CLIMATE UPDATE - JUNE 2021 UPDATED JUNE 01 2021.

Headlines.


  • Continuing with the wet signal for southern and western areas now carrying through the eastern inland with a two rain events over the east early this month.

  • Colder than normal for southern and western Australia will also now bring a better chance of colder weather at times to the east throughout the month.

CLIMATE DRIVERS


ENSO - Neutral

Indian Ocean - Neutral

SAM - Negative

% chance of exceeding the median rainfall for June 2021 - Valid June 1st 2021.

% chance of exceeding the median temperatures for June 2021 - Valid June 1st 2021.

The climate driver remain largely unchanged since the Friday update so that forecast generally stands.


In the short term, the climate outlooks can be changed dramatically with deterministic data picking up large weather events, that these climate models cannot. That is the case moving through the early part of June.


If you have been following for a little while, you may have noticed that I was mentioning that the end of May and early June could start out wet with more rainfall spreading across the nation, well that appears likely.


Areas that I was forecasting of having a less than 50% chance of exceeding the monthly rainfall, now stand better odds for the month, due to better guidance in the short term and the forecast now needs to be adjusted to compensate that change.


Rainfall for the next 10 days - Valid Tuesday June 1st 2021.

Rainfall over the east could become quite heavy, with that signal not strong last week, but now appearing to be strengthening with every run as we get closer to the event next week. Also better rainfall spreading through in the coming days over southern QLD could provide some locations more than the June rainfall in a sitting. So the forecasts above now reflect that chance occurring.

The Southern Annular Mode is the current main influence on the weather over the southern mainland. It is still negative as of the start of June, though coming back from the peak of that event, but longer term members, plunge the SAM back deeper into negative territory next week which is now being shown in the current short term deterministic forecast, depicted by that deep low and very cold air potential.


Deteminisitic Modelling below - Euro 12z run for next Tuesday and Wednesday showing that deep surge of colder air and unsettled weather over the east and south of the country. A new wave also advancing on the west coast too.

Can see that wave off the WA coast bringing windy weather and another rain event to the west coast, while the highs are also being kicked along at a rate. No blocking means more regular rainfall opportunities under such guidance.

The other ingredient is moisture, very important when you have a fast flow pattern under a negative SAM, to draw in moisture from the Indian Ocean and tropics through the jet stream. We have seen that moisture feed in place in recent days.


National Satellite Pictures over the past week showing the moisture influence over WA and then across the country in recent days. You can see the importance of weather systems picking up the moisture.


Satellite imagery from mid May 2021.

When the moisture is out of phase with a system moving through the southern ocean.

Satellite imagery late May 2021.

When the moisture is in phase with a system moving through the southern ocean.

There are signals for more rainfall developing for WA under this idea, of the moisture increasing from the northwest via the jet stream. But we need the cold fronts and troughs to pick up the moisture to make sure southern and eastern Australia can benefit from this, rather than just cloud and spitty rainfall.


In the coming week, we may see the first of these events being in phase provide inland areas reasonable rainfall, hence the increased chance of above average rainfall for June for southern and eastern Australia.


Moisture being utilized with the passage of an upper low over eastern Australia being drawn in from the north. Moderate rainfall is possible.


The longer the SAM remains negative, more strong cold fronts will tap into this moisture source through the coming 2 weeks at this stage.


GFS 18z run PW values - Valid Tuesday 1st June 2021.

The Indian Ocean is still anticipated to stay neutral through the coming 6-8 weeks June and July, but it could begin to turn negative during August through November, bringing up the rainfall chances from the northwest. A negative phase means more moisture in the atmosphere leading to better rainfall opportunities for southern and eastern Australia, with more productive cloud bands in place, not the thin versions we are seeing right now.


Global Models - Indian Ocean Dipole Forecast - September

Global Models - Indian Ocean Dipole Forecast - October

Note - the BoM model does suggest a negative IOD is in place, can explain the amount of moisture being drawn across the nation, but SSTs are near normal for a lot of the basin, slightly warmer, but I wouldn't call that a negative event at this time, but will watch closely in coming weeks with trends.


So with that said, rainfall still looks to be above average for the west of the nation, that has the strongest signals still. That will spread south and east across the country but peters out over the eastern inland, however the two systems coming up this week could provide rainfall for the eastern inland of Australia, before potentially turning back to dry with the negative SAM in place bringing more westerly zonal patterns back. But as I mentioned at the top, these are more guidance rather than specific forecasts, and can change from run to run, and especially when supported with deterministic short term forecasting.


June Rainfall Outlook - Issued on May 1st 2021.

Note the drier bias over the east is where there is expected rainfall this next week which could be near to above average in coverage for large parts of the east. Drier signal for the west but recent anomalies in the weeklies shows a wetter bias.

The Winter Rainfall Outlook - Euro Ensemble - Valid May 1st 2021.

A good season for a lot of Australia with a drier bias for the east coast, but once again, all it takes is one low pressure system to be in the right place over the east coast to bring above average rainfall and a prolonged spell high pressure over the south or west to bring below average rainfall. Note the smear of above average rainfall over central Australia. Could interpret that as cloud bands moving across interior parts of Australia ahead of cold fronts.

Expected Rainfall for the coming 6-7 weeks shows some better odds of rainfall increasing over large parts of Australia, in line with the shift to the wetter phase in the Indian Ocean and a prolonged negative SAM period for southern Australia.


Euro 7 week Rainfall Forecast - Valid June 1st 2021.

GFS also supporting a shift to wetter conditions over large parts of Australia, with that signal from the Indian Ocean supporting more moisture floating across from the northwest to southeast, and this likely being captured by more cold fronts if the SAM remains negative. The signal is positive for rainfall even though some parts of the south are dry.


GFS Rainfall for the coming 6 weeks - Valid June 1st 2021.

Temperature guide is largely unchanged though I will mention that the below average temperatures could extend further north over the coming fortnight, especially on current guidance for a bitterly cold airmass to be flung north through eastern Australia next week.


This will continue the run of cold nights and days for the east and south, where record cold May temperatures have been observed at night multiple times, after some record cold nights in April. I think that trend will continue.


Euro Seasonal Ensemble Outlook for June 2021 - Temperature Anomalies.

Remaining warmer than normal over northern Australia, the bias is not as strong as recent data sets and a flip of the coin from the models for the remainder of Australia. However the colder signal I think is stronger than Euro is showing for western, southern and eastern Australia than being drawn in here.

GFS Temperature Anomalies for June 2021.

Warm through parts of inland Australia, but it is uneven, due to the nature of more cloud being in play over inland Australia, hence the blotchy nature in the temperature distribution. Colder over the west and the southeast, that signal is increasing for the month of June. Perhaps good news for snow fans.

So not much has changed since the last update other than the signal for better rainfall early in the month for the south and east of the nation this first week of June, this was a greater than 50% chance of occurring from recent outlooks for southern Australia, but could impact the eastern inland a bit more than forecast which will bring mixed blessings to the region.


Need more tailored weather information and climate outlooks? Let me know - email me at karllijnders@weathermatters.org to find out how I can help you.







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