Rainfall Streams in the Adelaide and Ranges Locations. Page 1.

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Ever wondered why your neighbour gets more rain than you or why the rain always seems to fall on the same locations over and over? Its terribly frustrating to sit and watch the rain go within a few kilometres of where you are missing you completely! I should know because I live in one of those hills "dry spots" (relatively speaking).

So with much help from our local meteorologist, Ian Holton (visit his website here) we have put together a series of maps that show where the main moisture streams "flow". 

[*These articles can be reproduced and published providing they clearly state they are by the author Ian Holton, and that they have been copied from hillsrain or holtonweather]

Basic Meteorology

Lets start with the mechanics behind the scenes. We are concentrating on the moisture streams that form behind fronts and troughs and not so much on these events alone which tend to be fairly even and widespread (although on a small scale the effect is noticeable).

Quoting Ian Holtons description....

When streams run up the South Australian gulfs, & Lakes-Murray River areas at night in autumn, winter & spring seasons, converging land-breezes from either sides of the gulfs warm as they move over the warm Gulf water below. These land-breezes then collide and push up long or continuous shower stream lines in the middle of the gulfs/lakes. Nocturnal cloud-top cooling adds to the intensity of these shower lines. These shower lines eventually run up over sites, at, or near, the top of the gulfs/lakes, causing some moderate to high rainfall totals at times. Isolated Thunderstorms can also occur in these Gulf shower lines if the stream is very unstable. In the Spencers Gulf area , if the air is cold enough, they can form nocturnal snow shower lines in the Orroroo/ Peterborough area as they drift inland from Spencers Gulf on a cold night in a persistent SW to SSW'ly stream. Whyalla had been known to gain persistent overnight hail showers & showers if the cold stream is from a more southerly direction. Cleve and Cowell areas can gain good rains if the stream is from the SSE, and the Port Germein area can gain some of its heaviest yearly rainfall events in a SSW'ly overnight Gulf convergent/nocturnal cooled showery stream. In the St Vincents Gulf area, heavy falls can occur in a SSW'ly stream over the Roseworthy/Tarlee/Clare areas. Snow has fallen very occasionally in the Burra Area in cold winter/spring streams. And in a more Southerly stream the Balaklava/Port Wakefield and Hummocks areas can do well for rainfall. While in the SA Lakes and Lower Murray Rivers areas, a SSW'ly can bring good rainfalls to the Lower Murray River and Near Lower Murray River areas. While in a more southerly to SSE'ly flow, heavy rainfalls can occur as the shower lines are forced to rise up over the eastern Mt Lofty ranges. Feet deep snow falls have been recorded in the Mt Barker/ Nairne/ Gumeracha areas on rare occasions in a cold S to SSE winter/spring showery stream.
Text remains copyright of Ian Holton and may not be reproduced without permission.

This is better represented graphically.

The day time sea breeze stream development Air from the cooler waters move towards the land. Where they collide they form "cloud streets". This can be significantly enhanced by the orographic effect of hills and ranges.

The night time land breeze stream development Air from the cooler land move towards water. Where they can collide they form "cloud streets". As in the left hand scenario this can be significantly enhanced by the orographic effect of hills and ranges.

The streams around Adelaide and the ranges.

Taking the above into account it is possible to plot the regular moisture streams that develop and occur with regularity in the complex coastal structure of central South Australia around Adelaide and the Mt Lofty Ranges. There are certainly quite a few different streams that vary from daytime to night as can be seen in the image below.

 

My own location has been suffering a decline in rainfall intensity which has seen mine and others in a small area fail to have full dams at the end of winter. I am on the edge of many streams which still seem to be delivering good falls. So why my decline?

Well perhaps that can be answered by Ian Holton.

There have been suggestions made that the westerly wind belt that rings the Southern hemisphere is becoming stronger and shrinking back southwards towards the Antarctic continent because of Global Warming. The past ten years appear to show a southward movement of the Winter Westerly Wind Belt in the Australian Region. As a consequence rainfall appears to have lowered in southern areas of Australia during the Winter months. Also, many would have noticed that Dams are no longer are filling from heavy rains during the Winter months.
Text remains copyright of Ian Holton and may not be reproduced without permission.

This fits with my experience in this location where the only decent stream I am in is the westerly flow which as suggested above is on the move.

Move on to the next page for more larger images of the moisture streams.