Raven Run Nature Conservancy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Raven Run Nature Conservancy clear sky chart from 2005-11-06 to 2025-11-18.

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	14% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	126874
	Night	15% 9% 3 7% 5% 4 4 3 5% 7% 38%	123472
Transparency	Day	44% 7% 11% 22% 15% 2	130561
	Night	43% 6% 10% 22% 16% 3	127853
Seeing	Day	18% 10% 24% 23% 17% 9%	16290
	Night	17% 8% 24% 30% 18% 2	26121

By Month

Percentage Cloud Cover SE (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% 15% 7% 9% 5% 4 4 3 5% 6% 26%	4056
	11th to 20th	Day	14% 14% 7% 15% 4 4 3 2 3 4 31%	4060
	21st to end	Day	21% 11% 6% 7% 5% 4 3 3 4 5% 30%	4466
February	1st to 10th	Day	19% 12% 5% 9% 5% 3 4 3 4 6% 30%	1945
	11th to 20th	Day	20% 11% 4 8% 6% 4 3 3 5% 4 32%	1948
	21st to end	Day	20% 12% 3 7% 5% 4 3 4 5% 5% 32%	1650
March	1st to 10th	Day	19% 12% 3 7% 4 4 5% 3 3 5% 35%	4543
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 6% 8% 43%	4980
	21st to end	Day	15% 9% 3 8% 5% 4 4 4 5% 7% 36%	5465
April	1st to 10th	Day	15% 8% 3 7% 5% 4 3 4 6% 7% 39%	2335
	11th to 20th	Day	15% 8% 2 6% 4 4 5% 4 5% 6% 40%	2407
	21st to end	Day	16% 8% 3 8% 5% 5% 5% 3 6% 7% 36%	2600
May	1st to 10th	Day	18% 9% 4 9% 5% 6% 6% 5% 7% 8% 26%	5862
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 6% 33%	5861
	21st to end	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 10% 33%	6433
June	1st to 10th	Day	11% 5% 2 6% 6% 6% 5% 4 6% 7% 41%	2600
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 7% 9% 42%	2600
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 5% 8% 10% 41%	2731
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 4 4 6% 9% 42%	6043
	11th to 20th	Day	9% 6% 2 7% 5% 6% 7% 6% 8% 10% 34%	5900
	21st to end	Day	14% 8% 3 8% 6% 6% 6% 5% 6% 9% 28%	6424
August	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 7% 10% 45%	4234
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 11% 37%	4141
	21st to end	Day	6% 4 1 4 4 4 5% 3 6% 9% 54%	4312
September	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 5% 6% 8% 42%	2260
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 47%	2200
	21st to end	Day	15% 6% 2 6% 4 3 3 3 5% 6% 46%	2200
October	1st to 10th	Day	10% 4 2 5% 4 4 3 3 5% 6% 55%	2200
	11th to 20th	Day	13% 6% 1 6% 4 3 4 3 4 6% 51%	2045
	21st to end	Day	19% 8% 2 5% 3 3 4 3 4 6% 44%	2089
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 4 6% 51%	1852
	11th to 20th	Day	16% 9% 2 6% 4 3 3 3 4 6% 43%	1863
	21st to end	Day	17% 11% 4 6% 4 3 3 3 4 6% 39%	1800
December	1st to 10th	Day	17% 10% 4 8% 4 4 4 3 4 4 39%	2930
	11th to 20th	Day	21% 13% 5% 8% 5% 5% 4 3 4 5% 28%	3373
	21st to end	Day	20% 16% 4 10% 5% 5% 5% 3 5% 5% 22%	4466
January	1st to 10th	Night	16% 15% 6% 14% 5% 4 4 3 5% 5% 24%	5889
	11th to 20th	Night	18% 14% 5% 11% 6% 4 4 2 3 4 29%	5900
	21st to end	Night	20% 9% 4 7% 4 4 3 3 4 5% 37%	6490
February	1st to 10th	Night	21% 11% 4 9% 5% 3 4 3 5% 6% 29%	2450
	11th to 20th	Night	22% 11% 3 9% 4 3 3 3 4 6% 31%	2338
	21st to end	Night	22% 11% 3 8% 5% 4 4 2 5% 5% 31%	1980
March	1st to 10th	Night	19% 13% 2 6% 4 4 4 3 4 5% 36%	5309
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 5% 7% 48%	4980
	21st to end	Night	15% 8% 3 8% 6% 5% 4 4 5% 6% 35%	5467
April	1st to 10th	Night	12% 7% 2 6% 4 5% 5% 4 6% 7% 42%	2080
	11th to 20th	Night	14% 8% 2 6% 5% 4 4 3 5% 6% 43%	1941
	21st to end	Night	16% 7% 2 6% 6% 5% 4 4 5% 7% 38%	1800
May	1st to 10th	Night	19% 10% 4 8% 6% 5% 5% 4 6% 8% 26%	4033
	11th to 20th	Night	18% 8% 3 8% 6% 4 5% 4 6% 8% 31%	4032
	21st to end	Night	12% 6% 3 7% 5% 5% 5% 4 6% 9% 37%	4421
June	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 8% 11% 46%	1800
	11th to 20th	Night	6% 4 2 5% 4 4 5% 5% 8% 10% 47%	1800
	21st to end	Night	6% 4 2 5% 4 4 6% 4 9% 12% 43%	1649
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 4 5% 6% 9% 46%	3882
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 5% 7% 11% 40%	4057
	21st to end	Night	12% 7% 3 7% 5% 5% 6% 5% 8% 10% 32%	4427
August	1st to 10th	Night	8% 5% 2 6% 4 4 5% 3 6% 9% 46%	2915
	11th to 20th	Night	6% 5% 2 7% 5% 6% 5% 4 7% 8% 44%	2903
	21st to end	Night	4 3 1 4 3 3 4 3 5% 9% 60%	3586
September	1st to 10th	Night	11% 5% 2 6% 4 4 3 5% 5% 7% 49%	2120
	11th to 20th	Night	10% 4 2 6% 4 3 4 4 6% 8% 50%	2200
	21st to end	Night	12% 6% 2 6% 4 3 4 3 5% 6% 50%	2200
October	1st to 10th	Night	10% 4 1 5% 3 3 4 3 4 7% 56%	2200
	11th to 20th	Night	13% 6% 1 5% 4 3 3 3 4 8% 50%	2354
	21st to end	Night	17% 7% 2 5% 4 3 4 3 4 6% 45%	2749
November	1st to 10th	Night	12% 6% 3 6% 3 3 3 3 5% 6% 50%	2666
	11th to 20th	Night	15% 8% 3 5% 3 3 4 3 4 7% 45%	2692
	21st to end	Night	17% 10% 3 6% 4 3 3 3 5% 6% 40%	2600
December	1st to 10th	Night	18% 12% 3 8% 4 3 3 2 3 4 37%	4250
	11th to 20th	Night	21% 10% 5% 7% 4 4 3 2 4 5% 34%	4822
	21st to end	Night	18% 14% 5% 10% 6% 6% 5% 4 4 6% 21%	6490

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	57% 5% 10% 20% 7% 1	4057
	11th to 20th	Day	58% 5% 6% 17% 13% 2	4060
	21st to end	Day	56% 3 9% 20% 10% 2	4466
February	1st to 10th	Day	56% 5% 8% 19% 10% 1	1945
	11th to 20th	Day	55% 5% 8% 18% 11% 3	1958
	21st to end	Day	53% 6% 8% 20% 11% 3	1650
March	1st to 10th	Day	51% 4 7% 16% 16% 6%	4543
	11th to 20th	Day	38% 5% 11% 25% 20% 2	4980
	21st to end	Day	45% 7% 11% 25% 11% 1	5465
April	1st to 10th	Day	44% 6% 11% 23% 13% 3	2335
	11th to 20th	Day	44% 5% 10% 22% 15% 4	2407
	21st to end	Day	46% 7% 10% 23% 11% 2	2600
May	1st to 10th	Day	52% 9% 12% 18% 9% 1	5897
	11th to 20th	Day	50% 7% 12% 20% 10%	5865
	21st to end	Day	42% 8% 16% 19% 13% 1	6447
June	1st to 10th	Day	39% 9% 10% 25% 16% 1	2600
	11th to 20th	Day	36% 10% 14% 22% 17% 2	2600
	21st to end	Day	35% 11% 15% 19% 16% 4	2731
July	1st to 10th	Day	37% 7% 13% 23% 18% 1	5978
	11th to 20th	Day	40% 11% 14% 25% 8% 1	5831
	21st to end	Day	50% 8% 13% 19% 10% 1	6240
August	1st to 10th	Day	32% 9% 14% 33% 11% 1	4221
	11th to 20th	Day	37% 8% 13% 27% 13% 2	4180
	21st to end	Day	26% 8% 12% 33% 19% 3	4311
September	1st to 10th	Day	39% 8% 13% 17% 18% 5%	2260
	11th to 20th	Day	33% 6% 12% 23% 22% 3	2200
	21st to end	Day	39% 6% 9% 23% 21% 3	2200
October	1st to 10th	Day	22% 4 7% 25% 40% 3	3590
	11th to 20th	Day	24% 4 10% 28% 31% 3	3311
	21st to end	Day	31% 4 8% 29% 20% 9%	3352
November	1st to 10th	Day	35% 4 8% 26% 23% 4	1852
	11th to 20th	Day	42% 3 8% 23% 19% 4	1863
	21st to end	Day	48% 5% 8% 20% 18% 2	1800
December	1st to 10th	Day	50% 3 7% 23% 16% 1	2930
	11th to 20th	Day	59% 5% 8% 16% 11% 1	3370
	21st to end	Day	62% 7% 11% 15% 5% 1	4466
January	1st to 10th	Night	61% 6% 8% 16% 8% 1	5889
	11th to 20th	Night	59% 4 6% 16% 11% 3	5900
	21st to end	Night	50% 4 8% 22% 14% 2	6490
February	1st to 10th	Night	56% 5% 11% 18% 10% 1	2450
	11th to 20th	Night	55% 5% 7% 19% 12% 2	2339
	21st to end	Night	56% 5% 9% 15% 12% 3	1980
March	1st to 10th	Night	50% 4 7% 22% 13% 4	5309
	11th to 20th	Night	35% 5% 10% 26% 21% 3	4980
	21st to end	Night	48% 5% 9% 23% 13% 1	5467
April	1st to 10th	Night	39% 8% 12% 21% 17% 3	2080
	11th to 20th	Night	41% 6% 8% 21% 18% 6%	1941
	21st to end	Night	43% 8% 12% 22% 14% 2	1800
May	1st to 10th	Night	52% 10% 10% 18% 8% 2	4060
	11th to 20th	Night	49% 9% 12% 20% 9% 1	4033
	21st to end	Night	39% 10% 15% 21% 12% 2	4429
June	1st to 10th	Night	30% 8% 16% 26% 17% 4	1800
	11th to 20th	Night	29% 11% 17% 23% 19% 3	1800
	21st to end	Night	30% 10% 17% 22% 16% 5%	1649
July	1st to 10th	Night	34% 9% 12% 24% 20% 2	3839
	11th to 20th	Night	35% 11% 17% 24% 11% 1	4006
	21st to end	Night	43% 9% 13% 21% 13% 1	4297
August	1st to 10th	Night	32% 8% 15% 30% 14% 1	2904
	11th to 20th	Night	35% 8% 12% 28% 16% 1	2930
	21st to end	Night	21% 6% 14% 33% 22% 4	3586
September	1st to 10th	Night	32% 9% 12% 21% 20% 6%	2120
	11th to 20th	Night	31% 6% 13% 24% 24% 3	2200
	21st to end	Night	35% 7% 8% 22% 24% 4	2200
October	1st to 10th	Night	22% 4 8% 23% 40% 3	3590
	11th to 20th	Night	25% 4 7% 26% 34% 6%	3827
	21st to end	Night	30% 3 8% 22% 30% 7%	4436
November	1st to 10th	Night	35% 4 9% 25% 23% 4	2666
	11th to 20th	Night	40% 4 8% 21% 22% 5%	2692
	21st to end	Night	46% 4 8% 24% 16% 2	2600
December	1st to 10th	Night	51% 3 10% 21% 14% 1	4250
	11th to 20th	Night	52% 4 11% 20% 12% 1	4824
	21st to end	Night	62% 7% 9% 14% 6%	6490

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	26% 19% 33% 16% 6% 1	300
	11th to 20th	Day	28% 23% 31% 14% 4	300
	21st to end	Day	21% 22% 37% 16% 3	330
February	1st to 10th	Day	28% 16% 37% 14% 4	300
	11th to 20th	Day	35% 19% 33% 10% 4	300
	21st to end	Day	32% 17% 36% 12% 3	249
March	1st to 10th	Day	26% 20% 35% 12% 7%	324
	11th to 20th	Day	22% 18% 36% 19% 5% 1	500
	21st to end	Day	27% 15% 30% 20% 6% 1	550
April	1st to 10th	Day	19% 17% 30% 22% 10% 2	500
	11th to 20th	Day	21% 15% 27% 22% 11% 3	492
	21st to end	Day	21% 12% 29% 24% 9% 4	500
May	1st to 10th	Day	20% 12% 29% 21% 13% 4	503
	11th to 20th	Day	16% 10% 23% 27% 17% 8%	527
	21st to end	Day	15% 6% 22% 25% 18% 13%	573
June	1st to 10th	Day	14% 4 21% 24% 25% 12%	530
	11th to 20th	Day	10% 4 20% 28% 26% 12%	530
	21st to end	Day	8% 4 21% 31% 22% 14%	661
July	1st to 10th	Day	12% 3 16% 24% 21% 24%	590
	11th to 20th	Day	10% 2 17% 25% 27% 18%	524
	21st to end	Day	13% 3 13% 25% 29% 16%	576
August	1st to 10th	Day	13% 2 14% 25% 26% 19%	526
	11th to 20th	Day	12% 3 14% 28% 29% 14%	519
	21st to end	Day	9% 2 12% 28% 29% 20%	583
September	1st to 10th	Day	14% 3 14% 26% 26% 18%	530
	11th to 20th	Day	12% 2 10% 24% 33% 19%	530
	21st to end	Day	18% 7% 16% 24% 24% 10%	530
October	1st to 10th	Day	11% 5% 17% 32% 26% 10%	530
	11th to 20th	Day	13% 11% 26% 30% 15% 6%	530
	21st to end	Day	21% 13% 30% 24% 12% 1	472
November	1st to 10th	Day	18% 10% 31% 25% 12% 4	330
	11th to 20th	Day	23% 17% 27% 26% 6% 1	321
	21st to end	Day	25% 15% 30% 23% 6% 1	300
December	1st to 10th	Day	25% 20% 28% 22% 4 1	300
	11th to 20th	Day	23% 14% 36% 19% 9%	300
	21st to end	Day	29% 17% 32% 18% 4	330
January	1st to 10th	Night	23% 15% 33% 23% 5%	800
	11th to 20th	Night	29% 16% 30% 22% 3	800
	21st to end	Night	23% 14% 36% 25% 2	880
February	1st to 10th	Night	27% 12% 33% 26% 2	800
	11th to 20th	Night	29% 14% 36% 20% 2	783
	21st to end	Night	27% 14% 37% 20% 2	660
March	1st to 10th	Night	22% 16% 30% 27% 6%	800
	11th to 20th	Night	23% 11% 34% 25% 7%	800
	21st to end	Night	20% 13% 31% 28% 8%	880
April	1st to 10th	Night	17% 12% 32% 31% 8%	680
	11th to 20th	Night	16% 10% 30% 31% 13% 1	593
	21st to end	Night	17% 7% 34% 32% 10% 1	600
May	1st to 10th	Night	19% 7% 28% 30% 15% 2	600
	11th to 20th	Night	16% 6% 20% 36% 20% 2	591
	21st to end	Night	9% 4 15% 37% 30% 5%	650
June	1st to 10th	Night	9% 2 17% 44% 25% 3	600
	11th to 20th	Night	7% 2 14% 39% 33% 5%	600
	21st to end	Night	7% 3 15% 38% 33% 5%	600
July	1st to 10th	Night	7% 2 12% 35% 35% 9%	585
	11th to 20th	Night	6% 2 9% 35% 42% 5%	582
	21st to end	Night	11% 3 8% 33% 39% 6%	657
August	1st to 10th	Night	9% 3 8% 32% 43% 6%	597
	11th to 20th	Night	7% 3 10% 35% 38% 6%	594
	21st to end	Night	6% 1 10% 32% 42% 8%	660
September	1st to 10th	Night	12% 2 9% 34% 37% 6%	720
	11th to 20th	Night	11% 3 12% 29% 39% 6%	800
	21st to end	Night	14% 3 17% 34% 30% 3	800
October	1st to 10th	Night	11% 4 15% 34% 31% 4	800
	11th to 20th	Night	16% 6% 24% 35% 17% 2	800
	21st to end	Night	21% 8% 27% 31% 13% 1	880
November	1st to 10th	Night	15% 7% 25% 34% 17% 2	820
	11th to 20th	Night	19% 11% 31% 30% 9% 1	829
	21st to end	Night	21% 11% 26% 32% 10% 1	800
December	1st to 10th	Night	26% 10% 30% 28% 6%	800
	11th to 20th	Night	25% 10% 31% 28% 6% 1	800
	21st to end	Night	25% 15% 27% 28% 4	880

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