I just became aware of a neat interactive applet that lets you explore how temperature and moisture profiles in the atmosphere affect the type of precipitation you see (thanks to NWS Chicago for the "heads up" on this). A second applet lets you "grow" ice crystals in different parts of a cloud to see what type of crystal is produced. These applets were developed by the Cooperative Institute for Meteorological Satellite Studies at the Space Science Engineering Center, University of Wisconsin, and are part of the Explore the Atmosphere page.
|Screen shot of the Precipitation Type applet.|
- Drag the temperature and wet bulb lines at the first level above the surface so they both read 1.8°C, that is, the air is saturated.
- Drag the wet bulb (yellow) line at the surface to about -7.0°C, and the temperature (green) line to 0.9°C (that's about 33°F).
There are any number of scenarios you can set up. For example, if you separate the temperature and wet bulb at the very highest level, let's say, -10°C temperature and -19°C wet bulb, the cloud will disappear - it's too dry.
What's evident after playing with this enough is that it doesn't take much, a degree to two sometimes, to make a big difference in precipitation type. Add in other factors such as the depth of the warm or cold layers and you can see how forecasting winter precipitation can be very tricky.
|Screen shot of the Grow Snow applet.|
Have fun with these!