Topic: Frosts and cold mornings 2008

[Harley Pearman]

Cold air sinks called katabatic winds and cold air will pond in any low spot especially during a clear winters night. I have seen this occur so often. Cold air is more dense than warm air and being colder, it will sink to a lower elevation even if the rise or hill is not very high. The top of a hill can be warmer than the valley below. This certainly more prevalent on clear winter nights.

Jimmy, I have seen the frosts that have been occurring in outer north west Sydney on several mornings now and saw it again last Sunday morning too. I agree with you.

It is shaping up as the coldest August in a long time and almost daily I am seeing unusually low minimum temperatures being set somewhere. I have not seen this occur before. I read a report yesterday suggesting that this is starting to look like the coldest August in 10 years but I have seen other figures and quotes suggesting that this August is colder than that. I am not sure who is right. One thing is certain, the cold nights has become a weather event in itself and one that many have noticed.

Consider these minimums since my last post here.

Tenterfield

The August nights have been colder to date than that of July. Some unbelievable cold nights include minus 7.2C on 9, minus 8.3C on the 10, minus 7.1C on the 12 and a hard to fathom minus 9.5C on the 14. It was minus 6.6C on the morning of the 20.

Woolbrook

Minimums include minus 7.5C on the 10, 13 and 20, minus 8C on the 14 and minus 7C on the 19.

Armidale

The problem that Armidale suffers is that the town is built between North Hill and South Hill and is in a valley. Cold air ponds in this valley causing much colder temperatures. Obviously being 980 metres above sea level also helps. I think the weather station is at 2AD Radio Station in town (It was when I was at University  from 1990 to 1993). If I am wrong please correct me.

Armidale had another minus 7.4C on the 20, minus 6C on the 19 and minus 6.6C on the 18.

Tamworth:

This regional city is at the foot of the Moonbi Ranges in the north west slopes. I am amazed that minus 4C was recorded again on the 20. The cold is occurring here too.

Gunnedah had minus 4C on the 20 and Coonabarabran had a minus 5C on the 20 too.

Glenn Innes

Glenn Innes is at the foot of a rise too but elevated 1,030 metres above sea level. The minus 9C on the 20 is incredible.

Yet Thredbo being higher in elevation had minus 5C. It was colder in Glenn Innes on the morning of 20/8/08 than at Thredbo.

However, a place called Eyre in Western Australia (Coordinates appear to be 32 15 degrees south and 126 18 degrees east as this is not a town) has set a new Western Australian weather record for minimum temperatures on the morning of August 12 being minus 7.2C. It beat its previous record of minus 5.9C on the morning of June 14 2006. However it is qualified that weather records begun only in 1983 but records from the nearby telegraph station go back to 1885. It is the coldest temperature recorded anywhere in Western Australia.

Hence, it is not confined to New South Wales or southern Queensland. It is more widespread.

Harley Pearman

[Peter J]

Hi all,

For the first time in many years I had on Friday morning a 1 inch thick layer of ice on my car. Also Melbourne area experienced its first Black Ice warning in many years.

Just a nibbler for the winter-freaks.

Big Pete

[Harley Pearman]

Another cold morning 24/8/08

After a few nights respite from the cold, large areas of New South Wales suffered through another cold morning on 24/8/08.

Evidence is emerging that August 2008 is shaping up as the coldest in 10 to 30 years varying from place to place partly due to the cold mornings that have occurred.

I saw frost again in outer north west Blacktown Sunday morning. Additionally some towns across NSW had the coldest night for August. A sample of places that suffered again include:-

Woolbrook had minus 6C, Barraba minus 5C, Condobolin had minus 4C, Dunedoo minus 3C, Cootamundra minus 4.5C (The coldest morning this month), Temora minus 4C, Wagga Wagga minus 3.4C (The coldest morning this month), Young minus 4.6C, Armidale minus 5.4C, Inverell minus 4C, Lithgow minus 5.8C, Cooma, Mudgee and Tenterfield all had minus 5C.

Many other centres had minimum temperatures of between 0C and minus 3C.

Charlotte pass had minus 14C being the coldest of all places.

Given that is was again widespread, it would be interesting to see the damage the frost is causing to any crops that have been sown in the affected areas. Yet the frigid nights are occurring so late in August and in some areas, there has been little respite for the whole month.

Harley Pearman

[Michael Bath]

These photos were taken by Martha from the Guyra Argus newspaper yesterday morning (25th Aug). It was the first frost this season with a bit of moisture about - there was a heavy overnight fog.

[Steven]

Hi Steve,

I am specifically going to point out the importance of drier air and rate of cooling at the surface in the rarer cases of frost occurrences at say 4-5C. Where you are, I assume the dew points are relatively higher (moister air) so perhaps this may be the reason? Any other comments?

Regards,

Jimmy Deguara

Hi,

Well it was a particularly dry morning and dew points were quite low (although they're usually high at that time), that obviously explains this scenario. Oh and there was no wind whatsoever! Can't really have frost development without calm clear conditions.

Steve