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 2024-11-12.

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% 2 6% 4 4 4 3 5% 6% 50%	105366
	Night	9% 8% 3 7% 4 4 4 3 5% 6% 45%	102429
Transparency	Day	33% 6% 11% 21% 18% 10%	105135
	Night	38% 7% 12% 20% 15% 8%	102306
Seeing	Day	10% 7% 18% 26% 24% 14%	14388
	Night	13% 6% 20% 36% 22% 3	23445

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	15% 19% 6% 12% 7% 6% 5% 4 5% 5% 17%	2539
	11th to 20th	Day	21% 19% 6% 11% 5% 4 3 3 5% 5% 18%	2516
	21st to end	Day	25% 20% 7% 14% 6% 4 4 2 3 4 11%	2794
February	1st to 10th	Day	15% 13% 4 11% 9% 6% 5% 3 5% 5% 24%	1638
	11th to 20th	Day	12% 12% 4 9% 5% 5% 5% 4 5% 6% 33%	1732
	21st to end	Day	10% 10% 3 9% 5% 5% 7% 4 7% 8% 31%	1570
March	1st to 10th	Day	8% 8% 2 7% 5% 5% 5% 5% 7% 10% 36%	3138
	11th to 20th	Day	7% 6% 2 6% 4 4 4 3 4 7% 54%	3294
	21st to end	Day	10% 8% 3 9% 6% 6% 6% 6% 7% 8% 31%	4154
April	1st to 10th	Day	8% 9% 2 7% 6% 5% 5% 4 7% 8% 38%	2280
	11th to 20th	Day	6% 8% 2 6% 5% 5% 5% 4 6% 8% 46%	2252
	21st to end	Day	6% 6% 2 6% 5% 4 4 5% 6% 9% 48%	2441
May	1st to 10th	Day	8% 5% 1 4 3 3 4 4 5% 7% 55%	4415
	11th to 20th	Day	4 4 1 5% 4 3 3 3 5% 7% 62%	4377
	21st to end	Day	6% 6% 3 6% 5% 5% 5% 4 7% 7% 45%	4813
June	1st to 10th	Day	9% 6% 2 6% 5% 4 4 3 6% 8% 47%	2660
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 6% 9% 52%	2660
	21st to end	Day	3 4 1 4 3 3 4 3 4 6% 66%	2660
July	1st to 10th	Day	1 1 1 2 1 2 2 2 3 3 83%	4420
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 82%	4420
	21st to end	Day	1 1 2 2 2 2 2 3 4 80%	4790
August	1st to 10th	Day	3 2 1 2 2 2 2 2 3 5% 74%	4401
	11th to 20th	Day	1 1 1 2 2 2 3 3 4 6% 74%	4075
	21st to end	Day	3 4 1 4 3 2 3 2 4 5% 68%	4180
September	1st to 10th	Day	2 2 1 3 2 2 3 3 4 6% 73%	2280
	11th to 20th	Day	5% 4 1 5% 3 3 5% 4 5% 6% 58%	2232
	21st to end	Day	7% 4 2 6% 3 4 3 4 5% 7% 56%	2090
October	1st to 10th	Day	5% 3 1 3 3 3 3 3 6% 7% 62%	3225
	11th to 20th	Day	5% 4 2 6% 4 5% 5% 5% 7% 10% 48%	3109
	21st to end	Day	11% 6% 3 7% 5% 4 5% 4 6% 7% 41%	3101
November	1st to 10th	Day	13% 10% 3 9% 6% 5% 5% 4 6% 7% 33%	1764
	11th to 20th	Day	15% 14% 5% 10% 6% 5% 5% 3 5% 5% 26%	1587
	21st to end	Day	14% 12% 5% 13% 8% 7% 6% 4 4 5% 21%	1520
December	1st to 10th	Day	11% 17% 8% 13% 8% 5% 5% 4 3 6% 20%	1520
	11th to 20th	Day	17% 20% 9% 14% 7% 5% 4 3 4 4 12%	1925
	21st to end	Day	16% 15% 5% 17% 10% 7% 6% 3 4 4 14%	2794
January	1st to 10th	Night	19% 18% 5% 10% 6% 5% 5% 3 5% 6% 18%	4406
	11th to 20th	Night	19% 16% 5% 8% 4 4 4 4 6% 7% 23%	4382
	21st to end	Night	19% 17% 8% 15% 6% 5% 4 3 5% 5% 14%	4862
February	1st to 10th	Night	14% 13% 3 8% 6% 4 5% 4 5% 6% 31%	2542
	11th to 20th	Night	10% 10% 4 9% 5% 5% 4 4 6% 7% 36%	2333
	21st to end	Night	10% 9% 4 8% 6% 6% 5% 4 7% 7% 35%	1884
March	1st to 10th	Night	8% 8% 3 6% 5% 4 5% 5% 8% 10% 38%	3736
	11th to 20th	Night	7% 6% 2 5% 3 3 4 3 6% 6% 56%	3683
	21st to end	Night	8% 7% 3 8% 7% 7% 7% 6% 8% 8% 30%	3498
April	1st to 10th	Night	11% 10% 3 8% 6% 4 5% 3 7% 8% 35%	1900
	11th to 20th	Night	8% 7% 3 5% 4 3 4 3 6% 6% 49%	1879
	21st to end	Night	6% 8% 2 6% 4 5% 6% 5% 6% 8% 44%	1739
May	1st to 10th	Night	6% 6% 2 5% 5% 4 5% 4 5% 7% 52%	2541
	11th to 20th	Night	4 3 2 4 3 3 4 3 5% 7% 61%	2516
	21st to end	Night	5% 4 2 6% 4 5% 5% 5% 6% 7% 52%	2762
June	1st to 10th	Night	10% 4 1 4 4 4 4 4 7% 7% 49%	1520
	11th to 20th	Night	9% 6% 3 5% 4 3 3 3 4 7% 54%	1520
	21st to end	Night	3 3 2 4 3 4 5% 3 6% 5% 63%	1520
July	1st to 10th	Night	1 1 2 1 1 2 2 3 3 83%	2540
	11th to 20th	Night	2 1 1 1 1 1 2 3 4 83%	2540
	21st to end	Night	1 1 1 1 1 1 2 2 2 4 82%	2762
August	1st to 10th	Night	4 3 1 3 2 2 2 2 4 5% 73%	2529
	11th to 20th	Night	2 2 1 3 2 3 3 2 4 5% 73%	2759
	21st to end	Night	2 2 1 3 2 3 2 3 4 5% 71%	3498
September	1st to 10th	Night	2 2 1 3 1 2 2 2 4 5% 75%	1900
	11th to 20th	Night	4 3 2 4 3 3 4 3 5% 7% 61%	1947
	21st to end	Night	6% 4 1 4 2 4 3 3 6% 8% 60%	2090
October	1st to 10th	Night	5% 3 1 3 3 3 3 3 5% 6% 65%	3751
	11th to 20th	Night	7% 4 1 5% 4 3 4 4 7% 8% 52%	3825
	21st to end	Night	10% 5% 2 6% 5% 4 5% 3 5% 8% 47%	4457
November	1st to 10th	Night	13% 9% 3 8% 5% 5% 5% 4 5% 6% 37%	2535
	11th to 20th	Night	16% 10% 4 8% 6% 5% 5% 4 6% 6% 31%	2611
	21st to end	Night	13% 11% 3 7% 6% 6% 5% 5% 6% 7% 31%	2660
December	1st to 10th	Night	13% 15% 5% 10% 7% 5% 4 4 5% 6% 25%	2660
	11th to 20th	Night	19% 17% 7% 13% 6% 5% 4 4 5% 5% 14%	3280
	21st to end	Night	15% 18% 4 11% 7% 6% 5% 3 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	67% 10% 11% 9% 3	2539
	11th to 20th	Day	67% 10% 13% 8% 2	2540
	21st to end	Day	79% 7% 8% 4 1	2794
February	1st to 10th	Day	61% 9% 16% 10% 4	1638
	11th to 20th	Day	50% 9% 17% 17% 6%	1741
	21st to end	Day	47% 11% 16% 19% 7% 1	1570
March	1st to 10th	Day	36% 9% 16% 25% 14% 1	3138
	11th to 20th	Day	29% 6% 16% 38% 11%	3294
	21st to end	Day	43% 14% 17% 16% 9% 1	4154
April	1st to 10th	Day	40% 8% 16% 22% 12% 1	2280
	11th to 20th	Day	34% 7% 15% 24% 15% 5%	2252
	21st to end	Day	32% 6% 15% 26% 18% 3	2441
May	1st to 10th	Day	24% 7% 10% 29% 24% 5%	4415
	11th to 20th	Day	21% 5% 9% 29% 28% 9%	4380
	21st to end	Day	32% 10% 17% 28% 12% 2	4814
June	1st to 10th	Day	34% 6% 10% 25% 20% 5%	2660
	11th to 20th	Day	28% 5% 12% 28% 23% 5%	2660
	21st to end	Day	19% 5% 9% 29% 28% 11%	2660
July	1st to 10th	Day	9% 2 4 13% 27% 46%	4351
	11th to 20th	Day	9% 2 4 8% 24% 52%	4345
	21st to end	Day	10% 2 4 17% 35% 32%	4639
August	1st to 10th	Day	14% 2 5% 12% 38% 28%	4384
	11th to 20th	Day	12% 2 6% 35% 33% 11%	4117
	21st to end	Day	20% 3 7% 28% 33% 10%	4179
September	1st to 10th	Day	12% 4 9% 28% 31% 16%	2280
	11th to 20th	Day	25% 6% 12% 24% 26% 7%	2232
	21st to end	Day	27% 6% 14% 31% 17% 4	2090
October	1st to 10th	Day	22% 4 12% 36% 24% 3	3225
	11th to 20th	Day	30% 6% 22% 27% 13% 1	3109
	21st to end	Day	41% 6% 13% 28% 11% 1	3101
November	1st to 10th	Day	50% 9% 15% 18% 7% 1	1764
	11th to 20th	Day	59% 8% 15% 13% 4 1	1587
	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% 12% 12% 9% 2	4406
	11th to 20th	Night	58% 10% 17% 13% 2	4420
	21st to end	Night	70% 11% 11% 7% 1	4862
February	1st to 10th	Night	53% 9% 18% 15% 4	2542
	11th to 20th	Night	45% 10% 16% 21% 7%	2335
	21st to end	Night	46% 9% 16% 20% 7% 2	1884
March	1st to 10th	Night	35% 9% 14% 28% 13% 1	3736
	11th to 20th	Night	27% 5% 14% 36% 17% 1	3684
	21st to end	Night	42% 14% 17% 20% 6%	3498
April	1st to 10th	Night	44% 7% 14% 23% 11% 1	1900
	11th to 20th	Night	34% 6% 11% 25% 18% 5%	1879
	21st to end	Night	35% 8% 15% 22% 16% 5%	1739
May	1st to 10th	Night	28% 7% 10% 25% 26% 5%	2541
	11th to 20th	Night	21% 5% 10% 31% 28% 5%	2516
	21st to end	Night	27% 10% 19% 32% 11% 2	2762
June	1st to 10th	Night	32% 6% 12% 25% 20% 6%	1520
	11th to 20th	Night	31% 5% 8% 25% 25% 5%	1520
	21st to end	Night	21% 5% 7% 24% 29% 14%	1520
July	1st to 10th	Night	8% 2 4 14% 22% 50%	2500
	11th to 20th	Night	7% 2 4 10% 20% 58%	2492
	21st to end	Night	9% 1 3 13% 30% 44%	2674
August	1st to 10th	Night	16% 3 3 8% 31% 39%	2521
	11th to 20th	Night	14% 3 5% 28% 33% 16%	2783
	21st to end	Night	15% 3 7% 26% 28% 20%	3498
September	1st to 10th	Night	14% 3 8% 23% 30% 22%	1900
	11th to 20th	Night	22% 5% 10% 23% 26% 14%	1947
	21st to end	Night	23% 4 11% 29% 23% 9%	2090
October	1st to 10th	Night	21% 4 9% 31% 33% 2	3751
	11th to 20th	Night	28% 6% 15% 27% 22% 2	3825
	21st to end	Night	36% 6% 11% 31% 15% 2	4457
November	1st to 10th	Night	46% 7% 15% 22% 9%	2535
	11th to 20th	Night	52% 9% 16% 17% 5% 1	2611
	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% 18% 23% 19% 4	180
	11th to 20th	Day	27% 9% 17% 27% 14% 5%	180
	21st to end	Day	23% 8% 19% 24% 22% 5%	198
February	1st to 10th	Day	22% 9% 22% 26% 13% 7%	298
	11th to 20th	Day	19% 9% 20% 29% 17% 6%	397
	21st to end	Day	14% 15% 21% 27% 18% 4	382
March	1st to 10th	Day	17% 12% 26% 22% 18% 6%	460
	11th to 20th	Day	14% 9% 18% 27% 21% 12%	460
	21st to end	Day	13% 11% 26% 29% 17% 3	506
April	1st to 10th	Day	13% 14% 23% 27% 14% 9%	460
	11th to 20th	Day	10% 13% 30% 23% 15% 8%	452
	21st to end	Day	7% 9% 28% 27% 21% 8%	460
May	1st to 10th	Day	7% 9% 20% 31% 23% 10%	463
	11th to 20th	Day	10% 7% 19% 24% 24% 15%	488
	21st to end	Day	9% 6% 16% 27% 26% 16%	529
June	1st to 10th	Day	10% 8% 17% 23% 26% 17%	490
	11th to 20th	Day	7% 12% 21% 33% 18% 9%	490
	21st to end	Day	3 4 18% 24% 31% 20%	490
July	1st to 10th	Day	3 2 11% 28% 41% 15%	486
	11th to 20th	Day	1 2 12% 32% 37% 16%	484
	21st to end	Day	1 2 10% 25% 35% 28%	531
August	1st to 10th	Day	3 3 8% 23% 35% 28%	487
	11th to 20th	Day	2 2 8% 22% 34% 32%	477
	21st to end	Day	5% 5% 17% 24% 25% 24%	539
September	1st to 10th	Day	3 2 11% 28% 32% 23%	490
	11th to 20th	Day	6% 3 15% 28% 26% 22%	490
	21st to end	Day	8% 7% 16% 29% 27% 14%	490
October	1st to 10th	Day	9% 4 22% 23% 22% 19%	490
	11th to 20th	Day	11% 6% 16% 25% 26% 16%	463
	21st to end	Day	17% 8% 21% 30% 15% 8%	330
November	1st to 10th	Day	19% 8% 25% 24% 20% 4	300
	11th to 20th	Day	23% 10% 19% 21% 18% 9%	210
	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% 33% 18% 2	760
	21st to end	Night	19% 5% 17% 36% 21% 3	836
February	1st to 10th	Night	20% 6% 23% 34% 15% 2	760
	11th to 20th	Night	14% 7% 24% 33% 19% 2	744
	21st to end	Night	14% 12% 22% 35% 15% 2	628
March	1st to 10th	Night	15% 6% 25% 35% 16% 2	760
	11th to 20th	Night	13% 8% 20% 36% 21% 3	760
	21st to end	Night	13% 8% 26% 36% 15% 1	836
April	1st to 10th	Night	16% 6% 23% 34% 19% 2	760
	11th to 20th	Night	10% 9% 29% 31% 18% 3	751
	21st to end	Night	8% 9% 28% 35% 19% 2	599
May	1st to 10th	Night	6% 8% 25% 36% 21% 3	381
	11th to 20th	Night	9% 6% 18% 34% 29% 5%	374
	21st to end	Night	7% 3 19% 42% 25% 4	411
June	1st to 10th	Night	9% 3 26% 36% 23% 3	380
	11th to 20th	Night	9% 8% 30% 34% 18% 2	380
	21st to end	Night	4 5% 24% 40% 25% 2	380
July	1st to 10th	Night	4 4 16% 47% 28% 2	370
	11th to 20th	Night	3 3 18% 48% 26% 2	368
	21st to end	Night	1 2 13% 47% 33% 3	416
August	1st to 10th	Night	5% 1 12% 38% 39% 4	378
	11th to 20th	Night	4 2 11% 37% 37% 10%	521
	21st to end	Night	3 2 16% 40% 33% 5%	836
September	1st to 10th	Night	4 2 13% 43% 32% 6%	760
	11th to 20th	Night	5% 1 15% 35% 36% 7%	760
	21st to end	Night	7% 3 19% 35% 30% 6%	760
October	1st to 10th	Night	10% 4 17% 37% 28% 3	760
	11th to 20th	Night	11% 6% 17% 35% 26% 5%	760
	21st to end	Night	12% 6% 22% 36% 19% 5%	836
November	1st to 10th	Night	18% 6% 19% 41% 16% 1	780
	11th to 20th	Night	20% 8% 21% 30% 17% 4	764
	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

Page generated at 2024-11-08 19:45:37. Version ac07

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