Albireo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Albireo Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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% 5% 5% 4 6% 7% 39%	104847
	Night	12% 8% 3 7% 5% 4 5% 4 6% 7% 40%	104446
Transparency	Day	42% 7% 12% 23% 14% 2	108495
	Night	42% 7% 13% 23% 14% 2	108937
Seeing	Day	22% 14% 26% 21% 13% 4	15082
	Night	20% 12% 25% 30% 12% 1	24874

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% 14% 3 8% 5% 4 4 3 3 5% 37%	2903
	11th to 20th	Day	10% 13% 5% 12% 8% 6% 5% 3 4 4 31%	2930
	21st to end	Day	14% 12% 4 9% 5% 5% 5% 4 5% 6% 32%	3133
February	1st to 10th	Day	12% 15% 3 7% 4 4 4 5% 4 6% 35%	1710
	11th to 20th	Day	13% 9% 5% 7% 5% 5% 5% 3 5% 6% 35%	1663
	21st to end	Day	13% 10% 4 8% 5% 4 4 3 4 6% 39%	1599
March	1st to 10th	Day	17% 10% 4 8% 5% 4 4 3 4 6% 35%	3435
	11th to 20th	Day	11% 7% 2 6% 4 3 3 3 6% 7% 48%	3480
	21st to end	Day	15% 10% 3 8% 4 4 5% 3 5% 6% 38%	3815
April	1st to 10th	Day	11% 10% 4 8% 6% 5% 5% 4 6% 7% 37%	2231
	11th to 20th	Day	12% 8% 2 6% 5% 4 4 4 5% 6% 44%	2254
	21st to end	Day	17% 8% 2 8% 5% 4 4 4 6% 6% 38%	2382
May	1st to 10th	Day	20% 8% 3 8% 6% 5% 5% 4 5% 6% 29%	4082
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 4 5% 7% 32%	4081
	21st to end	Day	9% 4 2 6% 6% 6% 6% 5% 8% 9% 38%	4761
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 6% 6% 5% 8% 9% 37%	2660
	21st to end	Day	8% 5% 2 6% 5% 6% 5% 4 8% 10% 40%	2660
July	1st to 10th	Day	5% 4 3 6% 6% 6% 5% 6% 8% 9% 43%	4319
	11th to 20th	Day	7% 5% 2 6% 5% 6% 5% 5% 7% 11% 40%	4120
	21st to end	Day	11% 7% 3 8% 6% 5% 5% 4 6% 7% 36%	4466
August	1st to 10th	Day	13% 7% 3 6% 5% 6% 6% 6% 7% 9% 33%	4104
	11th to 20th	Day	7% 5% 2 7% 5% 6% 6% 5% 8% 9% 39%	4044
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 46%	4183
September	1st to 10th	Day	13% 5% 2 7% 5% 4 5% 4 5% 6% 44%	2280
	11th to 20th	Day	11% 6% 2 6% 4 3 5% 4 5% 7% 45%	2171
	21st to end	Day	19% 7% 3 6% 4 5% 5% 3 5% 5% 38%	2043
October	1st to 10th	Day	15% 7% 2 5% 3 4 4 3 4 6% 46%	1900
	11th to 20th	Day	15% 8% 2 6% 4 3 4 3 4 6% 44%	1900
	21st to end	Day	12% 8% 2 6% 4 4 3 3 5% 6% 46%	2090
November	1st to 10th	Day	9% 6% 2 5% 4 3 3 4 5% 5% 53%	1957
	11th to 20th	Day	12% 9% 3 7% 4 4 4 3 5% 7% 41%	1681
	21st to end	Day	12% 9% 3 7% 6% 5% 4 3 5% 7% 39%	1600
December	1st to 10th	Day	12% 7% 3 6% 4 4 5% 3 5% 6% 45%	2600
	11th to 20th	Day	19% 10% 5% 8% 4 4 3 3 4 6% 35%	2990
	21st to end	Day	16% 9% 3 9% 6% 5% 5% 5% 6% 7% 30%	3960
January	1st to 10th	Night	9% 12% 4 11% 6% 5% 5% 4 6% 5% 32%	4257
	11th to 20th	Night	11% 11% 4 10% 6% 4 4 3 5% 5% 38%	4250
	21st to end	Night	16% 12% 4 7% 5% 4 4 3 5% 5% 34%	4546
February	1st to 10th	Night	11% 9% 3 7% 6% 4 4 4 6% 6% 38%	2470
	11th to 20th	Night	12% 10% 3 9% 6% 6% 6% 3 5% 5% 35%	2403
	21st to end	Night	14% 10% 4 8% 4 5% 5% 4 6% 5% 35%	1850
March	1st to 10th	Night	19% 9% 3 8% 5% 3 4 4 4 5% 36%	3418
	11th to 20th	Night	9% 12% 4 7% 5% 4 3 3 5% 6% 44%	3480
	21st to end	Night	12% 6% 2 8% 3 5% 4 3 4 6% 47%	3817
April	1st to 10th	Night	13% 9% 3 8% 6% 4 4 4 5% 6% 38%	1948
	11th to 20th	Night	12% 6% 2 5% 5% 4 5% 5% 5% 7% 44%	1875
	21st to end	Night	15% 6% 2 6% 4 4 5% 4 5% 6% 42%	1815
May	1st to 10th	Night	22% 8% 3 8% 5% 4 4 4 6% 8% 29%	2813
	11th to 20th	Night	21% 9% 3 7% 4 4 4 3 4 5% 34%	2812
	21st to end	Night	10% 5% 2 6% 4 5% 6% 4 6% 10% 43%	2776
June	1st to 10th	Night	10% 5% 2 5% 4 5% 4 4 6% 9% 46%	1520
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 4 7% 10% 43%	1520
	21st to end	Night	7% 5% 2 5% 4 5% 6% 4 7% 10% 45%	1520
July	1st to 10th	Night	6% 4 2 6% 4 5% 5% 5% 8% 10% 45%	2636
	11th to 20th	Night	5% 5% 2 7% 5% 6% 6% 5% 8% 9% 42%	2840
	21st to end	Night	8% 6% 2 8% 5% 5% 5% 5% 8% 9% 37%	3087
August	1st to 10th	Night	11% 5% 3 8% 5% 5% 6% 6% 7% 9% 36%	2825
	11th to 20th	Night	9% 5% 2 6% 4 4 6% 4 7% 8% 44%	2785
	21st to end	Night	8% 4 2 6% 4 4 5% 4 6% 8% 49%	3439
September	1st to 10th	Night	13% 5% 1 5% 4 5% 4 4 4 7% 48%	1900
	11th to 20th	Night	10% 5% 2 5% 4 3 4 4 6% 7% 50%	2004
	21st to end	Night	18% 5% 2 6% 3 4 5% 4 4 7% 41%	2137
October	1st to 10th	Night	16% 6% 2 5% 3 4 4 3 5% 5% 46%	2280
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 5% 7% 49%	2280
	21st to end	Night	15% 6% 2 6% 4 4 4 3 4 5% 47%	2508
November	1st to 10th	Night	9% 8% 3 5% 4 3 4 4 5% 6% 50%	2341
	11th to 20th	Night	12% 10% 3 7% 4 3 4 4 5% 6% 41%	2713
	21st to end	Night	12% 8% 3 8% 6% 5% 5% 4 5% 5% 39%	2800
December	1st to 10th	Night	9% 7% 3 8% 4 4 6% 3 5% 8% 43%	4580
	11th to 20th	Night	16% 10% 3 8% 6% 5% 5% 4 5% 6% 34%	5205
	21st to end	Night	13% 12% 4 9% 5% 5% 6% 5% 6% 7% 28%	6996

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% 6% 7% 24% 11% 2	2904
	11th to 20th	Day	56% 5% 9% 15% 12% 2	2930
	21st to end	Day	53% 4 11% 19% 12% 1	3133
February	1st to 10th	Day	50% 5% 12% 21% 11% 1	1710
	11th to 20th	Day	50% 5% 10% 20% 13% 2	1672
	21st to end	Day	47% 5% 12% 20% 13% 3	1599
March	1st to 10th	Day	50% 4 10% 23% 11% 1	3435
	11th to 20th	Day	36% 5% 9% 29% 19% 2	3480
	21st to end	Day	48% 6% 11% 21% 13% 2	3815
April	1st to 10th	Day	46% 6% 12% 18% 14% 4	2231
	11th to 20th	Day	40% 6% 10% 22% 18% 5%	2254
	21st to end	Day	46% 5% 10% 23% 12% 2	2382
May	1st to 10th	Day	54% 7% 10% 20% 9% 1	4120
	11th to 20th	Day	51% 8% 9% 23% 8% 1	4085
	21st to end	Day	37% 11% 14% 22% 14% 2	4775
June	1st to 10th	Day	38% 9% 13% 23% 15% 1	2660
	11th to 20th	Day	39% 11% 14% 22% 12% 1	2660
	21st to end	Day	36% 9% 15% 25% 13% 2	2660
July	1st to 10th	Day	35% 10% 16% 26% 10% 4	4252
	11th to 20th	Day	35% 9% 15% 28% 11% 1	4051
	21st to end	Day	45% 7% 9% 23% 15% 1	4324
August	1st to 10th	Day	45% 10% 15% 22% 8%	4091
	11th to 20th	Day	37% 9% 12% 28% 13%	4083
	21st to end	Day	32% 8% 15% 27% 15% 1	4183
September	1st to 10th	Day	39% 7% 12% 18% 20% 3	2280
	11th to 20th	Day	37% 5% 10% 26% 18% 3	2171
	21st to end	Day	46% 7% 9% 21% 16% 1	2043
October	1st to 10th	Day	31% 4 10% 25% 25% 5%	3160
	11th to 20th	Day	35% 5% 9% 24% 18% 10%	3140
	21st to end	Day	27% 4 9% 31% 25% 4	3428
November	1st to 10th	Day	34% 5% 10% 25% 22% 4	1957
	11th to 20th	Day	42% 5% 12% 17% 20% 4	1681
	21st to end	Day	45% 5% 12% 23% 15% 1	1600
December	1st to 10th	Day	40% 7% 12% 26% 11% 4	2600
	11th to 20th	Day	50% 5% 13% 20% 10% 2	2986
	21st to end	Day	49% 8% 15% 16% 12%	3960
January	1st to 10th	Night	51% 6% 10% 20% 11% 2	4257
	11th to 20th	Night	48% 5% 12% 20% 12% 3	4250
	21st to end	Night	52% 6% 10% 23% 8% 1	4546
February	1st to 10th	Night	45% 6% 13% 23% 11% 1	2470
	11th to 20th	Night	51% 5% 11% 19% 13% 2	2405
	21st to end	Night	50% 6% 11% 19% 10% 4	1850
March	1st to 10th	Night	48% 6% 9% 26% 9% 1	3418
	11th to 20th	Night	43% 5% 9% 28% 14% 1	3480
	21st to end	Night	39% 6% 10% 25% 17% 3	3817
April	1st to 10th	Night	46% 6% 10% 19% 15% 3	1948
	11th to 20th	Night	38% 8% 13% 22% 15% 4	1875
	21st to end	Night	41% 7% 11% 25% 13% 3	1815
May	1st to 10th	Night	53% 8% 11% 18% 9% 2	2840
	11th to 20th	Night	50% 8% 10% 23% 8% 1	2813
	21st to end	Night	35% 10% 18% 25% 9% 4	2783
June	1st to 10th	Night	33% 11% 12% 28% 15% 1	1520
	11th to 20th	Night	36% 9% 15% 27% 12% 1	1520
	21st to end	Night	33% 9% 15% 25% 16% 1	1520
July	1st to 10th	Night	32% 10% 22% 19% 12% 4	2593
	11th to 20th	Night	36% 10% 17% 26% 11% 1	2786
	21st to end	Night	39% 10% 14% 22% 13% 1	2988
August	1st to 10th	Night	41% 10% 18% 24% 7%	2814
	11th to 20th	Night	35% 9% 14% 25% 17% 1	2812
	21st to end	Night	32% 7% 15% 32% 12% 1	3439
September	1st to 10th	Night	35% 8% 15% 20% 19% 4	1900
	11th to 20th	Night	32% 5% 12% 30% 19% 2	2004
	21st to end	Night	42% 7% 12% 22% 17% 1	2137
October	1st to 10th	Night	34% 5% 10% 26% 22% 2	3800
	11th to 20th	Night	30% 5% 10% 23% 25% 7%	3779
	21st to end	Night	27% 4 10% 30% 24% 4	4120
November	1st to 10th	Night	35% 6% 13% 23% 19% 5%	2341
	11th to 20th	Night	42% 5% 9% 23% 16% 4	2713
	21st to end	Night	46% 5% 13% 20% 14% 2	2800
December	1st to 10th	Night	38% 8% 14% 27% 12% 1	4580
	11th to 20th	Night	50% 5% 14% 18% 12% 1	5208
	21st to end	Night	50% 10% 14% 16% 10%	6996

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	39% 24% 20% 13% 3 1	295
	11th to 20th	Day	38% 18% 30% 12% 1	300
	21st to end	Day	37% 20% 29% 10% 4	300
February	1st to 10th	Day	36% 21% 28% 13% 2	270
	11th to 20th	Day	47% 18% 29% 5%	270
	21st to end	Day	36% 24% 24% 15% 1	329
March	1st to 10th	Day	30% 23% 23% 20% 3	460
	11th to 20th	Day	34% 22% 24% 13% 5% 1	460
	21st to end	Day	30% 20% 30% 14% 5% 1	506
April	1st to 10th	Day	27% 23% 27% 17% 5% 1	460
	11th to 20th	Day	23% 19% 29% 17% 10% 3	452
	21st to end	Day	29% 17% 27% 18% 7% 1	460
May	1st to 10th	Day	27% 18% 26% 17% 8% 4	463
	11th to 20th	Day	24% 15% 29% 18% 10% 3	487
	21st to end	Day	16% 10% 27% 22% 18% 7%	529
June	1st to 10th	Day	16% 13% 29% 20% 17% 5%	490
	11th to 20th	Day	16% 11% 26% 22% 18% 7%	490
	21st to end	Day	11% 12% 29% 29% 15% 4	490
July	1st to 10th	Day	9% 6% 29% 25% 22% 10%	485
	11th to 20th	Day	9% 5% 25% 29% 25% 8%	484
	21st to end	Day	15% 7% 24% 29% 19% 7%	532
August	1st to 10th	Day	12% 7% 21% 28% 24% 8%	486
	11th to 20th	Day	12% 5% 24% 26% 22% 11%	479
	21st to end	Day	10% 5% 22% 28% 24% 11%	539
September	1st to 10th	Day	16% 7% 20% 24% 24% 9%	490
	11th to 20th	Day	14% 4 21% 27% 24% 9%	490
	21st to end	Day	27% 9% 24% 22% 15% 3	490
October	1st to 10th	Day	20% 7% 23% 26% 20% 4	490
	11th to 20th	Day	23% 15% 23% 23% 14% 3	490
	21st to end	Day	21% 17% 28% 22% 9% 3	539
November	1st to 10th	Day	18% 15% 27% 26% 12% 2	495
	11th to 20th	Day	25% 15% 31% 21% 8%	262
	21st to end	Day	34% 16% 29% 18% 4 1	200
December	1st to 10th	Day	33% 19% 29% 14% 5% 2	200
	11th to 20th	Day	32% 19% 24% 20% 6%	200
	21st to end	Day	31% 15% 28% 19% 7%	220
January	1st to 10th	Night	25% 24% 32% 17% 3	800
	11th to 20th	Night	26% 18% 30% 24% 2	800
	21st to end	Night	25% 21% 34% 18% 1	841
February	1st to 10th	Night	23% 18% 31% 26% 2	760
	11th to 20th	Night	30% 25% 28% 15% 1	743
	21st to end	Night	29% 18% 35% 17% 1	628
March	1st to 10th	Night	24% 19% 32% 22% 3	760
	11th to 20th	Night	28% 20% 25% 21% 5% 1	760
	21st to end	Night	24% 17% 33% 20% 6% 1	836
April	1st to 10th	Night	26% 18% 29% 23% 5%	760
	11th to 20th	Night	19% 16% 29% 27% 8%	751
	21st to end	Night	24% 12% 26% 32% 7%	675
May	1st to 10th	Night	22% 9% 24% 31% 14% 1	570
	11th to 20th	Night	20% 7% 24% 35% 12% 1	561
	21st to end	Night	11% 3 23% 37% 23% 2	443
June	1st to 10th	Night	11% 5% 23% 39% 21% 2	380
	11th to 20th	Night	13% 4 19% 44% 18% 2	380
	21st to end	Night	7% 4 24% 47% 18% 1	380
July	1st to 10th	Night	10% 2 15% 43% 27% 4	431
	11th to 20th	Night	6% 2 11% 43% 34% 3	552
	21st to end	Night	9% 3 16% 39% 30% 2	624
August	1st to 10th	Night	8% 2 13% 46% 29% 2	567
	11th to 20th	Night	10% 3 11% 45% 27% 4	564
	21st to end	Night	10% 2 16% 39% 30% 3	812
September	1st to 10th	Night	14% 3 18% 36% 24% 5%	760
	11th to 20th	Night	13% 4 15% 32% 32% 3	760
	21st to end	Night	20% 7% 20% 31% 21% 1	760
October	1st to 10th	Night	19% 7% 20% 30% 21% 3	760
	11th to 20th	Night	19% 12% 25% 31% 12% 1	760
	21st to end	Night	21% 11% 27% 30% 10% 1	836
November	1st to 10th	Night	17% 10% 26% 35% 11% 1	780
	11th to 20th	Night	22% 15% 29% 26% 8% 1	800
	21st to end	Night	23% 16% 28% 27% 5%	800
December	1st to 10th	Night	26% 16% 29% 24% 4	800
	11th to 20th	Night	21% 17% 31% 28% 3	800
	21st to end	Night	23% 15% 30% 29% 2	880

Page generated at 2025-01-19 03:06:44. Version ac07

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