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How to Interpret Rain Percentage

Unexpected rainfall can cause significant inconvenience. Though weather can be extremely unpredictable, correctly interpreting forecasts offers the best opportunity to plan in advance. A 40 percent chance of rain could be misunderstood as a prediction for rain over 40 percent of the area, or even that rain will occur for that same percentage of the day. Meteorologists calculate probability of precipitation by multiplying their confidence that rain will occur by the percentage of the area likely to be affected. This number is then converted to a percentage, according to the National Weather Service.

Instructions

- 1
  Locate the probability of precipitation described by local news media. This figure is often described as chance of rainfall. The number is denoted as a percentage.
- 2
  Consider the equation used to derive this information. If the meteorologist is 60 percent confident that rain will occur over 100 percent of the area on a given day, he multiplies .6 by 1, with a result of .6 or 60 percent. Local residents will be informed that chances of rainfall on that day are 60 percent.
- 3
  Interpret the result to plan around the likelihood of precipitation. A 60 percent chance of rain means a 40 percent chance of staying dry. At any given point in the region, rain will fall six times out of 10.

Nature