Weather can play an important role in an adventure. The following section describes weather common on most habitable worlds. Additional rules for cold and heat dangers can be found in Environmental Rules.

Rain and Snow

Bad weather frequently slows or halts travel and makes it virtually impossible to navigate from one spot to another. Torrential downpours and blizzards obscure vision as effectively as dense fog. Most precipitation is rain, but in cold conditions it can manifest as snow, sleet, or hail. If the temperature drops from above freezing to 32° F or below, it might produce ice.

Rain

Rain reduces visibility ranges by half, resulting in a -4 penalty to Perception checks. It has the same effect on flames and Perception checks as severe wind (see below).

Snow

Falling snow has the same effects on visibility and skill checks as rain. Snow-covered squares count as difficult terrain. A day of snowfall leaves 1d6 inches of snow on the ground.

Heavy Snow

Heavy snow has the same effects as normal snowfall but also restricts visibility as fog does (see Fog below). A day of heavy snow leaves 1d4 feet of snow on the ground. Snow at this depth counts as difficult terrain, and it costs 4 squares of movement to enter a square covered with heavy snow. Heavy snow accompanied by strong or severe winds might result in snowdrifts 1d4 x 5 feet deep, especially in and around objects big enough to deflect the wind—a reinforced wall or a large force field, for instance. There's a 10% chance that a heavy snowfall is accompanied by lightning (see Thunderstorm).

Other Precipitation

There are other forms of precipitation, such as freezing rain, hail, and sleet. These generally function as rain when falling, but at the GM's discretion, they may also have effects on movement similar to snow once they accumulate on the ground.

Storms

The combined effects of precipitation (or dust) and wind that accompany storms reduce visibility ranges by three-quarters, imposing a -8 penalty to Perception checks. Storms make aiming with ranged weapons difficult, imposing a -2 penalty to attack rolls, and archaic ranged weapons can't be fired at all. Storms automatically extinguish unprotected flames. Storms commonly appear in three types: dust, snow, or thunder.

Dust Storm

These desert storms differ from other storms in that they have no precipitation. Instead, a dust storm blows fine grains of sand that obscure vision, smother unprotected flames, and can even choke protected flames (50% chance). Most dust storms are accompanied by severe winds and leave behind a deposit of 1d6 inches of sand. There is a 10% chance for a dust storm to be accompanied by windstorm-magnitude winds (see Table 11-6: Wind Effect); this greater dust storm deals 1d3 nonlethal damage each round to anyone caught out in the open without shelter and also poses a choking hazard (see Suffocation and Drowning). A greater dust storm leaves 2d3-1 feet of fine sand in its wake.

Snowstorm

In addition to the wind and precipitation common to other types of storms, a snowstorm leaves 1d6 inches of snow on the ground afterward.

Thunderstorm

In addition to wind and precipitation, a thunderstorm is accompanied by lightning that can pose a hazard to characters who don't have proper shelter (especially those in metal armor). As a rule of thumb, assume one bolt per minute for a 1-hour period at the center of the storm (GM rolls to hit). Each bolt deals between 4d8 and 10d8 electricity damage. One in 10 thunderstorms is accompanied by a tornado.

Powerful Storms

Very high winds and torrential precipitation reduce visibility to zero and can make Perception checks and ranged weapon attacks difficult. Powerful storms are divided into the following types.

• Blizzard: The combination of high winds, heavy snow (typically 1d4 feet), and extreme cold make blizzards deadly for those unprepared for them.
• Hurricane: In addition to very high winds and heavy rain, hurricanes are accompanied by floods. Most adventuring activity is extremely difficult under such conditions.
• Tornado: With incredibly high winds, tornadoes can severely injure and kill creatures pulled into their funnels.
• Windstorm: While accompanied by little or no precipitation, windstorms can cause considerable damage simply through the force of their winds (see Winds below).

Fog

Whether in the form of a low-lying cloud or a mist rising from the ground, fog obscures all sight beyond 5 feet, including darkvision. Creatures 5 feet away have concealment (20% miss chance).

Winds

Wind can create a stinging spray of dust, sand, or water, fan a large fire, rock an atmospheric transport midflight, and blow gases or vapors away. If powerful enough, it can even interfere with some ranged attacks and knock characters down. Below are the most common wind forces seen on habitable worlds.

Light Wind

A gentle breeze, having little or no game effect.

Moderate Wind

A steady wind often extinguishing small, unprotected flames.

Strong Wind

Gusts that automatically put out any unprotected flames. Such gusts impose a –2 penalty to nonenergy ranged weapon attack rolls.

Severe Wind

Nonenergy ranged weapon attack rolls take a –4 penalty.

Windstorm

Powerful enough to bring down branches, if not whole trees. Nonenergy ranged weapon attack rolls take a –4 penalty, while attacks with archaic ranged weapons are impossible. Perception checks that rely on sound take a –8 penalty due to the howling of the wind. Small characters might be knocked down.

Hurricane-Force Wind

Non-energy ranged weapon attack rolls take a –8 penalty, and archaic ranged weapon attacks are impossible. Perception checks based on sound are impossible: all characters can hear is the roaring of the wind. Hurricane-force winds often fell trees. Most characters are knocked down due to the force of these winds.

Tornado

All flames are extinguished. All nonenergy ranged weapon attacks are impossible, as are sound-based Perception checks. A creature in close proximity to a tornado that fails a DC 15 Strength check is sucked toward the tornado. All creatures that come into contact with the actual funnel cloud are picked up and whirled around for 1d10 rounds, taking 6d6 bludgeoning damage per round, before being violently expelled in a random direction (falling damage, described below, might apply). While a tornado's rotational speed can be as great as 300 mph, the funnel itself moves forward at an average of 30 mph (roughly 250 feet per round). A tornado uproots trees, destroys buildings, and causes similar forms of major destruction.

Table 11-6: Wind Effects

* This applies only to nonenergy ranged weapons. Larger weapons, such as starship weapons, ignore this penalty.