IRI NET ASSESSMENT FORECAST
In early January 1999 the IRI
Experimental Forecast Division prepared a Climate Outlook for January
to March 1999. The Precipitation and Temperature Probabilities presented
in this Outlook are based on predictions of the continued evolution of
cooler than average conditions in the eastern and central equatorial Pacific
Ocean (La Niña), and the persistence of warmer than average conditions
in the western equatorial Pacific. The sea surface temperatures of
the central and western tropical Indian Ocean have been cooling from their
record high temperatures, and this trend is expected to continue. It has
been assumed that the northern and tropical Atlantic Ocean will remain
warmer than normal, and that sea surface temperatures in the South Atlantic
will increase during the forecast period.
The Outlook for January to March and April to June 1999 can also be found
at http://iri.columbia.edu/climate/forecast/net_asmt. Maps are given showing 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" indicates equal probabilities
in each class i.e.; there is no basis for favoring the forecast of any
particular category. Areas marked "D" experience a pronounced dry season
during the forecast period, typically receiving less than 15% of their
annual precipitation total during this three-month period. Boundaries between
sub-regions should be considered transition zones, and their location considered
to be only qualitatively correct.
Jan-Mar 1999 Precipitation Probabilities
following procedures and information were used to prepare this Climate
Outlook: 1) Coupled ocean-atmosphere model predictions of tropical Pacific
SST Particularly heavy weighting has been given to the NOAA /NCEP, Climate
Modeling Branch coupled model which suggests continuation of moderate La
Niña conditions, slowly decaying during the forecast period with
the persistence of strong positive sea surface temperature anomalies near
Indonesia, 2) statistical forecasts of Indian Ocean and Atlantic Ocean
sea surface temperature, 3) Atmospheric global circulation model (GCM)
predictions response to the present and predicted SST patterns, 4) Statistical
analyses, 5) Appropriate Regional Climate Outlook Forum consensus guidance.
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 Climate Outlook dependent on the quality
of the SST predictions. For the tropical Pacific, these predictions can
be expected to provide useful information some uncertainty in coupled model
predictions concerning the detailed evolution of SSTs. This spread in predictions
is a primary source of uncertainty in the Outlook provided here.
Also, it is known that Indian and Atlantic Ocean SSTs play some role
in modulating precipitation and temperature patterns. Thus, the uncertainties
in Indian and Atlantic Ocean SST values during the forecast period lead
to additional uncertainty over some parts of the world.
It is stressed that 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
The Outlook for January to March can also be found at http://iri.columbia.edu/climate/forecast/net_asmt/.
The temperature map show expected probabilities that the seasonal temperatures
will fall into the warmest third of the years
(top number), the middle third of the years,
or the coldest third of the years (bottom
number). A qualitative outlook of climatology "C" 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.
Jan-Mar 1999 Temperature Probabilities
|Sources of information
include ACMAD, Caribbean Meteorological Institute, CPTEC, CPC/NOAA, Department
of Primary Industries (Queensland, Australia), ECMWF, Indian Meteorological
Department and the South African Weather Service.