The weather can be unpredictable in Europe and during the Viking era it was probably the same. The weather conditions are for one part dealt with in the four seasons and for the other part by a die roll. A number of different weather conditions are represented on the D12 die. You have 2x sunshine, 2x clouded, 2x light rainfall, 2x normal rainfall, 2x heavy rainfall, 1x thunderstorm and 1x fog. Many other real weather conditions such as hail have been left out or merged with others as the variation would be too great to manage in game. The result is that the weather die is pretty evenly balanced with good and bad weather effects.
Certain symbols on the weather die D12 are interpreted as rainfall or snowfall, this is determined by the active season. Light rainfall becomes light snowfall, normal rainfall becomes normal snowfall, heavy rainfall becomes heavy snowfall and thunderstorm becomes blizzard. The rest of the symbols on the D12 die stay the same. Snowfall and blizzard have a different effect then their rainfall and thunderstorm counterparts.
The D12 weather die is used in several actions such as travel, explore, camp, work and colonize. The outcome of the roll can have an effect on the action itself, some weather effects stay in effect for multiple actions. **An optional rule is to roll a weather die for actions such as investigate, combat and hide & seek too.
Traveling as an action let's you throw a weather die to see if the weather is good or bad. The travel distance will depend on the outcome. This is different for sea and land travel. For sea travel the weather can also do damage to the ship.
Only in severe weather conditions an investigation will be hindered, but overall it has no effect.
Exploration can be severely hindered by the weather. Storms and fog will lower the number of exploration points per action.
Hide & seek
Searching and hiding in bad weather has an effect on the search and hide skill. A fog will increase the hide value and lower the search value. Storms and rain will lower the search value.
The weather has an effect when fighting a siege. If there is a storm the attacker will lower it's attack by 1. Fog will lower the defender's defense by 1 and increases the attack of the attackers by 1.
When a group is camping the weather conditions can have a great impact on the daily affairs. Gathering food and supplies are effected, fog will lower the yield of gathering, storm will increase food and supply consumption by 1, snow increases food and supply consumption by 1 or 2.
Agricultural production is dependent on seasons and weather. Crops and fiber crops are greatly dependent on weather conditions, storms will lower productivity by 1 or 2.
Colonize or Build
The weather will slow down the building of houses and other facilities. The duration of the action will increase with 1 or 2 turns depending on the type of building or upgrade.
Next to the seasons and D12 die there are also weather card events which can trigger a prolonged weather condition. These events can take up multiple turns, the special cards always take precedent over the regular weather effects. The weather event cards are placed on the time track which has 4 spots. The card is put on the corresponding duration spot which is indicated on the card. When a turn ends all the cards move one spot down the time track to a spot with lower number. The cards on spot 1 will be discarded others will stay in effect for more turns. Multiple cards can be placed on the same spot, but there cannot be more then 1 weather card on the whole track. If a second weather card is added to the time track, the other one has to be discarded.