Cadmus Homestead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cadmus Homestead Observatory 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	16% 7% 2 6% 4 4 4 4 6% 7% 39%	138247
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 41%	134426
Transparency	Day	43% 5% 12% 24% 15% 2	141822
	Night	42% 4 11% 23% 16% 3	138938
Seeing	Day	22% 15% 28% 21% 11% 3	17066
	Night	20% 13% 29% 27% 10% 1	26382

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 8% 5% 5% 5% 4 5% 6% 40%	4661
	11th to 20th	Day	13% 10% 4 9% 5% 5% 4 3 4 6% 37%	4930
	21st to end	Day	15% 7% 3 8% 5% 5% 5% 4 6% 6% 37%	5780
February	1st to 10th	Day	15% 9% 3 7% 5% 4 5% 4 5% 7% 36%	1890
	11th to 20th	Day	15% 9% 4 8% 4 4 4 3 6% 6% 37%	1938
	21st to end	Day	18% 9% 3 7% 4 4 4 3 4 6% 36%	1730
March	1st to 10th	Day	21% 5% 2 5% 4 4 4 3 5% 5% 43%	4735
	11th to 20th	Day	11% 7% 3 6% 5% 5% 5% 4 5% 7% 42%	5090
	21st to end	Day	18% 7% 2 6% 4 4 4 3 5% 7% 42%	5815
April	1st to 10th	Day	17% 7% 3 6% 5% 4 4 4 5% 7% 37%	2520
	11th to 20th	Day	15% 8% 2 6% 4 4 4 4 6% 6% 41%	2494
	21st to end	Day	16% 6% 2 6% 5% 4 4 4 6% 7% 39%	2520
May	1st to 10th	Day	23% 6% 2 6% 4 4 4 4 6% 8% 33%	7632
	11th to 20th	Day	20% 7% 2 6% 4 4 4 4 6% 8% 36%	8221
	21st to end	Day	24% 6% 2 5% 3 4 4 3 6% 7% 35%	9060
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 5% 6% 9% 39%	2940
	11th to 20th	Day	14% 6% 2 6% 4 4 6% 4 7% 9% 38%	2940
	21st to end	Day	11% 5% 2 5% 5% 4 5% 4 6% 11% 41%	2940
July	1st to 10th	Day	8% 6% 2 6% 6% 6% 5% 5% 7% 10% 39%	6500
	11th to 20th	Day	12% 7% 2 7% 5% 5% 5% 5% 8% 10% 33%	6430
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	6659
August	1st to 10th	Day	20% 6% 2 6% 5% 5% 5% 4 6% 7% 33%	4234
	11th to 20th	Day	15% 6% 2 5% 4 4 5% 4 7% 8% 41%	3949
	21st to end	Day	13% 5% 2 5% 3 4 3 3 5% 8% 49%	4312
September	1st to 10th	Day	15% 6% 2 6% 4 3 4 3 5% 6% 46%	2400
	11th to 20th	Day	12% 5% 2 4 4 3 4 3 6% 7% 50%	2400
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 5% 37%	2137
October	1st to 10th	Day	18% 6% 2 4 3 4 4 3 5% 7% 44%	2000
	11th to 20th	Day	17% 5% 2 6% 3 4 5% 3 4 7% 45%	2000
	21st to end	Day	17% 6% 2 5% 3 3 3 3 6% 7% 44%	2180
November	1st to 10th	Day	13% 7% 2 4 3 3 3 4 5% 7% 50%	1851
	11th to 20th	Day	16% 5% 2 5% 5% 3 4 4 5% 8% 43%	1885
	21st to end	Day	16% 7% 2 5% 4 3 5% 3 6% 7% 41%	1680
December	1st to 10th	Day	15% 8% 2 6% 5% 4 4 4 6% 6% 41%	2680
	11th to 20th	Day	21% 9% 2 5% 3 3 3 3 5% 7% 39%	3066
	21st to end	Day	18% 7% 3 7% 4 4 4 4 6% 8% 34%	4048
January	1st to 10th	Night	12% 8% 3 7% 5% 5% 4 4 5% 8% 40%	8234
	11th to 20th	Night	14% 8% 3 6% 4 4 4 4 5% 7% 42%	7937
	21st to end	Night	15% 7% 2 6% 4 3 3 3 5% 7% 44%	8401
February	1st to 10th	Night	16% 8% 3 6% 4 3 5% 4 5% 7% 39%	2730
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 3 5% 6% 38%	2566
	21st to end	Night	17% 8% 2 7% 5% 4 4 4 5% 7% 38%	2076
March	1st to 10th	Night	18% 9% 2 6% 4 4 4 3 4 5% 42%	5308
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 6% 49%	5089
	21st to end	Night	15% 7% 3 6% 4 4 4 3 5% 6% 43%	5357
April	1st to 10th	Night	18% 7% 3 5% 6% 3 4 4 6% 7% 37%	2100
	11th to 20th	Night	15% 7% 2 7% 4 4 4 4 6% 8% 41%	2075
	21st to end	Night	18% 6% 2 5% 4 3 3 3 6% 6% 44%	2100
May	1st to 10th	Night	23% 7% 2 6% 4 4 5% 4 5% 6% 32%	5311
	11th to 20th	Night	21% 7% 2 7% 4 4 4 3 5% 8% 35%	4639
	21st to end	Night	26% 6% 3 6% 4 3 4 3 4 6% 35%	5114
June	1st to 10th	Night	14% 6% 2 6% 3 4 4 3 6% 8% 43%	1680
	11th to 20th	Night	14% 5% 2 5% 4 6% 5% 4 7% 9% 40%	1680
	21st to end	Night	12% 5% 2 5% 3 4 6% 5% 6% 9% 43%	1680
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 6% 5% 7% 8% 39%	3680
	11th to 20th	Night	12% 7% 3 8% 6% 6% 6% 5% 7% 10% 31%	3640
	21st to end	Night	12% 6% 2 6% 4 4 4 3 6% 8% 43%	4189
August	1st to 10th	Night	21% 6% 2 6% 4 4 4 3 7% 8% 35%	2915
	11th to 20th	Night	15% 7% 3 7% 5% 4 5% 4 5% 6% 41%	3065
	21st to end	Night	13% 5% 2 5% 3 4 4 4 6% 8% 48%	3586
September	1st to 10th	Night	14% 6% 2 6% 4 4 3 3 4 6% 48%	2000
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 6% 51%	2000
	21st to end	Night	20% 7% 2 5% 3 4 5% 4 5% 5% 40%	2258
October	1st to 10th	Night	20% 6% 2 5% 4 3 3 3 4 6% 46%	2400
	11th to 20th	Night	16% 6% 2 6% 3 3 3 3 4 6% 49%	2400
	21st to end	Night	18% 5% 2 4 4 3 3 2 5% 7% 47%	2659
November	1st to 10th	Night	12% 5% 2 4 4 3 4 3 5% 6% 52%	2667
	11th to 20th	Night	15% 7% 3 5% 4 3 4 3 5% 6% 45%	2732
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 8% 43%	2940
December	1st to 10th	Night	13% 8% 3 7% 4 4 5% 3 5% 7% 42%	4720
	11th to 20th	Night	22% 7% 2 5% 3 4 4 3 5% 6% 40%	5348
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 6% 35%	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	45% 3 11% 25% 15% 1	4662
	11th to 20th	Day	48% 3 9% 18% 16% 6%	4962
	21st to end	Day	47% 4 12% 23% 13% 1	5780
February	1st to 10th	Day	46% 6% 12% 23% 11% 2	1890
	11th to 20th	Day	48% 4 10% 23% 13% 2	1947
	21st to end	Day	50% 4 10% 23% 11% 3	1730
March	1st to 10th	Day	43% 4 9% 24% 14% 6%	4738
	11th to 20th	Day	40% 4 12% 27% 11% 5%	5090
	21st to end	Day	44% 3 10% 17% 21% 4	5815
April	1st to 10th	Day	45% 4 10% 22% 15% 5%	2520
	11th to 20th	Day	42% 5% 12% 21% 16% 4	2494
	21st to end	Day	43% 4 10% 23% 15% 4	2520
May	1st to 10th	Day	48% 5% 11% 22% 12% 1	7641
	11th to 20th	Day	46% 5% 11% 26% 12% 1	8225
	21st to end	Day	48% 5% 10% 22% 14% 1	9061
June	1st to 10th	Day	40% 7% 12% 23% 17% 1	2940
	11th to 20th	Day	41% 6% 15% 25% 12% 2	2940
	21st to end	Day	36% 7% 15% 26% 15% 1	2940
July	1st to 10th	Day	39% 9% 14% 22% 16% 1	6430
	11th to 20th	Day	43% 8% 16% 22% 10% 1	6355
	21st to end	Day	40% 5% 10% 21% 22% 1	6468
August	1st to 10th	Day	48% 7% 11% 24% 10%	4221
	11th to 20th	Day	40% 5% 12% 30% 13% 1	3988
	21st to end	Day	34% 5% 11% 30% 19% 2	4312
September	1st to 10th	Day	39% 5% 11% 21% 20% 4	2400
	11th to 20th	Day	33% 4 9% 27% 22% 3	2400
	21st to end	Day	49% 5% 8% 17% 19% 2	2137
October	1st to 10th	Day	37% 3 9% 21% 26% 5%	3260
	11th to 20th	Day	29% 3 12% 28% 23% 6%	3240
	21st to end	Day	26% 3 13% 27% 27% 3	3506
November	1st to 10th	Day	34% 4 14% 24% 20% 4	1851
	11th to 20th	Day	39% 4 11% 24% 18% 2	1885
	21st to end	Day	41% 5% 12% 30% 10% 2	1680
December	1st to 10th	Day	43% 3 17% 25% 10% 2	2680
	11th to 20th	Day	46% 3 13% 29% 8% 1	3066
	21st to end	Day	47% 4 14% 21% 13% 1	4048
January	1st to 10th	Night	42% 4 13% 24% 14% 3	8234
	11th to 20th	Night	41% 4 11% 20% 18% 6%	7980
	21st to end	Night	40% 3 10% 27% 19% 2	8401
February	1st to 10th	Night	45% 4 13% 25% 12% 2	2730
	11th to 20th	Night	47% 4 9% 21% 17% 3	2568
	21st to end	Night	46% 4 9% 22% 16% 3	2076
March	1st to 10th	Night	44% 4 10% 22% 12% 8%	5318
	11th to 20th	Night	35% 5% 14% 28% 13% 6%	5090
	21st to end	Night	43% 3 8% 18% 25% 4	5357
April	1st to 10th	Night	45% 4 10% 22% 15% 4	2100
	11th to 20th	Night	41% 6% 11% 20% 20% 2	2075
	21st to end	Night	40% 5% 11% 22% 17% 5%	2100
May	1st to 10th	Night	51% 5% 11% 19% 12% 2	5318
	11th to 20th	Night	47% 6% 13% 23% 10% 1	4640
	21st to end	Night	51% 4 9% 21% 13% 2	5115
June	1st to 10th	Night	39% 6% 10% 23% 20% 1	1680
	11th to 20th	Night	40% 7% 13% 25% 14% 2	1680
	21st to end	Night	35% 7% 15% 27% 15% 2	1680
July	1st to 10th	Night	41% 8% 14% 20% 15% 3	3640
	11th to 20th	Night	47% 7% 15% 20% 10% 1	3592
	21st to end	Night	37% 6% 12% 22% 22% 1	4065
August	1st to 10th	Night	46% 6% 17% 20% 10% 1	2904
	11th to 20th	Night	43% 4 11% 25% 16% 1	3092
	21st to end	Night	34% 4 12% 31% 18% 1	3586
September	1st to 10th	Night	38% 5% 10% 23% 20% 4	2000
	11th to 20th	Night	33% 5% 9% 25% 25% 4	2000
	21st to end	Night	45% 6% 8% 19% 20% 2	2258
October	1st to 10th	Night	43% 3 9% 22% 22% 2	3920
	11th to 20th	Night	28% 4 10% 29% 25% 5%	3899
	21st to end	Night	27% 3 11% 32% 24% 3	4283
November	1st to 10th	Night	32% 4 12% 27% 20% 4	2667
	11th to 20th	Night	40% 4 9% 25% 18% 4	2732
	21st to end	Night	40% 4 12% 28% 14% 1	2940
December	1st to 10th	Night	42% 3 13% 29% 12% 1	4720
	11th to 20th	Night	46% 4 12% 24% 12% 2	5348
	21st to end	Night	48% 5% 11% 20% 16% 1	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	29% 28% 25% 13% 3 1	220
	11th to 20th	Day	38% 25% 26% 9% 2	272
	21st to end	Day	27% 31% 27% 12% 2 1	363
February	1st to 10th	Day	28% 25% 32% 12% 3	330
	11th to 20th	Day	35% 19% 36% 8% 2	425
	21st to end	Day	32% 21% 30% 15% 2	446
March	1st to 10th	Day	29% 20% 31% 17% 3	540
	11th to 20th	Day	29% 24% 30% 13% 3 1	540
	21st to end	Day	30% 22% 30% 13% 4 1	594
April	1st to 10th	Day	29% 20% 28% 15% 6% 1	540
	11th to 20th	Day	25% 22% 28% 17% 6% 2	532
	21st to end	Day	27% 15% 33% 18% 5% 2	540
May	1st to 10th	Day	29% 18% 28% 17% 7% 2	543
	11th to 20th	Day	22% 16% 31% 21% 8% 2	567
	21st to end	Day	24% 7% 27% 23% 16% 3	617
June	1st to 10th	Day	16% 14% 29% 25% 14% 3	570
	11th to 20th	Day	20% 11% 28% 26% 13% 2	570
	21st to end	Day	15% 10% 31% 28% 12% 5%	570
July	1st to 10th	Day	13% 5% 23% 32% 20% 7%	565
	11th to 20th	Day	9% 5% 26% 33% 22% 6%	544
	21st to end	Day	11% 6% 30% 32% 16% 5%	576
August	1st to 10th	Day	12% 6% 24% 30% 19% 9%	526
	11th to 20th	Day	16% 6% 20% 30% 19% 9%	519
	21st to end	Day	13% 5% 24% 31% 16% 11%	583
September	1st to 10th	Day	18% 9% 21% 26% 19% 8%	530
	11th to 20th	Day	14% 5% 22% 30% 17% 12%	530
	21st to end	Day	26% 11% 24% 22% 15% 4	530
October	1st to 10th	Day	21% 9% 23% 25% 16% 6%	530
	11th to 20th	Day	20% 16% 28% 21% 13% 2	530
	21st to end	Day	20% 16% 32% 21% 9% 2	572
November	1st to 10th	Day	18% 16% 28% 25% 10% 3	425
	11th to 20th	Day	21% 21% 31% 20% 6%	425
	21st to end	Day	29% 20% 34% 12% 5% 1	220
December	1st to 10th	Day	28% 20% 35% 11% 5% 1	220
	11th to 20th	Day	31% 22% 30% 13% 3	220
	21st to end	Day	28% 22% 27% 16% 6% 1	242
January	1st to 10th	Night	21% 20% 38% 18% 3	840
	11th to 20th	Night	27% 18% 30% 21% 3	840
	21st to end	Night	19% 20% 38% 20% 2	924
February	1st to 10th	Night	22% 18% 34% 24% 2	840
	11th to 20th	Night	26% 23% 34% 15% 1	823
	21st to end	Night	24% 20% 35% 18% 3	692
March	1st to 10th	Night	23% 18% 34% 21% 4	840
	11th to 20th	Night	24% 20% 31% 19% 5%	840
	21st to end	Night	22% 18% 36% 19% 5%	924
April	1st to 10th	Night	25% 19% 34% 18% 4	840
	11th to 20th	Night	19% 16% 34% 23% 6%	831
	21st to end	Night	22% 13% 32% 26% 7%	840
May	1st to 10th	Night	26% 11% 28% 28% 7%	656
	11th to 20th	Night	19% 10% 32% 31% 8%	414
	21st to end	Night	19% 7% 24% 36% 13% 1	455
June	1st to 10th	Night	16% 5% 27% 36% 15%	420
	11th to 20th	Night	15% 8% 27% 40% 11%	420
	21st to end	Night	13% 4 25% 46% 12% 1	420
July	1st to 10th	Night	11% 4 20% 43% 20% 2	410
	11th to 20th	Night	8% 4 21% 41% 25% 2	398
	21st to end	Night	11% 3 18% 42% 25% 1	548
August	1st to 10th	Night	12% 3 14% 42% 26% 3	597
	11th to 20th	Night	15% 4 14% 38% 27% 2	706
	21st to end	Night	15% 3 19% 36% 25% 2	880
September	1st to 10th	Night	15% 5% 23% 34% 21% 3	800
	11th to 20th	Night	13% 5% 17% 36% 25% 3	800
	21st to end	Night	22% 6% 19% 32% 20% 1	800
October	1st to 10th	Night	21% 8% 23% 27% 19% 3	800
	11th to 20th	Night	20% 11% 27% 30% 12% 1	800
	21st to end	Night	21% 12% 29% 28% 10%	880
November	1st to 10th	Night	16% 11% 31% 30% 12% 1	820
	11th to 20th	Night	20% 17% 28% 27% 7% 1	840
	21st to end	Night	19% 17% 33% 25% 6%	840
December	1st to 10th	Night	26% 16% 33% 20% 5%	840
	11th to 20th	Night	22% 17% 33% 25% 4	840
	21st to end	Night	23% 16% 32% 27% 2	924

Page generated at 2026-07-13 03:14:48. Version ac07

Copyright © 2026 Attilla Danko.