The Fast Break Newsletter: December 2011
Seasonal climate risk information for Victoria
Volume 6/Issue 12 22 December 2011 | www.dpi.vic.gov.au/climaterisk | ISSN 1833-719
| Seasonal model forecasts for Victoria over the next three months: | |
|---|---|
| Current outlook (December 22) | Past outlook (October 28) |
|
PACIFIC OCEAN: Cool (La Nina) |
PACIFIC OCEAN: Cool (La Nina) INDIAN OCEAN: Neutral RAINFALL: Mixed TEMPERATURE: Average/slightly warmer |
 |
The SOI is strongly positive. The latest value is +21.6. This indicates that the air pressure conditions along the quator are consistent with a La Niña. http://www.bom.gov.au/climate/enso/
 |
The Southern Annular Mode has spent much of December in the positive phase. Over Summer this can increase the chance of rain in Eastern Victoria. http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_
 |
For the last 30 days high pressure over Australia has averaged at a close to normal position, however, this has been countered by slightly stronger pressure than normal. http://www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.gif
 |
The SST anomaly map still shows weak La Niña cooling of the equatorial Pacifi c Ocean. The Coral and Arafura Seas have rewarmed and the Timor sea remains warm. This is increasing the moisture feed chances for Victoria. www.osdpd.noaa.gov/ml/ocean/sst/anomaly.html
 |
Victoria has seen slightly more cloud for the past 30 days, as has much of Australia. Cloud is less than normal at the dateline on the equator, indicative of La Niña. Much of the Coral and Arafura Seas show more cloud orginating from evaporation in these warmer waters. http://www.bom.gov.au/climate/mjo/
| Editors | |||
|---|---|---|---|
| Dale Grey | Cobram DPI | 03 5871 0600 | dale.grey@dpi.vic.gov.au |
| Chris Sounness | Horsham DPI | 03 5362 2111 | chris.sounness@dpi.vic.gov.au |
| Chris Pittock | Horsham DPI | 03 5362 2111 | chris.pittock@dpi.com.au |
TABLE: Modelled Climate and Ocean Predictions 22 December 2011
2011 Rainfall Model Summaries for Victoria
Dale Grey DPI Cobram
We present again for your viewing pleasure a summary of how the climate models performed in
2011. For the fourth year, I bravely (stupidly?) present my unbiased, yet totally rudimentary attempt
at analysing the year’s predictions against reality (no correspondence will be entered into!).
For 2011 the Pacifi c Ocean declined from the strong La Nina going below the required threshold in
late March before levelling off at completely neutral through June and July. Things then progressively
cooled again and went above the La Nina threshold in October to the present day. The ECMWF
and JAMSTEC were the fi rst models in Autumn to indicate that the reforming of the La Nina was
possible, though at this stage they were picking it for winter. It took until August for many models to
detect the reforming but mainly for over summer; JAMSTEC and the UKMO were close with their
prediction for Spring. By September everyone was onto a La Nina for late spring and continuing
into summer, with some models now predicting its breakdown in Autumn 2012.
In the Indian Ocean, the dipole was neutral for much of the year but went positive in September
and October before collapsing at its normal time in November. POAMA was the fi rst model to get a
sniff of an IOD+ in April for the months of ASO. A number of models came on board in May but were
predicting an IOD+ for winter which did not quite occur. POAMA, NCEP and the UKMO were the
only models to pick the late spring IOD+ in May. ECMWF, JAMSTEC and UKMO continued to pick
it right for the spring IOD+ in the month of July. POAMA rejoined them in September.
Closer to Australia the Arafura and Timor Seas were cooler from March onwards, peaking for
coolness in July. This could have had some effect on the winter rainfall. The Coral Sea basically
played ball and was neutral for most of the year, retreating from January’s extreme warmth. In
January and February many models successfully predicted this winter cool ocean to the north of
Australia.
After last years purple patch performance for rainfall, many models struggled. As you can see
from the results table there is a lot of orange, meaning the models were getting some stuff right
and some not so accurate. Most of the better performance was during the summer La Nina and its
breakdown in autumn. After that the punters struggled, so this year’s gongs are pretty easy. The
only honourable mention goes to the BoM POAMA 1.5 and POAMA 2 computer models, which
were the only team to stick with a sniff of drier northern conditions throughout much of the growing
season. They also picked the drier winter in summer which was good work. Very few models
consistently picked the wetter Gippsland winter or the dry South West spring.
It wasn’t a particularly good year for statistical models. They struggled with the summer La Nina
and as to be expected, were constrained by the mainly neutral ocean conditions for much of the
year, but in fairness their more expensive computer cousins didn’t fair much better.
As an aside, in the data I haven’t presented for the 2010-11 summer, most of the computer models
did incredibly well at picking wetter conditions. What is even more amazing is the number of models
that predicted the wetter summer 4-6 month out, truly a great performance.
