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 2024-03-08.

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	24% 8% 3 6% 5% 3 4 4 5% 6% 32%	78043
	Night	29% 9% 3 6% 5% 3 4 4 4 6% 28%	81477
Transparency	Day	54% 10% 13% 15% 7% 1	77750
	Night	58% 8% 12% 14% 7% 1	81350
Seeing	Day	25% 8% 21% 26% 17% 3	14510
	Night	32% 6% 16% 24% 18% 3	22846

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% 5% 2 4 5% 4 5% 14%	2219
	11th to 20th	Day	29% 14% 4 8% 5% 3 4 3 5% 6% 19%	2199
	21st to end	Day	54% 10% 2 5% 4 2 3 3 3 4 9%	2720
February	1st to 10th	Day	33% 11% 4 6% 6% 3 5% 4 5% 5% 17%	1710
	11th to 20th	Day	27% 10% 3 7% 6% 4 4 4 5% 7% 23%	1665
	21st to end	Day	24% 10% 3 7% 6% 5% 6% 5% 4 6% 23%	1413
March	1st to 10th	Day	27% 14% 4 6% 5% 3 5% 5% 4 5% 21%	1950
	11th to 20th	Day	31% 12% 4 9% 6% 2 4 3 4 5% 21%	1980
	21st to end	Day	27% 10% 4 8% 6% 3 3 4 4 5% 24%	2209
April	1st to 10th	Day	26% 10% 4 6% 6% 3 5% 4 6% 6% 23%	2160
	11th to 20th	Day	23% 9% 4 6% 6% 3 5% 5% 5% 6% 28%	2259
	21st to end	Day	22% 10% 4 6% 5% 3 4 4 5% 6% 31%	2368
May	1st to 10th	Day	15% 8% 3 7% 6% 3 4 5% 5% 8% 37%	2520
	11th to 20th	Day	16% 6% 3 6% 6% 3 5% 6% 6% 9% 34%	2477
	21st to end	Day	18% 8% 3 6% 6% 3 5% 5% 6% 6% 35%	2834
June	1st to 10th	Day	21% 7% 3 6% 5% 3 4 5% 5% 8% 32%	2700
	11th to 20th	Day	18% 7% 3 6% 6% 5% 6% 6% 7% 7% 31%	2700
	21st to end	Day	14% 6% 2 5% 5% 3 4 5% 6% 8% 42%	2700
July	1st to 10th	Day	10% 6% 2 6% 4 3 4 4 4 6% 51%	2700
	11th to 20th	Day	10% 5% 2 3 4 3 4 4 5% 8% 54%	2700
	21st to end	Day	7% 3 1 3 3 2 3 3 4 7% 63%	2848
August	1st to 10th	Day	10% 4 2 4 3 3 4 4 4 6% 57%	2461
	11th to 20th	Day	7% 5% 2 5% 3 2 3 4 5% 7% 56%	2298
	21st to end	Day	11% 6% 2 4 4 3 4 5% 6% 8% 48%	2548
September	1st to 10th	Day	12% 6% 2 4 4 3 4 4 5% 7% 48%	2160
	11th to 20th	Day	18% 7% 3 5% 4 3 3 4 4 7% 41%	2124
	21st to end	Day	24% 4 3 4 4 3 5% 4 5% 8% 36%	1918
October	1st to 10th	Day	23% 9% 3 4 4 2 4 4 6% 7% 33%	1800
	11th to 20th	Day	32% 8% 3 6% 5% 3 4 5% 4 7% 24%	1800
	21st to end	Day	33% 7% 3 5% 5% 2 3 4 6% 7% 24%	1818
November	1st to 10th	Day	39% 9% 3 5% 4 2 5% 5% 4 5% 18%	1488
	11th to 20th	Day	36% 11% 3 6% 4 3 3 3 5% 4 22%	1520
	21st to end	Day	38% 10% 3 7% 4 2 3 4 3 5% 21%	1520
December	1st to 10th	Day	29% 15% 4 5% 5% 4 4 4 4 5% 21%	1430
	11th to 20th	Day	38% 14% 5% 7% 5% 3 5% 3 3 4 14%	1685
	21st to end	Day	43% 14% 3 7% 4 2 3 3 3 4 12%	2442
January	1st to 10th	Night	39% 12% 3 8% 6% 3 3 3 3 4 15%	4726
	11th to 20th	Night	31% 10% 3 7% 5% 3 4 4 6% 7% 20%	4699
	21st to end	Night	52% 11% 3 5% 4 2 2 3 3 4 11%	4936
February	1st to 10th	Night	33% 11% 4 6% 5% 3 5% 4 4 5% 19%	2470
	11th to 20th	Night	25% 12% 4 7% 6% 3 3 3 4 5% 29%	2402
	21st to end	Night	30% 11% 3 6% 5% 2 4 4 4 5% 26%	2041
March	1st to 10th	Night	29% 12% 4 7% 5% 3 4 4 5% 6% 23%	2168
	11th to 20th	Night	32% 11% 4 6% 5% 3 4 3 4 5% 23%	1979
	21st to end	Night	29% 10% 4 7% 7% 3 4 4 4 6% 21%	2147
April	1st to 10th	Night	26% 10% 4 7% 5% 3 6% 5% 5% 7% 24%	1800
	11th to 20th	Night	20% 10% 4 7% 6% 4 4 4 5% 7% 28%	1648
	21st to end	Night	23% 10% 3 6% 5% 3 4 5% 4 8% 30%	1590
May	1st to 10th	Night	17% 6% 3 5% 5% 4 4 4 5% 7% 39%	1440
	11th to 20th	Night	17% 7% 4 5% 5% 3 6% 5% 7% 8% 33%	1416
	21st to end	Night	15% 8% 4 7% 6% 4 5% 4 5% 7% 35%	1437
June	1st to 10th	Night	21% 8% 4 7% 6% 3 5% 4 4 5% 33%	1260
	11th to 20th	Night	16% 10% 3 6% 6% 4 5% 4 6% 7% 31%	1260
	21st to end	Night	12% 5% 3 7% 3 3 5% 5% 5% 8% 43%	1260
July	1st to 10th	Night	10% 5% 2 4 5% 3 4 3 4 6% 52%	1260
	11th to 20th	Night	7% 4 2 5% 4 3 4 4 5% 7% 56%	1260
	21st to end	Night	6% 2 1 3 4 2 3 5% 4 5% 64%	1469
August	1st to 10th	Night	7% 3 2 4 3 2 3 4 4 7% 62%	1475
	11th to 20th	Night	6% 2 1 3 3 2 4 5% 5% 7% 61%	1602
	21st to end	Night	12% 4 2 4 5% 4 5% 4 5% 9% 46%	1808
September	1st to 10th	Night	9% 4 2 3 4 3 4 4 5% 6% 57%	1800
	11th to 20th	Night	19% 7% 2 4 4 3 4 5% 5% 6% 42%	1835
	21st to end	Night	21% 8% 2 5% 4 2 4 4 4 6% 41%	2042
October	1st to 10th	Night	20% 7% 2 5% 5% 3 4 3 5% 6% 40%	2160
	11th to 20th	Night	30% 8% 2 5% 4 3 4 4 4 5% 31%	2160
	21st to end	Night	33% 7% 2 5% 4 2 4 3 3 5% 29%	2538
November	1st to 10th	Night	38% 10% 3 6% 5% 2 4 3 4 5% 19%	2590
	11th to 20th	Night	35% 10% 3 6% 5% 2 4 3 4 4 24%	2660
	21st to end	Night	37% 10% 3 6% 5% 2 4 3 4 6% 22%	2660
December	1st to 10th	Night	31% 11% 4 6% 5% 3 5% 4 3 5% 23%	2745
	11th to 20th	Night	43% 14% 4 6% 5% 2 3 4 3 4 13%	3520
	21st to end	Night	44% 13% 4 6% 4 2 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	65% 10% 12% 9% 4	1950
	11th to 20th	Day	70% 7% 8% 11% 4 1	1980
	21st to end	Day	65% 9% 11% 11% 3	2209
April	1st to 10th	Day	64% 11% 11% 10% 4	2160
	11th to 20th	Day	59% 10% 10% 13% 7% 1	2259
	21st to end	Day	59% 9% 10% 13% 8% 1	2368
May	1st to 10th	Day	50% 11% 15% 17% 6% 1	2520
	11th to 20th	Day	51% 10% 14% 20% 5% 1	2480
	21st to end	Day	52% 11% 13% 19% 4	2835
June	1st to 10th	Day	54% 10% 16% 13% 4 2	2700
	11th to 20th	Day	55% 13% 15% 12% 5%	2700
	21st to end	Day	44% 10% 17% 18% 8% 2	2700
July	1st to 10th	Day	38% 10% 16% 23% 10% 3	2626
	11th to 20th	Day	30% 11% 19% 29% 10% 1	2619
	21st to end	Day	23% 9% 19% 32% 13% 4	2690
August	1st to 10th	Day	31% 11% 16% 28% 12% 2	2444
	11th to 20th	Day	28% 10% 20% 26% 14% 3	2298
	21st to end	Day	36% 12% 18% 27% 6% 1	2548
September	1st to 10th	Day	38% 9% 16% 23% 11% 3	2160
	11th to 20th	Day	46% 8% 12% 18% 13% 2	2124
	21st to end	Day	48% 12% 14% 15% 9% 1	1918
October	1st to 10th	Day	50% 10% 16% 15% 10%	1800
	11th to 20th	Day	60% 10% 13% 12% 4 1	1800
	21st to end	Day	61% 7% 13% 11% 7% 1	1818
November	1st to 10th	Day	69% 8% 9% 7% 5% 1	1488
	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	62% 9% 12% 12% 5%	2168
	11th to 20th	Night	66% 6% 9% 12% 6% 1	1980
	21st to end	Night	66% 10% 11% 11% 3	2147
April	1st to 10th	Night	60% 9% 12% 16% 3	1800
	11th to 20th	Night	56% 9% 9% 17% 8% 1	1648
	21st to end	Night	54% 9% 12% 16% 9%	1590
May	1st to 10th	Night	45% 9% 17% 22% 7%	1440
	11th to 20th	Night	47% 11% 18% 19% 5% 1	1416
	21st to end	Night	48% 9% 16% 20% 5%	1437
June	1st to 10th	Night	53% 7% 15% 17% 4 4	1260
	11th to 20th	Night	52% 9% 18% 15% 5%	1260
	21st to end	Night	40% 10% 18% 19% 9% 3	1260
July	1st to 10th	Night	35% 8% 16% 25% 13% 4	1225
	11th to 20th	Night	28% 8% 24% 28% 11% 2	1218
	21st to end	Night	21% 8% 16% 32% 19% 5%	1387
August	1st to 10th	Night	25% 7% 19% 28% 18% 3	1467
	11th to 20th	Night	21% 11% 23% 24% 16% 6%	1602
	21st to end	Night	35% 10% 17% 29% 9% 1	1808
September	1st to 10th	Night	29% 8% 17% 27% 15% 3	1800
	11th to 20th	Night	44% 8% 11% 16% 16% 5%	1835
	21st to end	Night	46% 8% 15% 20% 10% 2	2042
October	1st to 10th	Night	45% 8% 15% 20% 12% 1	2160
	11th to 20th	Night	57% 6% 13% 17% 7%	2160
	21st to end	Night	60% 6% 11% 15% 8%	2538
November	1st to 10th	Night	69% 7% 10% 8% 5% 1	2590
	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% 25% 19% 10% 2	443
	11th to 20th	Day	33% 13% 20% 21% 13% 1	420
	21st to end	Day	34% 10% 26% 20% 9% 1	462
April	1st to 10th	Day	35% 12% 23% 18% 10% 1	420
	11th to 20th	Day	30% 10% 24% 20% 15%	412
	21st to end	Day	26% 11% 26% 23% 13% 1	420
May	1st to 10th	Day	19% 8% 23% 32% 18%	423
	11th to 20th	Day	19% 4 20% 31% 22% 4	448
	21st to end	Day	17% 6% 24% 31% 18% 3	596
June	1st to 10th	Day	24% 7% 22% 27% 19% 1	630
	11th to 20th	Day	18% 8% 25% 30% 17% 2	630
	21st to end	Day	16% 4 21% 34% 22% 3	630
July	1st to 10th	Day	16% 4 17% 33% 27% 4	621
	11th to 20th	Day	9% 5% 19% 39% 25% 3	618
	21st to end	Day	7% 3 14% 34% 36% 7%	594
August	1st to 10th	Day	11% 4 16% 28% 33% 9%	447
	11th to 20th	Day	9% 3 14% 35% 32% 7%	437
	21st to end	Day	15% 4 18% 37% 22% 2	495
September	1st to 10th	Day	18% 6% 25% 32% 17% 2	450
	11th to 20th	Day	26% 7% 18% 26% 18% 5%	450
	21st to end	Day	26% 7% 23% 24% 16% 4	450
October	1st to 10th	Day	31% 6% 19% 22% 18% 4	450
	11th to 20th	Day	38% 7% 17% 19% 15% 5%	450
	21st to end	Day	38% 14% 18% 20% 7% 4	369
November	1st to 10th	Day	40% 12% 23% 17% 8%	180
	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	34% 9% 21% 22% 12% 2	750
	11th to 20th	Night	42% 7% 16% 23% 11% 1	720
	21st to end	Night	37% 8% 18% 21% 14% 2	792
April	1st to 10th	Night	33% 7% 16% 26% 13% 5%	720
	11th to 20th	Night	27% 9% 20% 27% 16% 2	580
	21st to end	Night	29% 5% 20% 29% 15% 2	510
May	1st to 10th	Night	18% 4 18% 32% 23% 4	360
	11th to 20th	Night	21% 5% 9% 29% 31% 6%	354
	21st to end	Night	20% 4 14% 30% 27% 5%	389
June	1st to 10th	Night	25% 5% 10% 31% 24% 4	360
	11th to 20th	Night	24% 4 11% 32% 23% 6%	360
	21st to end	Night	15% 3 9% 35% 32% 6%	360
July	1st to 10th	Night	13% 1 10% 23% 43% 10%	350
	11th to 20th	Night	9% 3 8% 31% 39% 10%	348
	21st to end	Night	7% 2 4 26% 48% 13%	394
August	1st to 10th	Night	11% 2 5% 22% 44% 16%	401
	11th to 20th	Night	8% 1 5% 27% 49% 10%	534
	21st to end	Night	15% 4 10% 29% 37% 5%	620
September	1st to 10th	Night	13% 2 11% 35% 31% 8%	720
	11th to 20th	Night	23% 5% 12% 21% 29% 10%	720
	21st to end	Night	29% 4 14% 27% 24% 3	720
October	1st to 10th	Night	25% 5% 15% 29% 23% 3	720
	11th to 20th	Night	36% 5% 13% 26% 17% 2	720
	21st to end	Night	40% 8% 18% 24% 8% 2	792
November	1st to 10th	Night	44% 8% 19% 24% 5%	740
	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 2024-03-05 04:23:58. Version ac07

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