Originally Posted by
73qanda
Most definitions I can find on the net have ‘heavy rain’ defined as more than 7.6ml/hr
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Shame that don’t put +RA on the ATIS seeing as many airline ops manuals have specific runway requirements for landing in heavy rain.
ATIS includes rainfall in the last 10 minutes, 1.6 mm in the opening post. I guess you could deduce from the definition of heavy rain (that you found) that 1.6 in 10 mins fits the definition.
Cloud size (rainfall area), wind speed (and gust) and droplet size are other variables that will influence visibility.