Dolen
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dolen clear sky chart from 2005-11-06 to 2025-11-18.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	126698
	Night	14% 7% 2 6% 4 3 4 3 5% 7% 45%	123922
Transparency	Day	40% 7% 11% 19% 17% 7%	130333
	Night	37% 6% 11% 19% 18% 9%	128350
Seeing	Day	14% 9% 22% 26% 21% 8%	16288
	Night	16% 8% 23% 32% 19% 2	26078

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	20% 11% 2 5% 4 3 3 3 4 5% 42%	4077
	11th to 20th	Day	16% 6% 2 5% 4 3 3 2 3 4 51%	4080
	21st to end	Day	30% 8% 3 5% 3 3 2 2 4 6% 35%	4488
February	1st to 10th	Day	21% 8% 3 6% 5% 3 4 2 4 5% 38%	1829
	11th to 20th	Day	22% 9% 3 7% 4 3 3 3 4 5% 38%	1999
	21st to end	Day	21% 8% 3 7% 4 3 4 2 4 4 39%	1815
March	1st to 10th	Day	19% 8% 3 8% 5% 5% 4 3 4 6% 36%	4936
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 6% 46%	4980
	21st to end	Day	17% 8% 3 7% 5% 4 4 3 4 6% 38%	5462
April	1st to 10th	Day	15% 8% 3 8% 5% 5% 4 4 5% 6% 38%	2200
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 4 6% 6% 38%	2374
	21st to end	Day	11% 7% 3 7% 5% 4 6% 3 6% 7% 42%	2400
May	1st to 10th	Day	18% 7% 3 8% 6% 5% 5% 4 6% 8% 30%	5441
	11th to 20th	Day	11% 6% 3 7% 4 5% 4 4 6% 8% 42%	5862
	21st to end	Day	10% 6% 3 8% 5% 6% 5% 4 7% 10% 35%	6434
June	1st to 10th	Day	7% 5% 2 7% 7% 7% 6% 6% 8% 10% 35%	2600
	11th to 20th	Day	6% 4 2 6% 6% 6% 7% 6% 8% 12% 37%	2600
	21st to end	Day	6% 5% 3 9% 8% 7% 8% 7% 9% 9% 30%	2600
July	1st to 10th	Day	8% 5% 2 7% 7% 6% 7% 6% 8% 12% 33%	5900
	11th to 20th	Day	6% 5% 2 7% 6% 7% 7% 6% 9% 12% 32%	5900
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 5% 8% 10% 34%	6422
August	1st to 10th	Day	2 2 1 3 3 4 4 4 6% 11% 60%	4234
	11th to 20th	Day	3 3 1 4 4 4 5% 5% 9% 14% 48%	3956
	21st to end	Day	9% 5% 2 7% 6% 6% 6% 6% 7% 10% 37%	4312
September	1st to 10th	Day	8% 5% 2 7% 6% 6% 6% 6% 7% 9% 39%	2244
	11th to 20th	Day	14% 6% 2 6% 6% 5% 5% 5% 5% 7% 39%	2200
	21st to end	Day	8% 4 2 6% 5% 5% 5% 4 5% 7% 50%	2200
October	1st to 10th	Day	6% 4 2 5% 4 4 4 2 4 6% 59%	2041
	11th to 20th	Day	10% 4 2 5% 4 4 4 3 4 7% 54%	2000
	21st to end	Day	14% 5% 1 4 4 3 3 3 5% 6% 53%	2200
November	1st to 10th	Day	11% 5% 2 5% 4 5% 5% 3 4 5% 48%	2058
	11th to 20th	Day	11% 6% 2 7% 4 4 4 3 4 6% 50%	2070
	21st to end	Day	17% 7% 2 7% 4 4 3 2 4 5% 45%	1965
December	1st to 10th	Day	22% 8% 2 4 3 3 2 3 4 6% 41%	2940
	11th to 20th	Day	13% 8% 3 7% 5% 4 4 4 5% 6% 40%	3391
	21st to end	Day	16% 8% 2 6% 4 4 4 3 4 5% 46%	4488
January	1st to 10th	Night	18% 7% 2 6% 3 3 3 2 4 5% 46%	5888
	11th to 20th	Night	16% 8% 2 5% 3 3 2 2 3 5% 51%	5900
	21st to end	Night	30% 9% 3 5% 3 3 3 2 3 5% 35%	6490
February	1st to 10th	Night	19% 9% 3 6% 3 3 3 3 5% 6% 39%	2587
	11th to 20th	Night	22% 9% 3 6% 3 3 3 2 4 5% 40%	2285
	21st to end	Night	21% 9% 3 7% 4 3 3 3 4 4 39%	1815
March	1st to 10th	Night	23% 10% 2 5% 4 3 3 3 4 5% 37%	4919
	11th to 20th	Night	18% 8% 3 6% 3 3 3 2 4 5% 44%	4980
	21st to end	Night	19% 9% 3 6% 4 4 3 3 4 4 41%	5467
April	1st to 10th	Night	16% 7% 3 7% 4 4 4 4 5% 7% 39%	2200
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 5% 7% 42%	1975
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 6% 44%	2000
May	1st to 10th	Night	23% 10% 3 7% 4 3 4 4 6% 8% 27%	4451
	11th to 20th	Night	14% 7% 2 7% 4 4 4 4 6% 7% 40%	4053
	21st to end	Night	13% 9% 3 7% 5% 5% 5% 5% 7% 10% 33%	4443
June	1st to 10th	Night	6% 4 2 5% 3 4 5% 4 7% 11% 51%	1800
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 13% 53%	1800
	21st to end	Night	6% 5% 2 5% 5% 3 5% 5% 7% 11% 46%	1800
July	1st to 10th	Night	6% 5% 2 5% 5% 5% 4 5% 9% 15% 39%	4078
	11th to 20th	Night	4 4 2 6% 4 5% 5% 4 7% 13% 47%	4077
	21st to end	Night	9% 6% 2 7% 4 4 5% 4 6% 9% 44%	4449
August	1st to 10th	Night	1 2 1 2 2 3 3 3 5% 11% 67%	2926
	11th to 20th	Night	2 2 1 2 2 2 3 4 6% 13% 61%	3095
	21st to end	Night	6% 4 2 5% 4 5% 6% 5% 8% 11% 44%	3586
September	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 3 7% 10% 47%	2150
	11th to 20th	Night	11% 6% 2 7% 4 4 5% 4 6% 8% 42%	2200
	21st to end	Night	7% 4 2 4 4 3 4 3 6% 8% 55%	2200
October	1st to 10th	Night	5% 3 2 4 3 3 3 4 5% 7% 61%	2337
	11th to 20th	Night	10% 4 1 4 2 2 3 3 4 6% 60%	2400
	21st to end	Night	12% 5% 2 4 3 3 2 2 3 4 59%	2640
November	1st to 10th	Night	12% 5% 1 5% 4 3 3 3 4 6% 53%	2460
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 5% 5% 53%	2485
	21st to end	Night	16% 6% 2 5% 3 4 4 3 5% 5% 46%	2430
December	1st to 10th	Night	19% 9% 3 8% 4 3 3 3 4 6% 38%	4250
	11th to 20th	Night	17% 10% 3 6% 3 3 3 2 4 4 44%	4816
	21st to end	Night	15% 8% 3 5% 3 3 3 3 4 4 48%	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	46% 3 4 22% 18% 6%	4078
	11th to 20th	Day	38% 3 3 17% 27% 11%	4080
	21st to end	Day	53% 2 3 13% 15% 13%	4488
February	1st to 10th	Day	50% 5% 5% 13% 17% 11%	1829
	11th to 20th	Day	50% 4 6% 14% 16% 10%	2009
	21st to end	Day	48% 5% 7% 13% 16% 10%	1815
March	1st to 10th	Day	49% 5% 7% 11% 18% 11%	4936
	11th to 20th	Day	38% 5% 7% 12% 20% 18%	4980
	21st to end	Day	46% 5% 7% 19% 18% 5%	5464
April	1st to 10th	Day	47% 6% 7% 14% 17% 8%	2200
	11th to 20th	Day	44% 5% 8% 15% 17% 10%	2374
	21st to end	Day	40% 7% 9% 18% 21% 5%	2400
May	1st to 10th	Day	50% 7% 9% 21% 10% 3	5476
	11th to 20th	Day	39% 6% 13% 20% 20% 2	5866
	21st to end	Day	40% 8% 11% 27% 12% 2	6447
June	1st to 10th	Day	40% 10% 15% 20% 14% 1	2600
	11th to 20th	Day	36% 10% 16% 22% 14% 2	2600
	21st to end	Day	44% 12% 16% 19% 8%	2600
July	1st to 10th	Day	41% 11% 27% 19% 3	5836
	11th to 20th	Day	40% 11% 23% 21% 5%	5831
	21st to end	Day	42% 11% 17% 23% 7%	6240
August	1st to 10th	Day	18% 8% 14% 36% 23%	4220
	11th to 20th	Day	24% 10% 30% 30% 5% 1	3994
	21st to end	Day	41% 11% 16% 17% 14% 1	4311
September	1st to 10th	Day	41% 10% 12% 16% 15% 6%	2244
	11th to 20th	Day	43% 8% 14% 16% 15% 5%	2200
	21st to end	Day	33% 7% 12% 19% 17% 11%	2200
October	1st to 10th	Day	19% 4 6% 13% 19% 38%	3327
	11th to 20th	Day	20% 4 4 18% 34% 20%	3240
	21st to end	Day	26% 5% 5% 13% 38% 13%	3538
November	1st to 10th	Day	37% 5% 9% 17% 20% 12%	2058
	11th to 20th	Day	36% 5% 6% 15% 24% 13%	2070
	21st to end	Day	43% 4 6% 18% 18% 11%	1965
December	1st to 10th	Day	46% 4 5% 17% 24% 5%	2940
	11th to 20th	Day	43% 6% 7% 13% 21% 10%	3389
	21st to end	Day	41% 4 5% 15% 26% 9%	4488
January	1st to 10th	Night	40% 4 6% 22% 21% 7%	5888
	11th to 20th	Night	39% 2 4 18% 28% 10%	5900
	21st to end	Night	54% 3 3 13% 16% 11%	6490
February	1st to 10th	Night	47% 4 6% 13% 16% 13%	2587
	11th to 20th	Night	47% 4 7% 14% 18% 10%	2285
	21st to end	Night	49% 4 6% 13% 15% 12%	1815
March	1st to 10th	Night	50% 3 5% 12% 19% 10%	4919
	11th to 20th	Night	43% 5% 6% 13% 16% 16%	4980
	21st to end	Night	47% 5% 7% 15% 19% 7%	5467
April	1st to 10th	Night	44% 6% 9% 15% 15% 10%	2200
	11th to 20th	Night	42% 5% 8% 16% 15% 13%	1975
	21st to end	Night	40% 6% 8% 20% 20% 6%	2000
May	1st to 10th	Night	55% 5% 10% 17% 9% 3	4481
	11th to 20th	Night	41% 7% 12% 19% 19% 2	4054
	21st to end	Night	43% 9% 17% 23% 7% 1	4452
June	1st to 10th	Night	25% 9% 19% 31% 16%	1800
	11th to 20th	Night	22% 10% 20% 30% 16% 3	1800
	21st to end	Night	30% 11% 21% 28% 10% 1	1800
July	1st to 10th	Night	32% 9% 34% 22% 3	4035
	11th to 20th	Night	27% 10% 29% 28% 6%	4026
	21st to end	Night	35% 10% 19% 29% 7%	4320
August	1st to 10th	Night	11% 6% 20% 42% 20%	2916
	11th to 20th	Night	15% 7% 35% 36% 7%	3123
	21st to end	Night	31% 14% 20% 23% 11% 2	3586
September	1st to 10th	Night	30% 10% 20% 21% 13% 6%	2150
	11th to 20th	Night	37% 8% 16% 18% 15% 5%	2200
	21st to end	Night	28% 6% 13% 23% 19% 12%	2200
October	1st to 10th	Night	17% 4 7% 18% 18% 37%	3818
	11th to 20th	Night	16% 3 4 23% 32% 22%	3899
	21st to end	Night	24% 4 5% 13% 40% 15%	4252
November	1st to 10th	Night	32% 4 11% 18% 23% 11%	2460
	11th to 20th	Night	33% 4 8% 18% 23% 13%	2485
	21st to end	Night	40% 4 8% 18% 19% 11%	2430
December	1st to 10th	Night	49% 4 5% 17% 19% 6%	4250
	11th to 20th	Night	43% 4 8% 11% 21% 13%	4817
	21st to end	Night	40% 4 6% 14% 28% 9%	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	26% 18% 36% 15% 4 1	300
	11th to 20th	Day	28% 17% 31% 19% 4 1	300
	21st to end	Day	27% 21% 32% 17% 3	330
February	1st to 10th	Day	28% 18% 35% 14% 4	300
	11th to 20th	Day	31% 20% 31% 16% 2	300
	21st to end	Day	28% 24% 35% 10% 2	249
March	1st to 10th	Day	28% 21% 30% 16% 5%	300
	11th to 20th	Day	22% 31% 31% 13% 2	300
	21st to end	Day	22% 18% 40% 15% 4 1	330
April	1st to 10th	Day	25% 18% 35% 20% 2	300
	11th to 20th	Day	25% 19% 24% 22% 10%	492
	21st to end	Day	16% 17% 34% 23% 9% 2	500
May	1st to 10th	Day	19% 15% 32% 23% 10% 1	513
	11th to 20th	Day	12% 12% 29% 30% 15% 2	725
	21st to end	Day	9% 10% 31% 31% 15% 3	789
June	1st to 10th	Day	8% 3 19% 33% 28% 8%	730
	11th to 20th	Day	8% 3 20% 36% 26% 8%	730
	21st to end	Day	8% 1 15% 31% 30% 14%	730
July	1st to 10th	Day	7% 3 10% 28% 35% 17%	721
	11th to 20th	Day	5% 1 6% 29% 41% 17%	718
	21st to end	Day	8% 2 6% 28% 39% 17%	794
August	1st to 10th	Day	3 1 5% 28% 44% 19%	726
	11th to 20th	Day	5% 2 22% 48% 23%	590
	21st to end	Day	12% 2 6% 19% 35% 25%	583
September	1st to 10th	Day	8% 2 10% 29% 36% 16%	374
	11th to 20th	Day	11% 2 12% 30% 34% 11%	330
	21st to end	Day	11% 2 14% 34% 29% 10%	330
October	1st to 10th	Day	5% 4 20% 43% 22% 5%	330
	11th to 20th	Day	8% 5% 24% 42% 15% 6%	330
	21st to end	Day	20% 9% 26% 26% 16% 3	363
November	1st to 10th	Day	15% 9% 26% 32% 15% 2	330
	11th to 20th	Day	13% 12% 31% 34% 8% 1	321
	21st to end	Day	21% 19% 30% 20% 9% 2	300
December	1st to 10th	Day	20% 12% 34% 23% 7% 3	300
	11th to 20th	Day	24% 14% 35% 22% 3 1	300
	21st to end	Day	22% 18% 34% 19% 5% 1	330
January	1st to 10th	Night	24% 13% 30% 28% 6%	1000
	11th to 20th	Night	24% 13% 29% 27% 7% 1	1000
	21st to end	Night	26% 11% 28% 29% 5%	1100
February	1st to 10th	Night	25% 16% 30% 25% 3	987
	11th to 20th	Night	30% 12% 30% 23% 5%	731
	21st to end	Night	25% 17% 34% 23% 2	495
March	1st to 10th	Night	27% 12% 33% 24% 4	600
	11th to 20th	Night	20% 14% 35% 27% 5%	600
	21st to end	Night	20% 10% 38% 24% 8%	660
April	1st to 10th	Night	20% 12% 38% 25% 6%	600
	11th to 20th	Night	19% 13% 33% 27% 8%	593
	21st to end	Night	20% 12% 30% 30% 8%	600
May	1st to 10th	Night	18% 10% 34% 30% 7%	600
	11th to 20th	Night	15% 7% 29% 33% 14% 1	591
	21st to end	Night	8% 5% 29% 38% 19% 2	650
June	1st to 10th	Night	7% 3 16% 41% 31% 4	600
	11th to 20th	Night	4 3 20% 44% 26% 3	600
	21st to end	Night	7% 3 11% 37% 35% 7%	600
July	1st to 10th	Night	5% 2 7% 41% 35% 10%	585
	11th to 20th	Night	4 1 6% 41% 43% 6%	582
	21st to end	Night	5% 1 5% 41% 42% 6%	657
August	1st to 10th	Night	2 5% 41% 48% 5%	597
	11th to 20th	Night	5% 4 38% 45% 8%	594
	21st to end	Night	7% 1 5% 31% 47% 9%	660
September	1st to 10th	Night	8% 2 7% 30% 46% 8%	600
	11th to 20th	Night	12% 2 8% 28% 43% 7%	600
	21st to end	Night	8% 1 11% 36% 39% 6%	600
October	1st to 10th	Night	6% 2 14% 35% 38% 4	737
	11th to 20th	Night	11% 5% 24% 38% 22% 2	800
	21st to end	Night	13% 9% 24% 33% 20% 2	880
November	1st to 10th	Night	13% 5% 24% 35% 21% 2	820
	11th to 20th	Night	14% 10% 25% 38% 14% 1	829
	21st to end	Night	20% 10% 28% 27% 13% 1	830
December	1st to 10th	Night	23% 10% 27% 28% 12% 1	1000
	11th to 20th	Night	27% 11% 27% 29% 6%	1000
	21st to end	Night	23% 12% 29% 29% 7%	1100

Page generated at 2025-11-14 23:55:56. Version ac07

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