White Barn Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Barn Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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	14% 10% 4 8% 5% 4 4 4 6% 7% 34%	108828
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 35%	109816
Transparency	Day	47% 5% 12% 22% 13% 1	112497
	Night	48% 4 11% 22% 14% 2	114286
Seeing	Day	18% 9% 25% 24% 16% 8%	15801
	Night	19% 8% 27% 30% 15% 2	25707

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% 15% 9% 16% 6% 4 4 3 4 4 20%	3617
	11th to 20th	Day	13% 16% 7% 12% 8% 6% 7% 4 4 3 21%	3705
	21st to end	Day	21% 15% 8% 12% 6% 4 4 3 4 4 20%	4466
February	1st to 10th	Day	19% 14% 6% 11% 6% 5% 4 3 5% 5% 22%	1876
	11th to 20th	Day	15% 12% 4 12% 7% 6% 4 3 5% 6% 24%	1948
	21st to end	Day	16% 13% 5% 12% 5% 4 3 3 4 6% 29%	1570
March	1st to 10th	Day	21% 19% 5% 9% 5% 4 3 3 4 5% 22%	3139
	11th to 20th	Day	12% 10% 3 7% 6% 3 4 4 5% 7% 39%	3480
	21st to end	Day	18% 11% 3 10% 5% 5% 4 3 5% 6% 29%	3815
April	1st to 10th	Day	14% 12% 4 9% 6% 5% 4 3 5% 7% 32%	2253
	11th to 20th	Day	16% 9% 3 6% 5% 4 5% 4 6% 6% 37%	2319
	21st to end	Day	19% 8% 3 8% 5% 4 5% 3 6% 7% 32%	2470
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 3 6% 7% 30%	4082
	11th to 20th	Day	20% 7% 2 6% 4 4 4 3 5% 8% 36%	4081
	21st to end	Day	10% 6% 2 7% 6% 5% 6% 5% 7% 10% 36%	4476
June	1st to 10th	Day	12% 5% 3 6% 5% 4 6% 4 6% 8% 40%	2560
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 6% 11% 43%	2660
	21st to end	Day	9% 5% 2 6% 6% 4 5% 5% 7% 10% 39%	2660
July	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 4 7% 10% 35%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 7% 11% 47%	4413
	21st to end	Day	8% 7% 2 7% 6% 5% 6% 5% 7% 9% 37%	4466
August	1st to 10th	Day	9% 5% 2 5% 4 4 5% 5% 7% 10% 44%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 10% 43%	4044
	21st to end	Day	7% 5% 2 6% 5% 4 4 4 7% 10% 46%	4252
September	1st to 10th	Day	11% 5% 2 5% 5% 4 4 3 5% 7% 48%	2172
	11th to 20th	Day	10% 5% 2 6% 5% 3 4 4 6% 8% 48%	2090
	21st to end	Day	15% 7% 2 6% 4 3 4 2 5% 6% 46%	2090
October	1st to 10th	Day	11% 6% 2 6% 5% 5% 4 3 5% 6% 45%	2090
	11th to 20th	Day	14% 8% 2 5% 4 4 3 3 6% 7% 45%	1920
	21st to end	Day	18% 11% 2 8% 4 4 4 4 5% 7% 33%	1923
November	1st to 10th	Day	9% 9% 3 5% 4 3 4 3 5% 7% 48%	1762
	11th to 20th	Day	15% 13% 4 8% 5% 4 4 4 5% 6% 33%	1800
	21st to end	Day	19% 13% 4 9% 5% 4 3 3 4 6% 30%	1800
December	1st to 10th	Day	16% 12% 5% 8% 5% 3 3 3 4 5% 36%	2930
	11th to 20th	Day	18% 15% 6% 12% 5% 5% 4 3 5% 5% 22%	3373
	21st to end	Day	23% 20% 8% 10% 5% 5% 4 3 4 5% 14%	3982
January	1st to 10th	Night	15% 15% 7% 14% 7% 5% 4 3 4 4 20%	6348
	11th to 20th	Night	12% 19% 9% 14% 7% 7% 5% 3 4 4 17%	6253
	21st to end	Night	21% 14% 6% 9% 5% 4 4 3 4 5% 26%	6490
February	1st to 10th	Night	19% 14% 4 10% 6% 4 4 4 4 6% 26%	2520
	11th to 20th	Night	15% 12% 5% 10% 6% 5% 4 3 5% 6% 30%	2338
	21st to end	Night	19% 12% 6% 10% 5% 4 3 3 4 5% 27%	1885
March	1st to 10th	Night	20% 13% 4 6% 4 4 3 3 4 6% 34%	3713
	11th to 20th	Night	12% 8% 2 7% 5% 4 4 4 5% 7% 44%	3480
	21st to end	Night	18% 10% 4 7% 4 3 3 3 4 6% 38%	3817
April	1st to 10th	Night	14% 9% 3 7% 5% 4 5% 4 6% 7% 36%	1943
	11th to 20th	Night	16% 8% 3 6% 4 4 5% 4 6% 7% 37%	1808
	21st to end	Night	17% 7% 3 7% 5% 4 5% 3 6% 7% 36%	1710
May	1st to 10th	Night	19% 12% 3 8% 5% 4 5% 4 6% 7% 27%	2813
	11th to 20th	Night	20% 6% 2 5% 4 4 4 3 5% 8% 39%	2812
	21st to end	Night	9% 5% 2 5% 5% 4 4 4 7% 10% 44%	3079
June	1st to 10th	Night	8% 5% 2 6% 4 4 5% 5% 5% 9% 47%	1614
	11th to 20th	Night	8% 4 2 5% 5% 4 4 4 6% 9% 48%	1520
	21st to end	Night	7% 5% 1 5% 4 4 5% 5% 7% 10% 46%	1520
July	1st to 10th	Night	11% 5% 2 7% 4 5% 4 3 6% 7% 46%	2530
	11th to 20th	Night	6% 3 1 5% 3 4 4 5% 6% 8% 54%	2551
	21st to end	Night	10% 7% 2 6% 4 4 5% 4 7% 10% 42%	3087
August	1st to 10th	Night	11% 6% 2 6% 4 5% 5% 3 7% 8% 42%	2825
	11th to 20th	Night	6% 6% 2 7% 4 5% 5% 4 6% 8% 48%	2785
	21st to end	Night	4 3 1 6% 4 5% 5% 5% 7% 9% 51%	3401
September	1st to 10th	Night	12% 5% 2 4 3 3 3 4 5% 8% 51%	1987
	11th to 20th	Night	9% 4 2 5% 3 3 3 4 5% 8% 55%	2090
	21st to end	Night	14% 5% 2 5% 3 4 5% 3 5% 6% 48%	2090
October	1st to 10th	Night	9% 5% 2 6% 4 4 3 3 5% 7% 53%	2090
	11th to 20th	Night	16% 7% 2 7% 4 4 4 3 5% 6% 42%	2259
	21st to end	Night	19% 7% 3 6% 3 3 5% 3 4 6% 39%	2672
November	1st to 10th	Night	12% 8% 2 6% 4 3 3 3 5% 7% 46%	2536
	11th to 20th	Night	15% 10% 3 8% 5% 4 4 3 5% 7% 37%	2600
	21st to end	Night	18% 13% 4 9% 6% 5% 4 3 4 6% 27%	2600
December	1st to 10th	Night	16% 10% 4 8% 5% 4 4 4 5% 6% 34%	4250
	11th to 20th	Night	18% 17% 7% 12% 4 4 4 3 4 4 22%	4822
	21st to end	Night	25% 18% 7% 10% 5% 4 3 3 4 5% 14%	6978

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	68% 3 6% 16% 6%	3618
	11th to 20th	Day	69% 3 9% 8% 10% 1	3705
	21st to end	Day	69% 3 9% 10% 7% 2	4466
February	1st to 10th	Day	65% 3 9% 14% 8% 1	1876
	11th to 20th	Day	61% 4 9% 18% 8%	1958
	21st to end	Day	58% 3 11% 18% 8% 1	1570
March	1st to 10th	Day	65% 3 8% 17% 7%	3139
	11th to 20th	Day	45% 4 9% 29% 12% 1	3480
	21st to end	Day	55% 4 13% 21% 6%	3815
April	1st to 10th	Day	53% 4 12% 18% 12%	2253
	11th to 20th	Day	47% 5% 13% 21% 12% 3	2319
	21st to end	Day	50% 5% 12% 20% 11% 2	2470
May	1st to 10th	Day	53% 5% 11% 21% 9% 1	4120
	11th to 20th	Day	46% 5% 14% 25% 9% 1	4085
	21st to end	Day	39% 8% 14% 23% 14% 1	4489
June	1st to 10th	Day	40% 6% 12% 25% 15% 2	2560
	11th to 20th	Day	36% 6% 13% 25% 18% 1	2660
	21st to end	Day	37% 7% 15% 21% 15% 3	2660
July	1st to 10th	Day	43% 5% 12% 22% 16% 2	4371
	11th to 20th	Day	29% 7% 14% 28% 21% 1	4338
	21st to end	Day	40% 7% 14% 19% 17% 3	4324
August	1st to 10th	Day	32% 8% 16% 29% 14% 1	4091
	11th to 20th	Day	34% 5% 13% 32% 15% 1	4083
	21st to end	Day	32% 6% 13% 31% 15% 3	4251
September	1st to 10th	Day	35% 5% 12% 23% 22% 3	2172
	11th to 20th	Day	34% 5% 10% 26% 22% 3	2090
	21st to end	Day	40% 3 9% 24% 21% 1	2090
October	1st to 10th	Day	26% 4 11% 31% 28% 1	3480
	11th to 20th	Day	31% 3 11% 28% 25% 2	3173
	21st to end	Day	41% 3 10% 24% 20% 2	3147
November	1st to 10th	Day	36% 5% 11% 28% 19% 2	1762
	11th to 20th	Day	52% 3 9% 21% 11% 3	1800
	21st to end	Day	56% 3 10% 20% 9% 1	1800
December	1st to 10th	Day	51% 3 13% 24% 9%	2930
	11th to 20th	Day	65% 3 11% 15% 5%	3370
	21st to end	Day	75% 3 8% 10% 4	3982
January	1st to 10th	Night	68% 4 8% 14% 7%	6348
	11th to 20th	Night	71% 3 8% 9% 8% 1	6253
	21st to end	Night	61% 3 11% 16% 7% 2	6490
February	1st to 10th	Night	61% 3 10% 17% 7% 1	2520
	11th to 20th	Night	56% 3 10% 18% 12% 1	2339
	21st to end	Night	60% 3 10% 16% 9% 2	1885
March	1st to 10th	Night	53% 3 8% 24% 11% 1	3713
	11th to 20th	Night	39% 5% 12% 27% 15% 2	3480
	21st to end	Night	48% 4 10% 28% 8% 1	3817
April	1st to 10th	Night	47% 5% 12% 22% 13% 1	1943
	11th to 20th	Night	45% 5% 11% 19% 17% 4	1808
	21st to end	Night	46% 5% 11% 22% 13% 3	1710
May	1st to 10th	Night	55% 5% 9% 21% 8% 2	2840
	11th to 20th	Night	43% 6% 14% 27% 9% 1	2813
	21st to end	Night	33% 6% 16% 26% 15% 4	3087
June	1st to 10th	Night	33% 7% 12% 25% 22% 3	1614
	11th to 20th	Night	32% 7% 14% 26% 18% 4	1520
	21st to end	Night	31% 7% 17% 24% 17% 4	1520
July	1st to 10th	Night	37% 5% 12% 26% 15% 6%	2490
	11th to 20th	Night	26% 7% 14% 31% 22% 1	2503
	21st to end	Night	36% 6% 15% 20% 19% 4	2988
August	1st to 10th	Night	37% 7% 14% 27% 14% 1	2814
	11th to 20th	Night	33% 6% 11% 31% 19% 1	2812
	21st to end	Night	29% 7% 14% 27% 20% 3	3401
September	1st to 10th	Night	32% 5% 13% 24% 19% 6%	1987
	11th to 20th	Night	27% 5% 10% 29% 26% 3	2090
	21st to end	Night	36% 6% 9% 23% 24% 2	2090
October	1st to 10th	Night	23% 3 7% 32% 33% 2	3480
	11th to 20th	Night	32% 3 11% 26% 28% 1	3745
	21st to end	Night	34% 4 7% 28% 23% 4	4398
November	1st to 10th	Night	38% 4 10% 24% 21% 2	2536
	11th to 20th	Night	48% 3 8% 23% 15% 3	2600
	21st to end	Night	58% 4 10% 19% 9%	2600
December	1st to 10th	Night	51% 4 12% 24% 8% 1	4250
	11th to 20th	Night	65% 3 11% 14% 6%	4824
	21st to end	Night	73% 3 9% 12% 3	6978

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% 18% 33% 21% 6%	300
	11th to 20th	Day	26% 16% 37% 17% 3	300
	21st to end	Day	33% 14% 31% 19% 3 1	330
February	1st to 10th	Day	28% 16% 36% 14% 6%	300
	11th to 20th	Day	26% 20% 33% 14% 6%	300
	21st to end	Day	25% 13% 44% 15% 2	225
March	1st to 10th	Day	28% 16% 34% 18% 4	276
	11th to 20th	Day	24% 13% 34% 20% 7% 1	460
	21st to end	Day	30% 12% 33% 18% 7%	506
April	1st to 10th	Day	21% 16% 32% 20% 9% 2	460
	11th to 20th	Day	20% 15% 27% 22% 10% 5%	452
	21st to end	Day	23% 12% 31% 23% 9% 2	460
May	1st to 10th	Day	27% 10% 28% 24% 8% 3	463
	11th to 20th	Day	22% 7% 26% 24% 13% 9%	487
	21st to end	Day	12% 6% 26% 28% 17% 12%	529
June	1st to 10th	Day	13% 6% 22% 31% 19% 8%	580
	11th to 20th	Day	12% 5% 24% 30% 21% 8%	680
	21st to end	Day	12% 5% 26% 30% 18% 10%	680
July	1st to 10th	Day	12% 3 17% 25% 26% 17%	671
	11th to 20th	Day	9% 3 19% 29% 25% 15%	654
	21st to end	Day	10% 3 14% 29% 26% 19%	532
August	1st to 10th	Day	12% 3 11% 24% 32% 18%	486
	11th to 20th	Day	10% 4 17% 28% 29% 12%	479
	21st to end	Day	10% 3 11% 26% 33% 18%	539
September	1st to 10th	Day	12% 3 14% 26% 28% 17%	490
	11th to 20th	Day	9% 3 12% 27% 32% 18%	490
	21st to end	Day	20% 8% 20% 23% 20% 9%	490
October	1st to 10th	Day	11% 7% 22% 32% 18% 11%	490
	11th to 20th	Day	16% 14% 27% 26% 13% 5%	490
	21st to end	Day	26% 11% 34% 22% 6% 1	372
November	1st to 10th	Day	15% 14% 31% 26% 9% 5%	300
	11th to 20th	Day	24% 16% 29% 18% 10% 3	300
	21st to end	Day	28% 11% 40% 18% 3	300
December	1st to 10th	Day	21% 18% 36% 18% 6% 1	300
	11th to 20th	Day	24% 14% 40% 17% 5%	300
	21st to end	Day	33% 15% 32% 17% 4	330
January	1st to 10th	Night	23% 16% 34% 22% 5% 1	1000
	11th to 20th	Night	28% 13% 35% 19% 4	958
	21st to end	Night	25% 12% 36% 24% 3	880
February	1st to 10th	Night	26% 10% 34% 27% 3	800
	11th to 20th	Night	22% 15% 35% 25% 2	783
	21st to end	Night	27% 11% 36% 22% 3	629
March	1st to 10th	Night	23% 11% 31% 29% 6% 1	760
	11th to 20th	Night	20% 13% 33% 28% 5% 1	760
	21st to end	Night	27% 10% 29% 26% 8%	836
April	1st to 10th	Night	20% 12% 32% 29% 6% 1	613
	11th to 20th	Night	20% 11% 32% 26% 11% 1	563
	21st to end	Night	20% 6% 39% 23% 10% 1	570
May	1st to 10th	Night	23% 6% 29% 32% 10% 1	570
	11th to 20th	Night	21% 4 24% 33% 17% 1	561
	21st to end	Night	9% 2 23% 38% 25% 3	617
June	1st to 10th	Night	9% 2 22% 42% 23% 1	570
	11th to 20th	Night	9% 4 19% 43% 25% 1	570
	21st to end	Night	8% 3 22% 38% 28% 1	570
July	1st to 10th	Night	10% 3 14% 35% 32% 7%	555
	11th to 20th	Night	9% 2 13% 41% 30% 7%	552
	21st to end	Night	12% 3 8% 40% 35% 2	624
August	1st to 10th	Night	7% 2 12% 39% 37% 4	567
	11th to 20th	Night	7% 1 11% 43% 33% 5%	564
	21st to end	Night	6% 2 12% 33% 40% 6%	627
September	1st to 10th	Night	14% 4 13% 33% 32% 4	657
	11th to 20th	Night	9% 3 12% 36% 36% 5%	760
	21st to end	Night	17% 4 20% 32% 24% 3	760
October	1st to 10th	Night	12% 3 25% 33% 22% 5%	760
	11th to 20th	Night	19% 10% 27% 29% 13% 1	760
	21st to end	Night	22% 9% 32% 26% 10%	836
November	1st to 10th	Night	17% 8% 32% 28% 14% 1	780
	11th to 20th	Night	20% 14% 31% 27% 7% 1	800
	21st to end	Night	24% 13% 29% 28% 6% 1	800
December	1st to 10th	Night	25% 12% 33% 25% 5% 1	800
	11th to 20th	Night	25% 10% 34% 25% 5% 1	800
	21st to end	Night	30% 13% 31% 23% 4	1095

Page generated at 2025-02-18 03:26:27. Version ac07

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