Crater Lake National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crater Lake National Park clear sky chart from 2005-11-06 to 2025-06-10.

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	5% 10% 4 8% 4 4 4 3 5% 6% 48%	123859
	Night	5% 10% 4 10% 5% 4 4 3 5% 5% 44%	123210
Transparency	Day	36% 6% 9% 19% 19% 11%	123606
	Night	40% 7% 9% 17% 17% 10%	123050
Seeing	Day	19% 16% 26% 23% 13% 3	15526
	Night	17% 11% 18% 30% 20% 3	24661

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% 19% 9% 16% 6% 6% 5% 3 4 5% 19%	3639
	11th to 20th	Day	9% 12% 4 9% 4 4 3 2 4 5% 43%	3701
	21st to end	Day	8% 18% 5% 8% 4 3 3 3 4 5% 40%	4510
February	1st to 10th	Day	9% 16% 6% 10% 6% 4 5% 5% 6% 7% 26%	1800
	11th to 20th	Day	6% 17% 6% 13% 6% 5% 3 3 4 6% 28%	1755
	21st to end	Day	6% 17% 8% 15% 6% 5% 4 4 4 5% 27%	1635
March	1st to 10th	Day	5% 16% 8% 15% 6% 3 3 3 5% 7% 30%	4725
	11th to 20th	Day	5% 18% 6% 12% 6% 4 4 3 3 4 34%	5000
	21st to end	Day	4 22% 9% 13% 7% 6% 4 4 5% 7% 20%	5634
April	1st to 10th	Day	8% 18% 7% 13% 5% 5% 3 3 5% 6% 26%	2400
	11th to 20th	Day	8% 17% 5% 10% 5% 4 4 4 4 6% 33%	2369
	21st to end	Day	4 15% 5% 10% 5% 3 4 4 6% 7% 37%	2475
May	1st to 10th	Day	6% 9% 4 7% 3 3 4 3 5% 5% 50%	6115
	11th to 20th	Day	4 6% 2 8% 4 4 4 4 6% 6% 50%	6277
	21st to end	Day	4 7% 3 5% 4 3 3 3 5% 8% 54%	6902
June	1st to 10th	Day	8% 9% 3 6% 4 4 4 4 6% 7% 44%	2789
	11th to 20th	Day	4 6% 3 7% 4 4 4 3 4 6% 54%	2660
	21st to end	Day	4 4 1 4 3 2 3 3 4 5% 67%	2660
July	1st to 10th	Day	1 1 2 1 1 1 1 2 2 86%	4420
	11th to 20th	Day	2 2 1 2 2 2 3 2 3 3 78%	4420
	21st to end	Day	1 1 1 2 1 1 2 1 2 3 85%	4704
August	1st to 10th	Day	3 3 1 3 2 2 2 2 5% 5% 70%	4091
	11th to 20th	Day	2 2 1 3 3 3 3 3 3 5% 74%	4026
	21st to end	Day	4 3 1 3 2 2 2 1 3 4 75%	4180
September	1st to 10th	Day	1 1 1 3 2 3 3 2 3 5% 75%	2280
	11th to 20th	Day	5% 5% 2 5% 4 3 4 3 6% 5% 58%	2280
	21st to end	Day	4 6% 2 7% 3 3 2 2 4 6% 59%	2013
October	1st to 10th	Day	4 5% 2 4 3 2 2 3 3 5% 67%	3180
	11th to 20th	Day	5% 5% 3 7% 5% 4 5% 4 7% 7% 46%	3161
	21st to end	Day	7% 11% 3 9% 5% 4 5% 4 6% 7% 39%	3423
November	1st to 10th	Day	9% 14% 5% 10% 6% 4 4 3 4 9% 32%	1764
	11th to 20th	Day	8% 15% 6% 11% 7% 4 6% 5% 6% 5% 26%	1619
	21st to end	Day	8% 15% 5% 12% 6% 4 4 3 5% 6% 32%	1600
December	1st to 10th	Day	5% 8% 3 8% 5% 4 4 4 6% 7% 46%	2620
	11th to 20th	Day	8% 20% 7% 12% 6% 6% 5% 4 7% 7% 18%	3028
	21st to end	Day	8% 19% 8% 15% 9% 7% 6% 4 5% 4 15%	4004
January	1st to 10th	Night	5% 17% 6% 16% 9% 7% 6% 5% 5% 6% 18%	6306
	11th to 20th	Night	6% 12% 3 12% 6% 4 3 2 4 4 44%	6259
	21st to end	Night	9% 13% 6% 11% 6% 5% 4 3 3 4 37%	6468
February	1st to 10th	Night	8% 14% 5% 12% 7% 5% 4 5% 7% 5% 29%	2600
	11th to 20th	Night	6% 15% 5% 12% 7% 5% 4 4 5% 5% 31%	2532
	21st to end	Night	5% 15% 5% 14% 6% 5% 4 3 7% 6% 29%	1995
March	1st to 10th	Night	4 11% 6% 16% 8% 6% 5% 4 7% 6% 27%	5166
	11th to 20th	Night	3 14% 6% 14% 7% 5% 5% 4 4 5% 33%	5000
	21st to end	Night	3 15% 7% 17% 9% 7% 6% 4 6% 6% 21%	5341
April	1st to 10th	Night	8% 14% 5% 12% 8% 5% 5% 4 6% 7% 27%	2000
	11th to 20th	Night	4 13% 5% 12% 7% 5% 5% 3 5% 7% 34%	1979
	21st to end	Night	5% 11% 5% 10% 5% 5% 5% 5% 7% 8% 36%	1920
May	1st to 10th	Night	7% 8% 3 8% 4 4 3 2 4 4 53%	3852
	11th to 20th	Night	2 6% 3 9% 5% 5% 5% 4 5% 6% 50%	3616
	21st to end	Night	3 5% 2 6% 3 3 3 3 4 6% 61%	3972
June	1st to 10th	Night	9% 8% 3 8% 4 5% 3 4 4 7% 45%	1595
	11th to 20th	Night	3 6% 2 7% 3 4 4 3 5% 6% 59%	1520
	21st to end	Night	4 3 1 3 3 3 3 2 3 5% 70%	1520
July	1st to 10th	Night	1 2 1 1 2 1 1 2 3 3 84%	2540
	11th to 20th	Night	2 2 1 3 2 2 2 2 2 4 79%	2540
	21st to end	Night	1 2 1 1 2 2 2 2 3 3 82%	2846
August	1st to 10th	Night	2 2 1 3 3 2 3 2 5% 4 72%	2848
	11th to 20th	Night	1 1 2 3 2 2 3 2 4 4 76%	2812
	21st to end	Night	5% 3 1 2 1 1 2 2 3 4 75%	3497
September	1st to 10th	Night	1 1 1 2 2 2 2 2 4 4 79%	1900
	11th to 20th	Night	4 4 1 5% 3 4 3 3 4 6% 62%	1900
	21st to end	Night	6% 6% 2 4 3 2 3 3 4 6% 61%	2163
October	1st to 10th	Night	2 4 2 5% 4 2 2 2 3 4 70%	3800
	11th to 20th	Night	5% 6% 3 7% 4 3 4 3 5% 6% 53%	3777
	21st to end	Night	4 7% 4 11% 8% 5% 6% 5% 7% 7% 36%	4143
November	1st to 10th	Night	10% 12% 5% 11% 7% 5% 4 3 4 6% 32%	2535
	11th to 20th	Night	8% 11% 6% 12% 8% 6% 6% 5% 6% 6% 24%	2780
	21st to end	Night	6% 14% 5% 10% 6% 5% 6% 4 5% 6% 34%	2800
December	1st to 10th	Night	6% 7% 3 7% 4 3 4 4 6% 6% 48%	4560
	11th to 20th	Night	7% 20% 7% 13% 7% 7% 5% 4 5% 6% 18%	5176
	21st to end	Night	10% 18% 6% 13% 6% 6% 5% 4 4 5% 22%	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	62% 8% 10% 11% 5% 3	3639
	11th to 20th	Day	39% 10% 6% 16% 20% 9%	3701
	21st to end	Day	46% 6% 7% 11% 15% 16%	4510
February	1st to 10th	Day	55% 7% 12% 14% 9% 2	1800
	11th to 20th	Day	56% 6% 11% 14% 11% 3	1764
	21st to end	Day	58% 6% 12% 10% 11% 4	1635
March	1st to 10th	Day	51% 7% 9% 17% 12% 3	4725
	11th to 20th	Day	53% 6% 9% 17% 15% 1	5000
	21st to end	Day	59% 11% 12% 14% 4	5634
April	1st to 10th	Day	59% 6% 12% 13% 8% 2	2400
	11th to 20th	Day	51% 5% 13% 15% 12% 3	2372
	21st to end	Day	45% 7% 15% 20% 12% 1	2475
May	1st to 10th	Day	34% 5% 9% 22% 25% 4	6115
	11th to 20th	Day	32% 9% 8% 21% 26% 4	6280
	21st to end	Day	26% 7% 14% 39% 13%	6904
June	1st to 10th	Day	38% 7% 13% 25% 15% 1	2789
	11th to 20th	Day	30% 6% 13% 28% 19% 4	2660
	21st to end	Day	20% 3 9% 27% 29% 11%	2660
July	1st to 10th	Day	7% 2 5% 13% 21% 52%	4351
	11th to 20th	Day	13% 2 4 10% 24% 47%	4345
	21st to end	Day	8% 1 3 16% 42% 29%	4555
August	1st to 10th	Day	17% 3 4 16% 29% 31%	4076
	11th to 20th	Day	14% 3 5% 27% 36% 15%	4065
	21st to end	Day	16% 3 5% 27% 30% 19%	4179
September	1st to 10th	Day	13% 2 5% 21% 34% 25%	2280
	11th to 20th	Day	27% 4 8% 22% 28% 12%	2280
	21st to end	Day	28% 3 8% 22% 26% 13%	2013
October	1st to 10th	Day	22% 4 7% 17% 32% 17%	3180
	11th to 20th	Day	33% 9% 14% 23% 17% 4	3161
	21st to end	Day	41% 9% 7% 19% 18% 5%	3423
November	1st to 10th	Day	51% 6% 11% 14% 16% 3	1764
	11th to 20th	Day	56% 7% 12% 11% 10% 4	1619
	21st to end	Day	53% 5% 10% 12% 14% 8%	1600
December	1st to 10th	Day	35% 7% 6% 16% 24% 12%	2620
	11th to 20th	Day	63% 7% 11% 12% 6%	3028
	21st to end	Day	67% 11% 5% 10% 5% 1	4004
January	1st to 10th	Night	59% 11% 9% 10% 7% 3	6306
	11th to 20th	Night	39% 9% 5% 16% 20% 11%	6259
	21st to end	Night	50% 6% 5% 7% 15% 17%	6468
February	1st to 10th	Night	54% 7% 13% 13% 11% 2	2600
	11th to 20th	Night	55% 5% 10% 16% 10% 4	2534
	21st to end	Night	53% 8% 11% 14% 10% 3	1995
March	1st to 10th	Night	49% 10% 12% 15% 10% 4	5166
	11th to 20th	Night	51% 8% 10% 18% 14%	5000
	21st to end	Night	57% 11% 12% 14% 5%	5341
April	1st to 10th	Night	54% 7% 14% 15% 9% 1	2000
	11th to 20th	Night	48% 6% 13% 18% 11% 4	1979
	21st to end	Night	45% 8% 13% 20% 12% 2	1920
May	1st to 10th	Night	32% 6% 9% 23% 24% 6%	3849
	11th to 20th	Night	33% 10% 9% 21% 25% 2	3616
	21st to end	Night	22% 7% 18% 41% 11% 1	3972
June	1st to 10th	Night	40% 6% 12% 27% 14% 2	1595
	11th to 20th	Night	27% 6% 12% 30% 21% 4	1520
	21st to end	Night	19% 3 9% 32% 29% 9%	1520
July	1st to 10th	Night	8% 2 5% 13% 19% 54%	2500
	11th to 20th	Night	11% 2 3 12% 25% 47%	2492
	21st to end	Night	9% 2 3 15% 42% 29%	2757
August	1st to 10th	Night	16% 3 4 16% 32% 28%	2839
	11th to 20th	Night	13% 3 4 29% 35% 17%	2839
	21st to end	Night	15% 4 6% 27% 28% 21%	3497
September	1st to 10th	Night	11% 2 5% 23% 35% 24%	1900
	11th to 20th	Night	23% 4 10% 22% 29% 13%	1900
	21st to end	Night	25% 3 9% 24% 22% 17%	2163
October	1st to 10th	Night	21% 3 7% 19% 31% 19%	3800
	11th to 20th	Night	32% 5% 15% 23% 19% 6%	3777
	21st to end	Night	43% 10% 8% 16% 16% 7%	4143
November	1st to 10th	Night	53% 4 10% 14% 15% 4	2535
	11th to 20th	Night	56% 7% 11% 11% 12% 3	2780
	21st to end	Night	50% 6% 9% 12% 14% 9%	2800
December	1st to 10th	Night	34% 7% 6% 14% 26% 13%	4560
	11th to 20th	Night	64% 9% 8% 11% 7% 1	5176
	21st to end	Night	61% 9% 8% 12% 9% 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	36% 29% 19% 9% 7% 1	200
	11th to 20th	Day	33% 15% 23% 18% 7% 4	222
	21st to end	Day	25% 22% 21% 20% 11% 2	440
February	1st to 10th	Day	30% 19% 26% 18% 7% 1	400
	11th to 20th	Day	30% 25% 22% 15% 7%	395
	21st to end	Day	29% 19% 26% 20% 5% 1	407
March	1st to 10th	Day	30% 25% 21% 20% 4	500
	11th to 20th	Day	25% 22% 24% 20% 8% 1	500
	21st to end	Day	31% 22% 26% 17% 3	550
April	1st to 10th	Day	27% 21% 26% 17% 7% 2	500
	11th to 20th	Day	29% 19% 28% 15% 6% 2	492
	21st to end	Day	21% 26% 23% 20% 9% 2	500
May	1st to 10th	Day	18% 21% 31% 20% 8% 2	503
	11th to 20th	Day	29% 17% 21% 18% 12% 3	528
	21st to end	Day	21% 14% 25% 22% 14% 4	573
June	1st to 10th	Day	16% 16% 26% 21% 17% 3	527
	11th to 20th	Day	15% 19% 30% 23% 10% 2	490
	21st to end	Day	6% 13% 28% 30% 18% 6%	490
July	1st to 10th	Day	6% 8% 34% 33% 16% 4	486
	11th to 20th	Day	2 9% 36% 31% 17% 5%	484
	21st to end	Day	2 7% 33% 33% 18% 8%	531
August	1st to 10th	Day	2 7% 29% 33% 21% 8%	487
	11th to 20th	Day	5% 9% 25% 31% 22% 8%	477
	21st to end	Day	6% 9% 28% 31% 21% 5%	539
September	1st to 10th	Day	4 8% 29% 33% 21% 4	490
	11th to 20th	Day	13% 12% 25% 32% 16% 2	490
	21st to end	Day	13% 13% 28% 28% 17% 2	490
October	1st to 10th	Day	19% 14% 25% 25% 15% 2	490
	11th to 20th	Day	19% 12% 25% 24% 18% 2	490
	21st to end	Day	25% 16% 25% 17% 14% 4	526
November	1st to 10th	Day	25% 16% 24% 20% 14% 1	300
	11th to 20th	Day	24% 13% 32% 16% 11% 3	209
	21st to end	Day	28% 19% 17% 23% 13% 2	200
December	1st to 10th	Day	25% 17% 21% 22% 12% 5%	200
	11th to 20th	Day	34% 17% 24% 17% 8% 1	200
	21st to end	Day	31% 22% 20% 16% 10%	220
January	1st to 10th	Night	28% 17% 22% 19% 11% 3	800
	11th to 20th	Night	24% 16% 19% 24% 15% 3	800
	21st to end	Night	22% 14% 18% 26% 16% 4	880
February	1st to 10th	Night	24% 14% 23% 26% 13% 1	800
	11th to 20th	Night	20% 19% 21% 26% 13% 1	784
	21st to end	Night	23% 16% 24% 28% 8% 1	660
March	1st to 10th	Night	23% 19% 21% 24% 12% 2	800
	11th to 20th	Night	23% 14% 18% 28% 17% 1	800
	21st to end	Night	26% 19% 22% 23% 9% 1	880
April	1st to 10th	Night	23% 14% 23% 26% 12% 2	800
	11th to 20th	Night	16% 19% 24% 21% 16% 3	791
	21st to end	Night	15% 14% 24% 28% 17% 2	720
May	1st to 10th	Night	17% 11% 23% 29% 18% 3	495
	11th to 20th	Night	16% 11% 15% 34% 22% 3	394
	21st to end	Night	15% 6% 19% 31% 24% 4	433
June	1st to 10th	Night	18% 7% 14% 33% 27% 2	399
	11th to 20th	Night	7% 8% 21% 41% 21% 2	380
	21st to end	Night	8% 3 12% 46% 30% 2	380
July	1st to 10th	Night	3 1 10% 44% 40% 2	370
	11th to 20th	Night	3 1 8% 57% 30% 1	368
	21st to end	Night	2 1 7% 47% 38% 5%	465
August	1st to 10th	Night	2 1 7% 43% 42% 6%	567
	11th to 20th	Night	2 7% 37% 47% 7%	564
	21st to end	Night	4 2 15% 45% 31% 3	835
September	1st to 10th	Night	3 3 14% 43% 33% 4	760
	11th to 20th	Night	8% 6% 11% 34% 35% 6%	760
	21st to end	Night	13% 6% 13% 33% 28% 7%	760
October	1st to 10th	Night	10% 8% 18% 35% 26% 4	760
	11th to 20th	Night	17% 8% 14% 31% 26% 4	760
	21st to end	Night	19% 11% 19% 29% 17% 6%	836
November	1st to 10th	Night	22% 14% 19% 26% 15% 3	780
	11th to 20th	Night	28% 14% 19% 26% 12% 2	800
	21st to end	Night	20% 15% 21% 26% 15% 3	800
December	1st to 10th	Night	22% 12% 21% 27% 15% 3	800
	11th to 20th	Night	27% 16% 19% 24% 13% 2	800
	21st to end	Night	27% 21% 22% 21% 7% 1	880

Page generated at 2025-06-07 07:28:15. Version ac07

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