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

Review of Forecasts/Verification Potential Climate Features impacting U. S. Winter U. S. Outlooks Outline

3 December February 2011 Heidke = 41 Coverage = 57% Heidke = Coverage = 56%

NH Winter Arctic Oscillation (AO)

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

NH Winter (monthly) AO

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

Review of Forecasts/Verification Potential Climate Features impacting U. S. Winter U. S. Outlooks Outline

Sea Surface Temperature Departures Last 4 weeks

Niño Region SST Departures ( o C) Recent Evolution The latest weekly SST departures are: Niño ºC Niño ºC Niño ºC Niño ºC

During the last six weeks, positive subsurface temperature anomalies ( m) 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

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).

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 CFS.v2 is now operational. More information on version 2 is available at (not PDF corrected)

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

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

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

Climate Forecast System

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.

Optimal Climate Normal

20 Winter 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 ). Trends ( 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.

Review of Forecasts/Verification Potential Climate Features impacting U. S. Winter U. S. Outlooks Outline

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 February 2012

U. S. Drought Outlook valid through February 2012

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

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 Temperature and Precipitation Distribution MEAN Extreme Events + Extreme Events - Realm of most Common events # EVENTS many few

27 December – February Precipitation and Temperature Distribution Box-Whisker Web Page: Southern GA/Northern FL Strong tilt toward warm and dry

28 March-May Precipitation and Temperature Distribution Box-Whisker Web Page: Southern GA/Northern FL