Bickleton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bickleton 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	5% 6% 2 6% 4 4 4 4 5% 7% 52%	135988
	Night	6% 7% 3 7% 5% 4 4 4 5% 7% 49%	131656
Transparency	Day	32% 5% 10% 24% 21% 9%	130703
	Night	35% 5% 11% 24% 18% 6%	127943
Seeing	Day	11% 13% 24% 26% 20% 7%	15754
	Night	11% 12% 23% 30% 20% 4	24760

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	12% 13% 5% 11% 7% 6% 5% 5% 6% 8% 21%	3639
	11th to 20th	Day	8% 11% 4 8% 5% 4 4 4 5% 6% 41%	3640
	21st to end	Day	10% 12% 4 9% 5% 5% 5% 4 6% 6% 35%	4023
February	1st to 10th	Day	9% 12% 4 10% 6% 5% 5% 5% 6% 7% 30%	1800
	11th to 20th	Day	8% 12% 3 8% 5% 5% 5% 4 6% 7% 36%	1775
	21st to end	Day	6% 10% 3 6% 6% 5% 6% 5% 8% 8% 37%	1650
March	1st to 10th	Day	5% 7% 3 8% 6% 6% 7% 6% 8% 9% 35%	4518
	11th to 20th	Day	4 8% 3 8% 6% 5% 5% 4 6% 6% 45%	4885
	21st to end	Day	6% 9% 4 11% 7% 8% 7% 6% 8% 8% 27%	5832
April	1st to 10th	Day	7% 10% 3 7% 6% 5% 5% 5% 6% 8% 36%	2400
	11th to 20th	Day	7% 8% 2 6% 5% 5% 5% 4 6% 7% 46%	2369
	21st to end	Day	6% 7% 2 5% 5% 4 5% 4 7% 7% 48%	2557
May	1st to 10th	Day	8% 5% 2 5% 3 4 3 3 5% 6% 57%	6320
	11th to 20th	Day	5% 6% 3 7% 4 4 4 4 6% 8% 50%	6277
	21st to end	Day	6% 5% 2 6% 4 4 4 3 5% 7% 53%	6902
June	1st to 10th	Day	10% 5% 2 6% 4 3 4 4 7% 8% 49%	2800
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 4 6% 6% 54%	2800
	21st to end	Day	4 4 1 3 3 3 3 3 5% 6% 65%	2800
July	1st to 10th	Day	1 2 1 2 2 2 2 2 3 4 81%	6319
	11th to 20th	Day	1 1 2 1 1 1 2 2 3 84%	6320
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 76%	6880
August	1st to 10th	Day	3 4 1 3 2 3 3 3 5% 6% 67%	6210
	11th to 20th	Day	2 2 1 3 2 2 3 3 5% 6% 73%	5765
	21st to end	Day	4 4 2 5% 3 3 3 3 4 6% 63%	5984
September	1st to 10th	Day	3 2 1 3 2 2 3 3 4 7% 71%	2400
	11th to 20th	Day	4 5% 2 5% 3 4 4 3 5% 6% 59%	2399
	21st to end	Day	6% 5% 2 5% 2 4 3 2 4 6% 60%	2160
October	1st to 10th	Day	6% 4 1 4 3 3 3 3 5% 6% 63%	3280
	11th to 20th	Day	4 5% 2 7% 5% 5% 6% 4 7% 9% 47%	3261
	21st to end	Day	7% 6% 3 8% 5% 6% 5% 5% 6% 9% 41%	3251
November	1st to 10th	Day	7% 9% 3 9% 6% 4 5% 5% 6% 9% 36%	1854
	11th to 20th	Day	8% 9% 4 7% 6% 8% 6% 6% 7% 8% 30%	1666
	21st to end	Day	6% 10% 3 9% 7% 6% 6% 5% 7% 7% 33%	1600
December	1st to 10th	Day	6% 8% 4 8% 6% 5% 5% 4 6% 8% 42%	2620
	11th to 20th	Day	10% 12% 4 14% 8% 7% 6% 5% 6% 7% 19%	3028
	21st to end	Day	8% 13% 4 13% 8% 7% 6% 5% 5% 7% 23%	4004
January	1st to 10th	Night	10% 14% 5% 12% 8% 7% 7% 5% 6% 6% 20%	6306
	11th to 20th	Night	9% 9% 4 8% 4 3 3 3 5% 7% 44%	6320
	21st to end	Night	9% 11% 4 9% 5% 5% 4 4 5% 6% 38%	6930
February	1st to 10th	Night	9% 12% 4 9% 6% 5% 5% 5% 6% 7% 33%	2600
	11th to 20th	Night	9% 11% 4 8% 5% 4 4 5% 6% 5% 39%	2512
	21st to end	Night	7% 9% 4 8% 5% 4 5% 4 7% 8% 38%	1980
March	1st to 10th	Night	5% 5% 2 8% 6% 6% 7% 5% 8% 10% 40%	5376
	11th to 20th	Night	4 7% 4 8% 6% 5% 5% 4 5% 6% 48%	5098
	21st to end	Night	6% 8% 3 9% 6% 7% 7% 6% 8% 8% 31%	5143
April	1st to 10th	Night	8% 11% 3 7% 5% 4 5% 3 6% 9% 40%	2000
	11th to 20th	Night	7% 8% 2 6% 4 4 4 3 5% 6% 52%	1979
	21st to end	Night	8% 6% 2 5% 5% 5% 4 4 6% 8% 47%	1840
May	1st to 10th	Night	5% 6% 2 5% 3 3 3 2 4 6% 61%	3640
	11th to 20th	Night	5% 4 2 5% 3 3 3 3 4 7% 62%	3616
	21st to end	Night	5% 4 1 3 3 3 3 3 5% 9% 60%	3972
June	1st to 10th	Night	11% 4 1 5% 4 4 4 4 5% 6% 52%	1600
	11th to 20th	Night	8% 5% 1 4 3 3 4 2 5% 5% 59%	1600
	21st to end	Night	5% 3 1 5% 5% 4 3 3 5% 3 65%	1600
July	1st to 10th	Night	1 2 1 3 2 2 3 2 3 4 78%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 3 85%	3640
	21st to end	Night	2 2 1 2 2 1 1 1 4 7% 78%	3970
August	1st to 10th	Night	3 3 1 4 2 3 3 3 5% 8% 66%	3582
	11th to 20th	Night	3 2 1 3 3 3 3 3 4 6% 71%	4067
	21st to end	Night	3 3 1 5% 3 3 4 3 5% 6% 64%	5015
September	1st to 10th	Night	3 2 1 3 2 3 2 2 4 6% 72%	2000
	11th to 20th	Night	4 4 1 4 3 3 5% 3 4 5% 64%	2000
	21st to end	Night	5% 4 1 4 3 3 4 3 5% 5% 63%	2236
October	1st to 10th	Night	5% 3 1 4 3 4 3 3 4 7% 64%	3920
	11th to 20th	Night	7% 4 2 5% 4 4 5% 5% 7% 8% 50%	3897
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 7% 8% 46%	4538
November	1st to 10th	Night	10% 9% 3 8% 5% 4 6% 4 6% 7% 37%	2665
	11th to 20th	Night	8% 8% 3 8% 6% 5% 6% 5% 7% 7% 35%	2886
	21st to end	Night	7% 10% 3 8% 6% 5% 5% 5% 7% 7% 37%	2800
December	1st to 10th	Night	4 8% 2 7% 6% 4 4 3 6% 8% 47%	4560
	11th to 20th	Night	10% 15% 6% 13% 8% 7% 7% 4 6% 7% 18%	5176
	21st to end	Night	12% 11% 4 11% 7% 6% 5% 4 4 6% 30%	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	60% 6% 13% 16% 5%	3639
	11th to 20th	Day	45% 6% 15% 24% 10% 1	3640
	21st to end	Day	50% 5% 11% 19% 12% 2	4023
February	1st to 10th	Day	50% 10% 18% 17% 5% 1	1800
	11th to 20th	Day	46% 8% 15% 22% 9% 1	1784
	21st to end	Day	40% 11% 18% 18% 11% 1	1650
March	1st to 10th	Day	37% 7% 11% 26% 18% 1	4518
	11th to 20th	Day	38% 4 9% 32% 16%	4885
	21st to end	Day	50% 8% 14% 21% 7% 1	5832
April	1st to 10th	Day	42% 7% 12% 25% 13% 1	2400
	11th to 20th	Day	36% 6% 13% 26% 16% 4	2372
	21st to end	Day	30% 8% 12% 30% 17% 3	2557
May	1st to 10th	Day	26% 4 6% 23% 34% 6%	6320
	11th to 20th	Day	31% 3 8% 28% 25% 4	6280
	21st to end	Day	29% 6% 14% 33% 16% 2	6904
June	1st to 10th	Day	31% 6% 10% 30% 19% 4	2800
	11th to 20th	Day	28% 6% 9% 30% 24% 4	2800
	21st to end	Day	20% 4 9% 32% 27% 9%	2800
July	1st to 10th	Day	10% 2 3 18% 33% 34%	6251
	11th to 20th	Day	9% 1 2 12% 32% 44%	6245
	21st to end	Day	13% 1 3 24% 35% 23%	6681
August	1st to 10th	Day	17% 2 4 14% 36% 27%	4524
	11th to 20th	Day	14% 2 4 37% 33% 10%	4164
	21st to end	Day	22% 2 6% 26% 35% 9%	4311
September	1st to 10th	Day	14% 3 7% 29% 31% 15%	2400
	11th to 20th	Day	24% 5% 10% 27% 24% 9%	2399
	21st to end	Day	26% 4 12% 32% 20% 6%	2160
October	1st to 10th	Day	24% 3 9% 33% 29% 3	3280
	11th to 20th	Day	33% 4 16% 26% 19% 2	3261
	21st to end	Day	39% 5% 11% 31% 13% 1	3251
November	1st to 10th	Day	44% 7% 18% 22% 8% 1	1854
	11th to 20th	Day	49% 10% 18% 17% 6% 1	1666
	21st to end	Day	47% 9% 19% 17% 7% 1	1600
December	1st to 10th	Day	42% 5% 16% 27% 9%	2620
	11th to 20th	Day	63% 7% 15% 11% 4	3028
	21st to end	Day	59% 7% 14% 16% 4	4004
January	1st to 10th	Night	63% 7% 14% 13% 4	6306
	11th to 20th	Night	40% 5% 14% 29% 11%	6320
	21st to end	Night	50% 6% 11% 19% 12% 1	6930
February	1st to 10th	Night	47% 10% 17% 20% 5% 1	2600
	11th to 20th	Night	43% 8% 16% 21% 10% 1	2514
	21st to end	Night	41% 9% 15% 22% 11% 2	1980
March	1st to 10th	Night	35% 7% 10% 28% 19% 1	5376
	11th to 20th	Night	37% 4 11% 30% 18% 1	5098
	21st to end	Night	44% 8% 17% 25% 6%	5143
April	1st to 10th	Night	41% 5% 15% 26% 12% 1	2000
	11th to 20th	Night	32% 5% 13% 30% 17% 3	1979
	21st to end	Night	31% 7% 13% 28% 17% 3	1840
May	1st to 10th	Night	25% 3 6% 24% 36% 6%	3637
	11th to 20th	Night	23% 4 8% 33% 29% 3	3616
	21st to end	Night	21% 5% 20% 37% 16% 1	3972
June	1st to 10th	Night	31% 6% 8% 31% 19% 4	1600
	11th to 20th	Night	27% 4 9% 32% 23% 5%	1600
	21st to end	Night	22% 4 7% 30% 28% 9%	1600
July	1st to 10th	Night	13% 2 3 18% 31% 34%	3600
	11th to 20th	Night	8% 1 2 10% 37% 41%	3592
	21st to end	Night	10% 1 3 21% 37% 27%	3857
August	1st to 10th	Night	16% 2 3 13% 38% 29%	2601
	11th to 20th	Night	15% 2 3 38% 29% 13%	2944
	21st to end	Night	18% 2 6% 26% 32% 15%	3608
September	1st to 10th	Night	15% 2 7% 27% 31% 18%	2000
	11th to 20th	Night	22% 4 8% 29% 24% 13%	2000
	21st to end	Night	22% 5% 10% 32% 22% 9%	2236
October	1st to 10th	Night	22% 2 7% 31% 34% 3	3920
	11th to 20th	Night	31% 4 14% 28% 20% 2	3897
	21st to end	Night	35% 4 10% 32% 17% 2	4538
November	1st to 10th	Night	44% 6% 14% 23% 11% 1	2665
	11th to 20th	Night	45% 10% 17% 20% 7%	2886
	21st to end	Night	43% 9% 17% 22% 9%	2800
December	1st to 10th	Night	36% 6% 16% 31% 11% 1	4560
	11th to 20th	Night	65% 6% 15% 12% 2	5176
	21st to end	Night	56% 5% 14% 16% 8% 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	23% 16% 25% 21% 12% 5%	200
	11th to 20th	Day	19% 9% 29% 26% 15% 4	200
	21st to end	Day	16% 18% 21% 24% 17% 4	226
February	1st to 10th	Day	20% 19% 27% 23% 10% 1	400
	11th to 20th	Day	19% 18% 30% 22% 9% 2	405
	21st to end	Day	18% 21% 27% 22% 9% 2	414
March	1st to 10th	Day	13% 22% 31% 22% 10% 1	500
	11th to 20th	Day	13% 21% 23% 26% 13% 4	500
	21st to end	Day	16% 22% 28% 23% 10% 1	550
April	1st to 10th	Day	19% 18% 28% 20% 12% 4	500
	11th to 20th	Day	15% 15% 32% 23% 12% 4	492
	21st to end	Day	10% 16% 30% 24% 16% 5%	500
May	1st to 10th	Day	12% 13% 25% 29% 16% 5%	503
	11th to 20th	Day	13% 13% 25% 22% 19% 8%	528
	21st to end	Day	9% 10% 20% 29% 24% 9%	573
June	1st to 10th	Day	10% 12% 20% 27% 23% 8%	530
	11th to 20th	Day	10% 16% 27% 28% 15% 5%	530
	21st to end	Day	4 8% 22% 29% 27% 10%	530
July	1st to 10th	Day	1 4 20% 34% 32% 8%	526
	11th to 20th	Day	2 6% 21% 31% 30% 11%	524
	21st to end	Day	1 5% 15% 33% 31% 15%	575
August	1st to 10th	Day	5% 4 14% 32% 30% 15%	527
	11th to 20th	Day	3 3 17% 25% 36% 16%	517
	21st to end	Day	4 7% 20% 31% 26% 12%	583
September	1st to 10th	Day	4 5% 20% 32% 27% 12%	530
	11th to 20th	Day	7% 7% 22% 29% 27% 8%	530
	21st to end	Day	9% 10% 25% 28% 23% 6%	530
October	1st to 10th	Day	11% 12% 27% 25% 21% 5%	530
	11th to 20th	Day	11% 18% 22% 23% 19% 6%	530
	21st to end	Day	14% 19% 26% 24% 12% 4	402
November	1st to 10th	Day	17% 19% 23% 25% 14% 2	330
	11th to 20th	Day	21% 21% 18% 21% 14% 5%	219
	21st to end	Day	16% 14% 27% 23% 16% 5%	200
December	1st to 10th	Day	18% 15% 21% 21% 16% 10%	200
	11th to 20th	Day	16% 22% 27% 22% 13% 1	200
	21st to end	Day	19% 15% 27% 23% 16%	220
January	1st to 10th	Night	18% 18% 20% 28% 15% 2	800
	11th to 20th	Night	13% 13% 23% 29% 20% 3	800
	21st to end	Night	15% 10% 21% 30% 20% 4	880
February	1st to 10th	Night	15% 17% 22% 29% 14% 3	800
	11th to 20th	Night	13% 17% 23% 27% 19% 1	784
	21st to end	Night	15% 17% 26% 29% 12% 1	660
March	1st to 10th	Night	11% 15% 29% 26% 16% 2	800
	11th to 20th	Night	10% 17% 27% 28% 15% 2	800
	21st to end	Night	11% 18% 32% 25% 11% 2	880
April	1st to 10th	Night	14% 17% 25% 27% 16% 3	800
	11th to 20th	Night	10% 15% 30% 26% 16% 4	791
	21st to end	Night	8% 14% 28% 31% 16% 2	640
May	1st to 10th	Night	7% 11% 27% 32% 19% 4	400
	11th to 20th	Night	10% 6% 25% 31% 23% 5%	394
	21st to end	Night	7% 5% 27% 33% 24% 5%	433
June	1st to 10th	Night	11% 7% 30% 30% 18% 4	400
	11th to 20th	Night	9% 10% 31% 34% 15% 2	400
	21st to end	Night	6% 9% 18% 41% 24% 4	400
July	1st to 10th	Night	4 1 21% 45% 27% 3	390
	11th to 20th	Night	3 4 23% 45% 23% 2	388
	21st to end	Night	1 3 18% 41% 33% 4	438
August	1st to 10th	Night	3 3 14% 42% 34% 5%	398
	11th to 20th	Night	3 2 12% 34% 35% 14%	596
	21st to end	Night	3 6% 21% 35% 29% 6%	880
September	1st to 10th	Night	3 4 18% 35% 33% 7%	800
	11th to 20th	Night	6% 4 21% 29% 31% 10%	800
	21st to end	Night	7% 8% 22% 26% 29% 8%	800
October	1st to 10th	Night	9% 7% 19% 38% 22% 5%	800
	11th to 20th	Night	12% 12% 21% 26% 24% 5%	800
	21st to end	Night	11% 14% 26% 28% 16% 5%	880
November	1st to 10th	Night	16% 16% 21% 30% 15% 1	820
	11th to 20th	Night	15% 18% 25% 23% 15% 3	828
	21st to end	Night	10% 15% 21% 30% 20% 4	800
December	1st to 10th	Night	13% 12% 21% 29% 21% 4	800
	11th to 20th	Night	18% 16% 19% 31% 15% 1	800
	21st to end	Night	17% 18% 24% 29% 12% 1	880

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