of a given area [in Alaska]. Lower elevations in interior Alaska, such as the Yukon Flats and the Tanana Valley experience extreme cold in the winter as well as high summertime temperatures." Hawaii Hawaii has 11 different climate zones, influenced by altitude and topographical effect on wind and rainfall. These include tropical at sea level, arid, semi-arid, temperate, and alpine at the highest elevations. Snow sometimes occurs in high mountain areas. Caribbean territories Puerto Rico has different climatic zones, all tropical. The northeastern part of the territory is very wet, with a tropical rainforest climate (Köppen Af). This supports rainforests like El Yunque. The southern part is drier, mostly a savanna climate (Köppen Aw) with small locations on the southern coast dry enough to have a hot-semi arid climate (Koppen BSh). The U.S. Virgin Islands have a tropical savanna climate, with warm, dry winters, and rainy summers (Köppen Aw), typical of the Caribbean. The wet season is from May to October. In 2015, the Wall Street Journal reported that U.S. territories such as Puerto Rico are the areas of the U.S. most vulnerable to climate change. Pacific territories Guam and the Northern Mariana Islands both have a trade-wind tropical rainforest climate (Köppen Af). The dry season is from January to May, and the wet season from July to November. American Samoa is south of the equator, and therefore its wet/dry seasons are reversed. The wet season is from December–March, and the dry season is from April–September. Rainmaker Mountain on Tutuila traps trade-wind rainclouds, leading to very high rainfall and a tropical rainforest climate (Köppen Af). Precipitation Precipitation (whether by annual amount, annual distribution or characteristic[s]) varies significantly across the United States and its possessions. Late summer and fall extratropical cyclones bring a majority of the precipitation which falls across western, southern, and southeast Alaska annually. During the fall, winter, and spring, Pacific storm systems bring most of Hawaii and the western United States much of their precipitation. Most of Florida has a subtropical monsoon rainfall pattern (wet summer and dry winter). In the central and upper eastern United States, precipitation is evenly distributed throughout the year, although summer rainfall increases as one moves southeastward. Lake-effect snows add to precipitation potential downwind of the Great Lakes, as well as Great Salt Lake and the Finger Lakes during the cold season. The average snow to liquid ratio across the contiguous United States