Position 'R' is between areas of high and low pressure, virtually col conditions, with very few isobars on the chart. It is mid-summer.
'early morning fog lifting to low stratus'
Radiation fog or mist may form around dawn but it will burn off quickly and the wind will be too light to form a layer of turbulence could.
'increasing amounts of AS and NS - heavy rain'
No frontal lifting and no wind to give the extensive orographic lifting required to create the cloud.
'overcast with drizzle and hill fog'
See above.
'fine and warm at first - AC castellanus and CB in late afternoon with thunderstorms'
Convective lifting and conditional stability could produce these conditions.