Mountains Weather Myths and other
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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
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.
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