White soft hail-like pellets - GRAUPEL

Graupel is precipitation that forms when supercooled droplets of water are collected and freeze on a falling snowflake.

So, you start with a snowflake, it is falling from the sky but encounters more moisture. This water is supercooled, so below zero C, it should have frozen but it is remaining in a liquid state but quite unhappy. This water then encounters the cold snowflake and bonds/accretes around the frozen precipitation and the water then quickly turns to a solid layer itself.

This riming (coating with tiny water droplets which then freeze on contact) occurs in the convective updraughts of showers and the snow pellets can grow to a few mm in diameter.

The end result is small pellets of snow like balls, or soft hail which feel a bit like small bits of polystyrene/Styrofoam. They squidge slightly between your fingers, not like real hail with is hard ice. The graupel collects in clusters of little bits, in strong winds they run down the road and pavements. They collect in corners and on car windscreens.

The picture of the car shows a granular texture to the wintry precipitation, not flat smooth layers of snowfall. 

There have been plenty of convective showers in the cold northerly flow, accompanying the late April blast of Arctic air. There has been snow over the hills, not ideal for the Highland and Fell lambs. Reports of sleet and hail with thundersnow for the Grampians.

The SST (sea surface temps) are around 8 or 9C at the moment around northern Scotland. Nobody wants to go swimming in that but it is enough "warmth" underneath the cold air to set off convection. Over the land, with any strong April sunshine, the fields and roads are now holding a bit more warmth too. The flow is brisk enough to carry the showers right over the higher ground of northern Britain, more chance of snow at altitude but at lower levels there has been ice hail and a few flurries of graupel.

Photo credit -  D Johnson   Moray