Tyranny of the Plebiscite

March 25th, 2005

Posted by: Roger Pielke, Jr.

From AP Wednesday, “The National Weather Service (news – web sites) will stick with the familiar “skinny black line” on maps projecting the paths of hurricanes, despite concerns that the practice fails to convey the uncertainty in forecasting and can give the public a false sense of security. Scott Kiser, the tropical cyclone program manager with the weather service, made the announcement Wednesday before the opening of the annual National Hurricane Conference. The agency had looked at three options: keeping the skinny line, using a series of large colored dots to represent the projected path, or using large circles that would encompass the projected path and the margin for error. Kiser said the decision to stick with the line was made after the weather service sought opinions from the public, the news media and emergency service workers, receiving 971 e-mailed responses. He said 63 percent favored keeping the skinny line. He summed up the response as: “Show us your best forecast — we’re smart enough to figure it out.””

From a 1999 paper of mine looking at the role of NWS forecasts in the flood disaster in the Red River of the North, “Because the NWS issued its river stage predictions in terms of a single number, local decision makers did not have the information necessary to evaluate the risk they faced under alternative courses of action. Effectively, this put the NWS in a position it should not find itself — of implicitly deciding what level of risk a local community should face (i.e., in this case a river stage of 49 feet). This can lead to misjudged risk assessment, overconfidence in forecasts, and ultimately poor decisions about how to fight the flood. A more appropriate process would have provided local decision makers and the public with probabilities of different levels of inundation, and coupled with other relevant information, the community and particular individuals could have decided how they ought to respond. Some local decision makers in the region want this responsibility, but others do not. Many of the decision makers interviewed expressed the following sentiment: “We don’t want changes, just give us an accurate forecast that the NWS will stand behind.” The local resistance to change is understandable: the effect of providing probabilistic information would result in a shift in responsibility (and accountability) for decision making on the question of “what river height do we prepare for?” from the NWS to the local decision makers. For many local decision makers this added responsibility is not desired. But more generally, few would argue that such decisions belong at the local level and should not be made by the NWS.”

Sometimes, science and technology decisions ought not to be made simply through surveys of the public or decision makers. The NWS has learned this lesson but apparently has not taken it to heart.

One Response to “Tyranny of the Plebiscite”

  1. Harold Brooks Says:

    That’s a terribly disappointing decision. For a number of years, I’ve hoped that they’d make a number of changes to their forecast products and this would have been the minimum. I’d also like them to stop using the historical forecast errors as the only input into the probability ellipses and actually allow for case-to-case differences in the confidence. There’s a list of other changes I’d make, but adding the historical error statistics to the single line seemed like a minimal change, especially in this graphical age. There’s no reason they can’t put a line on the probabilities to indicate the best guess track. I like the last line in the article: “Encouraging people to pay less attention to the skinny line is one of themes of the conference.” I guess it isn’t a theme of the NWS.