There is no special rainy season
Avg. Temp. in Spring: max.: 7 – 18°C ( 47 - 64°F ); min: 0 - 7°C ( 32 - 47°F )
Avg. Temp. in Summer: max.: 21 – 22°C ( 70 - 71°F ); min: 10 - 12°C ( 50 - 53°F )
Avg. Temp. in Autumn: max.: 6 – 18°C ( 43 - 64°F); min: 1 - 8°C ( 34 – 48°F )
Avg. Temp. in Winter: max.: 2 – 3°C ( 36 - 38°F); min: -1 - 0°C ( 30 - 32°F )
Luggage and bags: Use Till Logistics (www.till-logistics.de, 0511.977.2006) I spent 2 weeks trying to figure out the best way to ship my stuff back to the US without spending a fortune, and this company was the best deal by far. Deutsche Post does not charge strictly by weight, and to save money you must use surface mail which takes up to 2 months. Extra bags on the plane are also not good value for money unless you can make each bag weigh the maximum (difficult), plus you have to lug them around. Till Logistics uses airfreight, they can pick up your stuff for a small fee, you can pack in suitcases or boxes, and it will arrive at your airport in around a week - together in one shipment. It turned out cheaper, easier, and faster, plus the owner speaks English and is very friendly and helpful. **Note that for airfreight or Deutsche Post you must pay CASH ONLY. Germany is not big on credit card use.
Rain gear, and layers. The weather is totally unpredictable (although the weathermen still try). It rains often, year-round, and the wet makes the temperature drop. I'm wearing fleece in June! When the sun manages to stay out for a day, it's plenty hot for shorts and sandals, but that's a rare treat.
Toiletries and Medical Supplies: The Apothekes (pharmacies) are well-stocked and staff often speak English, so you shouldn't have any trouble finding non-prescription medicine. It's always fun trying to describe your intimate medical needs, there are so many words they don't teach you in German class.
Miscellaneous: Make sure you ask me for my phone number before you come and pack it... so that you can call me when you are there and I will show you around :-) If I am around ;)