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A new software upgrade has been installed at the Duluth WSR-88D radar that will enable the radar to obtain low-level scans more frequently in severe weather events. Previously, the WSR-88D scanned the atmosphere at progressively higher angles to create a 3D profile of a storm. These scans would begin at 0.5° above the horizon (the lowest angle possible) and end at a maximum angle of 19.5 degrees. These scans form what is known as a Volume Coverage Pattern, or VCP. This maximum angle can vary depending on the distance the storms are from the radar. Last year, a feature called AVSET (Automatic Volume Scan Elevation Termination) was installed that allows the radar to terminate a VCP early (at a lower tilt) if the radar beam is overshooting the pertinent weather features.

Why is this Important?

When it comes to severe weather, frequent low-level radar scans are crucial to observe the development of tornadoes, which can form in a matter of seconds. With this latest upgrade, a new feature called SAILS (Supplemental Adaptive Intra-Volume Lowâ��Level Scan) will enable the radar to insert an additional 0.5° scan in the middle of a VCP. Thus, SAILS allows the forecasters to observe rapidly changing weather phenomenon with a greater degree of precision and issue more timely severe weather warnings and statements. Currently, the WSR-88D radar completes its lowest scan in 3 to 4.5 minutes (during severe weather), depending on the range of the storms from the radar (AVSET). With SAILS, the radar will now perform this low-level scan every 1.8 to 2.5 minutes, giving us low-level data almost twice as fast as before. SAILS is only available in the two severe weather VCPs, 12 and 212.

See the illustrations below for more details.

Scan pattern without SAILS

Bottom half SAILS scan

SAILS low-level scan

SAILS top-half scanning strategy

(Images courtesy of NWS Des Moines)


Other New Features

This upgrade will also bring several new enhancements in addition to SAILS. One new addition will be a radial noise filter, which will greatly reduce the "spikes" seen on the radar image at sunrise and sunset (see example from the Minneapolis radar below). Forecasters will also have additional options for "uncovering" storms that are moving through the velocity data "Purple Haze" or range folding. One new option enables the radar software to automatically determine the best settings for viewing velocity data for the three strongest storms in the radar's coverage area. This upgrade also includes an adjustment to the old manual mode, which allows the forecasters to "manually" uncover the relevant storms in certain VCPs (211, 212, and 221). With the previous radar software updates, those VCPs required automatic settings for viewing velocity data.

Regional radar mosaic demonstrating the absence of the MPX sunset spike

A "sun spike" removed from the Minneapolis radar while radars at Sioux Falls and Duluth (which had not been upgraded yet) still contain these spikes.
(Image courtesy of Minneapolis NWS)

The NWS Warning Decision Training Branch has a webpage dedicated to this software update, including training videos, available for anyone interested. You can visit the site at

NWS Des Moines provided content for this story.