NWS Louisville Doppler Radar Spectrum Width

Cold Front Moving Through the Northeast U.S. Monday; Atmospheric River to Impact the Pacific Northwest Midweek

A cold front will cross the Great Lakes and Northeast U.S. through Monday with gusty winds and areas of rain showers. A strong atmospheric river is expected to move into the Pacific Northwest by midweek bringing a threat for moderate to heavy rainfall, gusty winds, and mountain snows for parts of Washington, Oregon, northern California, and the Sierra Nevada. Read More >

NWS Doppler Radar (WSR-88D) Example Products

The image shows a 4-panel display of reflectivity (upper left), storm-relative velocity (upper right), and spectrum width data (bottom 2 panels) from the NWS Louisville radar on April 24, 2010.

Spectrum width (SW) depicts a measure of the variability of the radial velocity estimates due to the presence of wind shear, turbulence, and/or the quality of velocity samples. It is used to estimate turbulence associated with boundaries, thunderstorms, mesocyclones in supercells, mesovortices in convective lines, etc. Low values (gray shades at left) indicate smooth or uniform flow, while high values (red, pink, and white colors) denote turbulent or variable flow.

In this case, a bow echo was moving east over central Kentucky. Velocity (upper right) showed a low-level boundary (red-green interface) with mesovortices (red-green couplets) over southwest Larue County (center of image). Spectrum width clearly identified the boundary location ("S" shaped line), while the mesovortices showed up as small clusters of high SW values (especially lower left panel). SW is another tool available to NWS forecasters to enhance the severe weather warning decision process.