Climate Outlook - Rainfall & Temperature

Europe April - September 1998

The IRI Experimental Forecast Division has prepared this Climate Outlook for Europe for April - September 1998. Of relevance in the preparation of this Outlook has been the strong El Niño episode now subsiding in the tropical Pacific, and the expectation that warm El Niño conditions will persist for the next few months. Also relevant to this Outlook are the warm sea-surface temperature (SST) anomalies in the tropical Atlantic Ocean.

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 moderate, but weakening, El Niño conditions in the tropical Pacific through the forecast period.

B) Statistical predictions of the tropical Indian and Atlantic SST's.

C) Global atmospheric circulation model (GCM) predictions of the atmospheric response to the present and predicted sea surface temperature (SST) patterns.

D) Statistical analyses of the observed climate over Europe.

The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by the national meteorological services in Europe. Thus, this product may differ from the official forecasts issued in those areas. This Outlook has been prepared in the time available, using all information that was reasonably accessible. Inclusion of other climate information and guidance requires further arrangements. The IRI is engaged in establishing such collaborative arrangements with the goal of improving its capability to provide the best and most complete global climate guidance. The Climate Outlook is dependent on the quality of the SST predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is considerable spread in coupled model predictions concerning the evolution of SSTs. This spread in predictions is a source of uncertainty in the Outlook provided here, which assumes that tropical Pacific SST's will continue to decline at a modest rate. Also, it is known that Atlantic Ocean SSTs may play some role in modulating rainfall changes over parts of Africa. Thus, the uncertainties in Atlantic Ocean SST values during the forecast period may lead to additional uncertainty over some parts of Europe.

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 Services.

OUTLOOK -

This Outlook covers two seasons: April-June 1998 and July-September 1998. Maps are given showing expected tercile probabilities of precipitation. The maps 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). An additional 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. 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. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category. Otherwise, for example, in the case of Portugal in April-June 1998 (Map A), there is a 40% probability that the rainfall 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 30% chance that the rainfall will be in the driest third of the years. The numbers for each region on 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. Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct.

April-June 1998:

PRECIPITATION

The map is dominated by the following main regions of enhanced probabilities of rainfall anomalies:

P.A) Enhanced probability of above-average rainfall over most of Mediterranean Europe, extending north of the Alps and into Ukraine, Turkey, Armenia, Georgia, Azerbaijan, northern Iran, Turmenistan, Uzbekistan and western Kazakstan.

P.B) Enhanced probability of near-normal rainfall over most of Europe north of 50°N.

TEMPERATURE

The main features of the pattern of probabilities for temperature field are:

T.A) Enhanced probability of above-average temperatures over most of Europe west of about 20°E, excluding the Iberian peninsula.

T.B) Enhanced probability of near-normal temperatures over Spain and Portugal.

July-September 1998:

PRECIPITATION

The main features of this season are as follows:

P.i) Enhanced probability of above-average precipitation over most of Europe west of about 35°E and south of about 50°N.

TEMPERATURE

The main features of the pattern of probabilities for temperature field are:

T.i) Enhanced probability of above-average temperatures over the United Kingdom, northern France and southern Norway.

T.ii) Enhanced probability of above-average temperatures in the extreme south-western part of southern Africa.

T.iii) Enhanced probability of below-average temperatures in southern Spain.

Cutoffs and Max/Min extremes for AMJ and JAS.

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