Adams Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Adams Observing Site clear sky chart from 2005-11-06 to 2024-11-01.

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	15% 9% 3 7% 4 4 4 4 6% 7% 37%	101039
	Night	15% 9% 3 7% 4 4 4 3 5% 7% 38%	97855
Transparency	Day	46% 5% 10% 23% 14% 2	100851
	Night	45% 5% 9% 23% 15% 2	97712
Seeing	Day	23% 10% 25% 22% 14% 6%	14795
	Night	21% 9% 23% 28% 17% 2	24835

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	17% 17% 6% 10% 5% 4 4 3 5% 6% 23%	2836
	11th to 20th	Day	17% 16% 7% 14% 7% 4 3 2 3 4 23%	2840
	21st to end	Day	27% 19% 5% 6% 4 3 3 2 4 4 23%	3124
February	1st to 10th	Day	19% 13% 4 11% 5% 4 4 2 4 5% 30%	1790
	11th to 20th	Day	20% 11% 4 9% 4 4 5% 3 5% 5% 30%	1848
	21st to end	Day	21% 12% 3 7% 5% 3 4 3 5% 5% 31%	1570
March	1st to 10th	Day	23% 13% 3 8% 3 4 4 3 5% 5% 29%	3216
	11th to 20th	Day	15% 7% 3 6% 4 3 4 3 5% 7% 44%	3480
	21st to end	Day	17% 8% 2 7% 4 4 4 3 6% 7% 37%	3815
April	1st to 10th	Day	15% 9% 3 7% 5% 4 4 3 5% 7% 38%	2165
	11th to 20th	Day	17% 8% 3 6% 5% 4 4 4 5% 6% 39%	2329
	21st to end	Day	17% 7% 2 6% 5% 5% 5% 4 5% 7% 36%	2470
May	1st to 10th	Day	19% 10% 3 8% 6% 5% 5% 4 5% 6% 29%	4082
	11th to 20th	Day	18% 10% 3 7% 4 4 4 4 5% 7% 34%	4081
	21st to end	Day	11% 6% 3 7% 5% 6% 6% 5% 8% 10% 34%	4476
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 7% 41%	2470
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	2470
	21st to end	Day	10% 5% 2 6% 6% 5% 6% 5% 6% 9% 39%	2470
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 10% 39%	4120
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 4 8% 11% 40%	4120
	21st to end	Day	16% 10% 4 9% 6% 6% 6% 5% 6% 7% 25%	4466
August	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 7% 10% 42%	4104
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 11% 38%	4044
	21st to end	Day	6% 3 1 4 4 5% 4 4 6% 9% 54%	4261
September	1st to 10th	Day	13% 5% 2 6% 4 4 5% 3 5% 8% 45%	2114
	11th to 20th	Day	12% 6% 2 5% 3 4 4 4 5% 8% 47%	2090
	21st to end	Day	18% 5% 3 6% 3 4 3 3 4 6% 44%	2090
October	1st to 10th	Day	11% 5% 2 5% 3 4 3 2 6% 8% 51%	2090
	11th to 20th	Day	15% 6% 2 6% 3 3 4 3 4 5% 50%	1901
	21st to end	Day	21% 7% 2 6% 3 3 4 3 4 6% 42%	2028
November	1st to 10th	Day	12% 7% 1 5% 3 4 3 3 4 4 54%	1672
	11th to 20th	Day	15% 10% 3 6% 3 4 3 3 5% 5% 42%	1710
	21st to end	Day	18% 10% 3 7% 4 4 3 3 5% 5% 39%	1710
December	1st to 10th	Day	23% 13% 4 8% 4 3 4 3 6% 4 27%	1710
	11th to 20th	Day	16% 14% 5% 8% 4 5% 4 3 4 5% 32%	2153
	21st to end	Day	19% 17% 4 10% 6% 5% 4 4 5% 7% 20%	3124
January	1st to 10th	Night	16% 17% 6% 10% 6% 4 4 3 5% 5% 24%	4109
	11th to 20th	Night	20% 16% 5% 11% 5% 3 3 3 3 3 27%	4120
	21st to end	Night	23% 15% 6% 8% 5% 3 3 2 4 5% 27%	4532
February	1st to 10th	Night	21% 12% 4 8% 5% 5% 4 3 4 5% 29%	2387
	11th to 20th	Night	22% 11% 3 9% 5% 4 4 3 4 5% 31%	2218
	21st to end	Night	23% 12% 4 9% 4 4 4 3 4 5% 29%	1884
March	1st to 10th	Night	21% 13% 3 6% 4 4 4 3 5% 6% 33%	3622
	11th to 20th	Night	14% 7% 2 6% 3 4 4 3 4 6% 46%	3480
	21st to end	Night	13% 7% 3 7% 5% 4 5% 4 6% 8% 38%	3817
April	1st to 10th	Night	14% 7% 2 5% 4 4 4 4 6% 7% 41%	2030
	11th to 20th	Night	14% 7% 2 5% 5% 4 3 3 6% 7% 44%	1798
	21st to end	Night	17% 7% 3 7% 5% 4 5% 3 5% 6% 39%	1710
May	1st to 10th	Night	20% 11% 3 8% 5% 5% 6% 4 5% 6% 27%	2813
	11th to 20th	Night	19% 8% 2 6% 4 3 3 4 5% 8% 37%	2812
	21st to end	Night	8% 6% 2 6% 5% 5% 5% 5% 7% 9% 43%	3079
June	1st to 10th	Night	8% 6% 2 5% 4 4 4 5% 8% 9% 45%	1710
	11th to 20th	Night	5% 4 1 6% 5% 5% 5% 5% 7% 9% 47%	1710
	21st to end	Night	8% 5% 2 5% 4 4 5% 5% 7% 11% 44%	1710
July	1st to 10th	Night	7% 5% 2 6% 4 5% 5% 4 7% 10% 44%	2840
	11th to 20th	Night	7% 5% 2 6% 4 5% 4 4 7% 9% 46%	2840
	21st to end	Night	13% 9% 4 8% 5% 5% 5% 4 6% 8% 34%	3087
August	1st to 10th	Night	7% 5% 2 7% 4 4 5% 4 7% 10% 43%	2825
	11th to 20th	Night	9% 6% 3 8% 4 5% 5% 4 7% 9% 42%	2785
	21st to end	Night	4 4 1 4 3 4 3 4 5% 9% 58%	3378
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 5% 8% 48%	2047
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 6% 6% 50%	2090
	21st to end	Night	12% 6% 2 7% 6% 4 4 3 3 6% 47%	2090
October	1st to 10th	Night	11% 4 2 4 3 4 3 3 5% 7% 54%	2090
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 5% 7% 48%	2278
	21st to end	Night	18% 7% 2 5% 4 3 3 3 4 6% 44%	2567
November	1st to 10th	Night	13% 7% 2 5% 4 4 3 3 4 5% 51%	2413
	11th to 20th	Night	17% 8% 3 6% 3 3 3 4 4 6% 43%	2470
	21st to end	Night	18% 10% 3 4 4 3 3 4 4 6% 39%	2470
December	1st to 10th	Night	21% 14% 4 7% 3 4 4 3 5% 6% 30%	2470
	11th to 20th	Night	18% 12% 5% 8% 4 4 3 3 5% 5% 33%	3042
	21st to end	Night	19% 18% 4 9% 5% 5% 5% 4 5% 6% 20%	4532

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	61% 5% 9% 15% 9% 1	2837
	11th to 20th	Day	67% 3 6% 18% 6% 1	2840
	21st to end	Day	66% 3 6% 20% 5% 1	3124
February	1st to 10th	Day	59% 3 8% 18% 11% 1	1790
	11th to 20th	Day	57% 4 7% 19% 11% 2	1858
	21st to end	Day	55% 3 8% 21% 11% 3	1570
March	1st to 10th	Day	56% 5% 7% 18% 10% 4	3216
	11th to 20th	Day	40% 5% 10% 26% 17% 1	3480
	21st to end	Day	46% 5% 9% 26% 12% 1	3815
April	1st to 10th	Day	47% 4 8% 25% 13% 3	2165
	11th to 20th	Day	46% 4 7% 22% 16% 4	2329
	21st to end	Day	47% 6% 10% 23% 11% 3	2470
May	1st to 10th	Day	53% 7% 9% 21% 9% 1	4120
	11th to 20th	Day	50% 6% 9% 22% 12% 1	4085
	21st to end	Day	40% 10% 13% 18% 16% 3	4489
June	1st to 10th	Day	39% 7% 11% 26% 16% 1	2470
	11th to 20th	Day	38% 6% 14% 22% 18% 2	2470
	21st to end	Day	40% 7% 13% 21% 16% 3	2470
July	1st to 10th	Day	40% 7% 14% 23% 15% 1	4055
	11th to 20th	Day	37% 6% 11% 33% 13% 1	4051
	21st to end	Day	56% 6% 9% 17% 10% 2	4324
August	1st to 10th	Day	35% 7% 14% 31% 12% 1	4091
	11th to 20th	Day	39% 5% 11% 30% 15% 1	4083
	21st to end	Day	26% 5% 15% 31% 21% 3	4260
September	1st to 10th	Day	37% 5% 12% 21% 18% 6%	2114
	11th to 20th	Day	36% 3 11% 25% 22% 3	2090
	21st to end	Day	41% 4 8% 25% 21% 2	2090
October	1st to 10th	Day	32% 4 10% 26% 25% 3	2090
	11th to 20th	Day	37% 4 7% 26% 23% 3	1901
	21st to end	Day	44% 4 8% 25% 17% 2	2028
November	1st to 10th	Day	35% 3 8% 27% 23% 4	1672
	11th to 20th	Day	45% 2 7% 22% 19% 4	1710
	21st to end	Day	49% 3 8% 22% 18% 2	1710
December	1st to 10th	Day	60% 3 9% 19% 8% 1	1710
	11th to 20th	Day	55% 4 8% 18% 14% 1	2150
	21st to end	Day	63% 5% 9% 16% 5% 1	3124
January	1st to 10th	Night	62% 5% 7% 16% 9% 1	4109
	11th to 20th	Night	63% 3 5% 19% 9% 2	4120
	21st to end	Night	62% 3 7% 19% 8% 1	4532
February	1st to 10th	Night	58% 3 8% 20% 9% 1	2387
	11th to 20th	Night	56% 3 7% 20% 12% 1	2219
	21st to end	Night	60% 3 9% 14% 11% 3	1884
March	1st to 10th	Night	53% 4 6% 23% 13% 2	3622
	11th to 20th	Night	38% 6% 9% 28% 17% 2	3480
	21st to end	Night	43% 6% 9% 24% 16% 1	3817
April	1st to 10th	Night	40% 6% 10% 24% 18% 2	2030
	11th to 20th	Night	39% 5% 10% 21% 19% 6%	1798
	21st to end	Night	45% 5% 11% 23% 14% 2	1710
May	1st to 10th	Night	55% 7% 9% 19% 8% 2	2840
	11th to 20th	Night	45% 7% 12% 24% 11% 1	2813
	21st to end	Night	34% 9% 13% 24% 18% 4	3087
June	1st to 10th	Night	32% 8% 15% 26% 16% 4	1710
	11th to 20th	Night	31% 8% 15% 24% 19% 3	1710
	21st to end	Night	34% 7% 15% 25% 15% 5%	1710
July	1st to 10th	Night	35% 8% 14% 23% 17% 3	2795
	11th to 20th	Night	33% 6% 13% 30% 16% 2	2786
	21st to end	Night	48% 6% 9% 21% 14% 2	2988
August	1st to 10th	Night	35% 7% 14% 31% 12% 1	2814
	11th to 20th	Night	38% 5% 10% 28% 17% 1	2812
	21st to end	Night	22% 6% 15% 32% 22% 4	3378
September	1st to 10th	Night	34% 6% 11% 23% 19% 7%	2047
	11th to 20th	Night	33% 4 10% 24% 25% 4	2090
	21st to end	Night	39% 5% 7% 22% 24% 3	2090
October	1st to 10th	Night	30% 4 10% 25% 25% 5%	2090
	11th to 20th	Night	37% 4 8% 24% 23% 4	2278
	21st to end	Night	43% 3 6% 23% 20% 4	2567
November	1st to 10th	Night	37% 4 7% 25% 23% 4	2413
	11th to 20th	Night	43% 3 7% 20% 22% 5%	2470
	21st to end	Night	47% 4 8% 25% 15% 2	2470
December	1st to 10th	Night	56% 3 10% 19% 11% 1	2470
	11th to 20th	Night	55% 3 8% 22% 11% 1	3044
	21st to end	Night	64% 6% 8% 15% 8%	4532

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	33% 19% 31% 13% 3 1	270
	11th to 20th	Day	41% 16% 30% 12%	270
	21st to end	Day	36% 23% 28% 10% 3	297
February	1st to 10th	Day	33% 21% 31% 12% 2	270
	11th to 20th	Day	41% 22% 29% 6% 2	270
	21st to end	Day	38% 15% 39% 8% 1	225
March	1st to 10th	Day	36% 17% 29% 13% 4	327
	11th to 20th	Day	29% 20% 30% 16% 4	460
	21st to end	Day	35% 15% 30% 15% 6%	506
April	1st to 10th	Day	30% 15% 29% 17% 8% 2	460
	11th to 20th	Day	26% 15% 29% 20% 7% 4	452
	21st to end	Day	26% 16% 32% 19% 6% 2	460
May	1st to 10th	Day	28% 15% 27% 18% 9% 3	463
	11th to 20th	Day	23% 8% 29% 21% 13% 5%	487
	21st to end	Day	15% 6% 25% 27% 18% 8%	529
June	1st to 10th	Day	16% 5% 24% 30% 17% 8%	490
	11th to 20th	Day	13% 5% 22% 33% 18% 9%	490
	21st to end	Day	14% 6% 26% 27% 18% 10%	490
July	1st to 10th	Day	18% 2 16% 24% 20% 20%	485
	11th to 20th	Day	14% 3 18% 30% 20% 14%	484
	21st to end	Day	16% 3 17% 29% 22% 14%	532
August	1st to 10th	Day	15% 2 17% 26% 26% 13%	486
	11th to 20th	Day	14% 4 16% 31% 23% 12%	479
	21st to end	Day	11% 3 13% 31% 27% 16%	539
September	1st to 10th	Day	16% 2 14% 26% 29% 13%	490
	11th to 20th	Day	14% 3 13% 27% 31% 12%	490
	21st to end	Day	23% 7% 20% 23% 21% 7%	490
October	1st to 10th	Day	15% 4 21% 31% 22% 7%	490
	11th to 20th	Day	18% 12% 26% 25% 13% 5%	490
	21st to end	Day	28% 7% 29% 24% 10% 1	477
November	1st to 10th	Day	19% 9% 37% 25% 7% 4	270
	11th to 20th	Day	32% 10% 32% 18% 7% 1	270
	21st to end	Day	28% 13% 36% 16% 6% 1	270
December	1st to 10th	Day	34% 17% 29% 15% 5% 1	270
	11th to 20th	Day	32% 14% 32% 17% 5%	270
	21st to end	Day	37% 17% 31% 12% 4	297
January	1st to 10th	Night	29% 18% 29% 19% 5%	760
	11th to 20th	Night	34% 17% 28% 19% 3	760
	21st to end	Night	27% 18% 32% 22% 2	836
February	1st to 10th	Night	31% 14% 30% 22% 3	760
	11th to 20th	Night	33% 17% 31% 17% 2	743
	21st to end	Night	34% 14% 34% 16% 2	628
March	1st to 10th	Night	28% 15% 29% 23% 6%	760
	11th to 20th	Night	28% 17% 27% 20% 7% 1	760
	21st to end	Night	23% 14% 31% 25% 7%	836
April	1st to 10th	Night	23% 11% 30% 27% 10%	700
	11th to 20th	Night	21% 12% 28% 28% 11% 1	563
	21st to end	Night	21% 8% 33% 28% 9% 1	570
May	1st to 10th	Night	23% 7% 26% 28% 13% 3	570
	11th to 20th	Night	18% 4 22% 35% 20% 1	561
	21st to end	Night	11% 2 19% 35% 28% 5%	617
June	1st to 10th	Night	12% 3 17% 42% 24% 3	570
	11th to 20th	Night	7% 3 14% 41% 30% 5%	570
	21st to end	Night	12% 2 17% 38% 26% 5%	570
July	1st to 10th	Night	14% 1 12% 29% 33% 11%	555
	11th to 20th	Night	8% 1 11% 36% 38% 5%	552
	21st to end	Night	13% 2 9% 33% 37% 6%	624
August	1st to 10th	Night	10% 2 7% 35% 40% 7%	567
	11th to 20th	Night	11% 2 8% 37% 36% 7%	564
	21st to end	Night	11% 1 9% 31% 40% 8%	627
September	1st to 10th	Night	14% 2 9% 34% 36% 6%	717
	11th to 20th	Night	15% 2 11% 31% 35% 6%	760
	21st to end	Night	15% 5% 19% 31% 28% 2	760
October	1st to 10th	Night	13% 4 18% 32% 28% 5%	760
	11th to 20th	Night	19% 7% 24% 30% 17% 3	760
	21st to end	Night	23% 9% 26% 28% 13% 1	836
November	1st to 10th	Night	18% 8% 24% 31% 17% 2	743
	11th to 20th	Night	24% 12% 28% 26% 11%	760
	21st to end	Night	26% 10% 24% 29% 10% 1	760
December	1st to 10th	Night	32% 13% 26% 24% 5%	760
	11th to 20th	Night	25% 14% 28% 26% 6% 1	760
	21st to end	Night	32% 14% 27% 24% 4	836

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