CPC: Climate Assessment for 1994 -
Seasonal Summaries: December - February

Northern Hemisphere

In the Northern Hemisphere large circulation, surface temperature, and precipitation anomalies were evident during December-February 1993/94 (DJF). Over the Pacific/ North America sector, a pattern of above-normal heights at 500 mb was observed over the central North Pacific and the Bering Sea (Fig. 3.1, top). This pattern was associated with warmer than normal conditions (2-4C above normal) over much of Alaska and western North America and with drier than normal conditions over much of southern Alaska and the Pacific Northwest (Fig. 3.2).

Farther east large negative height anomalies and much colder-than-normal conditions covered central and eastern Canada, the northern Plains states, the upper Midwest, and the northeastern United States. Additionally, above-normal precipitation was observed in a broad band extending from the lower Mississippi Valley northeastward to southern New England. Accompanying this precipitation, many areas in Pennsylvania, New York and southern/central New England experienced their snowiest winter on record. These anomalously cold and wet conditions were particularly prominent over eastern North America between 23 December-22 January (Fig. 3.3, top). During this 30-day period, temperatures averaged 6-8C below normal over much of Canada east of the Rockies, and 4-6C below normal throughout the Northern Plains, the Midwest, and the Northeast. Minimum temperatures during this period dropped to -40C over large portions of Minnesota and eastern North Dakota, and to -25 to -35C across the north-central and northeastern United States (Fig. 3.3, bottom). Additionally, minimum temperatures reached -10 to -15C from northern New Mexico eastward to northern Georgia and the Carolinas, and freezing temperatures extended southward to central Florida.

Over the North Atlantic Ocean and Eurasia, negative 500-mb height anomalies were observed at high latitudes, with positive anomalies observed in the middle latitudes. This circulation pattern reflected a pronounced positive phase of the North Atlantic Oscillation. Accompanying this circulation, below-normal temperatures were observed over Scandinavia, while abnormally warm and wet conditions dominated much of Europe. Surface temperatures averaged 2-4C above normal throughout western and central Europe during the season, and averaged more than 4C above normal over eastern Europe.

Precipitation totals during December and January averaged 50-150 mm above normal throughout northern and western Europe (Fig. 3.4, bottom), with much of the region experiencing near-record precipitation totals. In excess of 250 mm of precipitation was recorded throughout western and northern France, the Benelux countries, England, Scotland, and Ireland during the season, and totals exceeding 400 mm were observed over eastern Austria and southwestern Germany (Fig. 3.4, top). During one extreme rainfall event in early January, parts of northern Italy, Switzerland, and southern France received daily amounts exceeding 150 mm, with 243 mm falling in St. Leger de Ventoux in southern France on 6 January.

Over Asia, below-normal heights at 500 mb were observed over much of central Siberia and central Russia, while above-normal heights were observed over eastern China and southeastern Asia. These features were associated with below-normal and above-normal surface temperatures in these regions, respectively, during the season (Fig. 3.2).

Southern Hemisphere

The Southern Hemisphere circulation was characterized by below-normal heights at 500 mb throughout the polar region, and by above-normal heights in the high latitude extratropics (Fig. 3.1, bottom). These conditions reflected a pronounced amplification of the Antarctic circumpolar vortex and an overall poleward shift of the midlatitude jet stream.

In South Africa, much above-normal precipitation was observed in the south and west during DJF for the first time in more than two years (Fig. 3.2, bottom). East of Africa, Madagascar was hit by two hurricanes and one tropical cyclone during the season (landfall dates of 13 January, 1 February and 17 February). The worst of these events was hurricane Geraldo (1 February), which had sustained winds of 57 m/s and which took nearly 200 lives. In Australia, significantly above-normal precipitation totals were observed over large portions of the southern and central sectors during DJF (Fig. 3.2, bottom). This season was followed by below-normal precipitation and severe drought over large portions of Australia during the rest of 1994 (see section 4).

Seasonal Summaries: March - May
Oceanic And Atmospheric Anomalies Related To ENSO:
The 1994 Pacific Warm Episode

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