August 20, 2011 - The Pacific Northwest

The Pacific Northwest

Despite a reputation for cloudy skies, the Pacific Northwest was cloud-free on August 16, 2011, allowing the Moderate Resolution Imaging Spectroradiometer MODIS) aboard NASAís Terra satellite to capture a remarkably clear view of the region. The clear skies extend from British Columbia, Canada to southern California, and from the Pacific Coast as far east as Montana, Utah and Arizona. Thick clouds cover the Strait of Juan de Fuca, covering the border between Canada and the United States. The clear skies allow a striking view of the contrast between vegetation-covered, dark green areas in the west with sparsely vegetation land east of the mountains.

The climate and ecology of the Pacific Northwest are largely shaped by the interactions that occur between seasonally varying atmospheric circulation patterns (weather patterns) and the regionís mountain ranges. There are two ranges of mountains that lie parallel to the coast and capture the moist air as it moves inland from the Pacific Ocean. In Washington, the Olympic Mountains sit near the coast; in Oregon it is the Coastal Range. To the east of these mountains lie the taller Cascade Mountains, which stretch north to south across both states. It is the western slope of the Cascade Range which causes the most significant orographic lifting and precipitation, leaving very little moisture to pass across the highest ridges.

The Pacific storm track brings rain to the region primarily in October to March, causing nearly two-thirds of the annual precipitation to fall during this time. From late spring until early fall, high pressure to the west can keep the Northwest much drier, giving rise to more clear days.

Other interesting features in this image include the Great Salt Lake in northern Utah, the green Rocky Mountains in Montana and Idaho, and Pyramid Lake in northwestern Nevada. Several red hotspots dot this image, most likely indicating active fires. In Idaho, smoke rises from a complex of several fires, which were most likely ignited by lightning on August 14.

Image Facts
Satellite: Terra
Date Acquired: 8/16/2011
Resolutions: 1km ( B), 500m ( B), 250m ( B)
Bands Used: 1,4,3
Image Credit: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC