The Bishop's Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Bishop's Ranch clear sky chart from 2005-11-06 to 2025-05-26.

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	9% 4 2 4 3 3 3 3 4 6% 59%	118158
	Night	11% 5% 2 5% 3 3 3 3 5% 6% 53%	119997
Transparency	Day	27% 4 9% 20% 22% 18%	117918
	Night	32% 5% 9% 18% 20% 15%	119827
Seeing	Day	12% 10% 23% 30% 19% 6%	16038
	Night	13% 5% 15% 32% 30% 6%	25383

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	13% 5% 2 6% 3 3 4 4 6% 7% 46%	3897
	11th to 20th	Day	17% 6% 2 5% 3 3 3 2 3 5% 50%	4100
	21st to end	Day	18% 5% 2 5% 3 3 3 3 4 6% 46%	4510
February	1st to 10th	Day	19% 4 2 6% 4 4 3 3 3 4 47%	1800
	11th to 20th	Day	14% 7% 3 6% 4 3 4 4 5% 7% 43%	1780
	21st to end	Day	15% 7% 2 5% 3 3 3 3 5% 5% 48%	1650
March	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 4 7% 36%	4952
	11th to 20th	Day	15% 4 1 5% 4 3 5% 3 6% 7% 47%	5000
	21st to end	Day	19% 5% 2 6% 4 5% 5% 4 6% 8% 36%	5499
April	1st to 10th	Day	14% 6% 2 6% 5% 4 4 3 5% 7% 44%	2400
	11th to 20th	Day	9% 5% 2 6% 3 4 4 4 4 6% 53%	2369
	21st to end	Day	6% 5% 2 3 4 3 3 3 6% 8% 58%	2400
May	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 5% 71%	4203
	11th to 20th	Day	4 3 1 3 2 2 2 2 4 5% 72%	4260
	21st to end	Day	3 3 1 2 2 2 2 2 3 5% 74%	4886
June	1st to 10th	Day	6% 5% 1 3 3 3 3 3 5% 8% 60%	2660
	11th to 20th	Day	2 3 1 2 2 2 3 2 4 6% 74%	2660
	21st to end	Day	3 2 1 3 2 2 2 2 3 4 77%	2660
July	1st to 10th	Day	1 2 1 3 2 2 1 1 2 3 81%	4420
	11th to 20th	Day	1 2 1 3 2 3 2 2 3 5% 76%	4113
	21st to end	Day	1 3 1 3 2 2 2 2 3 4 78%	4455
August	1st to 10th	Day	1 2 1 5% 3 3 4 3 4 7% 66%	4091
	11th to 20th	Day	1 2 1 2 1 2 2 2 3 5% 81%	3935
	21st to end	Day	1 3 2 4 3 2 2 2 4 5% 73%	4180
September	1st to 10th	Day	1 2 1 2 2 2 2 2 3 5% 77%	2280
	11th to 20th	Day	4 3 2 4 3 3 4 3 4 6% 66%	2257
	21st to end	Day	4 2 1 2 2 1 2 2 3 5% 75%	2009
October	1st to 10th	Day	4 2 1 2 2 2 2 2 4 5% 73%	3180
	11th to 20th	Day	8% 3 2 4 2 2 3 3 3 5% 66%	3161
	21st to end	Day	8% 3 1 4 3 3 3 3 5% 7% 59%	3448
November	1st to 10th	Day	10% 3 1 4 3 4 3 3 5% 6% 57%	1946
	11th to 20th	Day	13% 5% 2 5% 4 4 3 4 5% 6% 50%	1745
	21st to end	Day	11% 6% 1 4 3 4 4 3 4 5% 55%	1600
December	1st to 10th	Day	11% 3 1 4 3 3 3 3 7% 11% 50%	2620
	11th to 20th	Day	28% 8% 2 5% 4 3 4 4 6% 7% 29%	3028
	21st to end	Day	26% 7% 2 7% 4 4 4 4 5% 8% 30%	4004
January	1st to 10th	Night	12% 6% 2 4 3 4 5% 4 8% 10% 43%	6042
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 6% 7% 44%	5880
	21st to end	Night	19% 7% 2 6% 4 3 3 3 5% 6% 43%	6468
February	1st to 10th	Night	18% 6% 2 4 3 3 3 3 3 6% 49%	2600
	11th to 20th	Night	13% 8% 3 5% 3 3 5% 3 5% 7% 44%	2506
	21st to end	Night	13% 7% 2 3 3 3 3 3 3 6% 55%	1975
March	1st to 10th	Night	17% 9% 3 6% 5% 4 4 3 5% 7% 37%	4942
	11th to 20th	Night	17% 5% 2 5% 3 3 3 3 5% 5% 49%	5000
	21st to end	Night	16% 9% 3 7% 4 4 4 3 5% 7% 39%	5474
April	1st to 10th	Night	10% 7% 2 6% 4 4 3 3 5% 5% 52%	2000
	11th to 20th	Night	8% 6% 2 5% 3 4 4 3 4 7% 54%	1979
	21st to end	Night	6% 5% 1 4 3 3 3 3 5% 7% 60%	2000
May	1st to 10th	Night	4 4 1 4 2 2 2 2 3 5% 71%	2983
	11th to 20th	Night	2 5% 2 8% 4 4 3 2 5% 5% 58%	2858
	21st to end	Night	3 2 1 3 2 2 1 2 3 4 76%	2805
June	1st to 10th	Night	4 6% 2 4 3 3 3 3 5% 7% 60%	1520
	11th to 20th	Night	2 3 1 3 2 3 3 2 3 5% 74%	1520
	21st to end	Night	3 3 1 3 2 3 2 2 3 5% 72%	1520
July	1st to 10th	Night	1 2 2 2 2 2 2 2 3 4 79%	2540
	11th to 20th	Night	1 2 2 6% 3 3 2 2 4 4 71%	2851
	21st to end	Night	1 5% 5% 5% 3 3 3 2 6% 6% 63%	3109
August	1st to 10th	Night	2 4 2 13% 4 4 4 4 5% 6% 52%	2848
	11th to 20th	Night	2 1 3 2 2 2 2 4 5% 75%	2904
	21st to end	Night	1 4 2 7% 4 2 2 2 3 5% 67%	3498
September	1st to 10th	Night	1 2 2 3 2 2 3 2 4 6% 74%	1900
	11th to 20th	Night	5% 4 1 4 3 3 3 3 4 7% 62%	1918
	21st to end	Night	3 5% 1 4 2 2 2 2 4 4 71%	2171
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 5% 73%	3800
	11th to 20th	Night	5% 5% 3 6% 4 3 3 3 5% 5% 58%	3777
	21st to end	Night	8% 3 1 3 3 4 4 3 4 6% 60%	4121
November	1st to 10th	Night	10% 5% 2 4 4 2 4 2 5% 7% 55%	2350
	11th to 20th	Night	12% 6% 2 4 3 3 3 3 5% 7% 51%	2650
	21st to end	Night	11% 5% 2 5% 3 3 2 3 4 6% 56%	2800
December	1st to 10th	Night	12% 4 2 4 3 3 5% 4 9% 9% 46%	4560
	11th to 20th	Night	27% 7% 2 5% 4 4 4 4 7% 8% 28%	5176
	21st to end	Night	32% 8% 2 5% 3 3 3 2 4 5% 33%	6952

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	37% 8% 15% 21% 12% 6%	3897
	11th to 20th	Day	39% 5% 7% 14% 19% 15%	4100
	21st to end	Day	41% 4 7% 15% 14% 19%	4510
February	1st to 10th	Day	43% 4 7% 19% 20% 8%	1800
	11th to 20th	Day	41% 6% 10% 19% 19% 6%	1789
	21st to end	Day	38% 5% 10% 24% 16% 7%	1650
March	1st to 10th	Day	47% 6% 8% 20% 17% 2	4952
	11th to 20th	Day	34% 6% 15% 26% 10% 8%	5000
	21st to end	Day	43% 9% 16% 22% 9% 1	5499
April	1st to 10th	Day	40% 6% 12% 23% 16% 4	2400
	11th to 20th	Day	33% 5% 14% 23% 19% 6%	2372
	21st to end	Day	25% 5% 14% 30% 23% 4	2400
May	1st to 10th	Day	17% 3 12% 30% 22% 16%	4203
	11th to 20th	Day	15% 3 7% 30% 32% 13%	4263
	21st to end	Day	15% 3 11% 38% 29% 3	4887
June	1st to 10th	Day	24% 4 11% 29% 25% 6%	2660
	11th to 20th	Day	14% 3 10% 20% 38% 15%	2660
	21st to end	Day	15% 2 4 15% 36% 28%	2660
July	1st to 10th	Day	11% 1 2 8% 16% 61%	4351
	11th to 20th	Day	12% 2 4 9% 22% 52%	4043
	21st to end	Day	13% 1 3 8% 30% 45%	4315
August	1st to 10th	Day	19% 2 5% 11% 26% 37%	4076
	11th to 20th	Day	9% 1 4 15% 42% 30%	3974
	21st to end	Day	17% 2 6% 15% 35% 26%	4179
September	1st to 10th	Day	12% 2 4 12% 31% 40%	2280
	11th to 20th	Day	21% 3 7% 25% 34% 11%	2257
	21st to end	Day	14% 3 6% 22% 32% 23%	2009
October	1st to 10th	Day	15% 2 4 12% 25% 41%	3180
	11th to 20th	Day	24% 3 6% 22% 25% 20%	3161
	21st to end	Day	25% 4 9% 24% 26% 12%	3448
November	1st to 10th	Day	30% 5% 8% 29% 19% 11%	1946
	11th to 20th	Day	36% 5% 11% 24% 16% 8%	1745
	21st to end	Day	33% 4 11% 19% 20% 13%	1600
December	1st to 10th	Day	28% 6% 9% 26% 24% 8%	2620
	11th to 20th	Day	54% 5% 8% 17% 13% 3	3028
	21st to end	Day	52% 6% 12% 19% 8% 3	4004
January	1st to 10th	Night	35% 11% 20% 19% 12% 4	6042
	11th to 20th	Night	39% 8% 10% 16% 14% 12%	5880
	21st to end	Night	42% 5% 10% 10% 19% 14%	6468
February	1st to 10th	Night	39% 4 9% 19% 18% 11%	2600
	11th to 20th	Night	41% 5% 9% 20% 19% 7%	2508
	21st to end	Night	32% 4 12% 25% 21% 6%	1975
March	1st to 10th	Night	45% 7% 11% 18% 16% 2	4942
	11th to 20th	Night	36% 5% 12% 20% 19% 8%	5000
	21st to end	Night	43% 9% 13% 22% 10% 2	5474
April	1st to 10th	Night	35% 6% 13% 22% 20% 4	2000
	11th to 20th	Night	32% 4 13% 25% 18% 9%	1979
	21st to end	Night	25% 4 11% 31% 24% 6%	2000
May	1st to 10th	Night	19% 3 7% 27% 28% 17%	2983
	11th to 20th	Night	24% 4 7% 22% 26% 18%	2859
	21st to end	Night	14% 3 7% 40% 31% 5%	2805
June	1st to 10th	Night	24% 4 9% 23% 30% 9%	1520
	11th to 20th	Night	15% 3 7% 22% 35% 19%	1520
	21st to end	Night	18% 1 5% 12% 31% 33%	1520
July	1st to 10th	Night	12% 1 3 6% 19% 59%	2500
	11th to 20th	Night	16% 2 5% 11% 18% 48%	2798
	21st to end	Night	23% 2 4 7% 24% 40%	3011
August	1st to 10th	Night	32% 2 6% 11% 24% 24%	2839
	11th to 20th	Night	13% 2 4 13% 37% 32%	2931
	21st to end	Night	22% 1 5% 14% 34% 23%	3498
September	1st to 10th	Night	14% 1 5% 11% 30% 39%	1900
	11th to 20th	Night	25% 3 7% 18% 34% 14%	1918
	21st to end	Night	19% 2 5% 20% 27% 26%	2171
October	1st to 10th	Night	16% 2 5% 11% 24% 42%	3800
	11th to 20th	Night	29% 4 7% 19% 21% 20%	3777
	21st to end	Night	27% 3 7% 22% 26% 16%	4121
November	1st to 10th	Night	31% 4 11% 25% 19% 10%	2350
	11th to 20th	Night	33% 4 14% 23% 17% 8%	2650
	21st to end	Night	32% 4 9% 20% 22% 14%	2800
December	1st to 10th	Night	30% 9% 11% 22% 18% 10%	4560
	11th to 20th	Night	52% 6% 11% 15% 14% 3	5176
	21st to end	Night	56% 5% 10% 17% 10% 2	6952

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	28% 13% 24% 19% 14% 3	315
	11th to 20th	Day	23% 9% 24% 25% 16% 3	400
	21st to end	Day	18% 11% 23% 28% 18% 4	440
February	1st to 10th	Day	24% 11% 21% 22% 19% 4	400
	11th to 20th	Day	21% 18% 24% 24% 12% 1	408
	21st to end	Day	18% 15% 23% 29% 14% 1	414
March	1st to 10th	Day	26% 16% 25% 23% 7% 3	500
	11th to 20th	Day	24% 15% 27% 20% 11% 3	500
	21st to end	Day	20% 16% 29% 23% 11% 1	550
April	1st to 10th	Day	18% 16% 27% 24% 11% 3	500
	11th to 20th	Day	16% 18% 28% 23% 11% 4	492
	21st to end	Day	11% 15% 30% 27% 12% 6%	500
May	1st to 10th	Day	13% 15% 31% 24% 13% 5%	503
	11th to 20th	Day	13% 12% 30% 26% 15% 5%	528
	21st to end	Day	10% 11% 26% 30% 17% 7%	550
June	1st to 10th	Day	11% 11% 24% 32% 15% 6%	490
	11th to 20th	Day	6% 12% 30% 37% 12% 3	490
	21st to end	Day	3 4 27% 37% 23% 6%	490
July	1st to 10th	Day	6% 3 21% 43% 22% 6%	486
	11th to 20th	Day	1 1 18% 45% 27% 8%	484
	21st to end	Day	2 2 12% 47% 29% 8%	531
August	1st to 10th	Day	3 3 21% 42% 23% 8%	487
	11th to 20th	Day	3 3 23% 37% 26% 8%	477
	21st to end	Day	4 2 20% 38% 28% 9%	539
September	1st to 10th	Day	2 4 20% 39% 28% 9%	490
	11th to 20th	Day	7% 7% 23% 32% 23% 9%	490
	21st to end	Day	6% 6% 20% 34% 26% 8%	490
October	1st to 10th	Day	8% 7% 25% 24% 26% 11%	490
	11th to 20th	Day	9% 8% 19% 27% 27% 11%	490
	21st to end	Day	14% 7% 20% 28% 24% 6%	539
November	1st to 10th	Day	13% 10% 17% 28% 27% 6%	482
	11th to 20th	Day	13% 8% 19% 25% 23% 12%	273
	21st to end	Day	15% 8% 23% 25% 20% 10%	200
December	1st to 10th	Day	20% 13% 14% 23% 19% 12%	200
	11th to 20th	Day	28% 10% 21% 19% 14% 10%	200
	21st to end	Day	24% 12% 20% 26% 15% 4	220
January	1st to 10th	Night	22% 5% 17% 32% 22% 4	800
	11th to 20th	Night	21% 5% 15% 34% 20% 4	800
	21st to end	Night	20% 5% 15% 32% 25% 4	880
February	1st to 10th	Night	22% 6% 14% 34% 22% 2	800
	11th to 20th	Night	18% 7% 18% 32% 20% 4	784
	21st to end	Night	17% 10% 18% 35% 18% 2	660
March	1st to 10th	Night	22% 9% 18% 27% 20% 3	800
	11th to 20th	Night	20% 8% 16% 32% 21% 4	800
	21st to end	Night	19% 7% 22% 32% 17% 3	880
April	1st to 10th	Night	13% 9% 23% 32% 20% 4	800
	11th to 20th	Night	12% 11% 20% 30% 21% 5%	791
	21st to end	Night	9% 10% 24% 27% 24% 5%	800
May	1st to 10th	Night	10% 6% 21% 29% 30% 4	620
	11th to 20th	Night	7% 3 19% 32% 33% 6%	552
	21st to end	Night	7% 8% 18% 31% 32% 5%	422
June	1st to 10th	Night	7% 7% 20% 33% 31% 2	380
	11th to 20th	Night	4 6% 16% 44% 28% 2	380
	21st to end	Night	4 2 14% 36% 40% 4	380
July	1st to 10th	Night	2 1 10% 35% 46% 6%	370
	11th to 20th	Night	3 1 4 31% 48% 13%	544
	21st to end	Night	3 3 32% 51% 10%	624
August	1st to 10th	Night	5% 1 7% 31% 45% 11%	567
	11th to 20th	Night	2 6% 34% 49% 9%	617
	21st to end	Night	4 1 7% 29% 49% 10%	836
September	1st to 10th	Night	2 1 8% 28% 50% 10%	760
	11th to 20th	Night	6% 3 9% 33% 40% 9%	760
	21st to end	Night	5% 3 11% 33% 36% 12%	760
October	1st to 10th	Night	7% 4 13% 31% 35% 10%	760
	11th to 20th	Night	9% 3 12% 29% 38% 9%	760
	21st to end	Night	12% 2 12% 29% 35% 11%	836
November	1st to 10th	Night	12% 4 15% 27% 34% 8%	780
	11th to 20th	Night	15% 2 13% 35% 29% 5%	800
	21st to end	Night	13% 5% 15% 36% 26% 6%	800
December	1st to 10th	Night	23% 4 13% 30% 25% 6%	800
	11th to 20th	Night	28% 5% 14% 30% 20% 4	800
	21st to end	Night	26% 5% 19% 32% 16% 2	880

Page generated at 2025-05-23 06:21:02. Version ac07

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