Digital Monastery Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Digital Monastery Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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% 6% 2 6% 4 4 5% 4 6% 8% 41%	114143
	Night	15% 6% 2 6% 4 4 4 4 6% 7% 43%	115140
Transparency	Day	39% 6% 12% 24% 16% 3	117782
	Night	39% 6% 12% 24% 17% 3	119640
Seeing	Day	19% 11% 25% 24% 15% 5%	15582
	Night	17% 9% 29% 31% 12% 1	25185

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	14% 5% 2 6% 4 5% 5% 4 6% 7% 43%	3689
	11th to 20th	Day	13% 9% 3 7% 5% 4 4 3 4 5% 42%	4060
	21st to end	Day	15% 8% 2 6% 5% 4 4 4 6% 6% 41%	4466
February	1st to 10th	Day	14% 8% 3 7% 5% 4 5% 4 5% 6% 38%	1800
	11th to 20th	Day	16% 8% 2 6% 4 5% 4 3 5% 6% 39%	1783
	21st to end	Day	18% 7% 4 7% 4 5% 4 3 5% 6% 39%	1650
March	1st to 10th	Day	18% 5% 1 5% 4 4 5% 4 5% 6% 42%	4883
	11th to 20th	Day	12% 6% 2 5% 4 4 3 4 5% 8% 47%	4980
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 6% 7% 40%	5543
April	1st to 10th	Day	15% 6% 3 6% 5% 4 5% 4 6% 7% 38%	2400
	11th to 20th	Day	14% 6% 2 5% 5% 4 5% 4 5% 7% 44%	2374
	21st to end	Day	17% 7% 1 6% 5% 4 4 4 5% 7% 41%	2400
May	1st to 10th	Day	25% 6% 2 6% 4 4 5% 4 6% 8% 30%	4207
	11th to 20th	Day	24% 6% 2 6% 4 4 4 4 6% 9% 30%	4427
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 9% 45%	4893
June	1st to 10th	Day	12% 5% 2 5% 4 4 4 5% 7% 9% 42%	2660
	11th to 20th	Day	12% 5% 2 5% 4 5% 5% 5% 7% 9% 40%	2660
	21st to end	Day	10% 4 2 5% 4 5% 5% 4 7% 9% 46%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 6% 6% 6% 7% 10% 44%	4440
	11th to 20th	Day	9% 5% 2 5% 4 4 6% 4 7% 10% 43%	4317
	21st to end	Day	12% 6% 3 7% 6% 6% 5% 5% 6% 8% 37%	4466
August	1st to 10th	Day	17% 5% 2 6% 4 5% 6% 5% 7% 8% 35%	4104
	11th to 20th	Day	11% 4 2 6% 5% 5% 5% 5% 6% 9% 42%	3918
	21st to end	Day	13% 4 2 5% 4 4 5% 4 6% 8% 47%	4180
September	1st to 10th	Day	16% 6% 2 5% 4 4 3 3 5% 7% 46%	2280
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 6% 8% 47%	2280
	21st to end	Day	21% 7% 2 6% 4 4 4 3 5% 7% 37%	1988
October	1st to 10th	Day	17% 5% 2 5% 3 4 4 3 4 7% 45%	1900
	11th to 20th	Day	17% 4 1 4 4 4 4 3 4 6% 48%	1900
	21st to end	Day	13% 5% 2 5% 4 4 4 3 5% 6% 48%	2090
November	1st to 10th	Day	12% 5% 2 4 4 3 3 3 5% 7% 51%	1856
	11th to 20th	Day	16% 5% 1 4 3 4 4 4 6% 7% 47%	1739
	21st to end	Day	15% 6% 2 6% 4 4 4 4 6% 7% 43%	1600
December	1st to 10th	Day	13% 7% 2 6% 5% 4 4 4 6% 7% 42%	2600
	11th to 20th	Day	20% 9% 2 5% 4 3 4 3 5% 6% 39%	2990
	21st to end	Day	18% 9% 2 6% 4 4 5% 4 6% 9% 34%	3960
January	1st to 10th	Night	11% 7% 2 5% 4 4 4 3 5% 7% 47%	6239
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 5% 6% 48%	5900
	21st to end	Night	15% 7% 2 5% 3 3 3 4 6% 6% 45%	6490
February	1st to 10th	Night	15% 7% 2 6% 4 3 4 4 6% 7% 41%	2600
	11th to 20th	Night	17% 8% 2 7% 3 4 4 4 5% 5% 41%	2503
	21st to end	Night	16% 8% 3 7% 6% 4 4 3 5% 6% 38%	1980
March	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 4 6% 47%	4967
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 7% 49%	4980
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 7% 46%	5388
April	1st to 10th	Night	15% 7% 3 7% 5% 5% 5% 4 7% 6% 37%	2000
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 3 6% 8% 43%	1975
	21st to end	Night	17% 5% 2 4 3 3 5% 4 7% 6% 43%	2000
May	1st to 10th	Night	25% 9% 3 6% 4 4 4 3 4 8% 30%	2937
	11th to 20th	Night	25% 8% 3 7% 4 3 4 3 5% 6% 31%	2684
	21st to end	Night	12% 4 2 6% 4 5% 5% 6% 8% 9% 40%	2778
June	1st to 10th	Night	11% 5% 2 5% 3 4 3 4 6% 9% 47%	1520
	11th to 20th	Night	11% 5% 2 7% 5% 4 5% 4 8% 9% 40%	1520
	21st to end	Night	10% 4 2 6% 4 4 5% 4 7% 10% 44%	1520
July	1st to 10th	Night	7% 5% 2 6% 5% 6% 5% 4 8% 10% 40%	2520
	11th to 20th	Night	8% 5% 3 7% 5% 5% 6% 5% 9% 9% 39%	2638
	21st to end	Night	13% 7% 2 6% 4 4 5% 5% 7% 8% 39%	3087
August	1st to 10th	Night	18% 5% 2 7% 5% 5% 5% 4 7% 9% 33%	2825
	11th to 20th	Night	11% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	2876
	21st to end	Night	13% 4 2 5% 4 4 4 4 5% 7% 47%	3476
September	1st to 10th	Night	15% 5% 2 5% 4 5% 3 3 6% 8% 45%	1900
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 4 7% 53%	1900
	21st to end	Night	21% 6% 2 5% 4 4 4 3 3 6% 40%	2188
October	1st to 10th	Night	19% 6% 2 6% 4 3 4 3 4 6% 44%	2280
	11th to 20th	Night	14% 5% 2 4 3 4 4 3 4 6% 51%	2280
	21st to end	Night	16% 5% 2 4 3 3 4 3 5% 7% 49%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 4 7% 54%	2441
	11th to 20th	Night	14% 7% 2 5% 3 3 3 4 5% 7% 47%	2659
	21st to end	Night	13% 5% 2 6% 4 4 4 3 6% 8% 44%	2800
December	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 4 5% 7% 47%	4580
	11th to 20th	Night	21% 6% 2 5% 4 4 4 3 5% 6% 38%	5205
	21st to end	Night	17% 8% 2 6% 4 4 5% 4 6% 9% 33%	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	38% 6% 8% 26% 18% 5%	3690
	11th to 20th	Day	43% 4 9% 20% 19% 5%	4060
	21st to end	Day	43% 4 11% 25% 14% 2	4466
February	1st to 10th	Day	45% 6% 14% 23% 10% 2	1800
	11th to 20th	Day	46% 5% 10% 23% 13% 2	1792
	21st to end	Day	47% 5% 11% 20% 14% 4	1650
March	1st to 10th	Day	40% 6% 10% 22% 16% 6%	4883
	11th to 20th	Day	35% 5% 12% 26% 18% 5%	4980
	21st to end	Day	43% 5% 10% 19% 19% 4	5543
April	1st to 10th	Day	42% 7% 12% 19% 16% 4	2400
	11th to 20th	Day	38% 6% 11% 22% 18% 4	2374
	21st to end	Day	42% 5% 10% 23% 17% 3	2400
May	1st to 10th	Day	50% 7% 11% 21% 10% 1	4245
	11th to 20th	Day	48% 9% 13% 20% 8% 1	4431
	21st to end	Day	33% 8% 15% 26% 16% 2	4907
June	1st to 10th	Day	35% 9% 14% 25% 15% 1	2660
	11th to 20th	Day	36% 12% 14% 23% 13% 2	2660
	21st to end	Day	32% 8% 16% 27% 16% 2	2660
July	1st to 10th	Day	34% 8% 19% 23% 11% 5%	4370
	11th to 20th	Day	34% 6% 17% 29% 12% 1	4242
	21st to end	Day	43% 7% 11% 21% 17% 2	4324
August	1st to 10th	Day	45% 7% 15% 25% 8%	4091
	11th to 20th	Day	36% 6% 14% 28% 15% 1	3957
	21st to end	Day	35% 5% 15% 27% 16% 2	4180
September	1st to 10th	Day	38% 6% 12% 19% 21% 4	2280
	11th to 20th	Day	34% 6% 10% 26% 21% 3	2280
	21st to end	Day	46% 5% 10% 19% 18% 2	1988
October	1st to 10th	Day	37% 5% 7% 19% 26% 5%	3160
	11th to 20th	Day	27% 4 9% 28% 23% 8%	3140
	21st to end	Day	25% 3 12% 30% 26% 4	3428
November	1st to 10th	Day	33% 3 14% 26% 20% 4	1856
	11th to 20th	Day	35% 5% 12% 24% 20% 4	1739
	21st to end	Day	39% 6% 12% 29% 13% 1	1600
December	1st to 10th	Day	40% 5% 15% 28% 9% 4	2600
	11th to 20th	Day	46% 4 14% 26% 9% 2	2986
	21st to end	Day	46% 7% 17% 17% 13% 1	3960
January	1st to 10th	Night	34% 6% 9% 26% 21% 4	6239
	11th to 20th	Night	37% 4 10% 25% 18% 6%	5900
	21st to end	Night	38% 4 10% 28% 17% 2	6490
February	1st to 10th	Night	41% 7% 14% 24% 12% 1	2600
	11th to 20th	Night	44% 5% 11% 22% 16% 3	2505
	21st to end	Night	45% 5% 11% 20% 14% 5%	1980
March	1st to 10th	Night	39% 5% 9% 27% 12% 9%	4967
	11th to 20th	Night	35% 5% 12% 30% 14% 5%	4980
	21st to end	Night	38% 5% 10% 21% 22% 4	5388
April	1st to 10th	Night	45% 5% 11% 19% 16% 3	2000
	11th to 20th	Night	38% 7% 11% 21% 17% 5%	1975
	21st to end	Night	38% 6% 12% 24% 16% 4	2000
May	1st to 10th	Night	53% 6% 10% 18% 11% 3	2964
	11th to 20th	Night	51% 8% 12% 19% 9% 1	2685
	21st to end	Night	34% 10% 18% 26% 10% 2	2785
June	1st to 10th	Night	34% 8% 12% 27% 17% 3	1520
	11th to 20th	Night	38% 9% 13% 25% 14% 2	1520
	21st to end	Night	34% 8% 14% 25% 18% 2	1520
July	1st to 10th	Night	38% 8% 19% 18% 12% 5%	2480
	11th to 20th	Night	39% 8% 16% 22% 13% 2	2590
	21st to end	Night	39% 8% 15% 19% 17% 2	2988
August	1st to 10th	Night	45% 7% 18% 22% 7% 1	2814
	11th to 20th	Night	40% 6% 12% 27% 14% 1	2903
	21st to end	Night	35% 6% 13% 28% 16% 2	3476
September	1st to 10th	Night	37% 5% 13% 20% 19% 5%	1900
	11th to 20th	Night	33% 4 11% 27% 23% 3	1900
	21st to end	Night	45% 6% 9% 20% 17% 3	2188
October	1st to 10th	Night	41% 5% 10% 22% 21% 3	3800
	11th to 20th	Night	25% 3 11% 25% 29% 7%	3779
	21st to end	Night	24% 3 11% 32% 25% 4	4120
November	1st to 10th	Night	32% 3 11% 27% 22% 5%	2441
	11th to 20th	Night	36% 5% 10% 24% 20% 5%	2659
	21st to end	Night	37% 5% 13% 24% 18% 3	2800
December	1st to 10th	Night	37% 4 13% 30% 14% 1	4580
	11th to 20th	Night	46% 4 13% 19% 15% 2	5208
	21st to end	Night	45% 7% 15% 19% 14% 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	26% 26% 27% 15% 4 1	220
	11th to 20th	Day	30% 26% 27% 14% 3	300
	21st to end	Day	22% 25% 34% 13% 5% 1	330
February	1st to 10th	Day	23% 22% 39% 12% 4	300
	11th to 20th	Day	34% 23% 33% 8% 2	330
	21st to end	Day	27% 17% 35% 18% 3	414
March	1st to 10th	Day	20% 23% 29% 23% 5%	500
	11th to 20th	Day	24% 19% 32% 17% 6% 1	500
	21st to end	Day	22% 17% 33% 21% 6% 1	550
April	1st to 10th	Day	23% 20% 27% 22% 6% 2	500
	11th to 20th	Day	19% 15% 32% 17% 13% 4	492
	21st to end	Day	25% 13% 28% 21% 11% 2	500
May	1st to 10th	Day	24% 12% 29% 21% 10% 4	503
	11th to 20th	Day	21% 13% 26% 23% 13% 5%	527
	21st to end	Day	16% 6% 23% 25% 22% 7%	549
June	1st to 10th	Day	16% 6% 26% 24% 19% 8%	490
	11th to 20th	Day	15% 6% 25% 28% 20% 6%	490
	21st to end	Day	11% 4 25% 30% 23% 6%	490
July	1st to 10th	Day	10% 2 16% 31% 27% 13%	485
	11th to 20th	Day	6% 3 17% 30% 32% 12%	484
	21st to end	Day	12% 3 16% 34% 26% 8%	532
August	1st to 10th	Day	11% 3 17% 27% 28% 13%	486
	11th to 20th	Day	11% 2 18% 34% 22% 13%	479
	21st to end	Day	10% 4 16% 31% 24% 15%	539
September	1st to 10th	Day	18% 7% 14% 23% 26% 12%	490
	11th to 20th	Day	13% 4 17% 29% 26% 12%	490
	21st to end	Day	28% 7% 21% 24% 15% 5%	490
October	1st to 10th	Day	21% 6% 19% 25% 21% 8%	490
	11th to 20th	Day	17% 11% 24% 30% 16% 2	490
	21st to end	Day	14% 12% 32% 27% 12% 3	539
November	1st to 10th	Day	16% 10% 29% 30% 13% 3	444
	11th to 20th	Day	19% 12% 34% 24% 12% 1	339
	21st to end	Day	22% 18% 34% 18% 9% 1	200
December	1st to 10th	Day	22% 20% 33% 20% 4 2	200
	11th to 20th	Day	23% 19% 29% 22% 7% 1	200
	21st to end	Day	23% 16% 31% 21% 8% 1	220
January	1st to 10th	Night	18% 16% 42% 21% 3	800
	11th to 20th	Night	21% 14% 35% 27% 3	800
	21st to end	Night	17% 14% 43% 25% 1	880
February	1st to 10th	Night	19% 15% 34% 30% 2	800
	11th to 20th	Night	25% 17% 37% 20% 1	783
	21st to end	Night	22% 17% 38% 20% 3	660
March	1st to 10th	Night	20% 15% 38% 23% 4	800
	11th to 20th	Night	23% 14% 34% 24% 5% 1	800
	21st to end	Night	18% 14% 40% 25% 4 1	880
April	1st to 10th	Night	19% 17% 35% 25% 4	800
	11th to 20th	Night	15% 12% 35% 29% 8%	791
	21st to end	Night	20% 9% 33% 30% 8%	800
May	1st to 10th	Night	24% 7% 24% 34% 10%	621
	11th to 20th	Night	22% 5% 25% 35% 12%	464
	21st to end	Night	14% 2 21% 43% 19% 1	423
June	1st to 10th	Night	12% 2 26% 36% 24% 1	380
	11th to 20th	Night	11% 3 20% 44% 20% 2	380
	21st to end	Night	9% 2 19% 50% 19%	380
July	1st to 10th	Night	12% 2 15% 41% 27% 3	370
	11th to 20th	Night	7% 1 12% 43% 33% 3	434
	21st to end	Night	10% 2 12% 46% 29% 3	624
August	1st to 10th	Night	13% 2 10% 42% 31% 2	567
	11th to 20th	Night	12% 3 13% 39% 30% 3	616
	21st to end	Night	12% 3 14% 39% 29% 3	836
September	1st to 10th	Night	16% 2 16% 37% 26% 3	760
	11th to 20th	Night	13% 3 16% 37% 29% 3	760
	21st to end	Night	23% 4 19% 33% 20% 2	760
October	1st to 10th	Night	21% 4 20% 31% 20% 3	760
	11th to 20th	Night	15% 9% 28% 34% 13% 1	760
	21st to end	Night	18% 7% 31% 32% 11%	836
November	1st to 10th	Night	12% 7% 32% 39% 9% 1	780
	11th to 20th	Night	18% 10% 33% 31% 8%	800
	21st to end	Night	15% 13% 34% 31% 6%	800
December	1st to 10th	Night	20% 10% 40% 23% 6%	800
	11th to 20th	Night	19% 9% 40% 28% 4	800
	21st to end	Night	20% 8% 37% 32% 3	880

Page generated at 2025-05-23 09:20:57. Version ac07

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