La Niña and The U. S. Winter Outlook

Mike Halpert, Deputy DirectorClimate Prediction Center / NCEP

December, 2011

• Review of 2010-11 Forecasts/Verification

• Potential Climate Features impacting U. S. Winter

• 2011-12 U. S. Outlooks

Outline

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December 2010 - February 2011

Heidke = 41 Coverage = 57%

Heidke = -16.8 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

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March - May 2011

Heidke = 74 Coverage = 63%

Heidke = 45 Coverage = 35%

• Review of 2010-11 Forecasts/Verification

• Potential Climate Features impacting U. S. Winter

• 2011-12 U. S. Outlooks

Outline

Sea Surface Temperature Departures Last 4 weeks

Niño Region SST Departures (oC) 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

• 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 (oC) in the Equatorial Pacific

Most recent pentad analysisLongitude

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 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)

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

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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

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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.

• Review of 2010-11 Forecasts/Verification

• Potential Climate Features impacting U. S. Winter

• 2011-12 U. S. Outlooks

Outline

The seasonal outlooks combine the effects of long-term trends, soil moisture, and, when appropriate, the ENSO cycle.

Temperature Precipitation

U. S. Seasonal OutlooksDecember 2011 - February 2012

U. S. Drought Outlookvalid 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.

Temperature Precipitation

U. S. Seasonal OutlooksMarch - May 2012

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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 mostCommon events

# EVENTS

many few

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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

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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