Hyman Rim Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hyman Rim Ranch Observatory clear sky chart from 2005-11-06 to 2026-07-01.

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	2 4 2 5% 4 4 4 3 5% 6% 61%	146923
	Night	1 3 1 4 3 3 4 3 5% 7% 65%	143024
Transparency	Day	21% 5% 7% 15% 29% 22%	141757
	Night	18% 5% 8% 16% 30% 23%	139198
Seeing	Day	10% 19% 29% 26% 12% 3	17013
	Night	6% 14% 24% 33% 20% 3	27143

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 3 8% 4 5% 5% 3 5% 5% 58%	5318
	11th to 20th	Day	1 2 1 3 2 3 3 3 4 5% 74%	5340
	21st to end	Day	2 7% 3 6% 4 4 4 3 4 6% 58%	5844
February	1st to 10th	Day	1 7% 2 6% 4 3 4 3 6% 6% 59%	1890
	11th to 20th	Day	2 6% 2 5% 4 4 4 3 5% 8% 57%	2026
	21st to end	Day	1 5% 2 6% 5% 4 4 4 5% 7% 57%	1795
March	1st to 10th	Day	1 5% 2 4 4 4 4 3 5% 6% 61%	5064
	11th to 20th	Day	1 9% 3 8% 5% 4 4 4 6% 8% 49%	5110
	21st to end	Day	2 5% 2 5% 4 4 4 3 5% 7% 59%	5607
April	1st to 10th	Day	1 3 2 5% 3 3 3 3 5% 8% 64%	2310
	11th to 20th	Day	1 4 1 5% 3 3 4 3 4 6% 67%	2475
	21st to end	Day	2 3 1 4 3 3 3 3 4 5% 69%	2635
May	1st to 10th	Day	2 4 2 5% 3 4 4 3 4 4 65%	7626
	11th to 20th	Day	1 2 1 3 3 3 4 4 5% 5% 70%	7596
	21st to end	Day	2 2 1 3 2 2 3 2 3 5% 75%	8370
June	1st to 10th	Day	1 2 1 3 3 3 3 3 4 7% 69%	2730
	11th to 20th	Day	1 1 1 3 2 2 2 2 2 4 80%	2730
	21st to end	Day	1 3 1 4 4 3 5% 3 4 4 67%	2730
July	1st to 10th	Day	3 3 1 5% 4 4 4 3 5% 6% 62%	5880
	11th to 20th	Day	4 4 2 7% 6% 6% 7% 5% 8% 9% 42%	5880
	21st to end	Day	3 4 2 5% 5% 6% 7% 5% 8% 8% 45%	6401
August	1st to 10th	Day	3 4 2 6% 5% 5% 6% 5% 7% 8% 49%	5779
	11th to 20th	Day	3 4 2 7% 5% 7% 6% 6% 8% 9% 44%	5798
	21st to end	Day	4 4 2 7% 6% 6% 6% 6% 7% 8% 45%	6080
September	1st to 10th	Day	5% 5% 2 7% 5% 6% 6% 5% 7% 6% 45%	2208
	11th to 20th	Day	3 3 1 4 3 4 3 3 4 5% 67%	2200
	21st to end	Day	3 3 1 4 3 4 4 3 5% 5% 66%	2200
October	1st to 10th	Day	4 3 2 4 3 3 3 3 4 5% 66%	3435
	11th to 20th	Day	2 3 1 4 2 2 2 2 3 5% 73%	3250
	21st to end	Day	1 1 1 1 2 2 3 2 3 5% 80%	3548
November	1st to 10th	Day	1 3 1 2 3 3 3 3 5% 6% 70%	2059
	11th to 20th	Day	3 1 4 3 3 4 2 3 6% 70%	1971
	21st to end	Day	2 5% 2 5% 3 3 2 2 5% 7% 64%	1890
December	1st to 10th	Day	2 4 1 4 2 2 2 2 3 5% 73%	3040
	11th to 20th	Day	1 6% 2 6% 4 3 3 3 6% 10% 56%	3499
	21st to end	Day	2 5% 2 6% 5% 4 4 3 5% 7% 58%	4609
January	1st to 10th	Night	1 5% 2 7% 5% 4 4 4 5% 7% 56%	7605
	11th to 20th	Night	1 2 1 3 2 2 2 2 3 6% 78%	7650
	21st to end	Night	2 6% 3 7% 4 4 4 3 5% 6% 56%	8370
February	1st to 10th	Night	1 4 2 6% 5% 4 3 3 5% 5% 63%	2730
	11th to 20th	Night	1 4 2 6% 4 3 4 4 6% 6% 59%	2479
	21st to end	Night	1 4 1 6% 4 3 4 4 5% 8% 60%	2009
March	1st to 10th	Night	1 4 1 3 3 4 3 3 5% 8% 64%	5050
	11th to 20th	Night	1 4 1 7% 5% 5% 4 4 6% 9% 54%	5110
	21st to end	Night	1 3 2 6% 4 4 4 4 5% 7% 60%	5610
April	1st to 10th	Night	1 3 2 5% 4 3 4 3 5% 6% 65%	2310
	11th to 20th	Night	1 3 1 4 3 3 3 3 5% 5% 71%	2092
	21st to end	Night	1 1 2 2 2 3 3 4 7% 75%	1980
May	1st to 10th	Night	2 3 1 4 3 3 3 4 6% 5% 66%	5321
	11th to 20th	Night	1 2 1 2 2 2 2 2 4 5% 78%	5296
	21st to end	Night	1 1 1 2 2 2 2 2 3 4 80%	5837
June	1st to 10th	Night	1 2 1 2 3 2 3 3 4 7% 71%	1890
	11th to 20th	Night	1 1 1 2 2 1 2 2 3 3 83%	1890
	21st to end	Night	1 3 1 3 2 2 3 3 3 5% 73%	1890
July	1st to 10th	Night	1 2 1 3 3 4 4 3 5% 5% 68%	4100
	11th to 20th	Night	3 3 2 6% 6% 6% 7% 6% 9% 11% 41%	4100
	21st to end	Night	3 4 1 5% 4 4 5% 5% 7% 10% 51%	4472
August	1st to 10th	Night	2 2 1 5% 4 4 6% 5% 9% 11% 50%	4033
	11th to 20th	Night	2 2 1 3 3 3 4 5% 8% 12% 57%	4051
	21st to end	Night	3 3 2 6% 5% 6% 6% 5% 8% 9% 49%	4895
September	1st to 10th	Night	3 4 2 5% 3 4 4 4 7% 10% 55%	2188
	11th to 20th	Night	2 2 1 3 2 2 3 2 4 5% 76%	2200
	21st to end	Night	2 1 1 4 2 2 3 3 5% 5% 73%	2200
October	1st to 10th	Night	2 2 1 2 2 2 2 2 4 5% 75%	3758
	11th to 20th	Night	1 2 1 3 2 2 2 2 3 6% 76%	3898
	21st to end	Night	1 2 1 2 2 2 3 3 4 6% 76%	4252
November	1st to 10th	Night	1 3 1 3 3 3 3 3 4 5% 70%	2460
	11th to 20th	Night	1 1 4 3 2 3 3 4 5% 73%	2646
	21st to end	Night	1 4 2 4 3 4 3 3 5% 6% 64%	2730
December	1st to 10th	Night	2 2 1 3 3 3 3 3 4 7% 69%	4370
	11th to 20th	Night	1 4 3 4 3 4 4 3 5% 6% 63%	4941
	21st to end	Night	1 4 2 6% 4 4 4 3 4 5% 64%	6611

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	26% 4 5% 20% 34% 10%	5321
	11th to 20th	Day	13% 5% 5% 16% 28% 34%	5340
	21st to end	Day	26% 4 4 11% 29% 27%	5844
February	1st to 10th	Day	23% 4 9% 15% 29% 20%	1890
	11th to 20th	Day	24% 5% 8% 22% 24% 17%	2036
	21st to end	Day	23% 5% 9% 17% 26% 20%	1795
March	1st to 10th	Day	18% 6% 7% 15% 33% 21%	5064
	11th to 20th	Day	26% 7% 9% 18% 27% 12%	5110
	21st to end	Day	21% 6% 8% 24% 32% 10%	5607
April	1st to 10th	Day	19% 4 6% 18% 37% 16%	2310
	11th to 20th	Day	18% 3 5% 15% 35% 24%	2478
	21st to end	Day	16% 4 5% 17% 40% 18%	2635
May	1st to 10th	Day	21% 3 5% 16% 35% 19%	7626
	11th to 20th	Day	12% 5% 6% 13% 36% 29%	7599
	21st to end	Day	13% 3 2 6% 34% 41%	8371
June	1st to 10th	Day	14% 4 6% 11% 32% 33%	2730
	11th to 20th	Day	10% 2 3 7% 26% 51%	2730
	21st to end	Day	19% 4 6% 10% 25% 36%	2730
July	1st to 10th	Day	21% 6% 6% 9% 16% 42%	5817
	11th to 20th	Day	32% 9% 11% 24% 14% 10%	5811
	21st to end	Day	31% 11% 15% 14% 17% 13%	6217
August	1st to 10th	Day	38% 10% 18% 15% 11% 8%	4208
	11th to 20th	Day	31% 11% 12% 19% 18% 9%	4197
	21st to end	Day	33% 8% 13% 15% 21% 9%	4383
September	1st to 10th	Day	33% 8% 11% 14% 18% 16%	2208
	11th to 20th	Day	19% 5% 5% 16% 33% 24%	2200
	21st to end	Day	19% 4 8% 12% 33% 25%	2200
October	1st to 10th	Day	19% 4 5% 11% 25% 37%	3435
	11th to 20th	Day	14% 3 3 11% 46% 23%	3250
	21st to end	Day	9% 2 4 11% 39% 34%	3548
November	1st to 10th	Day	15% 3 5% 23% 33% 21%	2059
	11th to 20th	Day	15% 4 6% 16% 37% 22%	1971
	21st to end	Day	20% 4 6% 17% 34% 19%	1890
December	1st to 10th	Day	15% 3 5% 21% 38% 19%	3040
	11th to 20th	Day	24% 3 6% 16% 39% 13%	3498
	21st to end	Day	25% 5% 7% 23% 29% 11%	4609
January	1st to 10th	Night	25% 7% 8% 19% 32% 9%	7605
	11th to 20th	Night	10% 3 6% 15% 34% 32%	7650
	21st to end	Night	27% 4 4 9% 28% 27%	8370
February	1st to 10th	Night	21% 5% 8% 16% 28% 23%	2730
	11th to 20th	Night	21% 5% 9% 23% 24% 18%	2480
	21st to end	Night	19% 7% 8% 16% 28% 22%	2009
March	1st to 10th	Night	14% 5% 8% 16% 37% 20%	5050
	11th to 20th	Night	19% 9% 8% 22% 29% 13%	5110
	21st to end	Night	18% 8% 8% 24% 33% 10%	5610
April	1st to 10th	Night	19% 4 7% 19% 34% 18%	2310
	11th to 20th	Night	15% 3 6% 15% 37% 25%	2092
	21st to end	Night	10% 4 6% 20% 42% 19%	1980
May	1st to 10th	Night	17% 3 6% 18% 38% 17%	5319
	11th to 20th	Night	10% 3 4 14% 38% 31%	5297
	21st to end	Night	10% 2 2 7% 39% 40%	5838
June	1st to 10th	Night	13% 3 5% 10% 31% 38%	1890
	11th to 20th	Night	7% 2 3 6% 27% 55%	1890
	21st to end	Night	14% 3 6% 9% 23% 44%	1890
July	1st to 10th	Night	18% 4 6% 11% 18% 44%	4055
	11th to 20th	Night	31% 9% 15% 22% 13% 10%	4046
	21st to end	Night	26% 8% 18% 17% 16% 15%	4344
August	1st to 10th	Night	32% 10% 24% 13% 10% 11%	2928
	11th to 20th	Night	19% 8% 18% 26% 18% 11%	2928
	21st to end	Night	23% 7% 14% 20% 23% 12%	3523
September	1st to 10th	Night	23% 7% 14% 16% 23% 17%	2188
	11th to 20th	Night	13% 3 8% 18% 31% 27%	2200
	21st to end	Night	13% 4 8% 12% 33% 29%	2200
October	1st to 10th	Night	13% 4 5% 12% 26% 41%	3758
	11th to 20th	Night	12% 2 3 15% 42% 26%	3898
	21st to end	Night	10% 3 4 10% 39% 34%	4252
November	1st to 10th	Night	16% 3 5% 19% 37% 19%	2460
	11th to 20th	Night	13% 4 8% 16% 34% 25%	2646
	21st to end	Night	20% 4 7% 15% 32% 22%	2730
December	1st to 10th	Night	15% 4 6% 20% 31% 24%	4370
	11th to 20th	Night	22% 3 5% 14% 39% 18%	4941
	21st to end	Night	22% 5% 7% 21% 26% 19%	6611

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	15% 27% 31% 16% 9% 1	330
	11th to 20th	Day	15% 22% 28% 22% 11% 2	330
	21st to end	Day	10% 27% 30% 21% 11% 1	363
February	1st to 10th	Day	15% 24% 31% 19% 9% 2	330
	11th to 20th	Day	22% 30% 26% 19% 4	511
	21st to end	Day	17% 33% 30% 16% 3 1	446
March	1st to 10th	Day	20% 32% 31% 13% 4	540
	11th to 20th	Day	18% 27% 27% 18% 8% 2	540
	21st to end	Day	16% 34% 29% 14% 6% 1	594
April	1st to 10th	Day	10% 26% 37% 17% 8% 2	540
	11th to 20th	Day	16% 32% 31% 15% 5% 1	532
	21st to end	Day	14% 31% 31% 16% 7% 1	540
May	1st to 10th	Day	9% 27% 38% 20% 6% 1	543
	11th to 20th	Day	8% 23% 34% 23% 9% 3	568
	21st to end	Day	8% 22% 39% 22% 8% 2	617
June	1st to 10th	Day	5% 15% 38% 30% 10% 2	570
	11th to 20th	Day	4 19% 43% 22% 11% 2	570
	21st to end	Day	5% 14% 38% 30% 12% 2	570
July	1st to 10th	Day	5% 3 30% 42% 17% 4	527
	11th to 20th	Day	8% 1 18% 40% 25% 7%	524
	21st to end	Day	9% 3 16% 35% 30% 8%	575
August	1st to 10th	Day	7% 2 17% 43% 23% 7%	527
	11th to 20th	Day	4 6% 16% 43% 24% 7%	517
	21st to end	Day	5% 4 18% 39% 25% 8%	583
September	1st to 10th	Day	7% 7% 20% 36% 23% 8%	530
	11th to 20th	Day	5% 13% 34% 31% 14% 3	530
	21st to end	Day	7% 15% 27% 32% 15% 3	530
October	1st to 10th	Day	9% 20% 28% 25% 14% 4	430
	11th to 20th	Day	10% 16% 27% 27% 17% 2	330
	21st to end	Day	10% 18% 29% 24% 14% 4	363
November	1st to 10th	Day	10% 18% 29% 27% 13% 3	330
	11th to 20th	Day	9% 20% 25% 29% 14% 3	330
	21st to end	Day	13% 23% 28% 23% 11% 2	330
December	1st to 10th	Day	9% 23% 29% 28% 8% 3	330
	11th to 20th	Day	8% 23% 31% 23% 13% 3	330
	21st to end	Day	17% 26% 27% 23% 4 2	363
January	1st to 10th	Night	8% 18% 27% 29% 15% 3	840
	11th to 20th	Night	8% 16% 32% 26% 14% 3	840
	21st to end	Night	7% 24% 27% 28% 12% 2	924
February	1st to 10th	Night	6% 20% 30% 29% 12% 3	840
	11th to 20th	Night	9% 23% 33% 25% 9% 1	824
	21st to end	Night	8% 22% 31% 26% 11% 2	692
March	1st to 10th	Night	8% 26% 30% 27% 8% 1	840
	11th to 20th	Night	8% 19% 27% 27% 16% 3	840
	21st to end	Night	6% 22% 28% 31% 11% 2	924
April	1st to 10th	Night	5% 20% 31% 31% 12% 1	840
	11th to 20th	Night	8% 23% 30% 31% 9%	638
	21st to end	Night	5% 22% 29% 30% 12% 3	630
May	1st to 10th	Night	3 16% 30% 38% 11% 1	630
	11th to 20th	Night	3 13% 32% 30% 19% 2	621
	21st to end	Night	4 13% 30% 35% 16% 1	683
June	1st to 10th	Night	2 8% 31% 44% 15% 1	630
	11th to 20th	Night	2 7% 33% 39% 17% 1	630
	21st to end	Night	3 5% 23% 43% 24% 1	630
July	1st to 10th	Night	3 1 14% 44% 36% 3	585
	11th to 20th	Night	5% 1 8% 38% 43% 4	582
	21st to end	Night	7% 2 9% 29% 45% 9%	657
August	1st to 10th	Night	4 1 7% 35% 43% 10%	597
	11th to 20th	Night	4 2 8% 33% 44% 8%	594
	21st to end	Night	4 1 7% 33% 46% 9%	660
September	1st to 10th	Night	4 4 11% 35% 40% 7%	788
	11th to 20th	Night	3 5% 16% 40% 32% 4	800
	21st to end	Night	3 9% 16% 36% 31% 5%	800
October	1st to 10th	Night	5% 11% 25% 36% 21% 2	800
	11th to 20th	Night	5% 9% 23% 39% 20% 3	800
	21st to end	Night	4 13% 23% 32% 23% 5%	880
November	1st to 10th	Night	4 12% 26% 34% 19% 5%	820
	11th to 20th	Night	5% 14% 25% 33% 19% 5%	840
	21st to end	Night	7% 19% 26% 30% 15% 3	840
December	1st to 10th	Night	7% 17% 23% 33% 18% 2	840
	11th to 20th	Night	8% 16% 29% 29% 15% 2	840
	21st to end	Night	10% 18% 31% 29% 8% 3	924

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