From Hearts of Iron 4 Wiki
Jump to navigation Jump to search
See also: Terrain

A dynamic counterpart to terrain, weather can affect movement and combat of all types of units. It should be noted provinces do not always have weather, and some provinces have no temperature modifers.


Night gives the following effects:

  • -50% land attack
  • -20% air detection
  • -25% naval hit chance
  • Carrier aircraft cannot fly
  • -50% bombing targeting
  • +10% naval retreat speed
  • -90% close air support damage

Weather types[edit]

Weather can have an impact on the whole state or on single provinces.

State level[edit]

Condition Organization Regain Positioning Naval Detection Naval Hit Chance Naval Speed Naval Retreat Speed Naval Strike Carrier Traffic Air Detection Air Accidents Chance Air Mission Efficiency Ground Bombing Targeting
Rain.pngRain −5% −10% −5% −5% +5% −20% −10% +10% −10%
Storm.pngStorm −20% −10% −20% −20% −10% +10% -40% −80% −20% +30% −30% −50%
Snow.pngSnow −5% -10% −15% −5% −5% +5% −30% −15% +10% −10%
Blizzard.pngBlizzard −30% -20% −30% −10% −10% +15% -40% −100% −30% +30% −30% −70%
Sandstorm.pngSandstorm −50% -90% −90% +60% −50% −100%

Carrier Traffic -100% means that no planes from a carrier can fly.

Province level[edit]


Condition Heat Attrition Winter Attrition Division Attack Organization Regain Entrenchment speed Division speed Fleet speed while retreating Supply consumption Lower Bound in Degrees Upper Bound in Degrees
Extremely cold.pngExtremely cold +20% −50% −10% −60% -25% +10% -100 -25
Very cold.pngVery cold +10% -40% -5% −30% -25% +10% -25 -15
Very hot.pngVery hot +10% -5% 27 32
Extremely hot.pngExtremely hot +20% -10% −10% +50% 32 100

Note: Attrition from weather only applies if controller is at war.

While winter attrition can be reduced by appointing the armies to a commander with a Winter SpecialistWinter Specialist trait, there is no corresponding trait to reduce heat attrition. Commanders gain the Winter SpecialistWinter Specialist trait by fighting for a longer time in cold weather.

Flag of South Africa South Africa has a unique focus Desert Equipment reducing heat attrition.

Ground conditions[edit]

Condition Attrition Divisions speed Division Attack Division Defence Dig in Speed Organization Regain Naval Retreat Speed
Deep snow −25% −30% −5% +10%
Snow −10% −10%
Mud +70% −50% −40%
Flooding -50% +50% +20%

Very high snow will affect unit movement speed, but Mud is going to increase attrition levels a lot as well as slow the army down to a crawl. A smart player will try not to attack The Soviet Union just as mud season begins or they might find a lot of their panzer divisions bogged down.

If the area is set up as susceptible to mud that time of year and water levels over a time period is high enough mud develops. Either rain or melting snow can be the source of the water. The game logs how much rain has gone down in a special region. If the temperature is above 0, some of the stored water evaporates, the higher the temperature is, the higher the evaporation rate. If there is snow and the temperature is above 0, some snow will turn into water, the higher the temperature, the faster this conversion is. If there is mud (meaning there is a lot of water on the ground) and the temperature goes below 0, the mud disappears, because the water has frozen.

Terrain effects on weather[edit]

Some terrain makes it more or less likely for a weather effect to occur.

Weather Mountain Plains Marsh Desert Urban
Mud -10% +50% +80% +50%
Snow.png Snow and Blizzard.png Blizzard +80% -100% -40%
Sandstorm.png Sandstorm -100% +80%

Politics IdeologyFactionNational focusIdeasGovernmentPuppetDiplomacyWorld tensionCivil warOccupationIntelligence agency
Production TradeProductionConstructionEquipmentFuel
Research and technology ResearchInfantry technologySupport Companies technologyArmor technologyArtillery technologyLand doctrineNaval technologyNaval doctrineAir technologyAir doctrineEngineering technologyIndustry technology
Military and warfare WarfareLand unitsLand warfareDivision designerArmy plannerCommand groupCommanderBattle planCombat tacticsShipNaval warfareAircraftAir warfareExperienceAttrition and accidentsLogisticsManpowerNuclear bomb
Map MapProvinceTerrainWeatherState
Events Events