ForecastWatch.com July Customer Newsletter
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Climate and persistence forecasts are unskilled weather forecasts used to measure forecast skill. But climate and persistence forecasts can be used in their own right to discover interesting things. For example, what does temperature forecast error mean for persistence forecasts? It's really just a measure of the variability of temperature for a given location. The lower the average absolute error and standard deviation of error, the less variable the temperature is. This is because a persistence forecast just takes today's high and low temperatures and projects them out to tomorrow and beyond. If tomorrow's temperature is close to today's, then there will be lower error for the persistence forecast. Conversely, if the temperature is not close to today's, then the error for the persistence forecast will be higher.
Knowing that, a ranking of locations is possible, with those having the highest rank being cities where tomorrow is most like today. Looking at high temperature error for persistence forecasts for one- to five-days out in 2004, the top five cities would be Kailua-Kona, Hawaii; Honolulu, Hawaii; Key West, Florida; Kahului, Hawaii; and Pompano Beach, Florida. Conversely, the locations with the most high temperature variability day-to-day are Phillip, South Dakota; Rapid City, South Dakota; Chadron, Nebraska; Pierre, South Dakota; and Winner, South Dakota. I know to where I'll be planning my next vacation!
June accuracy data has been audited and loaded for viewing. In general, Midwest and Northeast high temperatures were under-forecast while the rest of the country on average was over-forecast. High temperature forecast bias remained positive at 0.07 degrees. One- to five-day out high temperature RMS error continues to improve as we enter the summer months. May's overall RMS average for all providers was 5.23 degrees in May, dropping to 4.58 degrees in June. To view the June data, as well as year-to-date and historical numbers, log on to http://www.forecastwatch.com
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