<P> The Pacific Northwest has a oceanic climate . The climate is wet and cool in autumn, winter, and spring, and stable and drier in the summer months, especially July and August . On average, the wettest month is typically November or December; the driest, July . In the summer months, average highs in cities like Seattle and Portland are from 70 to 79 ° F (21 to 26 ° C) with lows from 50 to 59 ° F (10 to 15 ° C), while in winter daily highs are from 40 to 49 ° F (4 to 9 ° C) and overnight lows from 30 to 39 ° F (− 1 to 4 ° C). (citation needed) </P> <P> In winter, the Pacific Northwest (especially coastal districts and other areas west, i.e. on the prevailing windward side, of the Olympic and Cascade mountain ranges), experiences a mostly overcast, wet and cool climate, but without severe cold like that found in the interior northern U.S. (i.e. Minnesota / North Dakota). At lower elevations, winter precipitation falls mostly as rain . However, snow does occur even at the lowest elevations, primarily when Pacific moisture interacts with cold air intruding into the Pacific Northwest from western Canada (i.e. Alberta and interior British Columbia). In Seattle, WA and Portland, OR, winter - season snowfall varies greatly from one winter season to the next; in Seattle, the average winter - season snowfall is about 7 inches . In January 1950 (also the coldest January and winter month in Seattle history), Seattle received an unprecedented monthly snowfall of over 57 inches . Summers in the Pacific Northwest are generally cool, especially along the coastline . The Great Basin and Columbia Plateau (the Intermontane Plateaus) are arid or semiarid regions, with high summer temperatures in the 90s to occasionally over 100 at lower elevations (e.g. at Boise, ID), with annual precipitation averaging less than 15 inches (380 mm) as a result of the rain shadow of the Sierra Nevada and Cascades. (citation needed). Both coastal and interior areas of Oregon and Washington, and southern Idaho, have a wet - winter, dry - summer precipitation pattern, but traveling eastward into Montana and Wyoming, this transitions progressively toward relatively drier winters and a May and eventually June precipitation maximum, the latter characteristic of the Northern Plains and much of the upper Midwest (i.e. both Dakotas, Nebraska, Iowa and Minnesota). </P> <P> The characteristics of precipitation across the United States differ 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). </P> <P> 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 is 13: 1, meaning 13 inches (330 mm) of snow melts down to 1 inch (25 mm) of water . The El Niño - Southern Oscillation affects the precipitation distribution, by altering rainfall patterns across the West, Midwest, the Southeast, and throughout the tropics . </P>

In which latitudinal region does the united states fall