NOAA/National Severe Storms Laboratory

Weckworth and Wilson

Hypothesis (Weckworth and Wilson) on thunderstorm initiation due to small-scale wave interactions with boundary-layer convergence zones

Tammy Weckwerth and Jim Wilson on November 14, 1997 at 17:19:37:

One cause for the periodicity and timing of thunderstorm initiation along boundary layer convergence zones is waves that can be bserved by an FMCW radar (wavelength <10 km) propagating atop the convective boundary layer.


Balaji and Clark (1988) simulated waves atop horizontal convective rolls which then acted to influence convection initiation along the rolls. Mahoney (1988) observed colliding boundaries and showed an undulating behavior in convection that appeared to be attributed to buoyancy oscillations with a wavelength of 2.5 km. Weckwerth and Wakimoto (1992) found that waves with a 3-km wavelength atop a cold-air outflow boundary organized convective cells generated by the gust front. When the wave motions do not exhibit linear cloud features and are therefore invisible in satellite imagery, then it has been difficult to observe real-time wave characteristics. The study of this hypothesis will use an FM-CW radar which has the ability to observe such wave features.


Balaji, V., and T.L. Clark, 1988: Scale selection in locally forced convective fields and the initiation of deep cumulus. J. Atmos. Sci., 45, 3188-3211.

Mahoney, W.P., 1988: Gust front characteristics and the kinematics associated with interacting thunderstorm outflows. Mon. Wea. Rev., 116, 1474-1491.

Weckwerth, T.M., and R.M. Wakimoto, 1992: The initiation and organization of convective cells atop a cold-air outflow boundary. Mon. Wea. Rev., 120, 2169-2187.


We would use WSR-88Ds, DOWs and ELDORA to determine the location of convergence zones. We require a scanning FMCW radar to identify the existence, wavelength, orientation and amplitude of waves propagating atop the boundary layer, as well as to determine the timing of their arrival and areas of intersections with the convergence zone. Rapid scan satellite imagery would also be useful in monitoring wave motions if there are associated cloud bands propagating toward the observational network. If the time of arrival of wave trains can be determined in advance, then mobile CLASS soundings would be launched in the pre-wave and post-wave environments to examine the variability in potential for deep moist convection, as well as to identify the layers in which the conditions are optimal for wave propagation. During wave existence within the dual-Doppler lobe, we would like soundings launched every ~60 min to monitor the variations in stability within the wave layers. The mobile surface mesonet would be useful to trace surface pressure perturbations associated with wave passages. We would then use dual-Doppler from the DOWs and/or ELDORA to identify hot spots of enhanced vertical velocities along BL convergence zones. Additionally, the radar reflectivity fields would confirm the development of deep convection at those hot spots. Systems to measure water vapor (e.g., vertical pointing DIAL, scanning DIAL, airborne DIAL, and/or a mobile radiometer) would be useful to determine if the intersection regions coincide with local maxima in moisture. Aircraft data would provide in situ validation of both the along-line vertical velocities and moisture distribution.

This hypothesis is refuted if FMCW-observed waves do not aid in thunderstorm initiation along convergence zones in a potentially unstable atmosphere.

The following appear in order; discussion points may directly refer to one or more comments preceeding it.


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