I plan to visit Norway for six days in mid-September. I am wondering about the likelihood of seeing the Northern Lights near the Norway in a Nutshell route. Is there somewhere we'd have a reasonable chance, without going far north on such a short trip, or should I not hold out much hope? Thank you very much.
I am no expert on NL, but I would venture to say it is highly unlikly to see it on the NiN route.
For NL you need the combination of darkness, clear skies and you need to be far enough north and the lights have to be 'on'. Bergen and the Fjord country is notorious for being rainy most of the time, so that alone lowers your chances significantly, plus september is not the darkest time and your are not that far north.
Most people who chase the NL go to northern Sweden or Finland in mid winter, where it's sufficiently dark and cloudless to optimize thier chances.
Much of the viewing is similar to what is needed for Milky Way viewing, that would be looking south instead of north.
I am definitely not an expert on Northern Lights (never seen them myself yet) but have photographed the Milky Way plenty of times.
I will say though September has plenty of hours of night in the area you are talking about. Sept is one of the few times you could see both NL and MW on the same night in Norway.
The sunsets around 8 and won't rise until 6 or so in the morning so you have more than enough hours of darkness, you will want to be looking a couple of hours past sunset and couple of hours before sunrise ; so say from 10 PM - 4 AM you have a chance.
You will need a clear view to the North (mountains could easily prevent this)
3 big issues make it unlikely though.
1.) you need clear skies ; clouds are the big potential issue. The aurora is very high up, so low clouds will make it totally invisible. Related 1b if you will is if there is a full moon or close to you are probably out of luck. Best with no moon or quarter or less otherwise brightens the sky too much ; so you do need to check not only the weather but the moon forecast/cycle for your dates. This is the same as Milky Way.
2.) Since you will not be very far north you need strong Aurora activity. This is measured by a KP number assigned, there are forecasts daily. The link below shows further down the lines of what KP number reaches what areas. The top of Norway has the Northern Lights visible most every single night (as long as the sun, and clouds or moon are not preventing you from seeing it) In the summer when the sun does not set seeing it would be impossible.
The further south you go the more hours of darkness you will have but the stronger you will need the activity to see it.
Depending on exactly where you will be, you are looking at needing a KP 4 or KP 5 number ; which is rare but not unheard of.
5 is classified as a "geomagnetic storm" type activity so definitely less common than 4 but where you are may be in the 5 not 4 region.
I remember less than 1 month ago we had a KP8 and the Aurora was visible in many US states that very, very rarely see it ; but that happens a couple of times a year I believe.
Usually any sort of advance forecast more than 12 hours or so is inaccurate so you need to check it each day if you might want to go out looking for it that evening.
Here is a link to a site which lists it for Europe. The same service has a US site as well.
http://www.aurora-service.eu/aurora-forecast/
3.) You need to be in a place far enough away from any city light pollution. here is a link to a light pollution map, you are going to want to be in a blue or darker area. Plenty of them between Oslo and Bergen but none very close to either city.
This is the same as Milky Way, though even green areas are sufficient for Milky Way viewing most of the time.
http://darksitefinder.com/maps/world.html
You will have to watch for these multiple variables/forecasts each day for the coming evening so takes some effort, not to mention the effort it takes to get up and out in the overnight hours and look north.
Make sure to let your eyes get adjusted on the type of night that will work it should be a nice starry sky but without much moon it will seem very dark until your eyes get adjusted. A red light works best to be able to see without ruining your eye's adjustment. White light sets your eyes backward and have to adjust again to be used to the darkness.
It will take some luck to get strong activity KP4 or higher forecast, the night for said forecast to also be clear and for you to be able to get to a place with sufficient light pollution so you can hold out hope but don't count on it.
1.) Clear weather forecast with quarter moon or less.
2.) Dark sky area
3.) Within the Aurora zone forecasted region for said forecast prediction
4.) View to the north that is not obstructed