Blue Mountains Weather Myths and other Information


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Document Updated: 12-10-08

The weather is something many of us talk about, especially during winter in the Blue Mountains. Its easy for all sorts of stories to circulate about our weird and wonderful weather and before you know it, they soon become faction - that strange mix of fact and fiction. So, here's a few myths about Blackheath weather that need clarifying. This is a work in progress so feel free to correct my observations, especially if you have better science knowledge to back it up, such comments are welcome.

1/ The wind needs to die down for it to snow. False. This is a common saying up here. When snow falls, it is often associated with fresh to strong winds in our area. Its true that strong winds melt settled snow but they definitely do not stop it from falling. In fact, without wind in the mid to upper levels of the atmosphere, the cold air from down south wouldn't get here in the first place. Still, snow can fall in calm surface conditions at times and Blackheath is very beautiful when this happens. Perhaps the biggest problem with snowfalls in our area is lack of moisture, as the ranges near Oberon can take most of the moisture out of the air, often leaving it fairly dry as it reaches us.

2/ Winds from the south or east never bring snow. False. Whilst most cold fronts arrive from the west or south-west, they usually don't bring a lot of snow to Blackheath. Even though air isn't typically as cold from the south or south east, its from these directions that you can occasionally see more snow, when the air is cold enough. As south-easterly air passes over coastal waters, moisture is picked up and directed towards us in higher amounts than the drier winds from the west or southwest. A low pressure system off the coast of Sydney is the optimal setup for good snow from the east or south/east, typically with a strong high pressure system to its west, ridging well south, feeding cold air into the warmer maritime air.

3/ Blackheath always gets snow! False. Sadly, with global warming and an average maximum temperature in winter of around 10C, our town is not renown for big snowfalls although they can very occasionally happen. These days, Blackheath averages around two days of settled snow per year and another five days of snow falling but not settling - this includes light falls overnight or early morning that can be easily missed if you are not aware of the approaching system. The Oberon area and places to its south gets much more snow as its higher there and picks up more moisture. Orange and its surrounds also usually get more snow than Blackheath per winter for even though it is slightly lower in altitude (although higher in the outskirts) it is more exposed to the cold westerlies and the moisture needed for snow to occur.

4/ Cold summers mean cold winters. False. There is no direct correlation between summer and winter. A cold winter may indeed follow a cold summer but a mild winter can also follow a cold summer. Its more about available moisture in a given season, the long wave trough, positioning of the jet stream and placement of surface high pressure systems. Also, drought years are usually warmer ie: less cloud.

5/ Its always ten degrees colder in Blackheath than Sydney. False. If the wind is from the west or south west its usually around ten degrees colder than Sydney but can be up to fourteen degrees colder if there is rain or snow here and its dry in Sydney. Conversely, winds from the east or south-east can see Blackheath around six degrees or so colder than Sydney. Its all to do with the way air warms or cools as it descends or ascends, depending on whether it is dry or saturated, a subject that can take a while to explain.

6/ Always use the Sydney television forecasts as a guide for our area. False. Our climate is vastly different and Sydney television forecasts rarely reflect this. How many times have you seen 'sunny and windy' for Sydney in winter but it turns out to be five degrees and wet here! Tune into Lithgow radio when possible as they give forecasts for the Central Tablelands.

7/ It has to be 0C for snow to fall. False. Snow can fall at 5C if the relative humidity is low enough. This occured in October 2001 when light flakes fell for a short period. Such falls in temperatures well above zero usually don't last long and rarely settle. Typically though, rain turns to sleet (mixture of rain and snow) at around 2C and snow usually occurs from about 1C and below.

8/ We are entering a colder period over the next few years and decades, so don't worry too much about Climate Change. False - (debatable!). The climate has definitely changed up this way. Its just hard to know how much of it is natural or because of human induced warming. As far as its possible to tell, Climate Change (Global Warming is not as descriptive) is here to stay, so periods of milder weather will probably become more common in winter and hotter periods will persist in summer. This doesn't mean we wont have cold periods in winter or summer, it just means less cold and more mild and warm weather on average. Snowfalls should still occur but they will become less frequent and of less intensity on average. The real question seems to be, is the Climate Change phenomenon man made or just natural climate variation or a bit of both?

9/ La Nina episodes are good for snow, El Nino is bad for snow. True! Well, sort of. La Nina is associated with a consistently positive Southern Oscillation Index (do a web search on these terms or go to the Weatherzone glossary link on my Cold Climate Information page for lots of definitions) and this usually means more moisture for our region. An example is the snowy year 2000 winter, which was during a La Nina event. However a positive SO Index might bring rain and not snow, depending on the strength of the cold changes. El Nino is usually associated with less rain and snow for our area and can be an indicator of a frosty season, ie: dry days can equal cold, clear nights.

The weather is a vast and complicated science but it can also be lots of fun. Happy weather watching!