An explanation of precipitation types and characteristics.
In the context of weather, precipitation is defined as water in any form - liquid or solid - that falls from the Earth's atmosphere towards the surface of the Earth.
Precipitation is the part of the water cycle that occurs after condensation, a process where water vapor in the atmosphere collects around particulate matter to create clouds and fog. In order for water vapor to condense, such matter must be present to create a "cloud condensation nucleus". This process occurs naturally due to dust and other airborne particles, but can also be triggered by the dispersement of chemical substances from human activity - either unintentionally through pollution or intentionally through direct cloud seeding efforts.
It is important to note that the precipitation variables included in Spire Weather's basic data bundle and Optimized Point API are actually the "liquid equivalent" total precipitation, which includes all frozen types if they were to melt.
Rain is liquid precipitation that falls to the Earth's surface in spherical water droplets.
Rain is one component of the precipitation values reported by Spire Weather's APIs.
Sleet and ice pellets are precipitation types that begin as rain but freeze into a solid before they reach the Earth's surface due to colder temperatures at lower altitudes.
Sleet and ice pellets are both included in the precipitation values reported by Spire Weather's APIs.
Hail is the product of storm clouds which become cold enough for supercooled water droplets to freeze upon impact with particulate matter. Strong updrafts of wind contribute to keeping hailstones aloft in the upper regions of such clouds, where they can continue to grow with additional layers of frozen water. Hailstones vary in size and shape, but they are all collections of layered ice that fall to the Earth as a solid.
Hail is another component of precipitation values reported by Spire Weather's APIs.
Snow, like hail, is a solid form of precipitation. However, the intricate structure of snowflakes is a result of the fact that they are formed by one or more tiny ice crystals rather than relatively thicker layers of frozen water droplets. The different patterns observed in snowflakes are dependent upon factors such as temperature and humidity. Snow generally forms at lower altitudes than hailstones, in environments where the atmosphere between the cloud base and the Earth's surface is cold enough to prevent melting and refreezing processes which would generate sleet instead.
Snow is also included in the precipitation values reported by Spire Weather's APIs.
Virga is precipitation that falls from a cloud but does not ultimately reach the Earth's surface, due to either evaporation of liquid forms or sublimation of solid forms. Virga can vary in its visual appearance, from obvious rain shafts that don't ever touch the ground to seeming extensions of the cloud base itself. It is important for pilots to take heed of virga since it is sometimes indicative of dangerous flying conditions such as downdrafts or microbursts.
Virga is not included in the precipitation values reported by Spire Weather's surface-level data bundles, but the aviation and thunderstorm bundles provide other variables such as overall icing potential which can be critical to ensuring flight safety.
For technical information on how to work with Spire's precipitation values, please see here.