Coma Via Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coma Via Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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% 4 1 3 3 2 3 3 4 6% 64%	78436
	Night	9% 5% 1 3 3 2 3 3 4 6% 62%	80561
Transparency	Day	23% 5% 8% 20% 26% 18%	78151
	Night	25% 5% 9% 21% 25% 16%	80370
Seeing	Day	9% 11% 28% 37% 14% 3	14284
	Night	9% 3 18% 38% 27% 4	24031

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	10% 12% 4 6% 4 3 4 4 5% 7% 42%	2539
	11th to 20th	Day	9% 7% 3 7% 5% 3 5% 6% 8% 9% 39%	2709
	21st to end	Day	16% 10% 3 5% 5% 3 4 5% 7% 7% 35%	3155
February	1st to 10th	Day	14% 8% 2 4 3 1 3 3 4 7% 50%	1891
	11th to 20th	Day	12% 8% 2 3 3 2 3 4 5% 7% 51%	1750
	21st to end	Day	16% 10% 3 5% 5% 3 3 3 4 5% 43%	1480
March	1st to 10th	Day	15% 9% 2 5% 4 3 4 4 5% 7% 42%	1800
	11th to 20th	Day	11% 8% 2 4 4 2 5% 5% 5% 8% 46%	1879
	21st to end	Day	12% 8% 2 5% 4 2 4 4 4 6% 47%	2365
April	1st to 10th	Day	11% 5% 2 5% 4 2 3 4 4 7% 54%	2160
	11th to 20th	Day	10% 5% 2 3 3 2 4 4 5% 6% 56%	2129
	21st to end	Day	9% 5% 1 3 3 2 3 3 4 7% 60%	2160
May	1st to 10th	Day	6% 4 1 2 3 1 3 3 5% 7% 65%	2236
	11th to 20th	Day	5% 3 1 3 2 1 3 3 4 7% 68%	2301
	21st to end	Day	6% 3 1 3 2 1 3 4 4 6% 67%	2602
June	1st to 10th	Day	3 3 1 2 2 2 3 3 4 6% 71%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 2 4 85%	2520
	21st to end	Day	1 1 1 1 1 1 1 2 2 3 86%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 3 3 4 83%	2520
	11th to 20th	Day	2 1 1 2 1 2 2 3 4 81%	2520
	21st to end	Day	2 1 1 2 2 1 2 3 3 5% 76%	2580
August	1st to 10th	Day	1 2 1 1 2 1 1 2 2 2 85%	2149
	11th to 20th	Day	1 1 1 1 1 2 2 4 85%	2122
	21st to end	Day	1 1 1 1 1 2 2 2 3 87%	2376
September	1st to 10th	Day	2 1 1 1 1 1 2 2 4 85%	2160
	11th to 20th	Day	1 1 1 1 1 1 2 1 2 3 86%	2070
	21st to end	Day	2 1 1 1 1 2 2 3 4 82%	1980
October	1st to 10th	Day	5% 3 1 3 3 2 2 4 4 5% 70%	1953
	11th to 20th	Day	4 3 1 3 3 2 2 3 3 4 73%	1800
	21st to end	Day	4 2 1 2 2 2 2 3 3 5% 72%	1940
November	1st to 10th	Day	7% 5% 2 3 3 2 3 3 4 6% 63%	1674
	11th to 20th	Day	6% 4 1 3 4 2 3 3 4 7% 64%	1710
	21st to end	Day	9% 5% 1 3 4 3 4 3 5% 6% 57%	1710
December	1st to 10th	Day	10% 4 1 4 4 2 3 4 5% 7% 55%	1710
	11th to 20th	Day	16% 9% 3 6% 4 3 5% 4 5% 7% 38%	1952
	21st to end	Day	14% 7% 2 5% 5% 4 4 5% 5% 8% 41%	2794
January	1st to 10th	Night	13% 11% 3 6% 4 3 3 4 4 5% 44%	4406
	11th to 20th	Night	12% 9% 3 4 4 2 4 4 6% 8% 43%	4251
	21st to end	Night	19% 8% 2 4 4 2 4 5% 6% 8% 38%	4509
February	1st to 10th	Night	15% 8% 2 5% 3 2 2 3 4 7% 50%	2273
	11th to 20th	Night	13% 6% 1 3 2 1 2 3 5% 8% 56%	2098
	21st to end	Night	15% 8% 2 4 3 2 3 3 4 6% 49%	1776
March	1st to 10th	Night	12% 5% 3 4 4 2 5% 4 5% 7% 47%	2160
	11th to 20th	Night	12% 6% 1 3 4 2 4 4 5% 8% 51%	2078
	21st to end	Night	15% 7% 2 4 3 2 3 4 4 7% 51%	1990
April	1st to 10th	Night	10% 5% 2 3 3 2 3 4 4 7% 58%	1800
	11th to 20th	Night	9% 3 1 3 2 2 3 4 4 5% 64%	1779
	21st to end	Night	9% 3 1 2 2 1 2 1 4 8% 67%	1800
May	1st to 10th	Night	7% 4 1 2 2 1 2 3 3 7% 68%	1724
	11th to 20th	Night	7% 2 2 2 1 3 2 4 5% 72%	1594
	21st to end	Night	7% 2 1 1 2 1 2 2 3 4 73%	1670
June	1st to 10th	Night	5% 2 1 2 2 1 2 2 3 7% 74%	1440
	11th to 20th	Night	2 1 2 1 1 2 2 3 85%	1440
	21st to end	Night	1 1 1 1 2 1 2 2 89%	1440
July	1st to 10th	Night	1 1 1 1 2 3 4 86%	1440
	11th to 20th	Night	2 2 2 1 1 2 2 3 4 83%	1440
	21st to end	Night	2 1 1 2 3 1 2 2 3 4 79%	1731
August	1st to 10th	Night	2 2 1 1 2 1 1 2 2 4 84%	1790
	11th to 20th	Night	1 1 1 1 1 1 2 3 89%	1780
	21st to end	Night	1 1 1 1 1 2 2 2 89%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 90%	1800
	11th to 20th	Night	1 1 1 1 1 2 2 3 3 86%	1889
	21st to end	Night	1 1 1 1 1 2 2 2 3 84%	1980
October	1st to 10th	Night	4 2 1 2 2 2 3 2 4 4 75%	2004
	11th to 20th	Night	4 2 1 2 2 1 3 4 4 4 74%	2160
	21st to end	Night	4 3 1 2 2 2 2 2 2 4 76%	2415
November	1st to 10th	Night	7% 5% 1 2 3 2 3 3 4 6% 65%	2405
	11th to 20th	Night	6% 4 1 2 3 1 3 3 4 9% 63%	2470
	21st to end	Night	8% 4 3 4 4 2 3 4 4 7% 58%	2470
December	1st to 10th	Night	10% 5% 2 4 4 3 3 4 4 6% 56%	2470
	11th to 20th	Night	17% 7% 2 5% 4 3 4 4 6% 7% 41%	3247
	21st to end	Night	10% 7% 2 6% 6% 4 5% 5% 6% 8% 40%	4862

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% 6% 16% 27% 13% 3	2539
	11th to 20th	Day	34% 9% 15% 24% 11% 7%	2709
	21st to end	Day	42% 8% 13% 19% 13% 4	3155
February	1st to 10th	Day	35% 5% 8% 22% 21% 9%	1891
	11th to 20th	Day	34% 5% 9% 21% 23% 9%	1760
	21st to end	Day	45% 5% 8% 22% 17% 2	1480
March	1st to 10th	Day	42% 8% 9% 18% 17% 6%	1800
	11th to 20th	Day	35% 9% 12% 21% 19% 5%	1879
	21st to end	Day	37% 8% 14% 24% 13% 4	2365
April	1st to 10th	Day	33% 6% 12% 26% 18% 6%	2160
	11th to 20th	Day	29% 7% 12% 25% 21% 7%	2132
	21st to end	Day	26% 5% 10% 34% 22% 3	2160
May	1st to 10th	Day	21% 6% 10% 27% 32% 4	2236
	11th to 20th	Day	19% 6% 8% 31% 30% 7%	2304
	21st to end	Day	20% 6% 7% 37% 27% 4	2602
June	1st to 10th	Day	16% 5% 10% 22% 35% 13%	2520
	11th to 20th	Day	7% 4 4 17% 43% 25%	2520
	21st to end	Day	7% 3 2 9% 41% 38%	2520
July	1st to 10th	Day	8% 3 2 10% 28% 49%	2451
	11th to 20th	Day	10% 3 3 12% 32% 40%	2445
	21st to end	Day	12% 4 4 16% 32% 32%	2437
August	1st to 10th	Day	9% 3 3 8% 35% 43%	2135
	11th to 20th	Day	6% 3 2 12% 38% 40%	2122
	21st to end	Day	7% 2 2 9% 39% 43%	2376
September	1st to 10th	Day	6% 3 3 10% 34% 44%	2160
	11th to 20th	Day	7% 2 2 18% 41% 29%	2070
	21st to end	Day	9% 3 2 20% 40% 27%	1980
October	1st to 10th	Day	17% 5% 5% 19% 25% 27%	1953
	11th to 20th	Day	17% 4 3 20% 30% 27%	1800
	21st to end	Day	16% 5% 5% 18% 30% 26%	1940
November	1st to 10th	Day	24% 5% 7% 18% 28% 18%	1674
	11th to 20th	Day	22% 4 9% 23% 27% 16%	1710
	21st to end	Day	29% 5% 7% 17% 26% 18%	1710
December	1st to 10th	Day	28% 5% 11% 19% 22% 14%	1710
	11th to 20th	Day	42% 8% 10% 15% 15% 9%	1952
	21st to end	Day	40% 7% 12% 21% 14% 5%	2794
January	1st to 10th	Night	38% 4 14% 22% 18% 4	4406
	11th to 20th	Night	35% 8% 14% 24% 10% 8%	4251
	21st to end	Night	40% 9% 10% 21% 14% 6%	4509
February	1st to 10th	Night	38% 5% 6% 21% 20% 10%	2273
	11th to 20th	Night	28% 5% 8% 21% 26% 10%	2099
	21st to end	Night	38% 6% 11% 23% 18% 4	1776
March	1st to 10th	Night	36% 7% 12% 21% 19% 6%	2160
	11th to 20th	Night	32% 7% 13% 23% 19% 6%	2078
	21st to end	Night	35% 7% 14% 27% 13% 3	1990
April	1st to 10th	Night	29% 7% 13% 28% 17% 7%	1800
	11th to 20th	Night	24% 7% 13% 28% 21% 6%	1779
	21st to end	Night	20% 5% 13% 39% 21% 2	1800
May	1st to 10th	Night	20% 5% 10% 30% 28% 5%	1724
	11th to 20th	Night	17% 5% 8% 31% 34% 4	1595
	21st to end	Night	18% 5% 9% 32% 33% 3	1670
June	1st to 10th	Night	15% 4 10% 23% 37% 11%	1440
	11th to 20th	Night	8% 3 6% 19% 39% 25%	1440
	21st to end	Night	5% 2 2 12% 46% 33%	1440
July	1st to 10th	Night	6% 2 2 11% 32% 47%	1400
	11th to 20th	Night	9% 2 4 14% 31% 41%	1392
	21st to end	Night	12% 3 5% 17% 27% 34%	1636
August	1st to 10th	Night	8% 2 3 11% 34% 41%	1780
	11th to 20th	Night	4 2 3 16% 39% 36%	1780
	21st to end	Night	6% 2 2 11% 41% 39%	1980
September	1st to 10th	Night	6% 2 1 12% 31% 49%	1800
	11th to 20th	Night	6% 2 4 17% 44% 26%	1889
	21st to end	Night	8% 2 3 22% 36% 29%	1980
October	1st to 10th	Night	14% 5% 6% 19% 29% 27%	2004
	11th to 20th	Night	15% 4 5% 20% 30% 26%	2160
	21st to end	Night	15% 4 5% 21% 30% 26%	2415
November	1st to 10th	Night	22% 5% 8% 18% 27% 20%	2405
	11th to 20th	Night	21% 4 10% 19% 25% 20%	2470
	21st to end	Night	29% 5% 7% 16% 26% 17%	2470
December	1st to 10th	Night	30% 5% 9% 18% 23% 15%	2470
	11th to 20th	Night	40% 8% 10% 18% 16% 9%	3247
	21st to end	Night	39% 9% 12% 22% 14% 5%	4862

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	22% 12% 27% 29% 10% 1	180
	11th to 20th	Day	15% 8% 31% 30% 13% 3	284
	21st to end	Day	16% 9% 29% 30% 14% 1	411
February	1st to 10th	Day	19% 11% 28% 30% 12% 2	457
	11th to 20th	Day	16% 14% 34% 26% 8% 2	415
	21st to end	Day	18% 13% 35% 27% 6%	346
March	1st to 10th	Day	19% 16% 33% 25% 6% 1	420
	11th to 20th	Day	16% 18% 30% 28% 7% 1	420
	21st to end	Day	19% 20% 33% 22% 5%	462
April	1st to 10th	Day	15% 17% 31% 27% 9% 1	420
	11th to 20th	Day	15% 24% 30% 25% 6% 1	412
	21st to end	Day	10% 20% 29% 28% 12% 2	420
May	1st to 10th	Day	9% 22% 31% 28% 10% 1	423
	11th to 20th	Day	10% 10% 32% 33% 13% 2	448
	21st to end	Day	11% 15% 26% 34% 10% 4	485
June	1st to 10th	Day	2 12% 29% 36% 15% 5%	450
	11th to 20th	Day	2 11% 26% 42% 16% 5%	450
	21st to end	Day	2 9% 27% 41% 16% 5%	450
July	1st to 10th	Day	2 2 22% 50% 18% 7%	446
	11th to 20th	Day	1 1 13% 50% 26% 9%	444
	21st to end	Day	2 2 13% 56% 21% 7%	487
August	1st to 10th	Day	3 4 27% 44% 17% 5%	447
	11th to 20th	Day	1 3 24% 50% 17% 5%	437
	21st to end	Day	1 1 22% 53% 20% 3	495
September	1st to 10th	Day	3 4 26% 47% 18% 3	450
	11th to 20th	Day	1 9% 32% 45% 12% 1	450
	21st to end	Day	3 9% 28% 41% 18%	450
October	1st to 10th	Day	4 14% 30% 36% 16% 1	450
	11th to 20th	Day	4 10% 31% 42% 13% 1	450
	21st to end	Day	5% 11% 26% 38% 18% 1	455
November	1st to 10th	Day	6% 12% 26% 39% 14% 3	270
	11th to 20th	Day	6% 10% 29% 32% 19% 4	270
	21st to end	Day	13% 10% 23% 36% 14% 4	270
December	1st to 10th	Day	13% 11% 33% 31% 11% 1	270
	11th to 20th	Day	15% 8% 25% 29% 22% 1	192
	21st to end	Day	23% 11% 27% 26% 11% 2	198
January	1st to 10th	Night	16% 7% 25% 33% 15% 3	760
	11th to 20th	Night	9% 4 30% 39% 14% 2	760
	21st to end	Night	17% 4 28% 35% 14% 2	836
February	1st to 10th	Night	17% 5% 25% 35% 16% 2	758
	11th to 20th	Night	14% 4 26% 34% 18% 4	704
	21st to end	Night	20% 6% 22% 34% 16% 2	592
March	1st to 10th	Night	15% 7% 22% 39% 15% 2	720
	11th to 20th	Night	13% 5% 22% 34% 22% 4	720
	21st to end	Night	17% 7% 18% 39% 19% 1	792
April	1st to 10th	Night	12% 4 22% 42% 18% 2	720
	11th to 20th	Night	10% 6% 23% 33% 24% 2	711
	21st to end	Night	10% 5% 22% 36% 24% 3	720
May	1st to 10th	Night	8% 5% 22% 39% 25% 1	644
	11th to 20th	Night	7% 5% 18% 40% 27% 3	531
	21st to end	Night	10% 6% 19% 37% 26% 3	508
June	1st to 10th	Night	5% 3 13% 43% 34% 1	360
	11th to 20th	Night	2 2 11% 48% 33% 4	360
	21st to end	Night	1 12% 42% 40% 5%	360
July	1st to 10th	Night	1 5% 36% 53% 5%	350
	11th to 20th	Night	1 2 31% 56% 9%	348
	21st to end	Night	1 2 5% 30% 49% 13%	549
August	1st to 10th	Night	2 1 7% 41% 43% 6%	716
	11th to 20th	Night	1 5% 37% 45% 11%	712
	21st to end	Night	2 5% 30% 53% 10%	792
September	1st to 10th	Night	1 1 6% 37% 45% 11%	720
	11th to 20th	Night	1 1 11% 45% 34% 7%	720
	21st to end	Night	2 1 14% 39% 39% 6%	720
October	1st to 10th	Night	3 2 16% 47% 28% 4	720
	11th to 20th	Night	4 2 16% 42% 30% 6%	720
	21st to end	Night	5% 2 18% 39% 30% 6%	792
November	1st to 10th	Night	9% 5% 15% 41% 25% 4	740
	11th to 20th	Night	9% 2 20% 41% 24% 4	760
	21st to end	Night	12% 2 25% 40% 19% 3	760
December	1st to 10th	Night	11% 4 29% 36% 16% 3	760
	11th to 20th	Night	17% 5% 23% 39% 14% 2	760
	21st to end	Night	17% 5% 29% 36% 11% 3	836

Page generated at 2024-02-07 03:11:58. Version ac07

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