Definition
A sensor component on an automated weather station (such as ASOS) that detects whether precipitation is occurring and identifies its type — for example, distinguishing rain from snow — so that the correct precipitation indicator is reported in the METAR.
Plain English
A part of an automated weather station that senses when something is falling from the sky and works out whether it is rain, snow, or another type of precipitation, so it can be reported correctly.
Context Anchor
Seen in METAR remarks, especially when interpreting AO1 and AO2 automated station codes.
Derivation
‘Discriminator’ comes from the Latin discriminare, meaning ‘to separate’ or ‘to distinguish between things.’ Here it tells one type of precipitation apart from another — it discriminates between rain and snow, not between people.
Why Pilots Care
Accurate precipitation type alerts pilots to icing hazards and runway contamination that affect takeoff and landing decisions.
Intuition Check
Do not read discriminator as a person making a judgment. Here it means a sensor feature that separates one precipitation type from another.
Example Sentence 1
Because the station was not equipped with a precipitation discriminator, the METAR noted unknown precipitation rather than identifying it as rain or snow.
Example Sentence 2
Before departure the pilot reviewed the precipitation discriminator output showing freezing drizzle at the destination.