Although not related to the aurora, polar stratospheric clouds (also known as nacreous clouds) are a beautiful winter sky phenomenon. They only form when conditions in the stratosphere, a layer of our atmosphere at around 15-25km in altitude, are just right. One very important condition is that the temperature in the stratosphere must be below -78°C.

As can be seen from the images below, current GFS forecasts suggest that the temperature in the stratosphere above the UK will drop to below -80°C over the next couple of days (purple regions).

The stratosphere temperature forecast for 1800 (UT) on Wednesday 25th January 2017 using the Global Forecast System (GFS). Graphic provided by theweatheroutlook.com

The nacreous clouds will only be visible when the sun is between 1° and 6° below the horizon, in a period called “nautical twilight”. So your best chances to see the clouds will be just before dawn and just after sunset.

The stratosphere temperature forecast for 0600(UT) on Thursday 26th January 2017 using the Global Forecast System. Graphic provided by theweatheroutlook.com

Even with this cold stratosphere over the UK, seeing nacreous clouds isn’t guaranteed. Unsurprisingly, the clouds need moisture to form but, unlike the troposphere were “normal” clouds form, the stratosphere is generally quite dry. If you are lucky enough to spot any nacreous clouds, though, do let us know via the comments below!