The IRI has prepared this experimental Climate Outlook for North America
for January 2001 - June 2001. Of relevance in the
preparation of this Outlook has been the near-average, but slightly cooler than normal,
sea-surface temperatures
(SSTs)
in the central equatorial Pacific Ocean.
Near neutral equatorial Pacific SST conditions are in effect for both seasons of the forecast,
January-February-March 2001 and
April-May-June 2001.
The SSTs of the tropical Indian Ocean were assumed to remain normal.
Tropical Atlantic SSTs are near-normal during the first forecast season and are expected
to become slightly cooler than normal during the second season.
METHODS -
This Outlook was prepared using the following procedures and information:
A) Coupled ocean-atmosphere model predictions of tropical Pacific SST covering
the forecast period. Particularly heavy weighting has been given to predictions
from the coupled model operated by the NOAA National Centers for Environmental
Prediction, Climate Modeling Branch. This model suggests a continuation of
slightly cool but near-average conditions during the first forecast season.
The forecast for near-neutral conditions is consistent with some, but not all,
numerical and statistical forecasts of central and eastern Pacific SSTs.
B) Forecasts of the tropical Atlantic and the Indian ocean using statistical
models developed by the CPTEC and IRI, respectively.
C) Global atmospheric general circulation model (GCM) predictions of the
atmospheric response to the present and predicted sea-surface temperature patterns.
D) Other sources of information include
Center for Ocean-Land-Atmosphere Studies;
Goddard Space Flight Center
.
The procedures, models, and data used to derive this Climate Outlook may be somewhat
different from those used by the national meteorological services in the region.
Thus, this product may differ from the official forecasts issued in
those areas. The Climate Outlook for January - June 2001 is dependent on the accuracy
of the SST predictions. For the tropical Pacific, these predictions can be expected
to provide useful information, but there is some uncertainty concerning the evolution
of SSTs. Spread (variation) in global SST predictions is a source of uncertainty in
the Outlook provided here.
Note that even if perfectly accurate SST forecasts were possible, there would
still be uncertainty in the climate forecast due to chaotic internal variability
of the atmosphere. These uncertainties are reflected in the probabilities given
in the forecast.
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, and variations within the 3-month period
should also be expected. For further information concerning this and other
guidance products, users are strongly advised to contact their
National Meteorological Services.
OUTLOOK -
This Outlook covers two seasons: January - March 2001 and April - June 2001. Maps are
given showing tercile probabilities of precipitation and temperature. The maps for
precipitation indicate the probabilities that the seasonal precipitation will fall
into the wettest third of the years (top number), the middle third of the years
(middle number), or the driest third of the years (bottom number). A qualitative
outlook of climatology ("C") indicates that there is no basis for favoring any
particular category. Areas that are marked by "D" represent regions experiencing
their dry season (less than 15% of annual precipitation) and for which less than
5 cm of precipitation typically occurs over the season. Otherwise, for example,
in the case of region IX in January - March 2001
(Map A), there is a 20% probability that the precipitation will be in the wettest
third of the years, a 30% chance it will be in the near-normal third
of the years, and a 50% chance that the precipitation will be in the driest third of the years.
An
additional precipitation map
is provided for the first season indicating probabilities for extreme precipitation
anomalies. Extremes are defined as anomalies that fall within the top and bottom 15th
percentile of the observed records. A priori, there is a 15% probability of being
within the extremely wet category, and a 15% probability of being within the extremely
dry category, leaving a 70% probability that the precipitation will not be extreme. The
maps indicate areas of increased risk of extreme precipitation totals. Three levels
of increased risk are defined:
slightly enhanced risk, enhanced risk, and greatly enhanced risk.
For slightly enhanced risk, there is a 25-40% probability that precipitation will
be within the indicated extreme, i.e. wet or dry. This represents an approximate doubling
of the climatological risk. For enhanced risk, there is a 40-50% probability that
precipitation will be within the indicated extreme. This represents an approximate
tripling of the climatological risk. For greatly enhanced risk, the probability that
precipitation will be within the indicated extreme exceeds 50%, i.e. the indicated
extreme is the most likely outcome.
Maps of temperature show expected probabilities that the seasonal temperatures will
fall into the warmest third of the years, the middle third of the years, or the
coldest third of the years
(Map A). The numbers for each region on the temperature
maps indicate the probabilities of temperatures to fall in each of the three categories,
above-, near-, and below-normal.
Boundaries between sub-regions should be considered as transition zones,
and their location considered to be only qualitatively correct.
January - March 2001:
PRECIPITATION
The following regions of enhanced probabilities of precipitation anomalies are indicated:
Region I) slightly enhanced probabilities of above-normal precipitation over the
Hawaiian Islands;
Region II) greatly enhanced probabilities of below-normal precipitation over
the southeastern United States.
TEMPERATURE
The following regions of enhanced probabilities of temperature anomalies are indicated:
Region I) slightly enhanced probabilities of below-normal temperatures over much
of western and central Canada;
Region II) large region of enhanced probabilities of above-normal temperatures over
northern Mexico, Baja California, the southern tier of the United States extending
up through the eastern states of the U.S. and including the Great Lakes region and
southeastern Canada;
Region III) slightly enhanced probabilities of near-normal to above-normal temperatures
the Caribbean Islands including the Bahamas, Cuba, Jamaica, Haiti, the Dominican Republic,
and Puerto Rico.
April - June 2001:
PRECIPITATION
The following regions of enhanced probabilities of precipitation anomalies are indicated:
Region II) slightly enhanced probabilities of above-normal precipitation over
Baja California, northern Mexico, and southwestern Texas in the U.S.;
Region III) slightly enhanced probabilities of below-normal precipitation over
the Caribbean Islands including the Bahamas, Cuba, Jamaica, Haiti, the Dominican Republic,
Puerto Rico, and the Lesser Antilles.
TEMPERATURE
The following regions of enhanced probabilities of temperature anomalies are indicated:
Region I) slightly enhanced probabilities of above-normal temperatures over
western Alaska;
Region II) enhanced probabilities of above-normal temperatures over a large region
covering southwestern Canada, western and central United States and northwestern Mexico;
Region III) a small region within region II for greatly enhanced probabilities of
above-normal temperatures over a large region
over Washington state in the U.S.;
Region IV) a small region within region II for greatly enhanced probabilities of
above-normal temperatures over southern California and Arizona in the U.S.;
Region V) enhanced probabilities of above-normal temperatures over the
eastern United States extending up through eastern Quebec and Newfoundland
in Canada;
Region VI) a small region within region V of greatly enhanced probabilities of
above-normal temperatures over Nova Scotia, Canada.
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