IRI Climate Digest
Feb-Mar-Apr Seasonal Forecast
Date and Period of Forecast
In December 2001, the IRI prepared a Climate Outlook for January-June 2002. Here we provide a subset of the December IRI Forecast. The forecasts are updated monthly and can be found in their entirety at http://iri.columbia.edu/climate/forecast/net_asmt/.
This Climate Outlook is dependent on the quality of the sea surface temperature (SST) predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is some uncertainty concerning the detailed evolution of SSTs. Spread in global SST predictions is a source of uncertainty in the Outlook provided here. The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by National Meteorological Services in particular regions and may differ from the official forecasts issued in those areas.
The current status of seasonal-to-interannual climate forecasting allows prediction of spatial and temporal averages, and does not fully account for all factors that influence regional and national climate variability. This Outlook is relevant only to seasonal time scales and relatively large areas; local variations should be expected. For further information concerning this and other guidance products, users are strongly advised to contact their National Meteorological Services.
The Outlook for other regions of the globe for the seasons December-January-February and March-April-May can be found at Net Assessment forecasts.
Maps show expected precipitation probabilities in tercile classes. The maps indicate probabilities that seasonal precipitation will fall into the wettest third of the years (top number), the middle third of years (middle number) or the driest third of the years (bottom). An outlook of climatology "C" (light grey) indicates equal probabilities in each class; i.e., there is no basis for favoring the forecast of any particular category. Boundaries between sub-regions should be considered transition zones, and their location considered to be only qualitatively correct. Color shading indicates which tercile class has the greatest probability of occurrence with darker shading indicating greater likelihood as shown by the legend to the right of the plots.
February-March-April 2002 Precipitation Probabilities for South America
This forecast consists of expected probabilities of temperature in tercile classes. The terciles refer to the seasonal temperature falling into the warmest third of the years (top tercile), the middle third of years (middle tercile) or the coldest third of the years (bottom tercile). Boundaries between sub-regions should be considered transition zones, and their location considered to be only qualitatively correct. Color shading indicates which tercile class has the greatest probability of occurrence with darker shading indicating greater likelihood as shown by the legend on the bottom of the plots. Note:
The IRI is in the process of implementing new graphics for its forecast products. Currently, global maps only indicate (by shading) the tercile class with the greatest probability of occurrence.
Please consult the regional maps at Net Assessment forecasts for the probabilities of each tercile class.
Of relevance in the preparation of this outlook is the prediction of near-average conditions in the central and eastern equatorial Pacific through early March 2002, followed by slightly warmer than normal sea surface temperatures (SSTs) from mid-March through June. Currently the SSTs across much of the eastern and central equatorial are near their long-term average, (SSTs), although slightly lower than average SSTs exist in the eastern portion of the tropical Pacific basin and warmer than average SSTs persist in the central and western parts of the basin. Thus, the Nino 4 region remains slightly above normal, Nino 3.4 is near to very slightly below normal, and Nino 3 and Nino 1+2 are slightly below normal. Overall, this particular "flavor" of near neutral equatorial Pacific SST conditions is expected to persist for the first two overlapping seasons of the forecast, January-March 2002, February-April 2002, while during the later two seasons, March-May 2002, April-June 2002, they are expected to become slightly above average even in the eastern tropical Pacific, suggesting the possibility of a developing mild warm ENSO state. The slightly warmer than average SSTs that continue in parts of the Indian Ocean are expected to decrease slowly toward normal through the forecast period. The area of above-average temperature in the tropical and subtropical north Atlantic Ocean, and the weaker pattern of slightly warm and slightly cold SST in parts of the equatorial and tropical south Atlantic, are expected to continue weakly, although uncertainty is quite high for the portion near and south of the equator.
The following procedures and information were used to prepare this Climate
- Coupled ocean-atmosphere model predictions of tropical Pacific SST
-- particularly heavy weighting has been given to the NOAA /NCEP,
Climate Modeling Branch coupled model
- Statistical forecasts of Indian Ocean and Atlantic Ocean sea surface
- The response of Atmospheric global circulation model (GCM) predictions
to the present and predicted SST patterns
- Statistical analyses
- Appropriate Regional Climate Outlook Forum consensus guidance.
Additional sources of information include ACMAD, COLA, CPTEC, CPC/NOAA,
CMC, Department of Natural Resources (Queensland, Australia), NIWA, ECMWF,
Indian Meteorological Department, PAGASA, Bureau of Meteorology, and the
South African Weather Service.