RASC Sunshine Coast Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the RASC Sunshine Coast 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	22% 9% 3 6% 4 4 4 3 5% 6% 34%	117523
	Night	26% 10% 3 7% 4 4 4 3 4 5% 30%	120458
Transparency	Day	52% 9% 13% 17% 8% 1	117269
	Night	57% 7% 12% 16% 7% 1	120358
Seeing	Day	26% 8% 21% 25% 17% 3	16130
	Night	32% 7% 16% 24% 17% 3	24361

By Month

Percentage Cloud Cover NW (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	39% 12% 3 6% 4 4 5% 4 4 5% 15%	3179
	11th to 20th	Day	20% 13% 4 8% 5% 5% 4 3 6% 7% 26%	3159
	21st to end	Day	42% 10% 2 6% 3 3 3 2 3 5% 22%	3916
February	1st to 10th	Day	32% 12% 4 7% 6% 4 5% 3 5% 5% 17%	1800
	11th to 20th	Day	27% 11% 2 8% 5% 5% 4 3 5% 7% 23%	1755
	21st to end	Day	25% 11% 3 8% 6% 6% 5% 4 4 6% 22%	1485
March	1st to 10th	Day	26% 15% 4 9% 5% 5% 5% 3 5% 5% 19%	4710
	11th to 20th	Day	23% 13% 3 8% 5% 4 4 3 5% 6% 26%	5000
	21st to end	Day	28% 13% 4 9% 6% 5% 4 3 4 5% 19%	5568
April	1st to 10th	Day	25% 11% 4 8% 5% 4 5% 4 7% 6% 22%	2400
	11th to 20th	Day	21% 10% 3 7% 5% 4 4 4 5% 6% 30%	2514
	21st to end	Day	22% 10% 3 6% 5% 4 4 3 5% 6% 32%	2632
May	1st to 10th	Day	14% 8% 3 6% 4 4 4 3 4 5% 45%	4560
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 5% 7% 12% 38%	4517
	21st to end	Day	25% 8% 2 6% 4 4 4 4 6% 7% 29%	5096
June	1st to 10th	Day	21% 8% 3 6% 5% 4 4 4 6% 8% 31%	2850
	11th to 20th	Day	17% 8% 2 7% 5% 6% 5% 5% 7% 7% 31%	2850
	21st to end	Day	14% 7% 2 7% 5% 4 4 4 6% 7% 40%	2850
July	1st to 10th	Day	6% 4 1 4 3 2 3 3 3 5% 66%	4740
	11th to 20th	Day	5% 3 1 2 2 2 2 2 3 6% 71%	4740
	21st to end	Day	11% 5% 2 5% 3 3 3 3 5% 7% 54%	4981
August	1st to 10th	Day	6% 3 1 3 2 2 3 2 4 6% 70%	4316
	11th to 20th	Day	11% 8% 3 6% 3 3 4 4 5% 8% 43%	4026
	21st to end	Day	14% 6% 2 5% 4 4 4 4 6% 7% 44%	4469
September	1st to 10th	Day	12% 6% 2 5% 3 4 4 3 5% 7% 49%	2280
	11th to 20th	Day	17% 8% 3 6% 3 4 4 4 4 7% 40%	2241
	21st to end	Day	24% 5% 2 6% 3 4 5% 3 5% 8% 35%	2024
October	1st to 10th	Day	24% 9% 3 7% 4 4 4 4 6% 7% 28%	3180
	11th to 20th	Day	34% 8% 2 7% 4 4 4 4 4 6% 24%	3161
	21st to end	Day	31% 10% 3 7% 5% 5% 4 3 6% 7% 20%	3153
November	1st to 10th	Day	39% 10% 3 7% 4 3 5% 4 4 4 17%	1568
	11th to 20th	Day	35% 12% 2 6% 3 4 3 3 5% 5% 21%	1600
	21st to end	Day	36% 11% 3 9% 4 3 3 3 3 5% 20%	1600
December	1st to 10th	Day	24% 13% 3 6% 5% 4 5% 4 5% 6% 25%	2460
	11th to 20th	Day	42% 14% 4 8% 4 3 4 2 3 4 12%	2645
	21st to end	Day	43% 14% 4 8% 4 4 3 2 3 4 11%	3498
January	1st to 10th	Night	37% 12% 4 10% 5% 4 3 2 3 4 16%	6766
	11th to 20th	Night	22% 9% 3 7% 4 4 4 4 6% 7% 30%	6739
	21st to end	Night	39% 9% 2 5% 3 3 3 2 3 4 24%	7043
February	1st to 10th	Night	31% 12% 4 7% 4 4 4 4 4 5% 20%	2600
	11th to 20th	Night	25% 12% 3 8% 5% 4 3 3 4 4 29%	2532
	21st to end	Night	29% 13% 3 7% 4 3 4 3 5% 5% 25%	2145
March	1st to 10th	Night	27% 13% 3 7% 4 4 4 3 4 7% 23%	5169
	11th to 20th	Night	23% 12% 3 7% 4 4 4 4 5% 5% 28%	4999
	21st to end	Night	34% 13% 4 8% 5% 4 4 3 4 5% 18%	5407
April	1st to 10th	Night	25% 11% 3 8% 5% 5% 6% 4 5% 6% 23%	2000
	11th to 20th	Night	18% 11% 4 8% 5% 5% 4 3 5% 7% 30%	1832
	21st to end	Night	22% 10% 2 7% 4 4 4 4 5% 7% 31%	1766
May	1st to 10th	Night	16% 8% 2 5% 4 4 3 2 4 5% 46%	2620
	11th to 20th	Night	13% 5% 3 5% 3 3 4 4 6% 11% 43%	2596
	21st to end	Night	21% 11% 4 10% 6% 5% 4 3 4 6% 27%	2590
June	1st to 10th	Night	21% 8% 4 8% 5% 4 4 3 4 5% 33%	1330
	11th to 20th	Night	16% 11% 2 7% 6% 6% 5% 3 7% 6% 31%	1330
	21st to end	Night	12% 6% 2 9% 3 4 5% 4 5% 8% 42%	1330
July	1st to 10th	Night	6% 3 2 4 3 3 3 2 3 5% 64%	2220
	11th to 20th	Night	4 2 1 3 3 2 2 2 4 5% 73%	2220
	21st to end	Night	8% 5% 2 5% 4 4 4 4 5% 6% 53%	2571
August	1st to 10th	Night	4 2 1 3 2 2 2 2 4 6% 74%	2614
	11th to 20th	Night	14% 5% 2 6% 4 3 4 4 5% 7% 46%	2812
	21st to end	Night	15% 5% 2 6% 4 4 4 3 4 6% 45%	3200
September	1st to 10th	Night	8% 4 2 3 3 4 3 3 5% 6% 58%	1900
	11th to 20th	Night	19% 7% 2 5% 4 3 4 4 5% 5% 42%	1937
	21st to end	Night	21% 8% 2 6% 4 3 4 3 4 6% 39%	2156
October	1st to 10th	Night	25% 9% 3 6% 5% 4 4 3 5% 6% 29%	3800
	11th to 20th	Night	31% 9% 3 6% 4 4 4 3 4 6% 28%	3777
	21st to end	Night	31% 8% 2 7% 4 4 4 3 4 6% 27%	4394
November	1st to 10th	Night	38% 10% 3 7% 5% 3 3 3 4 5% 18%	2730
	11th to 20th	Night	35% 10% 3 6% 5% 3 4 2 4 4 23%	2800
	21st to end	Night	35% 11% 3 7% 4 3 4 2 4 5% 21%	2800
December	1st to 10th	Night	26% 11% 3 6% 4 5% 5% 4 5% 6% 25%	4715
	11th to 20th	Night	41% 14% 3 7% 4 3 4 3 4 4 12%	5560
	21st to end	Night	40% 14% 4 8% 4 4 3 2 4 4 13%	7458

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	70% 8% 10% 8% 3 1	3179
	11th to 20th	Day	52% 10% 14% 14% 9% 1	3180
	21st to end	Day	68% 5% 6% 15% 6%	3916
February	1st to 10th	Day	69% 9% 9% 8% 3 3	1800
	11th to 20th	Day	62% 8% 11% 13% 5% 1	1764
	21st to end	Day	65% 10% 10% 9% 4 2	1485
March	1st to 10th	Day	66% 11% 10% 9% 4	4710
	11th to 20th	Day	61% 8% 9% 17% 4	5000
	21st to end	Day	69% 10% 12% 7% 2	5568
April	1st to 10th	Day	63% 11% 11% 10% 4	2400
	11th to 20th	Day	55% 10% 11% 15% 8% 2	2514
	21st to end	Day	58% 9% 11% 14% 8% 1	2632
May	1st to 10th	Day	43% 9% 15% 22% 11%	4560
	11th to 20th	Day	39% 19% 17% 20% 4	4520
	21st to end	Day	55% 15% 13% 14% 3	5097
June	1st to 10th	Day	54% 10% 16% 13% 4 2	2850
	11th to 20th	Day	54% 13% 15% 13% 5%	2850
	21st to end	Day	46% 10% 17% 18% 8% 2	2850
July	1st to 10th	Day	24% 7% 11% 24% 23% 10%	4666
	11th to 20th	Day	18% 7% 15% 37% 23% 1	4659
	21st to end	Day	32% 10% 20% 24% 12% 3	4824
August	1st to 10th	Day	19% 7% 13% 47% 14% 1	4299
	11th to 20th	Day	43% 11% 20% 16% 8% 2	4065
	21st to end	Day	42% 9% 17% 22% 8% 1	4468
September	1st to 10th	Day	37% 9% 16% 23% 12% 4	2280
	11th to 20th	Day	47% 9% 13% 18% 13% 2	2241
	21st to end	Day	49% 12% 14% 15% 9% 1	2024
October	1st to 10th	Day	56% 9% 16% 13% 6%	3180
	11th to 20th	Day	63% 7% 12% 11% 6%	3161
	21st to end	Day	66% 9% 11% 9% 4	3153
November	1st to 10th	Day	70% 8% 9% 7% 5% 1	1568
	11th to 20th	Day	67% 8% 9% 9% 6% 2	1600
	21st to end	Day	68% 6% 8% 11% 6% 1	1600
December	1st to 10th	Day	59% 7% 10% 17% 6% 1	2460
	11th to 20th	Day	78% 7% 7% 6% 1 1	2648
	21st to end	Day	81% 6% 6% 5% 1 1	3498
January	1st to 10th	Night	73% 5% 6% 10% 4	6766
	11th to 20th	Night	50% 10% 16% 16% 8% 1	6780
	21st to end	Night	65% 5% 8% 17% 5%	7043
February	1st to 10th	Night	66% 7% 8% 10% 6% 3	2600
	11th to 20th	Night	61% 7% 11% 12% 7% 1	2534
	21st to end	Night	62% 7% 11% 13% 6% 2	2145
March	1st to 10th	Night	60% 10% 11% 11% 7%	5169
	11th to 20th	Night	57% 9% 10% 18% 6%	5000
	21st to end	Night	70% 8% 11% 8% 2	5407
April	1st to 10th	Night	61% 9% 12% 15% 3	2000
	11th to 20th	Night	53% 9% 9% 18% 9% 2	1832
	21st to end	Night	53% 9% 12% 17% 8%	1766
May	1st to 10th	Night	41% 6% 16% 25% 11%	2620
	11th to 20th	Night	34% 11% 22% 26% 6% 1	2596
	21st to end	Night	57% 9% 16% 14% 3	2590
June	1st to 10th	Night	53% 7% 15% 17% 5% 3	1330
	11th to 20th	Night	51% 9% 18% 16% 6%	1330
	21st to end	Night	42% 10% 18% 18% 9% 3	1330
July	1st to 10th	Night	22% 6% 11% 26% 25% 10%	2185
	11th to 20th	Night	16% 4 14% 37% 26% 2	2178
	21st to end	Night	29% 8% 18% 27% 15% 4	2489
August	1st to 10th	Night	15% 4 14% 40% 26% 2	2606
	11th to 20th	Night	37% 10% 26% 15% 9% 3	2839
	21st to end	Night	40% 7% 18% 24% 10%	3200
September	1st to 10th	Night	29% 8% 16% 27% 15% 5%	1900
	11th to 20th	Night	44% 8% 12% 17% 15% 4	1937
	21st to end	Night	47% 8% 15% 19% 9% 2	2156
October	1st to 10th	Night	55% 8% 15% 14% 7%	3800
	11th to 20th	Night	60% 5% 11% 17% 7%	3777
	21st to end	Night	60% 7% 12% 15% 5%	4394
November	1st to 10th	Night	70% 7% 10% 8% 5% 1	2730
	11th to 20th	Night	67% 8% 9% 10% 5% 2	2800
	21st to end	Night	67% 7% 9% 9% 7% 1	2800
December	1st to 10th	Night	61% 6% 11% 17% 5% 1	4715
	11th to 20th	Night	78% 6% 7% 7% 3	5556
	21st to end	Night	78% 6% 6% 7% 2	7458

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	42% 9% 21% 17% 8% 4	200
	11th to 20th	Day	37% 17% 17% 18% 11% 1	200
	21st to end	Day	46% 9% 20% 14% 9% 2	270
February	1st to 10th	Day	37% 11% 25% 17% 9% 1	400
	11th to 20th	Day	36% 9% 25% 20% 9% 1	395
	21st to end	Day	32% 15% 27% 15% 10% 1	331
March	1st to 10th	Day	34% 12% 25% 20% 9% 1	493
	11th to 20th	Day	33% 12% 20% 21% 13% 1	500
	21st to end	Day	35% 12% 25% 19% 7% 1	550
April	1st to 10th	Day	34% 12% 24% 20% 9% 1	500
	11th to 20th	Day	26% 12% 28% 20% 14% 1	492
	21st to end	Day	26% 11% 26% 22% 14% 2	500
May	1st to 10th	Day	19% 10% 22% 31% 18% 1	503
	11th to 20th	Day	20% 7% 21% 29% 20% 3	528
	21st to end	Day	19% 8% 24% 30% 17% 3	669
June	1st to 10th	Day	24% 8% 23% 26% 18% 1	680
	11th to 20th	Day	18% 9% 25% 29% 16% 2	680
	21st to end	Day	17% 5% 21% 33% 21% 3	680
July	1st to 10th	Day	15% 4 18% 33% 26% 4	671
	11th to 20th	Day	8% 4 19% 40% 25% 4	668
	21st to end	Day	8% 5% 15% 33% 33% 6%	644
August	1st to 10th	Day	10% 3 16% 29% 32% 9%	487
	11th to 20th	Day	11% 4 14% 34% 30% 6%	477
	21st to end	Day	17% 5% 18% 36% 21% 3	539
September	1st to 10th	Day	17% 6% 24% 31% 20% 3	490
	11th to 20th	Day	26% 7% 19% 26% 17% 5%	490
	21st to end	Day	28% 8% 22% 23% 15% 3	490
October	1st to 10th	Day	31% 7% 19% 22% 17% 4	490
	11th to 20th	Day	38% 7% 18% 19% 14% 4	490
	21st to end	Day	37% 14% 18% 20% 7% 3	403
November	1st to 10th	Day	42% 12% 23% 17% 7%	200
	11th to 20th	Day	42% 10% 14% 19% 11% 5%	200
	21st to end	Day	48% 10% 17% 12% 8% 6%	200
December	1st to 10th	Day	41% 7% 22% 12% 13% 6%	200
	11th to 20th	Day	46% 10% 18% 20% 6% 1	200
	21st to end	Day	46% 10% 27% 14% 3	220
January	1st to 10th	Night	48% 10% 18% 15% 8% 1	900
	11th to 20th	Night	41% 7% 18% 22% 12%	900
	21st to end	Night	42% 7% 19% 21% 10%	923
February	1st to 10th	Night	37% 7% 23% 22% 10%	800
	11th to 20th	Night	34% 8% 21% 28% 9% 1	784
	21st to end	Night	37% 11% 18% 21% 11% 2	660
March	1st to 10th	Night	35% 10% 21% 21% 12% 2	800
	11th to 20th	Night	40% 8% 16% 24% 11% 1	800
	21st to end	Night	38% 9% 18% 20% 14% 2	880
April	1st to 10th	Night	32% 9% 16% 27% 13% 4	800
	11th to 20th	Night	26% 9% 23% 26% 15% 1	644
	21st to end	Night	28% 6% 20% 30% 15% 2	566
May	1st to 10th	Night	18% 5% 18% 33% 23% 4	400
	11th to 20th	Night	22% 5% 10% 29% 29% 5%	394
	21st to end	Night	21% 5% 15% 30% 25% 5%	422
June	1st to 10th	Night	25% 5% 11% 32% 23% 4	380
	11th to 20th	Night	23% 4 11% 32% 23% 6%	380
	21st to end	Night	16% 4 10% 34% 31% 5%	380
July	1st to 10th	Night	12% 1 10% 24% 42% 10%	370
	11th to 20th	Night	9% 2 8% 32% 39% 9%	368
	21st to end	Night	8% 2 5% 27% 46% 12%	416
August	1st to 10th	Night	10% 2 5% 22% 45% 15%	424
	11th to 20th	Night	9% 1 5% 26% 48% 11%	564
	21st to end	Night	16% 4 10% 29% 37% 5%	655
September	1st to 10th	Night	12% 2 11% 35% 32% 8%	760
	11th to 20th	Night	23% 5% 12% 22% 29% 10%	760
	21st to end	Night	29% 4 14% 27% 23% 3	760
October	1st to 10th	Night	26% 5% 16% 30% 21% 3	760
	11th to 20th	Night	36% 5% 13% 26% 17% 2	760
	21st to end	Night	40% 8% 19% 24% 8% 2	836
November	1st to 10th	Night	44% 8% 19% 23% 5%	780
	11th to 20th	Night	42% 8% 21% 19% 9% 1	800
	21st to end	Night	43% 7% 20% 21% 7% 1	800
December	1st to 10th	Night	36% 8% 18% 27% 11% 1	845
	11th to 20th	Night	49% 9% 20% 18% 4	900
	21st to end	Night	46% 12% 22% 15% 4	990

Page generated at 2025-05-23 06:21:02. Version ac07

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