NSW Seasonal Conditions Summary August 2017

Overview

During July, rainfall was below average across 71 per cent of NSW. Most of eastern, central, north western and south western NSW received below average rainfall. Areas of the central tablelands, central west, Sydney basin, Hunter valley and north coast recorded either their driest July for 20 years or the driest or equal driest on record.

Rainfall across most of NSW ranked at less than 20-40 per cent of normal for the month, with most coastal areas, the Hunter valley, central west and areas of the far west generally ranking at less than 20 per cent of normal. Only limited areas of the far south received near-average rainfall for the month.

Pasture growth remained limited across much of inland NSW as a result of the continued warmer than normal daytime temperatures, combined with a lack of topsoil moisture, heavy frosts and grazing pressure. Levels of growth were maintained across some areas of southern NSW. Growth improved across areas of the far north east, the north west and the central to north coast.

Relative to historical records, pasture growth was well below average across most of western NSW, the northern half of the central west and the central Riverina, areas of the north west and the upper Hunter valley. Growth was slightly above average across areas of the northern tablelands, north coast and the far south, but slightly below average to near-average elsewhere.

Other pasture growth models indicated well below average to extremely low growth across most of inland NSW, with the exception of the northern tablelands and areas of the far west, north west and Riverina. Growth was also below to well below average growth across most of the south east and the upper Hunter valley. Growth was above average from areas of the Illawarra to the north coast. Growth was mostly near-average elsewhere.

Pasture biomass was relatively unchanged during July. It remained generally quite low across most of NSW, with the exception of areas of the far south. Relative to historical records, biomass was generally below average across areas of northern and central NSW, the upper Hunter valley and central Riverina.

Limited rainfall in July saw winter crop prospects continue to decline, particularly in areas of the central west and western Riverina. Growers in these regions commenced grazing out struggling cereal crops. Rainfall during July across the central and eastern Riverina and some areas of the north west, southern tablelands and southern central west was sufficient to maintain crop growth and yield potential. This was particularly the case for crops sown in late April and early May. Prospects in many areas improved with follow up rainfall in early August. Crops will be reliant on good rainfall during August to maintain current yield potential.

Prospects for summer cropping in northern NSW continue to decline, with many areas of the northwest having limited subsoil moisture reserves. Areas not sown to winter crops this year will require significant rainfall to allow a summer crop to be sown.

During July, topsoil moisture declined across much of NSW. Particular declines occurred across western, north western and central NSW, as well as the coast and northern tablelands. Topsoil moisture improved across areas of the eastern and central Riverina and the far south. Relative to historical records, topsoil moisture was below average across most of NSW. Topsoil moisture was near-average across areas of the far north west, the eastern and central Riverina and the mid-north coast.

Run off during July was well below average across the majority of NSW, but near-average across the far north west and areas of the north east.

NSW Seasonal Conditions Report – August 2017

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Seasonal outlook

The Bureau of Meteorology’s rainfall outlook for August to October (see the Climatic Outlook Summary below) indicates drier than normal conditions are likely across much of western, central and southern NSW and areas of the south east. There is a near-equal chance of drier or wetter than normal conditions across much of eastern, northern and areas of central western NSW.

Daytime and overnight temperatures are likely to be warmer than normal across NSW.

During August, drier than normal conditions are likely across most of NSW, with warmer daytime and overnight temperatures.

These outlooks have been influenced by the warmer than normal sea surface temperatures in the Indian Ocean, the prospect of high atmospheric pressure south of the continent and the possibility of a positive Southern Annular Mode. These contribute to the likelihood of decreased westerly winds and a reduced likelihood of rain-bearing systems across inland NSW.

The NOAA Climate Forecast System (CFS) rainfall outlook for August to October is near-neutral (that is, a near equal chance of drier or wetter than normal conditions) for NSW. Wetter than normal conditions are possible along some areas of the coastal strip. The overall temperature outlook is near-neutral for most of NSW. Warmer than normal conditions are possible for areas of the far north east, areas of the Hunter valley and areas of the coast. Cooler than normal conditions are possible for areas of the southern tablelands.

For August, the CFS rainfall outlook is near-neutral for most of NSW. Wetter than normal conditions are possible for the alpine areas. The overall temperature outlook is near-neutral for most of NSW, with warmer than normal temperatures possible for the far north east and along the coastal strip.

A survey of the major global climate models in early August indicated that for the majority of NSW most models (73 per cent) favoured a generally near-neutral outlook for the August to October period (a near-equal chance of drier or wetter than normal conditions). The remainder of models favoured a generally drier than normal outlook. For temperature, just over half the models favoured a near-neutral outlook, while the remainder favoured warmer than normal conditions.

Of the major multi-model ensembles surveyed, most favoured a near-neutral outlook for August to October, with the remainder favouring drier than normal conditions. Over the period, the multi-model ensembles were equally split between warmer than normal and near-neutral conditions.

Overall NSW outlook -

major climate models

Rainfall Outlook

(number of models)

Temperature Outlook

(number of models)

Period

Generally wetter

Generally

near-neutral

Generally

drier

Generally warmer

Generally

near-neutral

Generally

cooler

August – October

0

8

3

5

6

0

September – November

1

4

3

5

3

0

The AussieGRASS pasture growth outlook for August to October suggests that near-average growth is possible for most of NSW, with slightly below to below average growth for areas of the far west, central west, north west, central Riverina and far south. Above average growth is possible for some areas of the far west and the northern tablelands.

The SOI phase seasonal rainfall outlook that the growth outlook is based upon is near-neutral for most of NSW between August to October, with wetter than normal conditions possible for areas of the far west, north west and central west. This was based on a rapidly rising SOI phase during June and July. In comparison, the Bureau of Meteorology’s August to October rainfall outlook suggests drier than normal conditions across much of NSW. If these eventuate, potential growth may be very different from the outlook.

The current growth outlook has a moderate to high past accuracy across eastern and areas of far western NSW, but a low past accuracy for areas of western, central and north western NSW and the central Riverina.

El Niño Southern Oscillation (ENSO)

The Pacific Ocean remains in an ENSO-neutral state, with the outlook from most global climate models suggesting ENSO neutral conditions will continue throughout 2017.

The Bureau of Meteorology’s ENSO outlook status is currently ‘Inactive’. The CPC/IRI also indicate that ENSO neutral conditions are present and are likely to continue into spring. Note that the Bureau and CPC/IRI use different ENSO thresholds.

Some models indicate that a positive or borderline positive Indian Ocean Dipole (IOD) event is possible in late winter to early spring. The Dipole Mode Index recently became borderline positive, but will need to remain at or above this level for several more weeks to be regarded as a positive IOD event. Positive IOD events tend to suppress rainfall across Australia during winter and spring, with even borderline events having some effect.

Sea-surface temperatures across most of the central equatorial Pacific are near-average, with near-average to slightly warmer than average temperatures in the west. There has been some cooling in areas of the east, with sea surface temperatures in this region now slightly below average. In the Indian Ocean, sea surface temperatures are slightly above average in the west and below average in areas of the east, leading to the recently borderline positive Dipole Mode Index.

In the sub-surface, conditions are neutral to slightly La Niña-like. Areas of weak warm anomalies are present across the western equatorial Pacific to a depth of about 100m. A cool anomaly is present in the central to eastern Pacific at a depth of 50-150m. Weak warm anomalies are present in the far east at the surface and at depth.

The easterly trade winds were close to normal throughout July, with some strengthening near the International Date Line and some reversal in the far east.

The Southern Oscillation Index (SOI) was borderline positive in late July to early August, but has recently fallen again to neutral levels.

Atmospheric pressure returned to more normal levels across Australia during July, with slightly lower than normal pressure in the Great Australian Bight. The subtropical ridge moving northward to near its normal winter position, allowing the passage of more fronts and low pressure systems.

The Southern Annular Mode (SAM) was variable, moving from moderately to strongly positive early in July to near-neutral then weakly to moderately negative in late July. It briefly returned to moderately positive in early August before returning to neutral. This also favoured the passage of fronts in late July and in early-mid August.

The short term outlook suggests the SAM may return to moderately positive in mid-late August before moving to neutral late in the month. However, the overall outlook suggests the likelihood of the SAM returning to positive throughout winter. A positive SAM acts to drag cold fronts to the south, reducing the likelihood of them passing over southern Australia.

Under ENSO-neutral conditions, other influences such as the SAM, atmospheric pressure and sea surface temperatures near the continent tend to have a greater effect on the climate.

Climatic outlook summary

NSW Seasonal Outlook (BoM)

Current outlook

Previous outlook

Quarterly Rainfall

Drier

(most of western, central and southern NSW and areas of the south east)

Near-neutral

(most of eastern and northern NSW and areas of the central west)

Drier

(most of NSW)

Near-neutral

(areas of the coast, north, Hunter valley and northern tablelands)

Quarterly Maximum Temperature

Warmer

Warmer

Quarterly Minimum Temperature

Warmer

Warmer

(most of NSW)

Near-neutral

(far south western NSW)

El Niño Southern Oscillation (ENSO)

ENSO (overall)

Neutral

Neutral

BoM ENSO Outlook Status

Inactive

Inactive

Southern Oscillation Index (SOI)

Neutral

Slightly negative

(as a result of high pressure over Darwin, rather than an El Niño signal)

Pacific Ocean (NINO3.4)

Neutral

Neutral

(warm)

Indian Ocean (IOD)

Neutral (weakly positive)

(western Indian Ocean warm, eastern slightly cool)

Neutral

(western Indian Ocean slightly warm)

Southern Annular Mode (SAM/AAO)

Neutral

(trending from weakly-moderately positive to near neutral, but with a positive outlook throughout winter)

Strongly positive

(trending to near neutral, but with a positive outlook throughout winter)

Note: Climate model outlooks are updated regularly. To check whether updates are available, use the hyperlinks provided.

Rainfall and temperature

July was the driest across NSW since 2002. Areas of the state, particularly the central west, Sydney basin, Hunter valley and southern highlands reported their driest or equal driest July on record.

During July, rainfall was below 20-40 per cent of average across most of NSW. Only limited areas, including the far south and Riverina, received rainfall above 60 per cent of average.

Rainfall across the state ranged from 0-175 mm, with most of NSW receiving between 1-25 mm. Falls across the inland were generally light and patchy. The best falls generally occurred in the south, particularly in the alpine areas, and extended into the eastern and central Riverina.

Daytime temperatures were well above average for the month across most of NSW. Overnight temperatures were below average to well below average across most of inland NSW, but near average over areas of the north, far west and some areas in the far south. Minimum temperatures were also near average across the north east and the Illawarra to central coast.

Relative rainfall

Rainfall across NSW during July was below average across 71 per cent of the state and near-average across 28 per cent of the state.

Most of eastern NSW, the north west, tablelands, Monaro, central west, south west, western Riverina and areas of the northern Riverina received well below average to extremely low rainfall (rainfall in the lowest 10-20 per cent of years).

Areas of the north west, the far west, far south and the central to eastern Riverina received slightly below average to near-average rainfall.

Quarterly relative rainfall was below average across 81 per cent of the state and near-average across 18 per cent, with above average rainfall restricted to just 1 per cent of the state. Below average rainfall occurred across most of inland NSW, as well as areas of the south coast and Hunter valley. Near-average rainfall occurred across areas of the far south east, the northern slopes, northern tablelands and north coast.

Soil moisture

During July, topsoil moisture declined across much of western, north western and central NSW, as well as the coast and northern tablelands. Topsoil moisture improved across areas of the eastern and central Riverina and the far south.

Relative to historical records, July topsoil moisture levels were well below average across much of inland NSW, apart from areas of the far north west, north west, northern tablelands, north coast and far south. Above average topsoil moisture was limited to small areas of the northern tablelands and northern slopes.

The most reliable soil moisture models indicated declines in subsoil moisture across much of inland NSW during July, with levels improving in the north east. With these models, relative to historical records subsoil moisture was below to well below average across inland and south eastern NSW and slightly above average in the north east. Other models suggested only a slight decline in subsoil moisture across inland NSW, with above average levels across western, southern and areas of north eastern NSW.

Streamflow

Run off during July was well below average across most of inland NSW due to the limited and patchy rainfall.

Yearly run off to July remained influenced by the wet conditions in 2016. It was above average to extremely high across much of western and southern NSW and across the tablelands, northern slopes and far north coast. Run off was below average across areas of the north west, the northern central west and the far south coast.

The Bureau of Meteorology's streamflow forecast indicates low to near-median streamflows are likely at most NSW monitoring stations during August to October. Near-median to above median streamflows are likely at some north eastern locations.

Relative pasture growth and biomass

Relative to historical records, AussieGRASS modelled pasture growth during July was below average across most of western NSW, the central west, the north west (west of the Newell Highway), the upper Hunter valley and the central Riverina. Growth was average to above average across the northern tablelands and the north coast, and near-average elsewhere.

Other pasture growth models indicated well below average to extremely low growth across much of north western, central, southern and south-eastern NSW as well as the far south west. Growth was also low across the southern and central tablelands, Monaro and the upper Hunter valley. Growth was near-average across most of the far north west and areas of the northern slopes, northern tablelands and central Riverina. Above average growth occurred across areas of the north coast, lower Hunter valley and Sydney basin.

Over the quarter, AussieGRASS relative growth remained below average across areas of the far west, north west, northern central west, central Riverina and upper Hunter valley. Growth was above average across areas of the far south, south east, mid-north to north coast and the northern tablelands and near-average elsewhere.

During July, relative biomass levels were below average across areas of the north west plains, northern slopes, upper Hunter valley, Sydney basin, central Riverina, southern tablelands and northern areas of the central west and central tablelands. Levels were above average across limited areas of the far south east, far south, north coast and northern tablelands and near-average elsewhere.


Figure 1: Relative monthly topsoil moisture

Small map of relative soil moisture (upper level) - average value for July 2017

Figure 2: Relative quarterly pasture growth

Small map of pasture growth relative to historical records from 1957 - May 2017 to July 2017

More information

For more information, contact the NSW Department of Primary Industries on 02 6391 3100 or Local Land Services on 1300 795 299.

Acknowledgements

Information used in this report was sourced from the Australian Bureau of Meteorology, CSIRO, the Queensland Department of Science, Information Technology and Innovation, the Queensland Alliance for Agriculture and Food Innovation, the U.S. Department of Agriculture, U.S. Department of Commerce, the U.S. National Oceanic and Atmospheric Administration, the International Research Institute for Climate and Society (Columbia University), the UK Meteorological Office, the APEC Climate Centre, NSW Local Land Services and NSW Department of Primary Industries.

External links

Disclaimer

The seasonal outlooks presented in this report are obtained from the Australian Bureau of Meteorology and other sources. These outlooks are general statements about the likelihood (chance) of (for example) exceeding the median rainfall or minimum or maximum temperatures. Such probability outlooks should not be used as categorical or definitive forecasts, but should be regarded as tools to assist in risk management and decision making. Changes in seasonal outlooks may have occurred since this report was released. Outlook information was up to date as at early August 2017.

Recognising that some of the information in this document is provided by third parties, the State of New South Wales, the author and the publisher take no responsibility for the accuracy, currency, reliability and correctness of any information included in the document provided by third parties.

The information contained in this publication is based on knowledge and understanding at the time of writing (11 August 2017). However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of the Department of Primary Industries, Local Land Services or the user’s independent adviser.