Seven Day Temperature Forecasts: Their Accuracy

Created 2004/04/02, modified 2004/12/23
Feedback welcome; email daveclarkecb@yahoo.com

Note that this page is probably out of date. The forecasting methods and accuracy of the particular weather service have probably changed since this study was done.
The page has been left here for archival reasons.

This page records the seven-day maximum daily temperature forecasts for Adelaide, as broadcast on South Australian TV, compares them to the temperatures that were actually measured on the days concerned, and summarizes the accuracy of the forecasts.

It covers the period from 5^th March 2004 to 31^st May 2004.

Also see 10-day forecast which examines the temperature forecasts published on uk.weather.com.

For the period over which I was able to calculate accuracies, the averages of the absolute errors are given in the table below. All temperatures are in degrees Celsius.

Days ahead 1 day 2 day 3 day 4 day 5 day 6 day 7 day
Ave. error 1.3 1.9 2.0 2.2 2.5 2.6 2.9

That is, for example, the one-day forecast was on average 1.3 degrees in error, either too high or too low. The temperature forecast for the second day in the future was, on average, 1.9 degrees in error, etc.

Days ahead	1 day	2 day	3 day	4 day	5 day	6 day	7 day
Ave. error	1.3	1.9	2.0	2.2	2.5	2.6	2.9

Convert .csv to .html
The software used to convert the table below from a .csv file produced by a spreadsheet to this html file is available free below.
To place these forecasts in some perspective one can consider how they compare to a forecast of the average maximum daily temperature for the time of year. The far right column in the table below shows the absolute difference from the 'average' maximum temperature. The reference figures I have used for the averages were taken from the uk.weather.com site. If one forecast these average temperatures then the average absolute error of the forecasts would be 3.3 degrees indicating that the seven-day forecast is little better than simply forecasting the average temperature for the time of year.

It seems that temperature variability in South Australia is less in the cooler months than in the warmer months.

Data

The data used to produce the above accuracy figures are given in the table below. Note that the table contains gaps because there were days when I was unable, or forgot, to record the forecast temperatures.

Weather forecasts - daily maximum temperatures
			Forecasts							Absolute errors Difference between forecast and actual temperature							Dif. from average
Day	Date	Actual temp.	1 day	2 day	3 day	4 day	5 day	6 day	7 day	1 day	2 day	3 day	4 day	5 day	6 day	7 day
Friday	5/03/2004	34.4	30							4.4							8.4
Saturday	6/03/2004	34.6	24	26						10.6	8.6						8.6
Sunday	7/03/2004	23.0	25	25	25					2.0	2.0	2.0					3.0
Monday	8/03/2004	31.0	29	27	22	22				2.0	4.0	9.0	9.0				5.0
Tuesday	9/03/2004	23.2	22	21	21	21	24			1.2	2.2	2.2	2.2	0.8			2.8
Wednesday	10/03/2004	25.1	23	25	25	25	23	25		2.1	0.1	0.1	0.1	2.1	0.1		0.9
Thursday	11/03/2004	24.0	24	23	26	26		23	26	0.0	1.0	2.0	2.0		1.0	2.0	2.0
Friday	12/03/2004	22.2	24	24	24	24			25	1.8	1.8	1.8	1.8			2.8	3.8
Saturday	13/03/2004	23.8	24	25	25	25	24			0.2	1.2	1.2	1.2	0.2			2.2
Sunday	14/03/2004	25.7	25	25	25	25	25	24		0.7	0.7	0.7	0.7	0.7	1.7		0.3
Monday	15/03/2004	26.1	27	25	25	25		25	25	0.9	1.1	1.1	1.1		1.1	1.1	0.1
Tuesday	16/03/2004	27.9	27	28	28	28	27		27	0.9	0.1	0.1	0.1	0.9		0.9	1.9
Wednesday	17/03/2004	27.9	26	26	26	26	26	28		1.9	1.9	1.9	1.9	1.9	0.1		1.9
Thursday	18/03/2004	26.8	29	29	29	29		27	26	2.2	2.2	2.2	2.2		0.2	0.8	0.8
Friday	19/03/2004	28.2	29	29	29	29			29	0.8	0.8	0.8	0.8			0.8	2.2
Saturday	20/03/2004		25	25	25	25	26										26.0
Sunday	21/03/2004	22.7		27	27	27	28	27			4.3	4.3	4.3	5.3	4.3		3.3
Monday	22/03/2004	27.0	26		28	28	27	29	28	1.0		1.0	1.0	0.0	2.0	1.0	1.0
Tuesday	23/03/2004	30.0	29	29		29	30	29	29	1.0	1.0		1.0	0.0	1.0	1.0	4.0
Wednesday	24/03/2004	31.7	32	30	30		31	32	30	0.3	1.7	1.7		0.7	0.3	1.7	5.7
Thursday	25/03/2004	30.1	30	30	30	33		32	34	0.1	0.1	0.1	2.9		1.9	3.9	4.1
Friday	26/03/2004	25.8	26	25	25	25			24	0.2	0.8	0.8	0.8			1.8	0.2
Saturday	27/03/2004	34.9	32	32	32	27	29			2.9	2.9	2.9	7.9	5.9			8.9
Sunday	28/03/2004	34.0	33	33	30	30	27	30		1.0	1.0	4.0	4.0	7.0	4.0		8.0
Monday	29/03/2004	21.1	22	23	23	23	24	25	29	0.9	1.9	1.9	1.9	2.9	3.9	7.9	4.9
Tuesday	30/03/2004	20.9	22	23	23	23	25	24	26	1.1	2.1	2.1	2.1	4.1	3.1	5.1	5.1
Wednesday	31/03/2004	20.0	21	23	25	25	23	27	26	1.0	3.0	5.0	5.0	3.0	7.0	6.0	6.0
		Averages of absolute errors for March data								1.6	1.9	2.1	2.5	2.4	2.1	2.6	4.5

Day	Date	Actual temp.	1 day	2 day	3 day	4 day	5 day	6 day	7 day	1 day	2 day	3 day	4 day	5 day	6 day	7 day
Thursday	1/04/2004	22.3	22	22	25	25	25	25	26	0.3	0.3	2.7	2.7	2.7	2.7	3.7	0.7
Friday	2/04/2004	22.0	24	23	23	25		27	25	2.0	1.0	1.0	3.0		5.0	3.0	1.0
Saturday	3/04/2004	23.8	23	23	23	23	25		25	0.8	0.8	0.8	0.8	1.2		1.2	0.8
Sunday	4/04/2004	25.4	25	25	25	25	26	23		0.4	0.4	0.4	0.4	0.6	2.4		2.4
Monday	5/04/2004	29.3	28		28	28	27	28	24	1.3		1.3	1.3	2.3	1.3	5.3	6.3
Tuesday	6/04/2004	27.0	22	24		27	25	24	28	5.0	3.0		0.0	2.0	3.0	1.0	4.0
Wednesday	7/04/2004	27.7	24	22	22		24	21	23	3.7	5.7	5.7		3.7	6.7	4.7	4.7
Thursday	8/04/2004	27.0	26	23	23	23		23	23	1.0	4.0	4.0	4.0		4.0	4.0	4.0
Friday	9/04/2004	29.9	28	26	26	26	27		24	1.9	3.9	3.9	3.9	2.9		5.9	6.9
Saturday	10/04/2004	27.2	27	27	27	27	26	25		0.2	0.2	0.2	0.2	1.2	2.2		4.2
Sunday	11/04/2004	27.5	25	25	28	25	23	25	27	2.5	2.5	0.5	2.5	4.5	2.5	0.5	5.5
Monday	12/04/2004	25.1	28	28	25	25	26	24	24	2.9	2.9	0.1	0.1	0.9	1.1	1.1	3.1
Tuesday	13/04/2004	31.5	30	27	27	27	25	25	24	1.5	4.5	4.5	4.5	6.5	6.5	7.5	9.5
Wednesday	14/04/2004	32.2	30	27	27	27	24	24	24	2.2	5.2	5.2	5.2	8.2	8.2	8.2	10.2
Thursday	15/04/2004	21.1	23	26	26	23		24	24	1.9	4.9	4.9	1.9		2.9	2.9	0.9
Friday	16/04/2004	20.4	21	22	22	22			23	0.6	1.6	1.6	1.6			2.6	1.6
Saturday	17/04/2004	21.5	21	22	22	22	23			0.5	0.5	0.5	0.5	1.5			0.5
Sunday	18/04/2004	20.6	22	22	24	24	21	23		1.4	1.4	3.4	3.4	0.4	2.4		1.4
Monday	19/04/2004	25.0	24	24	24	24	25	23	23	1.0	1.0	1.0	1.0	0.0	2.0	2.0	3.0
Tuesday	20/04/2004	27.8	26	26	26	26	25	25	24	1.8	1.8	1.8	1.8	2.8	2.8	3.8	6.8
Wednesday	21/04/2004	30.3	29	26	26	26	26	26	26	1.3	4.3	4.3	4.3	4.3	4.3	4.3	9.3
Thursday	22/04/2004	28.7	30	26	26	26	25	25	22	1.3	2.7	2.7	2.7	3.7	3.7	6.7	7.7
Friday	23/04/2004	18.4	19	19	19	19	20	20	19	0.6	0.6	0.6	0.6	1.6	1.6	0.6	2.6
Saturday	24/04/2004	16.7	19	20	20	20	22	19	19	2.3	3.3	3.3	3.3	5.3	2.3	2.3	4.3
Sunday	25/04/2004	16.5	19	21	21	21	22	21	20	2.5	4.5	4.5	4.5	5.5	4.5	3.5	4.5
Monday	26/04/2004	18.4	19	20	23	23	23	22	22	0.6	1.6	4.6	4.6	4.6	3.6	3.6	2.6
Tuesday	27/04/2004	17.8	20	20	20	23	24	24	24	2.2	2.2	2.2	5.2	6.2	6.2	6.2	3.2
Wednesday	28/04/2004	19.1	21	21	21	21	21	24	24	1.9	1.9	1.9	1.9	1.9	4.9	4.9	1.9
Thursday	29/04/2004	16.3	18	19	21	21	21	22	25	1.7	2.7	4.7	4.7	4.7	5.7	8.7	3.7
Friday	30/04/2004	18.0	18	19	19	19	19	19	21	0.0	1.0	1.0	1.0	1.0	1.0	3.0	2.0
		Averages of absolute errors for April data								1.6	2.4	2.5	2.5	3.1	3.6	3.9	4.0

Day	Date	Actual temp.	1 day	2 day	3 day	4 day	5 day	6 day	7 day	1 day	2 day	3 day	4 day	5 day	6 day	7 day
Saturday	1/05/2004	16.4	16	16	16	16	20	20	20	0.4	0.4	0.4	0.4	3.6	3.6	3.6	3.6
Sunday	2/05/2004	17.8	17	17	17	17	17	19	19	0.8	0.8	0.8	0.8	0.8	1.2	1.2	2.2
Monday	3/05/2004	18.3	17	17	17	17	17	17	19	1.3	1.3	1.3	1.3	1.3	1.3	1.3	0.7
Tuesday	4/05/2004	19.3	18	17	17	17	20	17	17	1.3	2.3	2.3	2.3	0.7	2.3	2.3	0.3
Wednesday	5/05/2004	18.5	18	18	18	18	21	21	17	0.5	0.5	0.5	0.5	2.5	2.5	1.5	0.5
Thursday	6/05/2004	19.7	20	20	20	20		22	22	0.3	0.3	0.3	0.3		2.3	2.3	0.7
Friday	7/05/2004	19.4	20	20	20	22	22		23	0.6	0.6	0.6	2.6	2.6		3.6	0.4
Saturday	8/05/2004	21.3	21	22	20	22	23	23		0.3	0.7	1.3	0.7	1.7	1.7		2.3
Sunday	9/05/2004	19.5	21	23	23	25	23	24	23	1.5	3.5	3.5	5.5	3.5	4.5	3.5	0.5
Monday	10/05/2004	20.5	21	23	23	25	23	24	23	0.5	2.5	2.5	4.5	2.5	3.5	2.5	1.5
Tuesday	11/05/2004	21.3	22	24	24	24	23	23	24	0.7	2.7	2.7	2.7	1.7	1.7	2.7	2.3
Wednesday	12/05/2004	22.2		24	24	24	22	22	22		1.8	1.8	1.8	0.2	0.2	0.2	4.2
Thursday	13/05/2004	20.4	19		19	17		18	18	1.4		1.4	3.4		2.4	2.4	2.4
Friday	14/05/2004	19.7	19	17		17			19	0.7	2.7		2.7			0.7	1.7
Saturday	15/05/2004	18.4	18	18	18		18			0.4	0.4	0.4		0.4			0.4
Sunday	16/05/2004	19.2	19	21	21	21		19		0.2	1.8	1.8	1.8		0.2		1.2
Monday	17/05/2004	17.6	18	18	18	22	21		20	0.4	0.4	0.4	4.4	3.4		2.4	0.4
Tuesday	18/05/2004	17.4	17	18	18	18	18	17		0.4	0.6	0.6	0.6	0.6	0.4		0.6
Wednesday	19/05/2004	17.7	18	19	19	19	22	18	17	0.3	1.3	1.3	1.3	4.3	0.3	0.7	0.3
Thursday	20/05/2004	19.2	19	19	19	19		20	19	0.2	0.2	0.2	0.2		0.8	0.2	1.2
Friday	21/05/2004	20.4	20	19	19	19			21	0.4	1.4	1.4	1.4				2.4
Saturday	22/05/2004	23.4	20	20	20	20	21			3.4	3.4	3.4	3.4	2.4			5.4
Sunday	23/05/2004	18.7	18	16	16	18	18	18		0.7	2.7	2.7	0.7	0.7	0.7		1.7
Monday	24/05/2004	18.4	17	17	17	17	17	17	17	1.4	1.4	1.4	1.4	1.4	1.4	1.4	1.4
Tuesday	25/05/2004	17.5	16	15	15	17	17	17	17	1.5	2.5	2.5	0.5	0.5	0.5	0.5	0.5
Wednesday	26/05/2004	15.4	16	15	15	15		17	17	0.6	0.4	0.4	0.4		1.6	1.6	1.6
Thursday	27/05/2004	14.7	16	17	17	17			18	1.3	2.3	2.3	2.3			3.3	2.3
Friday	28/05/2004	17.5	16	18	18	18				1.5	0.5	0.5	0.5				0.5
Saturday	29/05/2004	16.1	17	17	19	19				0.9	0.9	2.9	2.9				0.9
Sunday	30/05/2004	18.2	18	19	19	19	20			0.2	0.8	0.8	0.8	1.8			1.2
Monday	31/05/2004	19.3	20	19	19	19	22	21		0.7	0.3	0.3	0.3	2.7	1.7		2.3
		Averages of absolute errors for May data								0.8	1.4	1.4	1.7	1.9	1.7	1.9	1.6
		Averages of absolute errors for all data								1.3	1.9	2.0	2.2	2.5	2.6	2.9	3.3

Software used to copy the table from .csv to .html format

The table in this file was converted from a comma delimited (.csv) file produced by a spreadsheet program using a PASCAL program written for that purpose. The program, CsvToHtm.exe, should convert any .csv file to a table in html. You will probably want to polish-up the output html code.

Of course the same thing can be done using a spreadsheet program such as Excel, but that would give you a file at least six times larger. Size is important in Net pages.

Please contact me at the above email address if you'd like a (free) copy of the program. (If there is much interest I'll add it to this page as a download.)

Top
Home

Seven Day Temperature Forecasts: Their Accuracy

Note that this page is probably out of date. The forecasting methods and accuracy of the particular weather service have probably changed since this study was done. The page has been left here for archival reasons.

Data

Software used to copy the table from .csv to .html format

Note that this page is probably out of date. The forecasting methods and accuracy of the particular weather service have probably changed since this study was done.
The page has been left here for archival reasons.