Sagebrush Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sagebrush Skies Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	7% 7% 3 7% 4 4 4 3 5% 6% 50%	136239
	Night	9% 8% 3 7% 4 4 4 4 5% 6% 45%	132081
Transparency	Day	34% 6% 11% 22% 19% 9%	130945
	Night	39% 7% 11% 21% 16% 7%	128391
Seeing	Day	10% 7% 18% 26% 24% 14%	15719
	Night	13% 6% 20% 36% 22% 3	24824

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	16% 18% 9% 15% 7% 5% 4 4 4 5% 12%	3639
	11th to 20th	Day	14% 13% 5% 9% 5% 5% 5% 6% 6% 5% 27%	3640
	21st to end	Day	18% 14% 5% 11% 5% 4 4 4 5% 5% 24%	4004
February	1st to 10th	Day	15% 14% 5% 12% 7% 6% 5% 4 4 5% 23%	1725
	11th to 20th	Day	12% 14% 5% 9% 4 6% 5% 3 5% 6% 32%	1826
	21st to end	Day	10% 10% 3 9% 5% 6% 7% 4 7% 8% 31%	1650
March	1st to 10th	Day	7% 8% 3 8% 5% 6% 6% 5% 7% 10% 35%	4518
	11th to 20th	Day	7% 8% 3 8% 4 4 4 4 5% 7% 45%	4726
	21st to end	Day	9% 9% 4 11% 6% 6% 7% 5% 7% 8% 29%	5958
April	1st to 10th	Day	8% 8% 3 8% 5% 5% 5% 5% 8% 8% 37%	2400
	11th to 20th	Day	6% 7% 2 6% 4 4 5% 4 6% 8% 46%	2369
	21st to end	Day	6% 5% 2 5% 5% 4 5% 4 6% 9% 49%	2570
May	1st to 10th	Day	7% 5% 1 4 3 4 3 3 5% 8% 58%	6315
	11th to 20th	Day	5% 6% 2 6% 5% 4 5% 4 6% 6% 51%	6277
	21st to end	Day	5% 5% 2 5% 4 4 5% 4 6% 7% 53%	6902
June	1st to 10th	Day	8% 6% 2 6% 5% 4 4 4 6% 7% 48%	2800
	11th to 20th	Day	6% 5% 2 4 4 4 3 4 6% 8% 53%	2800
	21st to end	Day	3 4 1 4 3 3 3 3 4 6% 66%	2800
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 4 79%	6319
	11th to 20th	Day	1 1 1 2 2 2 1 1 2 3 83%	6320
	21st to end	Day	1 1 1 2 2 2 2 2 4 6% 77%	6880
August	1st to 10th	Day	3 4 1 4 2 2 3 2 4 6% 68%	6210
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 6% 74%	5858
	21st to end	Day	4 4 2 4 3 3 3 3 4 6% 64%	5984
September	1st to 10th	Day	3 2 1 3 2 2 2 3 4 6% 72%	2400
	11th to 20th	Day	4 4 1 5% 3 4 4 4 5% 7% 59%	2349
	21st to end	Day	6% 5% 2 5% 4 4 4 3 4 7% 57%	2200
October	1st to 10th	Day	5% 3 2 4 3 3 3 3 6% 7% 62%	3327
	11th to 20th	Day	4 4 2 5% 4 5% 5% 4 7% 9% 48%	3207
	21st to end	Day	11% 7% 2 7% 5% 5% 5% 5% 6% 7% 41%	3200
November	1st to 10th	Day	14% 9% 4 8% 7% 5% 5% 4 6% 6% 33%	1854
	11th to 20th	Day	14% 14% 4 12% 6% 6% 5% 4 5% 6% 24%	1744
	21st to end	Day	13% 13% 5% 14% 8% 7% 6% 4 4 5% 20%	1680
December	1st to 10th	Day	10% 11% 6% 13% 8% 9% 7% 4 5% 6% 20%	2700
	11th to 20th	Day	19% 17% 7% 16% 8% 5% 4 2 4 4 14%	3084
	21st to end	Day	17% 15% 5% 16% 10% 6% 4 3 4 4 15%	4004
January	1st to 10th	Night	19% 19% 11% 13% 6% 4 4 3 4 4 13%	6306
	11th to 20th	Night	13% 12% 4 7% 4 4 4 4 6% 8% 35%	6320
	21st to end	Night	14% 13% 6% 13% 5% 4 4 3 5% 5% 29%	6952
February	1st to 10th	Night	14% 13% 3 8% 7% 5% 5% 4 6% 5% 29%	2675
	11th to 20th	Night	11% 10% 4 8% 5% 5% 5% 4 5% 7% 36%	2459
	21st to end	Night	11% 10% 3 8% 6% 5% 5% 4 7% 8% 34%	1980
March	1st to 10th	Night	7% 8% 3 7% 4 5% 6% 5% 8% 9% 40%	5376
	11th to 20th	Night	8% 10% 3 7% 4 4 4 4 5% 6% 45%	5272
	21st to end	Night	7% 8% 3 9% 7% 7% 6% 6% 8% 8% 30%	5016
April	1st to 10th	Night	10% 10% 3 9% 5% 5% 4 4 7% 8% 35%	2000
	11th to 20th	Night	8% 7% 2 5% 4 3 4 3 6% 6% 50%	1979
	21st to end	Night	6% 6% 3 7% 5% 5% 5% 5% 7% 7% 45%	1830
May	1st to 10th	Night	5% 4 2 4 4 4 5% 4 5% 7% 56%	3641
	11th to 20th	Night	6% 5% 2 6% 4 4 5% 4 6% 7% 51%	3616
	21st to end	Night	5% 4 2 5% 3 4 4 4 5% 8% 55%	3972
June	1st to 10th	Night	8% 5% 2 5% 4 4 5% 5% 6% 7% 50%	1600
	11th to 20th	Night	8% 7% 3 5% 3 4 3 2 6% 6% 53%	1600
	21st to end	Night	3 4 2 5% 3 4 5% 3 5% 6% 62%	1600
July	1st to 10th	Night	2 1 1 2 1 1 2 2 4 4 79%	3640
	11th to 20th	Night	1 1 2 1 1 1 2 3 4 84%	3640
	21st to end	Night	2 2 1 2 1 1 2 2 3 6% 78%	3970
August	1st to 10th	Night	3 3 1 3 3 3 3 4 5% 7% 66%	3582
	11th to 20th	Night	2 2 1 4 3 3 3 3 4 5% 71%	3971
	21st to end	Night	3 3 1 4 3 3 3 3 5% 6% 65%	5015
September	1st to 10th	Night	3 3 3 2 2 3 2 4 6% 73%	2000
	11th to 20th	Night	5% 3 1 4 4 4 4 4 4 6% 62%	2050
	21st to end	Night	6% 3 1 4 2 4 3 3 6% 8% 59%	2200
October	1st to 10th	Night	4 3 1 3 3 3 3 3 4 7% 65%	3869
	11th to 20th	Night	7% 4 2 5% 4 3 5% 4 7% 8% 52%	3947
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 5% 7% 47%	4600
November	1st to 10th	Night	14% 8% 3 8% 5% 5% 5% 3 5% 7% 36%	2665
	11th to 20th	Night	16% 10% 3 9% 5% 5% 5% 4 6% 6% 31%	2872
	21st to end	Night	14% 11% 3 9% 5% 6% 5% 4 5% 7% 30%	2940
December	1st to 10th	Night	8% 9% 5% 9% 6% 6% 6% 5% 6% 7% 33%	4700
	11th to 20th	Night	19% 18% 6% 14% 7% 5% 5% 4 5% 5% 11%	5274
	21st to end	Night	17% 16% 5% 10% 7% 5% 5% 3 5% 5% 20%	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	72% 9% 10% 7% 3	3639
	11th to 20th	Day	55% 10% 15% 16% 4	3640
	21st to end	Day	61% 7% 10% 16% 7%	4004
February	1st to 10th	Day	62% 9% 15% 10% 4	1725
	11th to 20th	Day	51% 9% 16% 17% 7%	1835
	21st to end	Day	47% 10% 16% 19% 7% 1	1650
March	1st to 10th	Day	38% 7% 14% 24% 16% 1	4518
	11th to 20th	Day	37% 6% 13% 30% 15%	4726
	21st to end	Day	47% 11% 15% 19% 7% 1	5958
April	1st to 10th	Day	39% 8% 16% 23% 12% 1	2400
	11th to 20th	Day	34% 7% 15% 25% 15% 5%	2372
	21st to end	Day	31% 6% 14% 27% 18% 3	2570
May	1st to 10th	Day	23% 5% 8% 25% 31% 8%	6315
	11th to 20th	Day	30% 6% 10% 25% 23% 7%	6280
	21st to end	Day	26% 8% 15% 29% 20% 3	6904
June	1st to 10th	Day	33% 6% 10% 25% 21% 5%	2800
	11th to 20th	Day	27% 5% 12% 28% 24% 6%	2800
	21st to end	Day	19% 5% 9% 29% 28% 11%	2800
July	1st to 10th	Day	12% 2 4 16% 31% 36%	6251
	11th to 20th	Day	9% 2 3 11% 32% 44%	6245
	21st to end	Day	10% 2 5% 24% 36% 22%	6681
August	1st to 10th	Day	15% 2 5% 13% 38% 28%	4524
	11th to 20th	Day	12% 2 6% 35% 33% 12%	4248
	21st to end	Day	20% 3 7% 28% 32% 10%	4311
September	1st to 10th	Day	13% 4 9% 28% 31% 15%	2400
	11th to 20th	Day	24% 6% 12% 25% 26% 7%	2349
	21st to end	Day	26% 6% 14% 32% 18% 4	2200
October	1st to 10th	Day	22% 4 12% 36% 24% 3	3327
	11th to 20th	Day	31% 6% 22% 27% 14% 1	3207
	21st to end	Day	41% 6% 14% 27% 11% 1	3200
November	1st to 10th	Day	50% 9% 16% 18% 6% 1	1854
	11th to 20th	Day	59% 8% 16% 13% 4 1	1744
	21st to end	Day	65% 9% 13% 10% 4	1680
December	1st to 10th	Day	63% 9% 13% 13% 2	2700
	11th to 20th	Day	74% 7% 9% 8% 1	3084
	21st to end	Day	71% 8% 8% 11% 1	4004
January	1st to 10th	Night	73% 9% 9% 7% 2	6306
	11th to 20th	Night	47% 9% 19% 20% 5%	6320
	21st to end	Night	56% 9% 11% 16% 8%	6952
February	1st to 10th	Night	53% 9% 18% 15% 5%	2675
	11th to 20th	Night	46% 10% 16% 21% 8% 1	2461
	21st to end	Night	46% 9% 15% 20% 8% 2	1980
March	1st to 10th	Night	35% 8% 11% 28% 18% 1	5376
	11th to 20th	Night	38% 5% 12% 30% 15%	5272
	21st to end	Night	44% 11% 15% 23% 6%	5016
April	1st to 10th	Night	44% 7% 13% 24% 11% 1	2000
	11th to 20th	Night	33% 6% 10% 25% 19% 6%	1979
	21st to end	Night	34% 8% 14% 22% 17% 5%	1830
May	1st to 10th	Night	24% 6% 8% 19% 34% 7%	3638
	11th to 20th	Night	30% 6% 9% 29% 22% 3	3616
	21st to end	Night	25% 8% 15% 31% 18% 2	3972
June	1st to 10th	Night	30% 5% 12% 25% 21% 7%	1600
	11th to 20th	Night	31% 5% 8% 25% 26% 6%	1600
	21st to end	Night	22% 5% 8% 23% 29% 14%	1600
July	1st to 10th	Night	10% 2 3 18% 25% 41%	3600
	11th to 20th	Night	7% 1 3 9% 30% 49%	3592
	21st to end	Night	10% 2 4 18% 35% 31%	3857
August	1st to 10th	Night	16% 3 3 9% 30% 38%	2601
	11th to 20th	Night	14% 3 5% 29% 32% 17%	2871
	21st to end	Night	16% 3 7% 26% 28% 20%	3608
September	1st to 10th	Night	14% 4 8% 23% 30% 21%	2000
	11th to 20th	Night	22% 5% 10% 23% 26% 14%	2050
	21st to end	Night	23% 4 11% 29% 24% 9%	2200
October	1st to 10th	Night	21% 4 9% 31% 33% 2	3869
	11th to 20th	Night	29% 5% 15% 27% 22% 2	3947
	21st to end	Night	36% 5% 11% 31% 15% 2	4600
November	1st to 10th	Night	46% 7% 15% 21% 9%	2665
	11th to 20th	Night	52% 9% 15% 17% 5% 1	2872
	21st to end	Night	53% 9% 18% 15% 5% 1	2940
December	1st to 10th	Night	49% 10% 19% 18% 4	4700
	11th to 20th	Night	74% 8% 11% 6% 1	5274
	21st to end	Night	62% 10% 12% 11% 4	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	25% 9% 19% 25% 19% 4	200
	11th to 20th	Day	25% 9% 18% 27% 17% 6%	200
	21st to end	Day	21% 7% 18% 25% 24% 6%	220
February	1st to 10th	Day	22% 9% 23% 26% 13% 6%	325
	11th to 20th	Day	20% 9% 19% 29% 17% 6%	431
	21st to end	Day	14% 14% 22% 27% 19% 4	414
March	1st to 10th	Day	16% 11% 26% 23% 18% 6%	500
	11th to 20th	Day	14% 10% 19% 27% 20% 11%	500
	21st to end	Day	14% 11% 26% 28% 17% 4	550
April	1st to 10th	Day	13% 13% 23% 27% 15% 9%	500
	11th to 20th	Day	10% 12% 30% 24% 16% 8%	492
	21st to end	Day	7% 9% 27% 27% 22% 9%	500
May	1st to 10th	Day	7% 9% 20% 29% 24% 11%	503
	11th to 20th	Day	11% 7% 21% 24% 23% 14%	528
	21st to end	Day	9% 6% 17% 26% 25% 18%	573
June	1st to 10th	Day	9% 7% 16% 23% 26% 18%	530
	11th to 20th	Day	7% 11% 23% 33% 17% 9%	530
	21st to end	Day	3 3 18% 25% 31% 20%	530
July	1st to 10th	Day	3 2 11% 29% 40% 15%	526
	11th to 20th	Day	1 2 12% 32% 36% 17%	524
	21st to end	Day	1 1 10% 25% 35% 27%	575
August	1st to 10th	Day	4 3 9% 23% 35% 27%	527
	11th to 20th	Day	2 2 8% 23% 34% 31%	517
	21st to end	Day	5% 4 15% 23% 26% 25%	583
September	1st to 10th	Day	4 2 11% 27% 32% 25%	530
	11th to 20th	Day	6% 3 14% 28% 26% 22%	530
	21st to end	Day	7% 6% 15% 28% 27% 15%	530
October	1st to 10th	Day	9% 4 21% 25% 22% 19%	530
	11th to 20th	Day	11% 7% 17% 26% 24% 15%	501
	21st to end	Day	16% 7% 22% 30% 17% 8%	363
November	1st to 10th	Day	19% 8% 25% 25% 18% 4	330
	11th to 20th	Day	23% 11% 19% 21% 19% 8%	253
	21st to end	Day	11% 7% 20% 29% 25% 8%	220
December	1st to 10th	Day	22% 7% 16% 25% 17% 13%	220
	11th to 20th	Day	21% 10% 23% 28% 14% 5%	214
	21st to end	Day	24% 6% 23% 26% 17% 3	220
January	1st to 10th	Night	28% 7% 18% 29% 16% 2	800
	11th to 20th	Night	21% 6% 20% 34% 18% 2	800
	21st to end	Night	18% 5% 17% 37% 21% 3	880
February	1st to 10th	Night	20% 6% 23% 33% 15% 2	800
	11th to 20th	Night	15% 7% 23% 34% 19% 2	784
	21st to end	Night	15% 12% 22% 34% 15% 2	660
March	1st to 10th	Night	14% 6% 25% 36% 17% 2	800
	11th to 20th	Night	13% 9% 21% 36% 20% 2	800
	21st to end	Night	13% 8% 26% 36% 15% 1	880
April	1st to 10th	Night	15% 7% 23% 34% 20% 2	800
	11th to 20th	Night	9% 9% 29% 31% 18% 3	791
	21st to end	Night	7% 8% 27% 36% 20% 2	630
May	1st to 10th	Night	6% 8% 25% 37% 21% 3	401
	11th to 20th	Night	9% 5% 19% 35% 28% 5%	394
	21st to end	Night	7% 3 18% 41% 26% 4	433
June	1st to 10th	Night	9% 3 26% 36% 24% 3	400
	11th to 20th	Night	9% 8% 31% 34% 17% 2	400
	21st to end	Night	4 5% 25% 39% 26% 2	400
July	1st to 10th	Night	4 3 16% 47% 28% 2	390
	11th to 20th	Night	3 3 17% 49% 27% 2	388
	21st to end	Night	2 2 13% 47% 34% 3	438
August	1st to 10th	Night	5% 1 12% 39% 38% 4	398
	11th to 20th	Night	3 1 11% 38% 36% 9%	549
	21st to end	Night	4 2 15% 40% 34% 5%	880
September	1st to 10th	Night	4 2 13% 43% 33% 7%	800
	11th to 20th	Night	5% 1 14% 36% 36% 7%	800
	21st to end	Night	7% 3 18% 35% 31% 6%	800
October	1st to 10th	Night	10% 4 17% 38% 28% 3	800
	11th to 20th	Night	12% 6% 18% 35% 25% 5%	800
	21st to end	Night	11% 6% 23% 36% 18% 5%	880
November	1st to 10th	Night	18% 6% 19% 41% 16% 1	820
	11th to 20th	Night	20% 8% 22% 30% 17% 3	840
	21st to end	Night	19% 5% 18% 37% 19% 3	840
December	1st to 10th	Night	17% 5% 16% 37% 21% 3	840
	11th to 20th	Night	23% 6% 18% 35% 16% 1	828
	21st to end	Night	25% 6% 22% 33% 13% 1	880

Page generated at 2025-12-14 22:13:51. Version ac07

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