Strangely bright morning twilight over Switzerland
If these were polar stratospheric clouds, that could explain a brighter than normal sky either before sunrise or after sunset.  The higher the clouds are, the more lead/lag time you will have to observe the phenomena before the sun comes into view.  The reason for this is simply that the clouds are in direct line-of-sight with both you and the sun, but you and the sun are not in line-of-sight.  The sun illuminates these clouds and being cold icy clouds they reflect much of this light to your eyes.  100% of the light you see is scattered giving the light a diffuse glow.

Unfortunately, I'm not aware of any stratospheric forecast products for these clouds.  The closest thing is an analysis of the 450 K $\theta$-surface showing area within the polar vortex with temperature at or below -78 C.  These depict the area within the polar vortex that are favorable for polar stratospheric clouds.  However, these do not show where the favorable area is, nor give an indication if these clouds will actually form.  You can view the northern hemisphere plots here.  The other stratospheric products deal with the size of the polar vortex, UV-B penetration and ozone analysis which do not aid in the forecast of these clouds.