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 2024-09-14.

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% 9% 4 8% 5% 4 4 4 6% 8% 35%	100679
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 36%	97205
Transparency	Day	48% 5% 12% 22% 13% 1	100481
	Night	48% 5% 11% 22% 13% 2	97073
Seeing	Day	18% 9% 25% 24% 16% 8%	15283
	Night	19% 8% 27% 30% 15% 2	25042

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	17% 16% 9% 10% 5% 5% 4 4 4 5% 21%	2527
	11th to 20th	Day	16% 17% 7% 12% 6% 6% 8% 4 4 3 16%	2589
	21st to end	Day	26% 19% 10% 11% 5% 4 3 2 4 3 13%	3124
February	1st to 10th	Day	19% 14% 6% 10% 6% 5% 4 3 5% 5% 22%	1782
	11th to 20th	Day	15% 12% 4 13% 7% 6% 4 3 5% 6% 25%	1848
	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% 7% 47%	2014
	21st to end	Day	14% 6% 2 6% 4 3 3 2 5% 6% 48%	1980
October	1st to 10th	Day	12% 6% 3 6% 5% 6% 4 4 5% 6% 43%	1980
	11th to 20th	Day	14% 8% 2 5% 4 4 3 3 6% 7% 43%	1819
	21st to end	Day	18% 12% 3 8% 4 4 4 4 5% 7% 32%	1822
November	1st to 10th	Day	9% 9% 3 4 4 3 4 3 5% 7% 49%	1672
	11th to 20th	Day	15% 12% 4 8% 5% 4 3 4 5% 6% 34%	1710
	21st to end	Day	18% 12% 4 8% 5% 4 3 3 4 6% 31%	1710
December	1st to 10th	Day	18% 16% 7% 10% 6% 4 4 3 5% 6% 22%	1710
	11th to 20th	Day	15% 14% 7% 13% 5% 6% 4 3 5% 5% 24%	2153
	21st to end	Day	22% 21% 10% 10% 6% 5% 4 3 4 4 11%	2783
January	1st to 10th	Night	16% 17% 8% 12% 6% 4 4 3 5% 4 21%	4428
	11th to 20th	Night	14% 19% 8% 14% 6% 5% 5% 4 4 5% 16%	4375
	21st to end	Night	26% 19% 7% 9% 4 4 3 2 4 4 18%	4532
February	1st to 10th	Night	20% 14% 4 10% 6% 4 4 3 4 5% 26%	2394
	11th to 20th	Night	14% 12% 5% 9% 6% 5% 4 3 5% 6% 31%	2218
	21st to end	Night	19% 12% 6% 10% 5% 4 3 3 4 5% 27%	1884
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% 5% 2 5% 3 3 3 4 5% 8% 54%	2024
	21st to end	Night	12% 5% 2 5% 3 4 5% 3 5% 6% 50%	1980
October	1st to 10th	Night	10% 5% 2 6% 4 4 3 3 5% 6% 52%	1980
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 6% 40%	2140
	21st to end	Night	20% 8% 3 7% 3 3 5% 3 4 6% 38%	2531
November	1st to 10th	Night	12% 8% 2 6% 4 3 3 3 6% 6% 46%	2406
	11th to 20th	Night	15% 10% 3 8% 5% 4 4 3 5% 7% 37%	2470
	21st to end	Night	17% 13% 4 8% 6% 5% 5% 3 5% 7% 28%	2470
December	1st to 10th	Night	19% 14% 5% 9% 6% 4 4 3 5% 6% 25%	2470
	11th to 20th	Night	17% 14% 6% 10% 4 4 5% 4 5% 5% 26%	3042
	21st to end	Night	23% 18% 7% 10% 6% 4 4 3 4 5% 15%	4866

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	65% 4 7% 15% 9%	2528
	11th to 20th	Day	73% 3 9% 9% 5%	2589
	21st to end	Day	77% 3 7% 10% 3	3124
February	1st to 10th	Day	64% 3 10% 14% 9% 1	1782
	11th to 20th	Day	60% 4 9% 18% 8%	1858
	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	35% 5% 11% 26% 21% 2	2014
	21st to end	Day	38% 3 10% 26% 22% 1	1980
October	1st to 10th	Day	40% 5% 10% 25% 18% 2	1980
	11th to 20th	Day	40% 4 10% 25% 18% 3	1819
	21st to end	Day	52% 4 11% 21% 11% 2	1822
November	1st to 10th	Day	35% 5% 11% 27% 19% 2	1672
	11th to 20th	Day	51% 3 10% 22% 11% 3	1710
	21st to end	Day	55% 3 10% 21% 9% 1	1710
December	1st to 10th	Day	65% 3 11% 15% 6% 1	1710
	11th to 20th	Day	62% 4 9% 18% 7%	2150
	21st to end	Day	78% 3 7% 8% 5%	2783
January	1st to 10th	Night	67% 4 8% 14% 7%	4428
	11th to 20th	Night	72% 3 8% 13% 4	4375
	21st to end	Night	71% 3 8% 13% 5%	4532
February	1st to 10th	Night	61% 3 10% 17% 8% 1	2394
	11th to 20th	Night	54% 3 10% 19% 12% 1	2219
	21st to end	Night	60% 3 10% 16% 9% 2	1884
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	28% 5% 10% 29% 26% 2	2024
	21st to end	Night	34% 6% 10% 23% 25% 3	1980
October	1st to 10th	Night	33% 4 11% 27% 23% 2	1980
	11th to 20th	Night	45% 3 8% 24% 18% 1	2140
	21st to end	Night	47% 4 8% 23% 15% 3	2531
November	1st to 10th	Night	38% 4 10% 24% 21% 3	2406
	11th to 20th	Night	48% 3 9% 23% 15% 3	2470
	21st to end	Night	57% 4 10% 20% 9%	2470
December	1st to 10th	Night	60% 4 10% 18% 8% 1	2470
	11th to 20th	Night	59% 3 10% 20% 7% 1	3044
	21st to end	Night	72% 3 9% 11% 4	4866

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% 16% 34% 21% 6%	270
	11th to 20th	Day	27% 14% 37% 17% 4	270
	21st to end	Day	35% 11% 29% 20% 4 1	297
February	1st to 10th	Day	29% 16% 34% 15% 7%	270
	11th to 20th	Day	24% 19% 34% 16% 7%	270
	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	11% 3 12% 26% 30% 18%	463
	21st to end	Day	17% 8% 20% 23% 21% 10%	450
October	1st to 10th	Day	11% 7% 22% 31% 18% 11%	450
	11th to 20th	Day	16% 15% 27% 27% 13% 2	450
	21st to end	Day	28% 12% 33% 22% 5% 1	337
November	1st to 10th	Day	15% 14% 30% 27% 9% 6%	270
	11th to 20th	Day	24% 16% 27% 18% 11% 3	270
	21st to end	Day	28% 9% 40% 19% 4	270
December	1st to 10th	Day	20% 18% 34% 19% 7% 1	270
	11th to 20th	Day	22% 14% 40% 18% 5%	270
	21st to end	Day	33% 16% 30% 16% 4	297
January	1st to 10th	Night	23% 16% 34% 22% 5% 1	950
	11th to 20th	Night	29% 13% 34% 20% 4	911
	21st to end	Night	26% 11% 35% 25% 3	836
February	1st to 10th	Night	27% 9% 33% 28% 3	760
	11th to 20th	Night	22% 15% 35% 26% 3	743
	21st to end	Night	27% 11% 36% 22% 3	628
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% 35% 36% 5%	736
	21st to end	Night	15% 4 20% 33% 25% 3	720
October	1st to 10th	Night	13% 3 25% 32% 22% 5%	720
	11th to 20th	Night	20% 10% 28% 29% 12% 1	720
	21st to end	Night	24% 10% 31% 26% 9%	792
November	1st to 10th	Night	17% 8% 32% 27% 15% 1	740
	11th to 20th	Night	20% 14% 30% 27% 8% 1	760
	21st to end	Night	23% 12% 28% 29% 7% 1	760
December	1st to 10th	Night	25% 12% 32% 25% 5% 1	760
	11th to 20th	Night	25% 9% 35% 25% 5% 1	760
	21st to end	Night	29% 13% 31% 23% 4	1040

Page generated at 2024-09-11 10:00:03. Version ac07

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