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 2024-02-10.

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% 4 7% 6% 3 5% 5% 5% 7% 36%	78227
	Night	13% 9% 4 7% 6% 3 4 4 5% 6% 37%	80785
Transparency	Day	47% 6% 13% 23% 10% 1	77927
	Night	47% 5% 12% 23% 11% 1	80605
Seeing	Day	17% 10% 30% 26% 13% 4	14901
	Night	17% 9% 30% 31% 11% 1	24969

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	11% 16% 8% 15% 7% 3 4 3 4 5% 23%	2527
	11th to 20th	Day	6% 13% 5% 12% 11% 5% 8% 10% 7% 4 20%	2530
	21st to end	Day	12% 19% 7% 10% 6% 3 3 4 5% 6% 24%	3085
February	1st to 10th	Day	8% 11% 6% 8% 8% 5% 4 6% 5% 8% 31%	1701
	11th to 20th	Day	10% 11% 5% 9% 5% 3 5% 5% 5% 7% 34%	1574
	21st to end	Day	13% 11% 4 8% 7% 3 5% 4 5% 8% 31%	1431
March	1st to 10th	Day	14% 11% 6% 7% 6% 3 5% 4 4 6% 34%	1886
	11th to 20th	Day	15% 10% 4 7% 5% 3 4 4 5% 7% 35%	1980
	21st to end	Day	21% 9% 4 5% 6% 3 4 5% 5% 6% 30%	2234
April	1st to 10th	Day	18% 11% 4 7% 6% 2 4 4 5% 6% 34%	2160
	11th to 20th	Day	21% 11% 4 7% 5% 3 4 3 4 7% 32%	2134
	21st to end	Day	19% 11% 4 7% 6% 3 5% 4 5% 7% 29%	2284
May	1st to 10th	Day	17% 7% 4 7% 7% 3 5% 6% 6% 7% 33%	2474
	11th to 20th	Day	16% 7% 3 7% 6% 3 4 5% 5% 7% 38%	2479
	21st to end	Day	15% 5% 3 7% 6% 4 5% 5% 5% 7% 38%	2725
June	1st to 10th	Day	12% 4 3 4 4 3 5% 5% 5% 8% 46%	2520
	11th to 20th	Day	13% 6% 2 5% 6% 4 6% 5% 5% 8% 40%	2520
	21st to end	Day	10% 6% 2 5% 6% 4 5% 5% 6% 9% 41%	2520
July	1st to 10th	Day	7% 4 2 5% 5% 3 5% 4 6% 11% 47%	2520
	11th to 20th	Day	8% 4 2 3 5% 3 5% 6% 6% 9% 50%	2520
	21st to end	Day	7% 3 2 4 4 4 5% 7% 7% 10% 47%	2743
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 7% 8% 9% 41%	2344
	11th to 20th	Day	13% 6% 2 6% 5% 3 6% 4 6% 7% 43%	2301
	21st to end	Day	9% 5% 2 5% 4 3 4 4 5% 8% 50%	2417
September	1st to 10th	Day	13% 5% 2 5% 4 3 4 5% 4 7% 47%	2160
	11th to 20th	Day	12% 6% 3 5% 5% 3 4 4 5% 8% 45%	2160
	21st to end	Day	15% 7% 2 6% 5% 3 4 5% 5% 8% 41%	1890
October	1st to 10th	Day	16% 6% 2 5% 4 3 5% 5% 5% 7% 43%	1800
	11th to 20th	Day	15% 10% 4 6% 5% 2 4 5% 5% 7% 38%	1800
	21st to end	Day	19% 12% 5% 6% 4 2 2 4 4 6% 35%	1922
November	1st to 10th	Day	12% 10% 4 8% 6% 3 4 5% 5% 7% 37%	1625
	11th to 20th	Day	15% 13% 6% 7% 7% 4 4 4 5% 7% 28%	1520
	21st to end	Day	14% 11% 3 7% 6% 2 4 3 5% 8% 36%	1520
December	1st to 10th	Day	12% 11% 6% 13% 9% 4 6% 4 4 5% 27%	1520
	11th to 20th	Day	11% 12% 6% 9% 8% 4 5% 5% 6% 7% 27%	1918
	21st to end	Day	22% 15% 7% 16% 7% 3 3 3 3 4 19%	2783
January	1st to 10th	Night	9% 16% 10% 14% 7% 2 4 3 4 5% 27%	4428
	11th to 20th	Night	9% 11% 5% 12% 9% 5% 8% 8% 6% 5% 21%	4440
	21st to end	Night	13% 19% 7% 10% 6% 3 4 4 4 5% 25%	4564
February	1st to 10th	Night	6% 12% 6% 10% 8% 4 6% 4 5% 6% 34%	2464
	11th to 20th	Night	8% 8% 4 8% 6% 4 5% 5% 5% 7% 39%	2273
	21st to end	Night	14% 9% 5% 6% 6% 4 5% 5% 4 6% 36%	1823
March	1st to 10th	Night	13% 10% 4 7% 6% 3 4 4 5% 7% 37%	2088
	11th to 20th	Night	13% 11% 3 6% 5% 4 4 4 4 7% 38%	1980
	21st to end	Night	19% 9% 3 7% 5% 3 4 3 5% 8% 34%	2120
April	1st to 10th	Night	16% 10% 4 6% 6% 2 4 4 5% 7% 36%	1800
	11th to 20th	Night	23% 9% 4 6% 5% 3 4 4 4 5% 34%	1775
	21st to end	Night	19% 7% 3 6% 5% 2 4 4 5% 7% 38%	1674
May	1st to 10th	Night	20% 7% 3 5% 6% 2 4 4 5% 6% 38%	1486
	11th to 20th	Night	18% 5% 2 4 5% 3 3 5% 6% 8% 42%	1416
	21st to end	Night	13% 6% 3 6% 6% 4 5% 4 6% 7% 40%	1551
June	1st to 10th	Night	11% 4 1 5% 6% 3 4 5% 6% 8% 47%	1440
	11th to 20th	Night	12% 6% 2 5% 5% 4 4 4 5% 7% 46%	1440
	21st to end	Night	7% 4 3 4 4 3 5% 5% 6% 7% 52%	1440
July	1st to 10th	Night	5% 3 1 4 3 2 4 4 6% 12% 55%	1440
	11th to 20th	Night	5% 3 1 4 5% 3 4 4 7% 9% 55%	1440
	21st to end	Night	5% 3 1 4 3 2 4 6% 5% 9% 58%	1575
August	1st to 10th	Night	6% 5% 2 4 5% 3 5% 5% 6% 9% 50%	1593
	11th to 20th	Night	11% 4 2 4 4 2 4 5% 4 7% 53%	1600
	21st to end	Night	9% 4 2 4 5% 2 4 4 4 6% 55%	1939
September	1st to 10th	Night	10% 6% 2 4 4 3 3 5% 5% 6% 53%	1800
	11th to 20th	Night	11% 5% 2 4 4 3 3 4 5% 8% 52%	1800
	21st to end	Night	14% 5% 2 5% 5% 2 4 4 5% 7% 49%	2048
October	1st to 10th	Night	14% 6% 2 4 4 3 4 3 5% 6% 48%	2160
	11th to 20th	Night	16% 8% 3 5% 5% 3 4 4 4 6% 42%	2160
	21st to end	Night	18% 10% 3 5% 5% 3 4 4 5% 6% 38%	2434
November	1st to 10th	Night	12% 8% 4 6% 5% 3 4 4 4 7% 43%	2451
	11th to 20th	Night	14% 10% 5% 8% 7% 4 5% 5% 5% 6% 33%	2660
	21st to end	Night	15% 9% 4 8% 6% 3 5% 4 4 6% 37%	2660
December	1st to 10th	Night	12% 12% 5% 9% 7% 4 6% 5% 5% 7% 29%	2660
	11th to 20th	Night	12% 12% 5% 10% 8% 4 5% 5% 5% 6% 27%	3279
	21st to end	Night	24% 14% 6% 11% 7% 3 4 3 4 5% 21%	4884

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	65% 3 12% 16% 4	2528
	11th to 20th	Day	63% 6% 10% 15% 7%	2530
	21st to end	Day	61% 5% 14% 15% 5%	3085
February	1st to 10th	Day	50% 5% 15% 19% 10% 1	1701
	11th to 20th	Day	50% 5% 13% 23% 8% 1	1583
	21st to end	Day	54% 4 10% 20% 11% 1	1431
March	1st to 10th	Day	52% 5% 14% 19% 9% 2	1886
	11th to 20th	Day	48% 5% 13% 22% 10% 1	1980
	21st to end	Day	54% 5% 11% 21% 8% 1	2234
April	1st to 10th	Day	51% 5% 11% 21% 11% 1	2160
	11th to 20th	Day	54% 4 9% 19% 12% 2	2134
	21st to end	Day	55% 6% 12% 18% 9% 1	2284
May	1st to 10th	Day	50% 6% 13% 22% 9% 1	2474
	11th to 20th	Day	47% 6% 12% 22% 12% 1	2483
	21st to end	Day	45% 7% 10% 23% 13% 2	2725
June	1st to 10th	Day	35% 7% 13% 29% 14% 2	2520
	11th to 20th	Day	42% 7% 14% 23% 14% 1	2520
	21st to end	Day	38% 7% 16% 26% 11% 2	2520
July	1st to 10th	Day	31% 7% 16% 30% 15% 1	2451
	11th to 20th	Day	30% 8% 14% 27% 19% 2	2445
	21st to end	Day	29% 10% 16% 28% 15% 2	2591
August	1st to 10th	Day	36% 9% 14% 30% 9% 2	2329
	11th to 20th	Day	40% 7% 13% 29% 11%	2301
	21st to end	Day	32% 5% 13% 30% 18% 1	2417
September	1st to 10th	Day	37% 5% 14% 29% 14% 1	2160
	11th to 20th	Day	37% 6% 14% 33% 9% 1	2160
	21st to end	Day	41% 6% 12% 31% 10%	1890
October	1st to 10th	Day	41% 6% 12% 30% 11% 1	1800
	11th to 20th	Day	45% 6% 14% 22% 12% 1	1800
	21st to end	Day	51% 3 12% 23% 10%	1922
November	1st to 10th	Day	46% 6% 12% 19% 14% 2	1625
	11th to 20th	Day	57% 6% 11% 17% 9% 1	1520
	21st to end	Day	49% 5% 16% 22% 7% 1	1520
December	1st to 10th	Day	60% 5% 13% 15% 6%	1520
	11th to 20th	Day	55% 7% 16% 16% 5% 1	1915
	21st to end	Day	72% 4 8% 13% 4	2783
January	1st to 10th	Night	61% 4 10% 19% 6% 1	4428
	11th to 20th	Night	61% 6% 11% 15% 7%	4440
	21st to end	Night	62% 4 9% 19% 5% 1	4564
February	1st to 10th	Night	51% 4 12% 22% 9% 2	2464
	11th to 20th	Night	45% 5% 14% 25% 9% 1	2274
	21st to end	Night	50% 6% 10% 22% 10% 2	1823
March	1st to 10th	Night	47% 6% 14% 23% 8% 1	2088
	11th to 20th	Night	47% 4 12% 22% 14% 1	1980
	21st to end	Night	50% 5% 11% 21% 11% 1	2120
April	1st to 10th	Night	48% 4 9% 21% 16% 2	1800
	11th to 20th	Night	53% 5% 8% 18% 14% 3	1775
	21st to end	Night	47% 5% 10% 20% 15% 2	1674
May	1st to 10th	Night	46% 6% 13% 21% 13% 1	1486
	11th to 20th	Night	40% 6% 12% 24% 16% 2	1417
	21st to end	Night	42% 8% 10% 22% 18% 1	1552
June	1st to 10th	Night	33% 8% 12% 29% 17% 2	1440
	11th to 20th	Night	38% 6% 12% 23% 18% 3	1440
	21st to end	Night	29% 7% 16% 31% 15% 3	1440
July	1st to 10th	Night	23% 6% 15% 36% 20% 2	1400
	11th to 20th	Night	24% 6% 16% 31% 19% 3	1392
	21st to end	Night	21% 7% 17% 33% 17% 5%	1487
August	1st to 10th	Night	31% 7% 15% 29% 16% 3	1584
	11th to 20th	Night	32% 7% 14% 29% 17% 2	1600
	21st to end	Night	30% 5% 14% 29% 17% 4	1939
September	1st to 10th	Night	32% 5% 10% 34% 18% 1	1800
	11th to 20th	Night	31% 5% 15% 31% 17% 1	1800
	21st to end	Night	35% 5% 13% 31% 14% 1	2048
October	1st to 10th	Night	37% 4 10% 33% 15% 2	2160
	11th to 20th	Night	43% 5% 12% 26% 13% 1	2160
	21st to end	Night	48% 5% 12% 22% 13% 1	2434
November	1st to 10th	Night	42% 5% 12% 24% 15% 2	2451
	11th to 20th	Night	53% 5% 12% 18% 11% 1	2660
	21st to end	Night	49% 4 16% 23% 7% 1	2660
December	1st to 10th	Night	53% 6% 15% 20% 5%	2660
	11th to 20th	Night	57% 5% 13% 18% 6% 1	3281
	21st to end	Night	66% 5% 9% 15% 5%	4884

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% 31% 27% 10% 2	270
	11th to 20th	Day	19% 16% 37% 21% 5% 1	270
	21st to end	Day	20% 12% 34% 24% 9% 1	297
February	1st to 10th	Day	16% 16% 45% 18% 4 1	267
	11th to 20th	Day	18% 23% 37% 15% 6%	240
	21st to end	Day	23% 18% 38% 21% 1	198
March	1st to 10th	Day	19% 18% 39% 17% 8%	240
	11th to 20th	Day	23% 13% 36% 20% 6% 3	240
	21st to end	Day	26% 14% 30% 18% 9% 3	320
April	1st to 10th	Day	27% 13% 33% 20% 6% 1	420
	11th to 20th	Day	29% 15% 24% 23% 8% 1	412
	21st to end	Day	26% 14% 28% 22% 9% 2	544
May	1st to 10th	Day	20% 13% 33% 24% 9% 1	603
	11th to 20th	Day	21% 14% 27% 22% 13% 4	625
	21st to end	Day	19% 9% 25% 28% 14% 4	679
June	1st to 10th	Day	11% 8% 26% 33% 18% 4	630
	11th to 20th	Day	15% 9% 33% 29% 11% 3	630
	21st to end	Day	11% 7% 31% 28% 18% 5%	630
July	1st to 10th	Day	8% 5% 21% 30% 26% 11%	621
	11th to 20th	Day	10% 5% 27% 32% 18% 8%	618
	21st to end	Day	7% 3 28% 36% 18% 8%	684
August	1st to 10th	Day	11% 4 23% 33% 23% 7%	626
	11th to 20th	Day	16% 3 21% 32% 23% 7%	615
	21st to end	Day	13% 5% 24% 31% 21% 6%	536
September	1st to 10th	Day	15% 7% 25% 32% 16% 5%	450
	11th to 20th	Day	13% 5% 29% 32% 17% 5%	450
	21st to end	Day	19% 14% 28% 25% 11% 3	302
October	1st to 10th	Day	18% 13% 30% 21% 16% 3	270
	11th to 20th	Day	23% 16% 33% 21% 7%	270
	21st to end	Day	29% 14% 34% 14% 6% 2	297
November	1st to 10th	Day	21% 11% 36% 21% 10% 1	270
	11th to 20th	Day	20% 20% 39% 16% 5%	270
	21st to end	Day	23% 14% 39% 19% 6%	270
December	1st to 10th	Day	17% 11% 41% 26% 4 1	270
	11th to 20th	Day	20% 17% 38% 19% 6% 1	270
	21st to end	Day	26% 17% 37% 18% 2	297
January	1st to 10th	Night	13% 14% 36% 27% 8% 1	950
	11th to 20th	Night	17% 12% 36% 28% 7% 1	950
	21st to end	Night	20% 11% 34% 28% 7% 1	1045
February	1st to 10th	Night	13% 13% 39% 29% 6% 1	948
	11th to 20th	Night	13% 13% 40% 25% 8%	879
	21st to end	Night	20% 15% 32% 27% 6%	639
March	1st to 10th	Night	18% 11% 36% 27% 7% 1	648
	11th to 20th	Night	20% 9% 34% 30% 6%	540
	21st to end	Night	22% 9% 32% 27% 10% 2	594
April	1st to 10th	Night	21% 14% 32% 27% 5%	540
	11th to 20th	Night	29% 9% 28% 27% 7%	533
	21st to end	Night	24% 9% 29% 29% 9% 1	540
May	1st to 10th	Night	22% 8% 31% 32% 5% 1	540
	11th to 20th	Night	19% 7% 29% 33% 11% 1	531
	21st to end	Night	16% 6% 23% 39% 14% 1	584
June	1st to 10th	Night	13% 4 25% 43% 15%	540
	11th to 20th	Night	14% 4 30% 43% 10%	540
	21st to end	Night	9% 4 22% 46% 18% 1	540
July	1st to 10th	Night	5% 2 22% 39% 30% 2	525
	11th to 20th	Night	6% 4 22% 46% 20% 3	522
	21st to end	Night	7% 2 19% 48% 21% 2	591
August	1st to 10th	Night	7% 3 15% 48% 25% 2	537
	11th to 20th	Night	13% 2 17% 37% 27% 4	534
	21st to end	Night	11% 3 23% 35% 27% 2	594
September	1st to 10th	Night	13% 4 24% 37% 19% 4	540
	11th to 20th	Night	11% 4 28% 34% 19% 3	540
	21st to end	Night	16% 9% 29% 30% 16% 1	643
October	1st to 10th	Night	16% 9% 27% 31% 15% 2	720
	11th to 20th	Night	20% 12% 30% 30% 7% 1	720
	21st to end	Night	23% 10% 28% 32% 7% 1	792
November	1st to 10th	Night	17% 10% 34% 30% 9% 1	785
	11th to 20th	Night	19% 13% 36% 24% 7%	950
	21st to end	Night	20% 14% 34% 26% 6%	950
December	1st to 10th	Night	18% 9% 37% 27% 7% 1	950
	11th to 20th	Night	21% 11% 34% 26% 7% 1	950
	21st to end	Night	27% 12% 31% 24% 5%	1045

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