Weather Overview

Siberian winters are legendary for their length and low temperatures. Though March comes when the icy grip is starting to relax, the thermometer will still be one of the major elements in selection of an observing site. Over the northeastern portion of the track where cloud cover is lightest (Figure 7), average nighttime temperatures dip below -40° C. This will be a morning eclipse throughout Asia, so temperatures will be closer to the daily low than to the high.

During winter, most of the eclipse track is dominated by the Asiatic anticyclone (high) which typically lies southwest of Lake Baikal, virtually atop the eastern portion of the eclipse path. Air inside this high pressure cell is subsiding and flowing outward, so that persistent westerly and southwesterly winds will dominate the Mongolian and Lake Baikal portions of the eclipse track. Farther to the north, toward the Arctic coast, prevailing winds adopt a more easterly character.

The Siberian high is not a very deep structure, extending only 1 to 2 kilometers above the surface. The westerly surface winds are replaced aloft by a persistent stream of north and northwest winds which pump a continuous supply of Arctic air toward the eclipse track. Low pressure disturbances must force their way around the stubborn high, typically passing south of the Yakutsk area (60° N) on their way to the Sea of Okhotsk. Warm and cold fronts attached to these lows stretch southward toward the eclipse track and bring much of the springtime cloud cover to Mongolia. The cloud is modified by the mountainous terrain which dominates much of the early part of the track.

Over Mongolia, the gnawing cold of the Siberian winter is much subdued, and March begins to see the daytime highs flirting with the freezing point. The anticyclonic influence is characterized by strong surface inversions, which bring ground temperatures that are 10 degrees colder than those a kilometer above. The beginning portions of the eclipse must cross the Altai Mountains of western Mongolia, with peaks rising to 3500 meters (from valleys lying at about 800 meters). The persistent westerly winds approaching the Ulaanbaatar area are thus descending from higher ground and serve to bring a slightly sunnier climate to the capital than might otherwise be the case.

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