Weather influences in Alaska

Alaska weather is influenced the year round by storms that occur in the North Pacific Ocean. These storms follow various favored paths which are determined by upper level winds often referred to as the jet stream or the long wave pattern in the atmosphere.

The usual progression of these storms is to form and intensify just east of the low pressure trough along the east coast of Asia, then along a path from lower Kamchatka to the Aleutians and into the Gulf of Alaska. Some storms cross the Aleutians and move northward through the Bering Sea and into the Arctic. Storms in the Gulf of Alaska either dissipate there or move easterly across southern Alaska into Canada. This storm track is farther north in summer than in winter. Also, winter storms are more intense.

A second major influence on Alaska's weather is Arctic air masses which form and intensify over Alaska, Northern Canada, or Siberia. These air masses show up as large high pressure areas that sometimes persist for weeks at a time over Interior Alaska. A well-developed cold air mass will sometimes cross the mountains between Yukon Territory and Southeast Alaska. More often though, the primary effect of this persistent high pressure area is limited to mainland Alaska west of the 141-degree boundary between Canada and Alaska. The high pressure area forms only in winter.

There is a large amount of variability is Alaska's weather from one year to the next. The primary cause of the variability is a shift in the path of the jet stream. When the amplitude of the long waves which determine the path of the jet stream becomes large, Alaska is likely to have a warm, wet winter and a cool, wet summer. Cold winters and warm summers are more likely to occur when the storm track along the jet stream is well south of the state. Then the primary influence on the climate is the net gain or loss of heat from the surface. In summer, 24 hours of daylight and lots of solar radiation make for mild conditions with few clouds. However, in winter there is a new heat loss which produces extremely low temperatures which may persist for weeks at a time.