Collyer
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Collyer clear sky chart from 2005-11-06 to 2024-11-08.

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	7% 5% 2 5% 3 3 4 3 5% 7% 55%	105150
	Night	7% 5% 2 5% 3 3 4 3 5% 7% 55%	102614
Transparency	Day	28% 3 12% 28% 23% 6%	104906
	Night	29% 3 12% 26% 23% 7%	102448
Seeing	Day	10% 7% 29% 34% 16% 3	15645
	Night	10% 8% 34% 37% 10% 1	25543

By Month

Percentage Cloud Cover SW (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	6% 9% 3 6% 3 3 4 4 6% 7% 49%	2538
	11th to 20th	Day	6% 9% 3 7% 4 4 4 4 4 7% 47%	2610
	21st to end	Day	5% 9% 3 6% 3 3 3 2 4 7% 56%	3135
February	1st to 10th	Day	7% 8% 3 7% 5% 4 3 3 5% 7% 47%	1861
	11th to 20th	Day	4 7% 3 7% 4 4 5% 4 5% 7% 51%	1849
	21st to end	Day	5% 6% 2 5% 4 4 4 3 5% 5% 57%	1570
March	1st to 10th	Day	8% 6% 2 3 3 2 3 3 5% 6% 60%	3130
	11th to 20th	Day	8% 6% 2 5% 3 3 4 3 4 6% 57%	3449
	21st to end	Day	8% 7% 2 5% 3 4 4 4 6% 7% 51%	3814
April	1st to 10th	Day	8% 5% 1 5% 3 3 3 3 5% 6% 57%	2273
	11th to 20th	Day	9% 7% 2 5% 4 3 4 4 6% 7% 48%	2265
	21st to end	Day	12% 6% 2 4 4 3 4 4 5% 7% 47%	2470
May	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 48%	4120
	11th to 20th	Day	10% 4 2 5% 4 4 4 4 6% 9% 49%	4082
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 8% 50%	4489
June	1st to 10th	Day	4 3 1 4 4 3 3 4 5% 9% 61%	2537
	11th to 20th	Day	6% 4 2 4 4 3 4 4 5% 8% 58%	2660
	21st to end	Day	4 4 1 4 4 3 4 3 7% 9% 58%	2660
July	1st to 10th	Day	5% 4 2 5% 4 4 5% 4 6% 9% 51%	4430
	11th to 20th	Day	3 2 1 3 3 3 5% 4 7% 11% 58%	4381
	21st to end	Day	3 2 1 4 3 3 4 4 6% 10% 58%	4466
August	1st to 10th	Day	13% 6% 2 4 3 4 3 4 6% 7% 49%	4103
	11th to 20th	Day	7% 5% 1 5% 4 4 4 4 6% 9% 51%	3959
	21st to end	Day	4 3 1 4 3 3 4 3 6% 8% 60%	4180
September	1st to 10th	Day	9% 4 1 4 3 2 3 3 4 6% 60%	2212
	11th to 20th	Day	7% 5% 1 4 3 3 3 2 5% 7% 61%	2090
	21st to end	Day	7% 4 2 4 3 2 3 2 4 6% 63%	2090
October	1st to 10th	Day	8% 2 1 2 2 2 2 2 3 5% 71%	3480
	11th to 20th	Day	5% 3 1 3 3 2 4 4 5% 6% 64%	3246
	21st to end	Day	6% 5% 1 3 2 2 2 2 4 6% 66%	3122
November	1st to 10th	Day	7% 4 1 4 3 3 3 3 5% 7% 62%	1736
	11th to 20th	Day	4 5% 2 4 3 3 3 3 4 6% 64%	1710
	21st to end	Day	9% 5% 2 4 3 3 3 3 4 5% 60%	1710
December	1st to 10th	Day	4 6% 2 6% 4 4 3 3 4 8% 55%	1710
	11th to 20th	Day	6% 8% 2 5% 3 3 3 3 4 6% 57%	2161
	21st to end	Day	8% 14% 5% 8% 5% 3 4 3 4 6% 40%	2852
January	1st to 10th	Night	5% 8% 3 9% 5% 4 4 2 4 5% 49%	4417
	11th to 20th	Night	4 5% 2 6% 4 5% 4 3 5% 7% 56%	4355
	21st to end	Night	7% 8% 3 6% 3 3 4 3 4 6% 54%	4532
February	1st to 10th	Night	8% 9% 3 7% 4 4 4 3 5% 5% 48%	2337
	11th to 20th	Night	5% 6% 2 7% 4 4 4 4 6% 8% 49%	2218
	21st to end	Night	5% 6% 2 7% 4 3 3 3 4 6% 57%	1884
March	1st to 10th	Night	9% 5% 1 3 3 2 3 3 4 6% 61%	3734
	11th to 20th	Night	6% 4 2 5% 3 3 4 3 6% 8% 56%	3512
	21st to end	Night	8% 7% 2 6% 3 3 3 3 6% 8% 51%	3817
April	1st to 10th	Night	8% 6% 2 5% 4 4 3 3 6% 8% 53%	1904
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 5% 6% 51%	1863
	21st to end	Night	11% 5% 2 5% 2 4 5% 3 6% 8% 50%	1710
May	1st to 10th	Night	12% 7% 2 5% 4 4 5% 4 5% 7% 46%	2850
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 4 8% 49%	2823
	21st to end	Night	10% 4 2 5% 4 4 5% 5% 7% 9% 47%	3098
June	1st to 10th	Night	4 3 1 4 3 4 5% 4 7% 11% 54%	1637
	11th to 20th	Night	7% 3 1 5% 3 3 4 3 8% 10% 53%	1520
	21st to end	Night	5% 4 2 4 4 3 4 3 6% 11% 54%	1520
July	1st to 10th	Night	7% 4 2 6% 4 4 5% 4 6% 8% 50%	2540
	11th to 20th	Night	3 4 1 5% 4 4 5% 5% 8% 11% 49%	2588
	21st to end	Night	4 3 1 3 2 4 3 4 7% 11% 58%	3097
August	1st to 10th	Night	8% 4 2 5% 4 4 5% 5% 8% 9% 46%	2836
	11th to 20th	Night	9% 5% 2 5% 4 3 4 4 6% 10% 49%	2877
	21st to end	Night	3 3 2 4 3 4 5% 5% 9% 11% 51%	3487
September	1st to 10th	Night	6% 4 2 4 3 2 3 3 5% 7% 61%	1966
	11th to 20th	Night	8% 3 1 3 3 3 4 3 5% 6% 61%	2090
	21st to end	Night	7% 4 2 4 2 2 3 3 4 5% 64%	2090
October	1st to 10th	Night	6% 3 1 3 2 2 2 2 3 4 73%	3480
	11th to 20th	Night	5% 3 1 3 2 2 2 2 4 6% 68%	3641
	21st to end	Night	6% 3 1 3 2 2 3 2 4 5% 68%	4431
November	1st to 10th	Night	5% 3 1 3 2 3 3 3 4 7% 66%	2503
	11th to 20th	Night	5% 5% 1 3 3 3 3 3 4 4 67%	2470
	21st to end	Night	7% 5% 2 4 3 3 3 2 5% 6% 60%	2470
December	1st to 10th	Night	5% 5% 2 5% 4 4 3 3 4 7% 58%	2470
	11th to 20th	Night	7% 4 2 4 3 3 3 3 5% 7% 59%	3036
	21st to end	Night	9% 13% 4 6% 3 3 3 3 4 6% 47%	4811

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	35% 2 12% 29% 19% 2	2539
	11th to 20th	Day	39% 4 13% 24% 16% 5%	2610
	21st to end	Day	32% 2 15% 33% 16% 3	3135
February	1st to 10th	Day	37% 3 13% 25% 16% 5%	1861
	11th to 20th	Day	34% 3 13% 26% 18% 6%	1859
	21st to end	Day	29% 3 9% 25% 25% 9%	1570
March	1st to 10th	Day	26% 2 8% 20% 30% 13%	3130
	11th to 20th	Day	29% 3 9% 28% 27% 4	3449
	21st to end	Day	32% 3 18% 33% 11% 3	3814
April	1st to 10th	Day	28% 4 12% 25% 24% 8%	2273
	11th to 20th	Day	34% 4 12% 26% 19% 6%	2268
	21st to end	Day	36% 3 12% 28% 18% 3	2470
May	1st to 10th	Day	35% 3 12% 28% 12% 10%	4120
	11th to 20th	Day	32% 4 15% 31% 16% 1	4086
	21st to end	Day	32% 5% 14% 24% 22% 4	4489
June	1st to 10th	Day	21% 4 20% 35% 17% 4	2537
	11th to 20th	Day	25% 4 12% 28% 23% 8%	2660
	21st to end	Day	22% 3 10% 30% 26% 8%	2660
July	1st to 10th	Day	30% 4 10% 25% 25% 7%	4361
	11th to 20th	Day	20% 4 16% 27% 28% 5%	4306
	21st to end	Day	20% 4 14% 28% 24% 9%	4325
August	1st to 10th	Day	33% 4 13% 27% 20% 3	4090
	11th to 20th	Day	31% 5% 15% 25% 21% 4	3998
	21st to end	Day	22% 4 13% 27% 24% 9%	4179
September	1st to 10th	Day	27% 3 9% 27% 24% 11%	2212
	11th to 20th	Day	24% 3 9% 28% 29% 7%	2090
	21st to end	Day	24% 3 8% 29% 28% 8%	2090
October	1st to 10th	Day	19% 2 5% 21% 40% 13%	3480
	11th to 20th	Day	22% 2 9% 32% 23% 11%	3246
	21st to end	Day	21% 2 6% 27% 36% 8%	3122
November	1st to 10th	Day	24% 3 8% 29% 27% 9%	1736
	11th to 20th	Day	23% 2 7% 30% 30% 7%	1710
	21st to end	Day	28% 2 7% 25% 30% 8%	1710
December	1st to 10th	Day	30% 2 12% 28% 23% 4	1710
	11th to 20th	Day	29% 2 9% 38% 21% 2	2159
	21st to end	Day	47% 2 8% 23% 16% 3	2852
January	1st to 10th	Night	38% 3 11% 29% 17% 3	4417
	11th to 20th	Night	30% 3 14% 26% 22% 5%	4355
	21st to end	Night	34% 2 13% 28% 20% 2	4532
February	1st to 10th	Night	38% 3 13% 22% 18% 7%	2337
	11th to 20th	Night	33% 4 12% 26% 22% 3	2218
	21st to end	Night	29% 3 6% 25% 25% 12%	1884
March	1st to 10th	Night	25% 2 7% 22% 30% 13%	3734
	11th to 20th	Night	27% 2 10% 26% 27% 8%	3512
	21st to end	Night	33% 3 17% 35% 10% 2	3817
April	1st to 10th	Night	29% 5% 11% 25% 25% 6%	1904
	11th to 20th	Night	34% 3 12% 26% 19% 6%	1863
	21st to end	Night	32% 4 12% 27% 22% 3	1710
May	1st to 10th	Night	36% 4 13% 23% 16% 8%	2850
	11th to 20th	Night	35% 3 15% 27% 19% 1	2824
	21st to end	Night	33% 5% 17% 24% 16% 5%	3099
June	1st to 10th	Night	23% 4 19% 33% 17% 3	1637
	11th to 20th	Night	26% 5% 15% 27% 22% 5%	1520
	21st to end	Night	25% 5% 11% 28% 23% 8%	1520
July	1st to 10th	Night	32% 4 15% 19% 26% 4	2500
	11th to 20th	Night	27% 5% 16% 24% 23% 6%	2540
	21st to end	Night	19% 3 18% 25% 25% 10%	2999
August	1st to 10th	Night	33% 4 13% 25% 22% 3	2826
	11th to 20th	Night	32% 4 18% 25% 17% 3	2904
	21st to end	Night	25% 5% 14% 28% 19% 9%	3487
September	1st to 10th	Night	23% 4 10% 26% 26% 12%	1966
	11th to 20th	Night	24% 3 8% 26% 29% 9%	2090
	21st to end	Night	24% 2 7% 25% 31% 10%	2090
October	1st to 10th	Night	17% 2 5% 18% 44% 13%	3480
	11th to 20th	Night	18% 2 11% 24% 32% 13%	3641
	21st to end	Night	21% 2 7% 25% 36% 10%	4431
November	1st to 10th	Night	19% 2 9% 28% 29% 12%	2503
	11th to 20th	Night	22% 2 7% 29% 30% 10%	2470
	21st to end	Night	27% 2 9% 25% 26% 11%	2470
December	1st to 10th	Night	28% 3 11% 31% 21% 6%	2470
	11th to 20th	Night	25% 3 9% 37% 23% 4	3037
	21st to end	Night	41% 2 11% 28% 17% 2	4811

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	10% 6% 39% 33% 11% 2	270
	11th to 20th	Day	16% 11% 33% 31% 9% 1	270
	21st to end	Day	9% 7% 42% 31% 10% 1	297
February	1st to 10th	Day	14% 10% 40% 26% 9%	270
	11th to 20th	Day	11% 7% 46% 26% 9% 2	270
	21st to end	Day	7% 15% 52% 22% 4	225
March	1st to 10th	Day	11% 10% 41% 30% 7% 1	270
	11th to 20th	Day	17% 10% 35% 26% 10% 1	270
	21st to end	Day	16% 8% 45% 23% 7%	297
April	1st to 10th	Day	12% 19% 40% 23% 4 1	453
	11th to 20th	Day	15% 16% 40% 23% 6%	466
	21st to end	Day	17% 15% 35% 23% 9% 1	650
May	1st to 10th	Day	14% 9% 34% 29% 12% 2	653
	11th to 20th	Day	17% 8% 28% 31% 12% 3	675
	21st to end	Day	13% 10% 33% 30% 12% 2	734
June	1st to 10th	Day	4 6% 26% 36% 21% 8%	680
	11th to 20th	Day	8% 5% 31% 38% 17% 2	680
	21st to end	Day	6% 4 30% 42% 17% 1	680
July	1st to 10th	Day	6% 3 18% 41% 26% 5%	671
	11th to 20th	Day	5% 1 18% 43% 29% 4	668
	21st to end	Day	4 2 11% 45% 31% 6%	739
August	1st to 10th	Day	10% 2 12% 42% 30% 5%	676
	11th to 20th	Day	7% 3 19% 43% 26% 3	622
	21st to end	Day	6% 2 19% 44% 22% 7%	539
September	1st to 10th	Day	10% 3 18% 46% 20% 4	422
	11th to 20th	Day	5% 5% 25% 37% 22% 6%	300
	21st to end	Day	11% 6% 23% 33% 20% 6%	300
October	1st to 10th	Day	18% 5% 19% 33% 19% 5%	300
	11th to 20th	Day	4 11% 40% 29% 12% 4	300
	21st to end	Day	15% 12% 31% 28% 12% 2	330
November	1st to 10th	Day	12% 10% 34% 30% 10% 4	291
	11th to 20th	Day	11% 9% 40% 26% 12% 3	270
	21st to end	Day	17% 10% 28% 25% 18% 3	270
December	1st to 10th	Day	8% 8% 36% 32% 14% 2	270
	11th to 20th	Day	13% 14% 34% 29% 10% 1	270
	21st to end	Day	14% 16% 34% 27% 8%	297
January	1st to 10th	Night	9% 8% 35% 40% 8%	950
	11th to 20th	Night	10% 9% 36% 35% 9% 1	950
	21st to end	Night	8% 7% 41% 37% 6%	1045
February	1st to 10th	Night	12% 9% 40% 32% 7%	817
	11th to 20th	Night	8% 10% 44% 32% 6%	744
	21st to end	Night	8% 13% 44% 28% 5%	628
March	1st to 10th	Night	10% 13% 37% 34% 5%	760
	11th to 20th	Night	12% 12% 34% 34% 7% 1	589
	21st to end	Night	14% 13% 40% 27% 5%	627
April	1st to 10th	Night	11% 13% 44% 28% 4	570
	11th to 20th	Night	15% 15% 40% 26% 5%	563
	21st to end	Night	14% 13% 34% 30% 8%	570
May	1st to 10th	Night	14% 9% 38% 32% 7%	570
	11th to 20th	Night	13% 8% 34% 35% 9% 1	561
	21st to end	Night	13% 12% 37% 30% 9%	617
June	1st to 10th	Night	5% 5% 36% 39% 14% 1	570
	11th to 20th	Night	8% 8% 42% 33% 9%	570
	21st to end	Night	7% 5% 34% 44% 9% 1	570
July	1st to 10th	Night	8% 3 25% 47% 16%	555
	11th to 20th	Night	5% 2 23% 51% 19% 1	552
	21st to end	Night	6% 1 18% 48% 25% 1	624
August	1st to 10th	Night	9% 1 17% 51% 22% 1	567
	11th to 20th	Night	8% 1 22% 51% 16% 1	564
	21st to end	Night	4 2 24% 47% 21% 1	627
September	1st to 10th	Night	7% 3 26% 48% 14% 1	570
	11th to 20th	Night	8% 4 31% 40% 15% 1	570
	21st to end	Night	10% 6% 28% 41% 15% 1	570
October	1st to 10th	Night	12% 8% 30% 36% 14%	570
	11th to 20th	Night	9% 8% 35% 37% 11%	674
	21st to end	Night	12% 10% 31% 33% 13%	1021
November	1st to 10th	Night	8% 8% 31% 43% 9%	963
	11th to 20th	Night	9% 9% 37% 37% 8% 1	950
	21st to end	Night	11% 9% 31% 36% 12% 1	950
December	1st to 10th	Night	9% 8% 36% 39% 7%	950
	11th to 20th	Night	11% 11% 34% 36% 8% 1	950
	21st to end	Night	13% 8% 34% 37% 7%	1045

Page generated at 2024-11-05 07:15:53. Version ac07

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