Abstract
Spectrum width is a WSR-88D product that has been available to operational forecasters since the radar was deployed. In 2008, super-high-resolution reflectivity, velocity and spectrum width data became available. Six cases exemplifying operational use of spectrum width are presented; five are from after the upgrade. The cases were selected to depict the wide array of uses of spectrum width (SW). In one case, use of SW improved forecaster capability to evaluate the strength of horizontal shear within a bow echo’s mesovortex. One case shows that SW can be extremely helpful in determining location of boundaries, which aids in overall situational awareness. In another case, SW aided forecaster confidence to issue a tornado warning with lead time. If a storm is close to the radar (55 km in this example), SW can be used to clarify the location of the rear flank downdraft, assess where its wind damage may be a threat, and discern subsequent cutoff of the tornado from the warm, moist inflow. Finally, when used in a derecho case, SW helped a forecaster to identify more quickly where wind damage threats were likely.
Highlights
Of the three Doppler radar moments, the second—base velocity spectrum width (SW)—is the least used in detection of severe local storms
Lemon and Parker (1996) discussed SW values associated with deep convergence zone of the Lahoma, OK storm of 17 August 1994
A sounding released from Little Rock, AR at 0000 (Fig. 17) depicted an environment with surface-based CAPE close to 2500 J kg-1 and 0–3 km AGL storm-relative helicity (SRH) of 272 m2 s-2
Summary
Of the three Doppler radar moments, the second—base velocity spectrum width (SW)—is the least used in detection of severe local storms. This could be due to several factors, most importantly a lack of operational studies, which has led to under-training about the moment Lemon and Parker (1996) discussed SW values associated with deep convergence zone of the Lahoma, OK storm of 17 August 1994. Lemon (1998) showed large SW values associated with three-body scatter spike signatures. Lemon (1999) later suggested expanded operational uses, including detection of boundaries, intense updrafts, and estimating the depth of the orographically induced wind shear and turbulence. This paper expands the list of case studies by showing six wide-ranging operational examples of SW usage.
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