) Positive Arctic Oscillation (left) and negative Arctic Oscillation (right). Source: J. Wallace, University of Washington

6. NH Winter (monthly) AO

7. 7 March - May 2011 Heidke = 74 Coverage = 63% Heidke = 45 Coverage = 35%

8. Review of 2010-11 Forecasts/Verification Potential Climate Features impacting U. S. Winter 2011-12 U. S. Outlooks Outline

9. Sea Surface Temperature Departures Last 4 weeks

10. Niño Region SST Departures ( o C) Recent Evolution The latest weekly SST departures are: Niño 4 -0.6ºC Niño 3.4 -0.9ºC Niño 3 -1.0ºC Niño 1+2 -0.6ºC

11. During the last six weeks, positive subsurface temperature anomalies (100- 300m) in the western Pacific have shifted slightly eastward, while negative anomalies have been present in the eastern half of the Pacific. In the recent period, the positive anomalies have persisted in the western half of the Pacific, while the negative anomalies persisted in the eastern Pacific. Sub-Surface Temperature Departures ( o C) in the Equatorial Pacific Most recent pentad analysis Longitude Time Longitude Time Longitude Time

12. Pacific Niño 3.4 SST Outlook Figure provided by the International Research Institute (IRI) for Climate and Society (updated 15 November 2011). The majority of ENSO models predict the continuation of La Niña through the Northern Hemisphere winter (Niño-3.4 SST anomalies less than -0.5°C).

13. SST Outlook: NCEP CFS.v2 Forecast Issued 28 November 2011 The CFS.v2 ensemble mean (black dashed line) predicts La Niña conditions to strengthen and continue through the Northern Hemisphere spring 2012. CFS.v2 is now operational. More information on version 2 is available at http://cfs.ncep.noaa.gov/cfsv2/docs.html (not PDF corrected)

14. Typical US Temperature, Precipitation and Jet Stream Patterns during La Niña Winters

15. U.S. Precipitation Departures (mm) and Frequency of Occurrence (%) for La Niña during Dec.-Feb.

16. U.S. Temperature Departures (°C) and Frequency of Occurrence (%) for La Niña during Dec.-Feb.

17. Climate Forecast System

18. 18 Optimal Climate Normal (OCN) OCN, as it is used as a tool at CPC is, quite simply, a measure of the trend. For a given station and season, the OCN forecast is the difference between the seasonal mean temperature during the last 10 years and the 30 year climatology.

19. Optimal Climate Normal

20. 20 Winter 2011-12 Outlook Rationale La Niña conditions redeveloped across the Pacific during August. It is expected to persist through the winter. AO has been and continues to be erratic. Large swings possible in any year (e.g. DJF 2010-11). Trends (1981-2010 base period): Temperature: slightly negative over South; Precipitation: wet across North, dry across South. Forecast tilted toward La Niña impacts. Drought is expected to persist or develop across Florida and Georgia.

21. Review of 2010-11 Forecasts/Verification Potential Climate Features impacting U. S. Winter 2011-12 U. S. Outlooks Outline

22. The seasonal outlooks combine the effects of long-term trends, soil moisture, and, when appropriate, the ENSO cycle. TemperaturePrecipitatio n U. S. Seasonal Outlooks December 2011 - February 2012

23. U. S. Drought Outlook valid through February 2012

24. U.S. Precipitation Departures (mm) and Frequency of Occurrence (%) for La Niña during Mar. - May

25. The seasonal outlooks combine the effects of long-term trends, soil moisture, and, when appropriate, the ENSO cycle. TemperaturePrecipitatio n U. S. Seasonal Outlooks March - May 2012

26. 26 Temperature and Precipitation Distribution http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/box_whiskers/index.php MEAN Extreme Events + Extreme Events - Realm of most Common events # EVENTS many few

27. 27 December – February Precipitation and Temperature Distribution Box-Whisker Web Page: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/box_whiskers/index.php Southern GA/Northern FL Strong tilt toward warm and dry

28. 28 March-May Precipitation and Temperature Distribution Box-Whisker Web Page: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/box_whiskers/index.php Southern GA/Northern FL