Outback Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Outback Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	12% 9% 3 7% 5% 4 5% 4 6% 7% 38%	149825
	Night	12% 10% 4 8% 5% 4 4 4 5% 7% 38%	141964
Transparency	Day	44% 4 12% 26% 13% 1	153276
	Night	45% 4 12% 24% 14% 1	146588
Seeing	Day	19% 14% 32% 22% 10% 3	18690
	Night	19% 12% 32% 27% 10% 1	28455

By Month

Percentage Cloud Cover SE (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	9% 12% 4 12% 7% 5% 5% 4 5% 6% 29%	4691
	11th to 20th	Day	7% 14% 5% 10% 6% 5% 6% 5% 6% 7% 28%	4710
	21st to end	Day	8% 12% 5% 11% 4 4 5% 4 6% 7% 34%	5156
February	1st to 10th	Day	8% 11% 5% 10% 6% 4 6% 4 5% 7% 34%	1879
	11th to 20th	Day	10% 12% 3 8% 5% 4 4 5% 5% 7% 37%	1952
	21st to end	Day	10% 14% 4 9% 6% 5% 4 4 5% 6% 33%	1730
March	1st to 10th	Day	12% 9% 2 6% 3 4 4 3 4 6% 46%	4580
	11th to 20th	Day	11% 8% 3 9% 5% 4 5% 4 6% 8% 35%	4844
	21st to end	Day	22% 12% 3 10% 5% 4 4 3 4 5% 29%	6084
April	1st to 10th	Day	15% 13% 3 8% 6% 4 4 4 5% 6% 31%	2520
	11th to 20th	Day	20% 10% 4 8% 4 5% 4 4 5% 6% 32%	2494
	21st to end	Day	17% 11% 3 7% 6% 5% 4 4 6% 5% 31%	2664
May	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 7% 43%	8034
	11th to 20th	Day	12% 6% 3 6% 4 4 4 4 5% 6% 44%	8222
	21st to end	Day	13% 7% 2 6% 4 4 4 4 6% 8% 41%	9047
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 4 4 6% 8% 41%	2940
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 3 7% 7% 37%	2940
	21st to end	Day	12% 7% 2 7% 4 5% 5% 5% 6% 9% 37%	2940
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 7% 10% 40%	8280
	11th to 20th	Day	6% 3 2 5% 3 4 5% 4 6% 9% 53%	8280
	21st to end	Day	10% 6% 2 6% 4 5% 5% 4 6% 8% 45%	8990
August	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	6483
	11th to 20th	Day	12% 5% 1 5% 4 5% 5% 4 6% 7% 45%	5840
	21st to end	Day	13% 7% 2 7% 4 4 5% 4 6% 8% 40%	6080
September	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 6% 8% 44%	2520
	11th to 20th	Day	14% 6% 2 6% 4 3 5% 4 5% 8% 44%	2441
	21st to end	Day	12% 7% 3 7% 4 5% 5% 5% 6% 8% 39%	2288
October	1st to 10th	Day	15% 8% 2 6% 3 3 4 3 6% 8% 42%	2050
	11th to 20th	Day	19% 11% 3 8% 5% 4 4 4 5% 6% 31%	1976
	21st to end	Day	18% 11% 4 7% 4 4 4 3 5% 5% 34%	1980
November	1st to 10th	Day	14% 9% 3 6% 4 5% 5% 4 5% 8% 37%	1852
	11th to 20th	Day	12% 14% 5% 10% 6% 4 5% 4 5% 6% 29%	1810
	21st to end	Day	14% 12% 4 8% 5% 4 4 4 6% 6% 31%	1680
December	1st to 10th	Day	8% 11% 5% 14% 7% 7% 6% 4 5% 5% 26%	2690
	11th to 20th	Day	12% 18% 5% 11% 6% 4 4 3 5% 5% 26%	3088
	21st to end	Day	21% 23% 5% 10% 5% 3 3 2 4 4 20%	4070
January	1st to 10th	Night	11% 13% 5% 11% 6% 4 4 3 4 6% 33%	8232
	11th to 20th	Night	7% 13% 6% 12% 7% 5% 6% 4 6% 7% 25%	8280
	21st to end	Night	6% 11% 6% 12% 6% 6% 5% 4 5% 5% 34%	9058
February	1st to 10th	Night	9% 14% 5% 10% 5% 5% 4 4 5% 6% 34%	2740
	11th to 20th	Night	9% 10% 4 10% 5% 5% 5% 3 5% 6% 38%	2554
	21st to end	Night	13% 12% 4 10% 6% 4 4 3 5% 5% 34%	2076
March	1st to 10th	Night	12% 7% 2 6% 4 4 4 3 5% 6% 48%	5493
	11th to 20th	Night	10% 11% 3 9% 4 4 5% 4 6% 8% 35%	5379
	21st to end	Night	21% 10% 3 10% 4 4 4 3 4 6% 30%	5086
April	1st to 10th	Night	19% 12% 4 8% 4 3 4 3 4 6% 32%	2100
	11th to 20th	Night	21% 9% 3 5% 5% 4 3 4 5% 5% 36%	2075
	21st to end	Night	17% 9% 2 7% 4 3 4 4 6% 7% 36%	1954
May	1st to 10th	Night	12% 7% 3 6% 4 3 4 3 6% 9% 43%	4826
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 6% 7% 44%	4670
	21st to end	Night	15% 8% 3 7% 4 3 4 3 5% 7% 41%	5139
June	1st to 10th	Night	11% 7% 1 6% 5% 4 4 4 6% 7% 46%	1680
	11th to 20th	Night	13% 7% 2 8% 5% 4 5% 5% 7% 7% 38%	1680
	21st to end	Night	11% 5% 3 5% 4 4 4 4 6% 8% 45%	1680
July	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 10% 43%	4708
	11th to 20th	Night	7% 3 1 4 3 3 3 4 6% 11% 56%	4707
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 8% 50%	5117
August	1st to 10th	Night	11% 5% 2 7% 5% 4 4 3 6% 8% 45%	3687
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 6% 9% 46%	4198
	21st to end	Night	12% 7% 2 7% 4 4 4 3 5% 6% 46%	5046
September	1st to 10th	Night	9% 5% 2 5% 3 3 4 3 5% 7% 52%	2100
	11th to 20th	Night	12% 6% 2 6% 3 3 4 3 5% 6% 51%	2158
	21st to end	Night	12% 7% 2 5% 4 3 3 3 6% 8% 46%	2289
October	1st to 10th	Night	13% 6% 2 4 4 4 4 3 5% 8% 47%	2346
	11th to 20th	Night	15% 9% 3 7% 5% 4 4 4 5% 7% 38%	2423
	21st to end	Night	19% 10% 4 7% 5% 4 4 4 4 7% 33%	2860
November	1st to 10th	Night	15% 10% 3 6% 4 3 4 3 5% 7% 41%	2666
	11th to 20th	Night	13% 12% 5% 8% 5% 3 4 3 4 7% 35%	2808
	21st to end	Night	14% 12% 3 9% 5% 5% 5% 4 5% 7% 32%	2940
December	1st to 10th	Night	12% 11% 3 8% 5% 4 5% 5% 7% 8% 33%	4720
	11th to 20th	Night	11% 18% 7% 12% 5% 4 4 3 3 5% 28%	5339
	21st to end	Night	23% 17% 5% 9% 4 3 3 3 4 5% 25%	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	56% 3 11% 20% 10% 1	4692
	11th to 20th	Day	53% 4 8% 20% 12% 2	4710
	21st to end	Day	49% 3 10% 24% 14%	5156
February	1st to 10th	Day	50% 5% 11% 20% 12% 1	1879
	11th to 20th	Day	47% 4 10% 25% 12% 2	1961
	21st to end	Day	52% 4 11% 21% 10% 2	1730
March	1st to 10th	Day	40% 2 12% 23% 17% 6%	4580
	11th to 20th	Day	46% 4 14% 21% 14% 1	4844
	21st to end	Day	59% 3 9% 16% 13%	6086
April	1st to 10th	Day	53% 4 11% 19% 12% 1	2520
	11th to 20th	Day	54% 3 9% 21% 12% 1	2494
	21st to end	Day	54% 4 9% 20% 12% 2	2664
May	1st to 10th	Day	39% 4 9% 30% 17% 1	8070
	11th to 20th	Day	40% 4 10% 28% 18% 1	8226
	21st to end	Day	41% 4 9% 25% 20% 2	9061
June	1st to 10th	Day	40% 4 13% 29% 13% 1	2940
	11th to 20th	Day	44% 4 13% 25% 12% 1	2940
	21st to end	Day	42% 5% 16% 25% 11% 1	2940
July	1st to 10th	Day	39% 5% 17% 31% 8%	8211
	11th to 20th	Day	26% 4 14% 38% 16% 1	8205
	21st to end	Day	36% 5% 11% 30% 18% 1	8794
August	1st to 10th	Day	39% 5% 16% 29% 11% 1	6468
	11th to 20th	Day	37% 6% 16% 31% 10%	5882
	21st to end	Day	41% 6% 14% 29% 10% 1	6079
September	1st to 10th	Day	39% 4 13% 30% 14% 1	2520
	11th to 20th	Day	39% 4 17% 31% 9% 1	2441
	21st to end	Day	42% 5% 12% 29% 12% 1	2288
October	1st to 10th	Day	29% 3 11% 34% 23% 1	3336
	11th to 20th	Day	46% 4 10% 24% 16% 1	3192
	21st to end	Day	46% 3 14% 28% 8%	3180
November	1st to 10th	Day	46% 4 12% 24% 13% 1	1852
	11th to 20th	Day	56% 3 11% 20% 8% 1	1810
	21st to end	Day	53% 4 14% 23% 4 1	1680
December	1st to 10th	Day	58% 5% 12% 19% 6%	2690
	11th to 20th	Day	61% 2 9% 14% 13% 1	3085
	21st to end	Day	70% 2 5% 15% 9%	4070
January	1st to 10th	Night	53% 3 9% 23% 11% 1	8233
	11th to 20th	Night	56% 3 9% 17% 13% 1	8280
	21st to end	Night	51% 4 9% 21% 14% 1	9058
February	1st to 10th	Night	51% 3 9% 23% 12% 2	2740
	11th to 20th	Night	47% 5% 10% 24% 12% 2	2555
	21st to end	Night	52% 3 11% 22% 9% 2	2076
March	1st to 10th	Night	38% 3 15% 24% 16% 4	5493
	11th to 20th	Night	47% 4 15% 21% 11% 2	5379
	21st to end	Night	56% 3 9% 18% 13% 1	5086
April	1st to 10th	Night	53% 4 7% 18% 17% 1	2100
	11th to 20th	Night	49% 4 10% 20% 14% 3	2075
	21st to end	Night	47% 4 11% 22% 15% 1	1954
May	1st to 10th	Night	38% 3 11% 29% 15% 3	4851
	11th to 20th	Night	38% 5% 12% 25% 18% 2	4671
	21st to end	Night	43% 4 11% 22% 18% 3	5149
June	1st to 10th	Night	37% 4 14% 28% 16% 1	1680
	11th to 20th	Night	44% 4 13% 22% 16% 1	1680
	21st to end	Night	36% 4 15% 31% 11% 3	1680
July	1st to 10th	Night	37% 6% 18% 28% 10% 2	4670
	11th to 20th	Night	23% 4 15% 40% 16% 2	4662
	21st to end	Night	31% 4 14% 27% 22% 1	5002
August	1st to 10th	Night	36% 4 15% 28% 15% 1	3678
	11th to 20th	Night	34% 6% 18% 27% 12% 1	4222
	21st to end	Night	39% 5% 13% 28% 15% 1	5046
September	1st to 10th	Night	33% 4 12% 34% 16% 1	2100
	11th to 20th	Night	35% 3 14% 35% 12%	2158
	21st to end	Night	36% 4 14% 32% 13% 1	2289
October	1st to 10th	Night	29% 3 9% 37% 20% 2	3840
	11th to 20th	Night	36% 3 11% 32% 16% 1	3946
	21st to end	Night	50% 3 10% 23% 13%	4610
November	1st to 10th	Night	43% 3 11% 26% 15% 1	2666
	11th to 20th	Night	50% 3 14% 19% 13% 1	2808
	21st to end	Night	52% 3 13% 23% 7% 1	2940
December	1st to 10th	Night	46% 5% 21% 22% 5% 1	4720
	11th to 20th	Night	61% 2 9% 16% 11% 1	5341
	21st to end	Night	64% 2 7% 17% 10%	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	19% 18% 35% 22% 5% 1	330
	11th to 20th	Day	22% 22% 34% 19% 2 1	330
	21st to end	Day	20% 20% 40% 16% 3	363
February	1st to 10th	Day	16% 27% 38% 14% 4 1	330
	11th to 20th	Day	21% 29% 35% 12% 3	330
	21st to end	Day	23% 27% 40% 8% 1	273
March	1st to 10th	Day	25% 23% 36% 13% 3	330
	11th to 20th	Day	26% 21% 34% 13% 5% 1	330
	21st to end	Day	26% 18% 32% 17% 6% 1	579
April	1st to 10th	Day	27% 18% 33% 18% 4	540
	11th to 20th	Day	32% 16% 27% 17% 7% 2	532
	21st to end	Day	26% 15% 30% 18% 9% 1	540
May	1st to 10th	Day	21% 17% 36% 19% 7% 2	690
	11th to 20th	Day	21% 15% 33% 20% 8% 2	775
	21st to end	Day	17% 12% 34% 22% 11% 4	844
June	1st to 10th	Day	13% 12% 34% 26% 12% 3	780
	11th to 20th	Day	20% 12% 32% 24% 9% 3	780
	21st to end	Day	17% 11% 30% 25% 14% 3	780
July	1st to 10th	Day	9% 6% 26% 34% 18% 6%	771
	11th to 20th	Day	10% 10% 30% 29% 14% 7%	768
	21st to end	Day	8% 7% 30% 33% 16% 6%	849
August	1st to 10th	Day	12% 6% 28% 31% 18% 6%	776
	11th to 20th	Day	16% 6% 22% 31% 18% 6%	655
	21st to end	Day	17% 8% 27% 25% 18% 6%	627
September	1st to 10th	Day	17% 11% 27% 24% 14% 6%	570
	11th to 20th	Day	17% 6% 26% 31% 16% 4	570
	21st to end	Day	17% 14% 24% 26% 16% 4	562
October	1st to 10th	Day	20% 14% 27% 25% 12% 2	380
	11th to 20th	Day	23% 24% 32% 18% 3	330
	21st to end	Day	27% 21% 36% 13% 2 1	363
November	1st to 10th	Day	22% 17% 39% 17% 4 1	330
	11th to 20th	Day	25% 20% 35% 15% 4 1	330
	21st to end	Day	23% 23% 38% 12% 3 1	330
December	1st to 10th	Day	18% 19% 45% 12% 5%	330
	11th to 20th	Day	26% 24% 34% 12% 4 1	330
	21st to end	Day	31% 20% 32% 15% 2	363
January	1st to 10th	Night	17% 17% 38% 24% 3	1050
	11th to 20th	Night	20% 17% 38% 19% 5% 1	1050
	21st to end	Night	18% 15% 38% 24% 6%	1155
February	1st to 10th	Night	15% 19% 36% 23% 6%	1050
	11th to 20th	Night	16% 21% 35% 23% 6%	920
	21st to end	Night	23% 13% 37% 22% 4	692
March	1st to 10th	Night	19% 15% 35% 23% 8% 1	840
	11th to 20th	Night	19% 16% 38% 21% 5% 1	763
	21st to end	Night	22% 11% 33% 25% 8% 1	693
April	1st to 10th	Night	27% 12% 33% 21% 5% 1	630
	11th to 20th	Night	29% 11% 27% 27% 5% 1	623
	21st to end	Night	23% 10% 32% 27% 7%	630
May	1st to 10th	Night	21% 10% 34% 27% 8% 1	630
	11th to 20th	Night	21% 9% 33% 29% 8%	621
	21st to end	Night	15% 8% 30% 34% 12% 1	683
June	1st to 10th	Night	13% 8% 29% 39% 11%	630
	11th to 20th	Night	17% 8% 29% 37% 8% 1	630
	21st to end	Night	15% 4 28% 37% 15% 1	630
July	1st to 10th	Night	10% 3 24% 41% 21% 1	615
	11th to 20th	Night	9% 4 28% 38% 20% 1	612
	21st to end	Night	8% 3 29% 40% 17% 3	690
August	1st to 10th	Night	10% 2 26% 38% 22% 1	627
	11th to 20th	Night	13% 4 21% 37% 23% 3	624
	21st to end	Night	14% 5% 23% 36% 21% 1	693
September	1st to 10th	Night	13% 7% 24% 32% 20% 4	630
	11th to 20th	Night	14% 5% 29% 31% 18% 3	688
	21st to end	Night	17% 9% 25% 29% 18% 1	833
October	1st to 10th	Night	17% 11% 30% 26% 15% 2	800
	11th to 20th	Night	20% 16% 31% 26% 6%	800
	21st to end	Night	26% 11% 29% 24% 10% 1	880
November	1st to 10th	Night	22% 12% 37% 21% 7% 1	820
	11th to 20th	Night	21% 16% 36% 20% 6% 1	918
	21st to end	Night	21% 20% 32% 22% 5%	1050
December	1st to 10th	Night	21% 18% 34% 20% 6%	1050
	11th to 20th	Night	22% 17% 33% 22% 5% 1	1050
	21st to end	Night	28% 14% 34% 20% 3	1155

Page generated at 2026-09-26 03:18:43. Version ac07

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