WOW! So this just happened in Australia this evening (15th December 2020).
Max 3199 km on 144 MHz WSPR, Sydney to near Perth. Some type of Sporadic E we presume, double hop or maybe chordal hop. Unreal scenario these paths, over 1 hour past sun down in eastern Australia. Many people at the time were reporting 6m paths and well as FM Broadcast band signals across the same path, but not necessarily the full Sydney Perth distance.
I was hearing Kalgoorlie FM and also southern Northern Territory FMs for instance. Other reports of FM from Adelaide to WA and vice versa.
Well done to John Vk2ijm David VK2DVM Peter VK6KXW and also David VK5AYD & Nigel Hanwell VK6CPU.
While we understand these are not QSO's on WSPR, but the path just being completed in one direction is incredible in itself! They do indicate potential for QSOs if these paths became stronger.

   

Once in a lifetime opportunity? 
Maybe not, as last summer in the afternoon of the 6th December 2019, David VK2DVM also had his 2m WSPR signal received by Nigel VK6NI just west of Albany @ 3102 km. 
Although extremely rare, perhaps these paths are available more often than we may think, its just a matter of having people actually monitoring the bands more often, with more sensitive gear, which is what WSPR is able to do so long as people are prepared to set up beacons running WSPR or be monitoring or both, especially from Western Australia, as there are plenty on the eastern sea board. We were just lucky to have VK6NI, VK6KXW and VK6CPU monitoring at the time to bring these paths to light.
Other stations in different areas would possibly show up even more paths, such as NW VK6 and Darwin on 2m WSPR.
If you can help out, please do, time is running out as this type of activity only happens for around 2 months each year, and they are the month either side of the summer solstice, we have almost reached the middle of the peak period now so if you are able to get a good station on air now is the time.

Stations on both 6m & 2m WSPR are really advantageous.
In order to find the higher E MUF areas, we can evaluate what is happening on 50 MHz WSPR to get an idea of where high MUF paths may occur and get an early indication. This can be done by just overall observation of all signals reported, but also -
-certain signals indicate a backscatter area is around, which is a good indicator of a high MUF area forming or not in a usable position yet. These are usually shorter and weaker signals, such as those between 450 and 1200 km with signal less than about -5dB.
-Short signals between 400 and 900 km with high signal strength above +1dB generally indicate high MUF E areas at the mid points, approx.
-Longer paths give an indication that the paths exist and the MUF could move higher, but its difficult to tell the extent of the E MUF on these longer paths, so you just have to try, and monitor with 2m or watch the FM Broadcast band signals. You can only really tell if these paths have higher MUF potential if there are shorter paths mentioned above, along the longer run.

Hopefully today will be a good one.