Gedday,

I received an email from our model output statistician extraordinaire (Frank Woodcok) alerting me to some of the interesting temperatures in Melbourne over the holiday weekend.

The maximum temperature on Saturday was over 44C, which must be some kind of a record...
My question is a simple one... why did it get so warm... I have always believed that in Melbourne, near the sea, one doesn't get extreme high temperatures purely from the ground heating up in response to solar insolation.  On the contrary, such high temperatures can only come from advection.... On Saturday morning there was a very long overland trajectory; but the gradient wasn't all that strong.... the situation looked a bit innocuous for an extreme... any comments.

Even more interesting... late on Saturday a change of sorts (tied in with the seabreeze) came in and cooled the temperatures... through the night's early hours the temperatures were in the high 20's; but then between about
3.30 am and 5am they rose by more than 5 degrees (in 90 minutes) to about 32..... which is really interesting... any insights on this?

Still interesting, when I got up out of bed on Sunday morning, I logged on from home and checked the web... an east-west oriented change-line was lying across the northern suburbs..  (see maptool plot: wind (kts)/ temp .  I went to the VRO weather browser web page and pulled out the forecast for Sunday..... interesting: here are the forecast maximum temps for that day:
 

Forecast for Melbourne Issued at 0605 on Sunday the 26th of January 2003

                        Sunday
                        Partly cloudy with a few showers developing, mostly later today. Moderate to
                        fresh south to southwesterly winds.

                        Max 24

                        Suburban Temperatures

                        Laverton       Max 24    Yarra Glen     Max 38
                        Tullamarine    Max 30    Mt Dandenong   Max 36
                        Watsonia       Max 32    Scoresby       Max 32
                        Frankston      Max 25    Geelong        Max 25

Watsonia and Tullamarine are respectively about 10 km and 20 km north of
the city.  Scoresby is about 20 km directly east, Frankston about 30 km
southeast....

How did these temperature verify?
Ah...well... back to whatver it is I do on a Monday public holiday when
there is no cricket on TV, the tennis is finished...... hmmm...

John McB

Gary Weymouth

"The maximum temperature on Saturday was over 44C, which must be some kind of a record...
My question is a simple one... why did it get so warm... I have always believed that in Melbourne, near the sea, one doesn't get extreme high temperatures purely from the ground heating up in response to solar insolation.  On the contrary, such high temperatures can only come from advection.... On Saturday morning there was a very long overland trajectory; but the gradient wasn't all that strong.... the situation looked a bit innocuous for an extreme... any comments."

*    A very warm airmass (580+ gpdm) and enough of a gradient to keep out  the sea breeze in Melb - the main things.  *    Enough mixing but not so much  that all solar heating was mixed too deeply?  A very warm start.
*    Very dry soil - solar goes into sensible rather than latent heat.
*    Enough advection that air well north of Mildura would have been brought to Melb lats in 24 hr (Mildura and similar places about 42 on Friday)
*    Surprisingly little cloud with a change so close...
No doubt you're aware of these things really...

Even more interesting... late on Saturday a change of sorts (tied in with the seabreeze) came in and cooled the temperatures... through the night's early hours the temperatures were in the high 20's; but then between about
3.30 am and 5am they rose by more than 5 degrees (in 90 minutes) to about 32..... which is really interesting... any insights on this?

LAPS and mesolaps wind fields predicted this, aside from exact timing and position issues. (wind prog, temp prog) Nightmare to get the frontal forecast position right for Sunday morning. Apparently there was once a case of a front that lay between Melb and Geelong all day. I think that the evening before Black Friday, a weak change went through Melb, and was washed out again by morning?  No doubt someone else knows the situation better.

Blair Trewin

"The maximum temperature on Saturday was over 44C, which must be some kind
of a record..."

44.1, highest since 1939 and fourth-highest on record (it was incorrectly reported in Saturday's Notes on the Weather - and hence in the media - as second-highest, not sure why).

Blair

Graham Mills
John,

Without any deep analysis, all the models last week were moving a warm tongue ahead of the change, with the air mass characterised by 1000-500 thicknesses above 580 dam. My f160 shows that to indicate a potential temperature of 42+.
Thus in a sense the high temperatures were aresult of advection. Then we get back to the chicken and egg stuff - why did the temperature of that air get so high? Why did we get it down here?

William Wright
RE the high temperature.  I hope that the myth that  Melbourne's 44.1 was its second highest temperature does not become perpetuated; as Blair points out, it only comes in 4th.

The high temperatures were indeed due to advection - 850 hPa temps of 25-26C advected from NW. I dispute the lack of gradient - the 9am Laverton wind flight for Saturday morning indicated 44 knots at "gradient level" (900 hPa). Where I live, at 515 metres and often above the boundary layer, winds were quite strong - 20-25 knot northerlies most of the day (and a maximum of 39.3C). As my area is highly bushfire prone, this was of some concern. I understand Melbourne Airport had mean wind-speeds in the range 25-30 knots Saturday morning.

There is some evidence that on other noted extreme days such as Black Friday, 13.01.39 (Melb 45.6C) and Ash Wednesday 16.02.83 (43.0) the mean wind-speeds at stations at approx 500m elevation were probably of the order of 30 knots.

It would be interesting to know what the ridge-top wind-speeds in the Victorian high country were on Sunday - any info?

RE John's second point: the high overnight temperature spike in Melbourne was presumably due to a retrogression of the trough - again my own observations for Saturday were that the N wind got quite strong again for a time early Sunday morning (following an easing late Saturday). Presumably the warmer air mixed down to low levels for a time early a.m.

By the way, progs for next few days reveal - unfortunately - record-breaking temp potential in NSW for Thursday.

Bye for now,

Bill Wright

David Jones

John et al.,

One point that came from this event was how valuable the meso-scale models are for small scale forecasting. The 00Z Saturday meso-laps run very clearly showed a sea breeze frontal passage for Melbourne around 5pm Saturday, a
return to variable/light northerly winds during the night, and the synoptic wind change around 7-8am in the morning. These features verified extremely well with what was seen.

RE the verification, I think the official forecast underestimated the fairly rapid penetration of the synoptic front through Melbourne around 7-8am Sunday. This change went through our place (2km southeast of "Mt Dandenong" at 400m just prior to 7am), the official forecast for Mt Dandenong was approximately 13C to high... I'm not sure why this official guidance seemed to differ, somewhat, from the NWP output?

BTW, I think all those in the modeling and forecasting game really deserve a big pat on the back. The NWP models forewarned almost a week out that SE Australia was likely to face one of its hottest days on record - and this is
due to the hard work of modelers over the past few decades. The same also goes for the forecasters in VRO - I was talking to our local CFA captain last night and he heaped praise on the work of the BoM this year....

Regards,

David

Robin Hicks

"It would be interesting to know what the ridge-top wind-speeds in the
Victorian high country were on Sunday - any info? "
>>>>>>>
The wind speeds at Mt Hotham on Saturday afternoon were typically 17 to 19
knots gusting towards 30 knots
25 23:00 21.0 7.3 41 N 33 18 41 22 - 0.0
25 22:00 21.1 7.7 42 N 30 16 33 18 - 0.0
25 21:00 21.2 7.8 42 N 26 14 31 17 - 0.0
25 20:00 21.5 8.1 42 N 26 14 35 19 - 0.0
25 19:00 22.0 7.8 40 NNW 30 16 39 21 - 0.0
25 18:00 23.0 7.9 38 NNW 33 18 43 23 - 0.0
25 17:00 23.1 8.4 39 N 35 19 48 26 - 0.0
25 16:00 22.8 8.9 41 NNW 31 17 43 23 - 0.0
25 14:51 23.6 8.8 39 NNW 30 16 50 27 - 0.0
25 14:00 22.9 9.0 41 N 35 19 48 26 - 0.0
25 13:00 22.3 8.8 42 NNW 33 18 54 29 - 0.0
25 12:00 21.2 7.1 40 N 35 19 52 28 - 0.0
 

They were actually stronger on the Sunday afternnon, viz
26 14:59 23.2 4.2 29 NNW 44 24 67 36 - 0.0
26 14:00 23.4 3.9 28 NNW 48 26 68 37 - 0.0
26 12:54 22.7 2.8 27 N 50 27 68 37 - 0.0
26 12:00 22.4 2.5 27 N 44 24 63 34 - 0.0
26 11:00 22.1 3.3 29 N 46 25 63 34 - 0.0
26 10:00 21.0 3.2 31 N 43 23 57 31 - 0.0
26 09:00 20.0 4.1 35 N 41 22 59 32 - 0.0
(After 3pm there seems to have been a comms outage due to the bushfires.
However, comms seem to have been restored since about 4pm Monday)