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 2024-11-02.

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	21% 9% 3 6% 4 4 4 3 5% 6% 36%	101740
	Night	26% 10% 3 6% 4 4 4 3 4 5% 31%	97313
Transparency	Day	50% 10% 13% 17% 8% 1	101486
	Night	55% 8% 12% 16% 8% 1	97213
Seeing	Day	25% 8% 21% 26% 17% 3	15516
	Night	32% 7% 16% 25% 17% 3	23564

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	43% 10% 3 5% 4 3 5% 4 4 5% 14%	2219
	11th to 20th	Day	29% 15% 4 8% 5% 4 3 2 5% 6% 19%	2199
	21st to end	Day	54% 10% 2 6% 3 3 3 3 3 4 9%	2720
February	1st to 10th	Day	33% 12% 4 7% 6% 4 5% 3 5% 5% 17%	1710
	11th to 20th	Day	27% 11% 2 8% 5% 5% 4 3 5% 7% 23%	1665
	21st to end	Day	24% 11% 3 8% 5% 6% 5% 4 4 6% 23%	1413
March	1st to 10th	Day	25% 15% 4 9% 5% 5% 5% 4 5% 5% 17%	3279
	11th to 20th	Day	22% 10% 3 8% 4 4 4 3 5% 6% 33%	3490
	21st to end	Day	25% 13% 4 8% 5% 4 3 3 4 5% 25%	3881
April	1st to 10th	Day	25% 11% 4 8% 5% 4 5% 4 7% 6% 23%	2280
	11th to 20th	Day	22% 10% 3 7% 5% 4 4 4 5% 6% 29%	2387
	21st to end	Day	23% 11% 3 6% 5% 4 4 3 5% 6% 31%	2500
May	1st to 10th	Day	14% 8% 3 6% 4 4 4 3 4 5% 45%	4420
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 5% 7% 12% 39%	4377
	21st to end	Day	26% 8% 2 6% 4 4 4 4 6% 7% 29%	5022
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	23% 9% 3 5% 3 4 4 4 7% 7% 32%	1900
	11th to 20th	Day	32% 8% 3 7% 4 4 4 4 5% 6% 24%	1900
	21st to end	Day	32% 8% 3 6% 5% 3 3 3 6% 7% 24%	1918
November	1st to 10th	Day	39% 9% 3 6% 3 3 5% 4 4 5% 18%	1496
	11th to 20th	Day	36% 12% 2 6% 3 4 3 3 5% 4 22%	1520
	21st to end	Day	37% 11% 3 8% 4 3 3 3 3 5% 20%	1520
December	1st to 10th	Day	29% 16% 3 5% 5% 5% 4 3 4 5% 21%	1430
	11th to 20th	Day	38% 14% 4 8% 4 4 4 2 3 4 14%	1685
	21st to end	Day	43% 14% 3 8% 4 3 3 2 3 4 12%	2442
January	1st to 10th	Night	39% 13% 3 9% 4 4 3 2 3 4 15%	4726
	11th to 20th	Night	31% 10% 3 8% 4 4 3 3 6% 7% 20%	4699
	21st to end	Night	52% 12% 3 5% 3 3 2 2 3 4 11%	4936
February	1st to 10th	Night	33% 12% 3 7% 4 4 4 4 4 5% 19%	2470
	11th to 20th	Night	25% 12% 3 8% 5% 4 3 3 4 5% 28%	2402
	21st to end	Night	28% 13% 3 7% 4 3 4 3 5% 5% 26%	2041
March	1st to 10th	Night	29% 15% 3 7% 4 3 3 3 4 6% 22%	3581
	11th to 20th	Night	23% 10% 3 6% 4 3 3 3 4 5% 35%	3489
	21st to end	Night	30% 13% 4 8% 5% 4 4 2 3 5% 22%	3772
April	1st to 10th	Night	25% 10% 3 8% 5% 4 6% 4 5% 7% 23%	1900
	11th to 20th	Night	19% 11% 4 8% 5% 5% 4 3 5% 7% 29%	1740
	21st to end	Night	23% 11% 2 7% 4 4 4 4 5% 7% 29%	1678
May	1st to 10th	Night	16% 8% 2 5% 4 4 3 2 4 5% 46%	2540
	11th to 20th	Night	13% 5% 2 4 3 3 4 4 7% 12% 44%	2516
	21st to end	Night	21% 11% 4 10% 6% 5% 4 3 4 6% 27%	2549
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	21% 8% 2 5% 4 4 4 2 5% 6% 39%	2280
	11th to 20th	Night	30% 8% 2 6% 4 3 4 3 4 5% 31%	2280
	21st to end	Night	33% 7% 2 6% 4 3 4 2 4 5% 29%	2679
November	1st to 10th	Night	38% 10% 3 7% 4 3 3 3 4 5% 18%	2616
	11th to 20th	Night	35% 10% 3 6% 5% 3 4 2 4 4 23%	2660
	21st to end	Night	36% 11% 3 6% 4 3 4 2 4 5% 21%	2660
December	1st to 10th	Night	30% 12% 4 6% 5% 5% 4 3 4 4 23%	2745
	11th to 20th	Night	42% 15% 3 7% 4 2 3 3 3 4 13%	3520
	21st to end	Night	43% 14% 3 7% 4 3 3 2 3 3 15%	5214

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% 10% 9% 7% 4 1	2219
	11th to 20th	Day	62% 10% 11% 7% 8% 1	2220
	21st to end	Day	82% 5% 7% 5% 1	2720
February	1st to 10th	Day	70% 9% 8% 8% 3 2	1710
	11th to 20th	Day	62% 8% 11% 12% 5% 1	1674
	21st to end	Day	64% 10% 10% 10% 4 2	1413
March	1st to 10th	Day	63% 13% 12% 7% 4	3279
	11th to 20th	Day	53% 9% 10% 22% 5% 1	3490
	21st to end	Day	61% 11% 15% 10% 3	3881
April	1st to 10th	Day	64% 11% 11% 10% 4	2280
	11th to 20th	Day	57% 10% 10% 13% 8% 2	2387
	21st to end	Day	59% 9% 10% 14% 8% 1	2500
May	1st to 10th	Day	43% 9% 15% 21% 11%	4420
	11th to 20th	Day	38% 19% 17% 21% 5%	4380
	21st to end	Day	55% 16% 13% 14% 3	5023
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	50% 10% 16% 14% 9%	1900
	11th to 20th	Day	61% 9% 13% 12% 4 1	1900
	21st to end	Day	61% 8% 13% 11% 6% 1	1918
November	1st to 10th	Day	69% 8% 9% 7% 5% 1	1496
	11th to 20th	Day	67% 8% 9% 8% 6% 2	1520
	21st to end	Day	67% 6% 8% 11% 7% 1	1520
December	1st to 10th	Day	65% 7% 9% 11% 6% 1	1430
	11th to 20th	Day	74% 9% 8% 6% 2 1	1688
	21st to end	Day	76% 7% 7% 6% 2 1	2442
January	1st to 10th	Night	73% 6% 7% 10% 3 1	4726
	11th to 20th	Night	60% 8% 14% 10% 7% 1	4740
	21st to end	Night	80% 6% 5% 7% 2 1	4936
February	1st to 10th	Night	67% 7% 9% 10% 5% 2	2470
	11th to 20th	Night	62% 8% 11% 12% 7% 1	2404
	21st to end	Night	61% 7% 11% 13% 7% 2	2041
March	1st to 10th	Night	61% 10% 11% 12% 7%	3581
	11th to 20th	Night	50% 10% 12% 21% 7%	3490
	21st to end	Night	65% 10% 11% 11% 3	3772
April	1st to 10th	Night	60% 10% 12% 15% 3	1900
	11th to 20th	Night	54% 9% 9% 17% 9% 2	1740
	21st to end	Night	55% 9% 12% 15% 9%	1678
May	1st to 10th	Night	41% 6% 16% 25% 11%	2540
	11th to 20th	Night	33% 11% 23% 26% 7% 1	2516
	21st to end	Night	57% 9% 16% 14% 3	2549
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	46% 8% 15% 19% 12% 1	2280
	11th to 20th	Night	57% 6% 13% 17% 6%	2280
	21st to end	Night	60% 6% 11% 15% 8%	2679
November	1st to 10th	Night	70% 7% 10% 8% 5% 1	2616
	11th to 20th	Night	66% 8% 10% 10% 5% 2	2660
	21st to end	Night	66% 7% 9% 9% 7% 1	2660
December	1st to 10th	Night	66% 6% 9% 12% 6% 1	2745
	11th to 20th	Night	77% 6% 7% 5% 4	3516
	21st to end	Night	75% 6% 6% 9% 3 1	5214

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% 16% 8% 4	180
	11th to 20th	Day	41% 17% 16% 15% 11% 1	180
	21st to end	Day	49% 9% 20% 13% 8% 1	245
February	1st to 10th	Day	40% 10% 25% 17% 9% 1	370
	11th to 20th	Day	36% 10% 25% 20% 9% 1	365
	21st to end	Day	30% 15% 29% 16% 10% 1	307
March	1st to 10th	Day	33% 12% 24% 20% 9% 2	454
	11th to 20th	Day	31% 13% 19% 22% 14% 1	460
	21st to end	Day	34% 11% 25% 20% 8% 1	506
April	1st to 10th	Day	34% 12% 23% 20% 10% 1	460
	11th to 20th	Day	28% 11% 26% 20% 14%	452
	21st to end	Day	27% 11% 26% 22% 13% 1	460
May	1st to 10th	Day	19% 8% 22% 32% 19% 1	463
	11th to 20th	Day	18% 5% 22% 30% 22% 3	488
	21st to end	Day	19% 8% 24% 30% 17% 3	647
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	41% 12% 23% 17% 8%	182
	11th to 20th	Day	42% 10% 12% 19% 12% 6%	180
	21st to end	Day	48% 9% 18% 11% 8% 6%	180
December	1st to 10th	Day	43% 7% 23% 12% 9% 5%	180
	11th to 20th	Day	44% 9% 19% 21% 7% 1	180
	21st to end	Day	43% 9% 30% 14% 4	198
January	1st to 10th	Night	49% 9% 18% 14% 9% 1	850
	11th to 20th	Night	43% 8% 16% 21% 12%	850
	21st to end	Night	43% 7% 19% 20% 10%	875
February	1st to 10th	Night	39% 7% 23% 21% 10%	760
	11th to 20th	Night	34% 8% 21% 28% 9% 1	744
	21st to end	Night	36% 11% 19% 21% 11% 2	628
March	1st to 10th	Night	35% 10% 21% 21% 12% 2	760
	11th to 20th	Night	40% 7% 16% 24% 12% 1	760
	21st to end	Night	36% 8% 18% 21% 14% 2	836
April	1st to 10th	Night	32% 8% 16% 27% 13% 4	760
	11th to 20th	Night	26% 9% 22% 27% 15% 1	612
	21st to end	Night	29% 6% 20% 29% 14% 2	538
May	1st to 10th	Night	18% 5% 18% 33% 23% 4	380
	11th to 20th	Night	20% 5% 10% 30% 30% 6%	374
	21st to end	Night	21% 4 15% 30% 26% 5%	411
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	39% 8% 19% 24% 8% 2	836
November	1st to 10th	Night	44% 8% 19% 24% 5%	748
	11th to 20th	Night	41% 8% 21% 20% 9% 1	760
	21st to end	Night	44% 6% 21% 21% 7% 1	760
December	1st to 10th	Night	37% 8% 18% 26% 11% 1	800
	11th to 20th	Night	49% 8% 20% 19% 4	850
	21st to end	Night	46% 12% 22% 16% 4	935

Page generated at 2024-10-30 10:19:21. Version ac07

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