Northern Hemisphere
In the Northern Hemisphere, the primary circulation features during the September- November 1994 (SON) season included below-normal heights throughout the polar region and western North America, and above normal heights over the high latitudes of the North Pacific and eastern Canada (Fig. 3.9, top). Major surface features during the season included a continuation of abnormally warm conditions throughout Europe and China (Fig. 3.10, top). Anomalously warm conditions were also observed over much of eastern Canada during the season. In the United States, above-normal precipitation was observed over large portions of the Northwest, while drier than normal conditions covered much of the eastern part of the country (Fig. 3.10).
The circulation over North America was characterized by below-normal heights in the west and above-normal heights over Hudson Bay. This circulation was associated with below- normal surface temperatures throughout Alaska and the northwestern United States, and with above-normal temperatures throughout eastern Canada and the northeastern United States. Additionally, above-normal precipitation covered large portions of the west-central and northwestern United States, while much of the northeastern United States and eastern Canada experienced below-normal precipitation. These overall circulation, temperature and precipitation patterns are opposite to those observed throughout North America during the past three seasons.
Over the North Atlantic and Eurasia, above-normal heights were observed at high latitudes of the North Atlantic and the Caspian Sea during SON. This circulation pattern was again associated with above-normal surface temperatures (1-2C) across much of Europe, southwestern Russia, and the Middle East. These conditions were particularly acute over central and northwestern Europe during November (see section 4). Above-normal precipitation was also recorded throughout western Europe, Scandinavia and the eastern Mediterranean Sea during SON in conjunction with two major flood events. The first event occurred in the beginning of November, when extreme rainfall inundated northern Italy and southern France (Mount Aiguel, France recorded 411 mm of precipitation in 60 hours). The second event occurred during the latter half of November in the Middle East, where many regions recorded rainfall totals in excess of 400% of their normal monthly mean. During this event, higher elevations in Turkey also received significant snowfall and experienced blizzard conditions.
Over eastern Asia, above-normal temperatures (2-3C above normal) again covered much of northeastern China and eastern Siberia during SON. During October and November, this warmth brought abnormally low areal snow cover extent to large portions of eastern Mongolia and Manchuria, with large regions recording virtually no snow cover during the period (Fig. 3.11). Climatologically, large portions of this region average 15-25 days of snow cover during October and November. For 1994 as a whole, abnormally warm conditions dominated this region in all seasons. This warmth was associated with an extraordinarily persistent pattern of above- normal heights at 500 mb in the vicinity of China and southeastern Siberia, along with an apparent northeastward shift of the entrance region of the Pacific jet stream.
Southern Hemisphere
In the Southern Hemisphere, the circulation during SON was marked by below-normal heights at 500 mb over large portions of the middle latitudes, and by a continuation of above-normal heights and pressure over southwestern Australia (Fig. 3.9, bottom).
The major surface features during the season were a continuation of abnormally warm conditions over southwestern Australia, along with a continuation of below-normal precipitation and severe drought conditions over much of southeastern and southern Australia (Fig. 3.10). Queensland and South Australia recorded precipitation totals in the lowest 10% of the historical record during the season. These conditions were associated with an anomalously strong ridge at upper levels over the southwest and with a continuation of above-normal pressure throughout the country. These circulation, temperature, and rainfall anomalies have dominated the continent for three consecutive seasons, during which the southeastern and extreme southern regions have recorded one of their most severe droughts of the century (see section 4). During November, several good rainfall episodes brought much-needed, but very short-term, relief to southwestern Queensland and to northern and central New South Wales. However, by the end of the year, severe drought had redeveloped in these regions.
Regional Climate Summaries: Southern Africa
Seasonal Summaries: June - August
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