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 2026-10-14.

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 9% 3 7% 4 4 4 3 5% 6% 52%	158691
	Night	5% 9% 4 9% 5% 4 4 3 5% 5% 47%	150497
Transparency	Day	33% 6% 8% 19% 21% 12%	153524
	Night	38% 7% 8% 18% 18% 12%	146659
Seeing	Day	19% 16% 26% 23% 13% 3	17307
	Night	17% 11% 18% 30% 20% 3	26303

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% 20% 8% 17% 7% 6% 5% 4 4 5% 18%	4722
	11th to 20th	Day	7% 10% 3 7% 3 3 2 2 4 5% 53%	4815
	21st to end	Day	6% 14% 4 8% 5% 5% 5% 4 5% 6% 37%	5843
February	1st to 10th	Day	9% 16% 6% 9% 6% 4 5% 5% 6% 7% 27%	1890
	11th to 20th	Day	6% 17% 7% 13% 7% 6% 4 3 4 6% 27%	1845
	21st to end	Day	6% 17% 8% 15% 6% 5% 4 4 4 5% 26%	1714
March	1st to 10th	Day	5% 16% 8% 14% 6% 4 3 3 6% 7% 30%	4829
	11th to 20th	Day	5% 18% 6% 12% 6% 4 5% 3 4 4 34%	5110
	21st to end	Day	4 21% 8% 13% 7% 6% 5% 4 5% 7% 21%	5758
April	1st to 10th	Day	8% 18% 7% 12% 5% 5% 3 3 5% 6% 27%	2520
	11th to 20th	Day	8% 17% 5% 10% 5% 4 4 4 4 6% 32%	2489
	21st to end	Day	4 15% 5% 10% 5% 3 4 4 5% 7% 37%	2599
May	1st to 10th	Day	5% 7% 3 6% 4 4 4 4 6% 6% 50%	7925
	11th to 20th	Day	3 5% 2 7% 4 4 4 4 6% 6% 53%	8160
	21st to end	Day	5% 6% 3 6% 4 3 4 3 5% 8% 52%	8992
June	1st to 10th	Day	8% 9% 3 6% 4 4 4 4 6% 7% 44%	2940
	11th to 20th	Day	4 6% 2 7% 4 4 4 3 5% 6% 55%	2940
	21st to end	Day	4 4 1 4 3 2 3 3 4 5% 66%	2940
July	1st to 10th	Day	1 1 1 2 2 2 2 2 3 4 81%	8219
	11th to 20th	Day	3 2 1 2 2 2 3 2 3 4 76%	8220
	21st to end	Day	1 2 1 2 2 2 2 2 3 3 80%	8758
August	1st to 10th	Day	2 2 1 2 2 2 2 2 5% 5% 75%	7547
	11th to 20th	Day	2 2 1 2 2 2 3 3 4 5% 74%	7563
	21st to end	Day	4 3 1 3 2 2 3 2 4 5% 69%	7750
September	1st to 10th	Day	2 2 1 4 2 3 3 3 4 5% 72%	2520
	11th to 20th	Day	5% 5% 2 5% 4 4 4 3 5% 6% 58%	2520
	21st to end	Day	4 6% 2 7% 3 3 3 3 4 6% 59%	2225
October	1st to 10th	Day	4 5% 2 4 3 2 2 3 3 5% 66%	3380
	11th to 20th	Day	5% 5% 3 7% 5% 4 5% 4 7% 7% 47%	3292
	21st to end	Day	6% 11% 3 9% 5% 4 5% 4 7% 7% 39%	3532
November	1st to 10th	Day	9% 14% 5% 10% 6% 5% 4 3 5% 9% 32%	1854
	11th to 20th	Day	8% 15% 6% 11% 7% 5% 6% 5% 6% 5% 26%	1700
	21st to end	Day	7% 14% 5% 12% 6% 4 4 4 5% 7% 32%	1680
December	1st to 10th	Day	4 8% 3 8% 5% 4 4 4 6% 7% 46%	2700
	11th to 20th	Day	8% 19% 6% 12% 7% 6% 5% 4 7% 7% 19%	3108
	21st to end	Day	8% 19% 7% 15% 8% 7% 6% 4 5% 4 16%	4092
January	1st to 10th	Night	5% 18% 6% 16% 9% 7% 6% 5% 5% 6% 16%	8172
	11th to 20th	Night	4 10% 3 10% 4 3 3 2 4 5% 53%	8146
	21st to end	Night	7% 11% 5% 11% 7% 7% 6% 4 4 5% 35%	8371
February	1st to 10th	Night	7% 13% 5% 12% 7% 5% 4 5% 6% 6% 30%	2730
	11th to 20th	Night	6% 15% 5% 13% 8% 5% 4 4 5% 5% 30%	2662
	21st to end	Night	6% 15% 5% 14% 7% 5% 4 3 7% 6% 28%	2091
March	1st to 10th	Night	4 11% 6% 16% 8% 5% 5% 4 7% 6% 27%	5282
	11th to 20th	Night	3 14% 6% 13% 7% 5% 5% 4 4 5% 34%	5110
	21st to end	Night	3 14% 7% 17% 9% 7% 6% 4 6% 6% 21%	5459
April	1st to 10th	Night	7% 14% 5% 12% 8% 5% 5% 4 6% 7% 27%	2100
	11th to 20th	Night	4 12% 5% 13% 7% 5% 5% 4 5% 7% 33%	2079
	21st to end	Night	5% 11% 5% 10% 5% 5% 5% 5% 6% 7% 37%	2016
May	1st to 10th	Night	5% 6% 2 7% 3 4 4 2 4 5% 56%	5005
	11th to 20th	Night	2 5% 3 8% 4 4 5% 4 6% 7% 52%	4700
	21st to end	Night	5% 5% 2 6% 4 3 3 3 5% 6% 58%	5181
June	1st to 10th	Night	9% 8% 3 8% 4 5% 3 4 4 6% 46%	1680
	11th to 20th	Night	3 5% 2 6% 4 4 4 3 5% 6% 60%	1680
	21st to end	Night	4 3 1 4 3 3 2 2 3 5% 69%	1680
July	1st to 10th	Night	2 2 1 3 2 2 2 2 2 3 80%	4740
	11th to 20th	Night	3 3 1 3 2 2 2 2 2 3 79%	4740
	21st to end	Night	2 3 1 2 1 2 2 2 2 3 80%	5322
August	1st to 10th	Night	1 2 1 2 2 2 2 2 5% 6% 76%	5275
	11th to 20th	Night	1 1 1 3 2 2 3 2 4 6% 74%	5292
	21st to end	Night	4 3 1 3 2 2 3 2 4 6% 71%	6498
September	1st to 10th	Night	2 2 1 3 2 2 3 2 4 4 74%	2100
	11th to 20th	Night	4 4 2 5% 3 4 3 3 4 6% 62%	2100
	21st to end	Night	5% 6% 2 4 3 3 3 3 4 6% 61%	2391
October	1st to 10th	Night	3 4 2 5% 3 2 2 2 3 4 70%	4040
	11th to 20th	Night	5% 6% 3 7% 4 4 4 4 5% 6% 53%	3933
	21st to end	Night	4 7% 4 10% 8% 5% 6% 5% 7% 7% 37%	4276
November	1st to 10th	Night	10% 12% 5% 11% 7% 5% 4 3 4 6% 32%	2665
	11th to 20th	Night	8% 12% 6% 12% 8% 6% 6% 5% 6% 6% 24%	2919
	21st to end	Night	6% 13% 4 9% 6% 5% 6% 4 6% 6% 35%	2940
December	1st to 10th	Night	6% 7% 3 7% 4 4 4 4 6% 7% 48%	4700
	11th to 20th	Night	7% 20% 7% 13% 7% 6% 5% 4 5% 6% 19%	5316
	21st to end	Night	10% 18% 6% 13% 6% 6% 5% 4 4 5% 22%	7106

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	63% 10% 10% 11% 4 2	4723
	11th to 20th	Day	30% 9% 5% 13% 19% 25%	4815
	21st to end	Day	46% 8% 7% 11% 13% 16%	5843
February	1st to 10th	Day	54% 7% 12% 14% 10% 3	1890
	11th to 20th	Day	56% 6% 11% 13% 11% 3	1854
	21st to end	Day	59% 6% 11% 10% 11% 4	1714
March	1st to 10th	Day	51% 8% 9% 17% 12% 3	4829
	11th to 20th	Day	53% 7% 9% 16% 15% 1	5110
	21st to end	Day	58% 11% 12% 14% 4 1	5758
April	1st to 10th	Day	58% 7% 12% 14% 8% 2	2520
	11th to 20th	Day	52% 5% 13% 15% 12% 3	2492
	21st to end	Day	45% 6% 15% 20% 13% 2	2599
May	1st to 10th	Day	31% 7% 9% 24% 25% 3	7925
	11th to 20th	Day	29% 8% 9% 25% 26% 4	8163
	21st to end	Day	28% 7% 13% 38% 13% 1	8994
June	1st to 10th	Day	37% 7% 13% 26% 16% 1	2940
	11th to 20th	Day	29% 6% 12% 27% 22% 5%	2940
	21st to end	Day	21% 4 9% 27% 28% 11%	2940
July	1st to 10th	Day	10% 2 3 22% 32% 30%	8151
	11th to 20th	Day	14% 2 4 9% 28% 43%	8145
	21st to end	Day	11% 2 3 21% 40% 22%	8561
August	1st to 10th	Day	12% 2 3 12% 27% 43%	5976
	11th to 20th	Day	15% 3 5% 31% 34% 11%	5962
	21st to end	Day	16% 3 4 27% 36% 14%	6077
September	1st to 10th	Day	15% 3 5% 20% 33% 24%	2520
	11th to 20th	Day	26% 4 8% 22% 29% 11%	2520
	21st to end	Day	28% 3 8% 22% 26% 14%	2225
October	1st to 10th	Day	23% 4 7% 17% 32% 17%	3380
	11th to 20th	Day	33% 9% 14% 22% 17% 5%	3292
	21st to end	Day	41% 9% 7% 20% 18% 5%	3532
November	1st to 10th	Day	50% 6% 11% 14% 15% 3	1854
	11th to 20th	Day	57% 7% 12% 11% 10% 4	1700
	21st to end	Day	51% 5% 9% 13% 14% 7%	1680
December	1st to 10th	Day	36% 7% 7% 16% 23% 12%	2700
	11th to 20th	Day	62% 7% 11% 12% 6% 1	3108
	21st to end	Day	66% 11% 5% 10% 6% 1	4092
January	1st to 10th	Night	60% 13% 8% 11% 5% 3	8172
	11th to 20th	Night	31% 7% 4 13% 19% 27%	8146
	21st to end	Night	51% 6% 5% 7% 13% 18%	8371
February	1st to 10th	Night	53% 7% 12% 13% 12% 3	2730
	11th to 20th	Night	55% 6% 10% 15% 10% 4	2664
	21st to end	Night	54% 8% 11% 14% 10% 3	2091
March	1st to 10th	Night	49% 10% 12% 15% 10% 4	5282
	11th to 20th	Night	50% 8% 10% 17% 14% 1	5110
	21st to end	Night	57% 11% 12% 14% 5% 1	5459
April	1st to 10th	Night	54% 7% 14% 16% 9% 1	2100
	11th to 20th	Night	49% 7% 13% 17% 11% 4	2079
	21st to end	Night	44% 8% 13% 20% 13% 2	2016
May	1st to 10th	Night	29% 5% 9% 28% 24% 5%	5003
	11th to 20th	Night	31% 10% 9% 23% 25% 3	4700
	21st to end	Night	25% 7% 16% 39% 11% 1	5182
June	1st to 10th	Night	39% 6% 11% 27% 15% 2	1680
	11th to 20th	Night	26% 5% 11% 29% 23% 6%	1680
	21st to end	Night	19% 4 9% 31% 29% 9%	1680
July	1st to 10th	Night	13% 2 3 22% 28% 32%	4700
	11th to 20th	Night	13% 1 2 12% 27% 44%	4692
	21st to end	Night	12% 2 2 24% 38% 23%	5207
August	1st to 10th	Night	11% 2 3 12% 30% 42%	4169
	11th to 20th	Night	14% 3 6% 29% 36% 13%	4169
	21st to end	Night	15% 3 4 27% 34% 17%	5091
September	1st to 10th	Night	14% 2 5% 22% 34% 23%	2100
	11th to 20th	Night	24% 4 9% 22% 30% 13%	2100
	21st to end	Night	25% 4 8% 24% 22% 17%	2391
October	1st to 10th	Night	21% 3 7% 19% 31% 19%	4040
	11th to 20th	Night	32% 5% 15% 22% 20% 7%	3933
	21st to end	Night	42% 10% 8% 16% 16% 7%	4276
November	1st to 10th	Night	53% 5% 10% 14% 15% 4	2665
	11th to 20th	Night	57% 7% 11% 11% 12% 3	2919
	21st to end	Night	48% 7% 9% 12% 15% 9%	2940
December	1st to 10th	Night	33% 8% 7% 14% 26% 13%	4700
	11th to 20th	Night	63% 9% 8% 11% 7% 1	5316
	21st to end	Night	61% 9% 8% 12% 9% 1	7106

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	37% 29% 19% 8% 6% 1	220
	11th to 20th	Day	30% 14% 22% 20% 9% 5%	243
	21st to end	Day	24% 22% 22% 19% 11% 2	473
February	1st to 10th	Day	29% 18% 26% 18% 7% 1	430
	11th to 20th	Day	31% 25% 23% 15% 7%	425
	21st to end	Day	33% 18% 25% 18% 5% 1	438
March	1st to 10th	Day	31% 26% 21% 19% 4	540
	11th to 20th	Day	26% 23% 24% 19% 8% 1	540
	21st to end	Day	32% 23% 25% 17% 3	594
April	1st to 10th	Day	26% 21% 26% 18% 6% 2	540
	11th to 20th	Day	30% 18% 28% 15% 6% 2	532
	21st to end	Day	21% 26% 23% 19% 9% 2	540
May	1st to 10th	Day	16% 21% 32% 20% 8% 2	543
	11th to 20th	Day	28% 18% 22% 18% 11% 2	568
	21st to end	Day	22% 13% 25% 23% 13% 4	617
June	1st to 10th	Day	17% 17% 26% 21% 16% 3	570
	11th to 20th	Day	14% 19% 29% 25% 11% 2	570
	21st to end	Day	6% 14% 28% 28% 18% 6%	570
July	1st to 10th	Day	5% 9% 32% 33% 17% 4	566
	11th to 20th	Day	3 11% 35% 30% 16% 4	564
	21st to end	Day	3 8% 34% 31% 17% 8%	619
August	1st to 10th	Day	2 7% 29% 33% 20% 8%	567
	11th to 20th	Day	5% 9% 25% 31% 21% 8%	557
	21st to end	Day	7% 9% 28% 31% 20% 5%	627
September	1st to 10th	Day	6% 9% 29% 31% 20% 4	570
	11th to 20th	Day	13% 12% 25% 29% 16% 4	570
	21st to end	Day	13% 13% 27% 29% 16% 2	570
October	1st to 10th	Day	19% 15% 25% 25% 15% 2	570
	11th to 20th	Day	20% 14% 26% 23% 16% 2	543
	21st to end	Day	25% 15% 26% 17% 14% 3	569
November	1st to 10th	Day	26% 17% 23% 20% 13% 1	330
	11th to 20th	Day	24% 14% 31% 17% 11% 3	230
	21st to end	Day	25% 19% 19% 23% 13% 1	220
December	1st to 10th	Day	27% 17% 21% 20% 11% 5%	220
	11th to 20th	Day	36% 15% 22% 18% 8% 1	220
	21st to end	Day	33% 21% 19% 15% 11%	242
January	1st to 10th	Night	29% 18% 21% 19% 10% 3	840
	11th to 20th	Night	23% 15% 19% 25% 15% 3	840
	21st to end	Night	21% 14% 19% 26% 16% 4	924
February	1st to 10th	Night	24% 13% 23% 27% 12% 1	840
	11th to 20th	Night	20% 19% 21% 26% 13% 1	824
	21st to end	Night	24% 15% 24% 28% 8% 1	692
March	1st to 10th	Night	24% 18% 21% 23% 12% 2	840
	11th to 20th	Night	23% 14% 18% 27% 16% 1	840
	21st to end	Night	26% 19% 22% 23% 9% 1	924
April	1st to 10th	Night	23% 14% 23% 26% 13% 2	840
	11th to 20th	Night	17% 19% 24% 21% 16% 3	831
	21st to end	Night	15% 15% 24% 28% 17% 2	756
May	1st to 10th	Night	16% 10% 23% 30% 19% 3	520
	11th to 20th	Night	16% 11% 15% 34% 22% 2	414
	21st to end	Night	16% 7% 18% 31% 24% 4	455
June	1st to 10th	Night	18% 7% 15% 32% 26% 1	420
	11th to 20th	Night	6% 8% 22% 41% 21% 2	420
	21st to end	Night	8% 3 13% 46% 28% 1	420
July	1st to 10th	Night	3 1 11% 43% 39% 2	410
	11th to 20th	Night	4 1 11% 55% 28%	408
	21st to end	Night	3 1 7% 47% 38% 4	515
August	1st to 10th	Night	2 8% 43% 41% 6%	627
	11th to 20th	Night	2 1 8% 38% 46% 6%	624
	21st to end	Night	4 2 16% 45% 31% 2	923
September	1st to 10th	Night	4 4 14% 42% 32% 4	840
	11th to 20th	Night	8% 7% 13% 33% 35% 5%	840
	21st to end	Night	12% 6% 14% 34% 28% 6%	840
October	1st to 10th	Night	11% 8% 18% 34% 26% 4	840
	11th to 20th	Night	17% 9% 15% 31% 25% 4	812
	21st to end	Night	19% 11% 18% 29% 17% 6%	880
November	1st to 10th	Night	23% 14% 19% 27% 15% 3	820
	11th to 20th	Night	28% 14% 19% 26% 12% 2	840
	21st to end	Night	20% 15% 22% 26% 15% 3	840
December	1st to 10th	Night	23% 12% 21% 26% 15% 3	840
	11th to 20th	Night	27% 15% 19% 23% 13% 2	840
	21st to end	Night	28% 21% 22% 21% 7% 1	924

Page generated at 2026-10-11 02:06:33. Version ac07

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