Statistical note:

Some Frost/med-to-low humidity statistics (high-humidity rain) + corrections:

Post: #1099642 – 15-4-2012:


Revision taking into account recent obs-to-date:
~ (20/-7) to (15/-7) and (perhaps with rain) ~ (20/5) to (10/5)… (Winter)

2012: Sub-zero frost or near-frost conditions – Overnight Lows May-July to-date.

Bold indicates increasing severity of frosts.
*Indicates definite frost.

15th-16th-May: -4/~41%.*
16th-17th-May: -1/~36%.
20th-21st-May: -3/~58%.*
30th-31st-May: -1/~57%.
7th-8th-June: -2/~44%.*
9th-10th-June: -2/~34%.*
10th-11th-June: -6/~46%.*
…Major rainfall period… (20th-30th June)
22nd-23rd-June: -2/~83% (Rain)
26th-27th-June: -2/~45% (Little Rain)
30th-June-1st-July: -2/~67%.
2nd-3rd-July: -3/~51%.
5th-6th-July: -5/~33%.*
6th-7th-July: -5/~36%.*
7th-8th-July: -2/~40%.

I believe this important enough for a preliminary note: -5 degrees overnight (6th-7th) with a substantial frost. No substantial rain since the beginning of the month (river is flowing steadily), and the humidity has been falling in a corresponding fashion, down to 20-40% from around 80-90% between 20th and 30th June.

Note: for a period of 11 days starting 12th June (during the onset rain events) the minimum didn’t drop below zero.

Possible onset of period No. 2...starting the 9th just gone.

Visible change in flow already evident. Possible major flux in streamflow coming up within the next 7 days.

Bold Added.

Correlation perhaps, but not so much causation.

As a note of benefit (at the moment for rainfall, possibly):

• Blocking high-pressure system needs to start moving (east) – pressure needs to fall.
• Overnight lows need to rise more than they have (closer to 8-9 deg C rather than 0-8).
• Relative humidity (in diurnal pattern) needs to start increasing.

Written earlier today:

About 2 weeks ago a gradual drop in pressure was evident on the shorter-term GFS projections, and to a lesser extent the longer-term. The pressure was forecast to reach a low point sometime between the 25th and 27th of this month (probably closer to the 25th). In the period since the trend appears to have barely shifted, with the magnitude of what is (projected) to come being more the question than the likelihood of (rain/showers) falling sometime in that period.

The streamflow (runoff) forecast has been a bit all over the place in that sense, with the most recent run showing a change (in kilograms per squared metre) of up to maybe 20-30 x the current magnitude (not order of magnitude)… it seems very interesting, despite the idea the forecast could still change with what time is left (to reach the low point) or at the very last moment (hour or two).

I’m going to throw up for interpretation what others might think of the period to about 5th of August. I have noted that several things could happening in that period, a mix of possible conditions (or extremes).

For anyone who is interested in the implications of the could’s for that period, I would welcome your input.

The forecasts source: http://nomad3.ncep.noaa.gov/ncep_data/

19.3 mm overnight with visible and audible change in flow. Possibly more to come this afternoon/evening.

I believe somewhere, sometime ago I may have mentioned 150 mm might be necessary for a significant change (in run-off) over 2-3 days out to maybe a week. I think that could be more accurate than first realised (42.8 mm to midday, system total, moderate change in flow)…and this might be saying something as well.

13.8 mm 9 am yesterday to midday today.

The change in flow of the local river is a bit interesting; is 13.8 mm enough to cause it? It seems there could be some sort of sub-surface or groundwater contribution, maybe upwelling. I don’t know this for sure, but I’m a little curious about the flow rate compared to within the last day. The flow is quite audible, even from 50-100 metres away.

14.7 mm over 3 days, most falling to 9 am this morning.

Possible significant change in runoff pending (over next 2-3 days).

S''t, dramatic change in flow ! Over 30 mm system total (unchecked, probably higher).

Broken/breaking its banks. Low-lying flooding.

http://www.bom.gov.au/cgi-bin/wrap_fwo.pl?IDS20364.html
flood warning out

Thanks ... needed that (flooding issues/concerns).

64.5 mm to 4.15 pm today since the 13th.

Written yesterday:
Vigorous Cold Front/Low Pressure System…No. 1 (16/08/2012)
(Some photos may show poor quality due to time of day/conditions)

Approx. 5:15 pm, early on:







Approx. 6:05 pm, Evening:





Approx. 9:58 pm:



Approx. 12:15 pm, 20th (the aftermath):



In short, after the river water level rose moderately to 5 pm on the 16th, it only (apparently) took another 19 mm over 1.5 hours for the river to break or begin breaking its banks – rising another 2-3 metres. The volume of water seemed to pass a threshold for flow response (meaning the response was very rapid). My thinking is there would have been even more rain further upstream towards Lobethal, which seems possible given the higher totals seen on the Bureau’s website for that period.

This seems to imply there is sufficient moisture in the catchment system to bring the river to flood, and that there are thresholds between critical periods of hours, days, weeks and months of increasing or decreasing soil or sub-surface moisture. How much moisture is in the system at any given time is still likely important, and critical to determining when a threshold is reached, however, of more interest is how this moisture contributes to the flow response.

This may also be evidence of an idea (untested hypothesis) about antecedent soil moisture conditions which can lead to either droughts or flooding rains … but for now GFS is indicating the possibility of additional follow-up rains (another significant-to-major event) this week (Wednesday-Thursday), first noted as possible on the 17th.

Sfc. Pressure ~996 hPa @ 2pm.

Rainfall totals are insufficient to act significantly on runoff at the moment. Significant change in stream flow remains possible.

Possibility ended 24th August.

-1 degrees C noted 26th-27th.

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In my view, analysis of recent synoptic patterns/frontal/low activity suggests a change/shift in the pattern, possibly to wetter conditions.

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For information only:

Written 23rd August 2012:
Development of Zonal Pattern, Several Fronts/Lows, Winter-Spring 2012!?

This is my opinion based on recent observations.

Noted: low central pressure in Bight – 964 hPa, 4 am AEST 23rd August 2012 (Bureau’s website).

In the thread “Spring/Summer 2012-13: Predictions, Observations and General Discussion” I mentioned in post #1117896 - 03/08/2012 15:33 that I thought the Southern Ocean weather/climate pattern was beginning to show signs of becoming more zonal (pressure gradient more latitudinal), in particular (not mentioned) across the Indian Ocean and Central Australia. The implication further to this is that it has/is becoming more conducive to frontal/low activity. This may also be supported by the passage of three systems which have crossed the (Southeastern) region since the 3rd, bringing moderate to significant falls (the latter two at least 30 mm in the Adelaide Hills, BoM) – peaking on the 8th, 16th and 23rd respectively.

On the Bureau’s MSLP run – 12 UTC 22nd August 2012:

The evident change from apparently meridional to zonal pattern appears to be consistent with the (long wave) Southern Ocean hemispheric pattern, in which the low pressure belt (south of about 30 degrees, BoM) in the Southern Ocean rotates incrementally (zonal-to-meridional) every so often. Although several lows appear in the Southern Ocean at present, it is clear that in the Pacific high-pressure dominates over low-pressure, or presents more longitudinal gradients, the opposite being the true nearer the Indian Ocean. The significant zonally situated high-pressure system is also evident in the Indian Ocean nearer the equator. In the case of the observed (zonal) change this (rotational period) may be 1-3 months, or a season.

Update 12 UTC 24th August 2012 (see Bureau’s website):

The latitudinal pressure gradient of high-pressure cells has now shifted somewhat from the Indian Ocean to extend into South Australia, and consists of six cells with central pressures (west-to-east) of 1021, 1021, 1024, 1024, 1024 and 1023 hPa respectively. I believe there may be further possibility, given this feature, of more rain in the coming week (or two) which could increase soil moisture (if not streamflow) once again. Further activity may follow (into early spring).

Update 28th – 06 UTC 27th August 2012 Synoptic Map (see Bureau’s website):

On this particular run I have noted a low-pressure system with a central pressure of 930 hPa nearing the south-western coast of South America. While the high-pressure feature extending from the Indian Ocean into Western Australia is less apparent, its effects are noteworthy with both the Southeastern and Western areas receiving up to 50 mm in places in the week ending today, and over 100 mm in the month-to-date (BoM).

While there continues to be the high-pressure feature to the north and east (possibly a blocking high) of the Southern regions I think this [higher probability of consecutive fronts/lows] may continue.

This appears to be a significant contrast to the blocking high-pressure systems of 2006 (from memory) – in 2006 Winter rains did not properly eventuate, in that case situated more centrally rather in the east. The last major flood events occurred in 1996.

The first significant probability of rainfall (in my view) may be sometime between the 29th and 31st of August. The second likelihood (again, in my view) could be sometime between the 3rd and 5th of September, at this stage.

See the Bureau’s latest forecast details for more information.

Written (Wednesday) 5th September 2012:


The surface pressure dropped from around 1012 hPa on the 3rd to 993 hPa on the 5th (last hour or two from 3.30 pm). Humidity was 23% last night [Tuesday] around 8.45 pm. Winds yesterday [Tuesday] were consistently strong to gale force with very strong gusts, possibly enough to make walking difficult [see Bureau’s observations for Tuesday]. The forecast period start day/time shifted by perhaps 1-2 days forward (from the 3rd), while it could be extended another couple (may be today (5th) till the 7th or 8th sometime). The general forecast though (particularly from the Bureau) appears to be consistent: moderate-to-heavy falls today (Wednesday) into tomorrow (update: now probably Friday as well), 5-15 mm each 24-36 hour period, possibly 20-30 tops with the odd heavy shower/thunderstorm (more tomorrow – Thursday). No major change in flow is expected as yet, but that probably also depends on how the local catchment responds to increasing surface/atmospheric moisture levels. Rainfall has be increasing over the last several hours (Wednesday). Perhaps one thing in favour of more rain is the humidity increasing by about 25% in 6 hours (from the low 60s at approx. 3.30 pm).

Modifications indicated by [].

Written (Thursday) 6th September 2012:

25.9 mm in the 42.5 hours to 6.30 pm this evening – the river is beginning to respond more noticeably (8 to 10 pm). Passing moderate-to-heavy showers at present. Possible thunderstorms/hail noted on Bureau’s 4.10 pm forecast for early tomorrow.

Chance of rain for the rest of the day was said to be 100%.

Hail confirmed 10.30 pm.

Written (Friday) 7th September 2012:

34.3 mm in the 57 hours to 9 am this morning + hail and gale force winds (and debris). *[Moderate change in flow apparent]
[Debris also remains marking the water level from the previous minor flood event.]

* Added (Saturday) 8th September 2012.

Written Today (Sunday) 9th September 2012:

Possibility insect behavioural observations indicative of something coming this Spring. Too early (?) to tell, but noted.

River flow (including further downstream) appears to be healthy.

My views based on observations:

Developing an Understanding of the Earth’s Climate System:

Post #1114324 - 12-07-2012 11:45 AM


Longer-term observations suggest streamflow is gradually increasing [regionally], and that this increase may be linked to certain atmospheric conditions.

Analyses suggest a direct correlation with physical justification between weather variable(s) and soil moisture estimates...possibly to the extent of statistical significance, meaning some variable(s) could be used to predict or project soil moisture estimates in the near future within this region.

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Streamflow remains healthy and is gradually receding, possibly implying enough moisture is present in the soil and air above (Precipitable Water) to maintain flows above a threshold. Recent estimates seem to indicate soil moisture also remains above the 20% fractional content of soil volume.

It is somewhat interesting that 0 deg C was recorded overnight 10th-11th and 17th-18th, possibly implying humidity low enough for an impending change or changes (in weather conditions) in the near future (days to a week from said dates).