Albion
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Albion clear sky chart from 2005-11-06 to 2026-04-17.

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	12% 8% 3 7% 5% 4 4 4 6% 8% 40%	131344
	Night	14% 8% 3 7% 4 4 4 3 5% 7% 42%	131048
Transparency	Day	27% 37% 7% 16% 11% 1	134943
	Night	28% 36% 7% 16% 12% 2	135524
Seeing	Day	15% 9% 24% 25% 19% 8%	17432
	Night	17% 8% 27% 31% 16% 2	27351

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	13% 10% 5% 11% 5% 5% 5% 4 4 6% 33%	4691
	11th to 20th	Day	10% 8% 3 10% 6% 5% 4 4 5% 7% 38%	4710
	21st to end	Day	18% 13% 4 9% 5% 4 3 3 4 5% 30%	5710
February	1st to 10th	Day	16% 11% 4 8% 4 4 4 4 4 6% 35%	2074
	11th to 20th	Day	17% 10% 3 10% 5% 3 4 3 5% 5% 35%	2048
	21st to end	Day	14% 9% 4 9% 5% 4 4 4 5% 6% 36%	1730
March	1st to 10th	Day	18% 11% 3 6% 3 3 3 2 3 4 43%	4580
	11th to 20th	Day	11% 8% 3 6% 3 3 3 3 5% 7% 47%	4791
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	6099
April	1st to 10th	Day	13% 8% 2 6% 4 4 4 4 5% 8% 41%	2520
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 3 5% 6% 41%	2446
	21st to end	Day	17% 6% 2 6% 4 5% 4 3 6% 8% 39%	2416
May	1st to 10th	Day	17% 8% 3 8% 6% 5% 5% 5% 7% 9% 28%	5862
	11th to 20th	Day	16% 7% 3 7% 4 4 5% 4 6% 7% 35%	5861
	21st to end	Day	11% 7% 3 6% 5% 5% 5% 5% 7% 9% 37%	6790
June	1st to 10th	Day	9% 6% 3 5% 4 4 5% 4 6% 8% 46%	2800
	11th to 20th	Day	6% 5% 2 6% 5% 5% 6% 4 6% 9% 46%	2800
	21st to end	Day	7% 5% 2 6% 5% 4 5% 4 8% 9% 45%	2800
July	1st to 10th	Day	9% 4 2 6% 4 4 5% 4 7% 10% 44%	6360
	11th to 20th	Day	6% 6% 2 7% 5% 5% 6% 5% 7% 12% 39%	6360
	21st to end	Day	7% 6% 3 8% 6% 6% 7% 6% 8% 11% 33%	6924
August	1st to 10th	Day	6% 4 1 4 4 3 4 3 6% 11% 52%	4012
	11th to 20th	Day	7% 5% 3 6% 5% 4 5% 5% 7% 10% 43%	3849
	21st to end	Day	4 4 2 5% 4 4 4 4 6% 9% 54%	4312
September	1st to 10th	Day	10% 5% 2 6% 3 4 4 3 6% 8% 48%	2400
	11th to 20th	Day	7% 5% 1 7% 4 4 4 3 6% 8% 51%	2252
	21st to end	Day	12% 5% 2 4 4 3 4 3 4 7% 52%	2200
October	1st to 10th	Day	10% 5% 2 5% 4 3 3 2 4 6% 58%	2200
	11th to 20th	Day	12% 6% 2 5% 4 3 3 3 4 7% 50%	2001
	21st to end	Day	18% 7% 2 5% 3 4 3 2 4 5% 46%	2030
November	1st to 10th	Day	9% 6% 2 6% 4 5% 4 2 4 6% 53%	1852
	11th to 20th	Day	15% 7% 3 7% 4 3 3 2 5% 7% 44%	1890
	21st to end	Day	18% 11% 3 8% 4 4 3 3 4 4 40%	1890
December	1st to 10th	Day	11% 10% 3 6% 4 4 3 3 3 5% 49%	2926
	11th to 20th	Day	14% 10% 5% 11% 5% 4 4 3 6% 6% 33%	3088
	21st to end	Day	28% 14% 5% 9% 5% 4 3 3 3 4 21%	4070
January	1st to 10th	Night	15% 11% 5% 8% 4 4 4 4 5% 6% 35%	8232
	11th to 20th	Night	12% 11% 4 9% 4 5% 5% 3 4 5% 38%	8280
	21st to end	Night	18% 10% 4 7% 4 4 4 3 4 6% 36%	8485
February	1st to 10th	Night	19% 11% 4 8% 5% 4 4 4 5% 5% 32%	2543
	11th to 20th	Night	16% 9% 3 9% 5% 3 4 3 5% 6% 38%	2458
	21st to end	Night	19% 10% 3 8% 4 3 4 2 5% 4 39%	2076
March	1st to 10th	Night	20% 11% 4 6% 4 4 4 3 5% 5% 34%	5493
	11th to 20th	Night	12% 7% 2 6% 4 3 4 3 4 6% 49%	5433
	21st to end	Night	16% 8% 3 7% 5% 5% 4 4 5% 6% 36%	5072
April	1st to 10th	Night	12% 6% 2 6% 4 3 4 4 5% 7% 46%	2100
	11th to 20th	Night	15% 7% 2 5% 3 4 4 4 5% 7% 43%	2035
	21st to end	Night	17% 7% 3 7% 5% 4 3 3 6% 7% 38%	1981
May	1st to 10th	Night	16% 9% 3 8% 5% 5% 5% 3 6% 9% 31%	4033
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 5% 6% 8% 37%	4032
	21st to end	Night	12% 6% 3 7% 4 5% 5% 4 7% 9% 38%	4076
June	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 7% 8% 47%	1600
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 5% 9% 53%	1600
	21st to end	Night	5% 3 2 4 4 4 5% 4 8% 10% 52%	1600
July	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 49%	3618
	11th to 20th	Night	6% 4 2 6% 4 4 5% 4 6% 10% 48%	3617
	21st to end	Night	6% 6% 2 8% 5% 5% 5% 5% 8% 12% 39%	3947
August	1st to 10th	Night	5% 3 2 5% 3 3 3 4 6% 10% 57%	3133
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 6% 8% 52%	3200
	21st to end	Night	4 3 1 4 3 4 5% 4 6% 9% 58%	3586
September	1st to 10th	Night	9% 5% 3 6% 3 3 3 3 5% 6% 54%	2000
	11th to 20th	Night	8% 4 2 5% 4 4 4 4 6% 7% 53%	2126
	21st to end	Night	12% 5% 1 5% 3 3 4 4 6% 7% 50%	2200
October	1st to 10th	Night	8% 4 2 4 3 4 3 3 5% 5% 60%	2200
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 54%	2395
	21st to end	Night	18% 8% 2 5% 3 3 3 2 4 5% 45%	2808
November	1st to 10th	Night	11% 6% 2 5% 3 3 3 4 5% 5% 53%	2666
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 6% 49%	2730
	21st to end	Night	19% 7% 3 6% 4 3 3 3 4 6% 43%	2730
December	1st to 10th	Night	17% 9% 3 6% 3 3 3 3 4 5% 43%	4474
	11th to 20th	Night	18% 8% 3 6% 4 3 4 3 4 6% 41%	5339
	21st to end	Night	28% 14% 4 8% 4 4 4 3 3 4 24%	7150

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	44% 21% 10% 20% 5% 1	4692
	11th to 20th	Day	36% 21% 9% 20% 11% 2	4710
	21st to end	Day	47% 22% 8% 11% 8% 5%	5710
February	1st to 10th	Day	20% 59% 6% 9% 5% 1	2074
	11th to 20th	Day	23% 58% 3 10% 6%	2058
	21st to end	Day	19% 59% 4 10% 7% 2	1730
March	1st to 10th	Day	36% 28% 2 13% 17% 4	4580
	11th to 20th	Day	24% 29% 7% 24% 14% 2	4791
	21st to end	Day	30% 31% 10% 20% 9% 1	6101
April	1st to 10th	Day	21% 59% 6% 8% 5%	2520
	11th to 20th	Day	18% 61% 6% 10% 4 1	2446
	21st to end	Day	17% 62% 3 10% 6% 2	2416
May	1st to 10th	Day	37% 32% 10% 13% 8%	5897
	11th to 20th	Day	34% 31% 7% 21% 6%	5865
	21st to end	Day	31% 30% 8% 16% 14%	6804
June	1st to 10th	Day	14% 63% 3 11% 8% 1	2800
	11th to 20th	Day	16% 63% 3 9% 8% 1	2800
	21st to end	Day	14% 63% 8% 10% 5% 1	2800
July	1st to 10th	Day	25% 28% 8% 23% 14% 2	6291
	11th to 20th	Day	28% 30% 12% 21% 8%	6285
	21st to end	Day	33% 30% 14% 18% 6%	6728
August	1st to 10th	Day	16% 37% 10% 27% 10%	3998
	11th to 20th	Day	24% 38% 10% 17% 11%	3885
	21st to end	Day	17% 37% 10% 26% 10% 1	4311
September	1st to 10th	Day	10% 58% 4 16% 9% 3	2400
	11th to 20th	Day	11% 57% 6% 11% 13% 1	2252
	21st to end	Day	16% 57% 4 12% 11% 1	2200
October	1st to 10th	Day	10% 35% 2 18% 32% 2	3590
	11th to 20th	Day	12% 36% 5% 15% 29% 3	3241
	21st to end	Day	20% 35% 4 15% 24% 3	3255
November	1st to 10th	Day	20% 53% 5% 13% 8% 2	1852
	11th to 20th	Day	19% 54% 3 12% 10% 3	1890
	21st to end	Day	25% 54% 3 11% 6%	1890
December	1st to 10th	Day	24% 34% 10% 19% 13%	2926
	11th to 20th	Day	36% 31% 8% 17% 8% 1	3085
	21st to end	Day	56% 26% 7% 7% 4	4070
January	1st to 10th	Night	41% 22% 11% 19% 6%	8233
	11th to 20th	Night	39% 21% 4 17% 16% 3	8280
	21st to end	Night	40% 22% 9% 16% 13% 1	8485
February	1st to 10th	Night	22% 59% 4 9% 5% 1	2543
	11th to 20th	Night	22% 57% 4 10% 7%	2459
	21st to end	Night	19% 59% 3 10% 8% 1	2076
March	1st to 10th	Night	40% 29% 4 13% 12% 2	5493
	11th to 20th	Night	24% 29% 6% 20% 18% 4	5433
	21st to end	Night	35% 30% 7% 20% 7% 1	5072
April	1st to 10th	Night	18% 60% 5% 11% 5% 1	2100
	11th to 20th	Night	18% 60% 5% 9% 7% 1	2035
	21st to end	Night	17% 62% 5% 8% 6% 2	1981
May	1st to 10th	Night	35% 33% 11% 15% 6%	4060
	11th to 20th	Night	32% 32% 8% 20% 7%	4033
	21st to end	Night	31% 31% 10% 17% 10% 1	4084
June	1st to 10th	Night	14% 63% 5% 9% 8% 1	1600
	11th to 20th	Night	14% 62% 4 8% 10% 2	1600
	21st to end	Night	11% 63% 6% 12% 8% 1	1600
July	1st to 10th	Night	27% 27% 6% 18% 19% 2	3580
	11th to 20th	Night	24% 29% 13% 22% 11%	3572
	21st to end	Night	28% 29% 17% 19% 7% 1	3832
August	1st to 10th	Night	14% 38% 9% 32% 7%	3123
	11th to 20th	Night	19% 38% 9% 21% 13%	3230
	21st to end	Night	13% 37% 10% 24% 15% 1	3586
September	1st to 10th	Night	12% 56% 3 15% 12% 2	2000
	11th to 20th	Night	10% 58% 4 12% 14% 2	2126
	21st to end	Night	15% 58% 4 11% 11% 1	2200
October	1st to 10th	Night	8% 35% 3 11% 38% 5%	3590
	11th to 20th	Night	12% 35% 3 17% 30% 3	3894
	21st to end	Night	18% 36% 5% 16% 20% 5%	4533
November	1st to 10th	Night	19% 53% 4 12% 9% 2	2666
	11th to 20th	Night	17% 53% 3 12% 13% 2	2730
	21st to end	Night	22% 54% 5% 13% 6%	2730
December	1st to 10th	Night	29% 35% 7% 15% 14% 1	4474
	11th to 20th	Night	30% 31% 10% 17% 12%	5341
	21st to end	Night	51% 27% 8% 10% 4 1	7150

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% 15% 32% 22% 7% 1	330
	11th to 20th	Day	24% 16% 35% 21% 5%	330
	21st to end	Day	22% 17% 39% 16% 6%	363
February	1st to 10th	Day	23% 14% 41% 19% 3	330
	11th to 20th	Day	25% 18% 38% 15% 2 1	330
	21st to end	Day	25% 14% 38% 19% 4	273
March	1st to 10th	Day	22% 17% 35% 21% 5%	330
	11th to 20th	Day	25% 18% 34% 17% 5% 1	361
	21st to end	Day	25% 15% 34% 19% 6%	594
April	1st to 10th	Day	18% 16% 33% 26% 7% 1	540
	11th to 20th	Day	20% 18% 25% 22% 14% 1	516
	21st to end	Day	20% 11% 33% 23% 10% 3	500
May	1st to 10th	Day	17% 13% 27% 30% 10% 3	503
	11th to 20th	Day	20% 8% 23% 28% 13% 9%	527
	21st to end	Day	11% 6% 28% 27% 19% 10%	722
June	1st to 10th	Day	10% 6% 18% 29% 26% 11%	730
	11th to 20th	Day	8% 3 19% 34% 24% 11%	730
	21st to end	Day	7% 4 24% 30% 25% 10%	730
July	1st to 10th	Day	10% 2 15% 24% 26% 24%	721
	11th to 20th	Day	7% 3 14% 30% 30% 16%	718
	21st to end	Day	8% 3 11% 29% 35% 14%	794
August	1st to 10th	Day	9% 3 12% 24% 35% 17%	531
	11th to 20th	Day	11% 1 11% 29% 34% 14%	519
	21st to end	Day	7% 1 11% 25% 37% 19%	583
September	1st to 10th	Day	9% 3 14% 25% 35% 15%	530
	11th to 20th	Day	8% 3 8% 28% 35% 18%	530
	21st to end	Day	16% 3 19% 24% 26% 12%	530
October	1st to 10th	Day	10% 4 18% 35% 25% 8%	530
	11th to 20th	Day	11% 13% 31% 25% 14% 5%	331
	21st to end	Day	26% 11% 31% 24% 8%	363
November	1st to 10th	Day	12% 12% 32% 25% 15% 5%	330
	11th to 20th	Day	14% 20% 31% 23% 10% 3	330
	21st to end	Day	26% 12% 23% 28% 10% 1	330
December	1st to 10th	Day	16% 18% 34% 23% 5% 3	330
	11th to 20th	Day	21% 15% 37% 19% 7%	330
	21st to end	Day	29% 17% 32% 15% 6%	363
January	1st to 10th	Night	21% 12% 34% 28% 4	1050
	11th to 20th	Night	23% 14% 37% 22% 4	1050
	21st to end	Night	19% 12% 39% 27% 2	1155
February	1st to 10th	Night	25% 11% 37% 25% 2	863
	11th to 20th	Night	22% 15% 35% 26% 2	823
	21st to end	Night	24% 12% 38% 25% 1	692
March	1st to 10th	Night	23% 15% 32% 26% 4	840
	11th to 20th	Night	19% 12% 37% 26% 6%	822
	21st to end	Night	23% 12% 29% 30% 6%	693
April	1st to 10th	Night	15% 10% 35% 33% 6%	630
	11th to 20th	Night	17% 11% 30% 29% 12% 1	611
	21st to end	Night	19% 6% 33% 32% 9% 1	600
May	1st to 10th	Night	17% 7% 28% 37% 10% 1	600
	11th to 20th	Night	14% 4 24% 36% 19% 2	591
	21st to end	Night	8% 2 22% 40% 25% 3	650
June	1st to 10th	Night	12% 3 18% 41% 26% 2	600
	11th to 20th	Night	9% 1 16% 45% 26% 2	600
	21st to end	Night	5% 1 20% 41% 32% 2	600
July	1st to 10th	Night	9% 2 9% 33% 38% 9%	585
	11th to 20th	Night	5% 3 9% 37% 42% 5%	582
	21st to end	Night	9% 3 9% 36% 38% 6%	657
August	1st to 10th	Night	7% 2 8% 39% 38% 7%	597
	11th to 20th	Night	5% 1 9% 39% 41% 5%	594
	21st to end	Night	7% 1 7% 37% 42% 6%	660
September	1st to 10th	Night	10% 3 11% 35% 35% 7%	600
	11th to 20th	Night	8% 2 13% 34% 37% 7%	726
	21st to end	Night	13% 3 19% 31% 29% 5%	800
October	1st to 10th	Night	9% 4 21% 36% 27% 3	800
	11th to 20th	Night	16% 6% 29% 30% 16% 2	800
	21st to end	Night	22% 8% 31% 29% 10%	880
November	1st to 10th	Night	14% 6% 32% 36% 12% 1	820
	11th to 20th	Night	15% 11% 33% 31% 10%	840
	21st to end	Night	23% 10% 28% 29% 10%	840
December	1st to 10th	Night	24% 8% 34% 28% 6%	895
	11th to 20th	Night	25% 8% 30% 30% 6%	1050
	21st to end	Night	29% 11% 34% 22% 4	1155

Page generated at 2026-04-14 01:44:29. Version ac07

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