Archive for September, 2012

Spring-Summer Rain Outlook Update- 20 September 2012

September 20, 2012

This page will be regularly updated, as soon as I have enough RAINFALL and minimum temperature data.

This series of posts is a continuing public testing and refining of my hunch that surges in minimum anomalies indicate later upper level disturbances.   Since September last year my success rate is 80%.

Progress:

On September 5 I tipped for September 18 +/- 7 days, “Possibly an upper level system- Possible storm activity; probably only light rain.”

Exactly right.  I could have narrowed it down to +/- 2 days.

This is how we went:

Outlook:

SOI 30 day mean is 3.5.

NINO 3.4 Index for August was + 0.73 and rising.

The Indian Ocean Dipole is currently +0.48 and falling.

We are looking at a weak El Nino, with a positive IOD, so conditions will be generally dry in spring before returning to normal summer conditions.   Alternatively, we could be in for an early and heavier Wet, and a return to La Nina next year- I will discuss this possibility in a future post.  I’m not so sure about January now: earlier I thought it would be hot and dry but I will have to wait until further into the season.  Normal or above wet season rains are likely in early February.

For Central and Southern Queensland indications for the next 5 months are:

Commencement period Description Likely result
September  28 +/- 3 days,   linking to:- Possibly an upper level system Possible storms
October 3 +/- 7 days

October 18 +/- 3 days?

October 30 +/- 3 days

Upper system likely to start

Possible disturbance

“ “

Possible storm activity
November 13 +/- 10 days

Possibly November 26?

Enhanced weather activity to begin in this period Possible storms.  This may last   to early December.
December 4 +/- 4 days Possible upper system Possible storms
December 20 +/- 8 days (13-28 December)

December 26 +/- 2 days

Indications of a stronger system

Possible extra influence

Possible heavier storms or rain starting in this period, possibly   lasting past Xmas.
January- possible 13 +/- 3 days? 22 +/- 2 days?

Late January- February (in the region 28 January-onwards)

 

 

Probable upper system enhancing wet season begins in this period

Possible early storms?

 

Widespread rain, amount unknown (no-brainer- this is the wet season)

Here’s a graphical representation of when I expect upper level disturbances for the rest of this year. 

I will monitor conditions and refine my predictions as the season develops.

30 day mean Minimum percentage anomaly for the 10 Subtropical Queensland sites I monitor as at 20 September (almost the equinox) was -0.39.

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Rainfall Predictions- September – January

September 5, 2012

Ken Stewart, 05/09/2012

This page will be reposted at the end of September, as soon as I have enough RAINFALL and MINIMUM TEMPERATURE data.

Last month I tipped “For southern and central Queensland (Mackay to Longreach and south to the border), the next enhancements will be early to mid-August (which may last a week or two), another late September to mid-October, and maybe late October to early November.  Indications are that there will be heavier rain events starting in the period early to mid-November and early to mid-December.   These events may affect NSW as well, but I am restricting my study at this stage to Queensland.

Specifically, I’m expecting there may be a small rain event around 5-8 August and another probably larger one in the period 15-25 August, (I’m tipping close to 18-20 August).”

This is how we went:

The 5-8 August event did not eventuate, but the later one did, in fact for Mackay, the “18-20 August” event arrived on the afternoon of the 19th!  The system finally petered out by the end of August, again about a week later than I thought.  The system did not produce heavy rain, in fact this August was one of the driest we’ve had.

To put this in context, here’s a plot of 3 day average rainfall expressed as a percentage of median rain, for Rockhampton for 2012 (0 is median rain, -10 is zero, +10 is double the median; horizontal axis shows months):

As you can see, Rocky only received half its normal August rain.

It appears that my method indicates the timing, but not intensity, of a weather enhancement.  By enhancement I mean an upper level disturbance or upper trough, which can lead to anything from extra clouds, isolated showers and storms, through to widespread heavy rain.  In developing El Nino conditions such as we appear to be in, the influence is weaker and produces less rain, and is likely to come later.  In La Nina conditions the influence produces heavier and more widespread rain.

It is still too early to be specific about next year’s wet season rain just yet, however for Central and Southern Queensland indications for the next 5 months are:

Commencement period Description Likely result
September  18 +/- 7 days Possibly an upper level system Possible storm activity; probably only light rain
October 6 +/- 7 days Upper system likely to start Possible storm activity
November 15 +/- 10 days “ “ Possible storms.  This may last   to early December.
December 5 +/- 7 days Possible weak system Possible storms
December 16 +/- 7 days Indications of a stronger system Possible heavier storms or rain starting in this period, possibly   lasting past Xmas.
Late January to mid-February*.  *timing not clear yet, but not before 26   January. Probable upper system enhancing wet season begins in this period Widespread rain, amount unknown.    El Nino conditions would make it weaker and later.

All the above could be a week or so later.

I will monitor conditions and refine my predictions as the season develops.

Surface fronts will still come through of course bringing storms.  I would be surprised however if conditions are not generally dry until early October, and then again until early November or mid-December.  I expect January to be hot and dry.

Here’s the Bureau’s map of regions of Queensland they expect to have a 75% chance of exceeding various rainfall totals for September to November.

So we’ll see how we go with the timing.  Early days yet, and with El Nino, systems are likely to be later and weaker.

Coldest Month in 10 Years

September 3, 2012

Update- more detailed explanation below.

I have been monitoring minimum temperatures and rainfall since 2003 for 10 locations in South and Central Queensland.

These are: Rockhampton, Clermont, Longreach, Charleville, Cunnamulla, Surat, Oakey, Taroom, Maryborough, and Amberley.

If you thought August was cold, you’re right.

I have been calculating temperature anomalies using my own method, which is:

The difference between daily raw Tmin and the running 30 day mean of long term monthly means, both converted to Kelvin (to reduce the relative size of winter variation), expressed as a percentage of the monthly mean.  This smooths the transition from month to month of the daily anomalies.  I then calculate a 30 day running mean of these anomalies for the 10 locations.  (See below.)

On 21 August this value reached -1.273 -1.282.   The next lowest was on 25 August 2008 when it reached -1.252  -1.261.  (Made a small correction!)

Here’s the plot of the minimum percent anomalies from 2003 to the present:

The 4th order polynomial trend line shows the past, not the future, but there is no doubt that this is the coldest month and year of this decade.

It is not, however, the coldest 3 month period.  Here’s the 90 day running mean:

And 365 day running mean:

The trends (for this decade) are similar.

Update: My method is rather idiosyncratic and needs further explanation.

Download from Climate Data Online raw daily Tmin.

Convert to Kelvin (Celsius + 273.2) (TminK)

Enter BOM’s long term monthly mean for each month. Convert to Kelvin.

For each day of each month calculate the centred 31 day running mean of the long term monthly mean. (MeanK).

Calculate daily % anomalies ((TminK – MeanK)/ MeanK %).

Calculate 30 day, 90 day, and 365 day means.

Here’s a plot comparing the normal anomaly calculation with mine.  Notice how mine is smoother, but also is more conservative.  The normal (blue) trend is greater.

Vertical gridlines are at 30 day intervals.