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 2026-10-14.

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% 40%	149458
	Night	15% 6% 2 6% 4 4 4 4 6% 7% 42%	142311
Transparency	Day	40% 6% 13% 24% 15% 3	153054
	Night	40% 5% 12% 24% 16% 3	146786
Seeing	Day	19% 11% 26% 24% 15% 5%	17449
	Night	17% 9% 29% 32% 12% 1	26901

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	13% 5% 2 7% 5% 4 5% 4 5% 7% 41%	4781
	11th to 20th	Day	12% 9% 3 7% 4 3 4 3 4 5% 45%	5280
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 7% 39%	5780
February	1st to 10th	Day	13% 8% 3 7% 5% 4 5% 4 5% 6% 39%	1890
	11th to 20th	Day	16% 9% 3 6% 4 5% 4 3 5% 6% 38%	1875
	21st to end	Day	17% 7% 4 7% 5% 5% 4 3 5% 6% 38%	1730
March	1st to 10th	Day	18% 6% 1 5% 4 4 5% 4 5% 6% 42%	4992
	11th to 20th	Day	12% 6% 2 5% 4 4 3 4 5% 8% 47%	5090
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 6% 7% 40%	5665
April	1st to 10th	Day	15% 6% 3 6% 5% 4 5% 4 6% 7% 38%	2520
	11th to 20th	Day	14% 6% 2 5% 5% 4 5% 4 5% 7% 44%	2494
	21st to end	Day	18% 7% 2 6% 4 3 4 3 5% 7% 41%	2520
May	1st to 10th	Day	19% 6% 2 6% 4 4 5% 4 7% 9% 34%	7611
	11th to 20th	Day	20% 5% 2 5% 4 4 4 4 7% 10% 36%	8017
	21st to end	Day	23% 6% 2 5% 3 4 4 3 5% 8% 37%	9045
June	1st to 10th	Day	12% 5% 2 5% 4 4 4 5% 7% 9% 43%	2940
	11th to 20th	Day	12% 5% 2 5% 4 5% 5% 5% 7% 9% 41%	2940
	21st to end	Day	10% 4 2 6% 4 4 5% 4 7% 9% 46%	2940
July	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 5% 6% 9% 43%	8280
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 9% 12% 36%	8045
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	8340
August	1st to 10th	Day	15% 6% 3 7% 5% 6% 7% 5% 8% 9% 30%	6014
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 5% 7% 10% 39%	5766
	21st to end	Day	10% 4 1 5% 4 4 5% 4 6% 9% 47%	6080
September	1st to 10th	Day	15% 5% 2 5% 4 4 4 3 5% 8% 46%	2520
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 6% 8% 47%	2520
	21st to end	Day	22% 8% 2 6% 4 4 3 3 5% 7% 36%	2198
October	1st to 10th	Day	16% 5% 2 5% 3 4 4 3 5% 7% 46%	2100
	11th to 20th	Day	17% 4 1 4 4 4 4 3 4 7% 48%	2030
	21st to end	Day	13% 5% 2 5% 4 4 4 3 5% 6% 48%	2200
November	1st to 10th	Day	12% 5% 1 4 4 3 3 3 5% 7% 51%	1951
	11th to 20th	Day	15% 5% 1 4 3 4 4 4 6% 7% 47%	1826
	21st to end	Day	15% 6% 2 6% 4 4 4 4 6% 7% 43%	1680
December	1st to 10th	Day	13% 7% 2 6% 5% 4 4 4 6% 7% 42%	2680
	11th to 20th	Day	20% 9% 2 5% 4 3 4 3 5% 6% 39%	3070
	21st to end	Day	17% 9% 2 6% 4 4 5% 3 6% 9% 33%	4048
January	1st to 10th	Night	10% 8% 2 6% 5% 4 5% 4 6% 7% 43%	8095
	11th to 20th	Night	13% 7% 2 6% 3 3 3 3 5% 5% 49%	7680
	21st to end	Night	14% 6% 2 5% 3 3 4 4 6% 7% 46%	8401
February	1st to 10th	Night	14% 7% 2 6% 5% 4 4 4 6% 7% 41%	2730
	11th to 20th	Night	17% 8% 2 7% 4 4 4 4 5% 6% 40%	2631
	21st to end	Night	15% 8% 3 7% 6% 3 5% 3 5% 6% 39%	2076
March	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 4 6% 46%	5078
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 6% 49%	5090
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 7% 45%	5508
April	1st to 10th	Night	15% 7% 3 6% 5% 5% 5% 4 7% 6% 38%	2100
	11th to 20th	Night	13% 6% 2 6% 5% 3 4 3 6% 8% 43%	2075
	21st to end	Night	17% 5% 2 4 3 3 5% 4 7% 6% 43%	2100
May	1st to 10th	Night	22% 7% 2 7% 4 4 4 4 4 8% 33%	5298
	11th to 20th	Night	20% 6% 2 5% 4 4 4 4 7% 9% 35%	4841
	21st to end	Night	25% 6% 2 6% 4 4 4 4 5% 6% 33%	5108
June	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 6% 9% 47%	1680
	11th to 20th	Night	12% 5% 2 7% 5% 4 5% 4 8% 9% 40%	1680
	21st to end	Night	10% 5% 2 6% 4 4 5% 4 7% 9% 44%	1680
July	1st to 10th	Night	11% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	4678
	11th to 20th	Night	10% 7% 3 8% 5% 6% 6% 5% 7% 9% 33%	4907
	21st to end	Night	10% 5% 2 6% 4 5% 5% 4 7% 8% 43%	5736
August	1st to 10th	Night	16% 6% 2 8% 5% 5% 6% 5% 7% 9% 29%	4135
	11th to 20th	Night	12% 6% 2 7% 5% 6% 6% 4 6% 9% 37%	4231
	21st to end	Night	12% 5% 2 6% 4 5% 4 4 6% 8% 45%	5045
September	1st to 10th	Night	14% 5% 2 5% 4 4 3 3 6% 8% 46%	2100
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 4 7% 51%	2100
	21st to end	Night	21% 7% 2 6% 4 4 4 3 4 6% 38%	2418
October	1st to 10th	Night	18% 6% 2 6% 4 3 4 3 4 5% 46%	2520
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 4 6% 51%	2437
	21st to end	Night	15% 5% 2 4 3 3 4 3 5% 7% 49%	2640
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 7% 53%	2566
	11th to 20th	Night	14% 7% 2 5% 3 3 4 4 5% 6% 48%	2792
	21st to end	Night	13% 6% 2 6% 4 4 4 3 6% 8% 44%	2940
December	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 4 5% 7% 47%	4720
	11th to 20th	Night	21% 6% 2 5% 4 4 4 3 6% 6% 39%	5345
	21st to end	Night	17% 8% 2 6% 4 4 5% 4 6% 9% 33%	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	41% 5% 9% 25% 15% 4	4782
	11th to 20th	Day	42% 4 9% 20% 19% 7%	5280
	21st to end	Day	42% 4 11% 28% 12% 3	5780
February	1st to 10th	Day	44% 6% 13% 23% 11% 2	1890
	11th to 20th	Day	47% 4 10% 23% 13% 2	1884
	21st to end	Day	47% 4 11% 21% 13% 3	1730
March	1st to 10th	Day	41% 6% 10% 21% 15% 6%	4992
	11th to 20th	Day	35% 5% 12% 26% 17% 5%	5090
	21st to end	Day	42% 5% 10% 20% 19% 4	5665
April	1st to 10th	Day	42% 7% 13% 19% 16% 4	2520
	11th to 20th	Day	38% 6% 12% 22% 18% 4	2494
	21st to end	Day	42% 5% 10% 23% 16% 3	2520
May	1st to 10th	Day	46% 5% 13% 23% 12% 2	7646
	11th to 20th	Day	42% 6% 13% 28% 11% 1	8021
	21st to end	Day	45% 5% 11% 20% 16% 2	9061
June	1st to 10th	Day	34% 8% 14% 24% 17% 1	2940
	11th to 20th	Day	37% 11% 14% 23% 14% 2	2940
	21st to end	Day	33% 7% 16% 27% 16% 1	2940
July	1st to 10th	Day	37% 8% 15% 22% 14% 3	8210
	11th to 20th	Day	38% 6% 16% 28% 11% 1	7970
	21st to end	Day	37% 6% 11% 24% 20% 1	8156
August	1st to 10th	Day	49% 7% 15% 21% 7%	6001
	11th to 20th	Day	40% 6% 16% 26% 12% 1	5805
	21st to end	Day	33% 5% 17% 28% 16% 1	6080
September	1st to 10th	Day	37% 6% 13% 20% 20% 4	2520
	11th to 20th	Day	35% 5% 11% 26% 19% 3	2520
	21st to end	Day	48% 5% 9% 18% 17% 2	2198
October	1st to 10th	Day	36% 5% 7% 20% 27% 5%	3360
	11th to 20th	Day	27% 4 9% 28% 23% 8%	3270
	21st to end	Day	25% 3 12% 30% 27% 4	3538
November	1st to 10th	Day	33% 3 14% 26% 20% 4	1951
	11th to 20th	Day	36% 5% 12% 24% 20% 4	1826
	21st to end	Day	39% 5% 12% 29% 13% 1	1680
December	1st to 10th	Day	40% 5% 15% 28% 9% 4	2680
	11th to 20th	Day	46% 4 14% 26% 9% 2	3066
	21st to end	Day	46% 7% 17% 17% 13% 1	4048
January	1st to 10th	Night	38% 5% 11% 25% 17% 3	8096
	11th to 20th	Night	38% 3 8% 23% 21% 7%	7680
	21st to end	Night	36% 4 9% 31% 18% 3	8401
February	1st to 10th	Night	41% 6% 14% 24% 14% 2	2730
	11th to 20th	Night	44% 5% 11% 22% 16% 3	2633
	21st to end	Night	45% 5% 11% 21% 14% 5%	2076
March	1st to 10th	Night	40% 5% 9% 26% 12% 9%	5078
	11th to 20th	Night	35% 4 11% 30% 14% 5%	5090
	21st to end	Night	38% 5% 10% 21% 21% 4	5508
April	1st to 10th	Night	44% 5% 12% 20% 16% 3	2100
	11th to 20th	Night	38% 7% 12% 22% 17% 5%	2075
	21st to end	Night	38% 6% 13% 24% 15% 4	2100
May	1st to 10th	Night	50% 5% 11% 19% 13% 3	5325
	11th to 20th	Night	44% 6% 13% 26% 11% 1	4842
	21st to end	Night	50% 6% 11% 20% 11% 1	5115
June	1st to 10th	Night	34% 7% 11% 26% 19% 3	1680
	11th to 20th	Night	39% 9% 13% 24% 14% 2	1680
	21st to end	Night	35% 8% 13% 24% 18% 2	1680
July	1st to 10th	Night	42% 7% 14% 19% 15% 3	4640
	11th to 20th	Night	46% 7% 14% 20% 12% 1	4862
	21st to end	Night	36% 7% 14% 23% 18% 1	5606
August	1st to 10th	Night	49% 7% 16% 19% 8% 1	4124
	11th to 20th	Night	43% 6% 15% 23% 12% 1	4258
	21st to end	Night	37% 5% 14% 28% 15% 2	5045
September	1st to 10th	Night	36% 5% 13% 22% 19% 5%	2100
	11th to 20th	Night	34% 4 11% 26% 22% 2	2100
	21st to end	Night	47% 6% 9% 18% 17% 3	2418
October	1st to 10th	Night	40% 4 9% 22% 22% 3	4040
	11th to 20th	Night	26% 3 11% 25% 29% 7%	3936
	21st to end	Night	25% 3 11% 32% 25% 4	4252
November	1st to 10th	Night	32% 3 11% 27% 23% 4	2566
	11th to 20th	Night	36% 5% 10% 24% 20% 5%	2792
	21st to end	Night	38% 5% 13% 24% 17% 3	2940
December	1st to 10th	Night	37% 4 14% 30% 14% 1	4720
	11th to 20th	Night	46% 4 13% 20% 15% 3	5348
	21st to end	Night	45% 7% 15% 19% 13% 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	28% 24% 28% 15% 4 1	242
	11th to 20th	Day	31% 27% 27% 13% 3	330
	21st to end	Day	23% 26% 33% 12% 5% 1	363
February	1st to 10th	Day	24% 21% 38% 13% 5%	330
	11th to 20th	Day	35% 22% 34% 8% 2	362
	21st to end	Day	26% 17% 37% 17% 3	446
March	1st to 10th	Day	22% 22% 29% 23% 5%	540
	11th to 20th	Day	26% 19% 31% 18% 6% 1	540
	21st to end	Day	22% 18% 33% 20% 6% 1	594
April	1st to 10th	Day	23% 20% 27% 22% 7% 2	540
	11th to 20th	Day	19% 14% 33% 17% 13% 4	532
	21st to end	Day	25% 13% 28% 21% 11% 2	540
May	1st to 10th	Day	24% 13% 29% 21% 9% 3	543
	11th to 20th	Day	19% 14% 25% 23% 13% 5%	567
	21st to end	Day	20% 6% 23% 24% 21% 6%	617
June	1st to 10th	Day	15% 7% 27% 25% 18% 8%	570
	11th to 20th	Day	15% 8% 25% 28% 19% 6%	570
	21st to end	Day	12% 4 24% 31% 22% 8%	570
July	1st to 10th	Day	11% 3 15% 30% 28% 12%	565
	11th to 20th	Day	6% 2 17% 31% 31% 12%	564
	21st to end	Day	11% 3 17% 34% 25% 9%	620
August	1st to 10th	Day	12% 3 18% 27% 27% 13%	566
	11th to 20th	Day	13% 2 19% 33% 22% 12%	559
	21st to end	Day	9% 5% 20% 31% 22% 14%	627
September	1st to 10th	Day	16% 6% 16% 26% 25% 11%	570
	11th to 20th	Day	13% 4 17% 29% 25% 11%	570
	21st to end	Day	30% 7% 22% 23% 14% 4	570
October	1st to 10th	Day	19% 6% 20% 26% 20% 8%	570
	11th to 20th	Day	18% 11% 26% 29% 15% 2	542
	21st to end	Day	14% 14% 32% 26% 12% 2	583
November	1st to 10th	Day	16% 11% 29% 29% 12% 3	479
	11th to 20th	Day	20% 12% 32% 24% 11% 1	366
	21st to end	Day	23% 17% 34% 18% 8%	220
December	1st to 10th	Day	22% 20% 33% 20% 4 1	220
	11th to 20th	Day	23% 19% 30% 22% 6%	220
	21st to end	Day	25% 17% 31% 20% 7% 1	242
January	1st to 10th	Night	18% 15% 42% 22% 3	840
	11th to 20th	Night	21% 15% 35% 26% 3	840
	21st to end	Night	17% 14% 43% 25% 1	924
February	1st to 10th	Night	19% 15% 34% 30% 2	840
	11th to 20th	Night	25% 17% 37% 20% 1	823
	21st to end	Night	21% 17% 38% 21% 3	692
March	1st to 10th	Night	21% 15% 37% 23% 4	840
	11th to 20th	Night	23% 14% 34% 25% 5%	840
	21st to end	Night	17% 15% 40% 24% 3 1	924
April	1st to 10th	Night	19% 16% 35% 25% 5%	840
	11th to 20th	Night	15% 12% 34% 30% 8%	831
	21st to end	Night	20% 9% 33% 31% 8%	840
May	1st to 10th	Night	23% 7% 26% 34% 10%	652
	11th to 20th	Night	21% 5% 26% 35% 12%	488
	21st to end	Night	17% 2 21% 41% 18% 1	455
June	1st to 10th	Night	12% 2 26% 36% 24% 1	420
	11th to 20th	Night	12% 5% 20% 43% 19% 2	420
	21st to end	Night	10% 3 18% 49% 20%	420
July	1st to 10th	Night	12% 3 14% 40% 28% 3	410
	11th to 20th	Night	7% 1 12% 43% 33% 3	482
	21st to end	Night	10% 2 11% 46% 29% 2	690
August	1st to 10th	Night	13% 2 10% 41% 32% 2	627
	11th to 20th	Night	12% 3 13% 40% 30% 3	682
	21st to end	Night	12% 3 15% 40% 28% 3	924
September	1st to 10th	Night	15% 2 16% 38% 26% 3	840
	11th to 20th	Night	13% 3 15% 37% 29% 3	840
	21st to end	Night	24% 4 19% 33% 19% 2	840
October	1st to 10th	Night	20% 4 20% 32% 20% 3	840
	11th to 20th	Night	16% 8% 28% 34% 13% 1	813
	21st to end	Night	18% 8% 32% 31% 11%	880
November	1st to 10th	Night	12% 8% 31% 38% 9% 1	820
	11th to 20th	Night	18% 10% 34% 30% 7%	840
	21st to end	Night	15% 13% 34% 31% 6%	840
December	1st to 10th	Night	20% 10% 40% 24% 6%	840
	11th to 20th	Night	19% 9% 39% 28% 4	840
	21st to end	Night	21% 8% 37% 31% 3	924

Page generated at 2026-10-11 05:06:30. Version ac07

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