365 Days of Climate Awareness 130 – State of the Climate, North America and Europe, 1999

1999 US Climate Data

Global CO₂ concentration, 367.8 ppm, +2.1 over 1998

Average temperature: 55.5, +1.7 over 20^th century mean, 15^th warmest 1894-2021

Average precipitation: 26.74”, 0.85” less than 20^th century mean (37^th driest 1894-2021

12 named storms: 8 became hurricanes, 5 intense (≥3 Saffir-Simpson) (20^th c. aves: 10-5-2)

1351 tornadoes, below the 20^th century average of 1383

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1999 was a year of persistent, moderately strong La Niña conditions. Central America and the Caribbean were rainier than usual in the second half of the year, and September especially featured intense hurricane activity. As is common, the active North Atlantic hurricane season was balanced by a comparatively inactive northeast Pacific storm season. This Pacific-Atlantic dipole is a function of large-scale wind patterns. Wind shear—changes in wind speed and direction as you move up through the atmosphere—diminishes hurricane activity. The Atlantic and Pacific tend to oppose each other. In years, like 1999, when there is little wind shear in the Atlantic, there is much more in the Pacific, and vice versa.

1999 US regional average temperatures.  Larger version plus context

The Pacific northwest and down the coast to California received intense precipitation in the winter of 1998-1999. The American southwest also experienced wet monsoonal conditions, as is typical after a La Niña winter. La Niña usually results in reduced mountain snowfall in the southern Rockies. This leads to rapid warming of the land in late spring and a stronger monsoonal circulation.

1999 US regional precipitation.  Larger version plus context

29 US states experienced serious drought, particularly the northeast, and central region (upper Midwest down to Texas). Midwestern crops suffered badly, but the drought was replaced in the northeast by extremely rainy weather in the latter half of the year.

In winter 1999 Europe experienced a series of severe wind storms, with wind speeds in excess of 120 mph (category 3 Saffir-Simpson) across Denmark, Germany, France and Switzerland. These winds were associated with a positive NAO phase, with higher than average air pressure in the Azores and lower than average air pressure over Greenland. Early 1999 winter snowfall in the Alps and eastern Europe was well above average, but throughout most of the year, Europe had above-normal temperature.

Tomorrow: 1999 state of the world climate.

Be brave, and be well.