Berea
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Berea clear sky chart from 2005-11-06 to 2025-04-11.

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% 9% 3 7% 5% 4 4 4 5% 7% 37%	113749
	Night	14% 9% 3 7% 5% 4 4 3 5% 7% 39%	114568
Transparency	Day	45% 6% 10% 22% 15% 2	117493
	Night	44% 5% 9% 22% 16% 3	118962
Seeing	Day	19% 10% 23% 23% 17% 8%	15261
	Night	19% 8% 24% 29% 17% 2	25411

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	14% 18% 8% 11% 5% 4 4 3 4 5% 24%	4056
	11th to 20th	Day	13% 15% 7% 14% 4 4 3 2 3 3 32%	4060
	21st to end	Day	19% 11% 6% 7% 5% 4 4 3 4 5% 32%	4466
February	1st to 10th	Day	17% 13% 6% 9% 4 4 4 3 4 6% 30%	1945
	11th to 20th	Day	20% 12% 5% 8% 5% 5% 3 3 4 6% 30%	1948
	21st to end	Day	19% 12% 4 7% 4 4 5% 3 5% 4 32%	1650
March	1st to 10th	Day	18% 12% 4 7% 5% 4 3 3 4 5% 35%	4566
	11th to 20th	Day	13% 9% 3 6% 4 4 4 3 5% 7% 43%	4980
	21st to end	Day	15% 9% 2 7% 4 5% 5% 3 5% 7% 37%	5465
April	1st to 10th	Day	14% 8% 3 7% 5% 4 4 4 5% 7% 37%	2319
	11th to 20th	Day	15% 9% 3 7% 4 3 4 3 5% 6% 41%	2288
	21st to end	Day	16% 6% 3 6% 5% 5% 5% 4 7% 7% 37%	2470
May	1st to 10th	Day	18% 10% 3 8% 5% 5% 5% 4 5% 7% 29%	4082
	11th to 20th	Day	18% 9% 3 7% 5% 4 5% 3 5% 5% 35%	4081
	21st to end	Day	11% 6% 2 7% 5% 6% 5% 5% 7% 9% 37%	4476
June	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 5% 7% 7% 39%	2470
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 5% 6% 11% 41%	2470
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 4 7% 11% 40%	2470
July	1st to 10th	Day	9% 5% 3 7% 6% 5% 5% 5% 7% 9% 38%	4120
	11th to 20th	Day	8% 6% 2 6% 5% 5% 5% 4 8% 10% 42%	4120
	21st to end	Day	18% 10% 4 9% 6% 6% 6% 4 7% 8% 22%	4466
August	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 4 7% 9% 42%	4104
	11th to 20th	Day	10% 6% 2 6% 5% 5% 7% 5% 7% 10% 37%	4018
	21st to end	Day	6% 4 2 5% 3 4 4 4 6% 8% 54%	4180
September	1st to 10th	Day	14% 6% 3 6% 5% 4 5% 4 6% 7% 41%	2137
	11th to 20th	Day	13% 6% 2 6% 4 5% 4 3 6% 9% 44%	2090
	21st to end	Day	16% 5% 3 5% 4 4 4 3 4 6% 45%	2090
October	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 6% 7% 51%	2090
	11th to 20th	Day	12% 5% 2 6% 4 5% 4 3 4 5% 50%	1938
	21st to end	Day	19% 7% 2 4 3 3 3 3 5% 6% 44%	2003
November	1st to 10th	Day	12% 7% 2 4 4 3 3 4 4 6% 51%	1762
	11th to 20th	Day	15% 9% 3 6% 4 3 4 3 5% 5% 43%	1800
	21st to end	Day	16% 11% 4 6% 4 3 3 3 5% 5% 40%	1800
December	1st to 10th	Day	16% 12% 3 8% 5% 4 4 3 4 4 37%	2930
	11th to 20th	Day	18% 15% 5% 9% 5% 4 4 4 5% 5% 27%	3373
	21st to end	Day	17% 14% 4 11% 6% 5% 5% 4 4 6% 23%	4466
January	1st to 10th	Night	16% 17% 6% 15% 5% 4 3 3 3 5% 23%	5889
	11th to 20th	Night	18% 15% 5% 10% 6% 4 3 2 3 4 30%	5900
	21st to end	Night	19% 10% 4 7% 5% 3 3 2 4 5% 38%	6490
February	1st to 10th	Night	18% 11% 4 10% 5% 4 4 4 4 6% 29%	2452
	11th to 20th	Night	20% 11% 4 10% 5% 3 4 3 4 5% 31%	2338
	21st to end	Night	22% 12% 4 9% 5% 4 3 3 3 4 32%	1980
March	1st to 10th	Night	17% 14% 3 6% 4 4 4 3 4 5% 35%	5286
	11th to 20th	Night	12% 7% 2 5% 4 4 4 3 5% 6% 48%	4980
	21st to end	Night	13% 10% 3 9% 6% 5% 5% 4 6% 6% 34%	5467
April	1st to 10th	Night	13% 9% 2 6% 4 4 4 4 6% 7% 42%	2097
	11th to 20th	Night	14% 8% 2 5% 4 4 4 3 5% 6% 44%	1844
	21st to end	Night	16% 7% 2 7% 4 4 4 4 5% 7% 39%	1710
May	1st to 10th	Night	19% 9% 3 8% 6% 5% 5% 4 5% 7% 29%	2813
	11th to 20th	Night	19% 7% 2 5% 4 3 4 4 7% 8% 37%	2812
	21st to end	Night	8% 5% 3 5% 5% 5% 5% 4 6% 10% 43%	3079
June	1st to 10th	Night	9% 5% 2 5% 4 3 5% 4 7% 11% 44%	1710
	11th to 20th	Night	5% 4 2 6% 4 5% 6% 5% 8% 11% 45%	1710
	21st to end	Night	7% 4 1 7% 4 4 5% 4 9% 12% 42%	1710
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 6% 5% 7% 10% 43%	2840
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 10% 48%	2840
	21st to end	Night	13% 9% 3 10% 6% 5% 6% 5% 7% 9% 29%	3087
August	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 9% 47%	2825
	11th to 20th	Night	9% 6% 3 6% 5% 4 5% 5% 6% 9% 44%	2807
	21st to end	Night	4 3 1 4 3 3 3 4 6% 9% 61%	3476
September	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 6% 7% 47%	2023
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 6% 7% 47%	2090
	21st to end	Night	11% 6% 3 6% 3 4 3 3 4 6% 51%	2090
October	1st to 10th	Night	11% 4 2 4 4 3 3 4 5% 6% 54%	2090
	11th to 20th	Night	15% 5% 2 5% 3 4 3 3 5% 7% 49%	2242
	21st to end	Night	18% 6% 2 5% 4 3 4 4 4 5% 46%	2593
November	1st to 10th	Night	13% 6% 3 6% 3 4 3 3 5% 5% 50%	2536
	11th to 20th	Night	15% 9% 2 6% 4 3 3 3 4 6% 45%	2600
	21st to end	Night	17% 10% 4 5% 4 4 3 3 4 5% 41%	2600
December	1st to 10th	Night	15% 14% 4 10% 4 3 3 2 3 4 37%	4250
	11th to 20th	Night	19% 12% 5% 9% 4 3 4 2 4 5% 32%	4822
	21st to end	Night	15% 15% 4 10% 6% 6% 6% 4 5% 6% 22%	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	62% 3 9% 18% 7% 1	4057
	11th to 20th	Day	59% 3 5% 16% 15% 2	4060
	21st to end	Day	55% 3 7% 21% 12% 1	4466
February	1st to 10th	Day	56% 5% 7% 18% 12% 2	1945
	11th to 20th	Day	58% 3 6% 20% 11% 3	1958
	21st to end	Day	54% 4 8% 17% 12% 4	1650
March	1st to 10th	Day	51% 4 6% 15% 18% 6%	4566
	11th to 20th	Day	40% 5% 9% 22% 22% 2	4980
	21st to end	Day	45% 5% 10% 28% 12% 1	5465
April	1st to 10th	Day	45% 5% 10% 23% 14% 3	2319
	11th to 20th	Day	44% 5% 8% 22% 17% 4	2288
	21st to end	Day	46% 6% 10% 24% 11% 2	2470
May	1st to 10th	Day	52% 7% 11% 21% 8% 1	4120
	11th to 20th	Day	50% 6% 10% 22% 12% 1	4085
	21st to end	Day	39% 9% 13% 19% 16% 2	4489
June	1st to 10th	Day	42% 7% 10% 24% 15% 2	2470
	11th to 20th	Day	36% 8% 15% 22% 18% 2	2470
	21st to end	Day	36% 9% 14% 20% 17% 3	2470
July	1st to 10th	Day	41% 8% 16% 22% 12% 1	4055
	11th to 20th	Day	35% 7% 13% 34% 9% 2	4051
	21st to end	Day	59% 7% 10% 14% 8% 1	4324
August	1st to 10th	Day	36% 8% 14% 30% 13% 1	4091
	11th to 20th	Day	39% 8% 11% 28% 12% 2	4057
	21st to end	Day	26% 7% 12% 38% 15% 2	4179
September	1st to 10th	Day	42% 7% 11% 18% 17% 5%	2137
	11th to 20th	Day	38% 5% 11% 22% 21% 3	2090
	21st to end	Day	40% 5% 10% 23% 19% 3	2090
October	1st to 10th	Day	23% 4 7% 23% 40% 3	3480
	11th to 20th	Day	26% 3 10% 26% 32% 3	3204
	21st to end	Day	30% 3 8% 30% 19% 9%	3279
November	1st to 10th	Day	35% 4 8% 25% 24% 4	1762
	11th to 20th	Day	43% 4 7% 22% 20% 5%	1800
	21st to end	Day	47% 4 8% 21% 17% 3	1800
December	1st to 10th	Day	51% 4 6% 22% 17% 1	2930
	11th to 20th	Day	59% 4 8% 17% 11% 1	3370
	21st to end	Day	61% 6% 10% 17% 5% 1	4466
January	1st to 10th	Night	64% 4 7% 16% 8% 1	5889
	11th to 20th	Night	59% 3 5% 16% 13% 4	5900
	21st to end	Night	51% 3 7% 21% 16% 3	6490
February	1st to 10th	Night	56% 4 11% 17% 10% 1	2452
	11th to 20th	Night	57% 4 6% 18% 13% 2	2339
	21st to end	Night	58% 4 7% 16% 12% 3	1980
March	1st to 10th	Night	51% 4 6% 22% 13% 4	5286
	11th to 20th	Night	37% 4 8% 27% 20% 4	4980
	21st to end	Night	49% 6% 9% 23% 13% 1	5467
April	1st to 10th	Night	41% 6% 11% 22% 18% 3	2097
	11th to 20th	Night	41% 5% 9% 20% 19% 6%	1844
	21st to end	Night	44% 6% 11% 24% 13% 1	1710
May	1st to 10th	Night	52% 9% 10% 20% 7% 2	2840
	11th to 20th	Night	44% 8% 13% 25% 10% 1	2813
	21st to end	Night	34% 10% 13% 24% 17% 3	3087
June	1st to 10th	Night	32% 8% 16% 26% 15% 4	1710
	11th to 20th	Night	29% 9% 17% 23% 19% 3	1710
	21st to end	Night	33% 8% 17% 23% 15% 5%	1710
July	1st to 10th	Night	34% 9% 15% 26% 14% 2	2795
	11th to 20th	Night	30% 6% 15% 32% 14% 3	2786
	21st to end	Night	49% 9% 11% 19% 11% 1	2988
August	1st to 10th	Night	34% 6% 13% 30% 16% 1	2814
	11th to 20th	Night	36% 7% 13% 30% 13% 1	2834
	21st to end	Night	20% 6% 14% 35% 22% 3	3476
September	1st to 10th	Night	35% 8% 13% 20% 19% 6%	2023
	11th to 20th	Night	36% 5% 10% 24% 22% 2	2090
	21st to end	Night	34% 5% 9% 23% 25% 3	2090
October	1st to 10th	Night	24% 5% 7% 22% 39% 3	3480
	11th to 20th	Night	26% 3 7% 24% 31% 9%	3715
	21st to end	Night	29% 3 8% 23% 29% 9%	4267
November	1st to 10th	Night	37% 4 7% 24% 23% 5%	2536
	11th to 20th	Night	42% 3 7% 19% 22% 6%	2600
	21st to end	Night	46% 3 7% 25% 17% 2	2600
December	1st to 10th	Night	53% 3 8% 20% 15% 1	4250
	11th to 20th	Night	56% 3 8% 20% 12% 2	4824
	21st to end	Night	61% 7% 10% 15% 7%	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	27% 19% 31% 17% 5% 1	300
	11th to 20th	Day	29% 25% 30% 13% 3	300
	21st to end	Day	25% 20% 38% 15% 3	330
February	1st to 10th	Day	26% 19% 36% 15% 4	300
	11th to 20th	Day	36% 22% 28% 10% 2 1	300
	21st to end	Day	33% 16% 35% 13% 2	249
March	1st to 10th	Day	28% 19% 32% 16% 6%	334
	11th to 20th	Day	23% 19% 33% 19% 5% 1	500
	21st to end	Day	25% 18% 30% 20% 7% 1	550
April	1st to 10th	Day	21% 19% 28% 22% 8% 2	500
	11th to 20th	Day	20% 16% 27% 21% 12% 4	452
	21st to end	Day	20% 13% 28% 23% 11% 3	460
May	1st to 10th	Day	22% 11% 29% 22% 12% 4	463
	11th to 20th	Day	19% 7% 20% 29% 17% 8%	487
	21st to end	Day	14% 5% 19% 26% 23% 13%	529
June	1st to 10th	Day	13% 4 20% 28% 22% 13%	490
	11th to 20th	Day	10% 3 20% 30% 24% 13%	490
	21st to end	Day	11% 4 19% 31% 21% 13%	490
July	1st to 10th	Day	14% 4 12% 22% 23% 25%	485
	11th to 20th	Day	10% 3 16% 24% 29% 19%	484
	21st to end	Day	17% 2 11% 27% 28% 15%	532
August	1st to 10th	Day	13% 2 12% 27% 28% 17%	486
	11th to 20th	Day	12% 3 16% 28% 29% 12%	479
	21st to end	Day	11% 1 9% 25% 33% 21%	539
September	1st to 10th	Day	15% 3 12% 22% 30% 17%	490
	11th to 20th	Day	14% 4 11% 21% 31% 18%	490
	21st to end	Day	19% 6% 15% 26% 26% 9%	490
October	1st to 10th	Day	12% 4 17% 30% 26% 9%	490
	11th to 20th	Day	12% 11% 28% 27% 16% 6%	490
	21st to end	Day	23% 10% 27% 27% 13% 1	452
November	1st to 10th	Day	20% 6% 31% 24% 15% 3	300
	11th to 20th	Day	21% 16% 30% 25% 7% 2	300
	21st to end	Day	25% 13% 30% 25% 7% 1	300
December	1st to 10th	Day	24% 21% 28% 22% 5% 1	300
	11th to 20th	Day	24% 14% 35% 19% 8% 1	300
	21st to end	Day	25% 18% 35% 18% 4 1	330
January	1st to 10th	Night	25% 17% 34% 20% 5%	800
	11th to 20th	Night	30% 16% 30% 21% 3	800
	21st to end	Night	24% 13% 37% 24% 2	880
February	1st to 10th	Night	24% 14% 36% 23% 2	800
	11th to 20th	Night	29% 15% 35% 19% 2	783
	21st to end	Night	30% 15% 37% 17% 2	660
March	1st to 10th	Night	24% 13% 30% 28% 5%	800
	11th to 20th	Night	24% 12% 33% 23% 8%	800
	21st to end	Night	21% 11% 31% 29% 7%	880
April	1st to 10th	Night	18% 11% 32% 29% 9%	697
	11th to 20th	Night	17% 10% 30% 31% 11% 1	565
	21st to end	Night	19% 6% 35% 30% 9% 1	570
May	1st to 10th	Night	19% 7% 27% 30% 14% 3	570
	11th to 20th	Night	16% 5% 20% 36% 21% 2	561
	21st to end	Night	8% 2 16% 38% 30% 6%	617
June	1st to 10th	Night	10% 3 16% 42% 27% 3	570
	11th to 20th	Night	6% 2 17% 38% 33% 4	570
	21st to end	Night	8% 2 15% 42% 28% 4	570
July	1st to 10th	Night	12% 1 9% 32% 35% 11%	555
	11th to 20th	Night	6% 3 8% 34% 43% 6%	552
	21st to end	Night	13% 2 9% 33% 36% 6%	624
August	1st to 10th	Night	10% 2 9% 32% 39% 7%	567
	11th to 20th	Night	8% 2 12% 34% 37% 7%	564
	21st to end	Night	8% 1 6% 37% 40% 8%	627
September	1st to 10th	Night	13% 2 10% 30% 38% 6%	693
	11th to 20th	Night	13% 3 12% 28% 39% 6%	760
	21st to end	Night	14% 3 17% 33% 30% 3	760
October	1st to 10th	Night	12% 4 18% 32% 28% 5%	760
	11th to 20th	Night	19% 5% 26% 30% 18% 2	760
	21st to end	Night	21% 7% 27% 30% 14% 1	836
November	1st to 10th	Night	16% 7% 25% 33% 17% 2	780
	11th to 20th	Night	20% 11% 30% 29% 9% 1	800
	21st to end	Night	23% 11% 26% 31% 9% 1	800
December	1st to 10th	Night	29% 11% 28% 27% 5%	800
	11th to 20th	Night	25% 11% 32% 26% 6% 1	800
	21st to end	Night	26% 16% 28% 26% 3	880

Page generated at 2025-04-08 09:17:29. Version ac07

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