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 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	4 6% 2 6% 4 4 4 4 6% 8% 51%	108932
	Night	3 5% 2 5% 4 3 4 3 5% 8% 57%	108835
Transparency	Day	28% 6% 12% 25% 20% 9%	108673
	Night	25% 5% 13% 28% 21% 7%	108684
Seeing	Day	11% 16% 32% 24% 13% 4	15888
	Night	9% 20% 34% 26% 9% 1	26006

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	1 4 2 9% 6% 5% 3 2 5% 6% 55%	2586
	11th to 20th	Day	4 2 10% 7% 4 5% 4 8% 8% 47%	2540
	21st to end	Day	1 3 2 6% 3 4 3 3 6% 8% 61%	3127
February	1st to 10th	Day	2 5% 3 8% 6% 5% 4 4 5% 8% 50%	1710
	11th to 20th	Day	1 5% 3 6% 5% 4 4 3 5% 8% 55%	1783
	21st to end	Day	1 7% 2 7% 4 3 4 3 6% 8% 55%	1570
March	1st to 10th	Day	2 8% 3 7% 3 3 3 3 6% 8% 54%	3130
	11th to 20th	Day	4 8% 3 9% 5% 4 5% 3 6% 7% 47%	3448
	21st to end	Day	3 9% 3 8% 5% 5% 5% 5% 7% 10% 40%	4058
April	1st to 10th	Day	5% 8% 2 6% 4 3 4 4 6% 7% 51%	2280
	11th to 20th	Day	7% 12% 4 7% 5% 4 4 4 6% 7% 41%	2251
	21st to end	Day	9% 10% 3 6% 4 5% 5% 5% 6% 7% 40%	2280
May	1st to 10th	Day	9% 12% 4 8% 5% 5% 4 3 6% 6% 38%	4186
	11th to 20th	Day	8% 7% 2 6% 4 5% 6% 5% 8% 9% 39%	4388
	21st to end	Day	6% 7% 2 5% 4 5% 6% 5% 8% 9% 43%	4825
June	1st to 10th	Day	5% 5% 2 5% 5% 5% 6% 5% 8% 9% 45%	2660
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 5% 7% 8% 48%	2660
	21st to end	Day	4 3 1 4 5% 4 6% 6% 8% 9% 51%	2660
July	1st to 10th	Day	6% 5% 2 5% 4 4 5% 4 7% 8% 51%	4430
	11th to 20th	Day	3 3 1 5% 5% 6% 7% 5% 9% 9% 47%	4430
	21st to end	Day	5% 4 2 5% 5% 4 5% 5% 7% 9% 50%	4802
August	1st to 10th	Day	8% 5% 2 6% 4 5% 6% 5% 9% 10% 40%	4104
	11th to 20th	Day	4 4 1 5% 5% 5% 6% 5% 7% 8% 51%	3795
	21st to end	Day	4 4 2 5% 5% 4 5% 5% 6% 7% 53%	4180
September	1st to 10th	Day	5% 5% 2 4 4 4 4 4 5% 7% 57%	2280
	11th to 20th	Day	6% 3 1 4 3 4 4 4 5% 7% 59%	2267
	21st to end	Day	5% 5% 2 4 3 3 3 2 5% 7% 62%	2085
October	1st to 10th	Day	4 4 1 3 2 2 2 2 3 4 73%	3170
	11th to 20th	Day	5% 5% 2 4 3 3 4 3 5% 7% 59%	3150
	21st to end	Day	4 7% 2 4 2 3 3 3 5% 7% 61%	3266
November	1st to 10th	Day	3 4 1 5% 3 2 4 4 5% 7% 62%	1763
	11th to 20th	Day	2 5% 2 3 3 3 3 3 5% 9% 61%	1800
	21st to end	Day	2 5% 2 5% 5% 4 4 4 7% 8% 55%	1618
December	1st to 10th	Day	1 3 1 3 2 2 2 3 4 6% 71%	2620
	11th to 20th	Day	1 5% 2 4 3 3 3 3 5% 8% 62%	3026
	21st to end	Day	2 5% 2 8% 4 5% 4 4 6% 7% 53%	4004
January	1st to 10th	Night	1 5% 3 8% 5% 5% 5% 4 5% 7% 53%	4502
	11th to 20th	Night	3 2 7% 4 4 3 3 5% 8% 59%	4430
	21st to end	Night	1 6% 2 6% 4 4 4 3 5% 7% 59%	4557
February	1st to 10th	Night	1 5% 2 6% 4 4 4 4 5% 7% 56%	2470
	11th to 20th	Night	1 5% 2 6% 4 5% 4 3 5% 6% 57%	2283
	21st to end	Night	1 8% 3 6% 4 4 3 3 4 6% 58%	1884
March	1st to 10th	Night	1 7% 4 7% 3 3 4 3 5% 8% 55%	3734
	11th to 20th	Night	4 11% 3 6% 3 3 3 2 4 7% 53%	3526
	21st to end	Night	3 8% 3 6% 5% 4 5% 5% 6% 8% 48%	3586
April	1st to 10th	Night	4 7% 2 4 4 4 5% 4 5% 7% 55%	1900
	11th to 20th	Night	7% 9% 2 5% 4 4 3 4 5% 7% 51%	1877
	21st to end	Night	10% 9% 2 5% 3 4 3 3 5% 7% 48%	1900
May	1st to 10th	Night	8% 8% 3 8% 5% 4 5% 4 6% 6% 43%	2781
	11th to 20th	Night	9% 7% 2 4 4 4 5% 4 6% 9% 45%	2517
	21st to end	Night	7% 6% 1 4 3 3 4 3 6% 8% 53%	2762
June	1st to 10th	Night	6% 3 1 4 3 3 5% 4 7% 11% 53%	1520
	11th to 20th	Night	5% 3 1 5% 3 3 4 3 6% 8% 58%	1520
	21st to end	Night	4 4 1 4 3 4 3 3 6% 9% 60%	1520
July	1st to 10th	Night	4 3 1 4 4 4 5% 3 5% 9% 57%	2540
	11th to 20th	Night	2 3 1 4 4 5% 5% 5% 8% 11% 54%	2540
	21st to end	Night	3 2 1 4 4 4 4 5% 7% 9% 57%	2761
August	1st to 10th	Night	10% 4 1 5% 4 4 5% 4 7% 10% 47%	2832
	11th to 20th	Night	3 3 2 5% 4 5% 5% 4 7% 9% 52%	3042
	21st to end	Night	2 3 2 4 3 4 4 4 6% 9% 58%	3487
September	1st to 10th	Night	6% 5% 1 4 3 3 4 3 5% 7% 59%	1900
	11th to 20th	Night	5% 3 2 4 3 3 4 3 5% 6% 63%	1911
	21st to end	Night	6% 4 1 4 3 2 3 3 4 6% 63%	2090
October	1st to 10th	Night	4 4 1 2 2 2 2 2 4 5% 73%	3800
	11th to 20th	Night	4 6% 2 5% 3 3 3 3 5% 8% 58%	3778
	21st to end	Night	3 6% 2 4 3 3 3 3 4 7% 62%	4245
November	1st to 10th	Night	3 4 2 4 3 3 3 3 6% 8% 61%	2535
	11th to 20th	Night	2 5% 2 3 3 3 3 3 5% 9% 62%	2600
	21st to end	Night	2 6% 2 5% 3 3 4 4 7% 7% 58%	2780
December	1st to 10th	Night	1 3 1 4 3 2 3 2 4 6% 72%	4570
	11th to 20th	Night	1 5% 2 4 2 2 3 3 4 9% 64%	5181
	21st to end	Night	2 6% 3 6% 4 4 4 3 6% 8% 54%	6974

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% 5% 14% 27% 19% 6%	2587
	11th to 20th	Day	29% 10% 20% 24% 15% 3	2540
	21st to end	Day	20% 6% 17% 34% 18% 5%	3127
February	1st to 10th	Day	30% 8% 19% 25% 15% 4	1710
	11th to 20th	Day	26% 6% 14% 29% 20% 6%	1792
	21st to end	Day	26% 5% 15% 29% 19% 6%	1570
March	1st to 10th	Day	26% 5% 13% 28% 22% 6%	3130
	11th to 20th	Day	33% 8% 17% 30% 10% 3	3448
	21st to end	Day	36% 9% 13% 32% 9% 2	4058
April	1st to 10th	Day	30% 7% 15% 26% 16% 7%	2280
	11th to 20th	Day	40% 6% 14% 22% 14% 4	2254
	21st to end	Day	39% 8% 11% 26% 15% 1	2280
May	1st to 10th	Day	43% 7% 11% 19% 13% 6%	4186
	11th to 20th	Day	34% 9% 15% 25% 15% 3	4392
	21st to end	Day	31% 9% 13% 23% 19% 5%	4825
June	1st to 10th	Day	31% 8% 18% 20% 17% 6%	2660
	11th to 20th	Day	30% 7% 10% 20% 22% 11%	2660
	21st to end	Day	26% 7% 9% 26% 18% 14%	2660
July	1st to 10th	Day	28% 5% 8% 14% 24% 21%	4361
	11th to 20th	Day	28% 5% 8% 22% 19% 18%	4355
	21st to end	Day	27% 5% 8% 18% 22% 18%	4651
August	1st to 10th	Day	35% 5% 14% 22% 16% 9%	4089
	11th to 20th	Day	30% 4 10% 17% 22% 17%	3832
	21st to end	Day	27% 3 10% 19% 25% 16%	4179
September	1st to 10th	Day	25% 4 8% 19% 29% 16%	2280
	11th to 20th	Day	23% 5% 8% 24% 27% 13%	2267
	21st to end	Day	23% 3 8% 22% 34% 10%	2085
October	1st to 10th	Day	17% 3 5% 17% 32% 26%	3170
	11th to 20th	Day	25% 3 7% 35% 21% 8%	3150
	21st to end	Day	24% 3 8% 33% 27% 6%	3266
November	1st to 10th	Day	20% 6% 12% 28% 27% 7%	1763
	11th to 20th	Day	20% 5% 12% 32% 25% 7%	1800
	21st to end	Day	24% 6% 12% 29% 21% 7%	1618
December	1st to 10th	Day	14% 4 11% 35% 29% 7%	2620
	11th to 20th	Day	21% 3 11% 41% 20% 3	3024
	21st to end	Day	30% 5% 12% 28% 19% 7%	4004
January	1st to 10th	Night	28% 7% 13% 31% 16% 5%	4502
	11th to 20th	Night	23% 6% 21% 25% 16% 8%	4430
	21st to end	Night	25% 5% 19% 30% 17% 4	4557
February	1st to 10th	Night	25% 7% 17% 29% 18% 4	2470
	11th to 20th	Night	27% 6% 14% 30% 20% 4	2284
	21st to end	Night	26% 4 12% 27% 23% 8%	1884
March	1st to 10th	Night	25% 6% 10% 30% 21% 7%	3734
	11th to 20th	Night	29% 6% 14% 26% 21% 3	3526
	21st to end	Night	31% 8% 17% 32% 11% 2	3586
April	1st to 10th	Night	28% 7% 14% 27% 19% 6%	1900
	11th to 20th	Night	32% 6% 14% 29% 15% 5%	1877
	21st to end	Night	36% 4 11% 29% 19% 1	1900
May	1st to 10th	Night	34% 9% 12% 24% 15% 5%	2781
	11th to 20th	Night	31% 8% 18% 28% 11% 3	2518
	21st to end	Night	27% 7% 18% 26% 19% 3	2762
June	1st to 10th	Night	23% 8% 23% 28% 14% 5%	1520
	11th to 20th	Night	23% 5% 14% 24% 22% 13%	1520
	21st to end	Night	21% 6% 9% 29% 23% 13%	1520
July	1st to 10th	Night	24% 5% 9% 22% 26% 14%	2500
	11th to 20th	Night	23% 4 11% 27% 22% 12%	2492
	21st to end	Night	21% 4 12% 28% 20% 14%	2674
August	1st to 10th	Night	30% 4 18% 24% 20% 5%	2824
	11th to 20th	Night	28% 4 16% 22% 18% 12%	3071
	21st to end	Night	22% 3 14% 23% 25% 13%	3487
September	1st to 10th	Night	24% 5% 8% 21% 25% 17%	1900
	11th to 20th	Night	21% 5% 9% 25% 26% 14%	1911
	21st to end	Night	23% 4 7% 25% 32% 9%	2090
October	1st to 10th	Night	16% 3 7% 21% 32% 22%	3800
	11th to 20th	Night	26% 2 8% 30% 26% 7%	3778
	21st to end	Night	23% 3 8% 31% 27% 8%	4245
November	1st to 10th	Night	21% 5% 13% 26% 28% 7%	2535
	11th to 20th	Night	19% 4 12% 33% 24% 8%	2600
	21st to end	Night	24% 5% 10% 31% 24% 6%	2780
December	1st to 10th	Night	15% 3 11% 37% 27% 6%	4570
	11th to 20th	Night	18% 5% 11% 42% 22% 3	5182
	21st to end	Night	27% 5% 12% 29% 22% 5%	6974

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	13% 26% 38% 14% 6% 3	288
	11th to 20th	Day	10% 37% 33% 15% 4	270
	21st to end	Day	9% 32% 45% 9% 2 2	297
February	1st to 10th	Day	11% 40% 40% 7% 2	270
	11th to 20th	Day	11% 34% 41% 11% 2	270
	21st to end	Day	15% 32% 41% 11% 1	225
March	1st to 10th	Day	10% 27% 37% 19% 5% 1	270
	11th to 20th	Day	16% 21% 40% 16% 7% 1	431
	21st to end	Day	13% 23% 41% 17% 5% 1	506
April	1st to 10th	Day	15% 25% 37% 18% 5%	460
	11th to 20th	Day	21% 22% 38% 15% 3 1	452
	21st to end	Day	19% 18% 34% 18% 8% 3	460
May	1st to 10th	Day	19% 17% 30% 22% 10% 2	620
	11th to 20th	Day	19% 9% 29% 28% 12% 3	675
	21st to end	Day	10% 14% 30% 26% 17% 3	734
June	1st to 10th	Day	7% 7% 26% 34% 19% 6%	680
	11th to 20th	Day	10% 9% 37% 28% 13% 3	680
	21st to end	Day	6% 6% 33% 32% 16% 6%	680
July	1st to 10th	Day	9% 4 19% 32% 28% 7%	671
	11th to 20th	Day	5% 3 23% 40% 22% 7%	668
	21st to end	Day	7% 4 18% 33% 30% 8%	739
August	1st to 10th	Day	9% 3 28% 33% 21% 6%	499
	11th to 20th	Day	6% 6% 23% 39% 18% 7%	477
	21st to end	Day	8% 7% 29% 32% 19% 6%	539
September	1st to 10th	Day	7% 7% 28% 35% 18% 5%	490
	11th to 20th	Day	8% 10% 31% 29% 17% 5%	477
	21st to end	Day	9% 9% 32% 27% 14% 9%	300
October	1st to 10th	Day	11% 9% 31% 27% 15% 7%	300
	11th to 20th	Day	11% 17% 38% 21% 9% 3	300
	21st to end	Day	11% 26% 36% 22% 4 1	330
November	1st to 10th	Day	8% 22% 45% 16% 7% 3	300
	11th to 20th	Day	15% 28% 37% 17% 3	300
	21st to end	Day	13% 35% 35% 13% 4	300
December	1st to 10th	Day	14% 35% 32% 13% 5%	300
	11th to 20th	Day	19% 36% 37% 8%	300
	21st to end	Day	14% 38% 32% 11% 4 1	330
January	1st to 10th	Night	10% 34% 34% 15% 4 2	981
	11th to 20th	Night	11% 42% 30% 12% 4 1	950
	21st to end	Night	6% 37% 39% 13% 5%	859
February	1st to 10th	Night	8% 38% 39% 11% 4	760
	11th to 20th	Night	9% 33% 39% 16% 2	744
	21st to end	Night	11% 30% 45% 12% 1	628
March	1st to 10th	Night	7% 27% 41% 21% 4	760
	11th to 20th	Night	8% 19% 40% 26% 6% 1	760
	21st to end	Night	9% 20% 43% 23% 5% 1	697
April	1st to 10th	Night	11% 19% 42% 25% 3	570
	11th to 20th	Night	13% 17% 42% 21% 6% 1	563
	21st to end	Night	16% 15% 31% 30% 8%	570
May	1st to 10th	Night	15% 12% 31% 30% 10% 1	570
	11th to 20th	Night	19% 4 28% 35% 12% 2	561
	21st to end	Night	10% 8% 33% 31% 17% 1	617
June	1st to 10th	Night	6% 6% 28% 40% 18% 2	570
	11th to 20th	Night	8% 7% 33% 43% 9%	570
	21st to end	Night	5% 6% 29% 41% 18% 2	570
July	1st to 10th	Night	7% 2 19% 45% 25% 3	555
	11th to 20th	Night	3 2 20% 48% 24% 3	552
	21st to end	Night	5% 2 14% 45% 32% 2	624
August	1st to 10th	Night	9% 3 15% 50% 20% 2	567
	11th to 20th	Night	4 1 23% 48% 21% 3	564
	21st to end	Night	5% 2 22% 42% 28% 2	627
September	1st to 10th	Night	9% 4 19% 43% 22% 3	570
	11th to 20th	Night	7% 4 25% 41% 19% 3	570
	21st to end	Night	8% 5% 32% 39% 14% 1	570
October	1st to 10th	Night	10% 12% 32% 31% 12% 4	760
	11th to 20th	Night	8% 14% 39% 28% 9% 1	760
	21st to end	Night	8% 21% 42% 23% 5% 1	912
November	1st to 10th	Night	8% 19% 43% 24% 5% 1	975
	11th to 20th	Night	9% 30% 42% 17% 2 1	1000
	21st to end	Night	7% 27% 44% 19% 3	1000
December	1st to 10th	Night	11% 34% 37% 15% 3	1000
	11th to 20th	Night	11% 34% 38% 14% 3 1	1000
	21st to end	Night	11% 39% 34% 12% 3 1	1100

Page generated at 2025-01-04 01:24:01. Version ac07

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