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 2024-01-13.

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% 7% 3 6% 5% 3 4 4 5% 7% 47%	74795
	Night	10% 8% 3 6% 6% 3 5% 4 5% 7% 42%	74969
Transparency	Day	37% 7% 12% 21% 17% 7%	74498
	Night	41% 7% 12% 19% 14% 6%	74784
Seeing	Day	10% 7% 18% 26% 24% 14%	13256
	Night	13% 6% 20% 36% 22% 3	22457

By Month

Percentage Cloud Cover NW (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	19% 16% 6% 9% 9% 4 5% 4 4 6% 17%	1519
	11th to 20th	Day	18% 19% 5% 12% 8% 3 4 3 4 6% 16%	1459
	21st to end	Day	14% 17% 8% 13% 8% 4 6% 3 4 5% 17%	1584
February	1st to 10th	Day	16% 12% 5% 9% 9% 5% 5% 4 5% 5% 24%	1552
	11th to 20th	Day	12% 11% 5% 8% 6% 3 5% 5% 4 6% 34%	1639
	21st to end	Day	10% 9% 4 8% 6% 4 6% 6% 7% 9% 31%	1480
March	1st to 10th	Day	12% 9% 3 8% 6% 4 5% 5% 6% 9% 33%	1800
	11th to 20th	Day	12% 8% 5% 7% 6% 4 5% 6% 5% 8% 35%	1862
	21st to end	Day	11% 7% 3 8% 6% 4 7% 7% 7% 9% 31%	2365
April	1st to 10th	Day	8% 7% 3 6% 7% 4 6% 5% 7% 8% 38%	2160
	11th to 20th	Day	7% 7% 2 5% 6% 3 5% 5% 6% 8% 45%	2132
	21st to end	Day	7% 6% 2 5% 5% 3 5% 5% 5% 9% 49%	2312
May	1st to 10th	Day	5% 4 2 4 4 3 5% 6% 5% 8% 53%	2515
	11th to 20th	Day	7% 5% 3 6% 6% 4 5% 6% 7% 9% 42%	2477
	21st to end	Day	7% 6% 3 6% 5% 4 5% 5% 6% 7% 46%	2723
June	1st to 10th	Day	9% 5% 3 5% 6% 3 4 4 5% 8% 47%	2520
	11th to 20th	Day	7% 4 2 4 4 3 4 4 6% 9% 52%	2520
	21st to end	Day	3 3 1 3 3 2 4 4 4 6% 67%	2520
July	1st to 10th	Day	2 1 1 2 2 1 3 3 4 5% 74%	2520
	11th to 20th	Day	2 1 1 2 2 2 3 3 4 6% 76%	2520
	21st to end	Day	1 1 2 2 2 2 2 3 3 83%	2741
August	1st to 10th	Day	3 2 1 2 2 1 3 4 3 5% 76%	2507
	11th to 20th	Day	2 1 1 2 2 2 2 3 3 5% 77%	2337
	21st to end	Day	3 3 1 3 3 2 3 4 5% 6% 68%	2376
September	1st to 10th	Day	2 2 1 3 2 2 2 3 4 5% 74%	2160
	11th to 20th	Day	5% 3 2 4 4 3 4 5% 5% 7% 59%	2115
	21st to end	Day	7% 4 2 5% 5% 3 3 5% 5% 7% 54%	1980
October	1st to 10th	Day	8% 4 2 4 5% 3 4 4 6% 7% 53%	1832
	11th to 20th	Day	8% 5% 2 5% 5% 4 4 4 6% 9% 48%	1775
	21st to end	Day	13% 8% 3 5% 6% 3 5% 5% 5% 6% 40%	1782
November	1st to 10th	Day	14% 9% 3 8% 7% 4 5% 5% 6% 7% 33%	1674
	11th to 20th	Day	15% 13% 6% 9% 6% 3 5% 5% 5% 6% 26%	1578
	21st to end	Day	15% 11% 6% 12% 10% 5% 6% 5% 4 5% 21%	1520
December	1st to 10th	Day	12% 15% 8% 12% 9% 4 5% 5% 3 6% 20%	1520
	11th to 20th	Day	17% 18% 11% 12% 9% 4 5% 4 4 4 12%	1925
	21st to end	Day	16% 14% 5% 15% 11% 5% 6% 4 4 4 14%	2794
January	1st to 10th	Night	20% 16% 5% 9% 7% 3 5% 4 5% 7% 20%	2646
	11th to 20th	Night	16% 15% 6% 10% 7% 4 5% 4 5% 7% 21%	2562
	21st to end	Night	14% 14% 6% 10% 7% 4 5% 5% 6% 7% 23%	2772
February	1st to 10th	Night	14% 11% 4 6% 7% 3 6% 5% 5% 7% 32%	2408
	11th to 20th	Night	10% 10% 4 8% 6% 4 5% 5% 6% 7% 36%	2206
	21st to end	Night	10% 8% 4 7% 6% 4 5% 6% 6% 8% 35%	1776
March	1st to 10th	Night	13% 8% 4 6% 6% 3 5% 5% 5% 9% 36%	2160
	11th to 20th	Night	10% 7% 4 6% 5% 3 5% 6% 8% 8% 37%	2095
	21st to end	Night	10% 8% 4 7% 6% 4 7% 7% 7% 8% 33%	1990
April	1st to 10th	Night	12% 9% 4 7% 7% 3 5% 4 6% 8% 36%	1800
	11th to 20th	Night	8% 7% 3 5% 5% 3 4 4 6% 6% 48%	1779
	21st to end	Night	6% 7% 3 6% 5% 3 6% 6% 6% 8% 43%	1648
May	1st to 10th	Night	4 5% 2 5% 5% 3 5% 5% 6% 8% 53%	1441
	11th to 20th	Night	7% 5% 3 5% 4 4 5% 6% 7% 9% 44%	1416
	21st to end	Night	6% 4 2 5% 5% 4 6% 7% 8% 9% 45%	1552
June	1st to 10th	Night	10% 4 2 4 5% 3 5% 5% 7% 8% 50%	1440
	11th to 20th	Night	9% 6% 3 4 5% 2 3 4 4 6% 53%	1440
	21st to end	Night	4 3 2 4 4 2 5% 3 5% 6% 63%	1440
July	1st to 10th	Night	3 2 1 3 2 1 3 4 5% 6% 71%	1440
	11th to 20th	Night	3 1 1 2 3 1 2 3 3 5% 77%	1440
	21st to end	Night	1 1 1 1 1 2 3 3 4 81%	1576
August	1st to 10th	Night	3 3 1 1 3 1 2 2 3 6% 74%	1432
	11th to 20th	Night	2 2 2 2 2 3 2 4 5% 76%	1560
	21st to end	Night	2 2 1 3 3 2 2 3 5% 6% 70%	1980
September	1st to 10th	Night	3 2 1 2 2 2 2 2 4 5% 75%	1800
	11th to 20th	Night	4 3 2 3 3 2 4 4 4 7% 63%	1844
	21st to end	Night	6% 4 1 4 3 3 3 4 6% 8% 59%	1980
October	1st to 10th	Night	9% 5% 2 4 5% 2 4 4 5% 6% 54%	2124
	11th to 20th	Night	9% 5% 2 6% 5% 3 4 4 6% 6% 50%	2183
	21st to end	Night	10% 6% 2 5% 6% 4 4 4 4 7% 47%	2574
November	1st to 10th	Night	14% 8% 3 7% 7% 4 5% 5% 5% 7% 36%	2405
	11th to 20th	Night	16% 9% 4 7% 7% 3 6% 5% 6% 6% 32%	2598
	21st to end	Night	13% 10% 4 6% 7% 4 5% 6% 6% 7% 31%	2660
December	1st to 10th	Night	13% 12% 7% 9% 8% 4 5% 5% 5% 6% 25%	2660
	11th to 20th	Night	19% 16% 8% 12% 7% 4 4 5% 5% 5% 14%	3280
	21st to end	Night	15% 17% 4 10% 8% 4 6% 4 5% 5% 20%	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	71% 9% 11% 7% 2	1519
	11th to 20th	Day	70% 9% 11% 7% 2	1459
	21st to end	Day	70% 7% 12% 8% 3	1584
February	1st to 10th	Day	62% 9% 16% 10% 4	1552
	11th to 20th	Day	50% 9% 17% 17% 6%	1648
	21st to end	Day	47% 11% 16% 19% 7% 1	1480
March	1st to 10th	Day	46% 8% 17% 21% 8% 1	1800
	11th to 20th	Day	46% 7% 15% 23% 9%	1862
	21st to end	Day	47% 11% 18% 18% 7%	2365
April	1st to 10th	Day	40% 8% 16% 22% 12% 1	2160
	11th to 20th	Day	35% 7% 15% 25% 15% 4	2132
	21st to end	Day	32% 6% 14% 27% 18% 3	2312
May	1st to 10th	Day	25% 8% 12% 30% 21% 3	2515
	11th to 20th	Day	35% 7% 13% 25% 16% 3	2480
	21st to end	Day	35% 7% 13% 27% 15% 3	2724
June	1st to 10th	Day	34% 6% 10% 26% 19% 4	2520
	11th to 20th	Day	28% 5% 12% 29% 22% 4	2520
	21st to end	Day	19% 5% 9% 29% 28% 11%	2520
July	1st to 10th	Day	13% 3 7% 21% 35% 21%	2451
	11th to 20th	Day	12% 3 6% 14% 35% 29%	2445
	21st to end	Day	8% 2 4 15% 41% 30%	2589
August	1st to 10th	Day	13% 3 8% 19% 37% 21%	2490
	11th to 20th	Day	11% 3 7% 24% 38% 18%	2337
	21st to end	Day	17% 4 7% 28% 34% 11%	2376
September	1st to 10th	Day	12% 4 9% 29% 31% 15%	2160
	11th to 20th	Day	24% 6% 11% 23% 28% 8%	2115
	21st to end	Day	28% 6% 15% 30% 17% 4	1980
October	1st to 10th	Day	30% 6% 14% 30% 17% 2	1832
	11th to 20th	Day	32% 7% 20% 29% 10% 2	1775
	21st to end	Day	44% 8% 18% 22% 8% 1	1782
November	1st to 10th	Day	51% 9% 15% 18% 7% 1	1674
	11th to 20th	Day	58% 8% 15% 13% 4 1	1578
	21st to end	Day	65% 9% 12% 10% 4	1520
December	1st to 10th	Day	65% 8% 12% 11% 4	1520
	11th to 20th	Day	76% 9% 9% 5% 1	1928
	21st to end	Day	72% 9% 8% 8% 2	2794
January	1st to 10th	Night	65% 10% 13% 9% 3	2646
	11th to 20th	Night	61% 10% 15% 12% 3	2562
	21st to end	Night	59% 9% 16% 12% 2 1	2772
February	1st to 10th	Night	52% 9% 19% 15% 5%	2408
	11th to 20th	Night	46% 10% 16% 21% 7%	2208
	21st to end	Night	46% 9% 15% 20% 8% 2	1776
March	1st to 10th	Night	45% 8% 13% 23% 9% 1	2160
	11th to 20th	Night	41% 8% 18% 23% 10%	2096
	21st to end	Night	46% 9% 16% 20% 8%	1990
April	1st to 10th	Night	44% 7% 13% 23% 11% 1	1800
	11th to 20th	Night	35% 6% 11% 25% 18% 5%	1779
	21st to end	Night	36% 7% 14% 21% 16% 5%	1648
May	1st to 10th	Night	27% 6% 12% 28% 22% 5%	1441
	11th to 20th	Night	33% 7% 12% 22% 21% 5%	1416
	21st to end	Night	32% 9% 13% 25% 17% 3	1552
June	1st to 10th	Night	32% 5% 13% 25% 20% 5%	1440
	11th to 20th	Night	32% 5% 9% 26% 24% 4	1440
	21st to end	Night	21% 5% 8% 24% 29% 14%	1440
July	1st to 10th	Night	13% 4 7% 20% 29% 27%	1400
	11th to 20th	Night	11% 2 7% 17% 29% 34%	1392
	21st to end	Night	8% 1 4 12% 34% 41%	1488
August	1st to 10th	Night	14% 3 4 14% 36% 29%	1424
	11th to 20th	Night	13% 3 5% 19% 33% 27%	1560
	21st to end	Night	14% 3 8% 21% 35% 18%	1980
September	1st to 10th	Night	14% 3 8% 23% 30% 21%	1800
	11th to 20th	Night	21% 5% 10% 22% 27% 14%	1844
	21st to end	Night	24% 5% 12% 28% 23% 9%	1980
October	1st to 10th	Night	30% 6% 11% 26% 26% 2	2124
	11th to 20th	Night	33% 6% 11% 28% 18% 3	2183
	21st to end	Night	37% 7% 14% 26% 15% 2	2574
November	1st to 10th	Night	46% 8% 15% 22% 9%	2405
	11th to 20th	Night	51% 9% 16% 17% 5% 1	2598
	21st to end	Night	51% 9% 18% 16% 6% 1	2660
December	1st to 10th	Night	59% 9% 15% 14% 3	2660
	11th to 20th	Night	72% 9% 11% 6% 1	3276
	21st to end	Night	62% 12% 11% 10% 5%	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	26% 10% 19% 23% 19% 4	180
	11th to 20th	Day	28% 10% 16% 28% 13% 5%	165
	21st to end	Day	23% 7% 20% 23% 22% 5%	176
February	1st to 10th	Day	23% 10% 22% 26% 13% 7%	272
	11th to 20th	Day	19% 9% 20% 29% 17% 6%	364
	21st to end	Day	14% 14% 23% 27% 18% 4	346
March	1st to 10th	Day	18% 12% 26% 21% 18% 6%	420
	11th to 20th	Day	15% 10% 18% 27% 21% 10%	420
	21st to end	Day	14% 11% 26% 29% 18% 3	462
April	1st to 10th	Day	13% 14% 23% 27% 14% 9%	420
	11th to 20th	Day	11% 13% 31% 22% 15% 8%	412
	21st to end	Day	8% 9% 28% 27% 20% 8%	420
May	1st to 10th	Day	7% 9% 19% 31% 24% 9%	423
	11th to 20th	Day	11% 6% 20% 24% 24% 15%	448
	21st to end	Day	10% 6% 15% 26% 26% 16%	485
June	1st to 10th	Day	8% 8% 18% 23% 25% 18%	450
	11th to 20th	Day	7% 12% 20% 33% 18% 10%	450
	21st to end	Day	3 4 17% 25% 31% 20%	450
July	1st to 10th	Day	3 2 10% 28% 42% 14%	446
	11th to 20th	Day	2 2 12% 32% 36% 16%	444
	21st to end	Day	1 2 10% 24% 34% 30%	487
August	1st to 10th	Day	3 3 8% 24% 35% 28%	447
	11th to 20th	Day	2 2 8% 21% 33% 34%	437
	21st to end	Day	5% 4 16% 25% 26% 24%	495
September	1st to 10th	Day	4 2 12% 29% 33% 21%	450
	11th to 20th	Day	6% 4 15% 26% 26% 23%	450
	21st to end	Day	8% 7% 16% 29% 27% 14%	450
October	1st to 10th	Day	10% 4 22% 23% 21% 19%	450
	11th to 20th	Day	12% 7% 15% 25% 26% 16%	425
	21st to end	Day	18% 8% 22% 27% 15% 9%	297
November	1st to 10th	Day	19% 9% 24% 26% 19% 3	270
	11th to 20th	Day	22% 10% 19% 21% 18% 9%	207
	21st to end	Day	11% 8% 20% 26% 26% 8%	180
December	1st to 10th	Day	17% 7% 18% 28% 17% 12%	180
	11th to 20th	Day	21% 9% 23% 28% 14% 4	180
	21st to end	Day	24% 6% 22% 27% 18% 4	198
January	1st to 10th	Night	28% 8% 19% 28% 16% 2	760
	11th to 20th	Night	22% 6% 19% 32% 18% 2	732
	21st to end	Night	19% 5% 17% 36% 21% 3	792
February	1st to 10th	Night	21% 6% 23% 33% 15% 2	720
	11th to 20th	Night	14% 7% 24% 33% 20% 2	704
	21st to end	Night	14% 12% 22% 35% 15% 2	592
March	1st to 10th	Night	15% 6% 25% 36% 16% 3	720
	11th to 20th	Night	13% 8% 20% 35% 21% 2	720
	21st to end	Night	14% 8% 27% 36% 15% 1	792
April	1st to 10th	Night	16% 6% 23% 34% 19% 2	720
	11th to 20th	Night	10% 9% 29% 30% 18% 4	711
	21st to end	Night	8% 9% 28% 34% 20% 2	568
May	1st to 10th	Night	6% 8% 25% 36% 21% 3	361
	11th to 20th	Night	9% 5% 18% 33% 30% 5%	354
	21st to end	Night	7% 3 19% 42% 25% 4	389
June	1st to 10th	Night	10% 3 26% 37% 22% 3	360
	11th to 20th	Night	9% 8% 30% 33% 18% 2	360
	21st to end	Night	4 5% 24% 40% 26% 2	360
July	1st to 10th	Night	4 3 16% 47% 28% 2	350
	11th to 20th	Night	3 3 18% 47% 26% 2	348
	21st to end	Night	1 2 14% 46% 34% 3	394
August	1st to 10th	Night	6% 1 12% 37% 39% 4	358
	11th to 20th	Night	3 1 10% 36% 39% 11%	492
	21st to end	Night	3 2 16% 40% 33% 5%	792
September	1st to 10th	Night	3 2 14% 44% 31% 5%	720
	11th to 20th	Night	5% 2 14% 34% 37% 8%	720
	21st to end	Night	8% 3 18% 35% 30% 6%	720
October	1st to 10th	Night	11% 5% 17% 36% 28% 3	720
	11th to 20th	Night	12% 6% 17% 35% 25% 5%	720
	21st to end	Night	12% 7% 23% 34% 19% 5%	792
November	1st to 10th	Night	18% 6% 18% 41% 16% 1	740
	11th to 20th	Night	20% 8% 21% 30% 17% 4	760
	21st to end	Night	18% 5% 18% 37% 20% 3	760
December	1st to 10th	Night	17% 5% 17% 38% 20% 3	760
	11th to 20th	Night	23% 6% 18% 34% 17% 1	760
	21st to end	Night	25% 6% 21% 33% 14% 1	836

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