What Kp index do you need to see the northern lights in Tromsø?

Very little. Tromsø's geomagnetic latitude is about 66.9 degrees, close to the edge of the oval on quiet nights, so Kp 1-2 is often enough with a clear sky. Yr sets the Kp threshold at 0 for this latitude.

How accurate is the 27-day aurora forecast?

It is a rough guide. It assumes features on the Sun return after one 27-day rotation, which works for coronal holes but cannot predict new eruptions or clouds. Use it to pick a week, not a night.

Is there a 14-day aurora forecast for Tromsø?

No official source offers one. NOAA publishes 3-day and 27-day forecasts and Yr shows 3 days, so any 14-day aurora forecast is based on patterns or averages.

What does a negative Bz mean for the northern lights?

A negative Bz means the solar wind's magnetic field points south, which lets energy into Earth's magnetic field. When Bz stays south for a while, aurora activity usually picks up within the hour.

Are NOAA Kp forecast times in local time?

No, they are in UTC. In winter, add one hour for Tromsø, so the 21-00 UT block is 22:00-01:00 local time.

What matters more in Tromsø, Kp or clouds?

Clouds. Tromsø sits under the auroral oval, so some activity is common, but thick low cloud on the coast often blocks the view. Always check the hourly cloud forecast.

Aurora Forecast Tromsø: How to Read Kp, Bz and Clouds

How to read the aurora forecast for Tromsø: the Kp you need, what Bz, solar wind and hemispheric power mean, why clouds decide, and how good 27-day outlooks…