Northern Hemisphere
In the Northern Hemisphere, important circulation features during June-August 1994 (JJA) included below-normal heights throughout the polar region and the high latitudes of the North Atlantic, and above-normal heights over western Canada, the western United States, Europe, and northeastern China/ southeastern Siberia (Fig. 3.7, top). Significant surface features during the season included a continuation of abnormally warm and dry conditions over western North America and above-normal precipitation over eastern North America. Abnormally warm temperatures also continued over large portions of Europe and over eastern Asia/ northern China (Fig. 3.8).
Over western North America, the pattern of above-normal heights during JJA brought a continuation of abnormally warm and dry conditions to the western United States, western Canada, and southern Alaska. Farther east, an amplified trough and above-normal precipitation dominated eastern North America during the season, with the mid-Atlantic and northeastern United States experiencing a third consecutive season of above-normal precipitation.
Over the North Atlantic, the overall pattern of below-normal heights at high latitudes and above-normal heights in the middle latitudes continued for the third consecutive season. In Europe, this circulation was accompanied by above-normal surface temperatures, with anomalies averaging 1-2C above normal throughout the continent in each month. This anomalous warmth was particularly acute during July and the first two weeks of August, when one of the hottest spells ever to afflict central Europe became established (see section 4). Substantially below-normal precipitation was also observed over large portions of eastern Europe and western Russia. These conditions brought an end to the pattern of above-normal precipitation which had prevailed in these regions for the past two seasons.
Farther east, negative height anomalies persisted over the Caspian Sea sector for the third consecutive season, while above-normal heights were observed over eastern Asia. Accompanying this circulation, surface temperatures averaged 1-2C below normal in the region near the Caspian Sea, and abnormally warm conditions also covered northern China and southeastern Siberia.
Southern Hemisphere
In the Southern Hemisphere, major surface features during JJA 1994 included a continuation of abnormally warm conditions over southwestern Australia, and the development of severe drought conditions throughout southeastern and southern Australia (Fig. 3.8). The primary circulation feature during the season was a continuation of above-normal heights (Fig. 3.7, bottom) and above-normal surface pressure over Australia. Accompanying this circulation, the climatological long-wave trough normally located near 110E was generally weaker than normal and was displaced well west (near 80-100E) of normal.
These conditions were associated with a poleward shift and weakening of the storm track between the east Indian Ocean (equatorward of 40S) and the Great Australian Bight. These factors, in combination with an overall weaker magnitude of midlatitude frontal systems, resulted in well-below-normal rainfall over large areas of southern and eastern Australia. This situation was exacerbated by a general lack of significant tropical moisture incursions over the continent, which normally contribute substantially to rainfall in inland areas. Overall, above-normal surface temperatures (2-3C) were observed throughout western Australia during JJA, and severe precipitation deficits, along with severe drought conditions, were recorded throughout virtually all of southeastern and extreme southern Australia (see section 4).
Seasonal Summaries: September - November
Seasonal Summaries: March - May
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