The Fairweather Range is the steepest rise from tidewater anywhere in the world. The elevation rises from sea level to 15,000 feet in only a dozen miles. Steep terrain abounds, at lesser heights, throughout Southeast. Precipitation over this steep terrain, mostly in the form of snow, is the source of the Juneau Icefield, as well as several of the largest glaciers in North America. During weak onshore flow, these mountain barriers are the primary lifting mechanism.
Any onshore flow is likely to produce precipitation in the Panhandle.
Much of our rainfall occurs at a relatively high atmospheric pressure. This is often due to high pressure building over the eastern Gulf of Alaska, which gives an onshore component to the wind. In general, high pressure building from the south through west means wet weather for Southeast Alaska. This is the opposite of the continental climate of much of the Lower 48 states, where high pressure usually means a drying, clearing trend. In wet years Juneau has more than 250 days of precipitation.