Rain is spreading across such a large area of eastern Australia, that it is likely to drench the Murray-Darling Basin with its biggest falls since March.
By the weekend virtually all of the catchment will have received some rain, about 25-to-50 millimetres on average. This will make it the heaviest, most widespread rain the Murray-Darling Catchment has seen since March, when La Nina was still a major influence.
The wettest areas look like being on the inland slopes of the Great Dividing Range, from about Goondiwindi in Queensland to about Wangaratta in Victoria, where 50-to-100mm is likely. Some places along this stretch may gain more than 100mm.
Not only will this be the biggest rain in four months it will also be significant for July. Much of the region will gain near-or-above their monthly average in about three days.
It may turn out to be the biggest July rain in decades, giving many farmers what they need to get winter crops thriving after a fairly dry start to the season. Soil moisture will increase and some dams will fill.
This is quite an important event, given we are trending towards an El Nino. During an El Nino large parts of the country typically see drier-than-average seasons.
Since 9am Monday Broken Hill had already gained 29mm, 10mm more than its monthly average and its heaviest July rain in 16 years.
Even though we are no longer in a La Nina, a warmer-than-normal Coral Sea is supplying plenty of moisture, which is being carried inland by easterly winds. A low pressure trough over the inland is tapping into this moisture to bring the substantial rain. A front will bring colder air into the mix later in the week to bring a final burst of rain and storms. A high pressure system will then dry out the region over the weekend.
Unfortunately for some parts of the catchment, the South Australian stretch of the Murray River, less than 10mm is the likely rainfall this week. It will be too far from the major source of moisture.
Despite the lack of rain in the southern part of the catchment, there will be some flows from upstream in the coming month or so.
As of the 26th of June, the Murray-Darling was at 92% capacity.
© Weatherzone 2012
19:36 EST Over the past 24 hours, a northwest cloud band has delivered some spectacular rain from the northwest WA to the inland SA and the NT.