Sleet showers and snowflakes July 14th 2009.

by Chris Handler.

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Tuesday 14th July 2009 was definitely one of those days that absolutely take you by surprise. A late start to the day with a rare sleep-in (9:00am, which is a late one by our standards) had us awaken to a very nice looking radar. A good southwesterly flow with ample moisture.

With the promise of gushing waterways and a good chance of hail we decided to head for a trip up to the Mt Lofty summit, and then back down through Waterfall Gully. We rugged up with more layers than a cabbage and took the 15 minute trip to the summit lookout.

Shrouded in fog, raining steadily, and with a wind chill that hit you like a speed boat, we didn't spend too long looking around before we decided to head back towards the car. I decided before we left, that since we were already there, that I would grab a few quick pictures of the Lofty weather station. Why? I don't really know, but it was very tranquil to see the open paddock, with rivers of fog flowing between the bordering eucalyptus trees.

While out there, the rain began to pick up. I made my way back towards the fence when I started to notice little specks of ice sit briefly on my black jacket before melting almost instantly. I hopped back in the car and we sat there watching it for a little over a minute before the shower died down.

We left the summit area and drove down Summit Road towards Greenhill Road and started heading past the entrance to Mt Bonython. In almost an instant the showers picked back up, this time more intense than before. We pulled up to a gate and just sat there for a further minute watching and filming what was now heavy sleet splattering all over the windscreen. The sound sleet makes as it delicately falls all around is in my opinion, one of the most beautiful sounds in the world.

When it first started sleeting I took a video looking out through the car windscreen (see bottom of this page).

Before too long, the sleet had become so icy that a slurry had built up along the windscreen and bonnet. I stepped out of the car to take some pictures to find myself being covered head to toe in little flakes. Hayley and Thomas also stepped out and we just stood around soaking the moment up. We jumped back on into the car, all covered in flakes, I fumbled around with the camera trying to keep it dry and snapped a few more pictures of the snowflakes.

Now snow on Mt Lofty is definitely not unheard of, and the years without it are rarer than the years with. However this event was definitely not typical. When the temperature rises above zero, snow very rapidly changes its form. From 0 to 0.5 degrees centigrade snow is usually very dry. 0.5 to 1.5 degrees, snow still holds its form but is slightly damp and is known as wet snow. Then from 1.5 degrees snow becomes sleet and the amount of ice drops until about three degrees when it becomes solely rain.

During this event, the Mt Lofty station which was still only about two kilometers away recorded a minimum of 4.4 degrees! Incredibly at this warm temperature wet snow was still able to fall. Snow can theoretically fall at temperatures up to seven degrees; however the relative humidity has to be at absolute zero to allow for evaporative cooling. The relative humidity on Lofty at the time didn't drop below 100%.

To be sure what we had experienced was indeed snow, I forwarded photographs on to Jenny Dickins, of the Bureau of Meteorology, who confirmed that they were snowflakes and also commented on how interesting it was that they survived long enough to accumulate to that extent and were able to be photographed in such a saturated environment.

How this happened is uncertain. One idea I've contemplated is whether a parcel of cold air was pulled downwards by the orographic effect the two mountain peaks had either side of us. Perhaps this caused a very localized cooling in the immediate area between the peaks, but was too localized to be recorded by the station site?

Below are several photos I took including a panorama of the summit observation area immersed in fog and rain, and as mentioned above there's a video I filmed down near the entrance to Mount Bonython.

Chris Handler August 2009



Above: "I stepped out of the car to take some pictures to find myself being covered head to toe in little flakes. Hayley and Thomas also stepped out and we just stood around soaking the moment up. We jumped back on into the car, all covered in flakes." The time stamp on this image is 11:27:22 AM.



Above: "The flakes only lasted briefly on saturated surfaces, but on my dry jumper they held their shape for over 30 seconds. I took this picture just before the flakes finished melting on my jumper." The time stamp on the previous picture is 11:27:22 AM and on this picture it's 11:28:02 AM.



Above and below: "Before too long, the sleet had become so icy that a slurry had built up along the windscreen and bonnet."





Above: While on the summit, I took this panorama with the summit immersed in fog and the fire tower in the background barely visible.

When it first started sleeting I took a video looking out through the car windscreen - you can view it on Youtube here http://www.youtube.com/watch?v=QH_gN2uGf5A

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