Bobcat Trail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bobcat Trail 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	4 5% 2 6% 4 4 5% 4 6% 8% 51%	140672
	Night	3 5% 2 5% 4 4 4 3 5% 8% 57%	139290
Transparency	Day	29% 5% 11% 25% 21% 9%	135597
	Night	25% 4 12% 28% 22% 8%	135398
Seeing	Day	12% 17% 32% 24% 12% 3	17661
	Night	9% 20% 34% 26% 9% 1	27797

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	5% 3 9% 5% 5% 3 3 5% 7% 55%	4720
	11th to 20th	Day	3 1 7% 5% 3 3 3 6% 9% 59%	4740
	21st to end	Day	1 3 2 5% 4 4 3 3 6% 8% 62%	5825
February	1st to 10th	Day	1 5% 3 8% 5% 5% 4 3 5% 9% 51%	1890
	11th to 20th	Day	1 5% 3 6% 5% 5% 4 4 6% 9% 53%	1977
	21st to end	Day	1 7% 2 7% 4 3 4 3 6% 8% 58%	1730
March	1st to 10th	Day	2 9% 3 7% 3 3 3 3 5% 8% 53%	4600
	11th to 20th	Day	3 7% 3 8% 5% 4 5% 4 7% 8% 47%	5052
	21st to end	Day	3 8% 3 7% 5% 5% 5% 4 7% 10% 44%	5951
April	1st to 10th	Day	4 8% 2 6% 4 3 4 4 6% 8% 51%	2520
	11th to 20th	Day	7% 12% 4 6% 5% 4 4 4 6% 7% 42%	2491
	21st to end	Day	9% 10% 3 5% 4 5% 5% 5% 6% 7% 40%	2520
May	1st to 10th	Day	9% 10% 3 7% 4 4 4 3 5% 6% 43%	6003
	11th to 20th	Day	7% 6% 2 6% 4 5% 6% 5% 8% 9% 42%	6298
	21st to end	Day	8% 6% 2 5% 4 5% 5% 5% 8% 8% 43%	6925
June	1st to 10th	Day	5% 5% 2 5% 5% 5% 6% 5% 8% 9% 44%	2800
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 7% 8% 48%	2800
	21st to end	Day	4 4 1 4 5% 4 6% 6% 8% 9% 51%	2800
July	1st to 10th	Day	4 4 1 5% 4 5% 5% 5% 8% 9% 50%	6339
	11th to 20th	Day	2 3 1 5% 5% 6% 7% 6% 10% 10% 45%	6340
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 7% 9% 45%	6903
August	1st to 10th	Day	6% 4 2 5% 4 5% 6% 5% 8% 10% 44%	5791
	11th to 20th	Day	3 3 1 5% 5% 5% 6% 5% 6% 8% 53%	5461
	21st to end	Day	7% 6% 2 6% 5% 5% 6% 5% 7% 7% 45%	5984
September	1st to 10th	Day	5% 5% 2 4 4 4 4 4 6% 7% 57%	2400
	11th to 20th	Day	6% 4 1 4 3 4 4 4 5% 7% 58%	2386
	21st to end	Day	6% 4 2 4 3 3 3 2 5% 7% 62%	2195
October	1st to 10th	Day	4 5% 1 3 2 2 2 2 3 4 73%	3270
	11th to 20th	Day	5% 5% 2 4 3 3 4 3 5% 7% 60%	3250
	21st to end	Day	4 7% 2 4 2 3 3 3 5% 6% 61%	3371
November	1st to 10th	Day	2 4 1 4 3 2 4 4 5% 8% 62%	1853
	11th to 20th	Day	2 5% 2 4 3 3 3 3 5% 9% 60%	1890
	21st to end	Day	2 5% 2 5% 5% 4 4 4 7% 8% 54%	1699
December	1st to 10th	Day	1 3 1 3 3 2 2 3 4 7% 71%	2700
	11th to 20th	Day	1 5% 2 4 3 3 3 3 5% 8% 62%	3106
	21st to end	Day	2 5% 2 8% 4 5% 4 4 6% 7% 53%	4092
January	1st to 10th	Night	1 6% 3 8% 4 4 4 3 5% 8% 55%	8201
	11th to 20th	Night	3 2 6% 5% 4 3 3 5% 7% 63%	8250
	21st to end	Night	1 4 2 6% 4 4 4 3 4 7% 61%	8434
February	1st to 10th	Night	1 5% 2 6% 4 4 4 4 5% 8% 56%	2730
	11th to 20th	Night	1 5% 3 6% 5% 5% 5% 3 5% 7% 55%	2529
	21st to end	Night	1 8% 3 5% 4 4 3 3 4 6% 60%	2076
March	1st to 10th	Night	2 10% 4 6% 3 3 3 3 4 7% 54%	5494
	11th to 20th	Night	3 9% 3 6% 3 3 4 3 5% 9% 54%	5160
	21st to end	Night	4 8% 3 6% 5% 4 5% 5% 6% 8% 46%	5249
April	1st to 10th	Night	4 7% 2 4 4 4 5% 4 5% 7% 55%	2100
	11th to 20th	Night	6% 9% 2 5% 4 4 3 4 5% 6% 52%	2077
	21st to end	Night	9% 10% 2 6% 3 4 3 3 5% 7% 48%	2100
May	1st to 10th	Night	9% 8% 2 6% 4 4 5% 4 6% 6% 45%	3997
	11th to 20th	Night	6% 6% 2 5% 4 4 5% 4 7% 9% 47%	3617
	21st to end	Night	9% 7% 1 4 3 3 4 4 6% 8% 51%	3972
June	1st to 10th	Night	6% 4 2 4 3 4 5% 4 7% 11% 52%	1600
	11th to 20th	Night	5% 3 1 5% 3 3 4 3 6% 8% 59%	1600
	21st to end	Night	4 4 1 4 3 4 3 3 6% 8% 60%	1600
July	1st to 10th	Night	3 3 1 5% 4 4 5% 4 6% 9% 56%	3640
	11th to 20th	Night	3 3 1 4 3 4 5% 5% 8% 12% 52%	3640
	21st to end	Night	4 3 1 5% 4 4 5% 5% 7% 9% 52%	3970
August	1st to 10th	Night	7% 3 1 5% 4 4 5% 4 7% 9% 51%	4004
	11th to 20th	Night	2 3 1 5% 4 4 5% 4 7% 9% 56%	4373
	21st to end	Night	5% 5% 2 5% 4 4 5% 4 7% 9% 50%	4993
September	1st to 10th	Night	6% 5% 1 4 3 3 4 3 5% 7% 60%	2000
	11th to 20th	Night	6% 3 2 4 3 3 4 3 4 6% 62%	2012
	21st to end	Night	6% 4 1 4 3 2 3 3 4 6% 62%	2200
October	1st to 10th	Night	4 4 1 2 2 2 2 2 4 5% 72%	3920
	11th to 20th	Night	5% 6% 2 5% 3 3 3 3 5% 8% 58%	3898
	21st to end	Night	3 5% 2 4 3 3 3 3 4 7% 62%	4381
November	1st to 10th	Night	3 4 2 4 3 3 3 3 6% 8% 63%	2665
	11th to 20th	Night	2 5% 2 3 3 3 3 3 6% 9% 61%	2730
	21st to end	Night	2 5% 2 5% 3 3 4 4 6% 7% 59%	2919
December	1st to 10th	Night	1 3 1 4 3 2 3 2 4 6% 71%	4710
	11th to 20th	Night	1 5% 2 4 2 2 3 3 5% 9% 65%	5321
	21st to end	Night	2 6% 2 6% 4 4 4 3 6% 8% 54%	7128

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	29% 3 11% 30% 23% 5%	4723
	11th to 20th	Day	21% 6% 17% 26% 22% 8%	4740
	21st to end	Day	21% 4 12% 31% 25% 8%	5825
February	1st to 10th	Day	28% 7% 18% 26% 15% 5%	1890
	11th to 20th	Day	27% 6% 13% 29% 20% 6%	1986
	21st to end	Day	24% 5% 14% 28% 22% 8%	1730
March	1st to 10th	Day	29% 4 9% 23% 27% 9%	4600
	11th to 20th	Day	32% 6% 11% 27% 19% 4	5052
	21st to end	Day	33% 6% 14% 34% 12% 2	5951
April	1st to 10th	Day	29% 6% 14% 27% 17% 6%	2520
	11th to 20th	Day	39% 5% 13% 21% 15% 6%	2494
	21st to end	Day	39% 7% 10% 26% 16% 2	2520
May	1st to 10th	Day	40% 5% 10% 25% 15% 4	6003
	11th to 20th	Day	34% 7% 12% 21% 22% 4	6302
	21st to end	Day	33% 7% 12% 26% 19% 4	6926
June	1st to 10th	Day	32% 8% 18% 20% 17% 6%	2800
	11th to 20th	Day	30% 6% 10% 20% 22% 12%	2800
	21st to end	Day	26% 7% 9% 25% 19% 14%	2800
July	1st to 10th	Day	27% 4 6% 16% 24% 22%	6271
	11th to 20th	Day	29% 4 9% 26% 18% 14%	6265
	21st to end	Day	32% 5% 10% 16% 20% 17%	6705
August	1st to 10th	Day	35% 5% 14% 21% 16% 9%	4219
	11th to 20th	Day	30% 4 10% 17% 23% 17%	3954
	21st to end	Day	29% 3 10% 19% 24% 15%	4311
September	1st to 10th	Day	25% 4 8% 20% 28% 15%	2400
	11th to 20th	Day	24% 5% 8% 24% 27% 13%	2386
	21st to end	Day	23% 3 8% 22% 34% 10%	2195
October	1st to 10th	Day	17% 3 5% 18% 32% 26%	3270
	11th to 20th	Day	25% 3 7% 35% 22% 9%	3250
	21st to end	Day	24% 3 7% 33% 27% 6%	3371
November	1st to 10th	Day	20% 6% 11% 28% 27% 7%	1853
	11th to 20th	Day	21% 4 11% 33% 24% 6%	1890
	21st to end	Day	25% 6% 12% 30% 21% 7%	1699
December	1st to 10th	Day	15% 4 11% 35% 29% 7%	2700
	11th to 20th	Day	21% 3 11% 41% 20% 4	3104
	21st to end	Day	29% 5% 12% 28% 19% 7%	4092
January	1st to 10th	Night	27% 4 11% 32% 19% 6%	8202
	11th to 20th	Night	22% 4 15% 27% 23% 9%	8250
	21st to end	Night	24% 3 11% 27% 25% 10%	8434
February	1st to 10th	Night	25% 6% 16% 30% 19% 4	2730
	11th to 20th	Night	28% 5% 14% 30% 19% 4	2530
	21st to end	Night	24% 4 12% 26% 25% 9%	2076
March	1st to 10th	Night	29% 4 7% 23% 26% 10%	5494
	11th to 20th	Night	27% 5% 10% 21% 31% 7%	5160
	21st to end	Night	33% 5% 16% 32% 12% 2	5249
April	1st to 10th	Night	28% 6% 14% 28% 19% 6%	2100
	11th to 20th	Night	32% 5% 13% 28% 17% 5%	2077
	21st to end	Night	37% 4 11% 28% 19% 1	2100
May	1st to 10th	Night	35% 7% 11% 30% 13% 4	3995
	11th to 20th	Night	30% 6% 16% 27% 17% 4	3618
	21st to end	Night	30% 5% 17% 26% 19% 3	3972
June	1st to 10th	Night	24% 7% 22% 27% 15% 5%	1600
	11th to 20th	Night	22% 5% 13% 24% 22% 14%	1600
	21st to end	Night	21% 5% 8% 29% 23% 13%	1600
July	1st to 10th	Night	25% 4 9% 21% 27% 14%	3600
	11th to 20th	Night	24% 3 17% 28% 18% 9%	3592
	21st to end	Night	27% 4 12% 24% 19% 13%	3856
August	1st to 10th	Night	30% 3 17% 24% 20% 5%	2913
	11th to 20th	Night	27% 3 16% 23% 19% 12%	3168
	21st to end	Night	23% 3 15% 23% 24% 13%	3597
September	1st to 10th	Night	24% 4 8% 23% 25% 16%	2000
	11th to 20th	Night	22% 5% 9% 25% 26% 13%	2012
	21st to end	Night	23% 4 6% 25% 32% 9%	2200
October	1st to 10th	Night	16% 3 7% 22% 32% 21%	3920
	11th to 20th	Night	26% 2 8% 30% 27% 7%	3898
	21st to end	Night	23% 3 7% 31% 28% 8%	4381
November	1st to 10th	Night	20% 5% 12% 27% 28% 7%	2665
	11th to 20th	Night	20% 4 12% 33% 23% 7%	2730
	21st to end	Night	23% 5% 10% 32% 23% 6%	2919
December	1st to 10th	Night	16% 3 11% 37% 27% 6%	4710
	11th to 20th	Night	17% 5% 11% 42% 22% 3	5322
	21st to end	Night	27% 5% 12% 29% 22% 5%	7128

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	16% 28% 34% 13% 7% 2	330
	11th to 20th	Day	13% 38% 33% 12% 3	330
	21st to end	Day	12% 32% 43% 10% 2 1	363
February	1st to 10th	Day	13% 39% 38% 7% 2	330
	11th to 20th	Day	11% 34% 41% 12% 2	330
	21st to end	Day	21% 30% 37% 10% 2	273
March	1st to 10th	Day	12% 26% 37% 19% 5% 1	330
	11th to 20th	Day	19% 23% 38% 14% 6% 1	508
	21st to end	Day	14% 24% 41% 16% 5% 1	594
April	1st to 10th	Day	16% 24% 38% 17% 5% 1	540
	11th to 20th	Day	20% 22% 40% 14% 3 1	532
	21st to end	Day	19% 19% 35% 17% 8% 2	540
May	1st to 10th	Day	19% 16% 30% 21% 11% 2	673
	11th to 20th	Day	18% 10% 30% 28% 11% 3	725
	21st to end	Day	11% 14% 30% 26% 16% 3	789
June	1st to 10th	Day	8% 7% 27% 34% 18% 6%	730
	11th to 20th	Day	10% 9% 36% 29% 13% 3	730
	21st to end	Day	6% 7% 33% 32% 16% 6%	730
July	1st to 10th	Day	9% 4 19% 34% 27% 7%	721
	11th to 20th	Day	4 3 24% 40% 22% 7%	718
	21st to end	Day	7% 4 19% 34% 29% 8%	794
August	1st to 10th	Day	9% 3 31% 32% 20% 5%	539
	11th to 20th	Day	6% 6% 23% 39% 18% 8%	517
	21st to end	Day	8% 7% 29% 32% 19% 5%	583
September	1st to 10th	Day	7% 7% 29% 35% 17% 5%	530
	11th to 20th	Day	8% 10% 32% 29% 16% 5%	516
	21st to end	Day	9% 8% 32% 26% 15% 10%	330
October	1st to 10th	Day	11% 8% 33% 26% 15% 7%	330
	11th to 20th	Day	12% 20% 36% 20% 8% 3	330
	21st to end	Day	11% 25% 37% 23% 4 1	363
November	1st to 10th	Day	9% 23% 44% 15% 6% 2	330
	11th to 20th	Day	15% 29% 37% 17% 3	330
	21st to end	Day	13% 35% 34% 13% 4 1	330
December	1st to 10th	Day	16% 36% 31% 12% 5%	330
	11th to 20th	Day	22% 36% 35% 7%	330
	21st to end	Day	16% 38% 32% 10% 3 1	363
January	1st to 10th	Night	11% 34% 34% 15% 4 2	1050
	11th to 20th	Night	12% 42% 30% 12% 4 1	1050
	21st to end	Night	7% 37% 38% 13% 5%	949
February	1st to 10th	Night	8% 37% 41% 10% 4	840
	11th to 20th	Night	8% 32% 42% 16% 2	824
	21st to end	Night	13% 30% 43% 12% 1	692
March	1st to 10th	Night	8% 25% 41% 22% 4	840
	11th to 20th	Night	10% 21% 39% 23% 6% 1	840
	21st to end	Night	9% 20% 42% 24% 5% 1	770
April	1st to 10th	Night	11% 18% 42% 26% 3	630
	11th to 20th	Night	13% 17% 43% 22% 5%	623
	21st to end	Night	15% 15% 32% 30% 7%	630
May	1st to 10th	Night	15% 12% 31% 31% 11% 1	603
	11th to 20th	Night	18% 6% 29% 34% 11% 2	591
	21st to end	Night	10% 8% 33% 31% 16% 1	650
June	1st to 10th	Night	7% 6% 28% 40% 18% 2	600
	11th to 20th	Night	7% 6% 33% 44% 10%	600
	21st to end	Night	5% 6% 30% 40% 17% 2	600
July	1st to 10th	Night	7% 2 19% 45% 24% 3	585
	11th to 20th	Night	3 2 21% 48% 24% 2	582
	21st to end	Night	5% 2 16% 45% 31% 2	657
August	1st to 10th	Night	9% 3 18% 49% 19% 2	597
	11th to 20th	Night	4 1 23% 48% 21% 3	594
	21st to end	Night	5% 2 22% 42% 27% 2	660
September	1st to 10th	Night	9% 4 18% 45% 22% 3	600
	11th to 20th	Night	7% 4 26% 42% 18% 3	600
	21st to end	Night	9% 5% 31% 40% 13% 1	600
October	1st to 10th	Night	10% 11% 32% 32% 11% 4	800
	11th to 20th	Night	9% 15% 39% 27% 9% 1	800
	21st to end	Night	8% 20% 41% 24% 5% 1	960
November	1st to 10th	Night	8% 19% 43% 23% 5% 1	1025
	11th to 20th	Night	10% 29% 42% 17% 2 1	1050
	21st to end	Night	7% 27% 45% 19% 3	1050
December	1st to 10th	Night	12% 33% 36% 15% 3	1050
	11th to 20th	Night	13% 35% 36% 13% 3 1	1050
	21st to end	Night	11% 39% 35% 12% 3 1	1155

Page generated at 2026-04-29 00:21:44. Version ac07

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