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 2025-03-12.

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 4 4 5% 7% 37%	109079
	Night	12% 9% 4 9% 5% 4 4 4 5% 6% 37%	110133
Transparency	Day	27% 44% 7% 15% 7%	112661
	Night	28% 42% 6% 14% 8% 1	114691
Seeing	Day	17% 11% 30% 26% 13% 3	16388
	Night	17% 9% 31% 32% 11% 1	26466

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	7% 14% 7% 18% 7% 7% 4 3 4 5% 25%	3617
	11th to 20th	Day	6% 14% 7% 12% 7% 6% 8% 9% 8% 4 21%	3620
	21st to end	Day	8% 16% 7% 11% 5% 4 3 4 5% 5% 32%	4424
February	1st to 10th	Day	8% 12% 5% 9% 7% 5% 4 5% 5% 8% 31%	1800
	11th to 20th	Day	9% 11% 5% 10% 4 5% 5% 3 6% 7% 36%	1754
	21st to end	Day	12% 11% 4 9% 6% 4 4 3 6% 7% 33%	1596
March	1st to 10th	Day	13% 9% 3 6% 4 3 3 3 4 7% 46%	3381
	11th to 20th	Day	10% 10% 3 9% 4 4 4 3 5% 8% 40%	3491
	21st to end	Day	25% 12% 4 10% 5% 4 4 4 4 5% 24%	3925
April	1st to 10th	Day	18% 11% 4 7% 5% 4 4 3 5% 6% 34%	2280
	11th to 20th	Day	20% 11% 3 7% 5% 4 4 3 4 6% 32%	2254
	21st to end	Day	19% 12% 3 7% 6% 5% 4 4 5% 6% 29%	2411
May	1st to 10th	Day	18% 6% 3 6% 5% 4 5% 3 5% 7% 39%	4326
	11th to 20th	Day	13% 6% 3 6% 5% 4 4 4 5% 7% 43%	4399
	21st to end	Day	17% 7% 2 8% 5% 4 4 3 5% 7% 37%	4824
June	1st to 10th	Day	11% 5% 2 5% 4 5% 4 4 6% 9% 46%	2660
	11th to 20th	Day	13% 7% 2 6% 6% 4 5% 4 5% 8% 38%	2660
	21st to end	Day	10% 7% 2 6% 5% 5% 5% 5% 7% 8% 40%	2660
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 6% 4 7% 10% 37%	4440
	11th to 20th	Day	6% 3 1 3 3 4 4 4 5% 8% 58%	4440
	21st to end	Day	8% 4 2 6% 4 5% 5% 5% 7% 9% 45%	4813
August	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 7% 8% 42%	4120
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 3 6% 8% 44%	4041
	21st to end	Day	10% 5% 2 6% 4 5% 5% 4 6% 8% 44%	4249
September	1st to 10th	Day	12% 6% 2 5% 4 3 4 4 4 7% 49%	2280
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 3 5% 8% 45%	2280
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 8% 43%	1994
October	1st to 10th	Day	16% 6% 2 5% 4 4 5% 4 5% 6% 44%	1900
	11th to 20th	Day	14% 11% 3 7% 4 3 4 4 5% 6% 38%	1900
	21st to end	Day	18% 12% 4 7% 3 3 3 3 4 7% 36%	2028
November	1st to 10th	Day	13% 10% 3 8% 5% 4 5% 4 5% 7% 36%	1712
	11th to 20th	Day	14% 14% 6% 8% 6% 4 5% 3 6% 6% 28%	1600
	21st to end	Day	13% 13% 4 8% 6% 4 3 3 5% 8% 34%	1600
December	1st to 10th	Day	8% 9% 5% 15% 11% 7% 6% 4 5% 6% 25%	2610
	11th to 20th	Day	12% 16% 5% 10% 7% 5% 5% 3 6% 6% 25%	3008
	21st to end	Day	20% 19% 7% 18% 6% 4 3 2 3 3 14%	3982
January	1st to 10th	Night	7% 13% 6% 16% 8% 4 4 3 5% 6% 29%	6348
	11th to 20th	Night	8% 11% 5% 13% 8% 7% 9% 8% 7% 5% 20%	6360
	21st to end	Night	9% 16% 5% 10% 5% 4 4 3 6% 5% 32%	6536
February	1st to 10th	Night	7% 13% 5% 10% 7% 6% 5% 4 5% 6% 33%	2600
	11th to 20th	Night	7% 9% 5% 10% 6% 5% 5% 4 5% 7% 38%	2533
	21st to end	Night	13% 9% 4 7% 5% 5% 5% 3 5% 6% 37%	2032
March	1st to 10th	Night	10% 8% 3 7% 4 4 3 3 5% 7% 46%	3721
	11th to 20th	Night	9% 8% 2 9% 5% 5% 4 4 6% 8% 40%	3497
	21st to end	Night	26% 11% 3 11% 4 3 2 2 4 5% 28%	3704
April	1st to 10th	Night	16% 11% 3 7% 5% 3 4 3 5% 7% 36%	1900
	11th to 20th	Night	22% 10% 3 6% 4 4 4 3 5% 5% 35%	1875
	21st to end	Night	19% 8% 3 7% 4 4 4 3 5% 6% 38%	1766
May	1st to 10th	Night	16% 6% 3 7% 5% 4 5% 3 5% 6% 41%	2579
	11th to 20th	Night	15% 4 2 5% 3 3 3 3 4 7% 51%	2506
	21st to end	Night	12% 7% 3 7% 5% 4 4 3 6% 7% 41%	2743
June	1st to 10th	Night	11% 4 1 6% 5% 4 4 5% 6% 7% 47%	1520
	11th to 20th	Night	12% 6% 2 6% 4 5% 4 3 6% 7% 45%	1520
	21st to end	Night	8% 5% 2 4 3 5% 5% 4 6% 7% 50%	1520
July	1st to 10th	Night	11% 4 2 5% 3 4 4 4 6% 10% 48%	2530
	11th to 20th	Night	4 3 1 4 3 4 4 3 6% 9% 58%	2530
	21st to end	Night	5% 3 2 5% 3 3 4 4 5% 9% 56%	2750
August	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 3 5% 6% 47%	2804
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 5% 6% 52%	2798
	21st to end	Night	11% 6% 3 6% 4 3 4 3 4 7% 47%	3409
September	1st to 10th	Night	10% 6% 1 5% 4 3 3 3 5% 6% 54%	1900
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 5% 7% 52%	1900
	21st to end	Night	13% 5% 2 6% 4 3 3 3 5% 6% 50%	2163
October	1st to 10th	Night	13% 6% 2 5% 3 4 3 3 5% 6% 50%	2280
	11th to 20th	Night	15% 8% 2 6% 4 4 4 3 5% 6% 44%	2280
	21st to end	Night	18% 11% 3 6% 4 4 4 3 5% 6% 37%	2570
November	1st to 10th	Night	13% 9% 4 7% 4 4 4 3 4 7% 42%	2584
	11th to 20th	Night	13% 11% 4 9% 6% 5% 4 4 5% 6% 33%	2800
	21st to end	Night	15% 10% 3 9% 6% 4 5% 3 4 6% 36%	2800
December	1st to 10th	Night	7% 9% 4 13% 8% 7% 5% 4 6% 7% 29%	4580
	11th to 20th	Night	11% 17% 6% 13% 6% 5% 4 4 4 6% 23%	5199
	21st to end	Night	23% 15% 7% 15% 6% 4 3 2 3 4 17%	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	49% 26% 7% 14% 4	3618
	11th to 20th	Day	43% 28% 5% 13% 10%	3620
	21st to end	Day	38% 30% 11% 15% 7%	4424
February	1st to 10th	Day	20% 63% 5% 6% 6% 1	1800
	11th to 20th	Day	19% 60% 4 11% 5%	1763
	21st to end	Day	17% 61% 5% 11% 5%	1596
March	1st to 10th	Day	20% 40% 10% 17% 12% 1	3381
	11th to 20th	Day	25% 40% 5% 22% 8% 1	3491
	21st to end	Day	41% 41% 4 9% 4	3925
April	1st to 10th	Day	21% 65% 4 7% 3	2280
	11th to 20th	Day	20% 65% 3 8% 3 1	2254
	21st to end	Day	19% 65% 3 8% 4 1	2411
May	1st to 10th	Day	23% 41% 7% 18% 10% 1	4366
	11th to 20th	Day	22% 42% 7% 19% 9% 1	4403
	21st to end	Day	30% 40% 6% 16% 7%	4837
June	1st to 10th	Day	9% 66% 5% 12% 6% 1	2660
	11th to 20th	Day	18% 66% 5% 6% 4	2660
	21st to end	Day	16% 64% 6% 10% 4	2660
July	1st to 10th	Day	29% 39% 13% 14% 5% 1	4371
	11th to 20th	Day	14% 38% 11% 25% 13%	4365
	21st to end	Day	22% 39% 8% 18% 12% 1	4662
August	1st to 10th	Day	25% 39% 7% 18% 11%	4105
	11th to 20th	Day	24% 39% 8% 22% 6%	4080
	21st to end	Day	26% 40% 9% 19% 6%	4248
September	1st to 10th	Day	15% 61% 5% 13% 5%	2280
	11th to 20th	Day	14% 62% 7% 13% 4	2280
	21st to end	Day	18% 60% 4 13% 5%	1994
October	1st to 10th	Day	15% 37% 3 26% 19%	3160
	11th to 20th	Day	20% 38% 6% 19% 16% 1	3140
	21st to end	Day	26% 37% 10% 21% 6%	3318
November	1st to 10th	Day	24% 56% 5% 8% 6%	1712
	11th to 20th	Day	24% 57% 5% 10% 4 1	1600
	21st to end	Day	26% 57% 6% 8% 3	1600
December	1st to 10th	Day	39% 38% 9% 10% 4	2610
	11th to 20th	Day	39% 33% 8% 14% 5%	3005
	21st to end	Day	60% 27% 4 6% 3	3982
January	1st to 10th	Night	44% 26% 7% 16% 7%	6348
	11th to 20th	Night	47% 28% 5% 9% 10%	6360
	21st to end	Night	36% 29% 8% 19% 7%	6536
February	1st to 10th	Night	22% 61% 5% 6% 5% 1	2600
	11th to 20th	Night	21% 60% 4 11% 4	2534
	21st to end	Night	16% 62% 6% 9% 6% 1	2032
March	1st to 10th	Night	20% 40% 7% 18% 13% 2	3721
	11th to 20th	Night	24% 41% 6% 16% 12% 1	3497
	21st to end	Night	40% 40% 4 12% 4	3704
April	1st to 10th	Night	18% 65% 4 9% 4	1900
	11th to 20th	Night	17% 66% 4 6% 6% 1	1875
	21st to end	Night	15% 65% 4 8% 7% 1	1766
May	1st to 10th	Night	24% 42% 6% 11% 15% 1	2604
	11th to 20th	Night	19% 40% 5% 21% 12% 3	2507
	21st to end	Night	25% 42% 6% 18% 10%	2751
June	1st to 10th	Night	10% 66% 5% 11% 8% 1	1520
	11th to 20th	Night	15% 67% 5% 8% 5% 1	1520
	21st to end	Night	12% 65% 5% 12% 5%	1520
July	1st to 10th	Night	23% 38% 16% 15% 6% 1	2490
	11th to 20th	Night	14% 38% 11% 25% 13%	2482
	21st to end	Night	16% 38% 10% 21% 15% 1	2662
August	1st to 10th	Night	27% 38% 7% 18% 8% 1	2795
	11th to 20th	Night	23% 39% 9% 20% 9% 1	2825
	21st to end	Night	26% 40% 11% 17% 6%	3409
September	1st to 10th	Night	14% 61% 5% 14% 5%	1900
	11th to 20th	Night	12% 61% 7% 15% 5% 1	1900
	21st to end	Night	16% 60% 5% 11% 7% 1	2163
October	1st to 10th	Night	14% 36% 2 24% 21% 3	3800
	11th to 20th	Night	16% 37% 7% 19% 19% 2	3779
	21st to end	Night	30% 37% 6% 18% 9%	4230
November	1st to 10th	Night	23% 56% 5% 10% 5%	2584
	11th to 20th	Night	23% 57% 5% 9% 6%	2800
	21st to end	Night	25% 57% 5% 10% 3	2800
December	1st to 10th	Night	34% 38% 12% 13% 2	4580
	11th to 20th	Night	45% 32% 6% 12% 4 1	5201
	21st to end	Night	57% 27% 4 8% 4	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	15% 14% 32% 27% 10% 2	300
	11th to 20th	Day	18% 18% 37% 22% 5% 1	300
	21st to end	Day	19% 14% 34% 23% 9% 1	330
February	1st to 10th	Day	17% 18% 43% 17% 4 1	300
	11th to 20th	Day	16% 23% 38% 17% 6%	300
	21st to end	Day	20% 16% 41% 22%	249
March	1st to 10th	Day	18% 17% 41% 18% 6%	300
	11th to 20th	Day	21% 14% 37% 21% 5% 2	273
	21st to end	Day	26% 13% 31% 20% 8% 2	357
April	1st to 10th	Day	27% 12% 34% 20% 5% 1	460
	11th to 20th	Day	30% 15% 24% 22% 8% 1	452
	21st to end	Day	26% 14% 27% 22% 9% 2	591
May	1st to 10th	Day	20% 13% 33% 23% 9% 1	653
	11th to 20th	Day	19% 14% 27% 24% 13% 3	675
	21st to end	Day	19% 10% 26% 27% 14% 4	734
June	1st to 10th	Day	12% 8% 26% 32% 18% 4	680
	11th to 20th	Day	16% 9% 34% 28% 11% 2	680
	21st to end	Day	13% 7% 31% 28% 17% 5%	680
July	1st to 10th	Day	9% 5% 21% 29% 25% 10%	671
	11th to 20th	Day	9% 5% 27% 31% 19% 9%	668
	21st to end	Day	7% 4 27% 36% 19% 8%	739
August	1st to 10th	Day	11% 5% 23% 33% 22% 7%	676
	11th to 20th	Day	15% 3 20% 33% 22% 6%	665
	21st to end	Day	12% 5% 25% 31% 21% 6%	582
September	1st to 10th	Day	14% 7% 26% 32% 16% 6%	490
	11th to 20th	Day	12% 6% 29% 31% 18% 4	490
	21st to end	Day	17% 14% 28% 25% 12% 4	333
October	1st to 10th	Day	17% 13% 30% 22% 15% 2	300
	11th to 20th	Day	22% 15% 36% 20% 6% 1	300
	21st to end	Day	27% 15% 35% 15% 5% 2	330
November	1st to 10th	Day	22% 12% 36% 21% 9% 1	300
	11th to 20th	Day	21% 21% 38% 15% 6%	300
	21st to end	Day	23% 15% 38% 18% 5%	300
December	1st to 10th	Day	16% 13% 41% 25% 4 1	300
	11th to 20th	Day	22% 18% 37% 18% 5% 1	300
	21st to end	Day	26% 16% 36% 18% 4	330
January	1st to 10th	Night	13% 14% 36% 27% 9% 1	1000
	11th to 20th	Night	17% 13% 36% 28% 6% 1	1000
	21st to end	Night	19% 11% 35% 28% 6% 1	1100
February	1st to 10th	Night	14% 13% 39% 28% 6% 1	1000
	11th to 20th	Night	12% 13% 41% 25% 7%	979
	21st to end	Night	18% 14% 34% 28% 6%	712
March	1st to 10th	Night	17% 11% 37% 28% 7% 1	720
	11th to 20th	Night	20% 10% 33% 30% 6%	575
	21st to end	Night	23% 8% 32% 27% 9% 1	627
April	1st to 10th	Night	21% 14% 32% 27% 5%	570
	11th to 20th	Night	28% 9% 29% 27% 6%	563
	21st to end	Night	24% 9% 29% 29% 9% 1	570
May	1st to 10th	Night	21% 8% 31% 32% 5% 1	570
	11th to 20th	Night	19% 7% 29% 33% 11% 1	561
	21st to end	Night	16% 6% 24% 39% 14% 1	617
June	1st to 10th	Night	13% 5% 26% 42% 14%	570
	11th to 20th	Night	14% 4 30% 42% 10%	570
	21st to end	Night	11% 4 22% 45% 17% 1	570
July	1st to 10th	Night	6% 1 22% 39% 29% 2	555
	11th to 20th	Night	6% 4 21% 45% 20% 3	552
	21st to end	Night	7% 2 19% 48% 22% 2	624
August	1st to 10th	Night	7% 4 16% 48% 23% 2	567
	11th to 20th	Night	12% 2 17% 38% 27% 4	564
	21st to end	Night	11% 3 22% 36% 26% 2	627
September	1st to 10th	Night	12% 4 24% 38% 18% 4	570
	11th to 20th	Night	11% 4 28% 35% 19% 3	570
	21st to end	Night	15% 9% 27% 31% 17% 1	679
October	1st to 10th	Night	16% 9% 27% 32% 14% 2	760
	11th to 20th	Night	19% 12% 31% 31% 7% 1	760
	21st to end	Night	24% 10% 28% 32% 7% 1	836
November	1st to 10th	Night	18% 10% 34% 30% 8% 1	828
	11th to 20th	Night	19% 14% 35% 25% 7%	1000
	21st to end	Night	20% 14% 34% 26% 6%	1000
December	1st to 10th	Night	18% 10% 37% 28% 7% 1	1000
	11th to 20th	Night	21% 11% 34% 26% 7% 1	1000
	21st to end	Night	27% 12% 30% 25% 5%	1100

Page generated at 2025-03-09 07:08:48. Version ac07

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