Passau is a bit of a geographical freak. Honestly, where else do you have three massive rivers—the Danube, the Inn, and the Ilz—all slamming into each other in the middle of a medieval Old Town? Because of this "Dreiflüssestadt" setup, the weather in Passau Germany doesn't always play by the rules of the rest of Bavaria. You might check the forecast for Munich or Regensburg and think you're safe, but Passau has its own microclimate. It’s humid. It’s moody. Sometimes it’s so foggy you can’t see the Veste Oberhaus fortress from the riverbank, and other times the sun hits the water and makes the Italian-style architecture look like a postcard from Venice.
If you’re planning a trip, you need to know that this city is basically a giant humidity trap. Those rivers aren't just for show; they pump moisture into the air year-round. You’ve probably heard people call Passau the "Bavarian Venice," but that nickname applies to the dampness as much as the beauty.
The Reality of Seasons at the Three Rivers Confluence
Spring starts late here. You’ll see the first sprouts in April, but don’t pack your shorts just yet. Average highs in April hover around 15°C, but the wind coming off the Inn—which is filled with freezing Alpine meltwater—can make it feel like 5°C. By May, things get better. The mercury hits about 21°C, and the outdoor cafes start filling up. It’s a great time to visit if you don’t mind a random rain shower every other day.
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Summer is when the weather in Passau Germany gets genuinely heavy. July and August are the hottest months, with averages around 24°C or 25°C. That doesn't sound too bad, right? Well, the humidity levels usually stay above 65%, which makes those mid-20s feel much stickier. If you’re on a river cruise, the breeze helps, but if you’re hiking up to the Veste Oberhaus, you’re going to sweat. August is actually the wettest month on record, averaging over 100mm of rain. It's usually those big, dramatic summer thunderstorms that roll in fast and disappear just as quickly.
Autumn and the "Passau Fog"
September is arguably the best time to be here. The crowds thin out, the humidity drops, and the air gets crisp. The average high is a comfortable 18°C. But once October hits, the fog moves in. Because the Inn is often a different temperature than the Danube, a thick layer of "Nebel" (fog) frequently blankets the valley in the mornings. It’s hauntingly beautiful, but it can linger until noon, hiding the colorful Baroque facades.
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Winter is cold. Plain and simple. January is the coldest month, with daytime highs struggling to get above 1°C or 2°C and nights dropping to -5°C. Snow is common, turning the Christmas market at St. Stephen's Cathedral into a genuine fairy tale. Just be prepared for "grey" days—November and December are the cloudiest months of the year.
Flooding: The Elephant in the Room
You can't talk about Passau's climate without talking about high water. The city is a funnel. When heavy rains hit the Alps, the Inn swells. When the Bavarian Forest gets soaked, the Ilz rises. And the Danube? It carries everything from further west.
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The 2013 flood was a historic disaster, with water levels reaching 12.89 meters—high enough to submerge first-floor windows in the Old Town. More recently, in June 2024, the city hit a "Reporting Level 4" emergency when the Danube reached 10 meters. If you see locals looking nervously at the river gauges near the Rathaus (Town Hall), it’s usually because the Inn is looking "too green" and moving too fast.
Practical Tips for Your Trip
- The "Inn Wind" is real. Even on a sunny day, the air near the Inn river is cooler because of the glacial water. Always carry a light windbreaker or a scarf if you're walking the promenades.
- Layer up for the Cathedral. St. Stephen's is magnificent, but those thick stone walls hold the winter cold long into the summer. If you're attending an organ concert, you'll want an extra layer even in June.
- Check the "Pegel" (Water Levels). If you’re cycling the Danube Cycle Path, check the local gauges online. Path closures are common in early June during the snowmelt season.
- Footwear matters. Passau is full of cobblestones. When it rains (and it will), those stones get slick. Leave the heels at home and wear shoes with actual grip.
What to Pack for Passau
- A sturdy umbrella. Don't buy a cheap one; the wind at the "Dreiflüsseseck" (the point where the rivers meet) will flip it inside out.
- Waterproof shoes. Essential for those sudden August downpours or the slushy January streets.
- Lightweight wool. Merino wool is perfect for Passau because it handles the humidity and temperature swings better than cotton.
The weather in Passau Germany is part of the city's character. It's why the gardens are so green and why the beer halls are so cozy. If you're looking for the most reliable window of "good" weather, aim for late May to early June, or the first two weeks of September. You'll avoid the worst of the summer humidity and the biting dampness of the November fogs.
Keep an eye on the local forecast at the Bavarian Flood Service (Hochwassernachrichtendienst Bayern) if you're visiting in the spring, as that's when the rivers are most unpredictable. Once you've checked the water levels, grab a coffee at a riverside cafe and watch the three colors of the rivers merge—it's a sight that's worth a little rain.
Next Step: Download a local weather app that provides radar specifically for the Lower Bavaria region, as general German forecasts often miss the fast-moving storms that follow the Danube valley.