This category encompasses several phenomena. The particular type of storm that occurs depends on climatic region, temperature, and a die roll. Cross index the appropriate conditions on the table below and roll 1D6 to determine what kind of extreme precipitation occurs.
This kind of activity usually occurs during the first ten minutes of a lightning storm, but on rare occasions (16% chance) it can be a storm in and of itself, lasting from 5-10 (1D6+4) minutes. Hail consists of lumps of ice, typically no more than 1/4 of an inch in diameter, but can be as large as 2 – 3 inches across. When a hailstorm occurs at a temperature of 40 degrees or higher, the hail will melt withing a few minutes of hitting the ground. If the hail activity is followed by a lightning storm, the pellets will have melted by the time the storm ends.
Sleet is frozen or nearly frozen rain, formed when snow falls from a high altitude and passes through a layer of warmer air on its way to the ground. The warmer air melts the snow crystals back into droplets of water, and the water freezes during the remainder of its descent. When the sleet hits the ground, it will coat anything it touches: by the time the storm passes, stationary and inanimate objects may be carrying a coat of ice.
Depending on its intensity, an ice storm will last from 20 minutes (in the case of heavy precipitation) to several hours (as trace precipitation). The longer the storm, the thicker the ice buildup.
A lightning storm, or thunderstorm can occur as a separate phenomenon in and of itself or as the beginning stage of a longer rainstorm. If a lightning storm is indicated for a day on which moderate or light precipitation is supposed to fall, the the storm will occur by itself (and the light to moderate result is disregarded). If a lightning storm is indicated for a day on which heavy or downpour precipitation is supposed to fall, then the storm will occur at the beginning of th4e period of precipitation. A typical lightning storm lasts for about half an hour, during which 3/4 to 1" of rain is dropped and the sky is lit up at frequent intervals by bright flashes of lightning. Roughly half of all thunderstorms occur within two hours either way of sunrise or sunset.
If the normal maximum precipitation for the day in question is moderate this storm will dump 5-10 (1D6+4) inches of snow; if the normal maximum precipitation is heavy, a severe snowstorm will cause 7-12 (1D6+6) inches of accumulation. The snow will come down at the rate of 1 inch per hour until the indicated accumulation is reached. Wind velocity will be very strong at the start of the storm, but will taper off after 1 or 2 hours to a more moderate breeze( 15- 20 mph) at best, as the storm center becomes stalled over the area receiving the precipitation.