Fred Sanders' adjuration never to accept anything as fact

Six and a Half Unknown Knowns About Cold Fronts

Not all cold fronts slope rearward with height. Many cold fronts are vertical at their leading edges or tilt forward.
Rope clouds are commonly perceived to be the surface position of the front, but sometimes the cloud band may not be related to the surface cold front.
Depending on local effects such as cold-air pooling in valleys, sometimes cold-frontal passages are associated with rising temperatures.
Cold fronts are not necessarily collocated with the wind shift and pressure trough.
Fronts do not align along the axis of dilatation.
Cold fronts are not material surfaces.
Whether cold fronts are density currents remains unresolved.

An invitation to speak at the Fred Sanders Symposium at the 2004 American Meteorological Society (AMS) conference rekindled Dave Schultz's (CIMMS) interest in cold fronts. Fred Sanders' career was being honored for his 50-year influence on our understanding of many areas of atmospheric science. But his most important contribution may have been how he inspired others to take a weather phenomenon that is considered "solved" by the research community and showed that compelling research problems still exist. Cold fronts happened to be one of these phenomena, and Sanders returned to them three different times in his career: "Fronts are a real and important feature of our environment," said Sanders, "and an effort should be made to better understand them." It seemed there was a lot we thought we knew.

For Dave, the invitation was an honor because of what Fred Sanders meant to him and his career. Sanders was Dave's first meteorology professor as a freshman, encouraged him to join the AMS as a student member, and was the Ph.D. advisor to one of Dave's Ph.D. advisors. The invitation also meant an opportunity to get some research projects off the ground that had been on Dave's mind for a while. Preparation for the symposium turned into a two-year, four-paper quest to describe cold front "knowns," "unknowns," and "unknown knowns" (things we don't know we know).

The first paper was Dave's chapter in the Sanders monograph, presenting Sanders' research on cold fronts within the larger context of the attitude of the meteorology community. After the Norwegian cyclone model first discussed the structure of fronts, Sanders remarked, "The practice of frontal analysis of surface data spread virtually everywhere outside the tropics, despite disappointment in cyclone behavior which often deviated substantially from the Norwegian rules." One of these deviations was pre-frontal wind shifts (often seen in Oklahoma as a shift to north winds several hours before the cold frontal passage). Dave wrote two articles on pre-frontal wind shifts for Monthly Weather Review. The fourth article was written with Paul Roebber and will be published in the Sanders monograph. It is a model simulation of the cold front of 17-18 April 1953, which is the case analyzed by Sanders (1955). Dave calls Sanders (1955), "the first, the simplest, and, I would argue, still the best quantitative study of the structure and dynamics of a cold front." "There are so many good publications showing complexities in the structure and dynamics of cold fronts, but I think people sometimes have overly simplistic views of how fronts work," says Dave. His goal was to bring to light excellent research done over the years on fronts, highlight many instances where we were stuck in the past with regard to frontal structures and dynamics, and show we still have a lot to learn about fronts (see box).