Maiden Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maiden Rock clear sky chart from 2005-11-06 to 2026-07-16.

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% 8% 3 8% 5% 4 4 4 5% 7% 38%	138720
	Night	12% 9% 4 9% 5% 4 4 4 5% 6% 37%	134300
Transparency	Day	29% 36% 8% 18% 9% 1	142259
	Night	31% 36% 7% 16% 9% 1	138839
Seeing	Day	17% 11% 30% 25% 12% 3	18353
	Night	17% 10% 31% 31% 11% 1	28207

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% 13% 7% 19% 8% 6% 4 3 4 5% 22%	4691
	11th to 20th	Day	5% 13% 7% 13% 7% 5% 8% 9% 7% 4 22%	4710
	21st to end	Day	7% 12% 6% 9% 5% 4 6% 5% 6% 6% 34%	5734
February	1st to 10th	Day	8% 12% 5% 10% 7% 5% 5% 5% 5% 8% 30%	1890
	11th to 20th	Day	9% 11% 5% 10% 4 4 4 3 5% 7% 36%	1844
	21st to end	Day	11% 11% 4 9% 7% 4 4 3 5% 8% 34%	1674
March	1st to 10th	Day	14% 7% 3 4 3 3 3 3 4 7% 48%	4811
	11th to 20th	Day	11% 9% 3 8% 4 4 4 4 6% 8% 41%	5090
	21st to end	Day	24% 10% 4 9% 5% 4 4 4 5% 5% 27%	5739
April	1st to 10th	Day	18% 11% 4 7% 5% 3 4 3 5% 6% 34%	2520
	11th to 20th	Day	20% 12% 4 7% 5% 4 4 3 4 6% 31%	2494
	21st to end	Day	19% 12% 3 7% 6% 4 4 4 5% 6% 30%	2665
May	1st to 10th	Day	11% 5% 2 5% 5% 4 5% 4 5% 7% 48%	8069
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 5% 7% 45%	8222
	21st to end	Day	16% 7% 2 7% 5% 4 4 3 5% 7% 39%	9047
June	1st to 10th	Day	12% 5% 2 5% 4 5% 4 4 6% 9% 45%	2940
	11th to 20th	Day	14% 7% 2 7% 5% 4 6% 4 5% 8% 37%	2940
	21st to end	Day	11% 7% 2 6% 5% 5% 5% 5% 7% 8% 39%	2940
July	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 7% 10% 44%	6500
	11th to 20th	Day	8% 4 2 4 3 4 4 4 5% 8% 56%	6431
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 7% 9% 44%	6924
August	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 7% 8% 42%	4251
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 3 6% 8% 43%	4171
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 45%	4383
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 5% 7% 48%	2400
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 3 5% 9% 44%	2400
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 8% 43%	2099
October	1st to 10th	Day	15% 6% 2 5% 3 4 5% 4 5% 6% 45%	2000
	11th to 20th	Day	14% 11% 3 7% 4 3 4 4 5% 6% 38%	2000
	21st to end	Day	18% 13% 4 7% 3 3 3 3 4 7% 36%	2134
November	1st to 10th	Day	12% 10% 3 9% 5% 4 5% 4 5% 7% 36%	1799
	11th to 20th	Day	14% 14% 6% 8% 6% 4 5% 3 6% 6% 29%	1680
	21st to end	Day	13% 13% 4 8% 6% 4 3 3 5% 8% 33%	1680
December	1st to 10th	Day	8% 9% 5% 15% 11% 7% 6% 4 5% 6% 25%	2690
	11th to 20th	Day	12% 16% 5% 10% 7% 5% 5% 3 6% 7% 25%	3088
	21st to end	Day	20% 19% 7% 18% 6% 4 3 2 3 3 14%	4070
January	1st to 10th	Night	9% 13% 6% 15% 7% 4 4 3 4 6% 28%	8232
	11th to 20th	Night	6% 12% 5% 14% 8% 7% 9% 8% 6% 4 19%	8280
	21st to end	Night	7% 13% 4 10% 5% 5% 5% 4 6% 7% 34%	8462
February	1st to 10th	Night	7% 13% 5% 10% 7% 6% 5% 4 5% 6% 32%	2730
	11th to 20th	Night	8% 9% 4 9% 6% 5% 5% 4 5% 7% 39%	2663
	21st to end	Night	12% 9% 4 8% 6% 5% 5% 3 5% 6% 37%	2130
March	1st to 10th	Night	11% 6% 3 6% 4 4 4 3 5% 7% 46%	5305
	11th to 20th	Night	10% 8% 2 7% 5% 5% 5% 4 6% 10% 38%	5090
	21st to end	Night	26% 11% 4 10% 4 3 3 2 4 6% 28%	5430
April	1st to 10th	Night	16% 11% 3 7% 4 4 4 4 5% 7% 36%	2100
	11th to 20th	Night	21% 10% 3 6% 4 4 4 3 5% 5% 36%	2075
	21st to end	Night	20% 8% 3 7% 4 4 4 3 5% 6% 38%	1952
May	1st to 10th	Night	11% 7% 2 6% 4 3 4 3 5% 7% 47%	4814
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 5% 7% 48%	4670
	21st to end	Night	14% 8% 4 8% 6% 4 4 3 6% 6% 37%	5139
June	1st to 10th	Night	11% 4 1 6% 5% 5% 4 5% 6% 7% 46%	1680
	11th to 20th	Night	12% 7% 2 6% 4 5% 4 3 5% 7% 44%	1680
	21st to end	Night	8% 5% 2 5% 4 5% 5% 4 6% 7% 49%	1680
July	1st to 10th	Night	9% 4 1 5% 3 5% 4 4 6% 10% 49%	3698
	11th to 20th	Night	7% 4 1 4 3 3 4 3 6% 9% 55%	3657
	21st to end	Night	9% 4 2 5% 3 3 4 4 6% 9% 50%	3947
August	1st to 10th	Night	12% 5% 2 6% 4 4 5% 3 5% 7% 47%	2893
	11th to 20th	Night	13% 5% 2 6% 3 3 4 3 5% 6% 52%	2888
	21st to end	Night	11% 6% 3 6% 4 3 4 4 4 7% 48%	3517
September	1st to 10th	Night	10% 6% 1 5% 4 3 3 3 4 6% 54%	2000
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 6% 7% 51%	2000
	21st to end	Night	13% 5% 2 6% 4 3 3 3 5% 6% 51%	2277
October	1st to 10th	Night	13% 6% 2 5% 3 4 4 3 5% 6% 50%	2400
	11th to 20th	Night	16% 8% 2 6% 4 4 4 3 4 5% 43%	2400
	21st to end	Night	18% 10% 3 6% 4 4 4 3 5% 6% 38%	2705
November	1st to 10th	Night	13% 9% 4 7% 4 4 4 3 4 7% 42%	2717
	11th to 20th	Night	13% 11% 4 9% 6% 5% 4 4 5% 6% 33%	2940
	21st to end	Night	15% 10% 3 10% 6% 3 5% 3 4 6% 35%	2940
December	1st to 10th	Night	7% 9% 4 13% 8% 7% 5% 4 6% 7% 28%	4720
	11th to 20th	Night	11% 17% 6% 13% 7% 5% 5% 4 4 6% 23%	5339
	21st to end	Night	23% 15% 7% 15% 6% 4 3 2 3 4 17%	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	55% 21% 8% 11% 5%	4692
	11th to 20th	Day	48% 22% 5% 14% 10%	4710
	21st to end	Day	37% 24% 10% 21% 9%	5734
February	1st to 10th	Day	22% 60% 5% 7% 5% 1	1890
	11th to 20th	Day	20% 57% 4 13% 4	1853
	21st to end	Day	18% 58% 6% 12% 5%	1674
March	1st to 10th	Day	23% 29% 13% 21% 12% 3	4811
	11th to 20th	Day	29% 28% 11% 22% 9% 1	5090
	21st to end	Day	44% 29% 6% 11% 8% 1	5741
April	1st to 10th	Day	24% 59% 4 8% 5%	2520
	11th to 20th	Day	24% 59% 4 9% 4 1	2494
	21st to end	Day	22% 59% 4 10% 5%	2665
May	1st to 10th	Day	25% 24% 7% 27% 17% 1	8108
	11th to 20th	Day	31% 23% 6% 22% 16% 3	8226
	21st to end	Day	36% 23% 7% 23% 10% 2	9061
June	1st to 10th	Day	12% 60% 5% 14% 7% 1	2940
	11th to 20th	Day	22% 61% 6% 8% 4	2940
	21st to end	Day	19% 59% 6% 11% 4	2940
July	1st to 10th	Day	27% 28% 13% 27% 6%	6431
	11th to 20th	Day	20% 27% 11% 29% 12%	6356
	21st to end	Day	27% 28% 10% 22% 12%	6728
August	1st to 10th	Day	26% 38% 8% 18% 11%	4236
	11th to 20th	Day	25% 38% 8% 22% 6%	4210
	21st to end	Day	26% 39% 9% 20% 6%	4382
September	1st to 10th	Day	16% 59% 6% 14% 4	2400
	11th to 20th	Day	15% 59% 9% 13% 4	2400
	21st to end	Day	18% 57% 4 15% 6%	2099
October	1st to 10th	Day	15% 35% 3 27% 19%	3260
	11th to 20th	Day	21% 37% 6% 19% 16% 1	3240
	21st to end	Day	27% 36% 9% 21% 7%	3424
November	1st to 10th	Day	25% 54% 6% 9% 7%	1799
	11th to 20th	Day	25% 54% 5% 11% 4 1	1680
	21st to end	Day	27% 55% 6% 9% 4	1680
December	1st to 10th	Day	40% 37% 9% 10% 4	2690
	11th to 20th	Day	39% 32% 9% 14% 5%	3085
	21st to end	Day	60% 26% 4 6% 3	4070
January	1st to 10th	Night	48% 21% 11% 14% 6%	8233
	11th to 20th	Night	52% 22% 5% 10% 10%	8280
	21st to end	Night	36% 24% 8% 21% 11%	8462
February	1st to 10th	Night	23% 59% 5% 7% 5% 1	2730
	11th to 20th	Night	22% 57% 4 12% 5%	2664
	21st to end	Night	17% 59% 6% 11% 6% 1	2130
March	1st to 10th	Night	26% 29% 10% 19% 13% 4	5305
	11th to 20th	Night	29% 30% 11% 17% 12% 1	5090
	21st to end	Night	45% 28% 7% 11% 8%	5430
April	1st to 10th	Night	21% 59% 4 10% 6%	2100
	11th to 20th	Night	20% 60% 5% 8% 7%	2075
	21st to end	Night	19% 59% 4 9% 8% 1	1952
May	1st to 10th	Night	26% 25% 6% 25% 18% 1	4839
	11th to 20th	Night	29% 23% 7% 19% 18% 4	4671
	21st to end	Night	38% 24% 6% 22% 9% 1	5149
June	1st to 10th	Night	13% 60% 6% 12% 8% 1	1680
	11th to 20th	Night	18% 61% 5% 9% 6% 1	1680
	21st to end	Night	15% 60% 7% 13% 6%	1680
July	1st to 10th	Night	23% 29% 16% 23% 8% 1	3660
	11th to 20th	Night	20% 28% 12% 28% 11% 1	3612
	21st to end	Night	25% 28% 11% 21% 14% 1	3832
August	1st to 10th	Night	27% 37% 7% 18% 8% 1	2884
	11th to 20th	Night	23% 38% 9% 21% 9% 1	2915
	21st to end	Night	26% 38% 11% 18% 6%	3517
September	1st to 10th	Night	16% 58% 5% 16% 5%	2000
	11th to 20th	Night	14% 59% 8% 15% 5% 1	2000
	21st to end	Night	16% 57% 5% 13% 8% 1	2277
October	1st to 10th	Night	15% 35% 2 25% 21% 3	3920
	11th to 20th	Night	17% 36% 7% 19% 19% 2	3899
	21st to end	Night	30% 36% 6% 18% 10%	4365
November	1st to 10th	Night	23% 53% 6% 12% 6%	2717
	11th to 20th	Night	24% 54% 5% 11% 6% 1	2940
	21st to end	Night	27% 54% 5% 11% 3	2940
December	1st to 10th	Night	36% 37% 12% 13% 2	4720
	11th to 20th	Night	45% 32% 7% 12% 4 1	5341
	21st to end	Night	57% 26% 5% 8% 4	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	16% 13% 34% 26% 9% 2	330
	11th to 20th	Day	17% 18% 39% 21% 4 1	330
	21st to end	Day	18% 15% 34% 23% 9% 1	363
February	1st to 10th	Day	17% 18% 43% 16% 4 2	330
	11th to 20th	Day	16% 22% 40% 16% 6%	330
	21st to end	Day	20% 17% 40% 22% 1	273
March	1st to 10th	Day	18% 17% 42% 18% 6%	330
	11th to 20th	Day	23% 15% 37% 18% 5% 2	330
	21st to end	Day	26% 15% 32% 19% 7% 2	429
April	1st to 10th	Day	26% 14% 34% 20% 5% 1	540
	11th to 20th	Day	30% 16% 24% 21% 7% 1	532
	21st to end	Day	26% 14% 29% 21% 8% 1	685
May	1st to 10th	Day	19% 13% 32% 25% 9% 2	753
	11th to 20th	Day	20% 14% 26% 23% 13% 3	775
	21st to end	Day	19% 10% 27% 27% 14% 3	844
June	1st to 10th	Day	13% 9% 25% 32% 18% 3	780
	11th to 20th	Day	17% 10% 34% 26% 10% 2	780
	21st to end	Day	14% 8% 32% 26% 16% 4	780
July	1st to 10th	Day	10% 5% 20% 30% 25% 10%	771
	11th to 20th	Day	9% 5% 26% 32% 19% 9%	744
	21st to end	Day	7% 3 27% 37% 18% 7%	794
August	1st to 10th	Day	12% 5% 23% 33% 21% 7%	726
	11th to 20th	Day	16% 3 20% 32% 22% 6%	715
	21st to end	Day	11% 6% 25% 32% 20% 6%	628
September	1st to 10th	Day	13% 8% 26% 31% 16% 6%	530
	11th to 20th	Day	12% 6% 29% 31% 18% 4	530
	21st to end	Day	17% 13% 27% 24% 15% 5%	365
October	1st to 10th	Day	16% 14% 31% 23% 14% 3	330
	11th to 20th	Day	25% 15% 35% 18% 6% 1	330
	21st to end	Day	26% 16% 34% 16% 6% 2	363
November	1st to 10th	Day	21% 15% 35% 20% 8% 1	330
	11th to 20th	Day	21% 21% 37% 16% 5%	330
	21st to end	Day	23% 15% 38% 19% 5%	330
December	1st to 10th	Day	17% 13% 41% 24% 4 1	330
	11th to 20th	Day	22% 18% 37% 18% 5% 1	330
	21st to end	Day	26% 17% 37% 17% 3	363
January	1st to 10th	Night	14% 14% 36% 27% 8% 1	1050
	11th to 20th	Night	17% 14% 36% 27% 6% 1	1050
	21st to end	Night	19% 12% 35% 28% 6% 1	1155
February	1st to 10th	Night	14% 13% 39% 28% 6% 1	1050
	11th to 20th	Night	13% 13% 41% 25% 7%	1029
	21st to end	Night	18% 15% 34% 27% 6%	746
March	1st to 10th	Night	17% 12% 36% 27% 7% 1	756
	11th to 20th	Night	20% 11% 34% 29% 6%	630
	21st to end	Night	22% 9% 33% 27% 8% 1	693
April	1st to 10th	Night	21% 15% 32% 26% 5%	630
	11th to 20th	Night	27% 10% 30% 27% 7%	623
	21st to end	Night	25% 9% 28% 29% 8% 1	630
May	1st to 10th	Night	20% 9% 31% 32% 7% 1	630
	11th to 20th	Night	19% 8% 29% 32% 11% 1	621
	21st to end	Night	17% 7% 24% 39% 13% 1	683
June	1st to 10th	Night	13% 5% 26% 42% 14%	630
	11th to 20th	Night	13% 5% 31% 41% 9%	630
	21st to end	Night	11% 5% 23% 45% 16% 1	630
July	1st to 10th	Night	6% 2 20% 40% 29% 2	615
	11th to 20th	Night	6% 4 21% 46% 21% 3	597
	21st to end	Night	8% 2 19% 47% 21% 2	657
August	1st to 10th	Night	7% 4 15% 48% 24% 2	597
	11th to 20th	Night	12% 3 17% 38% 26% 4	594
	21st to end	Night	10% 3 22% 37% 26% 2	660
September	1st to 10th	Night	12% 5% 23% 37% 19% 4	600
	11th to 20th	Night	11% 4 28% 35% 20% 3	600
	21st to end	Night	15% 8% 26% 32% 18% 1	715
October	1st to 10th	Night	15% 9% 28% 32% 14% 2	800
	11th to 20th	Night	19% 13% 31% 30% 7% 1	800
	21st to end	Night	23% 10% 28% 32% 7% 1	880
November	1st to 10th	Night	17% 11% 34% 29% 8% 1	871
	11th to 20th	Night	19% 14% 35% 25% 7%	1050
	21st to end	Night	21% 14% 34% 25% 6%	1050
December	1st to 10th	Night	18% 10% 37% 27% 7% 1	1050
	11th to 20th	Night	21% 12% 34% 26% 6% 1	1050
	21st to end	Night	27% 11% 31% 25% 5%	1155

Page generated at 2026-07-13 02:14:48. Version ac07

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