CoolHaven Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CoolHaven Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	11% 7% 2 6% 4 4 4 4 5% 7% 46%	131333
	Night	11% 7% 2 6% 4 4 4 3 5% 6% 49%	131414
Transparency	Day	36% 5% 10% 25% 19% 4	134942
	Night	35% 5% 10% 25% 20% 5%	135882
Seeing	Day	16% 12% 26% 25% 16% 5%	17413
	Night	15% 11% 28% 30% 14% 2	27339

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	12% 11% 3 6% 5% 4 3 3 4 5% 44%	5289
	11th to 20th	Day	7% 8% 3 6% 4 4 4 3 4 5% 53%	5310
	21st to end	Day	17% 8% 3 6% 3 3 3 3 4 4 46%	5812
February	1st to 10th	Day	16% 10% 3 6% 5% 5% 3 3 4 5% 41%	1890
	11th to 20th	Day	13% 10% 2 7% 5% 4 3 3 5% 5% 42%	1894
	21st to end	Day	13% 11% 3 6% 4 4 4 4 4 6% 42%	1819
March	1st to 10th	Day	13% 11% 2 5% 3 3 3 3 4 6% 46%	5046
	11th to 20th	Day	9% 5% 1 4 3 3 3 3 5% 7% 55%	5090
	21st to end	Day	12% 8% 3 7% 5% 5% 5% 4 6% 7% 38%	5583
April	1st to 10th	Day	12% 7% 2 6% 4 4 5% 4 5% 6% 44%	2486
	11th to 20th	Day	15% 7% 2 8% 5% 4 4 4 5% 6% 41%	2494
	21st to end	Day	17% 9% 2 7% 5% 4 4 3 5% 5% 38%	2520
May	1st to 10th	Day	15% 7% 2 7% 5% 5% 5% 5% 7% 8% 35%	5686
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 4 5% 7% 41%	5862
	21st to end	Day	18% 7% 2 6% 5% 4 5% 3 5% 7% 37%	6474
June	1st to 10th	Day	8% 5% 2 5% 5% 5% 5% 4 7% 10% 43%	2800
	11th to 20th	Day	6% 4 2 5% 5% 5% 5% 5% 7% 9% 46%	2800
	21st to end	Day	4 4 1 5% 4 5% 5% 5% 7% 9% 52%	2709
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 4 7% 11% 42%	5900
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 4 7% 11% 45%	5900
	21st to end	Day	5% 4 2 5% 4 5% 6% 5% 8% 10% 46%	6422
August	1st to 10th	Day	5% 3 1 5% 4 3 4 3 5% 8% 58%	4234
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 9% 45%	4017
	21st to end	Day	5% 4 2 5% 4 5% 5% 4 6% 8% 52%	4312
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 5% 6% 49%	2400
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 3 5% 7% 45%	2338
	21st to end	Day	8% 4 2 5% 4 4 4 3 5% 7% 52%	2116
October	1st to 10th	Day	8% 4 2 5% 3 4 4 3 5% 6% 57%	2000
	11th to 20th	Day	13% 6% 1 4 3 3 3 2 3 5% 58%	2000
	21st to end	Day	18% 7% 2 5% 3 3 3 2 4 5% 49%	2200
November	1st to 10th	Day	11% 6% 2 5% 2 3 3 3 4 5% 57%	2058
	11th to 20th	Day	11% 6% 1 5% 4 4 4 3 5% 6% 52%	2016
	21st to end	Day	14% 7% 3 6% 3 3 3 3 5% 5% 48%	1701
December	1st to 10th	Day	11% 8% 2 6% 3 2 3 3 4 4 54%	2690
	11th to 20th	Day	11% 9% 3 6% 4 4 3 3 4 5% 48%	3088
	21st to end	Day	14% 19% 4 7% 3 4 3 3 4 4 33%	4377
January	1st to 10th	Night	12% 8% 3 8% 5% 4 3 3 5% 5% 43%	7634
	11th to 20th	Night	7% 6% 2 7% 4 4 4 2 4 5% 54%	7680
	21st to end	Night	17% 9% 4 6% 4 5% 3 2 4 4 42%	8402
February	1st to 10th	Night	14% 11% 3 6% 3 3 3 3 5% 6% 43%	2730
	11th to 20th	Night	15% 8% 3 7% 3 3 4 2 4 5% 45%	2611
	21st to end	Night	13% 9% 2 6% 3 3 3 3 5% 5% 48%	2005
March	1st to 10th	Night	17% 10% 3 6% 4 3 4 2 4 4 44%	5029
	11th to 20th	Night	9% 9% 2 5% 3 3 3 3 5% 6% 53%	5090
	21st to end	Night	10% 7% 3 7% 5% 4 5% 4 5% 8% 43%	5588
April	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 5% 7% 50%	2132
	11th to 20th	Night	12% 7% 3 5% 3 3 4 3 6% 7% 48%	2075
	21st to end	Night	17% 7% 2 6% 4 4 4 4 5% 6% 43%	2100
May	1st to 10th	Night	14% 8% 3 6% 4 3 4 3 5% 7% 44%	4239
	11th to 20th	Night	11% 7% 2 7% 4 5% 5% 4 7% 8% 40%	4053
	21st to end	Night	18% 8% 2 6% 4 4 4 3 5% 7% 38%	4398
June	1st to 10th	Night	7% 4 2 4 3 4 3 4 7% 10% 53%	1600
	11th to 20th	Night	5% 3 1 4 2 3 3 4 6% 11% 58%	1600
	21st to end	Night	2 2 1 3 3 4 4 4 5% 8% 62%	1682
July	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 4 6% 9% 45%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 3 5% 9% 59%	4077
	21st to end	Night	5% 4 2 5% 4 3 4 3 6% 10% 54%	4449
August	1st to 10th	Night	3 2 1 4 3 3 3 4 6% 9% 60%	2926
	11th to 20th	Night	6% 4 2 5% 4 4 5% 4 5% 8% 52%	3036
	21st to end	Night	4 3 2 4 3 3 3 4 5% 8% 61%	3586
September	1st to 10th	Night	9% 3 1 4 3 3 3 4 6% 8% 54%	2000
	11th to 20th	Night	10% 5% 2 6% 5% 4 3 3 4 6% 51%	2058
	21st to end	Night	8% 4 2 6% 4 3 3 3 4 6% 57%	2262
October	1st to 10th	Night	6% 4 1 4 3 4 4 3 4 6% 62%	2400
	11th to 20th	Night	13% 4 1 4 3 3 3 2 4 6% 57%	2400
	21st to end	Night	15% 8% 2 4 3 3 3 2 4 4 52%	2640
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 5% 59%	2460
	11th to 20th	Night	10% 6% 2 4 3 3 4 3 5% 6% 57%	2599
	21st to end	Night	14% 8% 2 4 3 3 3 3 4 6% 49%	2914
December	1st to 10th	Night	11% 9% 2 5% 3 3 3 2 4 6% 52%	4720
	11th to 20th	Night	12% 8% 3 8% 4 4 3 2 3 4 49%	5339
	21st to end	Night	17% 14% 5% 7% 4 4 4 3 4 4 34%	6822

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	43% 3 9% 25% 18% 2	5290
	11th to 20th	Day	33% 3 8% 26% 26% 5%	5310
	21st to end	Day	42% 3 6% 20% 22% 7%	5812
February	1st to 10th	Day	47% 4 10% 22% 14% 3	1890
	11th to 20th	Day	44% 4 9% 22% 18% 4	1903
	21st to end	Day	43% 4 8% 19% 18% 8%	1819
March	1st to 10th	Day	40% 4 7% 19% 15% 14%	5046
	11th to 20th	Day	30% 3 8% 22% 24% 13%	5090
	21st to end	Day	42% 6% 9% 30% 12% 1	5585
April	1st to 10th	Day	39% 5% 11% 22% 20% 2	2486
	11th to 20th	Day	43% 5% 11% 19% 18% 4	2494
	21st to end	Day	48% 6% 9% 22% 14% 2	2520
May	1st to 10th	Day	45% 7% 11% 23% 14% 1	5721
	11th to 20th	Day	40% 8% 12% 24% 15% 1	5866
	21st to end	Day	46% 6% 11% 18% 17% 1	6488
June	1st to 10th	Day	34% 8% 16% 26% 15% 1	2800
	11th to 20th	Day	32% 7% 15% 29% 15% 2	2800
	21st to end	Day	26% 7% 16% 30% 17% 4	2709
July	1st to 10th	Day	34% 8% 15% 26% 15% 3	5836
	11th to 20th	Day	31% 8% 15% 30% 15% 1	5831
	21st to end	Day	31% 8% 17% 30% 13% 1	6240
August	1st to 10th	Day	23% 6% 16% 31% 20% 3	4220
	11th to 20th	Day	36% 7% 15% 29% 13% 1	4056
	21st to end	Day	28% 7% 13% 34% 15% 3	4311
September	1st to 10th	Day	34% 5% 11% 25% 17% 8%	2400
	11th to 20th	Day	37% 6% 10% 23% 22% 3	2338
	21st to end	Day	30% 5% 8% 26% 27% 4	2116
October	1st to 10th	Day	17% 3 6% 17% 41% 17%	3260
	11th to 20th	Day	20% 2 4 21% 38% 14%	3240
	21st to end	Day	31% 3 7% 31% 24% 4	3538
November	1st to 10th	Day	31% 4 8% 27% 22% 8%	2058
	11th to 20th	Day	33% 4 7% 24% 23% 9%	2016
	21st to end	Day	39% 5% 8% 19% 24% 4	1701
December	1st to 10th	Day	35% 4 7% 30% 22% 2	2690
	11th to 20th	Day	38% 4 6% 26% 24% 2	3085
	21st to end	Day	52% 5% 8% 21% 11% 2	4377
January	1st to 10th	Night	41% 5% 9% 28% 15% 3	7635
	11th to 20th	Night	32% 4 8% 19% 33% 5%	7680
	21st to end	Night	45% 2 8% 18% 22% 4	8402
February	1st to 10th	Night	43% 4 10% 24% 15% 4	2730
	11th to 20th	Night	43% 3 8% 23% 19% 4	2612
	21st to end	Night	38% 3 8% 21% 21% 8%	2005
March	1st to 10th	Night	45% 4 6% 17% 18% 11%	5029
	11th to 20th	Night	33% 4 7% 23% 20% 12%	5090
	21st to end	Night	38% 7% 10% 28% 15% 2	5588
April	1st to 10th	Night	34% 5% 11% 25% 20% 5%	2132
	11th to 20th	Night	36% 5% 9% 25% 19% 6%	2075
	21st to end	Night	42% 5% 10% 26% 14% 2	2100
May	1st to 10th	Night	41% 6% 12% 26% 12% 2	4269
	11th to 20th	Night	39% 9% 12% 23% 13% 4	4054
	21st to end	Night	45% 7% 13% 21% 12% 3	4406
June	1st to 10th	Night	25% 8% 15% 32% 17% 4	1600
	11th to 20th	Night	20% 7% 15% 34% 20% 3	1600
	21st to end	Night	18% 6% 17% 31% 21% 7%	1682
July	1st to 10th	Night	33% 8% 16% 25% 16% 3	4035
	11th to 20th	Night	22% 6% 16% 36% 18% 1	4026
	21st to end	Night	25% 6% 17% 34% 17% 1	4320
August	1st to 10th	Night	20% 6% 16% 36% 22% 1	2916
	11th to 20th	Night	29% 6% 17% 30% 16% 2	3063
	21st to end	Night	21% 5% 13% 36% 22% 3	3586
September	1st to 10th	Night	25% 7% 12% 30% 18% 8%	2000
	11th to 20th	Night	34% 6% 11% 21% 24% 4	2058
	21st to end	Night	29% 4 10% 22% 31% 5%	2262
October	1st to 10th	Night	14% 3 7% 15% 38% 23%	3920
	11th to 20th	Night	20% 2 5% 18% 35% 20%	3899
	21st to end	Night	29% 3 6% 31% 25% 7%	4252
November	1st to 10th	Night	29% 4 8% 24% 27% 8%	2460
	11th to 20th	Night	29% 3 7% 27% 26% 7%	2599
	21st to end	Night	37% 4 8% 23% 23% 5%	2914
December	1st to 10th	Night	35% 4 8% 35% 16% 2	4720
	11th to 20th	Night	41% 3 6% 23% 23% 4	5341
	21st to end	Night	51% 5% 9% 22% 9% 3	6822

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	25% 22% 34% 15% 4	330
	11th to 20th	Day	28% 24% 36% 10% 2	330
	21st to end	Day	25% 28% 34% 10% 3	363
February	1st to 10th	Day	24% 28% 34% 12% 3	330
	11th to 20th	Day	27% 30% 28% 12% 3	330
	21st to end	Day	31% 27% 32% 8% 2	273
March	1st to 10th	Day	25% 24% 35% 14% 2	330
	11th to 20th	Day	30% 27% 29% 13% 1	330
	21st to end	Day	26% 25% 38% 8% 2	363
April	1st to 10th	Day	23% 22% 31% 17% 6% 1	506
	11th to 20th	Day	25% 20% 33% 15% 6% 1	532
	21st to end	Day	26% 16% 33% 19% 4 2	540
May	1st to 10th	Day	20% 16% 35% 22% 7%	620
	11th to 20th	Day	15% 12% 33% 24% 13% 2	725
	21st to end	Day	12% 9% 36% 24% 14% 4	789
June	1st to 10th	Day	11% 4 21% 33% 24% 6%	730
	11th to 20th	Day	7% 3 19% 40% 23% 7%	730
	21st to end	Day	4 3 26% 35% 27% 5%	730
July	1st to 10th	Day	9% 2 16% 31% 31% 10%	721
	11th to 20th	Day	5% 3 17% 31% 33% 11%	718
	21st to end	Day	8% 2 10% 32% 35% 13%	794
August	1st to 10th	Day	8% 3 13% 40% 28% 7%	726
	11th to 20th	Day	13% 2 11% 34% 33% 8%	626
	21st to end	Day	9% 2 13% 30% 31% 15%	583
September	1st to 10th	Day	10% 3 12% 36% 30% 9%	530
	11th to 20th	Day	11% 2 15% 35% 26% 10%	468
	21st to end	Day	11% 8% 25% 27% 22% 6%	330
October	1st to 10th	Day	11% 7% 28% 32% 20% 3	330
	11th to 20th	Day	16% 14% 35% 25% 9% 1	330
	21st to end	Day	30% 17% 30% 17% 6% 1	363
November	1st to 10th	Day	16% 17% 34% 22% 8% 2	330
	11th to 20th	Day	19% 18% 37% 18% 7% 1	330
	21st to end	Day	25% 19% 32% 16% 6% 1	330
December	1st to 10th	Day	21% 26% 31% 15% 5% 2	330
	11th to 20th	Day	24% 21% 33% 16% 6%	330
	21st to end	Day	26% 23% 35% 14% 3	363
January	1st to 10th	Night	19% 20% 33% 24% 4	1050
	11th to 20th	Night	20% 22% 35% 20% 3	1050
	21st to end	Night	19% 21% 37% 21% 3	1155
February	1st to 10th	Night	19% 17% 39% 20% 4	1050
	11th to 20th	Night	23% 19% 38% 19% 2	977
	21st to end	Night	20% 20% 38% 20% 2	621
March	1st to 10th	Night	22% 15% 36% 24% 3	630
	11th to 20th	Night	23% 15% 32% 27% 3	630
	21st to end	Night	19% 15% 39% 22% 5%	693
April	1st to 10th	Night	15% 19% 37% 25% 4	630
	11th to 20th	Night	17% 17% 35% 24% 6%	623
	21st to end	Night	20% 13% 35% 25% 7% 1	630
May	1st to 10th	Night	14% 9% 32% 37% 8%	603
	11th to 20th	Night	16% 7% 29% 28% 17% 2	591
	21st to end	Night	13% 5% 26% 34% 19% 4	650
June	1st to 10th	Night	9% 4 16% 39% 29% 3	600
	11th to 20th	Night	6% 2 18% 45% 27% 2	600
	21st to end	Night	2 2 21% 45% 28% 2	600
July	1st to 10th	Night	5% 2 11% 37% 39% 6%	585
	11th to 20th	Night	4 1 9% 43% 36% 7%	582
	21st to end	Night	6% 2 7% 42% 36% 7%	657
August	1st to 10th	Night	6% 2 9% 41% 38% 4	597
	11th to 20th	Night	7% 1 11% 42% 36% 3	594
	21st to end	Night	6% 2 11% 39% 37% 6%	660
September	1st to 10th	Night	9% 2 11% 39% 36% 2	600
	11th to 20th	Night	13% 1 10% 38% 34% 5%	600
	21st to end	Night	10% 4 19% 33% 29% 4	662
October	1st to 10th	Night	8% 4 22% 39% 25% 3	800
	11th to 20th	Night	15% 11% 29% 33% 13%	800
	21st to end	Night	21% 12% 29% 28% 10%	880
November	1st to 10th	Night	14% 11% 34% 30% 12%	820
	11th to 20th	Night	14% 13% 34% 30% 8%	840
	21st to end	Night	20% 14% 34% 24% 8%	1024
December	1st to 10th	Night	19% 13% 36% 26% 5%	1050
	11th to 20th	Night	21% 15% 34% 26% 4	1050
	21st to end	Night	22% 17% 35% 23% 3	1155

Page generated at 2026-04-29 01:21:48. Version ac07

Copyright © 2026 Attilla Danko.