clothing

Was in Rome and Florence in mid-May 2010. Wore short sleeve cotton shirts, and capri pants most of the time. The weather was nice and sunny most of the time. However, I took a light-weight jacket and long pants as there were a couple of rainy/misty days which made it nippy. I live in Florida and get cold easily. I took a small umbrella which I rarely used.

look at www.weather.com for average temperatures
for the big three in April

It varies and you need to prepare for a range of weather conditions. We were in Rome in the first week of June a few years and made the mistake of listening to everyone claim how hot Rome is. That week was chilly that on a couple of nights most of the sidewalk cafes did not open the outside part. And we were ill-prepared with only short sleeves. Return the next year for exactly the same week and there wasn't a day under 90. Obviously the long sleeves stayed in the luggage. Never know, just have to be prepared for a range. Look at the snow in Rome as I type.

Usually nice that time of year, pack light, you can always buy what you need over there.

I was in these cities last year: Venice in May, sunny and hot; Rome in July, the same; Florence in June, very pleasant. However, there was a huge rainy-cold spell at the beginning of May. It's very hard to predict. Layering is a good idea, with at least a light sweater or wrap for evenings.

2 words: FLEECE AND NYLON. We went to Italy for 3 wks at end Sept to late October. Mostly warm and sunny, but we needed fleece cover up a few times due to wind and chill temps, and had light, hooded nylon windbreakers that could be worn alone or layered over fleece. Needed the windbreaker for a chill trip on vaporetto to Murano during an otherwise warm week. These 2 items are almost weightless and dry quickly, and will get you through a lot of fall or spring weather almost anywhere. We each had at least one pr of long pants and some socks, too. We did check out weather history at the recommended websites before our trip. very helpful.
No matter where you are during these shoulder seasons, the temp on the south side of a stone building could be 25 degrees warmer than shade on the water.