Friday, May 26, 2017 at 03:40
Tony. I agree. I live in
Perth. Most 7 day forecasts by the BOM are unreliable. For about one month I tabulated the 7 day forecasts, day by day, against the 6, 5,4... etc day forecasts against the actuals in a spreadsheet.
Outcome was that there was only some reliability in the 2 day out forecasts. I simplified the reliability measures to the following. Max temp +/- 3C and did it rain or not. It was too difficult to deal with BOM's % chance of rain vs number of mm predicted. So I ignored the no of mm and just dealt with the % chance of rain.
At 2 days out the forecasts are reasonable about 70% of the time for temp and rain or no rain.
At 7 days out the forecasts were reasonable less than 10% of the time.
Conclusion, as you have stated, use climatic normals for estimating weather circumstances a week or more in advance.
The BOM have invested 100's of $M in technology in the last 10 years. It has resulted in much more data being available but it's difficult to see improvement in longer range forecasts.
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