Gedday,

  Since we are a weather Bureau and this is a "synoptic discussion" list, we really should be discussing the meteorology of the period of extreme high temperatures across the country during the period 6 to 20 February.  Blair Trewin of NCC has put together a nice internal document listing some of the extremes.  Possibly the most impressive are the new records for greatest number of days above specified thresholds:

South Australia:

Tarcoola 12 days over 40 (6-17 Feb);
Marree 4 nights over 30 (11-14 Feb)
Oodnadatta (17043/17114) 9 nights over 30 (12-20 Feb)
Snowtown (21046/21133)  16 days over 35 (5-20 Feb)
Adelaide (23000/23090)  17 days over 30 (4-20 Feb)
                                                     8 days over 35 (13 - 20 Feb)

New South Wales

Tibooburra   4 nights over 30 (14-17 Feb)
Wilcannia   16 days over 40 (6-21 Feb)
Scone   6 days over 37.8 (10-15 Feb)
        10 days over 35 (6-15 Feb)
Bathurst Ag   7 days over 35
Dubbo   7 days over 40 (10-16 Feb)
    10 days over 37.8 (7-16 Feb)

Sydney   10 nights over 22 (7-16 Feb)
Richmond 10 nights over 20 (7-16 Feb)
Cabramurra10 days over 25 (12-21 Feb)
Wagga Wagga 12 days over 35 (10-21 Feb)
Wyalong    7 days over 40 (10-16 Feb)

Queensland

Brisbane City  2 days over 40 (21-22 Feb)
 

Also from Blair's report I have put on my web-page a map of the highest tempertaure recorded at each point across the country during the fortnight ending 19th February.  it is very impressive with essentially the entire mainland above 30 and an absolutely huge area across the south above 42 and even 45.
 

So... the question is:  What is the mechanism by which thicknesses become so high.  I'll start looking through the charts and thinking; but I'm sure many of you out there have already put some thought into it.

cheers

John McB

 Geoff Crane
G'Day John,

It certainly was a dramatic hot spell. And the map is very impressive. But
on closer inspection I thought at first that it was wrong. Where is the 45
in Sydney's west? Where are Brisbane's two 40s? The problem is that the map
period stops before the heat wave was over. In fact in quite a few places
20/2 and 21/2 were the worst of the lot. And I think it might have missed
the start as well. What we need is a map of max max's over about three
weeks, starting a few days before and going to a few days after the period
of Blair's map.

Cheers,

Geoff

Jeff kepert
John

My impression (which could be wrong) is that it was remarkable not just
for the heat, but also for the relative lack thereof along the south
coast. Melbourne received little of the really hot air (only one day
over 40, well-picked by VRO), and the contrast was even more marked
along much of the S coast of WA (except around Esperance). I wouldn't
mind betting we set records for the Melbourne-Mildura temp difference -
Blair?? Presumably this is because there was a relative lack of strong
northerlies to keep the sea breeze out. I'd guess the two are related,
as strong northerlies would normally be followed by a change which would
push cooler air inland. But, as you say, why?

Jeff

Bruce Buckley

Hi All

One extra interesting feature of this heat wave (at least as far as it
affected the west) were the very high dew points associated with the high
temperatures. In Perth we had one day where the temperature was 41.4 with a
dew point of 21C - a combination of temp and dew point not previously seen
for Perth.

I do not know what the dew points were like for the remainder of the
country but it could also be investigated.

regards

Bruce

William Wright
G'day John and all,

This is not the first time I have observed the models predict, some days in advance, the
appearance (seemingly from nowhere) and maintenance of very high thicknesses. My subjective
impression is that these coincide with bursts of monsoon activity over tropical Australia,
possibly related to MJO pulses, and often accompanied by tropical cyclogenesis. Could it be
that the enormous amounts of latent heat released go to warming the adjacant dry subtropical
belt, with the meridional transport possibly via a local Hadley circulation, accentuated by
dry adiabatic subsidence?

Why this particular event was so extreme is not clear, but again: all the models predicted
the increases in thicknesses some days in advance. A study of the diagnostics might be
revealing.

Cheers all,

Bill Wright

David Jones

Geoff, your "wish" is granted. Please find attached mean max, mean anomaly, and highest max
temperature attached to this email. The mean max/min and anomalies are based on HQ sites
only, while the highest max temperature uses all data. I trust John will have this up in a
flash for those who don't receive the attachments through the majordoma server.

I have also attached the 200hPa Velocity Potential, MSLP , MSLP anomaly map  and hemispheric-mslp anomaly map for the first 24 days of the month, which includes the build up to the heat wave through to its "end" early this week.

Probably the first thing to say about this heat wave is that it is without precedent in February, and on a par with the January 1939 event as being the worst summer heatwave on record. However, unlike historically noteworthy heatwave such as January 1939 and January 1983, this one was not associated with precursory drought conditions, but instead very good
rains occurred in the months preceding (i.e. it wasn't simple a case of less latent and more sensible heat). In this regard, it shares some commonality with the other anomalous heatwave of recent times; that which occurred in January 2001 which interestingly enough had temperature anomalies which were spatially very similar to the most recent event (though did
not last for as long or so anomalies as large).

Quite simply based on the mean synoptic pattern I can see no good reason why the air mass should have got so hot... There was a slightly enhanced westerly pressure gradient over central Australia through much of the event, but the magnitude of this feature is unremarkable. The very high surface (and indeed column integrated moisture) during the heatwave also suggest subsidence warming did not play a major part - this latter point is borne out by the unremarkable upper divergence pattern.

On a day-by-day basis the period seemed to witness a remarkable lack of meridional air mass exchange (hot air south, cool air north); and hence the lack of blistering heat in south coastal parts as usually happens with such heatwave events.

Certainly an aspect that cannot be ignored in this event is that a good number of temperature records would not have fallen if it were not for the fact that Australia's background mean temperature is now approximately 1C higher than it was at the start of the 20th century. Dare I say, we can look forward to a good deal more of these record breakers on the basis of current global temperature trends.

Regards,

David

Dr David Jones

Head of Climate Analysis Section
National Climate Centre