January 1999 Global Climate Report

Strong easterly winds across equatorial Pacific Ocean promoted upwelling of cold water in the eastern half of the Pacific Basin. These conditions, known as La Niña, brought dramatic changes to temperature and precipitation throughout many areas of the world in January. Many locations that received above normal precipitation in January 1998, when El Niño was dominant, were dryer than normal under current conditions. Conversely, other areas that were dry in January 1998 received abundant precipitation in January 1999.

Temperature

Mean monthly temperature anomalies for January (using a base period 1880-1998) are show in the above figure. The combined land and sea surface temperauture anomaly for January 1999, 0.46C, shown in the top time series, remains well above the mean value, but it exhibits a considerable drop from the previous year. The ocean temperature anomaly for 1999, 0.27C , exhibits an even more pronounced drop from the 1998 value, which corresponds to the shift from warm to cold water in the east equatorial Pacific Ocean.

In contrast the land anomaly for January, 0.89C , remained well above the 1880-1998 average temperature. This was 0.02C above last years average temperature but 0.12C less than the highest January temperature recorded in 1932. This suggests that the land surface is retaining much of the warmth gained during the previous El Niño event.

In January 1999, temperatures were warmer throughout most of Canada where the difference reached 8.0C across the northern tier of the country. There was also a large area of warmer temperatures stretching eastward from the Mediterranean through the southern half of Russia into the Far East. The greatest difference occurred over south western Russia where values reached 7.0C.

In contrast, January 1999 brought colder temparatures across a band stretching from Finland through Siberia into Alaska. Some reporting stations near Moscow averaged more than 8.0C colder than they did in 1998. Temperatures were also colder in Eastern Europe and the western Mediterranean.

In January 1999, the sub-tropical jet stream was much weaker than the previous year, which reduced the precipitation over the western third of the U.S. At the same time a ridge dominated southeastern China and Japan, which promoted dry conditions. Colder sea surface temperatures in the equatorial Indian Ocean corresponded with dry conditions along adjacent East Africa.

In 1999 it was wetter in the southwest Pacific as sea surface temperatures rose above normal and the easterly waves brought tropical systems to the area. Most of South America was wetter in 1999 than in 1998, as strong easterlies returned Atlantic moisture to the continent. Although there was one notable exception: north eastern Argentina was exceedingly wet last year as well. The rainy season in North Africa was stronger than normal, and higher elevations received significant snowfall.

Further south in the 30N to 10N latitude band, precipitation amounts were similar to last years average; 12.2 mm versus 12.7 mm recorded in January 1998. But in the equatorial band (10N - 10S) precipitation dramatically increased. Due in large part to the heavy rains in the Southwest Pacific (previously discussed), precipitation in this latitude band was 100 mm (3.9 inches) above the long term mean. This was by far the most precipitation ever recorded in this latitude band. It is 33 mm (1.3 inches) above the previous record anomaly.

Numerous weather related natural disasters occurred in January 1999. In the U.S., a record number of tornadoes (169) occurred- that is about ten times the January climatological norm. A full report on selected global extremes is available at the Climate Watch-January 1999 WWW page