SEASONAL CLIMATE OUTLOOKAdapted from: Bureau of Meteorology website http://www.bom.gov.au/Milking the Weather Webinar Series – Webinar 1, held 2 March 2018. The Fast Break - Feb 2018 update

Climate models suggest further cooling of the tropical Pacific is likely during the early southern summer but anticipate it will be a short-lived event, with limited influence on Australian rainfall patterns during summer. Most models suggest a transition back to ENSO neutral by April 2018. A weak and short-lived La Niña continues to break down, with a return to neutral conditions expected by mid-autumn. In the past, the break-down of weak La Niña events has seen drier conditions during autumn.

Rainfall and temperature summaries for summer 2017-18 The eastern half of Victoria has been generally wetter this summer and the western half generally drier, as indicated by the dotted line, in the following 2 maps. In the quarterly Victorian summer rainfall decile map, the east west division “mostly above average” and “mostly below average” respectively. In the quarterly Victorian summer rainfall totals map the east west division was “mostly above 100 millimetres” and “mostly below 100 millimetres” respectfully.

http://www.bom.gov.au/jsp/awap/rain/index.jsp?colour=colour&time=latest&step=0&map=decile&period=3month&area=vc

http://www.bom.gov.au/jsp/awap/rain/index.jsp?colour=colour&time=latest&step=0&map=totals&period=3month&area=vc

The Normalised Difference Vegetation Index (NDVI) grids and maps are derived from satellite data. The data provides an overview of the status and dynamics of vegetation across Australia, providing a measure the amount

Live green vegetation absorbs visible light (solar radiation) as part of photosynthesis. At the same time plants scatter (reflect) solar energy in the near infrared. This difference in absorption is quite unique to live vegetation and provides a measure of the greenness of the vegetation. NDVI is an index which measures this difference, providing a measure of vegetation density and condition. It is influenced by the fractional cover of the ground by vegetation, the vegetation density and the greenness. It indicates the photosynthetic capacity of the land surface cover.

Looking at how green Victoria was compared to normal this summer, except for a few parts in the hills in the north, north east and west of the state, most of Victoria was browner than normal (the white areas are normal), by quite a way.

http://www.bom.gov.au/jsp/awap/ndvi/index.jsp?colour=colour&time=latest&step=0&map=ndvianomsd&period=month&area=vc

Temperature wise, this summer we had extreme temperatures. As the Maximum Temperature Anomaly map (appearing to the left) indicates, we had vast areas in the north-west part of the state where maximum temperatures were 2 to 3 degrees warmer than normal (tan colour). Elsewhere in the state the anomaly was 1 to 2 degrees warmer than normal (yellow section of this map). http://www.bom.gov.au/jsp/awap/temp/index.jsp?colour=colour&time=latest&step=0&map=maxanom&period=3month&area=vc

http://www.bom.gov.au/jsp/awap/rain/index.jsp?colour=colour&time=latest&step=0&map=totals&period=3month&area=vc

The Normalised Difference Vegetation Index (NDVI) grids and maps are derived from satellite data. The data provides an overview of the status and dynamics of vegetation across Australia, providing a measure the amount

During this summer, February in particular, was a pretty dry month with nowhere in the state recording decile ranges above average (the white bits in the Victoria map on the right). Most of the state was at Decile 2 to 3 (below average) indicated by the light red shaded parts in the map. Some areas in West Gippsland and the Western side of Victoria were very much below average at Decile 1, indicated by the darker red bits on the map. http://www.bom.gov.au/jsp/awap/rain/index.jsp?colour=colour&time=latest&step=0&map=decile&period=daily&area=vc

ENSO Wrap up – Current state of the Pacific and Indian Oceans

However, it is unlikely to arrest the imminent return to ENSO-neutral conditions, with seven of eight models

indicating a likely return to neutral by May 2018. This would be in line with typical El Niño / La Niña evolution,

where events tend to peak in December/January and transition back to neutral in the autumn months. Further

information on the current status of ENSO can be found at http://www.bom.gov.au/climate/enso/

The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

A strongly and consistently positive SOI pattern (e.g. consistently above about +6 over a two month period) is related to a high probability of above the long-term average (median) rainfall for many areas of Australia, especially areas of eastern Australia (including northern Tasmania) - La Niña.

Conversely, a 'deep' and consistently negative SOI pattern (less than about minus 6 over a two month period, with little change over that period) is related to a high probability of below median rainfall for many areas of Australia at certain times of the year - El Niño.

It is important to remember however, that the pattern of relationship between SOI and rainfall (and temperature) can vary depending on the particular season and region. Additionally, the change in SOI over a specified period can be as important in understanding relationships between SOI and rainfall as is the absolute value in SOI.

The main moisture source in the Coral Sea has been pushed further over toward Australia as a result of the La Niña behaviour over summer. The Indian Ocean and the Timor Sea are looking quite normal, although there has been a lot of stirring up due to the cyclonic activity that’s been happening over summer; remembering that the Indian Ocean is much shallower and is much more prone to changes from weather activities.

Southern Oscillation Index (SOI)Autumn is the worst time of year to be looking for predictors for rainfall. The SOI is greatly affected by the wet season at this time. Better to watch and follow its behaviour at the end of the Tropical wet season; winter and spring. For the latest 30 Day moving SOI chart go to:

http://www.bom.gov.au/climate/enso/#tabs=SOI

Although the La Niña continues to weaken as we head into autumn, its pattern remains weakly evident in the tropical Pacific. As such, the ENSO Outlook remains at La Niña status for another fortnight. While temperatures in the tropical Pacific Ocean have been warming back to neutral values in recent weeks, a recent pulse in tropical activity may temporarily stall this pattern.

http://www.ospo.noaa.gov/Products/ocean/sst/anoma ly/

Currently we have remnants of the La Niña with the Nino regions of 3 & 3.4 (refer to map below) being at -0.48 °C & -0.60°C respectively); having backed off of the threshold for La Nina of -0.8°C.

For more information about the Nino regions, go to www.ncdc.noaa.gov/teleconnections/enso/indicators/sst.php

Southern Annular Mode (SAM) continued

The SAM was positive over summer, which can often lead to a wetter than average summer in eastern Victoria. BoM & NOAA predictions suggest

The Southern Annular Mode (SAM)

Also known as the Antarctic Oscillation (AAO), the SAM describes the north–south movement of the westerly wind belt that circles Antarctica, dominating the middle to higher latitudes of the southern hemisphere. The changing position of the westerly wind belt influences the strength and position of cold fronts and mid-latitude storm systems, and is an important driver of rainfall variability in southern Australia. In a nutshell it’s a measure of the strength of polar westerlies in the Southern Ocean. The SAM index is calculated by the differences in pressure between 40° and 60° latitude (the red circles in the image on the left). The SAM essentially pushes or pulls rain bearing triggers away from southern Victoria. In winter stronger westerly polar winds pull fronts away and slower polar winds push fronts closer. In summer the outcome is reversed.

The position of the sub-tropical ridge plays an important part in the way the weather in Australia varies from season to season. During the warmer half of the year in southern Australia (November to April), the sub-tropical ridge is generally located to the south of the continent. High pressure systems (also called anticyclones), which are associated with stable and dry conditions; generally move eastwards along the ridge. In autumn the sub-tropical ridge moves northward and remains over the Australian continent for most of the colder half of the year in southern Australia (May to October). Conditions along the ridge, under the influence of the high pressure systems dry and descending air, tend to be stable and drier.

Currently the STR is sitting around Adelaide (indicated by the red line in the sea level pressure map above. By winter it should get up to the top of the Great Australian Bite (close to the SA/WA border). So as we start to come into the autumn season and we are all looking for rain, it’s a good time to look at those synoptic charts and note where the centres of the highs are placed. What we are hoping to see is that the STR starts moving northwards, progressing through autumn. As the high pressure mass of the STR moves towards the Bite, it will allow frontal rain triggers to come closer to southern Victoria. Over summer the pressure has been lower over Victoria, but this has only led to more rain in the east of the state.

https://www.esrl.noaa.gov/psd/map/images/fnl/slp_30a.fnl.html

Southern Annular Mode (SAM) continued

The SAM was positive over summer, which can often lead to a wetter than average summer in eastern Victoria. BoM & NOAA predictions suggest

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/aao_index_mrf.shtml

Model forecasts– The skill accuracy of models at this time of year is low to medium. Such lack of accuracy is normal for this time of year and it’s the worst time to be looking for reliable predictions of rainfall. The majority of the models expect the La Nina to continue to decay leaving the Pacific Ocean slightly cooler, the Indian Ocean neutral, average rainfall and average/slightly warmer temperature this autumn (March to April) predicated in February. The autumn break will come due to an act of weather rather than climate. So it’s not impossible to get an autumn break like we did last year. Don’t write off an autumn break quite yet on the basis of just one or two climate models suggesting that it might be drier.

The table above also gives February predictions for winter forecasts. Understandably there is much less consensus amongst all models given that the start of winter is still four months away from when these predictions were done.

MILKING THE WEATHER (MTW) WEBINAR SERIESThe first of four Milking the Weather Webinars developed by Agriculture Victoria Dairy and Climate staff, tailored to the Victorian Dairy Industry was held last Friday 2 March 2018. These webinars are linked to the quarterly "Milking the Weather" (MtW) e-newsletter, which focuses on climate risk management. All four webinars will be recorded and available as webcasts;

Midday Friday 2 March: MtW webinar - autumn 2018 seasonal climate outlook for Victorian dairy farmers & "deep soil moisture probes on dryland farms as a tool to better understand seasonal conditions. Recording of this webinar can be currently accessed via https://attendee.gotowebinar.com/recording/667014720053239043

Midday Monday 26 March: MtW webinar- Victorian dairy farmers managing climate risk successfully this autumn with a focus on South Gippsland historical climatic data and progress update on the MtW South Gippsland case study farmer’s climatic risk action plan for autumn. Also includes panel discussion with other MtW farmer case study farmers state-wide.

Midday Wednesday 6 June: MtW- winter 2018 seasonal climate outlook for dairy farmers; “What can soil probes tell us" with a focus on implications for dairy pastures.

Midday Wednesday 20 June: MtW Webinar- Victorian dairy farmers managing climate risk successfully this autumn with a focus on Western Victoria historical climatic data and progress update on a Western District case study farmer’s climatic risk action plan for autumn. Also includes panel discussion with other MtW farmer case study farmers state-wide.

For more information about these webinars contact Maria Rose via email: maria.rose@ecodev.vic.gov.au

POSITIVE LINKING In edition of Milking the Weather we feature websites that Climate Specialist Graeme Anderson’s (Agriculture Victoria) suggests to help keep your eye on rain that’s on the way. The Break (subscribe free via The.Break@ecodev.vic.gov.au) provides monthly updates on seasonal forecasts models for Victorian farmers.

Here are some popular sites that show expected rainfall for the week ahead. Sometimes rain-inducing events can have even the experts on the hop, and in those instances some farmers like to surf a few 7 day forecasts to get the overall “vibe”. Try out these sites and see which ones work best for you!

Next week's weatherBoM Chartsviewer - Next 7 days http://www.bom.gov.au/australia/charts/viewer/index.shtmlThis is an animated output from the BoM’s Access weather model.

BoM Water & Land - 4 & 7 day rainfall outlook http://www.bom.gov.au/jsp/watl/rainfall/pme.jspThis is the output of a composite average from seven weather models from around the world.

BoM Met Eye rain, wind, temp forecasts http://www.bom.gov.au/australia/meteye/This is the output from bureau forecasters using models and human experience.

Longer term rainfall outlooks The Break (subscribe free via The.Break@ecodev.vic.gov.au)DEDJTR Victoria - Very Fast Break - monthly updates https://www.youtube.com/channel/UClDCIII7gRZhUs03opGqH1g

http://us3.campaign-archive2.com/?u=f44262ae409950c15c3de4c99&id=31715131cb&e=1ec2eed1f9

BoM Seasonal Climate Outlook - 1 to 3 mths http://www.bom.gov.au/climate/outlooks/#/overview/summary/BoM Seasonal Climate Video Updates http://www.bom.gov.au/climate/outlooks/#/overview/videoBoM ENSO Wrap-ups (El Nino, La Nina, IOD etc.)http://www.bom.gov.au/climate/enso/BoM Seasonal Streamflow Forecasts (runoff) http://www.bom.gov.au/water/ssf/BoM/CSIRO Soil Moisture (shallow & deep) http://www.csiro.au/awap/BoM/AWRA Root Zone Soil Moisture (actual & relative to normal maps) http://www.bom.gov.au/water/landscape/