Slovenia/Croatia Travel in November

I would check the weather forecasts. We travelled in the same area for 17 days starting at the beginning of October in Dubrovnik. It was shorts and t shirt weather. Sailed for a week up the coast. It was pleasant and we swam off our boat, in cool water. By the time we got North into Slovenia, the weather was colder and wet. We finished in Zagreb which was cool.

I suspect November may be cooler, given the latitude and topography of the country. If possible, I would go earlier. I suspect September would provide more reliable weather and less rain.

You can take a look at actual, day-by-day, historical weather data for all the cities you're contemplating on the website timeanddate.com. I like to review the most recent five years' worth of data for the pertinent month(s). I think that's by far the best way to estimate the kind of temperatures to be expected. Monthly averages hide extremes, and some sources are basing those averages on time periods ending in the year 2000.

For precipitation (which could be a major issue in November), I usually just look at the summary climate chart found in most cities' Wikipedia entries.

The other thing about November is that the days are getting notably short by that time of the year. When you combine short days with overcast weather, you get conditions that don't appeal to me at all. However, I am abnormally bothered by lack of sunlight; I realize it's not that big a deal for most people.

But my answer is: No, November is not a particularly good month to visit any of the areas you mentioned. I was in Croatia during early October 2015. It was getting rainier as time went on.

If you just want to see the cities, then you could go in November if you are prepared to put up with rain. If you want to visit some of the islands or see the countryside, then you would be best served by visiting before the end of September, when many places away from the cities shut for the winter. Early October sees the ferries move onto their much reduced winter timetable. I wouldn’t opt for a November trip, personally.

Zagreb weather is the same as NY. Winter. Could be cold and snowy, could be nice. Split would be like North Carolina. They rarely see snow but could be cool. Ljubljana is west of Zagreb and has the same weather. They do get snow. We plan on going for the month of September to Croatia, Rijeka-Dubrovnik-Rijeka-Zagreb then home. We know we won’t be swimming. We then plan on going for the month of December to spend Christmas with family. But we will stay up North. I am hoping to maybe, stop in Paris either before or after the September trip, if at all possible.

We were in Dubrovnik in Nov. Very pleasant, but light jacket weather. Crowds were non-existent. We visited Sarajevo on the same trip. That was pretty chilly. The Balkans means "mountains" in Turkish. Some parts are quite cold. Sarajevo hosted the winter olympics.

Since Croatia was one of the last to close after fighting the idea tooth and nail, I think its not overly optimistic to expect it will be open in November.

Thank you all for the responses. Unfortunately, we can't change our date to a better time to visit as the transatlantic cruise leaves on 11/29/21. We wanted to make the most of the 14 hour flight from Phoenix, AZ and see more of Europe before getting on our cruise.
This could be our last trip to Europe as we are in our 70's and getting around isn't as easy as it used to be. We'll put up with the cold weather and rain to visit these beautiful countries.

If the trip is after mid November and you think you might have some time free at the start or the end, let me know and I might have an idea.

November is not the best month to travel to Slovenia or Croatia but there are benefits too. First, there is less tourists, this is most obvious in Croatia. Second, you might experience fresh wines, olive oil and other local produce.

November can be very rainy, this can be a bit annoying when in the Alps. And days will be shorter - if you do long drives you should consider that. There will be less ferries and less accommodation/ restaurant options in Croatia because of off season.

The bottom line is it is still well worth travelling to both countries in November.

If travel is permitted in November 2021

I believe that Travel is currently permitted to Croatia. But check me on that: https://travel.state.gov/content/travel/en/traveladvisories/COVID-19-Country-Specific-Information.html