Sunriver
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunriver clear sky chart from 2005-11-06 to 2025-07-06.

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	4 7% 3 7% 5% 5% 5% 4 6% 7% 48%	124165
	Night	3 7% 3 8% 6% 5% 6% 4 6% 7% 45%	123435
Transparency	Day	35% 5% 10% 21% 19% 10%	123909
	Night	37% 6% 12% 22% 17% 7%	123278
Seeing	Day	15% 17% 29% 24% 12% 3	15495
	Night	11% 14% 25% 32% 16% 2	24569

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	7% 15% 7% 13% 8% 7% 6% 5% 7% 5% 20%	3639
	11th to 20th	Day	5% 10% 4 8% 5% 6% 5% 4 5% 6% 42%	3640
	21st to end	Day	3 7% 4 8% 6% 7% 7% 5% 6% 8% 40%	4354
February	1st to 10th	Day	3 12% 6% 11% 7% 7% 7% 5% 7% 8% 28%	1800
	11th to 20th	Day	4 13% 5% 10% 8% 5% 6% 5% 7% 8% 30%	1760
	21st to end	Day	2 10% 6% 12% 10% 7% 7% 6% 7% 7% 26%	1650
March	1st to 10th	Day	4 10% 4 9% 7% 7% 6% 6% 8% 9% 31%	4596
	11th to 20th	Day	2 11% 4 11% 7% 7% 7% 5% 4 6% 35%	5000
	21st to end	Day	3 11% 4 12% 8% 8% 8% 6% 8% 8% 24%	5705
April	1st to 10th	Day	6% 14% 5% 11% 8% 7% 5% 4 5% 6% 29%	2400
	11th to 20th	Day	5% 12% 5% 10% 6% 4 5% 4 5% 7% 37%	2369
	21st to end	Day	4 11% 3 8% 5% 5% 5% 4 6% 8% 40%	2460
May	1st to 10th	Day	8% 9% 2 6% 4 3 4 4 5% 5% 50%	6274
	11th to 20th	Day	6% 7% 3 7% 5% 4 4 3 6% 6% 49%	6277
	21st to end	Day	5% 7% 2 6% 4 4 4 4 5% 9% 50%	6902
June	1st to 10th	Day	9% 9% 3 7% 5% 4 5% 4 6% 7% 42%	2800
	11th to 20th	Day	5% 7% 3 7% 5% 4 4 4 5% 6% 51%	2800
	21st to end	Day	2 4 2 5% 4 3 4 3 4 5% 64%	2800
July	1st to 10th	Day	1 1 1 2 1 2 2 2 3 3 82%	4491
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 79%	4420
	21st to end	Day	1 1 1 2 2 2 2 1 3 4 81%	4790
August	1st to 10th	Day	4 2 1 3 2 3 3 3 5% 6% 68%	4159
	11th to 20th	Day	1 2 1 4 3 3 3 3 3 5% 71%	4001
	21st to end	Day	4 3 1 3 2 2 2 2 3 5% 73%	4180
September	1st to 10th	Day	2 1 1 3 2 2 3 2 4 7% 74%	2280
	11th to 20th	Day	3 5% 2 5% 4 4 5% 4 6% 7% 56%	2280
	21st to end	Day	5% 6% 2 4 4 3 4 2 5% 7% 57%	2032
October	1st to 10th	Day	4 5% 2 5% 3 3 3 2 3 5% 65%	3180
	11th to 20th	Day	3 7% 3 8% 5% 5% 5% 4 6% 8% 46%	3161
	21st to end	Day	4 8% 3 9% 6% 6% 6% 4 7% 8% 39%	3324
November	1st to 10th	Day	4 11% 4 10% 7% 7% 5% 5% 7% 8% 33%	1764
	11th to 20th	Day	3 8% 4 12% 8% 8% 8% 6% 9% 9% 27%	1625
	21st to end	Day	3 10% 3 10% 9% 6% 6% 5% 8% 7% 33%	1600
December	1st to 10th	Day	3 6% 2 7% 5% 5% 5% 5% 8% 8% 47%	2620
	11th to 20th	Day	5% 11% 5% 11% 9% 8% 8% 6% 9% 8% 20%	3028
	21st to end	Day	2 11% 5% 13% 9% 8% 8% 6% 9% 8% 19%	4004
January	1st to 10th	Night	5% 12% 5% 11% 9% 9% 8% 6% 9% 8% 18%	6306
	11th to 20th	Night	3 9% 3 10% 6% 5% 6% 4 5% 6% 42%	6320
	21st to end	Night	2 8% 4 9% 7% 7% 7% 6% 6% 6% 39%	6601
February	1st to 10th	Night	3 11% 5% 11% 9% 6% 7% 6% 8% 7% 29%	2600
	11th to 20th	Night	3 10% 4 11% 7% 6% 7% 5% 7% 7% 33%	2527
	21st to end	Night	2 10% 5% 12% 8% 7% 9% 6% 6% 7% 29%	1980
March	1st to 10th	Night	3 8% 4 7% 5% 5% 7% 7% 9% 11% 34%	5293
	11th to 20th	Night	1 6% 4 9% 7% 7% 8% 6% 7% 8% 38%	5000
	21st to end	Night	2 11% 4 11% 8% 9% 9% 6% 8% 9% 25%	5270
April	1st to 10th	Night	5% 11% 5% 9% 7% 6% 8% 5% 5% 7% 33%	2000
	11th to 20th	Night	4 10% 5% 8% 6% 6% 5% 4 5% 7% 39%	1979
	21st to end	Night	4 9% 5% 8% 5% 5% 5% 4 6% 7% 40%	1936
May	1st to 10th	Night	6% 9% 3 7% 4 4 3 3 4 5% 52%	3686
	11th to 20th	Night	4 8% 3 7% 5% 5% 5% 3 4 6% 50%	3616
	21st to end	Night	4 8% 3 6% 4 4 3 3 5% 5% 56%	3972
June	1st to 10th	Night	8% 9% 3 7% 4 4 4 4 4 7% 46%	1600
	11th to 20th	Night	4 7% 2 4 3 3 3 3 6% 8% 56%	1600
	21st to end	Night	3 3 1 4 3 3 4 3 4 6% 67%	1600
July	1st to 10th	Night	1 1 2 1 1 2 2 2 3 85%	2580
	11th to 20th	Night	2 2 1 2 1 1 2 2 3 4 81%	2540
	21st to end	Night	1 1 2 2 2 2 2 3 3 83%	2761
August	1st to 10th	Night	2 3 1 4 2 3 2 2 4 5% 72%	2774
	11th to 20th	Night	1 2 1 3 2 2 2 2 3 5% 76%	2837
	21st to end	Night	3 2 1 2 2 2 2 2 3 4 77%	3498
September	1st to 10th	Night	1 1 1 3 2 2 2 2 4 4 79%	1900
	11th to 20th	Night	3 3 1 4 4 3 4 4 5% 7% 61%	1900
	21st to end	Night	4 5% 2 4 3 3 3 2 5% 6% 61%	2147
October	1st to 10th	Night	2 5% 2 5% 3 2 3 2 3 4 68%	3800
	11th to 20th	Night	4 6% 2 6% 4 5% 5% 4 6% 7% 52%	3777
	21st to end	Night	3 8% 3 9% 6% 6% 6% 5% 7% 8% 39%	4239
November	1st to 10th	Night	4 10% 4 10% 8% 6% 6% 5% 6% 8% 33%	2535
	11th to 20th	Night	3 8% 4 10% 9% 8% 7% 6% 8% 9% 29%	2773
	21st to end	Night	2 7% 3 9% 8% 8% 6% 6% 8% 8% 36%	2800
December	1st to 10th	Night	2 6% 2 6% 5% 4 4 4 7% 8% 51%	4560
	11th to 20th	Night	3 11% 5% 11% 8% 8% 10% 7% 8% 10% 20%	5176
	21st to end	Night	4 9% 4 11% 9% 9% 8% 5% 7% 9% 25%	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	61% 7% 12% 13% 6%	3639
	11th to 20th	Day	43% 5% 10% 22% 16% 3	3640
	21st to end	Day	42% 6% 10% 15% 19% 7%	4354
February	1st to 10th	Day	52% 6% 14% 17% 10% 1	1800
	11th to 20th	Day	50% 6% 15% 16% 10% 3	1769
	21st to end	Day	55% 7% 12% 14% 10% 2	1650
March	1st to 10th	Day	47% 6% 9% 25% 10% 4	4596
	11th to 20th	Day	46% 7% 13% 24% 11%	5000
	21st to end	Day	52% 8% 15% 19% 6%	5705
April	1st to 10th	Day	56% 5% 10% 18% 9% 2	2400
	11th to 20th	Day	47% 5% 12% 21% 13% 3	2372
	21st to end	Day	41% 6% 14% 25% 13% 2	2460
May	1st to 10th	Day	36% 5% 6% 26% 24% 3	6274
	11th to 20th	Day	33% 7% 10% 23% 24% 3	6280
	21st to end	Day	31% 5% 15% 36% 13%	6904
June	1st to 10th	Day	41% 4 10% 29% 14% 1	2800
	11th to 20th	Day	34% 4 8% 30% 21% 3	2800
	21st to end	Day	23% 4 9% 29% 27% 10%	2800
July	1st to 10th	Day	9% 2 4 13% 21% 50%	4422
	11th to 20th	Day	11% 2 3 9% 23% 52%	4345
	21st to end	Day	9% 2 3 16% 38% 32%	4639
August	1st to 10th	Day	18% 3 4 16% 37% 22%	4143
	11th to 20th	Day	16% 3 5% 25% 36% 15%	4040
	21st to end	Day	16% 3 5% 28% 28% 20%	4179
September	1st to 10th	Day	12% 3 4 25% 35% 21%	2280
	11th to 20th	Day	27% 4 7% 24% 26% 11%	2280
	21st to end	Day	28% 4 9% 26% 23% 11%	2032
October	1st to 10th	Day	24% 3 8% 21% 30% 14%	3180
	11th to 20th	Day	34% 6% 16% 25% 16% 3	3161
	21st to end	Day	40% 6% 11% 23% 18% 2	3324
November	1st to 10th	Day	48% 5% 12% 19% 15% 1	1764
	11th to 20th	Day	51% 8% 16% 14% 10% 1	1625
	21st to end	Day	48% 7% 12% 15% 17% 2	1600
December	1st to 10th	Day	31% 6% 11% 20% 24% 7%	2620
	11th to 20th	Day	57% 9% 14% 14% 6% 1	3028
	21st to end	Day	58% 9% 11% 16% 5%	4004
January	1st to 10th	Night	58% 8% 13% 14% 6% 1	6306
	11th to 20th	Night	42% 6% 8% 23% 17% 3	6320
	21st to end	Night	45% 5% 10% 12% 17% 10%	6601
February	1st to 10th	Night	51% 8% 14% 16% 10% 1	2600
	11th to 20th	Night	49% 6% 15% 18% 9% 3	2529
	21st to end	Night	52% 8% 12% 17% 10% 1	1980
March	1st to 10th	Night	40% 7% 14% 25% 10% 4	5293
	11th to 20th	Night	40% 7% 16% 26% 11%	5000
	21st to end	Night	50% 10% 16% 20% 5%	5270
April	1st to 10th	Night	51% 5% 16% 19% 8% 1	2000
	11th to 20th	Night	44% 5% 14% 23% 12% 2	1979
	21st to end	Night	43% 7% 15% 23% 12% 1	1936
May	1st to 10th	Night	34% 5% 8% 27% 25% 1	3683
	11th to 20th	Night	32% 6% 15% 27% 18% 1	3616
	21st to end	Night	30% 4 24% 34% 6%	3972
June	1st to 10th	Night	40% 5% 11% 32% 13%	1600
	11th to 20th	Night	27% 5% 12% 36% 18% 2	1600
	21st to end	Night	20% 3 11% 34% 26% 6%	1600
July	1st to 10th	Night	8% 1 6% 15% 20% 49%	2540
	11th to 20th	Night	11% 1 4 15% 23% 46%	2492
	21st to end	Night	9% 2 3 17% 42% 27%	2674
August	1st to 10th	Night	17% 2 5% 19% 41% 16%	2766
	11th to 20th	Night	13% 2 5% 35% 35% 9%	2864
	21st to end	Night	13% 3 8% 30% 29% 18%	3498
September	1st to 10th	Night	11% 3 3 26% 39% 17%	1900
	11th to 20th	Night	22% 6% 8% 25% 28% 11%	1900
	21st to end	Night	25% 3 9% 25% 25% 13%	2147
October	1st to 10th	Night	21% 3 7% 23% 32% 13%	3800
	11th to 20th	Night	31% 5% 17% 26% 17% 4	3777
	21st to end	Night	39% 6% 13% 23% 15% 3	4239
November	1st to 10th	Night	49% 5% 12% 16% 14% 3	2535
	11th to 20th	Night	50% 8% 12% 19% 10% 2	2773
	21st to end	Night	43% 8% 12% 16% 16% 4	2800
December	1st to 10th	Night	30% 6% 9% 22% 26% 7%	4560
	11th to 20th	Night	55% 11% 15% 13% 6%	5176
	21st to end	Night	53% 8% 15% 17% 6% 1	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	29% 24% 27% 17% 4 1	200
	11th to 20th	Day	26% 17% 32% 15% 9% 2	200
	21st to end	Day	18% 22% 27% 22% 9% 2	375
February	1st to 10th	Day	21% 23% 31% 18% 6% 1	400
	11th to 20th	Day	24% 27% 27% 14% 7%	398
	21st to end	Day	21% 23% 34% 14% 7%	414
March	1st to 10th	Day	23% 26% 32% 15% 4	500
	11th to 20th	Day	19% 23% 30% 20% 7% 1	500
	21st to end	Day	25% 23% 30% 17% 5%	550
April	1st to 10th	Day	24% 21% 29% 16% 8% 2	500
	11th to 20th	Day	24% 21% 30% 16% 5% 4	492
	21st to end	Day	19% 21% 29% 21% 8% 2	500
May	1st to 10th	Day	20% 18% 31% 19% 9% 3	503
	11th to 20th	Day	21% 19% 24% 20% 12% 4	528
	21st to end	Day	16% 14% 27% 25% 14% 4	573
June	1st to 10th	Day	13% 18% 26% 23% 16% 5%	530
	11th to 20th	Day	14% 22% 28% 24% 11% 1	530
	21st to end	Day	5% 12% 28% 32% 16% 6%	530
July	1st to 10th	Day	4 9% 34% 32% 17% 3	507
	11th to 20th	Day	4 9% 35% 31% 18% 5%	484
	21st to end	Day	2 10% 30% 33% 21% 5%	531
August	1st to 10th	Day	3 7% 28% 32% 23% 7%	487
	11th to 20th	Day	4 7% 24% 35% 20% 10%	477
	21st to end	Day	6% 7% 26% 35% 17% 8%	539
September	1st to 10th	Day	4 7% 29% 33% 19% 8%	490
	11th to 20th	Day	9% 10% 27% 33% 17% 4	490
	21st to end	Day	12% 13% 26% 28% 17% 3	490
October	1st to 10th	Day	12% 17% 27% 22% 20% 2	490
	11th to 20th	Day	15% 17% 25% 24% 16% 3	490
	21st to end	Day	19% 19% 28% 19% 11% 5%	464
November	1st to 10th	Day	20% 21% 30% 20% 9%	300
	11th to 20th	Day	24% 19% 28% 22% 6% 1	213
	21st to end	Day	16% 23% 31% 25% 6%	200
December	1st to 10th	Day	17% 21% 31% 18% 12% 2	200
	11th to 20th	Day	23% 24% 38% 12% 4	200
	21st to end	Day	27% 18% 36% 14% 5%	220
January	1st to 10th	Night	20% 21% 30% 19% 10% 1	800
	11th to 20th	Night	15% 18% 28% 23% 14% 1	800
	21st to end	Night	14% 16% 26% 32% 11% 2	880
February	1st to 10th	Night	14% 20% 30% 26% 9% 1	800
	11th to 20th	Night	15% 18% 29% 26% 11% 1	784
	21st to end	Night	16% 20% 29% 28% 7%	660
March	1st to 10th	Night	16% 22% 27% 27% 9% 1	800
	11th to 20th	Night	11% 20% 29% 27% 12% 1	800
	21st to end	Night	14% 20% 30% 26% 11%	880
April	1st to 10th	Night	14% 16% 29% 27% 13% 1	800
	11th to 20th	Night	10% 19% 30% 25% 14% 2	791
	21st to end	Night	13% 15% 28% 29% 15% 1	736
May	1st to 10th	Night	12% 10% 25% 35% 18% 1	420
	11th to 20th	Night	12% 8% 22% 34% 23% 1	394
	21st to end	Night	11% 7% 23% 34% 23% 2	433
June	1st to 10th	Night	14% 7% 22% 37% 19% 1	400
	11th to 20th	Night	10% 6% 27% 42% 15% 1	400
	21st to end	Night	4 4 20% 52% 20% 1	400
July	1st to 10th	Night	3 1 17% 55% 23% 1	380
	11th to 20th	Night	2 1 18% 57% 20% 1	368
	21st to end	Night	1 1 18% 52% 27%	416
August	1st to 10th	Night	3 1 10% 48% 34% 3	519
	11th to 20th	Night	2 1 11% 45% 36% 4	576
	21st to end	Night	2 3 24% 43% 25% 2	836
September	1st to 10th	Night	2 4 21% 41% 29% 3	760
	11th to 20th	Night	6% 6% 16% 39% 30% 4	760
	21st to end	Night	9% 7% 19% 35% 26% 3	760
October	1st to 10th	Night	6% 9% 28% 31% 23% 4	760
	11th to 20th	Night	12% 10% 21% 31% 22% 3	760
	21st to end	Night	15% 13% 26% 27% 15% 4	836
November	1st to 10th	Night	13% 16% 30% 29% 10% 1	780
	11th to 20th	Night	18% 20% 25% 26% 9% 2	800
	21st to end	Night	12% 20% 30% 25% 12% 2	800
December	1st to 10th	Night	14% 15% 26% 30% 13% 2	800
	11th to 20th	Night	17% 21% 29% 24% 9% 1	800
	21st to end	Night	17% 28% 28% 21% 6%	880

Page generated at 2025-07-02 22:30:18. Version ac07

Copyright © 2025 Attilla Danko.