Candlewyck Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Candlewyck Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 7% 2 6% 4 4 4 4 6% 7% 40%	131154
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	130032
Transparency	Day	41% 6% 12% 23% 16% 2	134683
	Night	41% 5% 11% 23% 17% 3	134589
Seeing	Day	23% 15% 28% 20% 10% 3	16563
	Night	20% 13% 30% 27% 10% 1	25964

By Month

Percentage Cloud Cover NE (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	14% 7% 2 6% 5% 5% 4 3 4 5% 45%	4661
	11th to 20th	Day	14% 9% 3 8% 4 4 4 3 4 5% 41%	4805
	21st to end	Day	15% 6% 2 7% 4 5% 5% 4 5% 6% 38%	5780
February	1st to 10th	Day	15% 8% 3 7% 5% 5% 3 4 6% 7% 39%	1890
	11th to 20th	Day	16% 9% 3 8% 5% 3 3 3 5% 7% 38%	1976
	21st to end	Day	19% 10% 3 6% 4 4 4 3 4 5% 39%	1730
March	1st to 10th	Day	21% 5% 2 5% 4 4 4 3 4 5% 44%	4537
	11th to 20th	Day	12% 7% 2 6% 4 5% 4 4 5% 6% 44%	4980
	21st to end	Day	19% 6% 2 6% 4 4 3 3 5% 6% 43%	5776
April	1st to 10th	Day	17% 7% 2 7% 5% 4 4 3 6% 6% 39%	2400
	11th to 20th	Day	17% 7% 3 5% 4 4 4 3 6% 7% 41%	2374
	21st to end	Day	16% 6% 2 6% 5% 4 4 4 6% 6% 41%	2400
May	1st to 10th	Day	27% 7% 2 5% 4 4 5% 4 6% 7% 29%	5873
	11th to 20th	Day	25% 8% 3 6% 4 4 4 3 5% 7% 32%	6318
	21st to end	Day	20% 6% 2 5% 4 4 4 4 6% 8% 36%	6949
June	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 8% 9% 39%	2800
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 4 7% 9% 37%	2800
	21st to end	Day	13% 5% 2 6% 5% 4 5% 5% 6% 9% 41%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 11% 39%	6360
	11th to 20th	Day	11% 7% 3 7% 5% 6% 6% 5% 8% 11% 32%	6360
	21st to end	Day	11% 7% 2 7% 5% 4 4 4 6% 9% 41%	6798
August	1st to 10th	Day	20% 6% 2 6% 5% 5% 5% 4 6% 8% 34%	4234
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 6% 10% 42%	3888
	21st to end	Day	12% 5% 2 5% 3 3 4 3 6% 9% 47%	4312
September	1st to 10th	Day	15% 6% 3 5% 4 3 5% 4 5% 6% 45%	2400
	11th to 20th	Day	13% 4 1 4 3 3 3 3 6% 7% 52%	2380
	21st to end	Day	19% 7% 3 7% 4 4 5% 3 4 6% 37%	2180
October	1st to 10th	Day	17% 6% 2 5% 3 4 4 3 6% 6% 44%	2000
	11th to 20th	Day	16% 5% 3 4 4 4 4 2 4 7% 47%	2000
	21st to end	Day	18% 6% 2 5% 3 3 3 4 4 6% 45%	2136
November	1st to 10th	Day	14% 6% 2 4 3 2 4 4 3 6% 52%	1851
	11th to 20th	Day	16% 6% 1 4 3 4 4 3 6% 7% 46%	1890
	21st to end	Day	15% 8% 3 5% 3 4 4 4 6% 7% 42%	1722
December	1st to 10th	Day	15% 8% 2 5% 3 4 5% 4 6% 7% 41%	2680
	11th to 20th	Day	22% 9% 2 5% 3 3 3 3 4 6% 41%	3066
	21st to end	Day	18% 6% 2 6% 5% 5% 4 4 6% 7% 37%	4048
January	1st to 10th	Night	12% 7% 3 7% 4 4 4 3 5% 6% 45%	8234
	11th to 20th	Night	14% 8% 3 6% 4 3 4 3 5% 7% 44%	8078
	21st to end	Night	16% 8% 2 5% 3 3 4 3 5% 6% 45%	8401
February	1st to 10th	Night	16% 9% 3 6% 5% 4 4 4 5% 7% 40%	2730
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	2528
	21st to end	Night	18% 8% 2 5% 3 3 4 4 5% 5% 41%	2076
March	1st to 10th	Night	19% 8% 2 5% 4 3 3 3 4 5% 43%	5343
	11th to 20th	Night	12% 7% 3 6% 4 3 3 3 5% 5% 50%	4979
	21st to end	Night	16% 8% 2 6% 4 4 4 3 4 6% 43%	5156
April	1st to 10th	Night	18% 6% 2 6% 5% 4 4 4 6% 6% 39%	2000
	11th to 20th	Night	16% 7% 2 7% 4 3 4 4 5% 7% 41%	1975
	21st to end	Night	20% 5% 2 5% 3 2 3 3 5% 8% 44%	2000
May	1st to 10th	Night	25% 9% 2 6% 4 4 4 4 6% 7% 29%	4106
	11th to 20th	Night	23% 9% 3 7% 4 4 4 3 5% 6% 32%	3575
	21st to end	Night	22% 6% 2 5% 4 4 4 4 5% 8% 37%	3926
June	1st to 10th	Night	15% 6% 2 6% 5% 4 3 4 6% 7% 42%	1600
	11th to 20th	Night	14% 6% 2 4 4 5% 5% 4 7% 8% 40%	1600
	21st to end	Night	12% 4 2 4 5% 4 5% 5% 6% 9% 44%	1600
July	1st to 10th	Night	9% 7% 3 8% 5% 5% 6% 5% 6% 10% 37%	3600
	11th to 20th	Night	15% 8% 3 9% 5% 5% 5% 5% 7% 9% 30%	3600
	21st to end	Night	12% 6% 2 5% 4 4 5% 4 6% 8% 44%	4051
August	1st to 10th	Night	21% 5% 3 6% 5% 4 4 5% 6% 8% 34%	2915
	11th to 20th	Night	14% 7% 3 6% 4 4 4 4 5% 7% 42%	3127
	21st to end	Night	12% 5% 2 5% 4 4 4 4 6% 7% 49%	3586
September	1st to 10th	Night	15% 6% 2 5% 4 5% 4 3 4 6% 46%	2000
	11th to 20th	Night	11% 6% 2 5% 3 3 4 2 6% 6% 53%	2020
	21st to end	Night	18% 8% 2 5% 4 3 4 3 5% 7% 41%	2215
October	1st to 10th	Night	19% 6% 2 5% 4 3 4 3 4 6% 45%	2400
	11th to 20th	Night	17% 5% 2 4 3 3 4 2 4 6% 50%	2400
	21st to end	Night	18% 6% 2 4 3 3 3 3 4 5% 49%	2701
November	1st to 10th	Night	12% 5% 1 4 3 3 4 4 5% 6% 52%	2667
	11th to 20th	Night	16% 7% 2 5% 3 3 4 2 5% 5% 47%	2730
	21st to end	Night	14% 6% 2 6% 5% 4 4 3 6% 7% 44%	2895
December	1st to 10th	Night	13% 8% 2 6% 4 4 4 3 5% 6% 45%	4720
	11th to 20th	Night	23% 7% 2 4 3 4 3 3 4 6% 41%	5348
	21st to end	Night	20% 8% 3 6% 4 4 3 3 5% 5% 39%	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	40% 4 9% 27% 18% 2	4662
	11th to 20th	Day	44% 4 9% 20% 17% 6%	4835
	21st to end	Day	45% 5% 12% 22% 15% 1	5780
February	1st to 10th	Day	43% 6% 14% 23% 12% 2	1890
	11th to 20th	Day	47% 4 9% 23% 14% 2	1985
	21st to end	Day	48% 4 10% 24% 11% 3	1730
March	1st to 10th	Day	42% 5% 8% 23% 15% 7%	4540
	11th to 20th	Day	38% 6% 12% 28% 12% 5%	4980
	21st to end	Day	42% 5% 10% 15% 23% 5%	5776
April	1st to 10th	Day	44% 6% 10% 21% 15% 5%	2400
	11th to 20th	Day	41% 6% 12% 22% 16% 4	2374
	21st to end	Day	41% 7% 10% 21% 17% 4	2400
May	1st to 10th	Day	51% 8% 13% 18% 9% 2	5882
	11th to 20th	Day	51% 7% 9% 21% 11% 1	6322
	21st to end	Day	43% 7% 11% 23% 14% 1	6949
June	1st to 10th	Day	39% 8% 13% 24% 14% 1	2800
	11th to 20th	Day	41% 9% 14% 23% 10% 2	2800
	21st to end	Day	37% 8% 15% 25% 14% 1	2800
July	1st to 10th	Day	39% 9% 14% 21% 15% 2	6290
	11th to 20th	Day	43% 8% 17% 21% 9% 1	6285
	21st to end	Day	39% 7% 10% 20% 23% 1	6602
August	1st to 10th	Day	46% 8% 12% 23% 10%	4221
	11th to 20th	Day	37% 6% 12% 30% 14% 1	3925
	21st to end	Day	33% 6% 11% 29% 20% 2	4312
September	1st to 10th	Day	38% 7% 11% 21% 21% 3	2400
	11th to 20th	Day	32% 5% 11% 26% 23% 3	2380
	21st to end	Day	47% 6% 8% 17% 19% 2	2180
October	1st to 10th	Day	37% 5% 9% 19% 26% 5%	3260
	11th to 20th	Day	27% 4 11% 28% 25% 5%	3240
	21st to end	Day	26% 4 13% 25% 29% 4	3426
November	1st to 10th	Day	33% 5% 14% 23% 21% 4	1851
	11th to 20th	Day	37% 5% 11% 25% 19% 3	1890
	21st to end	Day	39% 6% 13% 30% 10% 2	1722
December	1st to 10th	Day	42% 5% 15% 25% 10% 2	2680
	11th to 20th	Day	44% 4 13% 27% 10% 1	3066
	21st to end	Day	45% 6% 12% 22% 14% 1	4048
January	1st to 10th	Night	40% 5% 13% 23% 16% 3	8234
	11th to 20th	Night	41% 4 11% 21% 17% 6%	8123
	21st to end	Night	40% 4 9% 25% 20% 3	8401
February	1st to 10th	Night	44% 5% 13% 25% 11% 2	2730
	11th to 20th	Night	46% 4 10% 19% 17% 3	2530
	21st to end	Night	43% 5% 9% 23% 17% 3	2076
March	1st to 10th	Night	43% 5% 9% 22% 12% 9%	5353
	11th to 20th	Night	35% 6% 14% 26% 14% 5%	4980
	21st to end	Night	43% 5% 7% 16% 24% 5%	5156
April	1st to 10th	Night	44% 5% 11% 21% 15% 4	2000
	11th to 20th	Night	42% 6% 10% 20% 20% 2	1975
	21st to end	Night	38% 6% 11% 22% 18% 5%	2000
May	1st to 10th	Night	53% 7% 11% 16% 10% 2	4113
	11th to 20th	Night	52% 7% 11% 16% 12% 1	3576
	21st to end	Night	44% 8% 10% 22% 14% 2	3927
June	1st to 10th	Night	41% 7% 11% 22% 19% 2	1600
	11th to 20th	Night	38% 10% 15% 23% 13% 1	1600
	21st to end	Night	35% 9% 14% 26% 14% 2	1600
July	1st to 10th	Night	42% 9% 14% 18% 15% 2	3560
	11th to 20th	Night	48% 7% 16% 18% 9% 1	3552
	21st to end	Night	36% 7% 13% 23% 21% 1	3932
August	1st to 10th	Night	47% 8% 18% 17% 9% 1	2904
	11th to 20th	Night	41% 6% 13% 24% 15% 1	3156
	21st to end	Night	33% 6% 10% 29% 20% 1	3586
September	1st to 10th	Night	39% 6% 9% 21% 22% 2	2000
	11th to 20th	Night	32% 5% 11% 23% 26% 4	2020
	21st to end	Night	44% 6% 9% 20% 21% 2	2215
October	1st to 10th	Night	42% 4 9% 21% 21% 2	3920
	11th to 20th	Night	26% 4 10% 29% 27% 5%	3899
	21st to end	Night	27% 3 12% 31% 23% 3	4361
November	1st to 10th	Night	32% 6% 12% 25% 21% 5%	2667
	11th to 20th	Night	39% 5% 9% 23% 20% 4	2730
	21st to end	Night	39% 6% 12% 27% 15% 1	2895
December	1st to 10th	Night	40% 4 13% 29% 12% 2	4720
	11th to 20th	Night	45% 4 10% 25% 13% 3	5348
	21st to end	Night	46% 5% 11% 20% 17% 2	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	32% 26% 28% 11% 1 1	220
	11th to 20th	Day	41% 23% 29% 7% 1	248
	21st to end	Day	29% 32% 25% 10% 3 1	363
February	1st to 10th	Day	29% 25% 35% 8% 3 1	330
	11th to 20th	Day	34% 24% 32% 9% 1	464
	21st to end	Day	33% 23% 28% 13% 2	446
March	1st to 10th	Day	32% 19% 30% 16% 4	508
	11th to 20th	Day	27% 26% 31% 12% 3 2	500
	21st to end	Day	30% 25% 29% 12% 4 1	550
April	1st to 10th	Day	29% 24% 30% 12% 4 1	500
	11th to 20th	Day	24% 27% 25% 15% 6% 2	492
	21st to end	Day	27% 18% 33% 17% 4 2	500
May	1st to 10th	Day	30% 20% 29% 14% 5% 2	503
	11th to 20th	Day	26% 16% 29% 20% 8% 2	527
	21st to end	Day	21% 10% 27% 24% 15% 3	573
June	1st to 10th	Day	17% 14% 30% 23% 13% 3	530
	11th to 20th	Day	19% 12% 28% 25% 13% 3	530
	21st to end	Day	15% 10% 31% 27% 13% 4	530
July	1st to 10th	Day	11% 4 27% 29% 22% 6%	525
	11th to 20th	Day	10% 5% 25% 31% 24% 5%	524
	21st to end	Day	13% 6% 28% 32% 17% 3	576
August	1st to 10th	Day	11% 6% 26% 29% 21% 6%	526
	11th to 20th	Day	13% 6% 20% 34% 20% 7%	519
	21st to end	Day	11% 7% 27% 29% 17% 9%	583
September	1st to 10th	Day	18% 10% 22% 27% 15% 8%	530
	11th to 20th	Day	15% 4 28% 27% 15% 10%	530
	21st to end	Day	23% 13% 24% 23% 12% 4	530
October	1st to 10th	Day	24% 9% 24% 22% 15% 7%	530
	11th to 20th	Day	21% 17% 26% 23% 9% 3	530
	21st to end	Day	23% 17% 31% 17% 11% 2	547
November	1st to 10th	Day	21% 14% 30% 22% 10% 3	425
	11th to 20th	Day	24% 20% 32% 19% 5% 1	430
	21st to end	Day	30% 21% 30% 15% 3 1	262
December	1st to 10th	Day	35% 21% 30% 8% 6%	220
	11th to 20th	Day	38% 21% 27% 10% 3	220
	21st to end	Day	33% 15% 32% 12% 7%	242
January	1st to 10th	Night	21% 21% 37% 18% 3	840
	11th to 20th	Night	27% 18% 31% 21% 3	840
	21st to end	Night	20% 21% 37% 20% 2	924
February	1st to 10th	Night	23% 18% 38% 21% 2	840
	11th to 20th	Night	28% 22% 35% 14% 1	823
	21st to end	Night	25% 19% 38% 16% 2	692
March	1st to 10th	Night	23% 21% 31% 21% 3	809
	11th to 20th	Night	23% 21% 34% 17% 4	800
	21st to end	Night	23% 16% 38% 19% 5%	880
April	1st to 10th	Night	23% 21% 35% 18% 3	800
	11th to 20th	Night	20% 16% 36% 22% 6%	791
	21st to end	Night	21% 14% 32% 28% 5%	800
May	1st to 10th	Night	24% 13% 31% 25% 7%	627
	11th to 20th	Night	19% 9% 36% 29% 7%	394
	21st to end	Night	18% 9% 22% 38% 12% 1	433
June	1st to 10th	Night	15% 6% 27% 39% 13%	400
	11th to 20th	Night	12% 7% 27% 42% 13% 1	400
	21st to end	Night	11% 4 26% 46% 14%	400
July	1st to 10th	Night	11% 4 20% 44% 21% 2	390
	11th to 20th	Night	10% 3 21% 40% 25% 1	388
	21st to end	Night	11% 3 22% 41% 21% 3	488
August	1st to 10th	Night	13% 2 15% 44% 24% 2	597
	11th to 20th	Night	13% 4 18% 37% 26% 2	744
	21st to end	Night	14% 4 18% 40% 23% 2	880
September	1st to 10th	Night	16% 5% 25% 34% 19% 2	800
	11th to 20th	Night	13% 4 22% 36% 22% 4	800
	21st to end	Night	22% 5% 22% 31% 18% 1	800
October	1st to 10th	Night	21% 7% 25% 26% 19% 3	800
	11th to 20th	Night	19% 11% 29% 28% 13%	800
	21st to end	Night	22% 12% 32% 24% 9%	880
November	1st to 10th	Night	17% 11% 33% 28% 11%	820
	11th to 20th	Night	22% 18% 26% 26% 7%	840
	21st to end	Night	20% 16% 33% 24% 6%	840
December	1st to 10th	Night	25% 17% 34% 19% 5% 1	840
	11th to 20th	Night	23% 16% 34% 23% 4	840
	21st to end	Night	24% 16% 33% 25% 2	924

Page generated at 2026-02-28 01:40:22. Version ac07

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