THE Department of Primary Industries and Regional Development's (DPIRD) Statistical Seasonal Forecast (SSF) for the next three months has an overall prediction of a drier than normal season, with some variable predictions for different regions.
The SSF indicates the chances of exceeding median rainfall between May and July is less than average (40 per cent) in the northern and southern grainbelt, more favourable (60pc) in the far eastern areas and the shires of Ravensthorpe and Esperance and neutral (40-60pc) elsewhere.
Confidence in the prediction varies from poor to good (50-75pc consistent).
The most probable rainfall decile range is 2-3 for the northern and southern grainbelt, 8-10 for Ravensthorpe and Esperance and 4-7 elsewhere.
The Bureau of Meteorology's (BoM) seasonal outlook for the same period in the grainbelt is for a 30-70pc chance of exceeding median rainfall, with a lower chance (30-45pc) in southern parts of the northern grainbelt, western central grainbelt and the South West and a higher chance (60-70pc) in the Esperance and Ravensthorpe shires, based on a similar predictive skill.
BoM's temperature outlook for May to July indicates a 50-75pc chance of above average day time maxima for the grainbelt, based on a mostly good predictive skill, while it suggests a 50-70pc chance of above average night time minima, based on mostly poor predictive skill.
DPIRD research officer Meredith Guthrie said the SSF outlook for May to October was similar to the three-month outlook.
"Combining seasonal outlooks with multi-week rainfall forecasts suggests the 2019 growing season is likely to have a late break and will be similar to last year for many districts," Dr Guthrie said.
"Other climate models indicate drier conditions for much of the grainbelt, with the possibility of a positive Indian Ocean Dipole by September, which could reduce the chances of good finishing rains."
DPIRD's plant available soil water maps, available online, show stored soil moisture levels are extremely low across much of the grainbelt except for parts of the south coast.
Research officer Jeremy Lemon said growers across much of grainbelt were considering modifying their sowing program in response to low soil water and the late start to the season, by changing crops and reconsidering the use of poorer paddocks.
Mr Lemon said nitrogen fertiliser applications would also require review during the season and advised growers to closely assess their yield potential, stored soil water levels and weather forecast when deciding how much to apply and when.
"Department research has shown top-up nitrogen for canola in low and medium rainfall areas can be delayed until the start of flowering, about 12 weeks after sowing, without reducing yield," Mr Lemon said.
"Following a small starter nitrogen application at seeding, top-up nitrogen for barley and wheat should be delayed to the late tillering or early stem elongation stage.
"This delayed nitrogen does not reduce yield, while often providing higher grain protein."
Pasture growth rates have also been varied across the grainbelt, as shown by weekly Pastures from Space feed on offer (FOO) maps, now available for free from DPIRD's Season 2019 webpage.
DPIRD veterinary officer Danny Roberts encouraged livestock producers to adjust their feed budgets in line with the seasonal forecast as well as taking into account the amount of green pasture, as it becomes available.
"The FOO maps suggest the vast majority of livestock producers across the agricultural region could well be supplementary feeding until July," Dr Roberts said.
A range of climate and weather tools and live weather data is available at weather.agric.wa.gov.au to assist landholders to navigate the growing season, while more management support material is available on its Season 2019 webpage.