Howdy,

I was at home (of course) over Christmas and boxing day... Looking at the
charts superficuially this evening, I am a bit surprised at the current
wide-spread fire situation.  It looks like the fires flared up in
southerlies or southwesterlies.. Is this true?  How high were the NSW
temperatures?  What were the synoptics leading to high fire potential?

cheers
JMcB

Reply from Robin Hicks

It seems that the fires started in the hotter conditions ahead of the trough that moved up the coast. Temperatures were hot ahead of the trough, which resulted in 39C temps in Brisbane on Christmas day, and ambulance reports of Queenslanders falling off their twig in the heat.

I've attached the hourly AWS obs from Camden (the nearest to the Warragamba fires of Christmas day). On both 24th and 25th, temperatures climbed into the mid 30's as westerly winds picked up. Pressures started rising and the wind went around WSW on the Tuesday evening. Wednesday was cooler but with still quite fresh winds, that moderated yesterday.

Cheers
 

Robin Hicks

a/SRFA
Services Policy Branch
Bureau of Meteorology, GPO Box 1289K Melbourne, 3001
Tel 03 9669 4401
Fax 03 9669 4695
 

Reply from Elly Spark

Hi there,

Christmas day temps were 34 to 36C in Sydney, Dew points ~ -3C,Winds were W/NW
20/25kts Gusts around 40 knots.
Northern Rivers:T=35 to 41, Td=~10C Winds WSW to WNW  up to around 25 knots
Similar stuff between there and wollongong and ranges to west.

Synoptics: Low south of tassie, strong westerly circulation around it. gradient
winds @30 to 40 knots. MesoLaps did pretty well at the sigma 9875 level. (we
don't generally use any lower than that)
Also: very strong thermal gradient between Tassie and Sydney

Boxing Day:
Sydney : W/SW 15/20 knots  - light ESE on coast.
Blue Mountains: : W/SW 20/25 knots

if you want to check out the details AWS obs for NSW stations these are at:

http://serva.nsw.bom.gov.au/cgi-bin/cmcgi/webdir.pl?d=/archive/station/2001/12/

PS:
Do  you know what the changes are that have been made to the model which will
allegedly make Mlaps better over the ocean. ? How will they change it? ( ie in
what direction ? At the moment most of us (incl me) use sigma 9875. This seems to
give reasonable esimation of surface winds over both land and ocean. Some of us
prefer 9750 over land esp ranges. Some of us think 9974 is Ok over ocean.

I have not noticed any noticeable changes so far that encourage me to use lower
level winds. When talking to Graham Warren a while ago he intimated that he had
been told coming changes would incorporate better coupling between atmospher and
ocean. If this is what has happened, increased winds should increase ocean
surface roughness, which should decrease surface winds - and make them even lower
than before. Please tell me this arm-waving argument is wrong, 'cause I don't
like the conclusion.

cheers

Elly Spark

Reply from Chris Webb

Hi John,

The 04Z Sydney Airport temp trace showed a dry adiabat from the sfc to 640hpa
on xmas day.

Chris Webb
SAMU

From Russell Stringer

Hi all,

can anyone point me to a display of NWP output showing the same information
for Sunday?
(ie. 04Z Sydney Airport temp trace for 30 Dec?). Wait... I just discovered
http://cod.tas.bom.gov.au/forecast.html (just need to know your lat/long)
 

For that matter, can anyone point me to the latest observation of the same
information? Wait... I just discovered
http://serva.sa.bom.gov.au/data/skewt/map.html

Cheers, Russell

From Milton Speer

I've attached Kurnell radar reflectivities (smoke particles from pyrocumulus)
for each of the last 4 days including today.

25 Dec    26 Dec   27 Dec    28 Dec        27 Dec_PPI
 

On the 25th the fire from the largest smoke plume you can see crossing
southern Sydney was ignited by lightning early morning on the 24th. 90 to 100
km/hr gusts drove it through the Royal National Park to the coast by late on
the 25th. On the 26 and 27th milder W/SW winds although still fresh and gusty,
drove the plumes. Today, the wind is back to the NW although light. We are all
gearing up for Sunday with temps in the high 30s forecast and fresh W/NW winds
by a squally souhterly change in the evening.

The synoptic situation is very similar to early January 94 and looks like
being a problem well into mid-week.
It's a long wave trough over Vic/Tas longitudes, as in 1994, that's causing
the hot westerlies over coastal NSW.

Local convergence zones affect fire behaviour adversely by increasing flame
height e.g. on the following velocity display from Kurnell Doppler radar the
orange edge represents the seabreeze front across Sydney going away from the
radar and blue represents westerlies going towards the radar (yesterday). The
orange between Katoomba and YSRI is likely local anabatic flows up the east
slopes.

Milton