Weather end of March

We typically travel to Germany in April and there is a wide variety of weather conditions. We have had snow in April (Ansbach), rain often, and sunny/mild weather several times. I never take a heavy coat as it is a burden to lug around. I take layers: a light wind/rain resistant jacket, light polartec for warmth, and a very light base layer like silk/synthetic long underwear for the unexpected. I think 30-40 degrees with rain is the most difficult weather for staying comfortable.

BTW, we take the same clothing for December trips. Layering always seems to be the best answer in cool/cold months.

instead of heavier coat go with something waterproof and layering underneath as needed.

The weather in southern Germany is unpredictable at that time of the year. But apart from that the Stuttgart region is the second warmest in Germany after the upper Rhine valley. For obvious reasons this does not include the Black Forest and the Swabian Jura, as they are 'Mittelgebirge', i.e. mountains with a medium height. It's very unlikely you need a heavier coat.

Thank you for your replies, very helpful in making my decision.

I've never taken a "heavier" coat to Germany, even in January. I have a down parka that is very light, but warm. In addition, I take a sweater to wear under it on the coldest days. Remember, layers.