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Physical Basis For The Winter 01-02 Forecast. OPIS 2000 National Supply Summit. Recent Winter Temperature Anomalies (DJFM). El Nino 97/98. Average of La Nina 98/99. and 99/00. ENSO Neutral Winters. Decade of the 1990’s. Degrees Celsius. El Nino Southern Oscillation Phenomena.

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Presentation Transcript

Recent Winter Temperature Anomalies (DJFM)

El Nino 97/98

Average of

La Nina 98/99

and 99/00

ENSO Neutral Winters

Decade of the 1990’s

Degrees Celsius


Arctic Oscillation (AO)

High Index Phase

Low Index Phase

AO Index (JFM 1950-1999)



Global Temperatures the Past Three Years Were Primarily a Result of ENSO and the Underlying Warm Trend

Simulated Using

Observed Ocean




Status of the Natural Modes

Of Climate Variability This Winter

  • ENSO: Current forecasts indicate this will be near neutral
  • AO(NAO): Currently no capability to forecast seasonal phase: return to near neutral suggested by trends over the past 13 years

Implications for Winter Forecast:

  • The lack of ENSO related forcing suggests that the coming winter will likely not be as warm as those of the late 90’s and on par with last winter
  • The unpredictability of the AO introduces large uncertainty

Winter temperature Anomalies (0C)






Seasonal Forecasts are referenced to a 1961-1990 base period, i.e. a relatively cool period


Climate Outlook


January-March 2001

December-February 2001

This graphic will be updated with

the forecast issued Oct 12, 2000

Probability forecasts indicate changes in the likelihood of the favored category (i.e. above normal, normal, below normal). For example a value of “20” needs to be added to 33% (climatological odds) to arrive at the forecast odds of 53% change of being above normal.

Forecasts are relative to the 1961-1990 climatology.

“CL” indicates the forecast tools give no guidance, i.e. be prepared.


Four Estimate of Trends

OCN- untempered

OCN (ENSO-neutral)

Residual “Trend”

Class limits for standardized anomalies *100: upper 33% (45)

upper 20% (85)


Winter 00-01 Seasonal Forecast

  • This winter temperatures will likely be cooler than those experienced in the late 90’s.
  • The forecast tools indicate climatological odds should be used in the northern half of the US, except in the upper Midwest where temperatures are forecast to be below normal.
  • The southern third of the US is forecast to be warmer than normal, especially in the southwest where recent trends have been relatively large.