Barred Owl Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Barred Owl Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	16% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	127780
	Night	16% 11% 4 9% 5% 5% 4 4 5% 6% 30%	123903
Transparency	Day	50% 6% 12% 21% 10% 1	131258
	Night	53% 6% 11% 19% 10% 1	128512
Seeing	Day	21% 15% 30% 20% 10% 3	15885
	Night	22% 12% 29% 27% 10% 1	25083

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	14% 16% 5% 14% 8% 6% 5% 4 4 5% 20%	3677
	11th to 20th	Day	12% 15% 6% 14% 7% 6% 5% 4 5% 6% 21%	3618
	21st to end	Day	10% 17% 7% 14% 7% 6% 5% 3 5% 5% 20%	4164
February	1st to 10th	Day	14% 15% 4 12% 7% 6% 4 4 6% 5% 24%	1800
	11th to 20th	Day	12% 14% 5% 10% 6% 5% 4 4 5% 5% 28%	1753
	21st to end	Day	18% 12% 4 9% 6% 4 6% 4 5% 5% 26%	1645
March	1st to 10th	Day	19% 13% 4 11% 7% 5% 4 3 4 5% 26%	4512
	11th to 20th	Day	11% 12% 4 9% 6% 6% 5% 4 6% 8% 29%	4980
	21st to end	Day	17% 12% 3 8% 5% 4 4 3 4 4 38%	5754
April	1st to 10th	Day	22% 11% 3 7% 5% 4 4 3 4 5% 33%	2400
	11th to 20th	Day	22% 9% 2 7% 5% 4 3 3 4 4 36%	2374
	21st to end	Day	21% 10% 3 7% 5% 3 5% 4 4 5% 32%	2542
May	1st to 10th	Day	23% 10% 3 8% 5% 4 5% 4 5% 6% 27%	6346
	11th to 20th	Day	15% 10% 3 8% 6% 5% 5% 4 6% 7% 31%	6318
	21st to end	Day	20% 8% 3 7% 5% 4 4 4 5% 6% 34%	6949
June	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 4 5% 7% 31%	2800
	11th to 20th	Day	13% 6% 3 6% 5% 4 5% 5% 6% 8% 40%	2800
	21st to end	Day	17% 7% 3 6% 5% 5% 5% 5% 6% 7% 33%	2800
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 9% 34%	6360
	11th to 20th	Day	10% 5% 2 7% 4 4 5% 4 7% 8% 44%	6360
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 46%	6926
August	1st to 10th	Day	14% 6% 3 7% 5% 5% 6% 4 6% 8% 38%	4470
	11th to 20th	Day	16% 6% 2 7% 4 4 5% 4 6% 8% 38%	4141
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 7% 10% 40%	4312
September	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 4 5% 8% 43%	2400
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 6% 8% 47%	2400
	21st to end	Day	16% 7% 2 6% 4 5% 5% 4 6% 7% 39%	2130
October	1st to 10th	Day	18% 7% 3 7% 4 5% 4 3 6% 7% 36%	2000
	11th to 20th	Day	21% 8% 3 7% 5% 5% 6% 3 5% 7% 30%	2000
	21st to end	Day	24% 10% 3 7% 5% 4 5% 3 4 7% 28%	2049
November	1st to 10th	Day	16% 9% 4 7% 6% 5% 4 5% 6% 6% 33%	1846
	11th to 20th	Day	18% 13% 3 8% 5% 5% 5% 4 5% 6% 27%	1680
	21st to end	Day	21% 13% 4 10% 7% 5% 6% 4 5% 5% 20%	1680
December	1st to 10th	Day	19% 20% 5% 12% 6% 5% 6% 4 5% 5% 14%	2680
	11th to 20th	Day	17% 15% 5% 12% 7% 5% 5% 4 4 5% 23%	3066
	21st to end	Day	22% 15% 6% 13% 6% 4 5% 3 3 4 20%	4048
January	1st to 10th	Night	13% 19% 8% 16% 6% 4 4 3 3 5% 19%	6489
	11th to 20th	Night	11% 14% 6% 14% 8% 6% 5% 4 5% 5% 21%	6400
	21st to end	Night	13% 18% 7% 11% 7% 6% 5% 3 5% 5% 21%	6789
February	1st to 10th	Night	13% 15% 4 12% 8% 5% 6% 4 5% 6% 23%	2600
	11th to 20th	Night	13% 13% 5% 12% 8% 5% 3 4 4 5% 29%	2533
	21st to end	Night	16% 12% 4 9% 6% 5% 5% 3 6% 6% 28%	1983
March	1st to 10th	Night	21% 14% 4 10% 5% 4 4 3 3 4 28%	5326
	11th to 20th	Night	12% 12% 4 9% 5% 5% 5% 4 6% 8% 30%	4979
	21st to end	Night	18% 9% 3 9% 5% 4 4 3 5% 6% 33%	5177
April	1st to 10th	Night	20% 10% 3 8% 5% 4 4 3 4 6% 32%	2000
	11th to 20th	Night	19% 10% 2 8% 4 3 4 3 5% 6% 35%	1975
	21st to end	Night	20% 9% 3 8% 5% 5% 3 3 4 6% 33%	1875
May	1st to 10th	Night	23% 8% 3 7% 5% 5% 5% 5% 6% 7% 25%	3594
	11th to 20th	Night	15% 7% 3 7% 4 5% 4 4 5% 7% 39%	3575
	21st to end	Night	17% 8% 3 8% 4 5% 5% 4 6% 7% 32%	3926
June	1st to 10th	Night	14% 7% 2 8% 6% 5% 5% 5% 7% 8% 34%	1600
	11th to 20th	Night	14% 6% 2 7% 4 4 4 3 6% 8% 43%	1600
	21st to end	Night	18% 8% 2 5% 5% 4 4 4 6% 7% 37%	1600
July	1st to 10th	Night	13% 7% 3 8% 5% 6% 5% 4 6% 9% 33%	3600
	11th to 20th	Night	12% 5% 2 6% 5% 4 5% 4 6% 8% 43%	3600
	21st to end	Night	8% 6% 2 6% 5% 5% 5% 5% 6% 8% 46%	3926
August	1st to 10th	Night	10% 6% 3 8% 4 5% 5% 4 6% 9% 40%	2675
	11th to 20th	Night	12% 7% 3 7% 4 4 5% 4 6% 8% 42%	2875
	21st to end	Night	12% 6% 3 7% 5% 4 5% 4 6% 8% 40%	3586
September	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 4 5% 6% 48%	2000
	11th to 20th	Night	13% 4 2 5% 3 4 4 3 5% 7% 50%	2000
	21st to end	Night	17% 6% 2 6% 5% 3 3 4 5% 6% 43%	2265
October	1st to 10th	Night	16% 7% 3 6% 5% 4 5% 3 5% 6% 40%	2400
	11th to 20th	Night	20% 9% 4 6% 5% 5% 5% 3 5% 6% 31%	2400
	21st to end	Night	22% 10% 3 7% 4 5% 5% 4 5% 6% 29%	2790
November	1st to 10th	Night	19% 11% 3 8% 5% 4 4 3 5% 6% 33%	2667
	11th to 20th	Night	18% 12% 4 8% 5% 5% 5% 4 5% 6% 29%	2940
	21st to end	Night	20% 14% 4 10% 5% 5% 5% 3 5% 7% 22%	2940
December	1st to 10th	Night	18% 17% 4 12% 7% 6% 5% 4 5% 6% 16%	4720
	11th to 20th	Night	21% 14% 4 11% 6% 5% 4 3 4 5% 24%	5348
	21st to end	Night	26% 17% 4 10% 4 4 4 3 4 5% 20%	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	64% 7% 10% 14% 4 1	3678
	11th to 20th	Day	64% 5% 11% 12% 8%	3648
	21st to end	Day	65% 6% 10% 11% 8% 1	4164
February	1st to 10th	Day	60% 6% 9% 18% 5% 1	1800
	11th to 20th	Day	57% 5% 11% 17% 9% 1	1762
	21st to end	Day	59% 6% 9% 14% 10% 1	1645
March	1st to 10th	Day	59% 5% 8% 13% 12% 3	4515
	11th to 20th	Day	51% 5% 17% 15% 10% 1	4980
	21st to end	Day	50% 3 7% 19% 19% 3	5754
April	1st to 10th	Day	53% 4 7% 19% 14% 3	2400
	11th to 20th	Day	51% 4 7% 21% 16% 2	2374
	21st to end	Day	54% 5% 8% 15% 14% 4	2542
May	1st to 10th	Day	56% 6% 8% 19% 9% 2	6357
	11th to 20th	Day	51% 8% 11% 18% 11% 1	6322
	21st to end	Day	50% 6% 11% 21% 11% 1	6949
June	1st to 10th	Day	52% 7% 9% 19% 12% 1	2800
	11th to 20th	Day	41% 8% 11% 25% 13% 2	2800
	21st to end	Day	48% 7% 13% 21% 11% 1	2800
July	1st to 10th	Day	43% 7% 15% 26% 10%	6290
	11th to 20th	Day	35% 7% 13% 31% 14%	6285
	21st to end	Day	32% 6% 15% 36% 10%	6728
August	1st to 10th	Day	44% 7% 16% 23% 10%	4456
	11th to 20th	Day	42% 7% 14% 28% 9%	4180
	21st to end	Day	39% 7% 15% 27% 12% 1	4312
September	1st to 10th	Day	39% 6% 14% 29% 11%	2400
	11th to 20th	Day	34% 6% 13% 33% 13% 1	2400
	21st to end	Day	44% 7% 14% 25% 11%	2130
October	1st to 10th	Day	45% 6% 12% 29% 8%	3260
	11th to 20th	Day	45% 5% 16% 24% 9% 1	3240
	21st to end	Day	49% 5% 18% 20% 7%	3287
November	1st to 10th	Day	49% 6% 15% 22% 7% 1	1846
	11th to 20th	Day	56% 6% 12% 15% 9% 1	1680
	21st to end	Day	65% 7% 12% 10% 6% 1	1680
December	1st to 10th	Day	71% 6% 12% 10% 2	2680
	11th to 20th	Day	63% 5% 10% 14% 7%	3066
	21st to end	Day	68% 4 8% 16% 4	4048
January	1st to 10th	Night	68% 5% 10% 13% 4	6489
	11th to 20th	Night	64% 6% 11% 13% 6%	6445
	21st to end	Night	64% 6% 9% 10% 11% 1	6789
February	1st to 10th	Night	60% 6% 10% 16% 7% 1	2600
	11th to 20th	Night	58% 5% 10% 19% 8% 1	2535
	21st to end	Night	56% 5% 9% 19% 10% 1	1983
March	1st to 10th	Night	60% 5% 7% 15% 11% 3	5336
	11th to 20th	Night	51% 6% 17% 16% 8% 3	4980
	21st to end	Night	51% 4 9% 21% 13% 3	5177
April	1st to 10th	Night	53% 5% 8% 18% 14% 2	2000
	11th to 20th	Night	50% 5% 7% 21% 16% 1	1975
	21st to end	Night	51% 6% 8% 17% 16% 3	1875
May	1st to 10th	Night	55% 7% 9% 18% 8% 3	3600
	11th to 20th	Night	44% 7% 13% 20% 15% 1	3576
	21st to end	Night	48% 8% 12% 17% 13% 1	3927
June	1st to 10th	Night	46% 7% 12% 22% 11% 2	1600
	11th to 20th	Night	39% 6% 10% 26% 17% 2	1600
	21st to end	Night	45% 8% 12% 20% 14% 1	1600
July	1st to 10th	Night	46% 6% 15% 20% 13% 1	3560
	11th to 20th	Night	36% 7% 13% 31% 12%	3552
	21st to end	Night	35% 6% 13% 30% 16%	3809
August	1st to 10th	Night	41% 7% 14% 26% 12% 1	2665
	11th to 20th	Night	39% 6% 17% 29% 8%	2902
	21st to end	Night	39% 7% 14% 26% 11% 2	3586
September	1st to 10th	Night	36% 7% 12% 31% 15% 1	2000
	11th to 20th	Night	33% 7% 13% 36% 11% 1	2000
	21st to end	Night	41% 6% 12% 28% 13%	2265
October	1st to 10th	Night	39% 6% 13% 30% 13%	3920
	11th to 20th	Night	46% 5% 15% 24% 9%	3899
	21st to end	Night	48% 6% 17% 21% 8%	4502
November	1st to 10th	Night	51% 6% 14% 20% 8% 1	2667
	11th to 20th	Night	54% 6% 11% 18% 9% 1	2940
	21st to end	Night	61% 7% 12% 15% 5%	2940
December	1st to 10th	Night	67% 6% 13% 11% 3	4720
	11th to 20th	Night	63% 5% 8% 14% 10% 1	5348
	21st to end	Night	68% 4 7% 12% 9%	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	22% 19% 38% 17% 4	220
	11th to 20th	Day	25% 21% 33% 17% 4	212
	21st to end	Day	19% 17% 40% 20% 4	265
February	1st to 10th	Day	28% 24% 33% 12% 2	300
	11th to 20th	Day	24% 31% 36% 9% 1	300
	21st to end	Day	30% 22% 30% 15% 2	409
March	1st to 10th	Day	26% 20% 32% 18% 4	500
	11th to 20th	Day	25% 21% 33% 17% 3 1	500
	21st to end	Day	31% 20% 27% 14% 7% 1	550
April	1st to 10th	Day	31% 20% 28% 14% 6% 1	500
	11th to 20th	Day	33% 17% 23% 15% 9% 2	492
	21st to end	Day	29% 19% 30% 14% 6% 2	500
May	1st to 10th	Day	24% 16% 33% 19% 7% 2	503
	11th to 20th	Day	18% 17% 33% 21% 9% 3	527
	21st to end	Day	21% 14% 30% 23% 11% 1	573
June	1st to 10th	Day	23% 12% 32% 22% 9% 2	530
	11th to 20th	Day	14% 15% 33% 25% 12% 3	530
	21st to end	Day	19% 14% 32% 23% 9% 3	530
July	1st to 10th	Day	11% 8% 29% 34% 15% 3	525
	11th to 20th	Day	12% 8% 31% 31% 15% 4	524
	21st to end	Day	13% 8% 32% 28% 15% 4	576
August	1st to 10th	Day	13% 7% 26% 31% 19% 4	526
	11th to 20th	Day	13% 7% 25% 29% 18% 8%	519
	21st to end	Day	15% 11% 28% 24% 14% 8%	583
September	1st to 10th	Day	15% 12% 29% 19% 16% 9%	530
	11th to 20th	Day	11% 7% 25% 23% 22% 13%	530
	21st to end	Day	18% 11% 29% 22% 15% 5%	530
October	1st to 10th	Day	23% 12% 25% 21% 13% 5%	530
	11th to 20th	Day	24% 19% 29% 19% 7% 1	530
	21st to end	Day	27% 19% 27% 20% 6%	499
November	1st to 10th	Day	25% 19% 31% 17% 7% 1	420
	11th to 20th	Day	27% 18% 33% 14% 7% 1	220
	21st to end	Day	31% 18% 36% 10% 4 1	220
December	1st to 10th	Day	31% 14% 37% 15% 3	220
	11th to 20th	Day	28% 25% 34% 10% 4	220
	21st to end	Day	30% 19% 32% 14% 4 1	242
January	1st to 10th	Night	26% 14% 35% 21% 4	840
	11th to 20th	Night	27% 17% 28% 21% 6% 1	825
	21st to end	Night	19% 12% 38% 26% 5%	880
February	1st to 10th	Night	22% 16% 36% 22% 4	800
	11th to 20th	Night	22% 17% 39% 19% 4	783
	21st to end	Night	24% 18% 30% 24% 4	660
March	1st to 10th	Night	25% 14% 33% 24% 3	800
	11th to 20th	Night	22% 19% 32% 22% 5%	800
	21st to end	Night	24% 16% 27% 25% 7%	880
April	1st to 10th	Night	27% 14% 31% 24% 5%	800
	11th to 20th	Night	24% 19% 27% 22% 8%	791
	21st to end	Night	25% 12% 29% 26% 7% 1	675
May	1st to 10th	Night	24% 8% 28% 31% 9% 1	400
	11th to 20th	Night	20% 12% 28% 31% 9%	394
	21st to end	Night	15% 7% 37% 29% 13%	433
June	1st to 10th	Night	17% 6% 32% 35% 11%	400
	11th to 20th	Night	16% 8% 28% 34% 13% 1	400
	21st to end	Night	21% 6% 30% 31% 13% 1	400
July	1st to 10th	Night	9% 6% 26% 44% 14% 1	390
	11th to 20th	Night	13% 5% 23% 44% 14% 1	388
	21st to end	Night	10% 5% 24% 46% 14% 2	438
August	1st to 10th	Night	10% 4 20% 43% 22%	448
	11th to 20th	Night	11% 3 19% 39% 27% 2	594
	21st to end	Night	12% 7% 24% 36% 19% 2	880
September	1st to 10th	Night	13% 5% 30% 31% 19% 2	800
	11th to 20th	Night	15% 7% 19% 33% 22% 4	800
	21st to end	Night	18% 9% 25% 27% 20% 2	800
October	1st to 10th	Night	19% 12% 25% 28% 15% 1	800
	11th to 20th	Night	24% 12% 30% 25% 8% 1	800
	21st to end	Night	26% 14% 27% 27% 6%	880
November	1st to 10th	Night	27% 13% 28% 24% 8%	820
	11th to 20th	Night	23% 16% 33% 18% 9%	840
	21st to end	Night	29% 16% 27% 23% 6%	840
December	1st to 10th	Night	29% 15% 30% 22% 4	840
	11th to 20th	Night	28% 16% 30% 21% 4 1	840
	21st to end	Night	33% 15% 29% 19% 4	924

Page generated at 2026-01-14 01:14:25. Version ac07

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