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Monday 1 May 2017

 April a month of mixed climate fortunes

Whichever measure of temperature you use for April - maximum, minimum or mean - April had it all. Across the country, it ranged from areas in the top 10% of Aprils to the bottom 10% and everything in between with a few small pockets of record-breakers thrown in for good measure. It was much the same with rainfall, with April falls ranging from top 10% with a few areas receiving record April totals to figures in the bottom 10%. This makes it something of a challenge to describe.

Averaging all these variations into national figures, it was a warmer than average April - just 0.09° above average - and a slightly dry one at 17% below normal. The only stand-out feature was a broad band of above to very much above average rain extending diagonally across the country from NW WA to western NSW and central VIC. There were also two areas of below to very much below normal rain, one in the broader southwest area of WA and a second through large parts of central NT and QLD. Put in the context of the rainfall record of the last 118 years, only SA is significant with its average the tenth highest.

Some of the capital cities revealed a few points of interest. Sydney had its sunniest April at the Airport since 2010 and coolest April nights at Observatory Hill since 2008. It was also the driest April at Observatory Hill since 2010. In Melbourne, Burnside had the highest daily rainfall of 89.4mm on 10 April while Bullengarook East, Latrobe University at Bundoora and Wallan all had their highest April rain totals on record.

Perth had one of its driest Aprils on record with no rain at all recorded at Perth Airport, Perth Metro, Garden Island, Gosnells City, Pearce RAAF and Rottnest Island. The few places that did record precipitation had little more than a dribble from passing showers or dew. Perth Metro has had only three rain-free Aprils since 1876, in 1982, 1977 and 1920. Not surprisingly, the average daily sunshine hours reported in Perth for April, 9.4, equalled the record set in 2011 in a history going back to 1898.

Some of Australia's remote islands set records for April. Christmas Island's 24-hour rainfall of 155.2mm to 09.00 on 23 April was a new record in a 45-year history while Norfolk Island's maximum temperature of 27.9° on 4 April also set a new record in a 79-year history. Macquarie Island, with 70 years of climate history, won a trifecta of sorts with the highest daily minimum temperature (8.1° on the 5th), highest mean maximum (8.3°) and equal highest mean temperature (6.7°).

Newsbits

 Everybody loves snow...: Tassie looks like getting more than a dusting in the next two days, with cold air brought north by a passing cold front that will have minor impact on the mainland. The BoM is forecasting snow to begin falling down to the 900m level tonight and 600m tomorrow in southern areas.
...especially the skiers: Every year it's the same. Those with a passion for skiing begin to speculate in autumn, and sometimes earlier, about the prospects for the forthcoming snow season around the resorts. And when the inevitable first snow showers appear in April, there is great excitement that it's going to be biggest of seasons and we'll be digging our way out of the lodges. Unfortunately, snow just being rain in another form, you can only look to the main climatic drivers this far before the event for any sort of guidance as to the likely season ahead. That's what Ben Domensino on Weatherzone has done in this very good explanation of the current situation and what it bodes.
Another site for snow-lovers to bookmark for perceptive and thorough analysis of past, present and future snow in (mostly) the Snowy Mountains is Gerg's Net, and he kicks off the 2017 season with this detailed review of the 2016 season, the climatic drivers influencing it, full records for the year and what it all augurs for the decades to come. Oh, and you'd better like graphs.