Meteorologists who work in the energy commodities market continue to investigate ways to enhance predictions of seasonal temperature anomalies using oceanic/atmospheric indices. This study examines the relationship of three climate indices - ENSO (El Niño/Southern Oscillation), PNA (Pacific North American) and NAO (North Atlantic Oscillation) - to heating degree day (HDD) totals accumulated in 11 cities in the Midwest and northeastern United States, to determine which, if any, has predictive power. The data covers the 48-year period between 1951/52 and 1998/99, and focuses on two periods either side of 1 January (i.e. the winter months of October-December and January-April). The index most strongly related to the HDD anomalies during both winter periods was NAO. NAO values were negative for cold (above-average HDD) anomalies occurring prior to and after 1 January, while the NAO values were generally positive during warm (below-average HDD) anomalies. During cold anomalies, the PNA values were generally positive in the three months before 1 January and negative afterwards, indicating that different atmospheric teleconnection patterns cause similar temperature anomalies in these regions. The relationship between the equatorial Pacific sea-surface temperatures (SST) data and temperature anomalies was the weakest. Confidence in these relationships increased when the extreme HDD anomaly years were examined. These results indicated that the relationships of climate indices to HDD anomalies exist and that these would be useful in developing and improving seasonal predictions for business applications.

A cold air outbreak occurred in the third week of April 1999 in southern Brazil. A synoptic study of this rare event is undertaken. A surface high pressure cell in the Pacific Ocean off the coast of Chile slowly built up and moved eastward on 14 April. It started crossing the Andes, acquiring the characteristic shape of a bean on 15th, and separated into two cells later in the day. The cell on the lee side of the mountains moved gradually northwards over central South America affecting northern Argentina, Paraguay, Uruguay, Bolivia and southern Brazil. The temperature fell 15°C in the state of Mato Grosso (about 15°S). In southern Brazil temperatures below freezing were registered in some places on the 17th and 18th and frost occurred in many states. There was snowfall in the uplands of Santa Catarina on the 17th, and such an early snow had not been recorded for 30 years. Baroclinic synoptic wave intensification followed by surface low development in association with a cut-off low formation in the middle and upper troposphere were responsible for strong surface southerlies over Argentina on the 16th and 17th. Cold air advection by the southerlies in the eastern sector of the high-pressure centre was responsible for the northward projection of the high pressure cell east of the Andes. The whole event was well predicted by the Centro de Previsão de Tempo e Estudos Climáticos/Instituto Nacional de Pesquisas Espaciais (CPTEC/INPE) operational global and regional models with lead times of 120 and 60 hours respectively