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 2024-03-06.

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	10% 5% 2 4 4 2 3 3 4 6% 57%	78673
	Night	12% 5% 2 4 4 2 4 3 4 6% 53%	80859
Transparency	Day	30% 4 9% 20% 23% 14%	78393
	Night	34% 4 9% 18% 20% 14%	80661
Seeing	Day	13% 10% 23% 30% 19% 6%	14403
	Night	13% 5% 14% 31% 30% 6%	23792

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% 7% 3 7% 5% 3 3 4 5% 5% 41%	2713
	11th to 20th	Day	25% 9% 3 6% 5% 2 4 4 4 6% 32%	2860
	21st to end	Day	23% 7% 3 6% 5% 3 4 4 5% 6% 34%	3146
February	1st to 10th	Day	18% 4 3 6% 5% 3 4 3 4 4 47%	1710
	11th to 20th	Day	14% 6% 3 5% 4 3 4 4 4 8% 45%	1688
	21st to end	Day	16% 7% 2 4 4 3 3 4 4 6% 48%	1570
March	1st to 10th	Day	19% 8% 3 7% 6% 3 3 4 5% 6% 35%	2037
	11th to 20th	Day	18% 6% 3 5% 4 3 4 4 6% 8% 39%	1980
	21st to end	Day	16% 4 2 5% 4 2 5% 5% 5% 6% 46%	2179
April	1st to 10th	Day	15% 6% 3 5% 5% 3 4 4 5% 7% 42%	2160
	11th to 20th	Day	10% 4 1 5% 4 3 4 4 4 7% 54%	2129
	21st to end	Day	6% 4 2 3 3 2 3 4 5% 8% 58%	2160
May	1st to 10th	Day	6% 5% 2 4 3 2 3 3 4 7% 61%	2317
	11th to 20th	Day	7% 4 1 3 3 2 3 4 5% 7% 62%	2332
	21st to end	Day	6% 5% 2 4 4 2 4 3 4 7% 59%	2723
June	1st to 10th	Day	7% 5% 1 3 3 2 4 3 4 8% 60%	2520
	11th to 20th	Day	2 3 1 2 2 1 3 3 4 6% 74%	2520
	21st to end	Day	3 2 1 3 3 2 2 2 3 4 76%	2520
July	1st to 10th	Day	2 3 2 2 3 2 2 2 3 3 76%	2520
	11th to 20th	Day	1 3 1 3 2 2 3 2 3 6% 74%	2343
	21st to end	Day	1 3 1 3 3 2 2 3 3 5% 74%	2546
August	1st to 10th	Day	1 3 1 3 4 2 2 3 4 6% 71%	2328
	11th to 20th	Day	1 3 1 3 2 2 2 2 4 5% 75%	2246
	21st to end	Day	1 5% 2 3 3 2 3 2 3 5% 70%	2376
September	1st to 10th	Day	1 2 1 2 2 1 3 2 3 5% 77%	2160
	11th to 20th	Day	4 3 2 3 3 2 3 3 4 6% 67%	2139
	21st to end	Day	4 2 1 2 2 1 2 2 3 5% 75%	1904
October	1st to 10th	Day	7% 3 1 2 2 2 3 3 3 5% 69%	1800
	11th to 20th	Day	8% 3 1 3 3 2 3 4 3 5% 64%	1800
	21st to end	Day	11% 3 1 3 2 2 3 3 4 6% 61%	1980
November	1st to 10th	Day	10% 3 2 4 4 3 3 4 5% 6% 56%	1847
	11th to 20th	Day	12% 4 2 4 5% 3 3 5% 4 6% 51%	1658
	21st to end	Day	11% 5% 2 4 3 3 3 4 4 5% 56%	1520
December	1st to 10th	Day	19% 5% 2 4 4 3 3 3 4 7% 45%	1520
	11th to 20th	Day	33% 7% 3 4 4 1 3 4 4 4 32%	1928
	21st to end	Day	24% 7% 2 5% 5% 3 4 3 4 7% 36%	2794
January	1st to 10th	Night	16% 7% 3 4 4 2 5% 4 5% 7% 43%	4220
	11th to 20th	Night	23% 8% 3 5% 5% 4 5% 5% 4 5% 33%	4110
	21st to end	Night	25% 9% 3 6% 5% 3 4 4 4 5% 33%	4521
February	1st to 10th	Night	17% 5% 2 4 3 2 3 4 4 6% 50%	2470
	11th to 20th	Night	13% 7% 3 5% 4 2 5% 4 4 7% 45%	2378
	21st to end	Night	14% 6% 2 3 3 3 3 3 3 6% 55%	1879
March	1st to 10th	Night	18% 8% 4 5% 6% 2 5% 4 5% 5% 37%	2039
	11th to 20th	Night	16% 6% 3 4 4 2 4 4 6% 7% 43%	1980
	21st to end	Night	16% 5% 2 4 4 2 3 3 3 6% 51%	2175
April	1st to 10th	Night	11% 7% 3 5% 5% 3 4 3 4 6% 51%	1800
	11th to 20th	Night	9% 5% 2 4 4 3 5% 3 4 7% 55%	1779
	21st to end	Night	6% 4 1 3 3 1 3 4 4 8% 62%	1800
May	1st to 10th	Night	5% 6% 2 5% 3 2 3 4 3 7% 61%	1638
	11th to 20th	Night	4 4 2 4 4 3 4 4 4 7% 60%	1558
	21st to end	Night	5% 3 3 4 3 2 3 3 5% 6% 62%	1552
June	1st to 10th	Night	4 6% 2 3 3 2 3 3 5% 8% 60%	1440
	11th to 20th	Night	2 3 1 2 3 2 3 3 3 6% 73%	1440
	21st to end	Night	3 3 2 3 3 2 2 3 3 4 72%	1440
July	1st to 10th	Night	1 3 1 2 2 2 2 3 3 4 75%	1440
	11th to 20th	Night	2 3 1 3 3 2 2 3 4 5% 73%	1611
	21st to end	Night	1 4 3 4 4 2 3 3 6% 7% 62%	1773
August	1st to 10th	Night	2 5% 2 4 3 2 3 3 4 5% 67%	1611
	11th to 20th	Night	4 2 4 4 3 3 4 5% 6% 65%	1652
	21st to end	Night	1 5% 2 5% 4 2 3 3 3 6% 66%	1980
September	1st to 10th	Night	1 2 1 2 2 2 2 2 4 6% 75%	1800
	11th to 20th	Night	5% 4 1 4 3 2 3 4 4 8% 62%	1817
	21st to end	Night	3 4 1 3 2 1 2 2 3 4 72%	2056
October	1st to 10th	Night	5% 4 2 3 3 1 3 3 4 5% 67%	2160
	11th to 20th	Night	7% 3 2 3 3 3 4 4 5% 6% 60%	2160
	21st to end	Night	10% 3 1 3 4 2 4 3 4 6% 60%	2376
November	1st to 10th	Night	10% 4 2 3 4 2 4 3 5% 7% 54%	2229
	11th to 20th	Night	12% 5% 2 4 3 2 4 3 4 7% 51%	2517
	21st to end	Night	10% 4 2 4 4 2 3 4 4 6% 57%	2660
December	1st to 10th	Night	20% 6% 2 4 4 2 4 4 4 5% 46%	2660
	11th to 20th	Night	33% 6% 2 3 4 2 4 3 4 6% 33%	3276
	21st to end	Night	24% 7% 2 5% 5% 3 4 4 4 6% 37%	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	44% 6% 12% 27% 7% 4	2713
	11th to 20th	Day	55% 6% 9% 13% 9% 8%	2860
	21st to end	Day	53% 5% 9% 17% 11% 5%	3146
February	1st to 10th	Day	43% 4 7% 19% 20% 8%	1710
	11th to 20th	Day	41% 5% 9% 19% 19% 6%	1697
	21st to end	Day	39% 5% 10% 25% 15% 7%	1570
March	1st to 10th	Day	49% 7% 10% 15% 16% 3	2037
	11th to 20th	Day	45% 6% 9% 21% 15% 5%	1980
	21st to end	Day	40% 7% 13% 20% 17% 3	2179
April	1st to 10th	Day	42% 6% 12% 21% 16% 4	2160
	11th to 20th	Day	32% 5% 14% 23% 20% 5%	2132
	21st to end	Day	25% 5% 14% 30% 22% 4	2160
May	1st to 10th	Day	25% 4 9% 29% 27% 7%	2317
	11th to 20th	Day	22% 5% 10% 32% 24% 7%	2335
	21st to end	Day	26% 5% 15% 30% 20% 3	2724
June	1st to 10th	Day	25% 4 11% 28% 25% 6%	2520
	11th to 20th	Day	14% 3 11% 21% 37% 15%	2520
	21st to end	Day	15% 2 4 16% 36% 27%	2520
July	1st to 10th	Day	15% 2 3 13% 28% 38%	2451
	11th to 20th	Day	15% 2 6% 12% 31% 34%	2273
	21st to end	Day	16% 1 4 10% 28% 41%	2405
August	1st to 10th	Day	18% 2 6% 17% 31% 27%	2312
	11th to 20th	Day	15% 2 4 14% 38% 28%	2246
	21st to end	Day	19% 1 5% 14% 34% 25%	2376
September	1st to 10th	Day	12% 2 4 12% 31% 39%	2160
	11th to 20th	Day	22% 3 6% 24% 33% 12%	2139
	21st to end	Day	14% 3 6% 23% 31% 23%	1904
October	1st to 10th	Day	20% 3 6% 17% 31% 23%	1800
	11th to 20th	Day	25% 4 8% 19% 24% 21%	1800
	21st to end	Day	26% 4 8% 21% 25% 16%	1980
November	1st to 10th	Day	31% 5% 7% 28% 18% 11%	1847
	11th to 20th	Day	36% 5% 10% 24% 16% 8%	1658
	21st to end	Day	32% 4 11% 20% 20% 13%	1520
December	1st to 10th	Day	41% 5% 9% 16% 18% 9%	1520
	11th to 20th	Day	58% 4 6% 13% 14% 5%	1928
	21st to end	Day	49% 5% 12% 20% 10% 4	2794
January	1st to 10th	Night	41% 7% 18% 22% 8% 3	4220
	11th to 20th	Night	53% 8% 9% 12% 10% 8%	4110
	21st to end	Night	54% 6% 9% 12% 13% 6%	4521
February	1st to 10th	Night	38% 4 9% 20% 18% 11%	2470
	11th to 20th	Night	40% 5% 9% 19% 20% 7%	2380
	21st to end	Night	32% 4 12% 26% 20% 5%	1879
March	1st to 10th	Night	49% 6% 11% 13% 16% 4	2039
	11th to 20th	Night	42% 4 9% 21% 19% 5%	1980
	21st to end	Night	37% 5% 11% 24% 17% 6%	2175
April	1st to 10th	Night	36% 6% 13% 21% 20% 5%	1800
	11th to 20th	Night	31% 4 12% 25% 19% 9%	1779
	21st to end	Night	24% 4 10% 31% 25% 6%	1800
May	1st to 10th	Night	26% 4 7% 22% 31% 10%	1638
	11th to 20th	Night	24% 5% 8% 27% 27% 9%	1559
	21st to end	Night	24% 5% 12% 31% 23% 5%	1552
June	1st to 10th	Night	25% 4 9% 23% 30% 9%	1440
	11th to 20th	Night	15% 3 7% 23% 33% 20%	1440
	21st to end	Night	19% 1 5% 13% 31% 31%	1440
July	1st to 10th	Night	15% 1 4 9% 31% 40%	1400
	11th to 20th	Night	16% 1 6% 13% 28% 36%	1558
	21st to end	Night	25% 1 3 10% 21% 40%	1674
August	1st to 10th	Night	23% 1 3 14% 28% 30%	1602
	11th to 20th	Night	21% 2 5% 11% 28% 33%	1652
	21st to end	Night	23% 1 5% 14% 27% 30%	1980
September	1st to 10th	Night	13% 1 4 12% 30% 39%	1800
	11th to 20th	Night	25% 2 7% 18% 34% 14%	1817
	21st to end	Night	19% 2 5% 21% 26% 27%	2056
October	1st to 10th	Night	21% 3 8% 16% 28% 24%	2160
	11th to 20th	Night	27% 3 6% 18% 22% 23%	2160
	21st to end	Night	27% 4 7% 19% 25% 19%	2376
November	1st to 10th	Night	31% 4 11% 25% 19% 10%	2229
	11th to 20th	Night	34% 4 13% 24% 17% 8%	2517
	21st to end	Night	30% 4 10% 21% 22% 13%	2660
December	1st to 10th	Night	42% 4 8% 17% 19% 10%	2660
	11th to 20th	Night	54% 4 9% 13% 15% 4	3276
	21st to end	Night	50% 7% 12% 17% 12% 3	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	30% 13% 25% 17% 12% 3	289
	11th to 20th	Day	25% 9% 24% 24% 15% 3	370
	21st to end	Day	18% 11% 23% 27% 17% 3	407
February	1st to 10th	Day	21% 11% 21% 23% 20% 4	370
	11th to 20th	Day	22% 18% 24% 23% 12% 1	376
	21st to end	Day	19% 15% 24% 27% 13% 1	382
March	1st to 10th	Day	29% 17% 24% 21% 7% 2	441
	11th to 20th	Day	25% 15% 27% 19% 11% 3	420
	21st to end	Day	18% 17% 30% 24% 11%	462
April	1st to 10th	Day	20% 17% 27% 23% 10% 2	420
	11th to 20th	Day	17% 19% 29% 20% 10% 3	412
	21st to end	Day	11% 16% 30% 26% 12% 5%	420
May	1st to 10th	Day	14% 16% 30% 24% 13% 4	423
	11th to 20th	Day	14% 13% 31% 25% 13% 4	448
	21st to end	Day	11% 12% 24% 30% 17% 6%	485
June	1st to 10th	Day	12% 11% 25% 31% 15% 7%	450
	11th to 20th	Day	6% 12% 29% 37% 12% 3	450
	21st to end	Day	3 4 26% 37% 24% 6%	450
July	1st to 10th	Day	6% 3 22% 43% 21% 5%	446
	11th to 20th	Day	2 1 18% 44% 27% 8%	444
	21st to end	Day	2 2 11% 47% 30% 8%	487
August	1st to 10th	Day	3 4 20% 42% 23% 8%	447
	11th to 20th	Day	3 2 21% 38% 27% 8%	437
	21st to end	Day	4 1 20% 38% 28% 8%	495
September	1st to 10th	Day	2 4 19% 39% 28% 9%	450
	11th to 20th	Day	7% 7% 23% 32% 23% 8%	450
	21st to end	Day	7% 6% 19% 35% 26% 6%	450
October	1st to 10th	Day	9% 7% 25% 23% 24% 11%	450
	11th to 20th	Day	9% 8% 19% 26% 28% 11%	450
	21st to end	Day	15% 7% 19% 28% 25% 7%	495
November	1st to 10th	Day	14% 10% 15% 28% 27% 6%	443
	11th to 20th	Day	12% 7% 17% 25% 26% 13%	246
	21st to end	Day	13% 8% 24% 26% 19% 11%	180
December	1st to 10th	Day	22% 14% 15% 22% 17% 10%	180
	11th to 20th	Day	28% 9% 22% 17% 14% 9%	180
	21st to end	Day	23% 10% 21% 25% 17% 4	198
January	1st to 10th	Night	23% 5% 16% 30% 22% 4	760
	11th to 20th	Night	23% 6% 15% 33% 20% 4	760
	21st to end	Night	21% 5% 15% 32% 24% 4	836
February	1st to 10th	Night	20% 6% 14% 35% 23% 3	760
	11th to 20th	Night	18% 7% 18% 32% 22% 4	744
	21st to end	Night	18% 10% 18% 32% 19% 3	628
March	1st to 10th	Night	23% 9% 18% 26% 20% 4	742
	11th to 20th	Night	19% 8% 16% 32% 22% 4	720
	21st to end	Night	19% 7% 22% 32% 18% 3	792
April	1st to 10th	Night	14% 9% 23% 32% 19% 4	720
	11th to 20th	Night	13% 11% 20% 30% 20% 6%	711
	21st to end	Night	9% 11% 24% 27% 24% 5%	720
May	1st to 10th	Night	10% 6% 20% 29% 30% 4	558
	11th to 20th	Night	7% 3 18% 32% 33% 6%	496
	21st to end	Night	7% 9% 18% 29% 33% 5%	389
June	1st to 10th	Night	7% 7% 20% 33% 31% 3	360
	11th to 20th	Night	4 5% 16% 44% 28% 3	360
	21st to end	Night	4 3 14% 35% 41% 4	360
July	1st to 10th	Night	3 1 10% 34% 47% 6%	350
	11th to 20th	Night	3 1 4 30% 49% 13%	514
	21st to end	Night	4 1 3 32% 51% 10%	591
August	1st to 10th	Night	5% 1 7% 31% 46% 11%	537
	11th to 20th	Night	3 5% 32% 50% 9%	584
	21st to end	Night	4 1 7% 29% 50% 9%	792
September	1st to 10th	Night	2 1 8% 28% 51% 10%	720
	11th to 20th	Night	7% 2 8% 33% 41% 9%	720
	21st to end	Night	5% 3 11% 33% 36% 12%	720
October	1st to 10th	Night	8% 4 14% 30% 34% 10%	720
	11th to 20th	Night	8% 3 12% 29% 39% 9%	720
	21st to end	Night	12% 2 12% 28% 35% 11%	792
November	1st to 10th	Night	12% 4 15% 27% 34% 8%	740
	11th to 20th	Night	15% 2 12% 35% 31% 5%	760
	21st to end	Night	12% 5% 15% 36% 27% 6%	760
December	1st to 10th	Night	24% 4 13% 29% 24% 5%	760
	11th to 20th	Night	29% 5% 14% 29% 20% 4	760
	21st to end	Night	24% 5% 19% 33% 17% 2	836

Page generated at 2024-03-03 03:28:56. Version ac07

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