CLIMATE DRIVERS UPDATE - THE SAM

The Southern Annular Mode is playing funny buggers, as it usually does during the Spring, with the driver very erratic in the medium term, and this is being reflected in weather outlined in the Medium Term Forecast earlier today.


The SAM yesterday had a much sharper drop to the Neutral zone but it is starting to soften that decline from the positive phase we find ourselves in today, which is why we are seeing enhanced inland rainfall for QLD and NSW. This weather is a great example of when the SAM is positive, just as when we see the SAM negative, the south of the nation is colder with showery westerly winds about. Also note, the last time QLD saw decent rainfall chances was back in mid June and early July, the last time it was this positive. So something to remember.


Moving forward we can see a trend towards neutral conditions, but there has been a shift overnight towards keeping the mode north of neutral through the middle of the month with one outlier returning the phase into a full blown positive phase. At this time, things will remain neutral but not on the negative side of neutral.


That means less chance of the westerly wind belt coming into play bringing drier air and sweeping the rainfall chances out.


SAM Forecast - Next 2 weeks.

SAM yesterday was forecast to go more negative amongst the members - resulting in less rainfall in the outlook period for southern and eastern Australia. Note the GFS showing more westerly wind dominance.

SAM today has moved back towards neutral or slightly positive of neutral through the outlook period, which is why the models are reactive today and seeing more rainfall back through inland areas and over the southeast and the east. Note the GFS today favouring more low pressure sweeping the nation and the westerly winds further south again.

Bottom line is that we have got lower confidence in the driver today, and if the trend continues to turn more positive in the next 48hrs, then expect forecasts to turn wetter, and the inverse is also true. So more on this coming on Friday.

22 views0 comments