I've been in Germany for each month of the year. You will not find springlike weather in March, and even the possibility of a light snow shower. But for the most part, the daytime weather should be above 0 degrees Fahrenheit. Also, keep in mind that starting tomorrow, all long haul departures out of Germany will have an approximately $60 tax (coded "OY") added to their tickets. They have to pay down their budget deficit afterall. So it might be cheaper to fly out of BRU, AMS, or ZRH on the return (even with the cost of the train ticket added onto it). In fact, flying out of FRA to the U.S. will now have 4-times the amount of total tax as flying out of MAD or BCN to the U.S. Approximately $120 vs. $30. Enjoy.