Painting images: The art and science of monthly climate prediction
The prediction of monthly climate patterns is both an art and a science. The first monthly climate projections were started about a century ago, and were based on the anticipation of temperature, rainfall and air pressure based on climatological norms. Monthly climate guidance goes beyond the limits of weather forecasting models, which numerically predict daily weather patterns. Therefore any projections that are made, consist of painting pictures of general patterns for the entire month, rather than specific daily detail. Since the beginnings, our understanding of the behaviour of the climate system has dramatically improved to allow tuning of monthly patterns beyond the annual cycle of monthly climatological averages. Those factors that are recognised as being important on monthly time scales for New Zealand are long-waves in the atmosphere, sea surface temperatures in the Pacific and Indian Oceans, the role of the Quasi-biennial Oscillation, the phase of the Southern Oscillation, and the presence of stratospheric sulphate aerosols from volcanoes. All these, and other presently unknown factors perturb the climate on a monthly basis. The impact that these have on monthly climate, and how they are used in 'painting pictures' to produce monthly climate projections for New Zealand show a skill that is better than expected from climatology and persistence.