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- finds a warm (>0C) layer at or above the lowest model level (~10m) and precipitation falls from higher levels. Freezing rain is diagnosed.
- does not find a warm (>0C) layer. Either:
- the lowest model level (~10m) has temperature >0C. No warm layer is identified the algorithm diagnoses freezing drizzle. IFS does not capture the freezing level (i.e. the base of the warm layer) because that lies below the lowest model level (~10m). Freezing rain would be diagnosed in precipitation falls from above; freezing drizzle diagnosed if super-cooled very moist layer exists in lowest layers.
This is a fairly a rare occurrence, inspect the temperature and humidity structure of lowest layers to determine the correct type of precipitation.
- there is no warm (>0C) layer at all, and all temperatures at and above the lowest model level (~10m) are <0C and precipitation falls from higher levels. Snow, ice pellets etc are normally diagnosed.
- the lowest model level (~10m) has temperature >0C. No warm layer is identified the algorithm diagnoses freezing drizzle. IFS does not capture the freezing level (i.e. the base of the warm layer) because that lies below the lowest model level (~10m). Freezing rain would be diagnosed in precipitation falls from above; freezing drizzle diagnosed if super-cooled very moist layer exists in lowest layers.
The surface temperature should, of course, be below 0C.
In precipitation type presentations a precipitation rate threshold (e.g. 0.1 mm/h).
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