Climate in-brief

• Moisture levels and tropical divergence remains high to Australia’s north, albeit with MJO predictions offering little in terms of strength and its next move.

• The Southern Annular Mode is weakly-moderately positive and predicted to remain so, - assisting moisture flow through NSW and S Qld areas.

• Multi-week models showing some signs of low-air pressure and moisture continuing into the second week of January. Shorter-term guidance is showing only sporadic and smaller totals throughout the forecast area - staying in touch with information when it comes to hand will be critical in the coming days

• Temperatures to remain around normal or cooler through until mid-January, consistent with the presence of the MJO to Australia’s north

The chart above shows higher-than-normal air pressure in SE Australia for the last 30-days and lower air pressure to the NW.

Australian weekly rainfall and relative landscape water balance

Some handy falls confined to the Great Dividing Range and western slopes of the ranges in the last 24 -48 hrs. Click on the link for an updated map. http://www.bom.gov.au/australia/flood/?ref=ftr

Weekly rain shows the NSW north coast and ranges being in the sweet spot, along with the norther Territory and Western Australia.

Australian 7-day rainfall map courtesy http://www.bom.gov.au/climate/maps/rainfall/?variable=rainfall&map=totals&period=week&region=nat&year=2020&month=12&day=17

Climate in-brief

• A moderately active MJO pulse is making its way eastwards along the equator towards Australia’s north, which has been difficult to track on the spider diagram “Evaluation of individual circulation and convective variables supports a robust MJO over the Maritime Continent” (NCEP 1 Dec).

• The Southern Annular Mode is back above zero, and is predicted to stay in the positive (wet) phase in the coming fortnight - assisting moisture flow through NSW and S Qld areas.

• Anomalous high pressure has been the feature off eastern Australia over the last month, with many eastern locations achieving decile 1-2 November rainfall (see map opposite and bottom right).

• Multi-week models showing consensus for a more general wetter-than-normal period 11-31 December. Shorter-term guidance is showing little enthusiasm for general rain events at this stage - staying in touch with information when it comes to hand will be critical in the coming days

• Temperatures to remain around normal or cooler for December, with recent heat wave activity abating.

The chart above shows higher-than-normal air pressure across eastern/northern Australia for the last 30-days.

Australian weekly rainfall and relative landscape water balance

Some handy falls in northern NSW and border rivers overnight. Isolated patchy falls elsewhere in S Qld, the big rivers area of NT and Kununurra also. http://www.bom.gov.au/australia/flood/?ref=ftr

November rainfall decile map shows a sorry tale of dry weather during La Nina 2020 - perfect for grain harvest, although summer crop and livestock producers would beg to differ.

Australian decile map courtesy http://www.bom.gov.au/climate/maps/rainfall/?variable=rainfall&map=decile&period=month&region=nat&year=2020&month=11&day=30

Climate drivers - update

The story of this fortnight is the SAM and MJO finally going to script in-line with the La Niña signal. The air pressure at Darwin is below normal (1007 hPa) and the SOI has returned to above +8 a threshold for La Niña conditions. With a week-moderate MJO pulse approaching to the north of Australia, drivers look as primed as they have been for months to introduce the 2020 La Niña to many areas of eastern Australia in December, so far untouched.

What to know about the climate drivers and how they are measured? Click here

Monitoring the SAM

The SAM has bounced around a bit lately, but the outlook for the next 14-day period looks much more settled into a positive (wet) phase (above the dotted black line). This is good news and timely, with an approaching MJO.

Antarctic Oscillation or SAM values (4 Dec)

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/aao_index.html

Recent research by Hendon et al, (2014) at the Centre for Australian Weather and Climate Research found the Southern Annular Mode to be the leading mode of circulation variability through parts of inland eastern Australia where cotton is grown; particularly in the spring planting period.
 
A positive SAM has been proven to increase moisture supply into fronts and troughs forming in eastern Australia. The chart provided by Climate Prediction Center (US) shows the most recent observations of the SAM or (AAO). 

A negative SAM traditionally leads to a dry westerly circulation pattern through eastern Australian cropping areas.
 
BOM researchers Lim and Hendon (2013) found the SAM has the strongest connection with El-Niño Southern Oscillation in October and November – whereby the SAM is influenced most by El Niño or La Niña conditions.

Growers and advisors are encouraged to monitor the phases of the SAM together with seasonal forecasting, multi-week and short term weather models during planting. A short cartoon explaining the SAM can be found HERE. 

Global tropical hazards

(from U.S Climate Prediction Center)

Some action in the tropics at last! The noticeable features in the chart below show a potential cyclone development in the western Timor Sea and above normal rainfall for the Qld gulf and tropical coast next week (bottom chart).

Jason Nicholls (@jnmet) at ACCU weather reports this morning, the potential cyclone development occurring 7-12 December in Australia’s north-west.

Chart of the Week - water vapour prediction (Sat-Tue)

The water vapor content of the atmosphere is of critical importance to nearly every facet of atmospheric science. Observing the processes that determine the water vapor content of the atmosphere is, therefore, of fundamental importance. As the earth’s surface is the source of most atmospheric water vapor, observations of vertical turbulent transport of water vapor in the planetary boundary layer have been the subject of many research projects. Evapotranspiration can vary significantly across the earth’s surface due, for example, to variability in insolation, vegetation cover, soil properties, and precipitation. Area-averaged water vapor flux measurements are necessary to get a large-scale view of surface–atmosphere interactions. 

The Extreme Forecasting Index (EFI) is an integral measure of the difference between the ensemble forecast (ENS) distribution and the model climate (M-climate) distribution. This allows the abnormality of the forecast weather situation to be assessed without defining specific (space- and time-dependant) thresholds. The EFI takes values from -1 to +1. If all the ensemble members forecast values above the M-climate maximum, EFI = +1; if they all forecast values below the M-climate minimum, EFI = -1. Experience suggests that EFI magnitudes of 0.5 - 0.8 (irrespective of sign) can be generally regarded as signifying that "unusual" weather is likely whilst magnitudes above 0.8 usually signify that "very unusual" weather is likely. Although larger EFI values indicate that an extreme event is more likely, the values do not represent probabilities as such. 

Let’s hope the high levels of atmospheric water vapour can flow through to precipitation in parched N NSW and S Qld areas (image courtesy ECMWF).

https://apps.ecmwf.int/webapps/opencharts/products/efi2web_wvf?area=Australia&base_time=202010220000&day=2&player_dimension=base_time&quantile=1

9-day ECMWF rainfall outlook

Fresh today, the European ECMWF 9-day model shows rainfall deepening into desert areas of Western Australia with the MJO approaching. Kununurra, Katherine and Gulf areas should see a break in the next week or so. Some moisture also filtering down the Qld coast and scattered areas of NSW inland and ranges. Date range: 3rd - 13th December.

Updated multi-week models are still bullish this morning for a general rain event December weeks 2-4, consistent with the last fortnight.

Access courtesy https://meteologix.com/au

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