Prineville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prineville clear sky chart from 2005-11-06 to 2025-05-26.

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% 8% 3 6% 4 4 4 3 5% 6% 49%	118122
	Night	10% 9% 3 6% 4 4 4 3 5% 6% 45%	119975
Transparency	Day	37% 3 9% 22% 18% 10%	117865
	Night	40% 3 11% 23% 16% 6%	119821
Seeing	Day	14% 10% 25% 27% 18% 7%	15261
	Night	14% 6% 17% 39% 21% 3	24431

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% 4 10% 6% 6% 5% 4 6% 6% 19%	3639
	11th to 20th	Day	15% 13% 3 7% 4 4 4 3 4 4 39%	3640
	21st to end	Day	12% 10% 3 8% 4 4 4 3 6% 6% 41%	4250
February	1st to 10th	Day	12% 14% 4 9% 6% 5% 4 5% 6% 8% 29%	1800
	11th to 20th	Day	11% 14% 3 10% 5% 4 4 4 6% 7% 31%	1781
	21st to end	Day	10% 15% 4 9% 5% 5% 5% 5% 7% 7% 27%	1650
March	1st to 10th	Day	9% 13% 5% 9% 5% 5% 5% 4 5% 9% 31%	4518
	11th to 20th	Day	9% 16% 4 8% 5% 5% 4 3 4 6% 36%	4990
	21st to end	Day	10% 14% 4 10% 6% 6% 6% 4 6% 7% 27%	5781
April	1st to 10th	Day	11% 16% 4 9% 6% 4 5% 4 5% 6% 29%	2400
	11th to 20th	Day	9% 13% 4 7% 6% 4 4 3 5% 7% 38%	2369
	21st to end	Day	8% 10% 3 7% 5% 4 4 4 6% 7% 42%	2460
May	1st to 10th	Day	12% 9% 3 6% 4 4 4 4 5% 6% 45%	4560
	11th to 20th	Day	7% 5% 2 5% 3 3 3 3 4 5% 61%	4517
	21st to end	Day	8% 8% 2 5% 5% 4 5% 4 6% 7% 46%	4886
June	1st to 10th	Day	12% 8% 2 6% 5% 4 5% 4 5% 6% 42%	2660
	11th to 20th	Day	8% 6% 2 5% 4 4 4 3 5% 7% 52%	2660
	21st to end	Day	4 4 1 3 3 3 3 3 5% 5% 67%	2660
July	1st to 10th	Day	1 1 1 1 1 2 1 2 3 85%	4420
	11th to 20th	Day	2 1 2 2 1 2 2 3 3 82%	4420
	21st to end	Day	2 1 1 2 1 2 2 3 3 4 80%	4790
August	1st to 10th	Day	3 3 1 3 2 2 3 3 4 5% 70%	4256
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 6% 73%	3969
	21st to end	Day	3 3 1 3 2 2 3 2 3 5% 73%	4180
September	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 76%	2280
	11th to 20th	Day	5% 4 1 5% 3 4 3 3 5% 7% 60%	2280
	21st to end	Day	8% 5% 2 4 3 3 3 3 5% 6% 59%	2045
October	1st to 10th	Day	6% 5% 1 4 3 2 3 3 3 7% 64%	3180
	11th to 20th	Day	7% 5% 1 5% 4 4 5% 4 7% 8% 48%	3161
	21st to end	Day	12% 9% 3 8% 5% 5% 5% 5% 5% 6% 37%	3259
November	1st to 10th	Day	14% 11% 4 9% 6% 4 5% 4 5% 7% 32%	1764
	11th to 20th	Day	16% 10% 2 8% 7% 6% 6% 5% 7% 7% 27%	1645
	21st to end	Day	12% 12% 2 8% 4 4 4 4 6% 8% 34%	1600
December	1st to 10th	Day	9% 8% 3 5% 3 2 4 3 5% 8% 51%	2620
	11th to 20th	Day	15% 13% 4 9% 7% 6% 5% 5% 6% 7% 22%	3028
	21st to end	Day	13% 14% 5% 11% 7% 6% 6% 4 5% 7% 22%	4004
January	1st to 10th	Night	16% 15% 5% 11% 6% 6% 5% 4 6% 7% 19%	6306
	11th to 20th	Night	14% 13% 3 6% 4 4 4 3 4 4 40%	6320
	21st to end	Night	11% 11% 3 8% 4 5% 4 4 5% 6% 39%	6715
February	1st to 10th	Night	12% 13% 4 10% 6% 5% 5% 4 6% 7% 28%	2600
	11th to 20th	Night	10% 14% 4 8% 4 4 5% 3 5% 7% 34%	2505
	21st to end	Night	10% 16% 4 8% 6% 6% 5% 4 5% 7% 28%	1980
March	1st to 10th	Night	7% 12% 4 7% 5% 5% 5% 5% 7% 8% 35%	5376
	11th to 20th	Night	9% 11% 3 8% 5% 4 5% 3 6% 6% 40%	5008
	21st to end	Night	9% 14% 4 9% 7% 6% 6% 5% 6% 7% 26%	5193
April	1st to 10th	Night	11% 14% 3 8% 5% 4 4 4 6% 7% 33%	2000
	11th to 20th	Night	10% 12% 3 7% 4 5% 4 3 5% 7% 39%	1979
	21st to end	Night	9% 11% 2 7% 4 4 4 4 7% 8% 40%	1938
May	1st to 10th	Night	9% 10% 2 7% 4 4 4 3 5% 7% 43%	2620
	11th to 20th	Night	7% 5% 2 4 3 3 4 2 4 6% 61%	2596
	21st to end	Night	10% 7% 2 5% 4 3 3 3 5% 7% 51%	2805
June	1st to 10th	Night	13% 6% 2 4 4 4 5% 3 5% 6% 47%	1520
	11th to 20th	Night	8% 5% 2 6% 4 3 3 3 5% 8% 56%	1520
	21st to end	Night	5% 4 1 3 3 2 3 3 4 5% 68%	1520
July	1st to 10th	Night	1 1 1 1 2 2 2 3 85%	2540
	11th to 20th	Night	2 1 1 2 2 1 2 2 3 3 81%	2540
	21st to end	Night	2 2 1 2 1 1 1 2 3 4 82%	2761
August	1st to 10th	Night	2 2 1 4 3 3 3 2 4 5% 70%	2676
	11th to 20th	Night	1 1 1 3 2 2 3 2 4 5% 76%	2870
	21st to end	Night	1 2 1 3 2 2 2 2 4 4 76%	3498
September	1st to 10th	Night	3 1 1 2 2 1 2 2 3 5% 78%	1900
	11th to 20th	Night	5% 4 2 4 3 3 4 3 4 6% 62%	1900
	21st to end	Night	7% 5% 2 4 3 3 4 3 4 6% 60%	2133
October	1st to 10th	Night	6% 4 1 4 2 2 2 2 3 4 69%	3800
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 5% 8% 52%	3777
	21st to end	Night	9% 9% 2 7% 5% 5% 5% 4 6% 7% 40%	4303
November	1st to 10th	Night	15% 11% 3 8% 5% 5% 5% 4 5% 6% 34%	2535
	11th to 20th	Night	17% 11% 3 7% 6% 5% 6% 4 5% 6% 29%	2753
	21st to end	Night	12% 11% 3 7% 4 4 5% 4 6% 7% 38%	2800
December	1st to 10th	Night	7% 7% 2 5% 4 3 3 3 5% 7% 54%	4560
	11th to 20th	Night	15% 15% 4 11% 7% 5% 6% 5% 6% 7% 20%	5176
	21st to end	Night	16% 13% 4 9% 6% 5% 4 4 5% 6% 27%	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	65% 4 11% 16% 4	3639
	11th to 20th	Day	50% 2 11% 23% 12% 2	3640
	21st to end	Day	45% 3 10% 17% 20% 6%	4250
February	1st to 10th	Day	52% 7% 14% 19% 7%	1800
	11th to 20th	Day	51% 6% 13% 18% 9% 2	1790
	21st to end	Day	54% 7% 14% 15% 8% 2	1650
March	1st to 10th	Day	49% 4 7% 25% 12% 3	4518
	11th to 20th	Day	50% 3 8% 25% 14%	4990
	21st to end	Day	56% 4 12% 20% 7%	5781
April	1st to 10th	Day	54% 6% 11% 19% 10% 1	2400
	11th to 20th	Day	47% 4 11% 20% 14% 3	2372
	21st to end	Day	40% 5% 12% 27% 13% 3	2460
May	1st to 10th	Day	39% 5% 8% 28% 18% 1	4560
	11th to 20th	Day	26% 4 7% 29% 29% 5%	4520
	21st to end	Day	36% 5% 17% 28% 13% 1	4887
June	1st to 10th	Day	42% 4 10% 29% 14% 2	2660
	11th to 20th	Day	32% 4 9% 30% 21% 4	2660
	21st to end	Day	21% 2 9% 28% 30% 11%	2660
July	1st to 10th	Day	8% 2 4 13% 22% 52%	4351
	11th to 20th	Day	10% 1 3 9% 21% 55%	4345
	21st to end	Day	11% 1 2 16% 38% 32%	4639
August	1st to 10th	Day	19% 2 3 14% 37% 26%	4240
	11th to 20th	Day	15% 1 4 29% 34% 17%	4008
	21st to end	Day	16% 2 5% 28% 28% 20%	4179
September	1st to 10th	Day	12% 2 4 26% 33% 23%	2280
	11th to 20th	Day	25% 3 8% 25% 25% 13%	2280
	21st to end	Day	28% 3 9% 26% 23% 10%	2045
October	1st to 10th	Day	25% 3 9% 21% 26% 17%	3180
	11th to 20th	Day	33% 2 17% 25% 19% 3	3161
	21st to end	Day	48% 3 7% 24% 16% 2	3259
November	1st to 10th	Day	51% 3 12% 23% 10% 1	1764
	11th to 20th	Day	53% 6% 16% 17% 8%	1645
	21st to end	Day	48% 5% 14% 18% 14% 1	1600
December	1st to 10th	Day	34% 4 11% 28% 21% 1	2620
	11th to 20th	Day	60% 3 17% 16% 3	3028
	21st to end	Day	61% 3 13% 18% 4	4004
January	1st to 10th	Night	67% 4 12% 13% 4	6306
	11th to 20th	Night	49% 3 9% 26% 12% 2	6320
	21st to end	Night	47% 2 12% 16% 17% 6%	6715
February	1st to 10th	Night	55% 6% 15% 15% 9%	2600
	11th to 20th	Night	48% 6% 14% 20% 9% 2	2507
	21st to end	Night	54% 6% 10% 20% 8% 1	1980
March	1st to 10th	Night	44% 4 9% 28% 11% 3	5376
	11th to 20th	Night	45% 3 11% 31% 11%	5008
	21st to end	Night	56% 6% 13% 19% 5%	5193
April	1st to 10th	Night	49% 5% 16% 20% 8% 1	2000
	11th to 20th	Night	45% 5% 13% 22% 13% 1	1979
	21st to end	Night	41% 6% 14% 26% 11% 2	1938
May	1st to 10th	Night	41% 6% 10% 30% 13%	2620
	11th to 20th	Night	25% 4 10% 38% 22% 1	2596
	21st to end	Night	35% 4 27% 27% 6%	2805
June	1st to 10th	Night	38% 5% 13% 30% 13% 1	1520
	11th to 20th	Night	29% 4 14% 35% 15% 3	1520
	21st to end	Night	20% 3 11% 33% 26% 8%	1520
July	1st to 10th	Night	7% 2 7% 15% 26% 45%	2500
	11th to 20th	Night	12% 1 4 13% 22% 48%	2492
	21st to end	Night	10% 1 3 18% 36% 32%	2674
August	1st to 10th	Night	19% 2 3 18% 36% 23%	2668
	11th to 20th	Night	13% 1 5% 40% 30% 10%	2897
	21st to end	Night	14% 1 9% 30% 29% 17%	3498
September	1st to 10th	Night	12% 2 5% 28% 35% 18%	1900
	11th to 20th	Night	23% 3 9% 27% 25% 13%	1900
	21st to end	Night	27% 3 8% 25% 24% 13%	2133
October	1st to 10th	Night	22% 2 8% 23% 33% 12%	3800
	11th to 20th	Night	32% 2 19% 23% 20% 3	3777
	21st to end	Night	43% 3 9% 29% 14% 2	4303
November	1st to 10th	Night	52% 5% 10% 18% 14% 2	2535
	11th to 20th	Night	53% 5% 13% 20% 8%	2753
	21st to end	Night	44% 4 14% 20% 17% 1	2800
December	1st to 10th	Night	32% 3 11% 28% 25% 1	4560
	11th to 20th	Night	63% 3 14% 16% 4	5176
	21st to end	Night	59% 3 14% 18% 5%	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	35% 7% 27% 20% 11% 1	200
	11th to 20th	Day	19% 11% 30% 26% 12% 4	200
	21st to end	Day	17% 11% 27% 28% 15% 2	323
February	1st to 10th	Day	23% 13% 27% 25% 12% 1	400
	11th to 20th	Day	20% 14% 31% 23% 11% 1	409
	21st to end	Day	21% 13% 28% 29% 9%	414
March	1st to 10th	Day	21% 14% 28% 29% 8%	500
	11th to 20th	Day	20% 15% 25% 26% 13% 2	500
	21st to end	Day	22% 16% 26% 25% 11% 1	550
April	1st to 10th	Day	22% 15% 24% 25% 10% 4	500
	11th to 20th	Day	17% 13% 29% 25% 11% 5%	492
	21st to end	Day	13% 18% 25% 24% 14% 5%	500
May	1st to 10th	Day	16% 14% 25% 24% 16% 4	503
	11th to 20th	Day	20% 13% 24% 19% 17% 7%	528
	21st to end	Day	14% 10% 21% 26% 20% 10%	550
June	1st to 10th	Day	14% 11% 22% 23% 20% 10%	490
	11th to 20th	Day	11% 14% 29% 25% 17% 4	490
	21st to end	Day	4 7% 21% 33% 22% 12%	490
July	1st to 10th	Day	2 6% 28% 32% 21% 10%	486
	11th to 20th	Day	2 8% 26% 28% 25% 10%	484
	21st to end	Day	3 5% 28% 26% 25% 12%	531
August	1st to 10th	Day	4 5% 23% 29% 25% 14%	487
	11th to 20th	Day	2 4 20% 29% 27% 18%	477
	21st to end	Day	6% 6% 21% 26% 27% 14%	539
September	1st to 10th	Day	3 5% 21% 31% 28% 12%	490
	11th to 20th	Day	7% 6% 21% 31% 28% 7%	490
	21st to end	Day	10% 8% 19% 29% 26% 8%	490
October	1st to 10th	Day	13% 8% 21% 28% 22% 8%	490
	11th to 20th	Day	14% 9% 20% 27% 23% 8%	490
	21st to end	Day	18% 8% 26% 24% 20% 5%	425
November	1st to 10th	Day	18% 10% 23% 35% 12% 1	300
	11th to 20th	Day	21% 11% 26% 27% 13% 2	223
	21st to end	Day	17% 12% 25% 33% 12% 2	200
December	1st to 10th	Day	20% 8% 30% 25% 12% 7%	200
	11th to 20th	Day	26% 7% 35% 27% 6%	200
	21st to end	Day	20% 11% 26% 28% 11% 3	220
January	1st to 10th	Night	22% 8% 25% 29% 15% 2	800
	11th to 20th	Night	19% 8% 22% 30% 20% 2	800
	21st to end	Night	18% 6% 18% 39% 17% 3	880
February	1st to 10th	Night	18% 8% 22% 37% 15% 1	800
	11th to 20th	Night	17% 6% 21% 39% 15% 2	784
	21st to end	Night	18% 10% 19% 39% 13% 1	660
March	1st to 10th	Night	16% 11% 23% 36% 13% 1	800
	11th to 20th	Night	16% 8% 19% 37% 19% 1	800
	21st to end	Night	17% 10% 23% 36% 14% 1	880
April	1st to 10th	Night	18% 8% 19% 35% 18% 2	800
	11th to 20th	Night	16% 8% 22% 34% 18% 3	791
	21st to end	Night	15% 8% 19% 37% 18% 2	738
May	1st to 10th	Night	12% 5% 17% 44% 21% 1	400
	11th to 20th	Night	14% 5% 13% 43% 24% 2	394
	21st to end	Night	14% 4 13% 41% 27% 3	422
June	1st to 10th	Night	15% 3 13% 45% 21% 2	380
	11th to 20th	Night	10% 4 18% 46% 20% 1	380
	21st to end	Night	6% 2 14% 51% 27% 1	380
July	1st to 10th	Night	2 1 10% 50% 35% 1	370
	11th to 20th	Night	2 11% 60% 26% 2	368
	21st to end	Night	2 11% 52% 34% 2	416
August	1st to 10th	Night	2 1 5% 50% 37% 4	460
	11th to 20th	Night	2 1 6% 40% 43% 8%	596
	21st to end	Night	2 2 13% 46% 33% 4	836
September	1st to 10th	Night	3 2 11% 44% 36% 4	760
	11th to 20th	Night	5% 3 10% 42% 32% 8%	760
	21st to end	Night	9% 4 12% 39% 31% 5%	760
October	1st to 10th	Night	12% 3 11% 42% 28% 4	760
	11th to 20th	Night	13% 4 15% 40% 24% 4	760
	21st to end	Night	15% 5% 16% 40% 19% 4	836
November	1st to 10th	Night	19% 5% 18% 42% 15% 1	780
	11th to 20th	Night	21% 7% 20% 35% 15% 2	800
	21st to end	Night	18% 8% 18% 36% 17% 3	800
December	1st to 10th	Night	18% 5% 18% 36% 21% 2	800
	11th to 20th	Night	22% 6% 22% 35% 14% 2	800
	21st to end	Night	25% 10% 22% 31% 11% 1	880

Page generated at 2025-05-23 06:20:57. Version ac07

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