Yes - although the gradient of the flow changes, and the wind direction is modified by the developing trough, the air is still forecast to flow from the inland areas of Scandinavia. The 1000-500 hPa thicknesses become increasingly low as the forecast advances, indicating the advection of colder air into the area.

Not necessarily! Although there is an inversion present, there is also evidence of lower cloud top temperatures, e.g. the area of the surface trough, and south of Iceland. Any additional trigger such as a convergence line, or dynamic ascent from aloft could break the inversion.

The Met Office forecast frame valid for 18Z on the 5th develops a low centred at 66N, 0E, with depth 997hPa, as the trough located at the north Norwegian coast at 00Z moves slowly SW. The MSLP field in the Hirlam model does not show such deepening, although it does maintain and deepen the trough, and indicates precipitation. The upper air dynamics are important here too.

Between 00Z and 06Z we only have Meteosat images, so we are lacking in the detail available from AVHRR sensors. The location of the stratiform cloud discussed earlier corresponds with the position of the trough seen in the model MSLP field. By 06Z, this cloud area extends south as far at 63N, with coldest cloud tops in its leading edge. Enhanced convection is likely here, due to dynamic ascent. However, there is no cyclonic pattern visible, and so we do not diagnose this as a polar low from this imagery.

The sea temperatures in the Norwegian sea are 4 - 6C, and in the North Sea increase to 8C at this time of year. With land temperatures of -20, the sea will have a marked effect on low level stability. The higher the SSTs, the lower the 500hPa temperature needs to be to encourage polar low development. The higher the SSTs, the higher the 500hPa temperature threshold is to encourage polar low development.