Project Status: Inactive
8 Apr 2009: Weather of any kind has exited the project area. Thanks for the reports! Winter has passed, so it's time to find hail for HaSDEx.
What do the Precipitation types Mean?
On the observation reporting form, you will see the following categories for precipitation type:
- None
- Rain
- Hail
- Freezing Rain
- Drizzle
- Freezing Drizzle
- Snow
- Ice Pellets/Sleet
- Graupel/Snow Grains
Except for None, each category has very technical definitions, but for our purposes, we can keep this simple.
Liquid Precipitation:
Rain differs from drizzle only in the size of the droplets. If you can see individual drops falling (or hear them at night), it's rain. If it's very fine and the individual droplets can't be seen easily (or heard at night) it's drizzle.
Freezing Precipitation:
Freezing precipitation (freezing rain and freezing drizzle) may not always be easy to detect. Obviously, the air temperature must be below freezing for freezing precipitation and that's almost always sufficient. To be sure, look for ice forming on shrubs or tree limbs. Looking for ice on the ground isn't a good strategy, because the ground is almost always warmer than the air and is one of the last places to accumulate ice.
Frozen precipitation:
Snow is, well, snow. That's an easy one. You can read more about identifying the different types of snowflakes in the Snowflake Identification Manual.
Hail comes exclusively from thunderstorms. Hail in winter is rare, but especially in winter when thunderstorms occur, it's always a possibility. In winter, the temperature within the thunderstorm is cooler overall, allowing hail to be formed at lower altitudes. Because the temperature below the thunderstorm is also cooler than in spring or summer, even small hail is likely to survive to reach the ground.
Ice pellets/sleet looks like little ice BBs. A few are nearly perfect spheres, but most are hemispheres. They have the clear/translucent character of ice.
Graupel/snow grains are like bits of frost you might scrape off of a freezer or, alternatively, tiny bits of Styrofoam. They are white and sometimes shaped like tiny Apollo capsules. Graupel particles tend to be very light, fall more slowly than ice pellets, and can be easily crushed under finger pressure. They're literally grains of snow. We don't see graupel/snow grains here often so if you do see it, you're getting a real treat.
If you have any questions, feel free to contact Dr. Kim Elmore by email at Kim.Elmore@noaa.gov or telephone at (405) 325-6295.
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