Climate Outlook - Rainfall & Temperature

EUROPE January - June 1998

The IRI Climate Forecast Division has prepared this Climate Forecast Outlook for Europe for January - June 1998. Of special relevance in the preparation of this Outlook has been the exceptionally strong El Niņo episode now underway in the tropical Pacific, and the expectation that strong El Niņo conditions will persist through at least the first half of the forecast period. This present El Niņo appears to have peaked in December 1997 with the SST anomalies stronger than the ones during the major event in 1982-83 (at that time the strongest of the century) which was associated with severe climate anomalies around the globe that caused major socio-economic losses in many regions. Europe, although affected, saw only modest impacts due to the 1982-83 El Niņo.

METHODS -

This Outlook was prepared using the following procedures and information:

A) Statistical analyses of the observed historical response of the climate system over Europe during the strongest 12 El Niņo events over the period 1890-1989, and also the strongest 8 El Niņo events since 1950.

B) Coupled ocean-atmosphere model predictions of tropical Pacific sea surface temperatures (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 the slow decline of relatively strong El Niņo conditions, indicating that warm anomalies will persist in the tropical Pacific through the forecast period.

C) Global atmospheric circulation model (GCM) predictions of the atmospheric response to the present and predicted SST patterns in the tropical Pacific (especially) and in other oceans as well. These models have been shown to reproduce important aspects of the climatic response to El Niņo in simulations covering such significant events as the 1982-83 event described above.

The procedures, models and data used to derive this Climate Outlook are somewhat different from those used by the national meteorological services in Europe. Thus, this product may differ from the official forecast 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 for April-June, especially, are dependent on the quality of the SST predictions. For the tropical Pacific, these predictions can be expected to provide useful information. However, there is considerable spread in coupled model predictions concerning the rate at which tropical Pacific SSTs will decline. This spread in predictions is a primary source of uncertainty in the Outlook provided here, which assumes that tropical Pacific SSTs will decline at a modest rate during 1998. Also, the tropical and/or mid-latitude Atlantic SSTs may play some role in modulating rainfall and temperature changes over parts of western Europe. Thus, the uncertainties in Atlantic SST values during the forecast period may lead to some additional errors in predicted precipitation and temperature over the western Europe.

It is also 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; January-March 1998 and April-June 1998. Maps are given showing expected probabilities that the seasonal rainfall will fall into the wettest third of the years, the middle third of the years, or the driest third of the years. Similar maps for 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 (see Map Caption below for further details, cautions and caveats).

January-February-March 1998:

PRECIPITATION

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

P.A) Enhanced probability for below-normal rainfall over much of northern Europe including the northern part of Scandinavia, and extending into northern parts of western and central Russia.

P.B) Enhancement of probabilities for above normal rainfall across central and southern Europe especially within the five degrees width longitude belt centered at around 43N.

"Climate" conditions are expected over north-western Europe, including southern part of Scandinavia

TEMPERATURE:

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

T.A) Enhanced probability for colder temperatures over northern half of Europe especially over Scandinavia.

T.B) Enhanced probability for warmer temperatures over south-most parts of Europe.

"Climate" conditions are expected over the longitudinal belt centered at around 45N.

April-May-June 1998:

PRECIPITATION

The pattern of probabilities somewhat resemble that for January-March. The main modifications are:

P.i) The region of elevated probabilities for below-normal rainfall over northern Europe (see P.A above) is shifted north-westward. Enhanced probability for below-normal rainfall is observed over north-western part of Scandinavia.

P.ii) The region of increased probabilities for heavier than normal rainfall across southern Europe, from western Europe to the Urals (see P.B above), also shifts north-westward, and the probabilities of above-normal rainfall over these areas decrease.

Normal or climatological conditions are expected over most parts of north-western and central Europe.

TEMPERATURE:

The patterns of probabilities are as follows:

T.i) Slightly enhanced probability for colder temperatures over north and central parts of Europe.

T.ii) Enhanced probability for warmer temperatures over south-western Europe.

The probabilities given here are based mainly on the statistical analysis of the historical data. Further confidence is added from the atmospheric GCMs forced with a variety of predicted SST scenarios including persistence, statistical estimates, and dynamical forecasts. These atmospheric GCM climate predictions are in agreement with each other and with the statistical analysis for both the region of enhanced probabilities for below-normal precipitation over north-west Europe and the region of the enhanced probability for above-normal rainfall over southern Europe. Similarly, GCM climate predictions are in agreement with the statistical analysis for the region of enhanced probabilities for colder temperatures over northern Europe.

Map Caption

The numbers for each region indicate the probabilities of rainfall in each of the three categories, below-, near-, and above-normal. Above-normal rainfall is defined as within the wettest third of recorded precipitation totals in each region for the given season; below-normal rainfall is defined as within the driest third of rainfall totals; near-normal is the third centered around the climatological median. The top number indicates the probability of rainfall occurring in the above-normal category, the middle number is for near-normal, and the bottom for below-normal. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category. Otherwise, for example, in the case of southern France in January-March 1998 (Map A), there is a 50% 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 20% chance that the rainfall will be in the driest third of the years. Similarly, the numbers for each region on temperature maps indicate the probabilities of temperature anomalies 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.

Cutoffs and Max/Min extremes for JFM and AMJ.