ROCHESTER, N.Y. – This is a story with too much of a good thing. On one hand, parts of the Pacific Northwest do need additional rainfall. On the other, the incoming rainfall is expected to be far more than the region can reasonably handle.
A powerful atmospheric river which is a long, concentrated plume of moisture extending across the Pacific. This is already beginning to affect the region. This system is the first in a series of storms expected to deliver extremely heavy rainfall over the next several days. Forecasts call for four to ten inches of rain, which is an amount that would normally fall over two to three months in Western New York. With this much water arriving in such a short time, it is no surprise that flood watches have been issued across Washington, Oregon, and portions of Idaho and Montana.
What is an atmospheric river? It is a narrow, fast-moving band of moisture flowing through the sky. These “rivers” often form at altitudes between 15,000 and 20,000 feet and can span 200 to 300 miles in width. As the moisture moves inland and encounters the region’s mountains, the air is forced upward, enhancing rainfall totals. While snow is likely at higher elevations, the main concern with this event is the excessive rainfall.
The combination of intense rain and steep terrain will increase the risk of flooding and mudslides and damage to infrastructure. Rivers and streams may rise quickly, and saturated soils could lead to landslides in vulnerable areas.
The Atmospheric River Scale, developed by the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography in coordination with the National Weather Service, categorizes events from AR 1 (weak or mostly beneficial) to AR 5 (exceptional and largely hazardous). Early forecasts place this system in the AR 4 to AR 5 range, indicating a strong, long-lasting, and potentially dangerous event.
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