Climatology of Banded Precipitation over the Contiguous United States

摘要

A climatology of banded-precipitation features over the contiguous United States from 2003 to 2014 is constructed. A band is defined as a precipitation feature with a major axis of 100 km or greater and a ratio of major axis length to minor axis length (hereafter, aspect ratio) of 3: 1 or greater. By applying an automated feature-based detection algorithm to composite radar imagery, a database of 48 916 844 precipitation features is created, of which 7 213 505 (14.8) are bands. This algorithm produces the first climatology of precipitation bands over the contiguous United States. Banded-precipitation occurrence is broadly similar to total precipitation occurrence, with a maximum of 175 h of banded precipitation annually over the Ohio River valley. In the warm season, there is a strong diurnal signature associated with convective storm development for both the precipitation feature area and total area covered by precipitation, but little diurnal signature in aspect ratio. Strong west-east gradients in both precipitation occurrence and banded-precipitation occurrence exist, as areas west of the Rockies receive less frequent precipitation, which is much less likely to be banded. East of the Rockies, precipitation features are banded 30 of the time, versus 10-15 west of the Rockies. Areas downwind of the Great Lakes show prominent late autumn and winter maxima in banded precipitation associated with lake-effect snowbands. Local maxima of banded-precipitation percentage occur in the Dakotas and east of the Colorado Rockies during winter. Although banded-precipitation features compose only 14.8 of all precipitation features, they contribute 21.9 of the annual precipitation occurrence over the contiguous United States.