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 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	16% 7% 2 6% 4 4 4 4 6% 7% 39%	108857
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 41%	110134
Transparency	Day	42% 5% 12% 24% 15% 2	112477
	Night	41% 5% 11% 24% 17% 3	114677
Seeing	Day	21% 14% 28% 22% 11% 4	15266
	Night	20% 13% 29% 28% 10% 1	24743

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	13% 7% 2 8% 4 4 4 3 5% 6% 42%	3597
	11th to 20th	Day	14% 10% 4 11% 5% 5% 4 3 4 6% 34%	3780
	21st to end	Day	17% 9% 3 8% 5% 5% 4 3 5% 5% 37%	4466
February	1st to 10th	Day	15% 9% 3 7% 5% 4 5% 4 5% 7% 35%	1800
	11th to 20th	Day	15% 9% 3 8% 4 4 4 3 6% 6% 37%	1843
	21st to end	Day	18% 9% 3 7% 4 4 4 3 4 6% 36%	1650
March	1st to 10th	Day	25% 6% 2 5% 4 4 4 3 5% 6% 37%	3333
	11th to 20th	Day	10% 5% 2 6% 6% 5% 5% 4 6% 8% 43%	3491
	21st to end	Day	22% 8% 2 5% 4 3 3 2 4 5% 43%	3969
April	1st to 10th	Day	17% 7% 3 6% 4 5% 4 4 5% 7% 37%	2280
	11th to 20th	Day	16% 8% 2 6% 4 3 4 4 6% 6% 42%	2254
	21st to end	Day	17% 6% 2 6% 5% 4 4 4 6% 7% 39%	2280
May	1st to 10th	Day	28% 7% 2 6% 4 4 4 4 5% 7% 30%	4114
	11th to 20th	Day	25% 9% 3 7% 5% 4 4 4 5% 6% 28%	4398
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 44%	4837
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 5% 7% 10% 38%	2660
	11th to 20th	Day	13% 6% 2 6% 4 5% 6% 4 7% 9% 38%	2660
	21st to end	Day	11% 4 2 5% 5% 4 5% 5% 6% 11% 41%	2660
July	1st to 10th	Day	7% 5% 2 6% 6% 7% 6% 6% 9% 10% 36%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	4440
	21st to end	Day	11% 8% 3 8% 5% 6% 6% 5% 6% 7% 35%	4631
August	1st to 10th	Day	20% 6% 2 6% 5% 5% 5% 4 6% 7% 33%	4104
	11th to 20th	Day	15% 5% 2 5% 4 4 5% 4 7% 8% 41%	3826
	21st to end	Day	13% 5% 2 5% 3 4 3 3 5% 8% 48%	4180
September	1st to 10th	Day	16% 6% 2 6% 4 3 4 4 5% 6% 45%	2280
	11th to 20th	Day	12% 5% 2 4 4 3 4 3 6% 7% 50%	2280
	21st to end	Day	20% 8% 3 7% 4 4 4 3 5% 5% 38%	2031
October	1st to 10th	Day	19% 6% 2 4 3 4 4 3 5% 7% 43%	1900
	11th to 20th	Day	17% 5% 2 5% 3 4 4 3 4 7% 46%	1900
	21st to end	Day	18% 7% 2 5% 3 3 3 3 6% 7% 43%	2071
November	1st to 10th	Day	13% 7% 2 4 3 3 3 3 4 7% 50%	1761
	11th to 20th	Day	17% 5% 2 5% 4 3 4 4 5% 7% 45%	1795
	21st to end	Day	16% 7% 2 5% 5% 3 5% 3 6% 7% 41%	1600
December	1st to 10th	Day	15% 8% 2 6% 4 4 4 4 6% 6% 41%	2600
	11th to 20th	Day	22% 9% 2 5% 3 3 3 3 5% 7% 39%	2986
	21st to end	Day	18% 7% 3 7% 4 4 4 4 6% 8% 34%	3960
January	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 5% 7% 44%	6349
	11th to 20th	Night	14% 8% 2 5% 4 4 4 4 6% 7% 43%	6087
	21st to end	Night	17% 7% 3 7% 4 3 3 3 5% 6% 41%	6490
February	1st to 10th	Night	17% 8% 3 6% 5% 3 5% 4 5% 7% 38%	2600
	11th to 20th	Night	18% 7% 3 7% 5% 4 4 3 5% 6% 39%	2441
	21st to end	Night	18% 7% 2 7% 5% 4 4 3 5% 7% 38%	1980
March	1st to 10th	Night	21% 10% 3 6% 4 4 4 3 4 5% 37%	3723
	11th to 20th	Night	11% 7% 2 5% 5% 4 4 3 5% 6% 47%	3497
	21st to end	Night	16% 8% 3 5% 4 3 3 2 4 5% 46%	3661
April	1st to 10th	Night	17% 7% 3 5% 6% 4 4 4 6% 7% 37%	1900
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	1875
	21st to end	Night	18% 6% 2 5% 4 3 3 4 6% 6% 44%	1900
May	1st to 10th	Night	26% 8% 2 6% 3 4 4 4 5% 7% 31%	2857
	11th to 20th	Night	26% 8% 3 8% 5% 4 4 3 5% 7% 29%	2495
	21st to end	Night	14% 5% 3 6% 4 4 5% 4 6% 9% 42%	2738
June	1st to 10th	Night	14% 6% 2 7% 3 4 4 3 6% 8% 42%	1520
	11th to 20th	Night	13% 5% 2 6% 3 5% 5% 4 7% 9% 41%	1520
	21st to end	Night	11% 5% 2 5% 3 4 6% 5% 6% 9% 44%	1520
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 7% 5% 8% 9% 39%	2520
	11th to 20th	Night	8% 5% 2 7% 5% 6% 6% 5% 8% 11% 38%	2520
	21st to end	Night	15% 7% 3 6% 5% 4 5% 4 6% 7% 39%	2918
August	1st to 10th	Night	21% 6% 2 6% 4 4 4 3 7% 8% 34%	2825
	11th to 20th	Night	15% 7% 3 7% 5% 4 5% 4 5% 6% 41%	2969
	21st to end	Night	13% 5% 2 5% 3 4 4 4 6% 8% 48%	3476
September	1st to 10th	Night	14% 7% 2 6% 4 4 3 2 4 6% 47%	1900
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 6% 52%	1900
	21st to end	Night	20% 6% 2 5% 3 4 5% 4 5% 5% 41%	2144
October	1st to 10th	Night	20% 6% 2 5% 4 4 3 3 4 6% 44%	2280
	11th to 20th	Night	16% 6% 2 6% 3 4 3 3 4 6% 49%	2280
	21st to end	Night	18% 6% 2 4 4 3 3 2 5% 7% 46%	2526
November	1st to 10th	Night	11% 5% 2 4 4 3 4 3 5% 6% 53%	2537
	11th to 20th	Night	15% 7% 3 5% 4 3 3 3 4 6% 45%	2602
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 8% 43%	2800
December	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 5% 7% 42%	4580
	11th to 20th	Night	23% 7% 2 5% 3 4 4 3 5% 6% 39%	5208
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 6% 35%	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	43% 3 10% 25% 17% 2	3598
	11th to 20th	Day	51% 4 8% 18% 15% 4	3812
	21st to end	Day	49% 4 11% 21% 14% 1	4466
February	1st to 10th	Day	48% 6% 12% 22% 11% 1	1800
	11th to 20th	Day	47% 4 10% 23% 14% 2	1852
	21st to end	Day	50% 4 9% 22% 11% 3	1650
March	1st to 10th	Day	48% 5% 9% 26% 10% 2	3336
	11th to 20th	Day	38% 5% 11% 28% 14% 3	3491
	21st to end	Day	46% 3 9% 21% 19% 3	3969
April	1st to 10th	Day	44% 4 10% 22% 15% 5%	2280
	11th to 20th	Day	42% 5% 11% 22% 16% 4	2254
	21st to end	Day	43% 4 11% 22% 16% 4	2280
May	1st to 10th	Day	54% 5% 9% 20% 10% 2	4126
	11th to 20th	Day	55% 6% 12% 18% 8% 1	4402
	21st to end	Day	35% 7% 13% 27% 16% 2	4837
June	1st to 10th	Day	40% 7% 13% 24% 15% 2	2660
	11th to 20th	Day	40% 6% 15% 25% 11% 3	2660
	21st to end	Day	36% 7% 15% 26% 15% 1	2660
July	1st to 10th	Day	39% 8% 15% 22% 13% 2	4370
	11th to 20th	Day	37% 7% 16% 25% 14% 1	4365
	21st to end	Day	46% 6% 11% 19% 16% 1	4483
August	1st to 10th	Day	49% 7% 11% 24% 10%	4091
	11th to 20th	Day	39% 5% 11% 31% 13% 1	3865
	21st to end	Day	34% 5% 11% 29% 19% 2	4180
September	1st to 10th	Day	40% 5% 10% 21% 20% 4	2280
	11th to 20th	Day	33% 5% 9% 27% 23% 4	2280
	21st to end	Day	48% 4 7% 18% 20% 2	2031
October	1st to 10th	Day	38% 3 9% 21% 25% 4	3160
	11th to 20th	Day	28% 3 12% 28% 23% 6%	3140
	21st to end	Day	26% 3 13% 27% 27% 3	3397
November	1st to 10th	Day	35% 3 14% 25% 20% 4	1761
	11th to 20th	Day	39% 4 11% 25% 19% 2	1795
	21st to end	Day	40% 5% 12% 31% 10% 2	1600
December	1st to 10th	Day	43% 3 17% 25% 10% 2	2600
	11th to 20th	Day	46% 3 13% 29% 8% 1	2986
	21st to end	Day	47% 4 14% 21% 13% 1	3960
January	1st to 10th	Night	39% 3 11% 25% 19% 4	6349
	11th to 20th	Night	39% 5% 13% 22% 16% 6%	6130
	21st to end	Night	44% 3 11% 24% 17% 2	6490
February	1st to 10th	Night	46% 4 13% 25% 10% 2	2600
	11th to 20th	Night	47% 4 9% 21% 17% 3	2443
	21st to end	Night	46% 4 9% 22% 16% 3	1980
March	1st to 10th	Night	49% 4 9% 24% 12% 2	3733
	11th to 20th	Night	36% 5% 12% 29% 16% 2	3498
	21st to end	Night	42% 3 8% 19% 23% 5%	3661
April	1st to 10th	Night	44% 4 10% 22% 15% 4	1900
	11th to 20th	Night	41% 5% 10% 20% 21% 2	1875
	21st to end	Night	40% 5% 11% 22% 17% 5%	1900
May	1st to 10th	Night	53% 5% 9% 20% 11% 2	2864
	11th to 20th	Night	55% 7% 14% 13% 11% 1	2496
	21st to end	Night	39% 6% 13% 23% 15% 4	2739
June	1st to 10th	Night	40% 6% 10% 23% 19% 2	1520
	11th to 20th	Night	37% 7% 14% 26% 14% 2	1520
	21st to end	Night	34% 7% 15% 27% 14% 2	1520
July	1st to 10th	Night	39% 8% 16% 17% 14% 5%	2480
	11th to 20th	Night	38% 7% 16% 24% 13% 1	2472
	21st to end	Night	43% 6% 13% 18% 19% 1	2825
August	1st to 10th	Night	47% 6% 17% 20% 10% 1	2814
	11th to 20th	Night	43% 4 11% 24% 16% 1	2996
	21st to end	Night	34% 4 12% 31% 18% 1	3476
September	1st to 10th	Night	38% 5% 10% 23% 20% 4	1900
	11th to 20th	Night	32% 5% 9% 25% 25% 4	1900
	21st to end	Night	44% 6% 7% 19% 21% 2	2144
October	1st to 10th	Night	44% 3 9% 21% 21% 2	3800
	11th to 20th	Night	27% 4 9% 30% 25% 5%	3779
	21st to end	Night	27% 3 11% 33% 24% 3	4150
November	1st to 10th	Night	32% 5% 12% 27% 21% 4	2537
	11th to 20th	Night	40% 4 9% 25% 17% 4	2602
	21st to end	Night	39% 4 13% 28% 14% 1	2800
December	1st to 10th	Night	42% 3 13% 29% 12% 1	4580
	11th to 20th	Night	46% 4 12% 24% 12% 2	5208
	21st to end	Night	48% 5% 11% 20% 16% 1	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	30% 28% 26% 13% 4 1	200
	11th to 20th	Day	35% 25% 28% 10% 2	247
	21st to end	Day	24% 31% 29% 13% 2 1	330
February	1st to 10th	Day	29% 24% 31% 12% 3	300
	11th to 20th	Day	35% 21% 34% 8% 2	390
	21st to end	Day	33% 19% 30% 16% 2	414
March	1st to 10th	Day	27% 21% 32% 18% 3	500
	11th to 20th	Day	26% 26% 31% 13% 3 1	464
	21st to end	Day	29% 21% 31% 14% 4 1	506
April	1st to 10th	Day	27% 21% 29% 16% 6% 1	460
	11th to 20th	Day	24% 21% 28% 18% 6% 2	452
	21st to end	Day	28% 14% 33% 18% 4 3	460
May	1st to 10th	Day	29% 17% 25% 18% 8% 2	463
	11th to 20th	Day	23% 15% 30% 22% 8% 2	487
	21st to end	Day	19% 6% 29% 25% 19% 3	529
June	1st to 10th	Day	16% 14% 30% 24% 14% 3	490
	11th to 20th	Day	18% 10% 28% 27% 14% 3	490
	21st to end	Day	14% 10% 32% 27% 12% 4	490
July	1st to 10th	Day	13% 5% 23% 31% 20% 8%	485
	11th to 20th	Day	8% 5% 25% 34% 23% 6%	484
	21st to end	Day	11% 6% 30% 30% 17% 5%	532
August	1st to 10th	Day	13% 6% 24% 28% 20% 8%	486
	11th to 20th	Day	16% 5% 20% 30% 19% 9%	479
	21st to end	Day	13% 5% 24% 31% 16% 11%	539
September	1st to 10th	Day	18% 9% 20% 26% 19% 8%	490
	11th to 20th	Day	14% 6% 22% 29% 17% 12%	490
	21st to end	Day	27% 11% 23% 21% 15% 4	490
October	1st to 10th	Day	22% 10% 24% 23% 15% 5%	490
	11th to 20th	Day	19% 15% 28% 22% 14% 2	490
	21st to end	Day	20% 15% 32% 22% 10% 2	529
November	1st to 10th	Day	18% 15% 28% 26% 11% 3	395
	11th to 20th	Day	19% 21% 31% 21% 7%	395
	21st to end	Day	27% 20% 33% 14% 6% 1	200
December	1st to 10th	Day	27% 21% 35% 12% 5% 1	200
	11th to 20th	Day	31% 22% 30% 14% 4 1	200
	21st to end	Day	25% 22% 28% 17% 7% 1	220
January	1st to 10th	Night	21% 20% 37% 18% 3	800
	11th to 20th	Night	26% 18% 31% 22% 3	800
	21st to end	Night	19% 19% 38% 21% 2	880
February	1st to 10th	Night	23% 18% 34% 24% 2	800
	11th to 20th	Night	26% 23% 35% 15% 2	783
	21st to end	Night	25% 20% 35% 17% 3	660
March	1st to 10th	Night	22% 19% 34% 21% 4	800
	11th to 20th	Night	24% 20% 32% 19% 5% 1	767
	21st to end	Night	22% 17% 36% 20% 5%	836
April	1st to 10th	Night	24% 19% 34% 19% 4	760
	11th to 20th	Night	19% 16% 34% 23% 7%	751
	21st to end	Night	23% 13% 32% 25% 7%	760
May	1st to 10th	Night	25% 10% 28% 28% 8%	594
	11th to 20th	Night	20% 9% 31% 32% 9% 1	374
	21st to end	Night	16% 6% 25% 37% 14% 1	411
June	1st to 10th	Night	17% 5% 26% 37% 16%	380
	11th to 20th	Night	13% 6% 27% 41% 12%	380
	21st to end	Night	12% 3 25% 48% 12% 1	380
July	1st to 10th	Night	11% 4 21% 43% 20% 2	370
	11th to 20th	Night	7% 4 22% 40% 26% 2	368
	21st to end	Night	11% 3 18% 42% 24% 1	520
August	1st to 10th	Night	12% 3 14% 43% 25% 3	567
	11th to 20th	Night	15% 4 14% 38% 27% 2	670
	21st to end	Night	15% 3 18% 36% 25% 2	836
September	1st to 10th	Night	15% 5% 23% 33% 21% 3	760
	11th to 20th	Night	14% 5% 18% 34% 26% 4	760
	21st to end	Night	23% 6% 19% 31% 20% 1	760
October	1st to 10th	Night	21% 8% 23% 27% 17% 3	760
	11th to 20th	Night	19% 11% 27% 31% 13% 1	760
	21st to end	Night	22% 11% 28% 28% 10%	836
November	1st to 10th	Night	15% 11% 31% 30% 12% 1	780
	11th to 20th	Night	20% 17% 28% 27% 7% 1	800
	21st to end	Night	19% 17% 34% 24% 7%	800
December	1st to 10th	Night	26% 16% 32% 20% 6%	800
	11th to 20th	Night	21% 16% 34% 25% 4	800
	21st to end	Night	23% 15% 33% 28% 2	880

Page generated at 2025-03-09 08:08:43. Version ac07

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