Seasonal Climate Outlook Message for September to December 2003
The bottom line
SOI Remains Near Zero 30/09/03
The Queensland Department of Primary Industries seasonal outlook highlights a relatively mediocre chance of getting above the long term October to December median rainfall level for much of Queensland. Specifically, there is a 30 to 50% chance of getting above the long term October to December median rainfall across the state.
For Queensland drought conditions to break, sustained, well above average rainfall is needed. However, at this stage, there are no indications that this is likely in the short to medium term. For better chances of seasonal conditions improving, the SOI needs to return to more sustained positive values.
Many readers of this column like to follow the timing of the MJO (also know as the 40day wave). The MJO is simply a band of low atmospheric pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 50 days.
While it is a tropical phenomenon, it appears to indicate the timing of potential rainfall events (but unfortunately not rainfall amounts) over central and southern Queensland.
The next passage of the MJO is expected to influence our weather in the first half of October.
The full story
SOI Remains In "Near Zero" Phase 30/09/03
The monthly value of the SOI has remained stable from the end of August (minus 1.1) through to the end of September (minus 1.5). Based on the shift in value from the end of August to the end of September the SOI remains in a "Near Zero" (or neutral) phase.
For those interested in following historical patterns more closely, some of the more recent years that have had the same SOI pattern at the end of September include 1999, 1995, 1992, 1986, 1985, 1984, 1980, 1878, 1968, 1966, 1963 and 1961.
It can be useful to find out what rainfall and farming conditions where like in your area for October to December in those years. Information on what rainfall patterns where like in those years is available in Australian Rainman or at www.longpaddock.qld.gov.au
Rainfall Outlook
The Queensland Department of Primary Industries seasonal outlook highlights a relatively mediocre chance of getting above the long term October to December median rainfall level for much of Australia.
Specifically, there is a 30 to 50% chance of getting above the long term October to December median rainfall for most of Queensland, the Northern Territory, central and northern Western Australia, South Australia, central and northern New South Wales and parts of Victoria and Tasmania. Rainfall probabilities are marginally higher (at 50-60%) for the southern section of WA, eastern SA, southern NSW and scattered parts of Victoria and Tasmania.
For Queensland drought conditions to break, sustained, well above average rainfall is needed. However, at this stage, there are no indications that this is likely in the short to medium term. For better chances of seasonal conditions improving the SOI needs to return to more sustained positive values.
This forecast does not suggest or indicate the potential distribution or expected timing of rainfall over this period. This forecast is for the full 3 month period and does not suggest that expected rain will fall evenly across these 3 months.
The latest rainfall probability maps and a more detailed seasonal outlook can also be found at www.dpi.qld.gov.au/climate or at www.longpaddock.qld.gov.au
As always when using any probability based forecast system, it is important to consider the alternate view. For example, Emerald currently has a relatively low 35% chance of getting above the long term October to December median rainfall of 175mm. This also means that there is a 65% chance of not getting above the long term 3month median rainfall of 175mm.
Another way of looking at this is that in 3 to 4 years out of 10 (or around one third) with the current SOI pattern, Emerald has received more than 175mm for October to December. Therefore in 6 to 7 years out of 10 (around two thirds), Emerald has gotten less than 175mm for this period.
MJO
Many readers of this column like to follow the timing of the MJO (also know as the 40day wave). The MJO is simply a band of low atmospheric pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 50 days.
While it is a tropical phenomenon, it appears to indicate the timing of potential rainfall events (but unfortunately not rainfall amounts) over central and southern Queensland.
The next passage of the MJO is expected to influence our weather in the first half of October.
Queensland Winter Crop Outlook - Wheat
At the end of August, current crop conditions and the seasonal rainfall outlook indicated a forecast state wheat yield median of 1.40 t/ha for the 2003 wheat-growing season. This indicated a high chance of a near average yielding crop at the state level.
The outlook for the wheat crop yield in most of the state's cropping areas remains near the long-term median. This was mainly due to the average to slightly above average rainfall recorded in most of these areas during August.
For parts of central Qld there is a high chance of falling in the worst 10% of years. However apart from these areas, the remainder of the state (i.e. south east Qld and south west Qld) has a high chance of near to above median crop yield for the 2003 season. Departure of the forecast shire median yield for this year from the long-term median shire wheat yield is shown in Figure 2. Any areas coloured in light grey, yellow and red are expected to have crops below to very much below the long-term median yield, whereas areas coloured in dark grey, green and blue are expected to be above to very much above the long-term shire wheat yield median.
The calculation of benchmark yields and outlook chances do not take into account effects of poor crop nutrition or damage due to pests, diseases, frosts, and extreme high temperatures or depict estimates on crop area planted.
Key Points
When incorporating climate forecasts into management decisions, it could be worthwhile to consider some of the following general rules of thumb developed from feedback from climate users.
* The first point is to be sure of your source of information and what it is actually suggesting. Do not take a quick grab of information from any source including radio or TV and assume what you heard applies to your location.
* Try to access local information or at least be aware of the long term median for your location so you can correctly interpret the forecast.
* It has also been shown to be useful to do a cost benefit analysis of any decision with a climate risk factor eg What will I gain if I get the desired outcome from this decision? What will I lose if I don't get the desired outcome from this decision? What other cost neutral options do I have if any?
* Do not to take a forecast for a specific period (eg September to November) and expand it out (eg late summer).
SST Information
Both the United States Climate Prediction Centre www.cpc.ncep.noaa.gov/ and the Bureau of Meteorology www.bom.gov.au/ continue to highlight that a neutral sea temperature pattern continues to persist in the tropical Pacific Ocean.
Overall, very little net change has been observed in SST anomalies in the central equatorial Pacific over the last couple of months. Sea-surface temperatures have remained close to average (temperature anomalies of -1 to +1oC) with no strong signals towards the development of either an El Nino or La Nina in the next few months.
Subsurface temperature recordings have also generally shown near average throughout the central Pacific. The south east trade winds while varying have been also been generally near normal.
Ocean and coupled ocean/atmosphere forecast models (GCM's) give an indication as to likely ENSO development out to 9 months. Of 12 models that forecast out to January 2004, 11 indicate the development of a neutral sea temperature pattern and 1 indicates the potential development of an El Nino (or warm) sea temperature pattern.
Of the 8 models that forecast out to April 2004, all of them indicate the development of a neutral sea temperature pattern. While it is positive news that these models show the development of a neutral SST pattern (rather than an El Nino SST pattern) given current ocean and atmospheric conditions our policy remains to recommend a cautious approach when considering the longer term outlook.
More details can be found at www.bom.gov.au/climate/ahead/ENSO-summary.shtml
