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