Oak Ridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Ridge clear sky chart from 2005-11-06 to 2024-10-25.

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% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	100897
	Night	14% 6% 2 6% 4 4 4 4 6% 7% 41%	97880
Transparency	Day	42% 6% 12% 22% 15% 3	100709
	Night	41% 5% 12% 22% 16% 3	97737
Seeing	Day	17% 9% 22% 25% 19% 8%	14777
	Night	16% 6% 22% 32% 20% 3	24786

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	18% 11% 3 7% 5% 4 4 4 6% 7% 31%	2836
	11th to 20th	Day	20% 9% 5% 9% 5% 4 3 3 5% 5% 33%	2840
	21st to end	Day	22% 11% 3 7% 4 3 3 3 4 6% 34%	3126
February	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 2 5% 5% 36%	1900
	11th to 20th	Day	22% 8% 3 8% 5% 4 3 2 3 6% 35%	1848
	21st to end	Day	21% 8% 3 7% 4 4 4 4 5% 4 36%	1570
March	1st to 10th	Day	24% 11% 3 7% 4 4 4 3 3 5% 32%	3201
	11th to 20th	Day	14% 6% 3 6% 4 4 3 3 4 6% 48%	3480
	21st to end	Day	15% 8% 3 6% 4 4 5% 4 5% 6% 40%	3815
April	1st to 10th	Day	13% 6% 2 5% 5% 5% 5% 4 6% 7% 43%	2179
	11th to 20th	Day	14% 7% 2 7% 3 4 4 4 4 6% 44%	2259
	21st to end	Day	13% 6% 2 6% 5% 5% 4 4 6% 8% 41%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 4 5% 7% 34%	4082
	11th to 20th	Day	15% 8% 3 8% 5% 5% 4 4 6% 7% 35%	4081
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 5% 7% 8% 39%	4476
June	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 5% 8% 10% 36%	2470
	11th to 20th	Day	5% 3 2 5% 6% 6% 6% 6% 8% 11% 41%	2470
	21st to end	Day	7% 4 2 6% 6% 6% 7% 6% 7% 12% 38%	2470
July	1st to 10th	Day	6% 5% 2 7% 5% 6% 7% 6% 10% 12% 34%	4120
	11th to 20th	Day	10% 5% 2 7% 5% 6% 6% 5% 7% 11% 37%	4120
	21st to end	Day	17% 10% 5% 9% 7% 7% 6% 5% 7% 7% 18%	4466
August	1st to 10th	Day	6% 5% 3 7% 5% 5% 6% 6% 8% 11% 39%	4104
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 4 8% 11% 41%	3921
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 7% 53%	4180
September	1st to 10th	Day	11% 6% 2 6% 4 5% 4 4 6% 9% 42%	2119
	11th to 20th	Day	13% 5% 2 7% 4 5% 4 4 6% 7% 43%	2090
	21st to end	Day	15% 6% 2 4 4 4 4 4 5% 7% 46%	2090
October	1st to 10th	Day	10% 6% 2 4 3 3 4 3 5% 6% 54%	2090
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 4 6% 53%	1958
	21st to end	Day	16% 5% 2 4 3 3 3 3 6% 6% 49%	1987
November	1st to 10th	Day	11% 6% 2 5% 3 3 3 3 3 5% 56%	1672
	11th to 20th	Day	14% 5% 2 6% 4 3 3 3 5% 7% 49%	1710
	21st to end	Day	15% 6% 3 6% 4 3 4 3 4 6% 45%	1710
December	1st to 10th	Day	22% 9% 2 6% 4 4 4 4 4 6% 34%	1710
	11th to 20th	Day	16% 10% 2 7% 4 5% 4 4 6% 6% 36%	2153
	21st to end	Day	20% 10% 3 8% 5% 5% 4 4 5% 7% 30%	3124
January	1st to 10th	Night	17% 9% 3 7% 5% 5% 4 3 4 7% 36%	4109
	11th to 20th	Night	21% 8% 2 6% 5% 4 4 3 4 6% 35%	4120
	21st to end	Night	21% 11% 3 7% 5% 4 4 3 4 6% 33%	4528
February	1st to 10th	Night	17% 8% 2 6% 4 5% 5% 4 6% 7% 37%	2280
	11th to 20th	Night	22% 7% 3 6% 5% 4 4 4 4 5% 35%	2218
	21st to end	Night	24% 8% 2 6% 5% 4 4 3 5% 5% 33%	1884
March	1st to 10th	Night	23% 8% 3 7% 5% 4 4 4 5% 6% 31%	3651
	11th to 20th	Night	11% 6% 3 5% 4 4 4 4 5% 8% 48%	3480
	21st to end	Night	15% 7% 2 7% 4 4 5% 4 5% 7% 41%	3817
April	1st to 10th	Night	13% 4 2 5% 4 5% 4 4 5% 7% 48%	2015
	11th to 20th	Night	13% 7% 2 5% 3 4 4 3 5% 6% 47%	1870
	21st to end	Night	12% 5% 2 6% 5% 4 5% 4 6% 8% 43%	1710
May	1st to 10th	Night	15% 7% 3 8% 5% 5% 5% 4 7% 7% 34%	2813
	11th to 20th	Night	19% 6% 2 6% 4 3 4 4 6% 7% 39%	2812
	21st to end	Night	7% 6% 2 7% 5% 4 5% 4 7% 9% 42%	3079
June	1st to 10th	Night	9% 5% 3 6% 6% 5% 4 4 9% 10% 39%	1710
	11th to 20th	Night	4 3 1 5% 4 4 4 5% 9% 11% 49%	1710
	21st to end	Night	6% 5% 3 6% 5% 6% 5% 4 7% 11% 42%	1710
July	1st to 10th	Night	9% 5% 2 6% 6% 6% 6% 6% 9% 10% 36%	2840
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 4 7% 11% 46%	2840
	21st to end	Night	15% 9% 4 10% 7% 6% 6% 5% 7% 9% 23%	3087
August	1st to 10th	Night	5% 5% 2 6% 4 4 5% 5% 7% 10% 45%	2825
	11th to 20th	Night	8% 5% 2 7% 4 4 4 4 5% 9% 48%	2903
	21st to end	Night	5% 4 1 4 3 4 4 3 6% 9% 56%	3476
September	1st to 10th	Night	10% 5% 2 6% 4 4 6% 4 6% 6% 46%	2040
	11th to 20th	Night	10% 6% 2 7% 6% 4 5% 4 6% 8% 42%	2090
	21st to end	Night	14% 4 2 6% 3 4 3 3 6% 6% 49%	2090
October	1st to 10th	Night	11% 4 2 5% 3 3 2 2 4 6% 56%	2090
	11th to 20th	Night	15% 5% 2 4 3 3 3 2 5% 5% 53%	2220
	21st to end	Night	13% 5% 2 5% 3 3 3 2 3 5% 53%	2473
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 2 4 5% 53%	2406
	11th to 20th	Night	13% 7% 2 5% 3 3 4 3 5% 6% 48%	2470
	21st to end	Night	16% 6% 3 6% 4 4 4 4 5% 7% 43%	2470
December	1st to 10th	Night	21% 8% 2 6% 5% 4 4 3 5% 6% 35%	2470
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 5% 5% 40%	3042
	21st to end	Night	20% 8% 3 7% 6% 6% 6% 5% 6% 7% 26%	4532

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	50% 4 8% 20% 16% 2	2837
	11th to 20th	Day	53% 4 7% 18% 17% 1	2840
	21st to end	Day	51% 4 10% 21% 14%	3126
February	1st to 10th	Day	52% 3 8% 18% 16% 2	1900
	11th to 20th	Day	52% 4 8% 20% 14% 2	1858
	21st to end	Day	51% 4 8% 16% 15% 6%	1570
March	1st to 10th	Day	55% 4 6% 18% 11% 6%	3201
	11th to 20th	Day	39% 4 8% 25% 20% 4	3480
	21st to end	Day	45% 4 8% 28% 13% 2	3815
April	1st to 10th	Day	39% 6% 11% 24% 17% 3	2179
	11th to 20th	Day	40% 5% 8% 18% 24% 4	2259
	21st to end	Day	40% 6% 11% 27% 15% 2	2470
May	1st to 10th	Day	48% 6% 11% 22% 12% 1	4120
	11th to 20th	Day	46% 8% 11% 23% 10% 1	4085
	21st to end	Day	38% 9% 14% 20% 17% 2	4489
June	1st to 10th	Day	39% 10% 14% 22% 14% 2	2470
	11th to 20th	Day	32% 11% 17% 23% 14% 2	2470
	21st to end	Day	36% 10% 17% 19% 14% 4	2470
July	1st to 10th	Day	37% 10% 22% 20% 11% 1	4055
	11th to 20th	Day	39% 7% 21% 24% 7% 2	4051
	21st to end	Day	60% 8% 12% 13% 5% 1	4324
August	1st to 10th	Day	36% 7% 18% 29% 10%	4091
	11th to 20th	Day	35% 7% 18% 24% 15% 1	3960
	21st to end	Day	28% 7% 14% 35% 15% 2	4179
September	1st to 10th	Day	39% 7% 13% 19% 17% 6%	2119
	11th to 20th	Day	39% 7% 11% 22% 18% 3	2090
	21st to end	Day	37% 5% 13% 21% 19% 6%	2090
October	1st to 10th	Day	32% 5% 8% 24% 26% 6%	2090
	11th to 20th	Day	34% 4 9% 22% 24% 7%	1958
	21st to end	Day	36% 3 7% 25% 23% 5%	1987
November	1st to 10th	Day	32% 3 7% 24% 28% 5%	1672
	11th to 20th	Day	36% 3 7% 24% 25% 5%	1710
	21st to end	Day	40% 4 8% 24% 21% 3	1710
December	1st to 10th	Day	51% 5% 7% 23% 12% 2	1710
	11th to 20th	Day	48% 5% 11% 19% 15% 2	2150
	21st to end	Day	52% 5% 11% 21% 9% 1	3124
January	1st to 10th	Night	48% 5% 9% 21% 15% 2	4109
	11th to 20th	Night	48% 4 8% 18% 17% 5%	4120
	21st to end	Night	53% 3 10% 17% 16% 1	4528
February	1st to 10th	Night	46% 4 10% 22% 16% 2	2280
	11th to 20th	Night	51% 4 7% 20% 14% 5%	2219
	21st to end	Night	53% 4 8% 16% 15% 5%	1884
March	1st to 10th	Night	51% 5% 12% 14% 14% 3	3651
	11th to 20th	Night	34% 5% 8% 27% 16% 10%	3480
	21st to end	Night	43% 5% 9% 26% 16% 2	3817
April	1st to 10th	Night	35% 6% 11% 24% 21% 3	2015
	11th to 20th	Night	38% 4 8% 20% 23% 7%	1870
	21st to end	Night	37% 7% 12% 28% 15% 2	1710
May	1st to 10th	Night	45% 8% 12% 22% 10% 1	2840
	11th to 20th	Night	42% 8% 15% 20% 14% 1	2813
	21st to end	Night	34% 9% 14% 24% 17% 1	3087
June	1st to 10th	Night	35% 8% 17% 23% 15% 2	1710
	11th to 20th	Night	25% 9% 22% 28% 15% 2	1710
	21st to end	Night	36% 8% 14% 24% 13% 5%	1710
July	1st to 10th	Night	39% 8% 22% 20% 10% 1	2795
	11th to 20th	Night	32% 6% 22% 28% 8% 3	2786
	21st to end	Night	55% 9% 15% 14% 6% 1	2988
August	1st to 10th	Night	32% 6% 19% 30% 12% 1	2814
	11th to 20th	Night	33% 6% 18% 28% 14% 1	2930
	21st to end	Night	24% 5% 15% 39% 15% 2	3476
September	1st to 10th	Night	36% 8% 14% 19% 17% 6%	2040
	11th to 20th	Night	39% 7% 14% 17% 21% 2	2090
	21st to end	Night	35% 5% 13% 20% 22% 5%	2090
October	1st to 10th	Night	31% 3 8% 23% 26% 9%	2090
	11th to 20th	Night	33% 4 8% 23% 25% 7%	2220
	21st to end	Night	34% 3 5% 23% 27% 8%	2473
November	1st to 10th	Night	34% 3 7% 22% 25% 8%	2406
	11th to 20th	Night	37% 5% 6% 21% 25% 7%	2470
	21st to end	Night	41% 4 7% 25% 21% 3	2470
December	1st to 10th	Night	50% 4 9% 20% 13% 3	2470
	11th to 20th	Night	45% 3 9% 21% 19% 2	3044
	21st to end	Night	53% 6% 12% 16% 13% 1	4532

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	27% 17% 34% 18% 3 1	270
	11th to 20th	Day	30% 19% 30% 15% 6%	270
	21st to end	Day	21% 23% 38% 14% 4	297
February	1st to 10th	Day	28% 16% 34% 18% 3	270
	11th to 20th	Day	34% 20% 33% 9% 3	270
	21st to end	Day	37% 18% 34% 8% 2	225
March	1st to 10th	Day	25% 17% 36% 17% 4 1	312
	11th to 20th	Day	23% 18% 32% 20% 6% 1	460
	21st to end	Day	25% 14% 32% 21% 7% 1	506
April	1st to 10th	Day	21% 17% 25% 23% 12% 2	460
	11th to 20th	Day	19% 12% 31% 25% 10% 2	452
	21st to end	Day	19% 10% 32% 24% 12% 3	460
May	1st to 10th	Day	16% 11% 33% 24% 11% 6%	463
	11th to 20th	Day	14% 9% 27% 23% 18% 10%	487
	21st to end	Day	14% 7% 18% 26% 21% 15%	529
June	1st to 10th	Day	14% 2 20% 28% 23% 12%	490
	11th to 20th	Day	6% 3 14% 31% 30% 16%	490
	21st to end	Day	8% 2 20% 30% 25% 16%	490
July	1st to 10th	Day	10% 3 10% 25% 28% 23%	485
	11th to 20th	Day	11% 4 11% 24% 33% 17%	484
	21st to end	Day	14% 2 8% 26% 32% 18%	532
August	1st to 10th	Day	11% 3 9% 28% 34% 15%	486
	11th to 20th	Day	11% 2 13% 31% 33% 10%	479
	21st to end	Day	12% 2 7% 24% 36% 19%	539
September	1st to 10th	Day	10% 3 12% 25% 31% 18%	490
	11th to 20th	Day	13% 3 11% 26% 31% 16%	490
	21st to end	Day	19% 4 13% 28% 28% 7%	490
October	1st to 10th	Day	13% 3 19% 28% 29% 8%	490
	11th to 20th	Day	14% 9% 23% 30% 21% 3	490
	21st to end	Day	20% 8% 19% 35% 16% 4	474
November	1st to 10th	Day	17% 8% 30% 29% 12% 4	270
	11th to 20th	Day	17% 10% 34% 29% 9%	270
	21st to end	Day	14% 11% 33% 30% 12% 1	270
December	1st to 10th	Day	29% 14% 30% 20% 6% 1	270
	11th to 20th	Day	23% 13% 33% 23% 7% 1	270
	21st to end	Day	25% 16% 32% 20% 6% 1	297
January	1st to 10th	Night	21% 13% 31% 29% 5%	760
	11th to 20th	Night	25% 10% 32% 29% 4	760
	21st to end	Night	21% 9% 38% 30% 2	836
February	1st to 10th	Night	21% 9% 35% 32% 4	760
	11th to 20th	Night	26% 14% 35% 24% 2	743
	21st to end	Night	28% 14% 32% 23% 3	628
March	1st to 10th	Night	21% 11% 30% 33% 4	760
	11th to 20th	Night	18% 10% 34% 30% 7% 1	760
	21st to end	Night	20% 9% 33% 31% 7%	836
April	1st to 10th	Night	16% 10% 30% 34% 9%	685
	11th to 20th	Night	16% 8% 32% 30% 14%	563
	21st to end	Night	14% 6% 30% 38% 11% 1	570
May	1st to 10th	Night	12% 4 25% 37% 18% 3	570
	11th to 20th	Night	15% 4 19% 36% 22% 4	561
	21st to end	Night	9% 2 16% 30% 36% 6%	617
June	1st to 10th	Night	10% 2 14% 36% 33% 5%	570
	11th to 20th	Night	4 2 13% 36% 36% 9%	570
	21st to end	Night	8% 2 9% 36% 38% 7%	570
July	1st to 10th	Night	11% 2 8% 26% 45% 8%	555
	11th to 20th	Night	9% 2 5% 29% 44% 11%	552
	21st to end	Night	10% 2 8% 30% 41% 10%	624
August	1st to 10th	Night	8% 3 7% 29% 44% 10%	567
	11th to 20th	Night	12% 2 8% 33% 40% 5%	564
	21st to end	Night	10% 1 6% 29% 44% 9%	627
September	1st to 10th	Night	11% 2 9% 29% 41% 7%	710
	11th to 20th	Night	14% 2 11% 31% 36% 6%	760
	21st to end	Night	15% 3 16% 34% 29% 3	760
October	1st to 10th	Night	12% 6% 14% 30% 31% 7%	760
	11th to 20th	Night	16% 4 21% 37% 20% 2	760
	21st to end	Night	15% 6% 20% 39% 18% 2	812
November	1st to 10th	Night	16% 5% 20% 38% 19% 3	740
	11th to 20th	Night	15% 8% 31% 35% 11% 1	760
	21st to end	Night	18% 7% 28% 35% 12% 1	760
December	1st to 10th	Night	24% 10% 26% 33% 8%	760
	11th to 20th	Night	22% 6% 30% 34% 7%	760
	21st to end	Night	25% 12% 24% 34% 5%	836

Page generated at 2024-10-22 20:21:03. Version ac07

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