Dan Keyser graciously provided guidance and comments that benefited this paper. Mike Branick, Todd Hutchinson, Jay Shafer, and three anonymous reviewers provided comments on an earlier version of this manuscript. Equation (4), the alternate expression for normalized frontogenesis, was noted by one of the anonymous reviewers. NCDC provided, and Grant Goodge helped decode, the 1-min ASOS data in Fig. 3. Thanks to Todd Hutchinson for providing the dates of the events from Hutchinson and Bluestein (1998). Composite maps in Figs. 10–12 were provided by NOAA–CIRES Climate Diagnostics Center, Boulder Colorado, from their Web site (http://www.cdc.noaa.gov). The Storm Prediction Center provided access to their archives of NMC maps on microfilm. Funding was provided by NOAA/OAR/NSSL under NOAA–OU Cooperative Agreement NA17RJ1227. This paper evolved from my contribution to the Fred Sanders Symposium at the 2004 American Meterological Society Annual Meeting (manuscript submitted to Amer. Meteor. Soc.) and my review of prefrontal troughs and wind shifts (Schultz 2004, manuscript submitted to Mon. Wea. Rev.) to coincide with that symposium. I would like to thank Fred Sanders for his unknowing, but very influential, contribution to this research.
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