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 2025-05-26.

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	13% 9% 3 8% 5% 4 5% 4 5% 7% 37%	114086
	Night	13% 10% 4 8% 5% 4 4 3 5% 7% 37%	115414
Transparency	Day	46% 4 12% 25% 13% 1	117584
	Night	46% 4 12% 24% 13% 1	120057
Seeing	Day	19% 14% 31% 22% 10% 3	16712
	Night	19% 12% 32% 27% 10% 1	26701

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	8% 11% 4 12% 7% 5% 6% 4 5% 6% 33%	3617
	11th to 20th	Day	9% 12% 5% 9% 7% 6% 7% 5% 6% 8% 26%	3620
	21st to end	Day	10% 15% 6% 12% 4 4 4 3 5% 6% 30%	3982
February	1st to 10th	Day	9% 12% 5% 9% 6% 4 6% 4 5% 7% 34%	1789
	11th to 20th	Day	10% 12% 3 8% 5% 4 5% 5% 5% 7% 36%	1857
	21st to end	Day	10% 14% 4 9% 6% 4 4 4 5% 7% 33%	1650
March	1st to 10th	Day	12% 9% 2 6% 3 4 4 3 4 6% 46%	4480
	11th to 20th	Day	11% 8% 3 9% 5% 4 5% 4 6% 8% 36%	4740
	21st to end	Day	22% 12% 3 10% 5% 4 4 3 4 5% 29%	5953
April	1st to 10th	Day	15% 13% 3 8% 6% 5% 4 4 5% 6% 31%	2400
	11th to 20th	Day	20% 10% 4 7% 4 5% 4 4 5% 6% 32%	2374
	21st to end	Day	17% 12% 3 7% 6% 5% 4 4 6% 5% 31%	2537
May	1st to 10th	Day	16% 7% 2 7% 5% 4 4 3 5% 6% 40%	4442
	11th to 20th	Day	13% 7% 3 6% 4 4 4 3 5% 7% 44%	4539
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 4 6% 6% 37%	4895
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 4 3 6% 9% 42%	2660
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 3 7% 7% 38%	2660
	21st to end	Day	11% 6% 2 7% 4 6% 5% 4 7% 9% 38%	2660
July	1st to 10th	Day	14% 4 2 5% 5% 5% 5% 4 7% 10% 38%	4440
	11th to 20th	Day	5% 3 2 5% 3 4 5% 5% 7% 9% 51%	4440
	21st to end	Day	8% 6% 2 6% 4 5% 5% 4 6% 8% 46%	4813
August	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 5% 6% 8% 39%	4423
	11th to 20th	Day	13% 5% 1 5% 5% 4 5% 4 6% 7% 46%	3964
	21st to end	Day	13% 8% 3 8% 5% 4 4 4 6% 7% 39%	4180
September	1st to 10th	Day	13% 7% 2 5% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	13% 6% 2 6% 4 3 5% 3 5% 8% 45%	2209
	21st to end	Day	13% 7% 3 7% 4 5% 5% 5% 6% 8% 38%	2090
October	1st to 10th	Day	16% 8% 2 6% 4 3 4 3 6% 9% 41%	1948
	11th to 20th	Day	19% 11% 3 7% 5% 4 4 4 5% 6% 31%	1877
	21st to end	Day	19% 11% 4 7% 5% 4 4 3 5% 5% 33%	1881
November	1st to 10th	Day	15% 9% 2 6% 4 5% 5% 4 5% 8% 38%	1762
	11th to 20th	Day	13% 14% 6% 10% 6% 4 5% 4 6% 6% 28%	1724
	21st to end	Day	14% 12% 5% 8% 5% 4 4 5% 6% 6% 31%	1600
December	1st to 10th	Day	8% 11% 5% 14% 7% 7% 6% 4 6% 5% 27%	2610
	11th to 20th	Day	12% 19% 5% 11% 5% 4 4 3 5% 5% 26%	3008
	21st to end	Day	21% 23% 5% 10% 5% 3 3 2 4 4 20%	3982
January	1st to 10th	Night	9% 12% 5% 11% 6% 4 4 3 4 6% 36%	6348
	11th to 20th	Night	8% 13% 5% 11% 7% 5% 6% 4 6% 7% 27%	6360
	21st to end	Night	8% 14% 7% 13% 5% 5% 4 3 4 5% 30%	6996
February	1st to 10th	Night	9% 14% 5% 9% 5% 5% 4 4 4 6% 35%	2610
	11th to 20th	Night	9% 10% 4 9% 5% 5% 5% 4 5% 6% 38%	2429
	21st to end	Night	13% 13% 4 9% 6% 4 4 3 5% 6% 34%	1980
March	1st to 10th	Night	11% 7% 2 6% 4 4 4 2 5% 6% 48%	5373
	11th to 20th	Night	10% 11% 3 9% 4 4 5% 4 6% 8% 35%	5263
	21st to end	Night	21% 11% 3 10% 4 4 4 3 4 6% 30%	4975
April	1st to 10th	Night	18% 12% 4 7% 4 3 4 3 4 6% 33%	2000
	11th to 20th	Night	21% 9% 3 5% 5% 4 4 4 5% 5% 36%	1975
	21st to end	Night	18% 9% 2 8% 4 3 4 4 6% 7% 36%	1861
May	1st to 10th	Night	17% 8% 3 7% 5% 4 4 4 5% 7% 36%	2666
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 5% 7% 45%	2586
	21st to end	Night	16% 7% 3 7% 4 4 4 3 6% 7% 38%	2788
June	1st to 10th	Night	12% 6% 1 6% 4 5% 4 3 5% 7% 46%	1520
	11th to 20th	Night	11% 7% 2 8% 5% 4 5% 5% 7% 7% 39%	1520
	21st to end	Night	10% 5% 3 5% 4 4 4 5% 6% 9% 46%	1520
July	1st to 10th	Night	14% 5% 1 5% 4 4 4 3 5% 8% 46%	2530
	11th to 20th	Night	5% 3 1 4 3 3 3 4 6% 9% 57%	2530
	21st to end	Night	9% 6% 3 6% 4 3 3 3 5% 7% 51%	2750
August	1st to 10th	Night	11% 5% 3 7% 6% 4 4 3 6% 8% 44%	2517
	11th to 20th	Night	12% 6% 2 5% 3 4 4 3 5% 8% 49%	2867
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 5% 47%	3476
September	1st to 10th	Night	9% 5% 2 6% 3 3 4 3 5% 7% 53%	1900
	11th to 20th	Night	11% 6% 2 6% 3 3 4 3 5% 6% 52%	1952
	21st to end	Night	13% 7% 2 6% 4 3 3 3 6% 8% 46%	2090
October	1st to 10th	Night	13% 6% 2 4 4 4 4 4 5% 8% 47%	2228
	11th to 20th	Night	14% 9% 3 7% 5% 4 4 4 6% 7% 38%	2302
	21st to end	Night	19% 10% 4 7% 5% 4 4 4 5% 7% 32%	2717
November	1st to 10th	Night	15% 10% 3 6% 4 3 3 3 5% 7% 41%	2536
	11th to 20th	Night	13% 12% 5% 8% 5% 3 4 3 4 7% 34%	2674
	21st to end	Night	14% 12% 3 9% 5% 5% 5% 4 5% 8% 32%	2800
December	1st to 10th	Night	12% 10% 3 7% 5% 4 6% 5% 7% 8% 34%	4580
	11th to 20th	Night	12% 18% 7% 12% 5% 4 4 3 3 5% 28%	5199
	21st to end	Night	23% 17% 5% 9% 4 3 3 3 4 5% 25%	6996

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	52% 3 11% 22% 11% 1	3618
	11th to 20th	Day	55% 4 9% 18% 12% 2	3620
	21st to end	Day	56% 2 12% 20% 10%	3982
February	1st to 10th	Day	50% 5% 12% 20% 12% 1	1789
	11th to 20th	Day	48% 4 10% 25% 12% 2	1866
	21st to end	Day	52% 4 12% 21% 10% 2	1650
March	1st to 10th	Day	40% 2 12% 22% 18% 6%	4480
	11th to 20th	Day	45% 4 14% 22% 14% 1	4740
	21st to end	Day	59% 3 9% 16% 13%	5955
April	1st to 10th	Day	53% 4 10% 19% 12% 1	2400
	11th to 20th	Day	53% 3 8% 22% 12% 1	2374
	21st to end	Day	54% 4 9% 19% 12% 2	2537
May	1st to 10th	Day	45% 3 9% 27% 15%	4481
	11th to 20th	Day	41% 3 10% 32% 14% 1	4543
	21st to end	Day	47% 4 9% 23% 15% 1	4908
June	1st to 10th	Day	40% 4 13% 30% 12% 1	2660
	11th to 20th	Day	44% 4 13% 25% 13% 1	2660
	21st to end	Day	40% 5% 17% 26% 11% 1	2660
July	1st to 10th	Day	41% 4 16% 28% 10% 1	4371
	11th to 20th	Day	27% 5% 15% 37% 15% 2	4365
	21st to end	Day	35% 5% 11% 30% 18% 1	4662
August	1st to 10th	Day	41% 5% 14% 25% 13% 1	4408
	11th to 20th	Day	36% 6% 13% 33% 12%	4006
	21st to end	Day	42% 6% 13% 25% 13% 1	4179
September	1st to 10th	Day	39% 4 13% 29% 14% 1	2280
	11th to 20th	Day	39% 3 17% 31% 9% 1	2209
	21st to end	Day	43% 5% 13% 29% 10%	2090
October	1st to 10th	Day	29% 3 12% 34% 23% 1	3234
	11th to 20th	Day	45% 4 10% 25% 16% 1	3093
	21st to end	Day	47% 3 14% 27% 8%	3081
November	1st to 10th	Day	45% 4 12% 25% 12% 1	1762
	11th to 20th	Day	57% 3 11% 19% 8% 1	1724
	21st to end	Day	52% 4 15% 23% 4 1	1600
December	1st to 10th	Day	58% 5% 12% 20% 5%	2610
	11th to 20th	Day	61% 2 10% 14% 12%	3005
	21st to end	Day	69% 2 5% 15% 9%	3982
January	1st to 10th	Night	50% 3 8% 24% 13% 1	6348
	11th to 20th	Night	55% 3 9% 19% 14% 1	6360
	21st to end	Night	56% 3 10% 20% 10% 1	6996
February	1st to 10th	Night	51% 3 9% 23% 13% 2	2610
	11th to 20th	Night	47% 5% 10% 24% 12% 2	2430
	21st to end	Night	52% 3 11% 22% 10% 2	1980
March	1st to 10th	Night	37% 3 15% 24% 16% 4	5373
	11th to 20th	Night	46% 4 16% 21% 11% 2	5263
	21st to end	Night	56% 2 9% 19% 13% 1	4975
April	1st to 10th	Night	52% 4 7% 18% 18% 1	2000
	11th to 20th	Night	48% 4 10% 21% 13% 3	1975
	21st to end	Night	47% 4 10% 22% 15% 1	1861
May	1st to 10th	Night	48% 3 14% 20% 14% 1	2691
	11th to 20th	Night	38% 4 11% 30% 14% 2	2587
	21st to end	Night	45% 4 14% 19% 16% 2	2796
June	1st to 10th	Night	37% 4 14% 29% 15% 1	1520
	11th to 20th	Night	43% 3 14% 22% 17% 1	1520
	21st to end	Night	35% 4 16% 31% 11% 3	1520
July	1st to 10th	Night	37% 5% 17% 24% 13% 3	2490
	11th to 20th	Night	23% 5% 17% 37% 16% 2	2482
	21st to end	Night	32% 4 12% 28% 21% 2	2662
August	1st to 10th	Night	39% 4 15% 23% 17% 2	2508
	11th to 20th	Night	33% 6% 15% 29% 15% 2	2891
	21st to end	Night	38% 5% 14% 24% 18% 1	3476
September	1st to 10th	Night	31% 4 11% 35% 17% 1	1900
	11th to 20th	Night	34% 3 14% 36% 13%	1952
	21st to end	Night	37% 4 14% 32% 12% 1	2090
October	1st to 10th	Night	29% 3 9% 37% 20% 2	3722
	11th to 20th	Night	36% 4 11% 33% 16% 1	3825
	21st to end	Night	51% 3 10% 23% 13%	4467
November	1st to 10th	Night	43% 3 12% 26% 14% 1	2536
	11th to 20th	Night	51% 3 14% 18% 13% 1	2674
	21st to end	Night	52% 4 14% 24% 6% 1	2800
December	1st to 10th	Night	45% 5% 22% 22% 4 1	4580
	11th to 20th	Night	61% 2 9% 16% 11% 1	5201
	21st to end	Night	64% 2 6% 17% 10%	6996

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% 17% 34% 23% 6% 1	300
	11th to 20th	Day	23% 21% 34% 18% 3 1	300
	21st to end	Day	22% 18% 40% 16% 3	330
February	1st to 10th	Day	16% 26% 38% 14% 5% 1	300
	11th to 20th	Day	21% 30% 33% 12% 4	300
	21st to end	Day	23% 26% 41% 8% 1	249
March	1st to 10th	Day	24% 24% 36% 13% 3	300
	11th to 20th	Day	25% 21% 32% 14% 5% 1	300
	21st to end	Day	26% 18% 31% 17% 7% 1	536
April	1st to 10th	Day	27% 18% 32% 19% 4	500
	11th to 20th	Day	32% 17% 27% 16% 7% 1	492
	21st to end	Day	27% 15% 31% 18% 9% 1	500
May	1st to 10th	Day	21% 16% 35% 19% 7% 2	643
	11th to 20th	Day	20% 14% 33% 21% 9% 3	725
	21st to end	Day	18% 13% 33% 23% 11% 4	760
June	1st to 10th	Day	13% 13% 34% 26% 12% 3	680
	11th to 20th	Day	19% 11% 31% 25% 10% 3	680
	21st to end	Day	15% 10% 31% 24% 15% 4	680
July	1st to 10th	Day	10% 6% 27% 33% 18% 6%	671
	11th to 20th	Day	11% 10% 29% 29% 14% 7%	668
	21st to end	Day	8% 7% 29% 32% 17% 7%	739
August	1st to 10th	Day	12% 6% 28% 31% 18% 6%	676
	11th to 20th	Day	17% 6% 20% 30% 20% 7%	566
	21st to end	Day	17% 8% 25% 25% 19% 6%	539
September	1st to 10th	Day	17% 10% 27% 24% 16% 6%	490
	11th to 20th	Day	15% 6% 28% 31% 16% 4	490
	21st to end	Day	18% 15% 26% 23% 15% 3	490
October	1st to 10th	Day	22% 15% 26% 24% 12% 1	348
	11th to 20th	Day	24% 24% 31% 18% 3	300
	21st to end	Day	29% 22% 35% 11% 2	330
November	1st to 10th	Day	21% 16% 40% 17% 4 1	300
	11th to 20th	Day	24% 21% 36% 16% 3 1	300
	21st to end	Day	22% 24% 37% 13% 3 1	300
December	1st to 10th	Day	20% 20% 43% 12% 6%	300
	11th to 20th	Day	26% 24% 33% 12% 4 1	300
	21st to end	Day	31% 18% 33% 16% 2	330
January	1st to 10th	Night	16% 17% 39% 25% 4	1000
	11th to 20th	Night	21% 16% 37% 19% 6% 1	1000
	21st to end	Night	18% 14% 37% 24% 6%	1100
February	1st to 10th	Night	15% 19% 36% 23% 6% 1	1000
	11th to 20th	Night	16% 21% 35% 23% 5%	875
	21st to end	Night	23% 13% 37% 22% 4	660
March	1st to 10th	Night	19% 15% 36% 22% 8% 1	800
	11th to 20th	Night	18% 16% 38% 22% 6% 1	727
	21st to end	Night	23% 10% 32% 26% 8% 1	660
April	1st to 10th	Night	27% 12% 34% 22% 5% 1	600
	11th to 20th	Night	29% 11% 27% 27% 5% 1	593
	21st to end	Night	24% 10% 32% 27% 7% 1	600
May	1st to 10th	Night	22% 10% 33% 27% 8% 1	600
	11th to 20th	Night	21% 8% 33% 30% 8% 1	591
	21st to end	Night	15% 8% 31% 33% 12% 1	634
June	1st to 10th	Night	13% 8% 28% 38% 11%	570
	11th to 20th	Night	16% 7% 29% 39% 8% 1	570
	21st to end	Night	13% 5% 28% 38% 16% 1	570
July	1st to 10th	Night	10% 3 24% 40% 21% 1	555
	11th to 20th	Night	10% 3 29% 37% 20% 1	552
	21st to end	Night	9% 3 28% 39% 19% 3	624
August	1st to 10th	Night	11% 2 26% 38% 22% 2	567
	11th to 20th	Night	13% 3 20% 35% 25% 4	564
	21st to end	Night	15% 5% 22% 36% 21% 1	627
September	1st to 10th	Night	12% 6% 25% 33% 19% 4	570
	11th to 20th	Night	13% 5% 29% 32% 17% 4	622
	21st to end	Night	17% 9% 27% 28% 17% 1	760
October	1st to 10th	Night	17% 11% 30% 26% 15% 1	760
	11th to 20th	Night	20% 16% 32% 26% 6%	760
	21st to end	Night	26% 11% 30% 23% 10% 1	836
November	1st to 10th	Night	22% 11% 38% 21% 7% 2	780
	11th to 20th	Night	22% 16% 37% 19% 6%	874
	21st to end	Night	20% 19% 33% 23% 5%	1000
December	1st to 10th	Night	21% 18% 35% 20% 6%	1000
	11th to 20th	Night	22% 17% 33% 23% 5% 1	1000
	21st to end	Night	28% 14% 34% 20% 4	1100

Page generated at 2025-05-23 08:21:03. Version ac07

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