Above: IR satellite hourly images from midnight to 8pm WST. The cold air pool is marked by the bright (cold) cloudmass that begins to cross the southwest coast at 2am, and the attached second dumbelling cloudmass that crosses the coast at 9am. The two continue to dumbell as they move ENE into the area north of Kalgoorlie. Weatherzone, BoM. (GMS-5 backup with GOES-9 operated by the joint effort of JMA and US NOAA NESDIS over the Western Pacific) Below: Surface chart (coloured contours) and 1000-500hPa thickness chart (black contours) for 8pm Thursday and 8am and 8pm WST today. At the surface, a low of around 990hPa skirts the WA South Coast, weakening to around 997hPa by 8pm today. The thickness contours show a very cold airmass curling around the upper low, which lay just to the north of the surface low. COLA Bottom: The upper air chart at 500hPa shows a closed low developing and deepening rapidly in the trough between 8pm yesterday and 8 this morning before moving east and weakening. COLA

In a rare event for WA, snow fell to low levels in parts of the Great Southern this morning. Snow is reported every year or two on the Stirling Ranges, which rise to about 1000m north of Albany, but is seldom experienced elsewhere in the state.

The most significant reports of snow came from an area north to northeast of the Stirlings. Light falls were reported at Gnowangerup, Ongerup and Jerramungup, all 200 to 300m above sea level. At Ongerup, snow fell continuously from around 7am to 7.40am, and the 2 to 3cm that accumulated was enough to bring the town's 500 residents out to enjoy snowfights. The West Australian claimed it was the town's first significant snowfall in 50 years. The paper also reported that a farm 20km NW of Ongerup received 5 to 7cm accumulation. The ABC reported that snow lay on a farm near Jerramungup for about half an hour with the temperature at 1C. Reports of snow also came on the Weatherzone Forum from Woogenellup, located on the southern side of the Stirlings, 20km NE of Mt Barker.

The charts and satellite images at right give some clues to the cause of this rare event. An upper low developed rapidly in the upper trough as it moved over the southern wheat belt and Great Southern mid morning. The coldest air actually curled around this low farther to the north of the Stirlings. At 9am, the freezing level was about 1,500m above Albany, but 1,300m over Perth and 1,400m over Meekatharra. At 9am, the surface low was situated about 200km east of Albany, shooting a tongue of cold but moist air onto the Stirlings, and into an area of high instability, with tot-tots ratings around 55.

The satellite animation shows the leading edge of the snow-bearing cloud mass crossing the coast west of Albany around 2am and moving over the area of the Stirlings around 7am. Heavy rain fell from this cloud soon after the snow, with local flooding reported along the North Stirling Road. Jacup, 70km east of Ongerup, recorded 16mm between 9am and noon (and a noon temperature of 6.6C!)

Hail was reported in the strong, squally southwesterly stream during the day. Wind gusted to 111km/h on Rottnest Island, and roof and tree damage was reported in Albany and Walpole on the South Coast. Most locations west of a line from Carnarvon to Esperance recorded 30 to 40mm out of the event, with Perth Metro registering 41.6mm and Karnet 56.4.