Heavy showers after a front moves through the area and our summer showers, including the very infrequent thundershowers, are the result of that instability. However, the one lifting mechanism that is constant and is available year-round is orographic lifting. The steep terrain of Southeast Alaska forces any onshore flow to rise. 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.