Posted December 8, 2007, 5:20 PM.

Official forecasts call for snow levels of 3,000 feet or lower tonight, but some inland temperatures, particularly in the Menifee, Perris and San Jacinto Valleys, may be near or at freezing in the morning.

Much of the Western Riverside County valleys are between 1,000 and 2,000 feet elevation above sea level.

In addition, there is a chance of thunderstorms, which have a convective effect, bringing colder air down to lower elevations. Hail, grauple or ultimately snow can be caused by thunderstorms this time of year in Southern California. One of the most recent inland valley snowstorms, in the Temecula, Menifee and San Jacinto Valleys on November 21st, 2004. was the product of a thunderstorm and convection.

The National Weather Service forecasts have also warned of waterspout and tornado activity.

Note that just because conditions are similar to those that have led to snowfall in the past do not necessarily mean that it will happen this time.

The last inland snowfall was on January 12th, 2007. Snow that day was reported in Perris, Lake Elsinore, Sun City, Menifee, Hemet and Riverside, as well as Mira Loma and the Banning/Beaumont pass area. The major cause of that event was a cold storm.

Snowfall in the valleys is notoriously hard to predict. The November 21st, 2004 snowfall was a Sunday morning surprise, although "inside slider" storms like it had produced similar events in the distant past.

Sometimes grauple is mistaken for snow. Grauple, unlike snowflakes, is a form of freezing rain, and it characterized by soft ice pellets. Hail is characteristically hard ice pellets. Some of the January 12th, 2007 snow was mixed with grauple.