Putman Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Putman Mountain Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	9% 5% 2 5% 3 4 4 4 5% 7% 52%	126383
	Night	9% 4 2 4 3 3 3 3 5% 7% 56%	123300
Transparency	Day	31% 5% 10% 21% 21% 12%	130188
	Night	29% 5% 10% 21% 21% 14%	127558
Seeing	Day	11% 9% 24% 31% 20% 5%	16113
	Night	11% 8% 31% 36% 13% 1	25969

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% 9% 3 4 2 2 3 2 4 5% 56%	4077
	11th to 20th	Day	12% 5% 1 4 2 3 3 3 4 6% 58%	4080
	21st to end	Day	18% 7% 2 5% 3 3 3 2 3 6% 48%	4925
February	1st to 10th	Day	13% 6% 2 5% 2 3 3 2 4 6% 53%	2000
	11th to 20th	Day	12% 7% 2 5% 2 3 4 4 5% 6% 50%	1949
	21st to end	Day	13% 6% 2 4 3 3 3 3 5% 5% 54%	1650
March	1st to 10th	Day	8% 6% 2 5% 3 3 4 3 4 7% 56%	4755
	11th to 20th	Day	12% 4 2 5% 4 3 3 3 4 5% 55%	4980
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 7% 52%	5462
April	1st to 10th	Day	10% 6% 2 6% 5% 4 4 4 5% 7% 49%	2200
	11th to 20th	Day	13% 7% 2 6% 3 3 4 3 5% 6% 48%	2284
	21st to end	Day	9% 5% 2 5% 5% 4 4 3 5% 6% 52%	2503
May	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 5% 7% 8% 41%	5862
	11th to 20th	Day	8% 6% 2 6% 4 4 5% 4 6% 8% 46%	5862
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	6434
June	1st to 10th	Day	4 3 1 4 4 4 5% 4 7% 10% 53%	2600
	11th to 20th	Day	4 4 2 4 3 4 4 4 7% 10% 56%	2600
	21st to end	Day	5% 3 1 4 4 5% 5% 6% 7% 10% 51%	2600
July	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 8% 41%	5900
	11th to 20th	Day	3 3 2 4 3 4 5% 4 7% 10% 55%	5900
	21st to end	Day	5% 3 1 5% 3 4 5% 4 6% 11% 53%	6422
August	1st to 10th	Day	1 1 1 2 2 3 3 3 5% 8% 72%	4089
	11th to 20th	Day	4 2 1 3 3 3 4 3 6% 9% 62%	3846
	21st to end	Day	3 3 2 4 4 4 6% 5% 8% 11% 51%	4227
September	1st to 10th	Day	10% 5% 2 6% 4 4 5% 3 4 7% 49%	2200
	11th to 20th	Day	10% 5% 2 6% 4 5% 4 4 6% 7% 48%	2200
	21st to end	Day	9% 2 1 4 3 4 5% 4 6% 7% 55%	2200
October	1st to 10th	Day	4 4 1 5% 3 3 3 3 5% 7% 62%	2123
	11th to 20th	Day	10% 5% 1 5% 3 3 3 2 5% 5% 59%	2009
	21st to end	Day	9% 4 2 4 2 3 2 2 4 5% 62%	2090
November	1st to 10th	Day	10% 6% 2 4 3 3 4 3 5% 7% 53%	1935
	11th to 20th	Day	8% 3 1 5% 3 3 3 4 5% 7% 59%	1800
	21st to end	Day	12% 6% 2 5% 4 3 3 2 4 6% 53%	1800
December	1st to 10th	Day	19% 9% 3 6% 4 2 3 2 4 5% 44%	2940
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 4 6% 6% 47%	3391
	21st to end	Day	8% 6% 1 4 2 3 2 2 3 5% 63%	4488
January	1st to 10th	Night	12% 6% 2 5% 3 2 3 2 3 5% 57%	5888
	11th to 20th	Night	9% 3 1 3 2 1 2 2 4 6% 67%	5900
	21st to end	Night	20% 8% 2 5% 3 3 3 2 3 5% 46%	6094
February	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 6% 55%	2400
	11th to 20th	Night	13% 7% 2 5% 2 3 3 2 4 6% 53%	2338
	21st to end	Night	13% 5% 2 4 3 3 3 3 5% 7% 51%	1980
March	1st to 10th	Night	7% 5% 2 5% 3 3 4 3 6% 9% 53%	5105
	11th to 20th	Night	11% 5% 1 4 4 3 4 3 4 5% 55%	4980
	21st to end	Night	8% 5% 2 5% 3 3 3 3 5% 8% 55%	5467
April	1st to 10th	Night	8% 5% 2 4 3 4 4 3 5% 8% 55%	2200
	11th to 20th	Night	9% 5% 2 5% 4 4 3 3 5% 7% 52%	2061
	21st to end	Night	9% 4 2 4 4 2 3 4 6% 8% 55%	1895
May	1st to 10th	Night	14% 6% 2 5% 4 3 4 3 5% 8% 47%	4053
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 4 6% 8% 52%	4053
	21st to end	Night	8% 5% 2 6% 4 4 4 4 7% 11% 44%	4443
June	1st to 10th	Night	2 2 1 3 3 4 4 3 7% 11% 62%	1800
	11th to 20th	Night	3 2 1 3 3 2 3 3 6% 9% 66%	1800
	21st to end	Night	3 3 2 3 3 3 3 4 6% 8% 62%	1800
July	1st to 10th	Night	7% 5% 2 6% 4 4 5% 3 7% 10% 47%	4078
	11th to 20th	Night	2 2 1 3 3 3 3 3 6% 11% 63%	4077
	21st to end	Night	2 2 1 4 3 4 4 4 8% 12% 57%	4449
August	1st to 10th	Night	1 1 2 2 2 3 2 4 6% 77%	3052
	11th to 20th	Night	2 2 1 3 2 3 4 4 6% 9% 64%	3213
	21st to end	Night	3 2 1 4 3 3 4 4 7% 12% 57%	3678
September	1st to 10th	Night	7% 5% 2 4 3 4 5% 3 6% 8% 54%	2200
	11th to 20th	Night	9% 4 2 4 4 5% 4 4 6% 9% 49%	2200
	21st to end	Night	8% 2 1 3 3 4 4 4 6% 8% 59%	2200
October	1st to 10th	Night	4 2 1 2 2 3 3 2 4 7% 69%	2123
	11th to 20th	Night	10% 3 1 3 3 3 3 3 4 6% 61%	2150
	21st to end	Night	10% 5% 1 3 3 3 2 3 4 4 63%	2508
November	1st to 10th	Night	10% 4 1 4 3 3 3 2 4 6% 61%	2359
	11th to 20th	Night	6% 4 2 4 3 3 3 3 4 7% 62%	2600
	21st to end	Night	13% 4 2 4 4 4 4 3 5% 6% 53%	2600
December	1st to 10th	Night	17% 7% 2 5% 3 3 4 3 5% 5% 45%	4250
	11th to 20th	Night	8% 7% 2 6% 4 4 4 4 5% 6% 50%	4816
	21st to end	Night	8% 4 2 5% 2 3 3 2 4 5% 63%	6490

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	33% 3 3 23% 24% 14%	4078
	11th to 20th	Day	30% 2 5% 17% 27% 19%	4080
	21st to end	Day	40% 2 5% 10% 27% 15%	4925
February	1st to 10th	Day	36% 4 6% 13% 21% 21%	2000
	11th to 20th	Day	35% 4 6% 20% 19% 16%	1959
	21st to end	Day	35% 3 5% 16% 22% 19%	1650
March	1st to 10th	Day	30% 4 5% 17% 19% 26%	4755
	11th to 20th	Day	34% 3 7% 8% 15% 33%	4980
	21st to end	Day	33% 4 8% 18% 22% 14%	5464
April	1st to 10th	Day	36% 5% 8% 17% 18% 16%	2200
	11th to 20th	Day	39% 4 7% 16% 22% 12%	2284
	21st to end	Day	36% 5% 6% 23% 20% 10%	2503
May	1st to 10th	Day	40% 5% 11% 17% 19% 7%	5900
	11th to 20th	Day	35% 5% 10% 15% 22% 13%	5866
	21st to end	Day	40% 6% 11% 25% 15% 4	6447
June	1st to 10th	Day	27% 5% 13% 29% 21% 4	2600
	11th to 20th	Day	25% 6% 12% 27% 23% 6%	2600
	21st to end	Day	29% 8% 14% 25% 19% 5%	2600
July	1st to 10th	Day	41% 7% 16% 29% 7%	5836
	11th to 20th	Day	24% 7% 16% 35% 16% 3	5831
	21st to end	Day	25% 7% 18% 29% 19% 1	6240
August	1st to 10th	Day	12% 4 11% 39% 32% 1	4075
	11th to 20th	Day	20% 4 21% 38% 14% 2	3882
	21st to end	Day	27% 10% 17% 24% 19% 3	4226
September	1st to 10th	Day	35% 6% 9% 21% 18% 10%	2200
	11th to 20th	Day	36% 6% 13% 19% 21% 5%	2200
	21st to end	Day	29% 6% 8% 22% 21% 13%	2200
October	1st to 10th	Day	14% 3 6% 12% 28% 36%	3513
	11th to 20th	Day	22% 4 6% 18% 25% 24%	3314
	21st to end	Day	21% 3 5% 19% 39% 14%	3428
November	1st to 10th	Day	35% 5% 7% 20% 22% 12%	1935
	11th to 20th	Day	27% 5% 8% 19% 22% 19%	1800
	21st to end	Day	36% 3 5% 19% 22% 15%	1800
December	1st to 10th	Day	45% 3 5% 17% 20% 10%	2940
	11th to 20th	Day	37% 4 8% 12% 23% 15%	3389
	21st to end	Day	27% 2 4 17% 27% 23%	4488
January	1st to 10th	Night	33% 3 4 19% 27% 15%	5888
	11th to 20th	Night	21% 2 3 19% 29% 26%	5900
	21st to end	Night	44% 2 3 10% 22% 19%	6094
February	1st to 10th	Night	34% 4 6% 13% 23% 21%	2400
	11th to 20th	Night	35% 4 5% 17% 20% 17%	2338
	21st to end	Night	36% 4 6% 13% 21% 21%	1980
March	1st to 10th	Night	29% 5% 7% 19% 22% 17%	5105
	11th to 20th	Night	33% 3 7% 11% 16% 30%	4980
	21st to end	Night	31% 4 8% 19% 22% 16%	5467
April	1st to 10th	Night	31% 5% 10% 20% 18% 17%	2200
	11th to 20th	Night	35% 5% 8% 16% 20% 16%	2061
	21st to end	Night	31% 7% 9% 21% 21% 11%	1895
May	1st to 10th	Night	40% 8% 8% 19% 14% 11%	4080
	11th to 20th	Night	32% 5% 12% 19% 17% 16%	4054
	21st to end	Night	36% 6% 14% 26% 13% 4	4452
June	1st to 10th	Night	19% 6% 16% 35% 21% 3	1800
	11th to 20th	Night	17% 6% 16% 32% 22% 7%	1800
	21st to end	Night	22% 6% 16% 31% 21% 4	1800
July	1st to 10th	Night	33% 8% 23% 30% 6% 1	4035
	11th to 20th	Night	16% 7% 24% 35% 16% 2	4026
	21st to end	Night	20% 9% 23% 30% 16% 3	4320
August	1st to 10th	Night	10% 4 13% 39% 33% 1	3042
	11th to 20th	Night	17% 5% 27% 36% 13% 2	3243
	21st to end	Night	20% 10% 22% 25% 20% 2	3678
September	1st to 10th	Night	28% 7% 13% 23% 19% 9%	2200
	11th to 20th	Night	32% 6% 15% 24% 17% 6%	2200
	21st to end	Night	26% 6% 11% 23% 21% 13%	2200
October	1st to 10th	Night	11% 3 8% 15% 23% 40%	3513
	11th to 20th	Night	19% 4 8% 18% 30% 20%	3571
	21st to end	Night	20% 3 5% 21% 34% 16%	4120
November	1st to 10th	Night	28% 5% 7% 20% 24% 15%	2359
	11th to 20th	Night	26% 5% 6% 22% 22% 20%	2600
	21st to end	Night	35% 3 8% 16% 21% 17%	2600
December	1st to 10th	Night	43% 4 7% 16% 19% 12%	4250
	11th to 20th	Night	35% 5% 6% 13% 22% 18%	4817
	21st to end	Night	28% 3 4 17% 28% 19%	6490

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	18% 17% 37% 21% 5% 1	300
	11th to 20th	Day	21% 15% 33% 24% 7% 1	300
	21st to end	Day	15% 18% 38% 22% 6%	330
February	1st to 10th	Day	21% 17% 32% 24% 7%	300
	11th to 20th	Day	20% 20% 37% 19% 4	300
	21st to end	Day	21% 18% 40% 18% 3	249
March	1st to 10th	Day	19% 18% 40% 19% 4	300
	11th to 20th	Day	18% 20% 38% 18% 6%	300
	21st to end	Day	15% 19% 44% 17% 5%	330
April	1st to 10th	Day	15% 22% 41% 18% 4	300
	11th to 20th	Day	16% 19% 39% 20% 5%	402
	21st to end	Day	14% 17% 43% 19% 7%	603
May	1st to 10th	Day	12% 14% 40% 26% 7%	703
	11th to 20th	Day	15% 11% 35% 27% 10% 2	725
	21st to end	Day	12% 9% 30% 35% 13% 2	789
June	1st to 10th	Day	5% 3 23% 42% 22% 4	730
	11th to 20th	Day	5% 3 20% 51% 18% 3	730
	21st to end	Day	5% 1 15% 42% 32% 6%	730
July	1st to 10th	Day	8% 2 10% 37% 32% 10%	721
	11th to 20th	Day	4 1 6% 43% 38% 7%	718
	21st to end	Day	3 1 7% 40% 37% 12%	794
August	1st to 10th	Day	3 4 39% 41% 13%	646
	11th to 20th	Day	8% 1 6% 34% 38% 14%	517
	21st to end	Day	5% 1 7% 28% 42% 17%	537
September	1st to 10th	Day	11% 2 5% 27% 38% 16%	330
	11th to 20th	Day	6% 1 7% 28% 44% 15%	330
	21st to end	Day	11% 1 7% 33% 36% 11%	330
October	1st to 10th	Day	6% 4 11% 34% 35% 10%	309
	11th to 20th	Day	10% 5% 23% 41% 20% 2	300
	21st to end	Day	19% 13% 25% 26% 16% 1	330
November	1st to 10th	Day	18% 8% 28% 33% 11% 2	300
	11th to 20th	Day	14% 14% 28% 29% 9% 6%	300
	21st to end	Day	20% 16% 35% 18% 8% 3	300
December	1st to 10th	Day	17% 10% 33% 27% 10% 3	300
	11th to 20th	Day	16% 17% 35% 23% 8% 1	300
	21st to end	Day	16% 15% 34% 25% 11%	330
January	1st to 10th	Night	15% 10% 38% 30% 6%	1000
	11th to 20th	Night	15% 12% 37% 31% 6%	1000
	21st to end	Night	16% 12% 37% 28% 6%	925
February	1st to 10th	Night	17% 11% 41% 25% 6%	800
	11th to 20th	Night	18% 14% 41% 24% 3	784
	21st to end	Night	17% 17% 45% 20% 1	660
March	1st to 10th	Night	14% 18% 40% 27% 1	687
	11th to 20th	Night	15% 12% 43% 26% 4	600
	21st to end	Night	11% 14% 49% 23% 3	660
April	1st to 10th	Night	9% 14% 50% 24% 2	600
	11th to 20th	Night	12% 16% 47% 22% 3	593
	21st to end	Night	11% 11% 51% 20% 6%	600
May	1st to 10th	Night	10% 13% 46% 28% 4	600
	11th to 20th	Night	9% 9% 41% 31% 9% 1	591
	21st to end	Night	8% 7% 42% 32% 10%	650
June	1st to 10th	Night	2 1 31% 47% 18% 1	600
	11th to 20th	Night	4 3 37% 46% 10%	600
	21st to end	Night	4 3 21% 50% 21% 2	600
July	1st to 10th	Night	6% 2 11% 52% 26% 2	585
	11th to 20th	Night	3 1 11% 59% 25% 1	582
	21st to end	Night	3 11% 59% 24% 2	657
August	1st to 10th	Night	1 8% 58% 30% 3	597
	11th to 20th	Night	5% 9% 55% 27% 4	594
	21st to end	Night	5% 1 7% 50% 32% 5%	660
September	1st to 10th	Night	10% 2 11% 42% 32% 5%	600
	11th to 20th	Night	10% 1 9% 42% 34% 3	600
	21st to end	Night	9% 1 14% 47% 28% 2	600
October	1st to 10th	Night	5% 2 16% 49% 28% 1	579
	11th to 20th	Night	12% 2 25% 45% 15% 1	630
	21st to end	Night	13% 9% 31% 30% 16% 1	836
November	1st to 10th	Night	12% 7% 29% 38% 13% 1	799
	11th to 20th	Night	9% 9% 33% 36% 13% 1	1000
	21st to end	Night	16% 11% 33% 30% 10% 1	1000
December	1st to 10th	Night	14% 8% 34% 36% 8%	1000
	11th to 20th	Night	16% 11% 36% 32% 6%	1000
	21st to end	Night	13% 12% 36% 32% 7%	1100

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