If you’re dry sowing or trying to work out what the year will bring, you don’t want to miss this update.
Rain is the big decider of a season, and we know that in order for it to rain you have to have moisture and instability work together. We know plenty about the moisture part (and in good news, we have buckets of it ready at our disposal), but the instability part is the harder thing to forecast.
The Pacific Ocean has some models diving back into La Nina, some models grazing the El Nino threshold - and most of them remaining in Neutral. There isn’t a clear signal coming from the Pacific, but we do have warmer than average water off the Queensland coast that delivers plenty of moisture anyway.
The Indian Ocean looks to be slowly heading towards a Negative phase (the ‘La Nina of the Indian Ocean’). Sitting in Neutral for the next few months, then crossing the Negative threshold in late Winter or Spring. We also have warmer than average water off the northwest coast that delivers plenty of moisture, and this may be enhanced further as the year goes on.
So, that’s our buckets of moisture sorted, a big tick mark for this part.
The instability part is a lot harder to determine.
Think back to late March and early April and how a trough sat to the west of Queensland for an extended period, delivering huge rainfalls anywhere to its east.
When you have decent instability it can turn that moisture into significant rain.
Think back over the past 12 months, and how parts of southeastern Australia keep missing the rain systems - particularly between Melbourne and Ceduna and all areas inland from there.
The coastal part of this area gets its cool season rain from regular cold fronts passing through, and the much anticipated ‘Break’ is when these regular systems return after a hiatus over summer. You could set your clock by it: every few days you would get a top up as the next front arrived.
That Break is traditionally around Anzac Day - and last year, those fronts failed to arrive.
They weren’t strong enough to break through the dominant high pressure, or they’d deliver just a little bit as they slid past.
High pressure also acted in a way to block a connection to the tropics - where our big sources of moisture come from. Without that connection, the front or trough (or low) has the instability part of the equation, but it's lacking in moisture.
Are we going to see a repeat this year?
Potentially yes… but we don’t know for sure.
Over the next week there will be plenty of rain in the southwest, with much of the wheatbelt experiencing a great start to the season - while the southeast misses out as weather systems slide past. High pressure is in the right spot to make it dry, and incredibly warmer than average for an extended period of time.
In the last week of April there is a hint in the following map that a weather system could graze the southeast.
Will a trough/front/low push through the high pressure barrier? Will the weather system connect with tropical moisture (there is a heap of that with a cyclone up in the northwest)? Will we see a juicy northwest cloudband on the satellite actually make it through to the southeast?
These are certainly things to watch as Anzac Day comes and goes.
Looking further ahead and one model, the Euro, shows us there is hope on the horizon for the southeast:
Will the increase in moisture from the northwest as the season progresses connect with weather systems in the south? Will the highs move out of the way to let these systems connect?
That is the thing to watch this season, and unfortunately it’s not something that we have a definitive answer to ahead of time. To understand more, don't miss the full video where I go through each of our climate drivers in detail showing you how they may impact us over the next six months:
