Mr. Perriss also offered forecasts beyond 2001.
A wide array of experts at universities and in government essentially agreed that -- despite the recent progress -- any detailed forecast beyond a week should be handled with skepticism.
He wrote in response: At the time, the prediction I made here — that "computer simulations will never produce accurate day-by-day forecasts beyond a limit of two weeks or so" — was surprising, and maybe even controversial.
Dr. Laver, at the federal Climate Prediction Center, said that at the very least, anyone offering daily forecasts beyond a week should indicate that accuracy drops sharply and steadily with time.
"As far as I know, the skill of daily forecasts beyond Day 7 has not been improved enough to warrant the extension out to Day 15," said Dr. Schemmung E. Schemm, a weather and climate modeler at the government's Climate Prediction Center.
The recent experience of North America shows that anomalies can and will occur, not least because man-made climate change has altered the distribution of Arctic air masses, making forecasts beyond five days far more difficult.
That model happened to coincide with the end of the fiscal year, but it's false to suggest, as Lawler does, that the forecast was driven by the fiscal year, and would have miraculously tracked with the Congressional Budget Office's projections over the next four years if only O.M.B. had extended its forecast beyond FY 2003.
Nock is now running it and other tests on hundreds of people — those who have tried to kill themselves, those who have had suicidal thoughts and those who have not — to see how the initial scores differ from one group to another and whether those scores will end up having forecasted, beyond what current methods can, who will try to kill themselves in the future.
Most forecasts beyond 72 hours are pretty iffy.
What this means is that long-term forecasts, beyond the next few hours, are currently of limited reliability.
