11-5-18 - Cold Outbreak
This system turned out to be cold throughout the layers of the atmosphere but lacked moisture. -32C at 500hPa, -12C at 700hPa and around -2C at 850hPa is a colder than average system for May. Thursday afternoon saw the first frontal band arrive at Shooters Hill at around 4pm. At 2pm it was around 12C out there and by 4:30pm it was 1C. Light snow occured at just after 4pm but did not settle. Overnight on Thursay the snow become heavier on the Oberon Plateau at times and by Friday there was a nice settling (a few cm) at Oberon township and even as far east as Hampton. Sunny Corner saw a nice settling to a few cm and even Lithgow township observed snow showers on Friday. Blackheath didn't really see anything more than snow showers at times on Friday morning. There was a lack of moisture over this way, as the system was drying out as it slid across the Oberon Plateau.
Contrary to local lore, our lack of snow in Blackheath is not because it gets too windy but rather its a lack of moisture and sometimes a lack of surface level cold, that prevents us from seeing a good settling these days. I've seen many good settled falls on the Oberon Plateau during strong winds and also numerous good falls in Blackheath with winds of 100km/r and more. You can have snow not settling in light winds or strong winds and also snow settling well in strong winds or light winds. Its not the wind that is the problem, its the lack of low to mid level moisture and also our lack of significant, lower level cold, during cold fronts these days as well. In the old days, the Oberon Plateau may have seen falls of 15cm to 30cm in their bigger falls and we would see maybe 5cm to 10 across the upper Blue Mountains. These days, the OP more often sees 5cm to 10cm and the upper mountains sees snow showers and perhaps a light settling if we are lucky. Of course, bigger falls do occur across the Blue Mountains but much less often than they did in decades previous.