diff --git a/tests/testWeather.cpp b/tests/testWeather.cpp
new file mode 100644
index 0000000..3b33c8d
--- /dev/null
+++ b/tests/testWeather.cpp
@@ -0,0 +1,148 @@
+#include "testHarness.h"
+#include "vf/Weather.h"
+
+using namespace vf;
+
+namespace {
+
+void runToState(Weather& weather, WeatherState target, long long limit) {
+    for (long long i = 0; i < limit && weather.state() != target; ++i) weather.tick();
+}
+
+} // namespace
+
+VF_TEST(weatherStartsClearWithZeroGradient) {
+    Weather weather(1u);
+    CHECK(weather.state() == WeatherState::Clear);
+    CHECK(!weather.isRaining());
+    for (int i = 0; i < 5; ++i) {
+        weather.tick();
+        CHECK_NEAR(weather.rainGradient(), 0.0, 1e-9);
+    }
+}
+
+VF_TEST(clearEventuallyBecomesRain) {
+    WeatherConfig cfg;
+    cfg.clearMin = 40;
+    cfg.clearMax = 40;
+    Weather weather(7u, cfg);
+    runToState(weather, WeatherState::Rain, 200);
+    CHECK(weather.state() == WeatherState::Rain);
+    CHECK(weather.isRaining());
+}
+
+VF_TEST(rainGradientRampsUpWhileRainingAndDownWhenClear) {
+    WeatherConfig cfg;
+    cfg.clearMin = cfg.clearMax = 40;
+    cfg.rainMin = cfg.rainMax = 60;
+    cfg.thunderChance = 0;
+    cfg.rainRampPerTick = 0.25;
+    Weather weather(3u, cfg);
+
+    runToState(weather, WeatherState::Rain, 200);
+    for (int i = 0; i < 20; ++i) weather.tick();
+    double wet = weather.rainGradient();
+    CHECK(wet > 0.9);
+
+    runToState(weather, WeatherState::Clear, 200);
+    for (int i = 0; i < 20; ++i) weather.tick();
+    double dry = weather.rainGradient();
+    CHECK(dry < 0.1);
+    CHECK(wet > dry);
+}
+
+VF_TEST(precipitationDependsOnStateAndTemperature) {
+    WeatherConfig cfg;
+    cfg.clearMin = cfg.clearMax = 30;
+    Weather weather(5u, cfg);
+    CHECK(weather.precipitationAt(-1.0f) == Precipitation::None);
+
+    runToState(weather, WeatherState::Rain, 200);
+    CHECK(weather.precipitationAt(-1.0f) == Precipitation::Snow);
+    CHECK(weather.precipitationAt(1.0f) == Precipitation::Rain);
+}
+
+VF_TEST(lightningOnlyStrikesWhileThundering) {
+    WeatherConfig cfg;
+    cfg.clearMin = cfg.clearMax = 20;
+    cfg.rainMin = cfg.rainMax = 20;
+    cfg.thunderMin = cfg.thunderMax = 300;
+    cfg.thunderChance = 256;
+    cfg.strikeInterval = 8;
+    Weather weather(11u, cfg);
+
+    long long strikesBeforeThunder = 0;
+    for (int i = 0; i < 40; ++i) {
+        weather.tick();
+        if (!weather.isThundering()) strikesBeforeThunder += weather.strikesThisTick().size();
+    }
+    CHECK_EQ(strikesBeforeThunder, static_cast<long long>(0));
+
+    runToState(weather, WeatherState::Thunder, 200);
+    long long strikesDuringThunder = 0;
+    for (int i = 0; i < 200; ++i) {
+        weather.tick();
+        for (const LightningStrike& strike : weather.strikesThisTick()) {
+            CHECK(strike.pos.x >= cfg.strikeMinX && strike.pos.x < cfg.strikeMaxX);
+            CHECK(strike.pos.z >= cfg.strikeMinZ && strike.pos.z < cfg.strikeMaxZ);
+            ++strikesDuringThunder;
+        }
+    }
+    CHECK(strikesDuringThunder > 0);
+}
+
+VF_TEST(sameSeedProducesIdenticalWeatherAndStrikes) {
+    WeatherConfig cfg;
+    cfg.clearMin = 50;
+    cfg.clearMax = 200;
+    cfg.rainMin = 50;
+    cfg.rainMax = 200;
+    cfg.thunderMin = 50;
+    cfg.thunderMax = 200;
+    cfg.thunderChance = 128;
+    cfg.strikeInterval = 20;
+
+    Weather left(99u, cfg);
+    Weather right(99u, cfg);
+    for (int i = 0; i < 3000; ++i) {
+        left.tick();
+        right.tick();
+        CHECK(left.state() == right.state());
+        CHECK_NEAR(left.rainGradient(), right.rainGradient(), 1e-12);
+        CHECK_NEAR(left.thunderGradient(), right.thunderGradient(), 1e-12);
+        CHECK_EQ(left.strikesThisTick().size(), right.strikesThisTick().size());
+        for (std::size_t k = 0; k < left.strikesThisTick().size(); ++k) {
+            CHECK(left.strikesThisTick()[k].pos == right.strikesThisTick()[k].pos);
+        }
+    }
+    CHECK_EQ(left.totalStrikes(), right.totalStrikes());
+}
+
+VF_TEST(differentSeedsDivergeInStrikeTiming) {
+    WeatherConfig cfg;
+    cfg.clearMin = cfg.clearMax = 20;
+    cfg.rainMin = cfg.rainMax = 20;
+    cfg.thunderMin = cfg.thunderMax = 400;
+    cfg.thunderChance = 256;
+    cfg.strikeInterval = 8;
+
+    Weather left(1u, cfg);
+    Weather right(2u, cfg);
+    bool diverged = false;
+    for (int i = 0; i < 600; ++i) {
+        left.tick();
+        right.tick();
+        if (left.strikesThisTick().size() != right.strikesThisTick().size()) {
+            diverged = true;
+            break;
+        }
+        for (std::size_t k = 0; k < left.strikesThisTick().size(); ++k) {
+            if (left.strikesThisTick()[k].pos != right.strikesThisTick()[k].pos) {
+                diverged = true;
+                break;
+            }
+        }
+        if (diverged) break;
+    }
+    CHECK(diverged);
+}