A NWS Doppler radar software algorithm calculates wind direction and speed at various atmospheric levels based on cloud and precipitation movement. The resulting product is called the Velocity Azimuth Display (VAD) Wind Profile (VWP), as shown at left. The x-axis is time in UTC (e.g., 1638 UTC is 1238 PM EDT); the y-axis is thousands of feet altitude (e.g., 5 is 5000 ft). Green color indicates the least potential error in estimated winds. VWP provides an estimate of the vertical wind profile at the radar site.
Vertical wind shear (change in wind speed and/or direction with height) is crucial to potential thunderstorm organization and severity. The greater the shear, the greater the potential for organized severe weather, assuming storm development.
In this image, winds show excellent low-level (surface to 5000 ft) speed and directional shear at 1638 UTC, with slowly increasing winds aloft to 40,000 ft. By 1725 UTC, low level winds had "veered" from south to southwest, while winds continued to increase slowly aloft. The VWP indicates very good winds and wind shear.