April 5, 2004: When trying to look at yesterdays NAM blipmaps, I found that the “previous day” link displayed a map with todays date! What is happening?
DrJack sez: This is evidence that the processing program has not run normally! At the program’s daily startup, it must “age” all the existing forecast files such that existing “current day” forecasts become “previous day” forecasts – new “current day” files will then be written as the processing proceeds. And for the NAM model additional forecast days are also aged, e.g. “current+1” forecasts become “current” forecasts, etc (though all but the “previous day” files will get overwritten as the processing proceeds and newer forecasts are produced). However, on occasion “stuff happens” and the program can get started twice in a single day – at the second start the aging will overwrite what should be a “previous day” file with a “current day” file and this is what occurred in the case you describe. If there happened to be multiple starts then the “previous day” file could even have a date which is ahead of the true current day!. Of course, this is another reason why the date at the top of a
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