Breyo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Breyo Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	16% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	130931
	Night	17% 10% 4 9% 5% 5% 5% 4 5% 6% 32%	130221
Transparency	Day	48% 6% 12% 21% 11% 1	134420
	Night	51% 6% 12% 19% 11% 1	134819
Seeing	Day	23% 13% 29% 22% 11% 3	16416
	Night	22% 12% 30% 27% 8% 1	25598

By Month

Percentage Cloud Cover NE (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% 11% 7% 15% 7% 6% 5% 4 5% 5% 23%	4661
	11th to 20th	Day	13% 12% 4 11% 6% 6% 5% 5% 6% 7% 25%	4650
	21st to end	Day	14% 11% 3 7% 6% 5% 5% 3 5% 7% 33%	5302
February	1st to 10th	Day	15% 10% 4 8% 7% 5% 5% 5% 7% 8% 26%	1890
	11th to 20th	Day	13% 13% 4 10% 7% 5% 5% 4 6% 6% 27%	2022
	21st to end	Day	17% 11% 3 11% 5% 4 5% 4 6% 5% 29%	1730
March	1st to 10th	Day	21% 11% 5% 8% 5% 4 4 4 4 5% 29%	4496
	11th to 20th	Day	15% 12% 3 8% 4 4 3 3 4 6% 38%	4704
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 3 4 5% 33%	5965
April	1st to 10th	Day	19% 10% 4 7% 5% 4 4 4 5% 6% 33%	2400
	11th to 20th	Day	17% 9% 3 7% 4 5% 5% 4 5% 6% 36%	2374
	21st to end	Day	20% 8% 3 7% 4 5% 4 4 5% 6% 34%	2492
May	1st to 10th	Day	29% 9% 3 8% 5% 4 4 4 4 6% 24%	5995
	11th to 20th	Day	15% 8% 3 9% 5% 5% 5% 4 5% 7% 31%	6318
	21st to end	Day	18% 7% 2 8% 5% 5% 5% 4 6% 8% 32%	6949
June	1st to 10th	Day	15% 6% 2 7% 5% 6% 6% 5% 7% 8% 34%	2800
	11th to 20th	Day	15% 6% 3 6% 5% 5% 5% 5% 7% 10% 33%	2800
	21st to end	Day	15% 7% 3 7% 4 5% 5% 5% 6% 8% 35%	2800
July	1st to 10th	Day	9% 7% 2 8% 5% 5% 6% 5% 7% 10% 35%	6360
	11th to 20th	Day	9% 6% 3 8% 5% 6% 6% 5% 7% 10% 36%	6360
	21st to end	Day	12% 5% 2 6% 4 5% 5% 4 7% 8% 41%	6926
August	1st to 10th	Day	15% 7% 2 7% 5% 5% 6% 4 7% 8% 34%	4531
	11th to 20th	Day	13% 7% 2 7% 5% 5% 6% 5% 8% 9% 33%	3850
	21st to end	Day	10% 6% 2 6% 4 5% 5% 5% 7% 10% 39%	4312
September	1st to 10th	Day	12% 6% 2 5% 4 4 5% 4 5% 9% 44%	2400
	11th to 20th	Day	12% 5% 2 5% 3 4 4 4 5% 8% 48%	2306
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 7% 7% 40%	2200
October	1st to 10th	Day	17% 8% 3 9% 5% 4 4 4 4 5% 37%	2090
	11th to 20th	Day	15% 8% 3 8% 3 5% 4 4 6% 7% 39%	2000
	21st to end	Day	23% 8% 2 6% 5% 4 4 5% 5% 6% 31%	1986
November	1st to 10th	Day	14% 8% 2 6% 4 4 4 4 6% 6% 42%	1851
	11th to 20th	Day	15% 9% 3 7% 5% 4 5% 4 5% 5% 37%	1890
	21st to end	Day	18% 10% 3 7% 5% 5% 5% 4 5% 7% 31%	1727
December	1st to 10th	Day	17% 14% 5% 9% 5% 5% 5% 4 5% 7% 24%	2680
	11th to 20th	Day	20% 12% 3 8% 5% 4 4 3 4 5% 31%	3066
	21st to end	Day	21% 15% 4 9% 5% 4 5% 3 4 5% 24%	4048
January	1st to 10th	Night	15% 12% 6% 15% 6% 5% 5% 3 4 5% 23%	8234
	11th to 20th	Night	11% 16% 6% 13% 7% 5% 5% 4 5% 6% 23%	8235
	21st to end	Night	13% 9% 4 9% 7% 6% 6% 4 6% 7% 31%	8877
February	1st to 10th	Night	15% 12% 5% 10% 6% 5% 4 4 6% 6% 28%	2730
	11th to 20th	Night	12% 11% 5% 11% 7% 5% 5% 5% 6% 5% 28%	2483
	21st to end	Night	16% 11% 4 10% 6% 5% 4 4 5% 6% 29%	2076
March	1st to 10th	Night	19% 10% 5% 8% 6% 5% 5% 4 5% 6% 27%	5389
	11th to 20th	Night	17% 11% 3 8% 5% 4 5% 4 4 6% 35%	5240
	21st to end	Night	21% 10% 4 10% 5% 4 4 3 4 4 30%	4967
April	1st to 10th	Night	19% 11% 3 7% 5% 4 4 4 5% 7% 30%	2000
	11th to 20th	Night	20% 8% 2 8% 5% 5% 4 3 5% 6% 34%	1975
	21st to end	Night	20% 6% 3 7% 5% 3 4 4 5% 6% 38%	1906
May	1st to 10th	Night	29% 9% 3 8% 5% 4 4 3 4 5% 25%	3975
	11th to 20th	Night	16% 9% 3 11% 6% 5% 6% 3 6% 7% 28%	3575
	21st to end	Night	19% 9% 3 8% 5% 5% 4 4 5% 7% 30%	3926
June	1st to 10th	Night	17% 7% 2 6% 5% 5% 4 3 5% 8% 38%	1600
	11th to 20th	Night	15% 6% 2 5% 4 4 5% 5% 7% 8% 38%	1600
	21st to end	Night	13% 5% 2 6% 4 5% 4 4 6% 9% 42%	1600
July	1st to 10th	Night	8% 6% 3 8% 6% 5% 6% 4 7% 8% 39%	3600
	11th to 20th	Night	12% 7% 2 9% 5% 6% 6% 4 6% 8% 35%	3600
	21st to end	Night	10% 7% 2 7% 4 4 4 3 5% 7% 46%	3926
August	1st to 10th	Night	20% 7% 2 7% 4 4 5% 3 6% 7% 34%	2586
	11th to 20th	Night	15% 7% 2 7% 5% 5% 4 4 6% 7% 38%	3182
	21st to end	Night	12% 6% 2 6% 4 4 4 4 6% 8% 42%	3586
September	1st to 10th	Night	13% 8% 3 6% 4 3 4 4 5% 6% 44%	2000
	11th to 20th	Night	13% 4 2 4 3 3 4 3 5% 7% 51%	2093
	21st to end	Night	15% 6% 3 6% 5% 4 4 4 5% 6% 42%	2200
October	1st to 10th	Night	17% 8% 3 8% 4 4 5% 3 5% 6% 37%	2305
	11th to 20th	Night	16% 6% 2 7% 5% 5% 4 5% 5% 6% 40%	2400
	21st to end	Night	23% 8% 3 7% 5% 4 4 4 5% 7% 31%	2852
November	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 5% 41%	2667
	11th to 20th	Night	16% 8% 3 8% 5% 5% 5% 4 5% 5% 36%	2730
	21st to end	Night	16% 10% 3 7% 4 4 5% 4 6% 6% 34%	2888
December	1st to 10th	Night	17% 13% 5% 9% 5% 5% 5% 4 6% 6% 24%	4720
	11th to 20th	Night	25% 11% 4 7% 4 3 3 4 5% 5% 28%	5348
	21st to end	Night	24% 15% 5% 8% 5% 4 4 3 4 5% 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	60% 7% 9% 18% 6%	4662
	11th to 20th	Day	55% 7% 10% 14% 12% 2	4680
	21st to end	Day	49% 5% 11% 23% 11% 1	5302
February	1st to 10th	Day	55% 6% 13% 17% 8% 1	1890
	11th to 20th	Day	56% 5% 10% 19% 8% 1	2031
	21st to end	Day	55% 6% 11% 18% 10% 1	1730
March	1st to 10th	Day	57% 5% 11% 15% 9% 4	4499
	11th to 20th	Day	48% 4 16% 21% 7% 3	4704
	21st to end	Day	52% 7% 6% 15% 18% 2	5965
April	1st to 10th	Day	52% 4 8% 22% 12% 2	2400
	11th to 20th	Day	48% 6% 10% 20% 15% 2	2374
	21st to end	Day	51% 5% 10% 18% 14% 3	2492
May	1st to 10th	Day	61% 6% 8% 16% 8% 1	6006
	11th to 20th	Day	50% 6% 14% 20% 9% 1	6322
	21st to end	Day	49% 6% 12% 22% 10% 1	6949
June	1st to 10th	Day	46% 7% 14% 21% 11% 1	2800
	11th to 20th	Day	45% 6% 15% 20% 12% 1	2800
	21st to end	Day	44% 6% 15% 22% 12% 1	2800
July	1st to 10th	Day	43% 8% 13% 23% 13% 1	6290
	11th to 20th	Day	40% 8% 15% 24% 12% 1	6285
	21st to end	Day	39% 6% 13% 29% 13%	6728
August	1st to 10th	Day	46% 7% 15% 22% 10% 1	4517
	11th to 20th	Day	44% 7% 18% 25% 6% 1	3886
	21st to end	Day	37% 8% 15% 29% 11% 1	4312
September	1st to 10th	Day	37% 7% 13% 28% 15% 1	2400
	11th to 20th	Day	35% 5% 11% 27% 21% 1	2306
	21st to end	Day	41% 7% 12% 26% 13% 2	2200
October	1st to 10th	Day	44% 7% 8% 24% 17% 1	3402
	11th to 20th	Day	38% 5% 13% 29% 15% 1	3240
	21st to end	Day	38% 6% 14% 28% 13% 1	3186
November	1st to 10th	Day	41% 6% 14% 26% 12% 1	1851
	11th to 20th	Day	47% 6% 11% 21% 14% 2	1890
	21st to end	Day	52% 6% 15% 20% 6% 1	1727
December	1st to 10th	Day	60% 6% 12% 17% 5%	2680
	11th to 20th	Day	55% 5% 12% 17% 10% 1	3066
	21st to end	Day	62% 4 7% 17% 9%	4048
January	1st to 10th	Night	62% 6% 11% 13% 8% 1	8234
	11th to 20th	Night	60% 6% 11% 12% 9% 2	8280
	21st to end	Night	51% 4 11% 16% 14% 3	8877
February	1st to 10th	Night	56% 5% 12% 19% 7% 1	2730
	11th to 20th	Night	55% 6% 12% 18% 8% 1	2485
	21st to end	Night	56% 4 13% 17% 8% 1	2076
March	1st to 10th	Night	56% 5% 10% 15% 12% 2	5399
	11th to 20th	Night	50% 4 17% 20% 7% 2	5241
	21st to end	Night	55% 6% 4 17% 15% 2	4967
April	1st to 10th	Night	54% 4 11% 20% 10% 1	2000
	11th to 20th	Night	50% 5% 9% 20% 14% 1	1975
	21st to end	Night	46% 5% 11% 19% 15% 3	1906
May	1st to 10th	Night	61% 6% 10% 13% 9% 1	3981
	11th to 20th	Night	54% 7% 11% 19% 8% 1	3576
	21st to end	Night	53% 6% 12% 18% 11% 1	3927
June	1st to 10th	Night	45% 5% 12% 24% 13% 1	1600
	11th to 20th	Night	42% 6% 17% 23% 12% 1	1600
	21st to end	Night	38% 8% 16% 25% 14% 1	1600
July	1st to 10th	Night	40% 8% 14% 22% 15% 1	3560
	11th to 20th	Night	45% 7% 13% 21% 13%	3552
	21st to end	Night	37% 5% 12% 33% 13% 1	3809
August	1st to 10th	Night	48% 8% 14% 22% 8% 1	2576
	11th to 20th	Night	45% 6% 17% 22% 9%	3212
	21st to end	Night	37% 7% 14% 31% 11% 1	3586
September	1st to 10th	Night	40% 6% 10% 27% 16% 1	2000
	11th to 20th	Night	33% 4 12% 28% 22% 1	2093
	21st to end	Night	41% 6% 11% 24% 17% 1	2200
October	1st to 10th	Night	48% 6% 11% 21% 13% 1	3773
	11th to 20th	Night	36% 6% 12% 27% 19% 1	3899
	21st to end	Night	43% 5% 12% 29% 10%	4602
November	1st to 10th	Night	43% 6% 10% 22% 16% 2	2667
	11th to 20th	Night	48% 5% 10% 22% 12% 2	2730
	21st to end	Night	50% 5% 15% 21% 8%	2888
December	1st to 10th	Night	58% 8% 11% 19% 4	4720
	11th to 20th	Night	56% 5% 12% 14% 12% 1	5348
	21st to end	Night	63% 4 8% 15% 9% 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	25% 22% 29% 19% 5% 1	220
	11th to 20th	Day	33% 20% 30% 15% 2 1	220
	21st to end	Day	26% 19% 33% 16% 5% 1	275
February	1st to 10th	Day	30% 22% 35% 11% 2	330
	11th to 20th	Day	30% 21% 34% 12% 2	510
	21st to end	Day	28% 20% 32% 18% 2	446
March	1st to 10th	Day	29% 16% 32% 18% 4	508
	11th to 20th	Day	28% 19% 30% 17% 4	500
	21st to end	Day	32% 20% 26% 13% 8% 1	550
April	1st to 10th	Day	33% 18% 25% 17% 6% 1	500
	11th to 20th	Day	29% 20% 25% 16% 8% 1	492
	21st to end	Day	29% 15% 31% 16% 6% 2	500
May	1st to 10th	Day	30% 12% 29% 19% 8% 2	503
	11th to 20th	Day	19% 14% 33% 24% 8% 2	527
	21st to end	Day	19% 9% 30% 28% 11% 3	573
June	1st to 10th	Day	18% 12% 30% 24% 12% 3	530
	11th to 20th	Day	19% 10% 29% 26% 15% 2	530
	21st to end	Day	17% 10% 33% 24% 13% 2	530
July	1st to 10th	Day	12% 8% 28% 32% 15% 6%	525
	11th to 20th	Day	12% 6% 28% 32% 18% 4	524
	21st to end	Day	14% 5% 30% 30% 18% 4	576
August	1st to 10th	Day	15% 3 25% 31% 19% 7%	526
	11th to 20th	Day	16% 4 25% 30% 17% 8%	519
	21st to end	Day	13% 9% 26% 29% 17% 7%	583
September	1st to 10th	Day	16% 8% 25% 25% 18% 9%	530
	11th to 20th	Day	15% 6% 25% 20% 21% 14%	530
	21st to end	Day	19% 8% 25% 25% 15% 7%	530
October	1st to 10th	Day	22% 11% 25% 20% 14% 7%	530
	11th to 20th	Day	20% 15% 30% 22% 11% 2	530
	21st to end	Day	29% 11% 30% 23% 7%	465
November	1st to 10th	Day	24% 17% 25% 20% 12% 2	425
	11th to 20th	Day	26% 19% 29% 19% 7% 1	430
	21st to end	Day	31% 18% 27% 19% 5%	267
December	1st to 10th	Day	25% 18% 35% 17% 4 1	220
	11th to 20th	Day	28% 22% 33% 13% 4	220
	21st to end	Day	29% 18% 33% 17% 2 1	242
January	1st to 10th	Night	23% 15% 36% 22% 2	840
	11th to 20th	Night	27% 17% 31% 23% 3	840
	21st to end	Night	20% 18% 35% 23% 3	924
February	1st to 10th	Night	24% 16% 37% 21% 3	840
	11th to 20th	Night	22% 18% 38% 22% 1	823
	21st to end	Night	25% 18% 35% 19% 3	692
March	1st to 10th	Night	25% 19% 34% 19% 2	809
	11th to 20th	Night	26% 18% 33% 21% 3	800
	21st to end	Night	25% 18% 29% 22% 5%	880
April	1st to 10th	Night	27% 17% 32% 22% 3	800
	11th to 20th	Night	27% 15% 32% 21% 5%	791
	21st to end	Night	23% 15% 32% 25% 5%	706
May	1st to 10th	Night	27% 14% 28% 25% 7%	573
	11th to 20th	Night	19% 12% 32% 29% 7% 1	394
	21st to end	Night	14% 8% 31% 37% 9% 1	433
June	1st to 10th	Night	21% 5% 31% 32% 11% 1	400
	11th to 20th	Night	17% 6% 31% 37% 10%	400
	21st to end	Night	14% 6% 29% 40% 12%	400
July	1st to 10th	Night	13% 3 28% 43% 14% 1	390
	11th to 20th	Night	14% 4 24% 40% 17% 1	388
	21st to end	Night	12% 4 22% 49% 13% 1	438
August	1st to 10th	Night	13% 3 20% 46% 18% 1	398
	11th to 20th	Night	14% 4 20% 38% 20% 4	775
	21st to end	Night	17% 4 22% 36% 19% 2	880
September	1st to 10th	Night	16% 5% 25% 37% 16% 1	800
	11th to 20th	Night	17% 4 23% 31% 21% 4	800
	21st to end	Night	18% 5% 26% 35% 15% 2	800
October	1st to 10th	Night	21% 8% 25% 30% 15% 2	800
	11th to 20th	Night	19% 9% 31% 31% 9%	800
	21st to end	Night	28% 8% 31% 27% 5%	880
November	1st to 10th	Night	23% 12% 32% 25% 7%	820
	11th to 20th	Night	22% 13% 34% 23% 7% 1	840
	21st to end	Night	23% 13% 34% 25% 5%	840
December	1st to 10th	Night	27% 17% 34% 19% 4	840
	11th to 20th	Night	28% 14% 30% 24% 4	840
	21st to end	Night	31% 15% 31% 21% 2	924

Page generated at 2026-02-28 01:40:21. Version ac07

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