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 2024-11-03.

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 5% 6% 49%	101517
	Night	3 7% 3 8% 6% 5% 6% 4 6% 7% 45%	97625
Transparency	Day	36% 5% 9% 21% 19% 11%	101260
	Night	39% 5% 11% 21% 16% 7%	97471
Seeing	Day	15% 17% 29% 24% 13% 3	14696
	Night	11% 14% 25% 32% 17% 2	23723

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	6% 15% 7% 13% 7% 6% 7% 5% 7% 5% 22%	2539
	11th to 20th	Day	7% 14% 6% 11% 7% 7% 7% 5% 5% 5% 25%	2540
	21st to end	Day	4 10% 5% 10% 7% 9% 8% 7% 8% 8% 25%	3032
February	1st to 10th	Day	3 12% 6% 11% 7% 6% 7% 5% 7% 8% 28%	1710
	11th to 20th	Day	4 12% 5% 10% 8% 5% 6% 5% 7% 8% 31%	1669
	21st to end	Day	2 11% 6% 12% 10% 7% 7% 6% 7% 7% 24%	1570
March	1st to 10th	Day	2 9% 4 11% 8% 8% 7% 6% 8% 9% 29%	3190
	11th to 20th	Day	1 9% 4 9% 6% 6% 5% 4 4 7% 47%	3490
	21st to end	Day	3 11% 4 12% 8% 8% 7% 6% 8% 8% 23%	3979
April	1st to 10th	Day	6% 14% 5% 12% 8% 7% 5% 4 5% 6% 29%	2280
	11th to 20th	Day	5% 13% 5% 10% 6% 4 5% 4 5% 7% 35%	2249
	21st to end	Day	4 11% 3 8% 6% 5% 5% 4 6% 8% 39%	2337
May	1st to 10th	Day	8% 12% 3 8% 5% 4 4 4 5% 5% 42%	4387
	11th to 20th	Day	5% 6% 2 5% 4 3 3 3 4 5% 59%	4377
	21st to end	Day	7% 9% 3 7% 4 4 4 4 5% 8% 43%	4813
June	1st to 10th	Day	9% 9% 3 7% 5% 4 5% 4 6% 7% 40%	2660
	11th to 20th	Day	6% 7% 3 7% 5% 4 4 4 5% 6% 50%	2660
	21st to end	Day	2 4 2 5% 4 3 4 3 4 5% 64%	2660
July	1st to 10th	Day	1 1 2 1 2 2 1 3 3 83%	4420
	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	6% 7% 3 7% 5% 4 4 3 4 5% 52%	1900
	11th to 20th	Day	4 7% 3 8% 6% 5% 4 4 5% 8% 45%	1900
	21st to end	Day	5% 7% 3 10% 6% 6% 5% 3 6% 7% 43%	2015
November	1st to 10th	Day	4 11% 4 10% 7% 7% 5% 5% 7% 8% 33%	1692
	11th to 20th	Day	3 8% 4 11% 8% 7% 7% 6% 9% 9% 27%	1544
	21st to end	Day	3 10% 3 10% 9% 6% 6% 5% 8% 7% 33%	1520
December	1st to 10th	Day	3 8% 3 9% 7% 8% 6% 5% 9% 9% 34%	1520
	11th to 20th	Day	5% 9% 4 10% 8% 7% 7% 6% 10% 10% 24%	1928
	21st to end	Day	2 11% 6% 12% 10% 8% 7% 6% 9% 8% 22%	2794
January	1st to 10th	Night	4 12% 5% 10% 8% 9% 9% 6% 9% 9% 19%	4406
	11th to 20th	Night	5% 12% 5% 13% 8% 7% 8% 5% 7% 7% 24%	4420
	21st to end	Night	3 11% 5% 12% 10% 8% 9% 6% 7% 7% 23%	4615
February	1st to 10th	Night	3 10% 5% 11% 8% 6% 7% 6% 8% 7% 30%	2470
	11th to 20th	Night	3 10% 4 11% 7% 6% 7% 5% 7% 7% 33%	2398
	21st to end	Night	2 10% 5% 12% 8% 7% 9% 6% 7% 7% 28%	1884
March	1st to 10th	Night	2 8% 4 8% 6% 6% 8% 8% 9% 11% 31%	3679
	11th to 20th	Night	1 5% 3 6% 6% 5% 7% 5% 7% 7% 48%	3490
	21st to end	Night	2 10% 5% 12% 9% 9% 9% 6% 8% 8% 23%	3674
April	1st to 10th	Night	5% 11% 5% 10% 7% 6% 8% 5% 5% 6% 32%	1900
	11th to 20th	Night	4 11% 5% 9% 7% 6% 5% 4 5% 8% 37%	1879
	21st to end	Night	5% 10% 5% 9% 5% 5% 5% 5% 6% 7% 38%	1839
May	1st to 10th	Night	8% 12% 4 9% 4 4 3 3 4 5% 43%	2572
	11th to 20th	Night	3 4 2 5% 4 3 4 2 4 6% 61%	2516
	21st to end	Night	4 10% 4 7% 4 4 4 4 5% 4 50%	2762
June	1st to 10th	Night	9% 9% 3 7% 4 4 4 4 4 7% 44%	1520
	11th to 20th	Night	5% 8% 2 4 3 3 3 3 6% 8% 56%	1520
	21st to end	Night	3 3 1 4 3 3 4 3 4 5% 68%	1520
July	1st to 10th	Night	1 1 2 1 1 2 2 2 3 85%	2540
	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	3 7% 2 7% 4 3 4 3 5% 6% 55%	2280
	11th to 20th	Night	5% 6% 2 7% 4 5% 5% 3 5% 6% 52%	2280
	21st to end	Night	4 8% 3 10% 6% 6% 5% 4 6% 6% 42%	2581
November	1st to 10th	Night	4 10% 4 10% 8% 6% 6% 5% 6% 8% 32%	2431
	11th to 20th	Night	3 8% 3 9% 9% 8% 7% 6% 9% 9% 29%	2634
	21st to end	Night	2 7% 3 9% 8% 8% 6% 6% 8% 8% 35%	2660
December	1st to 10th	Night	3 9% 3 8% 7% 6% 7% 6% 8% 9% 34%	2660
	11th to 20th	Night	2 9% 4 10% 8% 9% 10% 7% 7% 9% 24%	3276
	21st to end	Night	2 9% 4 11% 8% 8% 8% 5% 7% 9% 28%	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	61% 7% 14% 13% 5% 1	2539
	11th to 20th	Day	61% 5% 10% 15% 5% 3	2540
	21st to end	Day	57% 7% 12% 16% 7% 2	3032
February	1st to 10th	Day	52% 6% 14% 18% 9% 1	1710
	11th to 20th	Day	50% 6% 15% 17% 10% 3	1678
	21st to end	Day	56% 7% 12% 14% 9% 1	1570
March	1st to 10th	Day	52% 5% 10% 22% 11% 1	3190
	11th to 20th	Day	38% 5% 12% 31% 14%	3490
	21st to end	Day	55% 7% 13% 18% 6%	3979
April	1st to 10th	Day	57% 5% 9% 18% 9% 2	2280
	11th to 20th	Day	49% 4 12% 20% 12% 3	2252
	21st to end	Day	42% 6% 14% 25% 12% 2	2337
May	1st to 10th	Day	43% 5% 8% 25% 18% 1	4387
	11th to 20th	Day	27% 5% 6% 26% 33% 4	4380
	21st to end	Day	39% 5% 16% 29% 10%	4814
June	1st to 10th	Day	43% 4 11% 28% 13% 1	2660
	11th to 20th	Day	34% 4 8% 31% 20% 3	2660
	21st to end	Day	23% 3 8% 29% 27% 10%	2660
July	1st to 10th	Day	9% 2 4 13% 21% 51%	4351
	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	36% 4 8% 18% 25% 9%	1900
	11th to 20th	Day	36% 6% 12% 22% 20% 5%	1900
	21st to end	Day	40% 6% 12% 20% 20% 2	2015
November	1st to 10th	Day	48% 5% 12% 18% 15% 1	1692
	11th to 20th	Day	50% 7% 16% 15% 10% 1	1544
	21st to end	Day	49% 6% 12% 15% 16% 2	1520
December	1st to 10th	Day	44% 9% 13% 22% 11% 2	1520
	11th to 20th	Day	53% 8% 15% 15% 8% 1	1928
	21st to end	Day	59% 7% 10% 18% 5% 1	2794
January	1st to 10th	Night	60% 7% 14% 14% 5% 1	4406
	11th to 20th	Night	58% 7% 10% 16% 5% 4	4420
	21st to end	Night	60% 5% 13% 13% 8% 2	4615
February	1st to 10th	Night	50% 8% 14% 16% 10% 1	2470
	11th to 20th	Night	49% 6% 15% 18% 9% 3	2400
	21st to end	Night	53% 8% 12% 17% 9% 2	1884
March	1st to 10th	Night	45% 7% 13% 25% 9% 1	3679
	11th to 20th	Night	35% 6% 14% 32% 14%	3490
	21st to end	Night	55% 8% 15% 17% 4	3674
April	1st to 10th	Night	52% 5% 16% 17% 8% 1	1900
	11th to 20th	Night	46% 6% 14% 22% 11% 2	1879
	21st to end	Night	44% 7% 15% 23% 11% 1	1839
May	1st to 10th	Night	43% 5% 10% 30% 12%	2572
	11th to 20th	Night	23% 5% 9% 35% 25% 2	2516
	21st to end	Night	36% 5% 28% 26% 5%	2762
June	1st to 10th	Night	42% 5% 11% 30% 11%	1520
	11th to 20th	Night	27% 5% 13% 36% 16% 3	1520
	21st to end	Night	20% 3 11% 34% 26% 7%	1520
July	1st to 10th	Night	8% 1 6% 15% 20% 50%	2500
	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	30% 4 10% 22% 26% 9%	2280
	11th to 20th	Night	33% 5% 13% 23% 20% 6%	2280
	21st to end	Night	42% 6% 12% 17% 19% 4	2581
November	1st to 10th	Night	50% 5% 12% 16% 14% 3	2431
	11th to 20th	Night	50% 8% 12% 19% 10% 2	2634
	21st to end	Night	43% 8% 13% 16% 16% 5%	2660
December	1st to 10th	Night	45% 9% 13% 19% 12% 2	2660
	11th to 20th	Night	55% 7% 12% 15% 9% 1	3276
	21st to end	Night	53% 7% 12% 19% 8% 1	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	28% 24% 24% 18% 4 1	180
	11th to 20th	Day	28% 18% 28% 15% 8% 2	180
	21st to end	Day	18% 23% 27% 21% 9% 2	345
February	1st to 10th	Day	21% 22% 33% 18% 6%	370
	11th to 20th	Day	24% 28% 27% 14% 7%	367
	21st to end	Day	20% 24% 34% 14% 7% 1	382
March	1st to 10th	Day	23% 25% 32% 16% 4	460
	11th to 20th	Day	17% 22% 31% 22% 8% 1	460
	21st to end	Day	24% 23% 30% 17% 5%	506
April	1st to 10th	Day	24% 21% 30% 16% 7% 2	460
	11th to 20th	Day	25% 22% 30% 15% 5% 3	452
	21st to end	Day	20% 22% 28% 21% 8% 1	460
May	1st to 10th	Day	20% 18% 31% 20% 9% 3	463
	11th to 20th	Day	20% 18% 25% 21% 12% 4	488
	21st to end	Day	17% 14% 26% 24% 14% 4	529
June	1st to 10th	Day	14% 18% 26% 22% 15% 4	490
	11th to 20th	Day	14% 22% 28% 24% 11% 1	490
	21st to end	Day	4 12% 29% 32% 16% 6%	490
July	1st to 10th	Day	4 9% 34% 32% 18% 3	486
	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% 19% 10%	276
	11th to 20th	Day	21% 18% 30% 23% 6% 2	192
	21st to end	Day	17% 21% 31% 26% 6%	180
December	1st to 10th	Day	18% 21% 32% 16% 11% 2	180
	11th to 20th	Day	22% 23% 37% 13% 4	180
	21st to end	Day	24% 19% 36% 15% 5% 1	198
January	1st to 10th	Night	20% 20% 29% 19% 11% 1	760
	11th to 20th	Night	16% 19% 27% 23% 14% 1	760
	21st to end	Night	14% 16% 26% 31% 11% 2	836
February	1st to 10th	Night	14% 19% 30% 27% 9% 1	760
	11th to 20th	Night	15% 17% 29% 27% 12% 1	744
	21st to end	Night	15% 21% 30% 28% 7%	628
March	1st to 10th	Night	15% 22% 26% 26% 9% 1	760
	11th to 20th	Night	10% 19% 29% 28% 13% 1	760
	21st to end	Night	12% 20% 31% 26% 11%	836
April	1st to 10th	Night	15% 16% 29% 26% 13% 1	760
	11th to 20th	Night	10% 20% 29% 25% 14% 2	751
	21st to end	Night	13% 15% 27% 29% 15% 1	699
May	1st to 10th	Night	12% 11% 25% 34% 17% 1	399
	11th to 20th	Night	11% 7% 21% 36% 24% 1	374
	21st to end	Night	12% 7% 23% 33% 24% 2	411
June	1st to 10th	Night	15% 7% 21% 38% 18% 1	380
	11th to 20th	Night	10% 6% 26% 41% 15% 1	380
	21st to end	Night	4 4 19% 52% 20% 1	380
July	1st to 10th	Night	2 1 16% 56% 24% 1	370
	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	14% 17% 30% 28% 10% 1	748
	11th to 20th	Night	16% 20% 26% 27% 9% 2	760
	21st to end	Night	11% 20% 30% 25% 12% 2	760
December	1st to 10th	Night	14% 16% 27% 29% 13% 2	760
	11th to 20th	Night	16% 21% 29% 25% 9% 1	760
	21st to end	Night	16% 28% 28% 22% 6%	836

Page generated at 2024-10-31 00:39:26. Version ac07

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