What kind of temperatures to expect in early June

Wunderground.com has the seasonal averages as well as extremes. Anything else is only anecdotal.

If I had to choose 3 weeks when you are likely to have the best weather in Italy, I would choose exactly the period when you are going. Of course occasionally you have the weird weather that might bring temperatures that are above or below average for the season, but generally early June is a stable period where temperatures tend to be very warm during the day, but not unbearably hot. Expect maximum temperatures around 25-30 degree Celsius (77 F - 86 F) with lows at night around 15 C-17 C (59 F - 63 F). Rain is possible, but June is generally dry. Since weather is impossible to predict beyond one week to 10 days out out, I recommend to check the weather forecast on Wunderground.com or Weather.com just before you depart, to have a more accurate picture.

Thank you

I will attest to the range. First trip to Rome was the first week of June about ten years ago. Everyone said it would be hot so only brought light weight clothing and a light jacket. It was so cold that week that a couple of nights the sidewalk cafes did not open. We had to buy long sleeve clothing. We returned exactly one year late - same week - with heavier clothing, jacket etc., and it was so damn hot and humid that we huddled in the hotel's ac during the mid day. You need to be prepared for a range of weather. That is why you have seen a wide range on the internet because that is the way it is or can be.

Go to the Weather Underground site recommended above. There's a section called trip planner. You may have to enter the data 2 or 3 times, but eventually, if you put in a time span of 14 days or less for a specific city, it will show a graph with the averages, and underneath it will show the actual conditions for every day in that period for the last 12 years or so - highs, lows, humidity, rain . . . .