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 2025-01-07.

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% 45%	104577
	Night	11% 7% 2 5% 4 3 4 3 5% 6% 49%	104540
Transparency	Day	36% 6% 11% 25% 18% 4	108225
	Night	34% 5% 10% 26% 20% 5%	109032
Seeing	Day	16% 12% 26% 25% 17% 5%	15672
	Night	15% 11% 28% 30% 14% 2	25570

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% 11% 4 6% 4 2 3 3 4 5% 46%	2901
	11th to 20th	Day	10% 8% 3 7% 4 4 4 3 4 6% 47%	2850
	21st to end	Day	22% 9% 3 6% 3 2 3 2 4 4 43%	3135
February	1st to 10th	Day	15% 11% 3 6% 5% 5% 3 3 3 4 41%	1710
	11th to 20th	Day	13% 10% 2 7% 5% 4 4 3 5% 5% 43%	1708
	21st to end	Day	14% 11% 3 6% 4 4 4 4 4 6% 39%	1651
March	1st to 10th	Day	15% 9% 3 6% 3 3 3 3 4 5% 46%	3436
	11th to 20th	Day	12% 7% 2 5% 3 3 3 3 4 7% 51%	3480
	21st to end	Day	15% 10% 3 7% 5% 5% 4 3 5% 5% 38%	3814
April	1st to 10th	Day	10% 7% 2 6% 4 4 5% 4 6% 6% 44%	2249
	11th to 20th	Day	15% 7% 2 8% 4 4 4 4 5% 6% 41%	2254
	21st to end	Day	18% 9% 2 7% 5% 4 4 3 4 4 39%	2280
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 7% 36%	3950
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 4 6% 7% 41%	4082
	21st to end	Day	13% 6% 2 7% 6% 5% 6% 4 5% 8% 38%	4503
June	1st to 10th	Day	8% 5% 2 5% 5% 5% 5% 4 7% 11% 43%	2660
	11th to 20th	Day	6% 4 2 5% 5% 5% 5% 5% 7% 9% 47%	2660
	21st to end	Day	4 4 1 5% 4 5% 5% 5% 7% 9% 52%	2574
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 42%	4120
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 7% 12% 48%	4120
	21st to end	Day	7% 5% 3 6% 5% 5% 6% 5% 8% 10% 39%	4465
August	1st to 10th	Day	5% 3 1 5% 4 3 4 3 5% 8% 58%	4104
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 45%	3892
	21st to end	Day	5% 4 2 5% 4 5% 5% 4 6% 9% 53%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 5% 6% 49%	2280
	11th to 20th	Day	12% 6% 2 5% 5% 4 5% 3 5% 7% 46%	2221
	21st to end	Day	8% 4 2 5% 4 5% 4 3 5% 7% 52%	2010
October	1st to 10th	Day	9% 4 2 5% 3 4 4 3 5% 6% 56%	1900
	11th to 20th	Day	13% 6% 1 4 2 3 3 2 3 5% 58%	1900
	21st to end	Day	17% 7% 2 5% 3 3 3 2 4 5% 49%	2090
November	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 4 5% 56%	1958
	11th to 20th	Day	11% 6% 1 5% 4 3 3 3 5% 6% 52%	1920
	21st to end	Day	14% 7% 3 5% 4 3 3 3 5% 4 48%	1620
December	1st to 10th	Day	11% 8% 2 5% 3 3 3 3 4 4 54%	2610
	11th to 20th	Day	11% 9% 3 6% 4 4 3 3 4 5% 48%	3008
	21st to end	Day	15% 20% 4 7% 3 4 3 3 4 4 32%	4282
January	1st to 10th	Night	12% 7% 4 8% 5% 4 4 4 6% 6% 41%	4187
	11th to 20th	Night	10% 7% 3 8% 4 5% 6% 3 4 6% 46%	4120
	21st to end	Night	22% 11% 4 5% 2 2 2 2 3 4 42%	4532
February	1st to 10th	Night	14% 11% 3 7% 4 3 3 3 5% 6% 42%	2470
	11th to 20th	Night	15% 8% 3 7% 3 3 4 3 4 5% 46%	2357
	21st to end	Night	14% 9% 2 6% 3 3 3 3 5% 5% 47%	1820
March	1st to 10th	Night	20% 8% 3 5% 3 3 3 2 4 4 44%	3419
	11th to 20th	Night	12% 7% 2 5% 4 3 3 2 4 6% 52%	3480
	21st to end	Night	12% 9% 3 8% 5% 4 5% 4 5% 7% 39%	3817
April	1st to 10th	Night	10% 7% 2 5% 3 3 4 3 5% 6% 51%	1929
	11th to 20th	Night	12% 7% 3 5% 3 3 4 3 6% 7% 48%	1875
	21st to end	Night	17% 6% 2 6% 4 4 4 4 5% 5% 43%	1900
May	1st to 10th	Night	13% 7% 2 5% 4 4 4 3 5% 7% 46%	2947
	11th to 20th	Night	12% 7% 2 5% 4 4 4 4 6% 8% 42%	2823
	21st to end	Night	11% 7% 2 6% 5% 4 5% 4 6% 9% 41%	3059
June	1st to 10th	Night	7% 4 2 4 3 3 3 4 7% 10% 54%	1520
	11th to 20th	Night	4 3 2 4 2 3 3 4 6% 11% 59%	1520
	21st to end	Night	3 3 1 3 3 4 4 5% 5% 9% 62%	1598
July	1st to 10th	Night	8% 4 2 6% 4 4 5% 4 5% 8% 49%	2850
	11th to 20th	Night	5% 2 1 3 3 2 4 4 5% 8% 62%	2850
	21st to end	Night	6% 5% 2 7% 4 4 4 3 7% 9% 48%	3098
August	1st to 10th	Night	3 2 1 4 3 3 3 4 6% 9% 60%	2836
	11th to 20th	Night	7% 4 2 5% 4 4 5% 4 5% 9% 52%	2941
	21st to end	Night	4 3 2 4 3 3 3 4 5% 8% 62%	3476
September	1st to 10th	Night	9% 3 1 4 3 3 3 4 6% 8% 56%	1900
	11th to 20th	Night	10% 6% 2 6% 5% 4 3 3 4 6% 51%	1955
	21st to end	Night	7% 4 2 6% 3 3 3 3 4 6% 58%	2149
October	1st to 10th	Night	6% 4 1 4 3 4 4 3 4 6% 62%	2280
	11th to 20th	Night	13% 5% 1 4 2 3 3 2 4 6% 56%	2280
	21st to end	Night	15% 7% 2 4 3 3 3 2 4 4 53%	2508
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 4 5% 58%	2340
	11th to 20th	Night	10% 6% 2 4 3 3 4 3 5% 6% 56%	2475
	21st to end	Night	13% 8% 2 3 3 3 3 3 4 6% 50%	2775
December	1st to 10th	Night	11% 9% 2 5% 3 3 3 2 4 6% 52%	4580
	11th to 20th	Night	13% 8% 3 8% 4 4 3 2 3 4 48%	5199
	21st to end	Night	18% 14% 5% 7% 4 4 4 3 4 4 33%	6675

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% 4 7% 27% 20% 2	2902
	11th to 20th	Day	35% 5% 12% 26% 18% 4	2850
	21st to end	Day	44% 5% 8% 19% 19% 5%	3135
February	1st to 10th	Day	47% 4 10% 22% 14% 3	1710
	11th to 20th	Day	44% 4 8% 23% 17% 4	1717
	21st to end	Day	45% 4 9% 19% 15% 9%	1651
March	1st to 10th	Day	41% 5% 7% 18% 19% 10%	3436
	11th to 20th	Day	34% 4 9% 27% 20% 6%	3480
	21st to end	Day	46% 8% 9% 24% 13% 1	3814
April	1st to 10th	Day	38% 6% 11% 23% 20% 3	2249
	11th to 20th	Day	43% 6% 11% 19% 18% 4	2254
	21st to end	Day	48% 6% 8% 22% 15% 2	2280
May	1st to 10th	Day	44% 8% 11% 22% 14% 1	3985
	11th to 20th	Day	39% 10% 13% 25% 13% 1	4086
	21st to end	Day	41% 8% 13% 21% 15% 1	4516
June	1st to 10th	Day	34% 8% 16% 26% 15% 1	2660
	11th to 20th	Day	30% 8% 15% 30% 15% 2	2660
	21st to end	Day	26% 7% 16% 29% 17% 4	2574
July	1st to 10th	Day	35% 8% 16% 26% 13% 2	4056
	11th to 20th	Day	27% 7% 13% 33% 19% 2	4051
	21st to end	Day	36% 9% 19% 27% 9%	4325
August	1st to 10th	Day	23% 7% 17% 30% 21% 3	4090
	11th to 20th	Day	36% 7% 15% 28% 13% 1	3931
	21st to end	Day	27% 7% 13% 34% 15% 3	4179
September	1st to 10th	Day	34% 5% 11% 24% 17% 8%	2280
	11th to 20th	Day	36% 6% 10% 22% 23% 3	2221
	21st to end	Day	30% 5% 8% 27% 26% 4	2010
October	1st to 10th	Day	17% 3 6% 17% 40% 17%	3160
	11th to 20th	Day	20% 2 4 20% 38% 15%	3140
	21st to end	Day	30% 3 7% 31% 24% 4	3428
November	1st to 10th	Day	32% 4 8% 27% 22% 8%	1958
	11th to 20th	Day	33% 4 7% 23% 23% 10%	1920
	21st to end	Day	39% 5% 8% 19% 25% 4	1620
December	1st to 10th	Day	35% 4 7% 30% 22% 2	2610
	11th to 20th	Day	39% 4 6% 25% 24% 2	3005
	21st to end	Day	54% 5% 8% 20% 11% 2	4282
January	1st to 10th	Night	41% 6% 8% 24% 19% 2	4187
	11th to 20th	Night	37% 6% 12% 23% 19% 3	4120
	21st to end	Night	46% 4 9% 20% 18% 3	4532
February	1st to 10th	Night	44% 4 10% 23% 15% 4	2470
	11th to 20th	Night	41% 4 8% 23% 19% 4	2358
	21st to end	Night	40% 3 8% 21% 20% 8%	1820
March	1st to 10th	Night	44% 5% 7% 18% 18% 9%	3419
	11th to 20th	Night	35% 5% 9% 27% 19% 4	3480
	21st to end	Night	41% 8% 10% 26% 14% 1	3817
April	1st to 10th	Night	33% 5% 11% 24% 22% 6%	1929
	11th to 20th	Night	35% 5% 9% 25% 19% 6%	1875
	21st to end	Night	41% 6% 10% 26% 15% 2	1900
May	1st to 10th	Night	38% 7% 13% 24% 15% 3	2977
	11th to 20th	Night	36% 10% 14% 24% 14% 1	2824
	21st to end	Night	38% 9% 15% 26% 12% 1	3067
June	1st to 10th	Night	24% 8% 15% 33% 17% 4	1520
	11th to 20th	Night	18% 7% 16% 36% 21% 3	1520
	21st to end	Night	19% 6% 16% 31% 21% 8%	1598
July	1st to 10th	Night	33% 7% 17% 24% 15% 4	2805
	11th to 20th	Night	20% 5% 11% 38% 24% 2	2796
	21st to end	Night	31% 7% 18% 32% 13%	2999
August	1st to 10th	Night	20% 6% 16% 35% 22% 1	2826
	11th to 20th	Night	29% 6% 17% 30% 16% 2	2968
	21st to end	Night	20% 5% 13% 37% 22% 3	3476
September	1st to 10th	Night	24% 7% 12% 30% 19% 8%	1900
	11th to 20th	Night	34% 5% 10% 21% 25% 5%	1955
	21st to end	Night	28% 4 10% 23% 30% 5%	2149
October	1st to 10th	Night	14% 3 7% 15% 38% 23%	3800
	11th to 20th	Night	20% 2 4 18% 35% 21%	3779
	21st to end	Night	28% 3 6% 31% 25% 7%	4120
November	1st to 10th	Night	30% 4 8% 24% 26% 8%	2340
	11th to 20th	Night	30% 3 7% 25% 27% 8%	2475
	21st to end	Night	35% 4 9% 23% 24% 5%	2775
December	1st to 10th	Night	34% 4 8% 35% 17% 2	4580
	11th to 20th	Night	41% 3 6% 23% 23% 4	5201
	21st to end	Night	52% 5% 8% 22% 9% 3	6675

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	23% 22% 35% 15% 5%	288
	11th to 20th	Day	30% 22% 35% 11% 2	270
	21st to end	Day	25% 30% 31% 10% 4	297
February	1st to 10th	Day	24% 27% 34% 12% 2	270
	11th to 20th	Day	24% 32% 27% 14% 3	270
	21st to end	Day	36% 25% 31% 7% 1	225
March	1st to 10th	Day	25% 22% 37% 14% 2	270
	11th to 20th	Day	29% 27% 30% 13% 1	270
	21st to end	Day	28% 25% 37% 8% 2	297
April	1st to 10th	Day	21% 23% 32% 17% 6% 1	429
	11th to 20th	Day	23% 20% 33% 16% 7% 1	452
	21st to end	Day	27% 16% 33% 17% 5% 2	460
May	1st to 10th	Day	20% 16% 35% 22% 7%	570
	11th to 20th	Day	15% 11% 33% 25% 14% 2	675
	21st to end	Day	11% 9% 35% 25% 15% 5%	734
June	1st to 10th	Day	10% 4 20% 34% 25% 6%	680
	11th to 20th	Day	6% 3 19% 41% 24% 7%	680
	21st to end	Day	4 4 28% 33% 26% 5%	680
July	1st to 10th	Day	9% 2 16% 31% 32% 9%	671
	11th to 20th	Day	5% 2 17% 32% 33% 11%	668
	21st to end	Day	8% 2 10% 32% 34% 14%	739
August	1st to 10th	Day	8% 3 12% 40% 29% 7%	676
	11th to 20th	Day	13% 2 12% 34% 31% 7%	581
	21st to end	Day	9% 2 11% 31% 32% 16%	539
September	1st to 10th	Day	10% 3 12% 35% 30% 10%	490
	11th to 20th	Day	11% 2 16% 37% 25% 9%	431
	21st to end	Day	10% 9% 26% 27% 22% 6%	300
October	1st to 10th	Day	12% 7% 28% 31% 21% 3	300
	11th to 20th	Day	17% 14% 35% 24% 9% 1	300
	21st to end	Day	27% 17% 32% 18% 6% 1	330
November	1st to 10th	Day	16% 15% 34% 23% 9% 3	300
	11th to 20th	Day	19% 18% 37% 17% 7% 1	300
	21st to end	Day	24% 19% 33% 17% 6% 1	300
December	1st to 10th	Day	20% 27% 31% 14% 6% 2	300
	11th to 20th	Day	25% 21% 31% 17% 6%	300
	21st to end	Day	27% 25% 33% 12% 3	330
January	1st to 10th	Night	19% 21% 33% 23% 4	981
	11th to 20th	Night	21% 21% 34% 21% 3 1	950
	21st to end	Night	19% 20% 36% 22% 3	1045
February	1st to 10th	Night	20% 18% 38% 20% 4	950
	11th to 20th	Night	21% 19% 39% 19% 2	883
	21st to end	Night	22% 20% 38% 17% 2	564
March	1st to 10th	Night	21% 14% 37% 25% 3	570
	11th to 20th	Night	22% 15% 31% 29% 3	570
	21st to end	Night	20% 14% 37% 23% 6%	627
April	1st to 10th	Night	14% 19% 37% 25% 5%	570
	11th to 20th	Night	17% 17% 34% 25% 6%	563
	21st to end	Night	19% 13% 36% 24% 7% 1	570
May	1st to 10th	Night	14% 8% 32% 37% 8%	570
	11th to 20th	Night	16% 7% 28% 29% 18% 2	561
	21st to end	Night	12% 5% 26% 35% 19% 4	617
June	1st to 10th	Night	8% 4 15% 39% 30% 2	570
	11th to 20th	Night	5% 2 18% 46% 26% 2	570
	21st to end	Night	2 2 21% 45% 28% 2	570
July	1st to 10th	Night	5% 2 11% 37% 38% 6%	555
	11th to 20th	Night	4 1 9% 42% 36% 8%	552
	21st to end	Night	6% 2 7% 42% 35% 8%	624
August	1st to 10th	Night	6% 2 8% 40% 40% 5%	567
	11th to 20th	Night	7% 1 12% 43% 34% 3	564
	21st to end	Night	6% 2 10% 38% 38% 6%	627
September	1st to 10th	Night	9% 2 11% 39% 36% 2	570
	11th to 20th	Night	13% 1 10% 39% 33% 5%	570
	21st to end	Night	9% 4 20% 33% 30% 4	629
October	1st to 10th	Night	8% 4 22% 38% 25% 3	760
	11th to 20th	Night	15% 11% 30% 32% 12%	760
	21st to end	Night	20% 12% 29% 29% 10%	836
November	1st to 10th	Night	14% 10% 34% 30% 12% 1	780
	11th to 20th	Night	15% 14% 34% 29% 9%	800
	21st to end	Night	19% 14% 34% 24% 9%	975
December	1st to 10th	Night	19% 13% 36% 26% 6%	1000
	11th to 20th	Night	21% 15% 34% 26% 4	1000
	21st to end	Night	23% 18% 34% 23% 3	1100

Page generated at 2025-01-04 02:23:58. Version ac07

Copyright © 2025 Attilla Danko.