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6th - 10th July 2008 Low and Front

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This had looked promising on the charts for a while (see image to the right) . A possible NW infeed, a front, a massive pool of cold air and best of all a cut off low (possible retrograde). The NW infeed was weak but the first in some time and the front was pretty standard in the big scheme of things, but still a rareity this year. The low was the fickle creature. Its final position and direction of travel would determine the final rainfall outcomes. All too often these systems are at their strongest in the SW streams which pretty much rules out any rain of significance for all those that suffer the SWstreams (my location does for example) What would be the outcome this time? The NW rainband on the 6th was mostly benign down south. One or 2 impressive lines moved over Noarlunga but only made it inland as far as Kuitpo. Some small hail was reported from various metro locations. Just light intermittant rain was to be had down my location. It was over the mid north where it was most impressive. See the radar snippets from varying times in the evening of the 6th below.

Rainfall was generally around the 8mm mark, even higher in those heavy areas as highlighted on the radar images to the lef. Down my location 3.75mm had fallen. The directions were changing as the cold air arrived. The temp plummeted to be just 5 degrees by midnight and around 3 at Mt Lofty. The BOM saw a slim possibility of snow on Mt Lofty and the higehr peaks of the Southern Flinders. Still needed to be colder yet! Not quite there. My coldest overnight temp was 3.6. Mt Lofty 2.4. Enough for the odd hail shower, but no snow yet.

The low began to show influence and gentle rotation could be clearly seen on the radar loops. The streams went SW and despite the presence of the cold air truly significant falls stayed north. Again impressive radar echoes could be seen in similar areas as highlighted in the above radar images. I recorded one small hail shower early morning but the SW rain shadow was doing its thing and little more than drizzle and moderate rain was seen in my area. Still such falls accumulate and by morning I had 18.5mm in the gauge, 23mm near Bull Knob, 20mm in Meadows Township, 25mm at Kuitpo 14mm at Macclesfield and the highest local fall being 39mm at Ashton.

There were also some stand out falls across the ag areas. These included - Coles Point 22, Darke Peak 20, Elliston 19, Lock 25, Pt Lincoln 20, Streaky Bay 17, Melrose 14, Auburn 21, Hoyleton 21, Mintaro 18, Watervale 23, Maitland 19, Minlaton 18, Flinders Chase 29, Freeling 19, Riverton 21, Stockport 21, Loxton Ag 11, Alawoona 13, Mindarie 17, Pinnaroo 22, Kingston 21 to mention but a few.

During the day of the 7th temperatures remained very low under the influence of the cold pool. My maximum temperature was just 6.7 during 10 minutes of sun at 12:33 in the afternoon. Most of the day hovered between 4 and 5 degrees. By 7:30 that evening the temperature had dropped to just 3 degrees. This was my coldest July day since 2006.
Mt Lofty was even colder with a maximum of just 4 degrees and a minimum of 1.8! Cold enough for passing hail and maybe, just maybe a drop of sleet. It is not outside the bounds of possibility that a light flaking of snow might have been seen in the higher parts of the northern lofties/ southern flinders. No reports have yet to conform this. There were certainly significant snowfalls in the Victorian Alps. As usual the lowlanders in the city complained of the cold. Adelaide recorded a maximum temperature of 11.2. Certainly not cold (this has been my average max for the last month) but was still the cities coldest July day in 3 years! My temperature graph for the 6th is a chilly one.(see below)

White line - air temperature (deg C) in stevenson screen

Rainfall during the day was typical SW streams. My area got wet and stayed cold, but the real rain followed the well worn paths of the S/Westerly By 8pm on the evening of the 6th the higher parts of the Lofties to Mt Crawford had generally falls between 15 and 19mm. Adelaide City 13mm and my location just 9mm. Even Strathalbyn scored more rainfall during the day than me with 11.8mm to 8pm! Thats not often able to be said!
Its also not often that it happens that Adelaide records more rainfall than my location. Up until 8pm on the 7th the city had recorded 28mm in total from the system to date. To the same time I had recorded 27mm. Ashton, so often the highest daily fall recording station has now had and amazing 55mm to 8pm on the 7th!!! More to come for them likely.

Final update 8th to 10th...
By the morning of the 8th just 1 more mm had fallen at my location to make 10mm for the 24 hour period. Another miss for us as even Macclesfield was higher with 12mm, Kuitpo a lot higher at 17mm. Again though best falls were over the northern hills with Ashton (and a few other higher stations) the highest at 21mm. This makes Ashton's total now at 59mm!

Another frontal band was on approach. Like a rocket this was on a mission and accompanying it were strong and gale force winds. Yet again the BOM issued a storm force wind warning for the SE coast. The rain band associated with the front hit the ranges in a due westerly direction - then disappeared!! The radar loops are amazing and show the strongest rain shadow you can find. Anyone interested in the archives contact the website for the loop - its incredible. As a result yet again the south eastern ranges fared poorly in rainfall. In fact totals were not that high across the board from this band with 5mm at my spot, 2.4mm at Meadows township and yet again Ashton one of the highest at 10mm.

Then the SW followed. Forecast conditions were impressive and a decent cold pool could be seen on the sat pictures. Stock loss warnings were issued along with small hail and other warnings for the hills and surrounds. But nothing really happened! The SE got pounded with cold air hail showers but nothing centrally. It was cold and the wind was gusty but that was about it. The SW stream did deliver some rain though and as always it followed its usual dump zones. By the morning of the 10th I had a further 12mm in the gauge, Meadows township 10, Kuitpo 17, and as always the best further north with Ashton again taking the trophy at 22mm! The system was mostly spent now and some decent totals were to be had from across the ranges. 48mm for my location, just 5km away at Kuitpo 63mm, Meadows Township 42mm and Ashton, wait for it - 91mm!! Rainfall distributions were as they always are generally more consistent and higher over the northern ranges. The weekly rainfall bulletin from the BOM can be seen HERE.

13-14th July 2008 The PERFECT Low

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This is amazing. You could almost call it a "temperate cyclone"! Read more HERE

28th July Coldest temp of the year to date

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Frosts are somewhat rare at my particular location. The height and exposure makes for sub zero temps an almost unheard of event. And so while it was cold, it was also not quite sub zero. Dropping to 0.6 it was still cold enough at ground level to leave the ever so slightest touch of frost on my lawn. But all was not so "warm" in the gullies. Here the temperature was well below zero with a very heavy frost and it was even cold enough to freeze over the shallower puddles along the dams edge. This is the coldest temperature for this year for me and the coldest since the 22-09-07 when it dropped to 0.5 degC.

Also unusual at my location was the 10 hours of dead calm conditions in the preceeding night. Indiciatve of a dominating high pressure.

Another more significant record was also set today when Adelaide recorded its coldest July temp since 1982. The BOM issued a press release through the "adevertiser" that read as follows.

July 28, 2008 08:20am

THERE have been delays at Adelaide Airport this morning as the coldest morning in years ices up wings.The managing director of the airport Phil Baker said up to 400 passengers were due to leave about 7am but the flights were delayed until about 8.15am when the air temperature increased and the ice melted.

"It is very unusual for jet aircraft, I don't recall that happening in my ten years here,'' he said.

"I know it happened with Rex last year, they had two or three aircraft over a few days delayed,they have a small de-icing rig here but that obviously would not work on the bigger aircraft.''
The temperature fell to 0.5C at the airport this morning with the Bureau of Meteorology at Kent Town recording 0.7C at 6.31am.
Duty forecaster Simon Chang said it was the coldest Adelaide temperature since June 2006 when the thermometer dropped to 0.2C with the previous coldest July day was in 1982 when the minimum was 0.4C.
The lowest temperature recorded was Naracoorte with -2.7C.

The previous few days have also been cold and with a deep southerly and cold pool delivering some impressive cloud formations. These shallow but almost not quite classic style "coldies" delivered hail to my location and the odd reasonable shower. Hail was seen over much of the Adelaide hills and east of the ranges. Over the Mid north in the higher inland spots there were uncomfirmed reports of sleet and "maybe" a light snowfall falling at Jamestown.

Classic cold winter stuff of the old days. (click on image for larger version)

Its been a cold July to date. Some stats from my WX are as follows.
Av max : 10.3 deg C
Av min : 4.8 deg C
coldest day : 6.7 C
warmest day : 13.4 C
lowest recorded temp : 2 deg C
highest minimum : 8.6 deg C

I think though that the median stats tell a better story at the cool
maximums.
Median Max : 9.7 deg C(sub 10 degrees)
Median minimum : 4.4 deg C

To compare to.
Adelaide so far for July 2008 mean max 14.8 and mean min 8.5
mean July normal max 15.3 and mean July normal min 7.4

Renmark so far for July 2008 15.9 and 5.2
mean normals 16.2 and 5.1
(this data courtesy Ian Holton)

August 2008 Consecutive Rain days and snow!

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Blocking patterns are responsible for many or our weather extremes. In most cases they result in heat and dry. This was never more evident as in the case of Adelaides record breaking heatwave in march of 2008. This "event" is also the result of a blocking pattern. But hot and dry it isn't. Quite the opposite, cold and wet.

Firstly lets look at the cold. The synoptic below is typical of the patterns that dominated. Very little variation occurred for almost 3 weeks! A large mostly stationary high anchored off the south west of WA allowed a steady stream of cold air to move over the continent day in and day out. Temperatures remained consistently low. My stats to the 25th read as follows.

August av max - 9.8 degrees (normal - ~12 degrees)
Av Min 3.3 degrees.
Coldest Maximum - 7, Highest Maximum - 13.5
Coldest Minimum - 1.2, Highest Minimum - 5.4

An amazing 2 degrees below my average maximum for August are the result of the blocking pattern. This unusually low temperature situation was repeated across the whole of Australia. This is significant enough to warrant a speacial report by the BOM which I will include here when it becomes available.

Next lets look at rainfall. In this case we will look not only at the rain but at numurous South Australian snow events! A rareity indeed. Rains started on the 30th July with 9mm at my location. With the persistent blocking patterns regular frontal systems one after the other followed by constant wet West to South airstreams delivered rain for the next 21 consecutive days! On the 20th August this was broken by a rain free 24 hours then followed by yet another 4 days of rain. So in 26 days we experienced an incredible 25 rain days!!
However during this period not one fall on its own could be considered significant. The highest 24 hour fall was just 17mm and the average daily fall was just 6mm. The regular accrual of rain over the 26 days did total a nice 150mm. While more rain has been experienced in the ranges in less time it is certainly not common for it to occur on so many consecutive rain days.
Also unusual was the behaviour of the SW rain shadow in my area. Normally the SW streams deliver nothing to my location. However the presence of the cold air (as previously noted) resulted in a shift and wider spread of these streams and kept my area well and truly in the rainfall lists. Be nice if this could happen more often!
It must be noted that good average rainfalls were confined to a small part of South Australia. Most of the continent suffered under abnormally dry conditions, especially South West WA which was under serious and severe rainfall deficiencies! Locally the Riverland especially was also in deficet with the frontal systems not penetrating inland due in the most part to the absence and inability of NW moisture infeeds to flow through.

Then there was the Mt Lofty ranges snow. The tounge of cold antarctic air was able to move significantly north with the blocking pattern. This at times enabled a very deep and long southerly fetch of cold air. This can be well seen on the synoptic below.

Such a deep grab of cold air delivered such daily maximums at my place of just 7 degrees where in fact most of the day hovered at 5 degrees C. Moisture too was present, the thicknesses were appropriately low and by late in the evenings temperatures were close to zero on many of the higher peaks of the Mt Lofty Ranges. Twice such conditions prevailed that peaked on the 10th August and later in the month on the 21st. On both occasions Snow was seen at Mt Lofty settling on the ground. By the 21st even the press had gotten alerted to the cold and snow chances. Not often that mainstream media in South Australia report snow. But with "snow flurries" on the Bureau's forecasts its pretty hard to ignore!

To add to the rareity of events the evening of the 21st saw sleet and the odd snowflake at my spot! I am at just 420 metres and with temps at 1.6 degrees and the south south west stream shifted far enough under the cold air influence to bring me in its line saw numerous beautiful sleet showers. Nestled amongst the sleet was the odd snowflake that survived the descent. I stood out in the sleet in bare feet until my feet froze! Well worth the chill. Not often you experience sleet at just 420 metres!!!! Rain itself was the odd one out and most falls if not sleet were small hail.

I have a small gallery of images showing the cold air structure a sleet shower and some snow shots from Mt Lofty. These can be seen HERE.

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