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 2026-09-29.

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	8% 4 2 4 3 3 3 3 4 6% 62%	157780
	Night	10% 6% 2 5% 3 3 3 3 5% 6% 53%	151200
Transparency	Day	25% 4 8% 20% 24% 19%	152666
	Night	32% 5% 9% 18% 21% 15%	147307
Seeing	Day	12% 9% 23% 30% 19% 6%	17852
	Night	13% 5% 14% 32% 30% 6%	27055

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	17% 6% 2 6% 3 3 4 4 6% 6% 43%	5064
	11th to 20th	Day	13% 5% 2 4 3 3 3 2 4 6% 55%	5340
	21st to end	Day	15% 6% 2 6% 4 4 4 3 5% 7% 44%	5843
February	1st to 10th	Day	18% 4 2 6% 5% 4 3 3 4 4 47%	1890
	11th to 20th	Day	14% 7% 3 6% 4 4 4 4 5% 7% 42%	1871
	21st to end	Day	16% 7% 2 5% 4 4 3 3 5% 6% 46%	1730
March	1st to 10th	Day	17% 9% 3 7% 5% 4 4 3 4 7% 37%	5062
	11th to 20th	Day	15% 4 1 5% 4 3 4 3 6% 7% 48%	5110
	21st to end	Day	18% 5% 2 6% 4 5% 5% 4 6% 8% 36%	5620
April	1st to 10th	Day	13% 7% 2 6% 5% 4 4 3 5% 8% 44%	2520
	11th to 20th	Day	10% 5% 2 6% 3 4 3 4 4 7% 52%	2489
	21st to end	Day	6% 5% 2 4 4 3 3 3 6% 8% 57%	2520
May	1st to 10th	Day	5% 4 1 3 2 3 3 2 4 6% 68%	7565
	11th to 20th	Day	2 2 1 2 2 1 2 2 4 5% 78%	7704
	21st to end	Day	2 2 1 3 2 2 2 2 4 6% 74%	8992
June	1st to 10th	Day	6% 5% 1 3 3 3 3 2 4 8% 62%	2940
	11th to 20th	Day	1 3 1 2 2 2 3 2 4 6% 75%	2940
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	2940
July	1st to 10th	Day	1 2 1 4 2 2 2 2 3 3 79%	8219
	11th to 20th	Day	2 4 2 5% 3 3 2 2 3 4 71%	7653
	21st to end	Day	1 3 1 3 2 2 2 1 3 4 79%	8304
August	1st to 10th	Day	1 1 4 2 2 2 2 3 5% 76%	7547
	11th to 20th	Day	1 4 2 3 2 2 2 2 4 5% 74%	7394
	21st to end	Day	2 3 2 5% 3 3 3 2 4 6% 66%	7750
September	1st to 10th	Day	1 3 1 2 3 2 2 2 3 6% 75%	2520
	11th to 20th	Day	4 3 2 4 3 3 3 3 4 5% 67%	2495
	21st to end	Day	4 2 1 3 2 2 3 2 3 5% 74%	2202
October	1st to 10th	Day	4 2 1 3 2 2 2 2 4 5% 72%	3280
	11th to 20th	Day	8% 3 2 4 2 2 3 3 3 5% 65%	3261
	21st to end	Day	8% 3 1 4 3 4 3 3 5% 7% 59%	3558
November	1st to 10th	Day	10% 4 1 4 3 4 3 3 5% 7% 56%	2045
	11th to 20th	Day	13% 5% 2 5% 4 4 3 4 5% 6% 49%	1832
	21st to end	Day	11% 5% 1 4 3 4 4 3 4 5% 56%	1680
December	1st to 10th	Day	11% 3 1 3 3 3 3 3 7% 11% 50%	2700
	11th to 20th	Day	28% 8% 2 5% 4 3 4 4 6% 7% 29%	3108
	21st to end	Day	26% 7% 2 7% 4 4 4 4 5% 7% 30%	4092
January	1st to 10th	Night	20% 6% 2 4 3 3 4 3 7% 9% 39%	7830
	11th to 20th	Night	12% 5% 2 4 3 3 4 3 8% 10% 45%	7650
	21st to end	Night	16% 7% 3 7% 4 4 4 4 6% 7% 38%	8371
February	1st to 10th	Night	17% 5% 2 5% 3 3 3 3 4 6% 48%	2730
	11th to 20th	Night	14% 8% 3 5% 3 3 4 3 5% 7% 44%	2634
	21st to end	Night	14% 6% 2 3 3 3 3 3 4 6% 53%	2071
March	1st to 10th	Night	16% 9% 3 6% 5% 4 4 3 5% 6% 37%	5052
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 5% 5% 49%	5110
	21st to end	Night	15% 9% 3 7% 4 4 4 3 5% 7% 39%	5595
April	1st to 10th	Night	10% 7% 2 6% 4 4 3 3 5% 5% 51%	2100
	11th to 20th	Night	8% 6% 2 5% 3 4 4 2 4 7% 54%	2079
	21st to end	Night	6% 5% 1 4 3 3 4 3 5% 7% 59%	2100
May	1st to 10th	Night	6% 6% 2 6% 2 2 2 3 4 5% 62%	5381
	11th to 20th	Night	2 3 1 5% 3 3 3 2 4 5% 67%	5176
	21st to end	Night	3 3 2 4 2 3 2 2 3 5% 72%	5181
June	1st to 10th	Night	4 6% 2 4 3 3 3 3 5% 7% 60%	1680
	11th to 20th	Night	2 3 1 3 2 3 3 2 3 5% 73%	1680
	21st to end	Night	3 3 2 4 2 3 2 2 3 4 72%	1680
July	1st to 10th	Night	1 4 3 5% 3 3 2 2 4 4 70%	4740
	11th to 20th	Night	3 9% 4 8% 3 3 3 2 3 3 58%	5331
	21st to end	Night	1 8% 4 4 3 3 3 2 5% 5% 63%	5806
August	1st to 10th	Night	1 2 1 10% 3 3 2 3 5% 5% 65%	5275
	11th to 20th	Night	1 9% 4 7% 3 2 2 2 4 5% 61%	5468
	21st to end	Night	2 3 2 9% 5% 4 4 3 5% 6% 58%	6499
September	1st to 10th	Night	1 2 2 3 2 2 3 2 4 6% 73%	2100
	11th to 20th	Night	4 4 2 5% 3 3 3 3 4 7% 62%	2120
	21st to end	Night	4 5% 2 4 2 2 2 2 4 4 70%	2375
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 5% 72%	3920
	11th to 20th	Night	5% 5% 3 6% 4 3 3 3 5% 5% 58%	3897
	21st to end	Night	8% 3 1 4 3 4 4 3 4 6% 59%	4253
November	1st to 10th	Night	10% 5% 2 4 3 2 4 2 5% 7% 54%	2471
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 7% 50%	2783
	21st to end	Night	10% 5% 2 5% 4 3 3 3 4 6% 55%	2940
December	1st to 10th	Night	11% 4 2 4 3 3 5% 4 9% 9% 45%	4700
	11th to 20th	Night	27% 7% 2 5% 4 4 5% 4 7% 8% 28%	5316
	21st to end	Night	33% 8% 2 5% 3 3 3 2 4 5% 33%	7106

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	40% 8% 13% 23% 11% 5%	5065
	11th to 20th	Day	32% 5% 6% 13% 24% 20%	5340
	21st to end	Day	40% 5% 8% 19% 11% 16%	5843
February	1st to 10th	Day	43% 4 7% 18% 20% 8%	1890
	11th to 20th	Day	43% 6% 10% 18% 18% 6%	1880
	21st to end	Day	40% 5% 10% 23% 15% 7%	1730
March	1st to 10th	Day	46% 6% 8% 21% 17% 2	5062
	11th to 20th	Day	34% 6% 15% 26% 11% 9%	5110
	21st to end	Day	42% 9% 16% 22% 10% 1	5620
April	1st to 10th	Day	40% 6% 12% 22% 16% 4	2520
	11th to 20th	Day	33% 5% 14% 23% 19% 6%	2492
	21st to end	Day	25% 5% 14% 30% 22% 4	2520
May	1st to 10th	Day	19% 4 9% 28% 26% 14%	7565
	11th to 20th	Day	10% 2 6% 30% 38% 13%	7707
	21st to end	Day	13% 3 8% 35% 37% 4	8994
June	1st to 10th	Day	23% 4 11% 28% 27% 7%	2940
	11th to 20th	Day	13% 3 9% 20% 38% 16%	2940
	21st to end	Day	14% 2 4 16% 36% 28%	2940
July	1st to 10th	Day	13% 1 3 8% 28% 48%	8151
	11th to 20th	Day	19% 1 3 5% 18% 53%	7583
	21st to end	Day	13% 1 5% 13% 26% 42%	8119
August	1st to 10th	Day	16% 1 4 8% 26% 44%	5976
	11th to 20th	Day	15% 2 4 23% 35% 21%	5829
	21st to end	Day	20% 2 5% 16% 37% 20%	6077
September	1st to 10th	Day	13% 2 5% 13% 31% 37%	2520
	11th to 20th	Day	21% 3 7% 24% 34% 11%	2495
	21st to end	Day	16% 2 6% 22% 32% 22%	2202
October	1st to 10th	Day	15% 2 5% 12% 25% 40%	3280
	11th to 20th	Day	24% 3 6% 23% 25% 19%	3261
	21st to end	Day	25% 4 9% 24% 25% 11%	3558
November	1st to 10th	Day	30% 5% 8% 29% 19% 10%	2045
	11th to 20th	Day	38% 5% 11% 23% 16% 8%	1832
	21st to end	Day	31% 5% 11% 19% 21% 13%	1680
December	1st to 10th	Day	28% 6% 9% 26% 24% 8%	2700
	11th to 20th	Day	53% 5% 8% 17% 13% 3	3108
	21st to end	Day	52% 6% 11% 19% 8% 3	4092
January	1st to 10th	Night	41% 9% 17% 19% 11% 3	7830
	11th to 20th	Night	32% 7% 12% 17% 19% 14%	7650
	21st to end	Night	43% 7% 9% 12% 17% 12%	8371
February	1st to 10th	Night	38% 5% 9% 19% 18% 11%	2730
	11th to 20th	Night	41% 5% 9% 20% 18% 6%	2636
	21st to end	Night	34% 5% 12% 24% 20% 6%	2071
March	1st to 10th	Night	45% 7% 11% 19% 16% 2	5052
	11th to 20th	Night	35% 5% 12% 20% 19% 8%	5110
	21st to end	Night	43% 9% 13% 22% 11% 2	5595
April	1st to 10th	Night	35% 6% 12% 22% 20% 4	2100
	11th to 20th	Night	32% 4 13% 25% 18% 9%	2079
	21st to end	Night	26% 4 11% 31% 24% 5%	2100
May	1st to 10th	Night	25% 4 8% 20% 30% 14%	5379
	11th to 20th	Night	18% 2 6% 27% 31% 16%	5177
	21st to end	Night	16% 4 9% 30% 37% 5%	5182
June	1st to 10th	Night	24% 4 9% 23% 30% 10%	1680
	11th to 20th	Night	15% 3 7% 21% 34% 20%	1680
	21st to end	Night	18% 1 6% 12% 32% 31%	1680
July	1st to 10th	Night	18% 1 6% 10% 25% 40%	4700
	11th to 20th	Night	30% 1 6% 7% 16% 40%	5278
	21st to end	Night	22% 3 7% 10% 20% 39%	5679
August	1st to 10th	Night	28% 2 6% 9% 24% 32%	4169
	11th to 20th	Night	26% 3 4 15% 29% 22%	4306
	21st to end	Night	26% 3 7% 14% 33% 18%	5092
September	1st to 10th	Night	15% 2 5% 12% 30% 36%	2100
	11th to 20th	Night	24% 3 7% 18% 35% 13%	2120
	21st to end	Night	21% 2 5% 20% 28% 25%	2375
October	1st to 10th	Night	17% 2 5% 11% 24% 40%	3920
	11th to 20th	Night	29% 4 7% 20% 21% 19%	3897
	21st to end	Night	27% 4 7% 22% 25% 15%	4253
November	1st to 10th	Night	31% 4 11% 26% 19% 10%	2471
	11th to 20th	Night	35% 4 14% 23% 16% 8%	2783
	21st to end	Night	32% 4 9% 21% 21% 13%	2940
December	1st to 10th	Night	30% 9% 12% 22% 18% 10%	4700
	11th to 20th	Night	52% 6% 11% 15% 13% 3	5316
	21st to end	Night	56% 5% 10% 17% 10% 2	7106

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	29% 12% 24% 18% 14% 3	341
	11th to 20th	Day	21% 8% 23% 24% 20% 4	430
	21st to end	Day	16% 10% 21% 30% 18% 4	473
February	1st to 10th	Day	22% 10% 20% 23% 20% 3	430
	11th to 20th	Day	21% 19% 24% 23% 12% 1	439
	21st to end	Day	19% 15% 22% 29% 13% 1	446
March	1st to 10th	Day	24% 16% 26% 23% 8% 3	540
	11th to 20th	Day	22% 14% 25% 21% 13% 4	540
	21st to end	Day	19% 15% 28% 24% 11% 2	594
April	1st to 10th	Day	18% 16% 26% 25% 12% 4	540
	11th to 20th	Day	16% 17% 28% 22% 12% 5%	532
	21st to end	Day	11% 14% 31% 27% 12% 6%	540
May	1st to 10th	Day	13% 14% 31% 24% 14% 5%	543
	11th to 20th	Day	12% 13% 30% 26% 15% 5%	568
	21st to end	Day	9% 11% 26% 30% 17% 7%	617
June	1st to 10th	Day	10% 10% 26% 32% 16% 6%	570
	11th to 20th	Day	5% 11% 30% 37% 13% 4	570
	21st to end	Day	3 5% 26% 37% 22% 6%	570
July	1st to 10th	Day	5% 3 23% 42% 21% 6%	566
	11th to 20th	Day	2 2 19% 44% 26% 8%	564
	21st to end	Day	2 1 15% 45% 28% 8%	619
August	1st to 10th	Day	2 4 19% 42% 25% 9%	567
	11th to 20th	Day	3 3 23% 37% 26% 8%	557
	21st to end	Day	4 2 19% 37% 27% 10%	627
September	1st to 10th	Day	3 5% 20% 37% 26% 9%	570
	11th to 20th	Day	6% 8% 23% 32% 22% 9%	570
	21st to end	Day	7% 6% 20% 34% 25% 8%	563
October	1st to 10th	Day	9% 7% 24% 24% 25% 12%	530
	11th to 20th	Day	9% 8% 19% 26% 26% 12%	530
	21st to end	Day	14% 7% 19% 28% 24% 7%	583
November	1st to 10th	Day	13% 9% 17% 28% 26% 7%	521
	11th to 20th	Day	13% 9% 20% 26% 21% 11%	300
	21st to end	Day	13% 7% 21% 25% 23% 11%	220
December	1st to 10th	Day	18% 11% 14% 22% 23% 12%	220
	11th to 20th	Day	29% 9% 20% 17% 15% 10%	220
	21st to end	Day	26% 11% 19% 25% 15% 3	242
January	1st to 10th	Night	23% 5% 16% 31% 21% 4	840
	11th to 20th	Night	20% 5% 14% 35% 22% 4	840
	21st to end	Night	19% 5% 15% 33% 24% 4	924
February	1st to 10th	Night	20% 6% 14% 35% 22% 2	840
	11th to 20th	Night	19% 8% 18% 32% 19% 3	824
	21st to end	Night	18% 9% 18% 35% 17% 2	692
March	1st to 10th	Night	21% 9% 19% 28% 19% 3	840
	11th to 20th	Night	19% 7% 16% 33% 22% 4	840
	21st to end	Night	18% 7% 22% 34% 17% 3	924
April	1st to 10th	Night	13% 9% 23% 31% 20% 4	840
	11th to 20th	Night	12% 11% 20% 30% 21% 5%	831
	21st to end	Night	9% 10% 24% 28% 24% 5%	840
May	1st to 10th	Night	11% 6% 20% 29% 30% 4	651
	11th to 20th	Night	7% 3 19% 32% 32% 6%	580
	21st to end	Night	6% 7% 18% 32% 32% 5%	455
June	1st to 10th	Night	6% 6% 19% 35% 30% 2	420
	11th to 20th	Night	4 5% 16% 46% 27% 2	420
	21st to end	Night	4 3 15% 35% 39% 4	420
July	1st to 10th	Night	2 1 11% 37% 44% 5%	410
	11th to 20th	Night	4 1 4 32% 47% 12%	604
	21st to end	Night	4 1 3 34% 49% 10%	690
August	1st to 10th	Night	4 1 7% 30% 45% 12%	627
	11th to 20th	Night	3 1 6% 35% 47% 8%	683
	21st to end	Night	4 1 8% 30% 48% 9%	924
September	1st to 10th	Night	2 1 10% 30% 48% 9%	840
	11th to 20th	Night	6% 3 9% 34% 39% 9%	840
	21st to end	Night	6% 3 11% 33% 36% 11%	832
October	1st to 10th	Night	8% 4 13% 32% 35% 10%	800
	11th to 20th	Night	9% 4 12% 30% 38% 9%	800
	21st to end	Night	12% 2 12% 29% 35% 10%	880
November	1st to 10th	Night	12% 4 15% 26% 35% 8%	820
	11th to 20th	Night	16% 3 13% 35% 29% 5%	840
	21st to end	Night	12% 5% 14% 36% 26% 6%	840
December	1st to 10th	Night	22% 4 13% 30% 26% 6%	840
	11th to 20th	Night	28% 5% 13% 29% 20% 4	840
	21st to end	Night	27% 5% 19% 32% 15% 2	924

Page generated at 2026-09-26 01:18:42. Version ac07

Copyright © 2026 Attilla Danko.