These charts show forecasts that include the estimated range of possibilities that may occur.  This type of forecast is more useful for decision-making and risk analysis than a single-valued ("deterministic") forecast.

    In each forecast chart, the darker shading shows the range of outcomes that is 50% likely to occur.  This means that there is a 50-50 chance that the actual outcome will fall within the range.  It is equally probable that the outcome will be outside the range.

    The lighter shading in each chart shows the range of outcomes that is 90% likely to occur.  On average, the actual outcome will fall within this range on 9 out of 10 occasions.  On 1 out of 10 occasions, the outcome will fall outside the 90% range.

    The range of forecast possibilities is calculated from a historical sequence of forecasts and the corresponding observed outcomes.  Thus although the forecast uncertainty may seem very large, it accurately reflects the true uncertainty that is inherent in the forecast.