The accuracy of the DRYDAY® Planning Weather Forecast system will vary throughout the country, depending upon how often it usually rains/snows in a particular month, at the location you have in mind.

We recently did a thorough day-by-day verification for five years in a row in Northern California (Sacramento and north) for the forecast DRY periods (DRYDAYS).   The system was 88% accurate in forecasting specific days expected to be dry.  Assuming that some critics would stress the fact that during the months of July and August (N. CA) one does not expect much rainfall, we removed all the months of July and August, and the system still performed at 84%

One must remember that the system is specifically designed to forecast DRY periods, not rain/snow periods.  The RISKY (black) and TRANSITIONAL (gray)days are simply weak spots in the month.  The weather forecast says, “IF IT’S GOING TO RAIN IN THE MONTH, EXPECT MOST (not ALL) OF THE RAIN TO LAND ON RISKY DAYS”.  Granted, the height of the risky days does suggest more chance of rainfall during the higher ones, but still it is not an aggressive weather forecast for rain or snow.

Other areas, that usually have 20-25 days of rain/snow in a month, will have very few DRYDAY® days forecast, but those that are forecast become more important.  Those areas like Seattle, Washington and Indianapolis, Indiana will score lower due to the percentage of regularly wet days.

If you see a large number of RISKY days in a group on the weather forecast chart, you know that the “gate is open” for a storm to come through.  The question is, “is there a storm out there ready to come through”?