South Tamworth Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Tamworth Observatory clear sky chart from 2005-11-06 to 2026-04-17.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	17% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	131191
	Night	16% 8% 3 7% 5% 4 5% 4 5% 6% 36%	130969
Transparency	Day	45% 6% 12% 22% 13% 2	134698
	Night	45% 6% 12% 22% 13% 2	135549
Seeing	Day	24% 16% 29% 20% 9% 2	16656
	Night	22% 12% 27% 30% 10% 1	25644

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	10% 8% 3 11% 7% 6% 5% 4 6% 6% 33%	4661
	11th to 20th	Day	11% 11% 4 7% 5% 4 5% 3 5% 7% 38%	4650
	21st to end	Day	9% 9% 2 7% 6% 5% 5% 4 5% 6% 42%	5124
February	1st to 10th	Day	13% 10% 3 7% 6% 6% 5% 4 5% 7% 35%	1855
	11th to 20th	Day	11% 7% 3 9% 6% 5% 6% 4 6% 7% 37%	2048
	21st to end	Day	14% 11% 3 7% 5% 5% 5% 4 5% 5% 34%	1730
March	1st to 10th	Day	18% 11% 3 10% 5% 4 4 4 4 5% 31%	4576
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 3 5% 6% 36%	4872
	21st to end	Day	24% 9% 2 6% 4 4 4 3 5% 7% 33%	5909
April	1st to 10th	Day	19% 11% 3 7% 4 3 5% 3 5% 6% 35%	2520
	11th to 20th	Day	17% 7% 2 6% 5% 4 5% 3 6% 7% 38%	2489
	21st to end	Day	21% 8% 3 7% 6% 4 4 3 4 5% 35%	2600
May	1st to 10th	Day	32% 11% 3 8% 5% 4 4 3 4 5% 21%	5886
	11th to 20th	Day	20% 8% 3 8% 6% 5% 5% 4 5% 8% 28%	6130
	21st to end	Day	19% 7% 2 6% 5% 5% 5% 5% 7% 8% 31%	6949
June	1st to 10th	Day	20% 9% 2 7% 5% 4 5% 4 6% 8% 29%	2800
	11th to 20th	Day	16% 7% 2 6% 5% 6% 4 4 6% 7% 36%	2800
	21st to end	Day	18% 7% 3 6% 5% 5% 5% 4 6% 8% 32%	2800
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 10% 33%	6360
	11th to 20th	Day	11% 6% 2 6% 4 4 6% 5% 8% 10% 38%	6360
	21st to end	Day	15% 6% 2 5% 4 4 4 4 6% 8% 42%	6926
August	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 5% 6% 8% 35%	4372
	11th to 20th	Day	17% 8% 3 8% 4 4 5% 5% 6% 7% 33%	4175
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 10% 45%	4327
September	1st to 10th	Day	12% 4 2 5% 4 4 4 4 6% 8% 47%	2400
	11th to 20th	Day	12% 5% 2 4 3 4 4 3 3 7% 52%	2204
	21st to end	Day	16% 5% 2 5% 4 4 5% 3 5% 6% 45%	2200
October	1st to 10th	Day	20% 6% 3 6% 4 4 4 3 4 6% 40%	2200
	11th to 20th	Day	16% 7% 2 5% 5% 5% 5% 3 5% 6% 41%	1910
	21st to end	Day	22% 8% 2 7% 4 4 4 4 5% 5% 35%	1980
November	1st to 10th	Day	13% 7% 2 6% 4 3 3 4 6% 7% 44%	1851
	11th to 20th	Day	17% 5% 2 5% 5% 4 5% 4 5% 7% 41%	1890
	21st to end	Day	19% 8% 2 5% 4 5% 4 4 5% 6% 37%	1843
December	1st to 10th	Day	15% 10% 3 8% 5% 6% 6% 5% 6% 7% 30%	2680
	11th to 20th	Day	18% 8% 2 6% 4 4 4 4 5% 7% 37%	3066
	21st to end	Day	19% 10% 3 8% 5% 4 4 3 5% 5% 34%	4048
January	1st to 10th	Night	11% 9% 3 9% 5% 5% 5% 4 5% 6% 38%	8234
	11th to 20th	Night	11% 11% 4 11% 7% 6% 6% 5% 6% 6% 28%	8235
	21st to end	Night	11% 7% 2 7% 5% 5% 6% 5% 7% 7% 38%	9057
February	1st to 10th	Night	12% 9% 4 7% 5% 5% 5% 4 7% 7% 35%	2758
	11th to 20th	Night	10% 9% 3 7% 6% 4 5% 5% 6% 8% 39%	2458
	21st to end	Night	12% 10% 3 6% 5% 5% 5% 4 6% 7% 39%	2076
March	1st to 10th	Night	20% 10% 3 7% 5% 4 4 4 6% 6% 31%	5484
	11th to 20th	Night	13% 10% 4 8% 6% 6% 5% 4 5% 6% 33%	5306
	21st to end	Night	23% 10% 3 6% 4 3 4 3 5% 7% 33%	5260
April	1st to 10th	Night	19% 10% 3 6% 5% 4 5% 3 4 6% 36%	2100
	11th to 20th	Night	17% 8% 2 8% 6% 5% 4 3 5% 7% 35%	1992
	21st to end	Night	20% 8% 2 6% 4 4 4 3 5% 6% 38%	1800
May	1st to 10th	Night	35% 9% 3 6% 4 3 4 4 5% 5% 22%	4054
	11th to 20th	Night	15% 10% 4 10% 6% 5% 5% 4 6% 7% 28%	3805
	21st to end	Night	19% 8% 3 7% 5% 4 5% 4 6% 6% 33%	3926
June	1st to 10th	Night	20% 7% 2 7% 5% 4 5% 4 5% 7% 34%	1600
	11th to 20th	Night	17% 7% 2 6% 4 4 5% 4 5% 8% 39%	1600
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 6% 7% 37%	1600
July	1st to 10th	Night	14% 6% 2 7% 4 4 5% 4 7% 9% 38%	3600
	11th to 20th	Night	14% 7% 3 7% 5% 4 5% 3 5% 7% 38%	3600
	21st to end	Night	12% 5% 1 4 4 4 5% 4 6% 7% 49%	3926
August	1st to 10th	Night	21% 8% 2 8% 5% 4 4 3 5% 6% 33%	2743
	11th to 20th	Night	16% 7% 3 6% 4 4 5% 4 5% 7% 38%	2872
	21st to end	Night	9% 5% 2 4 4 3 4 4 7% 9% 48%	3553
September	1st to 10th	Night	12% 6% 2 4 3 3 3 3 6% 7% 52%	2000
	11th to 20th	Night	14% 5% 1 4 4 4 3 3 4 6% 52%	2195
	21st to end	Night	16% 6% 2 5% 3 4 4 3 5% 7% 45%	2200
October	1st to 10th	Night	19% 5% 2 7% 3 4 4 4 5% 5% 40%	2200
	11th to 20th	Night	15% 6% 2 6% 4 5% 5% 4 6% 8% 39%	2485
	21st to end	Night	22% 8% 3 5% 4 4 5% 3 5% 6% 36%	2860
November	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	2667
	11th to 20th	Night	15% 6% 2 7% 4 4 4 4 6% 6% 42%	2730
	21st to end	Night	15% 8% 2 7% 5% 4 4 4 5% 6% 40%	2775
December	1st to 10th	Night	15% 10% 4 8% 5% 5% 5% 4 6% 6% 33%	4720
	11th to 20th	Night	23% 8% 2 5% 4 4 4 4 4 6% 36%	5348
	21st to end	Night	19% 10% 3 7% 4 5% 4 4 4 4 35%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	46% 7% 11% 23% 12%	4662
	11th to 20th	Day	44% 4 12% 23% 14% 3	4680
	21st to end	Day	39% 5% 12% 23% 18% 3	5124
February	1st to 10th	Day	47% 4 14% 20% 12% 3	1855
	11th to 20th	Day	45% 6% 11% 20% 14% 4	2057
	21st to end	Day	50% 4 11% 18% 14% 3	1730
March	1st to 10th	Day	54% 5% 9% 13% 12% 8%	4579
	11th to 20th	Day	48% 4 15% 19% 11% 4	4872
	21st to end	Day	50% 4 6% 18% 18% 4	5909
April	1st to 10th	Day	49% 4 9% 20% 14% 3	2520
	11th to 20th	Day	45% 6% 11% 20% 16% 2	2489
	21st to end	Day	52% 5% 7% 18% 15% 3	2600
May	1st to 10th	Day	64% 5% 9% 14% 7% 1	5897
	11th to 20th	Day	53% 7% 14% 16% 8% 2	6134
	21st to end	Day	46% 8% 13% 21% 11% 1	6949
June	1st to 10th	Day	50% 6% 12% 22% 10% 1	2800
	11th to 20th	Day	44% 6% 12% 21% 14% 3	2800
	21st to end	Day	48% 8% 12% 19% 12% 1	2800
July	1st to 10th	Day	44% 7% 14% 22% 13%	6290
	11th to 20th	Day	37% 8% 17% 23% 13% 1	6285
	21st to end	Day	37% 6% 13% 27% 15%	6728
August	1st to 10th	Day	44% 8% 15% 23% 10%	4358
	11th to 20th	Day	47% 7% 15% 24% 8%	4214
	21st to end	Day	31% 6% 17% 27% 17% 1	4327
September	1st to 10th	Day	32% 7% 13% 31% 16% 1	2400
	11th to 20th	Day	33% 4 9% 32% 20% 2	2204
	21st to end	Day	38% 6% 11% 26% 18% 2	2200
October	1st to 10th	Day	44% 7% 10% 21% 16% 2	3590
	11th to 20th	Day	38% 4 13% 27% 15% 3	3087
	21st to end	Day	37% 4 11% 27% 17% 4	3180
November	1st to 10th	Day	38% 5% 14% 26% 15% 2	1851
	11th to 20th	Day	40% 4 13% 21% 19% 3	1890
	21st to end	Day	47% 5% 16% 21% 11% 1	1843
December	1st to 10th	Day	47% 7% 15% 23% 7% 1	2680
	11th to 20th	Day	43% 6% 10% 19% 19% 3	3066
	21st to end	Day	52% 4 8% 18% 12% 7%	4048
January	1st to 10th	Night	44% 6% 13% 24% 12% 2	8234
	11th to 20th	Night	51% 6% 11% 18% 11% 3	8280
	21st to end	Night	40% 5% 10% 22% 17% 5%	9057
February	1st to 10th	Night	46% 5% 12% 21% 14% 2	2758
	11th to 20th	Night	42% 6% 11% 23% 15% 3	2460
	21st to end	Night	44% 5% 12% 22% 13% 4	2076
March	1st to 10th	Night	52% 5% 10% 15% 14% 5%	5494
	11th to 20th	Night	49% 5% 15% 17% 11% 2	5307
	21st to end	Night	50% 5% 5% 15% 21% 4	5260
April	1st to 10th	Night	50% 4 9% 19% 15% 3	2100
	11th to 20th	Night	48% 5% 8% 23% 15% 1	1992
	21st to end	Night	47% 4 11% 19% 16% 3	1800
May	1st to 10th	Night	64% 5% 10% 13% 7% 1	4060
	11th to 20th	Night	53% 7% 12% 18% 8% 2	3806
	21st to end	Night	48% 7% 15% 20% 9% 1	3927
June	1st to 10th	Night	48% 6% 13% 20% 13%	1600
	11th to 20th	Night	43% 7% 16% 19% 13% 2	1600
	21st to end	Night	44% 7% 14% 23% 10% 1	1600
July	1st to 10th	Night	39% 8% 18% 23% 12%	3560
	11th to 20th	Night	42% 8% 14% 20% 15%	3552
	21st to end	Night	32% 7% 14% 34% 12% 1	3809
August	1st to 10th	Night	51% 6% 13% 21% 9%	2733
	11th to 20th	Night	44% 8% 16% 21% 11%	2899
	21st to end	Night	29% 8% 17% 30% 16% 1	3553
September	1st to 10th	Night	31% 7% 14% 31% 17% 1	2000
	11th to 20th	Night	33% 5% 10% 29% 21% 2	2195
	21st to end	Night	38% 6% 11% 29% 14% 2	2200
October	1st to 10th	Night	42% 8% 14% 22% 13% 1	3590
	11th to 20th	Night	34% 5% 12% 28% 17% 4	4047
	21st to end	Night	40% 4 11% 28% 15% 2	4610
November	1st to 10th	Night	39% 6% 12% 26% 16% 2	2667
	11th to 20th	Night	41% 6% 10% 24% 17% 2	2730
	21st to end	Night	44% 5% 15% 24% 11% 1	2775
December	1st to 10th	Night	47% 5% 13% 28% 6%	4720
	11th to 20th	Night	48% 5% 11% 16% 18% 2	5348
	21st to end	Night	52% 4 9% 19% 14% 3	7150

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	26% 20% 30% 18% 6%	220
	11th to 20th	Day	29% 23% 27% 16% 3 1	220
	21st to end	Day	22% 23% 32% 18% 5%	242
February	1st to 10th	Day	25% 24% 31% 17% 3	357
	11th to 20th	Day	26% 22% 33% 17% 2	536
	21st to end	Day	28% 19% 30% 20% 4	446
March	1st to 10th	Day	31% 18% 30% 19% 3	540
	11th to 20th	Day	29% 22% 30% 12% 6% 1	540
	21st to end	Day	28% 21% 30% 14% 5% 3	594
April	1st to 10th	Day	34% 18% 26% 15% 6% 1	540
	11th to 20th	Day	33% 20% 25% 14% 6% 2	516
	21st to end	Day	29% 21% 30% 12% 6% 2	500
May	1st to 10th	Day	33% 18% 27% 15% 4 2	503
	11th to 20th	Day	21% 19% 33% 18% 7% 2	527
	21st to end	Day	22% 14% 34% 21% 7% 2	573
June	1st to 10th	Day	22% 15% 34% 18% 8% 2	530
	11th to 20th	Day	19% 16% 33% 22% 8% 2	530
	21st to end	Day	21% 15% 34% 18% 10% 2	530
July	1st to 10th	Day	19% 10% 32% 24% 13% 3	525
	11th to 20th	Day	14% 7% 36% 28% 12% 3	524
	21st to end	Day	16% 9% 35% 27% 11% 2	576
August	1st to 10th	Day	11% 11% 29% 28% 16% 4	526
	11th to 20th	Day	19% 9% 27% 23% 16% 6%	519
	21st to end	Day	14% 9% 29% 28% 14% 5%	583
September	1st to 10th	Day	15% 11% 26% 25% 17% 6%	530
	11th to 20th	Day	18% 10% 23% 24% 15% 10%	530
	21st to end	Day	17% 13% 28% 24% 13% 6%	530
October	1st to 10th	Day	24% 15% 22% 20% 14% 5%	530
	11th to 20th	Day	22% 16% 25% 22% 13% 2	457
	21st to end	Day	32% 13% 26% 22% 6% 1	462
November	1st to 10th	Day	25% 17% 26% 24% 7% 2	425
	11th to 20th	Day	27% 19% 26% 20% 8% 1	430
	21st to end	Day	33% 18% 27% 17% 5% 1	383
December	1st to 10th	Day	27% 24% 25% 15% 8% 1	220
	11th to 20th	Day	31% 21% 31% 13% 3	220
	21st to end	Day	29% 17% 31% 18% 4 1	242
January	1st to 10th	Night	21% 14% 34% 28% 4	840
	11th to 20th	Night	24% 15% 28% 28% 5%	840
	21st to end	Night	18% 18% 32% 26% 5%	924
February	1st to 10th	Night	19% 15% 34% 29% 3	840
	11th to 20th	Night	19% 17% 38% 21% 4	823
	21st to end	Night	20% 16% 33% 27% 4	692
March	1st to 10th	Night	26% 14% 32% 24% 4	840
	11th to 20th	Night	23% 15% 30% 26% 6%	840
	21st to end	Night	24% 14% 28% 24% 8% 1	924
April	1st to 10th	Night	26% 13% 29% 27% 5%	840
	11th to 20th	Night	23% 15% 29% 26% 6%	772
	21st to end	Night	27% 13% 25% 28% 7%	600
May	1st to 10th	Night	30% 8% 26% 28% 8% 1	600
	11th to 20th	Night	20% 10% 31% 27% 11%	494
	21st to end	Night	22% 6% 22% 36% 13% 1	433
June	1st to 10th	Night	21% 7% 24% 36% 10% 1	400
	11th to 20th	Night	20% 7% 22% 37% 14% 1	400
	21st to end	Night	21% 6% 23% 38% 12% 1	400
July	1st to 10th	Night	17% 4 19% 43% 16%	390
	11th to 20th	Night	15% 3 19% 41% 19% 2	388
	21st to end	Night	15% 3 17% 47% 17% 1	438
August	1st to 10th	Night	16% 4 16% 40% 22% 1	490
	11th to 20th	Night	16% 6% 24% 32% 20% 2	592
	21st to end	Night	16% 5% 19% 37% 20% 4	860
September	1st to 10th	Night	14% 6% 23% 34% 20% 2	800
	11th to 20th	Night	17% 6% 17% 32% 23% 5%	800
	21st to end	Night	18% 7% 22% 32% 17% 3	800
October	1st to 10th	Night	22% 10% 19% 30% 17% 2	800
	11th to 20th	Night	20% 11% 25% 31% 13% 1	800
	21st to end	Night	29% 13% 23% 28% 8%	880
November	1st to 10th	Night	20% 13% 28% 29% 9% 1	820
	11th to 20th	Night	22% 15% 29% 26% 7% 1	840
	21st to end	Night	23% 18% 25% 28% 6%	840
December	1st to 10th	Night	25% 14% 30% 25% 6%	840
	11th to 20th	Night	26% 15% 27% 27% 4	840
	21st to end	Night	26% 15% 27% 28% 4	924

Page generated at 2026-04-14 02:44:24. Version ac07

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