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 2026-06-16.

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% 5% 5% 4 6% 7% 34%	137264
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 35%	134856
Transparency	Day	48% 5% 12% 22% 13% 1	140889
	Night	48% 4 11% 22% 14% 2	139303
Seeing	Day	18% 10% 26% 23% 15% 8%	17620
	Night	19% 9% 27% 30% 15% 2	27425

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% 14% 8% 15% 6% 4 4 3 5% 5% 19%	4691
	11th to 20th	Day	11% 14% 6% 13% 9% 7% 7% 4 4 3 21%	4821
	21st to end	Day	18% 14% 7% 13% 6% 6% 5% 3 4 5% 19%	5780
February	1st to 10th	Day	19% 15% 6% 11% 6% 5% 4 3 5% 5% 22%	1970
	11th to 20th	Day	15% 13% 4 12% 7% 6% 4 3 5% 6% 24%	2048
	21st to end	Day	15% 13% 5% 12% 5% 4 3 3 4 6% 31%	1730
March	1st to 10th	Day	18% 14% 7% 10% 5% 4 3 3 4 5% 27%	4613
	11th to 20th	Day	11% 10% 3 7% 5% 4 4 3 5% 7% 40%	5090
	21st to end	Day	17% 12% 4 9% 5% 5% 4 3 5% 6% 30%	5586
April	1st to 10th	Day	15% 11% 3 9% 5% 5% 5% 3 5% 7% 31%	2491
	11th to 20th	Day	15% 9% 3 6% 5% 4 5% 4 6% 6% 37%	2567
	21st to end	Day	18% 8% 2 8% 5% 4 5% 3 6% 7% 34%	2730
May	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 6% 31%	7616
	11th to 20th	Day	17% 7% 3 6% 4 4 4 3 6% 8% 37%	7626
	21st to end	Day	16% 7% 2 7% 5% 4 5% 4 7% 9% 32%	8391
June	1st to 10th	Day	12% 6% 3 6% 5% 4 6% 4 6% 8% 40%	2830
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 6% 10% 42%	2871
	21st to end	Day	9% 5% 2 6% 6% 5% 5% 5% 7% 11% 40%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 11% 38%	6319
	21st to end	Day	10% 7% 2 8% 6% 6% 6% 5% 7% 9% 35%	6424
August	1st to 10th	Day	9% 5% 2 5% 4 4 5% 5% 7% 10% 44%	4234
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 10% 43%	4174
	21st to end	Day	7% 5% 2 6% 5% 4 4 4 7% 10% 46%	4386
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 5% 7% 50%	2286
	11th to 20th	Day	9% 5% 2 6% 5% 3 4 4 6% 8% 49%	2200
	21st to end	Day	15% 7% 2 6% 4 3 4 2 5% 6% 46%	2200
October	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 5% 6% 46%	2200
	11th to 20th	Day	13% 8% 2 5% 4 4 3 3 6% 7% 46%	2021
	21st to end	Day	18% 11% 3 8% 4 4 4 4 5% 7% 34%	2024
November	1st to 10th	Day	9% 9% 3 5% 4 4 4 3 5% 7% 48%	1852
	11th to 20th	Day	15% 13% 4 8% 5% 4 4 4 4 6% 34%	1890
	21st to end	Day	19% 13% 4 10% 5% 4 3 3 4 6% 30%	1890
December	1st to 10th	Day	16% 12% 5% 8% 5% 3 3 3 4 5% 36%	3020
	11th to 20th	Day	18% 15% 6% 12% 5% 5% 4 3 5% 5% 22%	3463
	21st to end	Day	23% 20% 8% 10% 5% 5% 4 3 4 5% 14%	4070
January	1st to 10th	Night	14% 15% 6% 14% 8% 5% 5% 4 5% 5% 19%	8232
	11th to 20th	Night	10% 17% 8% 15% 6% 7% 5% 3 4 4 20%	8145
	21st to end	Night	18% 13% 5% 8% 5% 5% 4 3 5% 6% 27%	8401
February	1st to 10th	Night	19% 13% 5% 10% 6% 5% 4 4 4 6% 26%	2646
	11th to 20th	Night	15% 12% 5% 10% 6% 5% 4 3 5% 6% 31%	2458
	21st to end	Night	18% 12% 6% 10% 5% 4 3 3 4 6% 28%	2076
March	1st to 10th	Night	19% 12% 4 7% 4 4 3 3 4 5% 36%	5459
	11th to 20th	Night	11% 7% 3 7% 5% 5% 5% 4 5% 7% 42%	5090
	21st to end	Night	18% 9% 4 8% 4 4 4 3 5% 6% 35%	5588
April	1st to 10th	Night	16% 9% 3 7% 5% 3 5% 4 6% 7% 35%	2147
	11th to 20th	Night	15% 8% 3 7% 4 5% 5% 4 6% 7% 37%	2000
	21st to end	Night	17% 7% 2 6% 5% 4 5% 3 6% 8% 37%	1890
May	1st to 10th	Night	21% 9% 3 8% 5% 4 5% 4 6% 6% 30%	5237
	11th to 20th	Night	16% 6% 2 6% 4 4 4 3 5% 8% 41%	5234
	21st to end	Night	15% 7% 3 6% 4 4 5% 4 6% 9% 37%	5761
June	1st to 10th	Night	9% 5% 2 6% 4 4 5% 5% 5% 9% 46%	1784
	11th to 20th	Night	9% 4 2 5% 5% 4 4 4 6% 9% 47%	1640
	21st to end	Night	7% 5% 1 5% 4 4 5% 5% 7% 10% 47%	1600
July	1st to 10th	Night	9% 4 2 7% 5% 5% 5% 4 6% 8% 46%	3618
	11th to 20th	Night	8% 4 2 7% 4 4 5% 5% 6% 9% 46%	3651
	21st to end	Night	9% 6% 2 6% 5% 4 5% 4 7% 10% 41%	4427
August	1st to 10th	Night	11% 6% 2 6% 4 5% 5% 3 7% 8% 43%	2915
	11th to 20th	Night	6% 6% 2 7% 4 5% 5% 4 6% 8% 48%	2875
	21st to end	Night	5% 3 1 6% 4 5% 5% 5% 7% 9% 51%	3509
September	1st to 10th	Night	12% 5% 2 4 3 3 3 3 5% 8% 52%	2092
	11th to 20th	Night	8% 4 2 5% 3 3 3 4 5% 8% 56%	2200
	21st to end	Night	14% 5% 2 5% 3 4 4 3 5% 6% 48%	2200
October	1st to 10th	Night	9% 5% 2 5% 4 4 3 3 5% 6% 53%	2200
	11th to 20th	Night	15% 7% 2 7% 4 4 4 3 5% 5% 43%	2378
	21st to end	Night	18% 7% 3 6% 3 4 5% 3 4 6% 39%	2813
November	1st to 10th	Night	12% 8% 2 6% 4 3 3 3 5% 7% 47%	2666
	11th to 20th	Night	15% 10% 3 8% 5% 4 4 4 5% 7% 37%	2730
	21st to end	Night	18% 14% 4 9% 5% 5% 4 3 4 6% 27%	2730
December	1st to 10th	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 33%	4380
	11th to 20th	Night	18% 17% 7% 12% 4 4 4 3 4 5% 23%	4952
	21st to end	Night	25% 18% 7% 10% 5% 4 3 3 4 5% 14%	7132

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 10% 14% 5%	4692
	11th to 20th	Day	68% 3 8% 9% 11% 1	4821
	21st to end	Day	69% 3 9% 12% 6% 1	5780
February	1st to 10th	Day	64% 3 9% 15% 8% 1	1970
	11th to 20th	Day	61% 4 9% 18% 8%	2058
	21st to end	Day	56% 3 12% 18% 9% 1	1730
March	1st to 10th	Day	61% 3 7% 19% 9%	4613
	11th to 20th	Day	44% 4 10% 30% 12% 1	5090
	21st to end	Day	55% 4 13% 18% 8% 2	5586
April	1st to 10th	Day	53% 4 12% 18% 12%	2491
	11th to 20th	Day	47% 5% 13% 21% 12% 3	2567
	21st to end	Day	48% 5% 12% 22% 11% 2	2730
May	1st to 10th	Day	52% 5% 12% 20% 11%	7651
	11th to 20th	Day	44% 5% 14% 24% 13%	7630
	21st to end	Day	46% 6% 12% 21% 13% 3	8405
June	1st to 10th	Day	41% 6% 11% 23% 17% 2	2830
	11th to 20th	Day	37% 6% 13% 25% 17% 1	2871
	21st to end	Day	37% 7% 15% 21% 16% 3	2800
July	1st to 10th	Day	39% 5% 11% 27% 17% 2	6291
	11th to 20th	Day	37% 8% 15% 23% 16% 1	6244
	21st to end	Day	42% 7% 13% 20% 16% 2	6240
August	1st to 10th	Day	32% 7% 17% 29% 14% 1	4221
	11th to 20th	Day	34% 6% 13% 32% 15% 1	4213
	21st to end	Day	32% 6% 13% 31% 15% 3	4385
September	1st to 10th	Day	34% 5% 12% 24% 22% 3	2286
	11th to 20th	Day	33% 5% 10% 26% 23% 3	2200
	21st to end	Day	40% 4 9% 23% 22% 1	2200
October	1st to 10th	Day	25% 4 11% 31% 28% 2	3590
	11th to 20th	Day	31% 3 11% 28% 25% 2	3274
	21st to end	Day	41% 3 10% 25% 20% 2	3248
November	1st to 10th	Day	36% 4 11% 28% 18% 2	1852
	11th to 20th	Day	52% 3 9% 22% 11% 3	1890
	21st to end	Day	57% 3 10% 20% 9% 1	1890
December	1st to 10th	Day	52% 3 13% 23% 9%	3020
	11th to 20th	Day	65% 3 11% 16% 6%	3460
	21st to end	Day	75% 3 8% 10% 4	4070
January	1st to 10th	Night	67% 4 9% 14% 6%	8233
	11th to 20th	Night	68% 3 8% 11% 9% 1	8145
	21st to end	Night	58% 3 13% 18% 7% 1	8401
February	1st to 10th	Night	60% 3 10% 17% 7% 1	2646
	11th to 20th	Night	55% 3 10% 19% 12% 1	2459
	21st to end	Night	58% 4 11% 17% 9% 2	2076
March	1st to 10th	Night	52% 3 7% 26% 11% 2	5459
	11th to 20th	Night	40% 5% 13% 28% 14% 1	5090
	21st to end	Night	50% 3 10% 26% 10% 1	5588
April	1st to 10th	Night	48% 5% 11% 22% 13% 1	2147
	11th to 20th	Night	44% 5% 12% 19% 16% 3	2000
	21st to end	Night	46% 5% 11% 23% 13% 2	1890
May	1st to 10th	Night	54% 5% 9% 19% 10% 2	5264
	11th to 20th	Night	41% 6% 12% 26% 15% 1	5235
	21st to end	Night	42% 5% 13% 22% 12% 5%	5771
June	1st to 10th	Night	34% 7% 11% 23% 23% 2	1784
	11th to 20th	Night	33% 6% 13% 25% 18% 4	1640
	21st to end	Night	31% 7% 17% 24% 17% 4	1600
July	1st to 10th	Night	35% 6% 13% 25% 18% 5%	3580
	11th to 20th	Night	33% 8% 15% 27% 16% 1	3606
	21st to end	Night	37% 6% 15% 21% 19% 3	4297
August	1st to 10th	Night	37% 7% 14% 28% 14% 1	2904
	11th to 20th	Night	33% 6% 11% 31% 18% 1	2902
	21st to end	Night	28% 7% 14% 28% 20% 3	3509
September	1st to 10th	Night	32% 4 13% 26% 20% 6%	2092
	11th to 20th	Night	27% 5% 9% 29% 27% 3	2200
	21st to end	Night	37% 6% 9% 22% 24% 2	2200
October	1st to 10th	Night	23% 3 7% 32% 34% 2	3590
	11th to 20th	Night	32% 3 10% 26% 28% 1	3864
	21st to end	Night	34% 4 7% 28% 23% 4	4539
November	1st to 10th	Night	38% 4 10% 25% 21% 2	2666
	11th to 20th	Night	47% 3 9% 23% 14% 3	2730
	21st to end	Night	58% 4 10% 19% 9%	2730
December	1st to 10th	Night	52% 4 12% 23% 8% 1	4380
	11th to 20th	Night	65% 3 11% 14% 6%	4954
	21st to end	Night	73% 3 9% 12% 3	7132

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	24% 17% 32% 21% 6%	330
	11th to 20th	Day	25% 19% 36% 15% 3	330
	21st to end	Day	32% 15% 29% 18% 4 1	363
February	1st to 10th	Day	26% 16% 37% 14% 7% 1	330
	11th to 20th	Day	25% 20% 33% 15% 6%	330
	21st to end	Day	22% 15% 47% 15% 2	273
March	1st to 10th	Day	28% 16% 36% 17% 4	337
	11th to 20th	Day	26% 14% 34% 19% 7% 1	540
	21st to end	Day	28% 15% 33% 18% 6%	594
April	1st to 10th	Day	22% 17% 31% 19% 8% 2	540
	11th to 20th	Day	19% 16% 29% 22% 9% 4	532
	21st to end	Day	21% 12% 31% 23% 11% 2	540
May	1st to 10th	Day	26% 11% 29% 22% 8% 3	543
	11th to 20th	Day	21% 8% 27% 24% 13% 8%	567
	21st to end	Day	15% 6% 25% 27% 16% 11%	617
June	1st to 10th	Day	13% 7% 23% 31% 18% 8%	670
	11th to 20th	Day	13% 5% 25% 29% 20% 8%	756
	21st to end	Day	12% 5% 25% 30% 18% 10%	730
July	1st to 10th	Day	12% 4 17% 25% 26% 17%	721
	11th to 20th	Day	9% 3 19% 29% 25% 15%	703
	21st to end	Day	10% 3 14% 28% 26% 19%	576
August	1st to 10th	Day	11% 3 11% 23% 33% 19%	526
	11th to 20th	Day	10% 3 16% 28% 29% 13%	519
	21st to end	Day	9% 3 12% 26% 33% 16%	583
September	1st to 10th	Day	12% 4 15% 25% 28% 18%	530
	11th to 20th	Day	9% 3 11% 25% 32% 20%	530
	21st to end	Day	19% 8% 19% 23% 22% 9%	530
October	1st to 10th	Day	10% 6% 21% 31% 20% 12%	530
	11th to 20th	Day	15% 14% 26% 28% 13% 4	530
	21st to end	Day	26% 12% 34% 22% 6% 1	407
November	1st to 10th	Day	15% 15% 31% 26% 8% 5%	330
	11th to 20th	Day	25% 16% 30% 17% 9% 2	330
	21st to end	Day	29% 11% 40% 17% 3	330
December	1st to 10th	Day	20% 18% 38% 18% 6% 1	330
	11th to 20th	Day	24% 15% 40% 17% 5%	330
	21st to end	Day	32% 17% 31% 16% 3	363
January	1st to 10th	Night	22% 16% 34% 22% 5% 1	1050
	11th to 20th	Night	27% 14% 35% 19% 4	1006
	21st to end	Night	24% 12% 37% 23% 3	924
February	1st to 10th	Night	25% 10% 35% 27% 3	840
	11th to 20th	Night	22% 14% 36% 25% 2	823
	21st to end	Night	25% 12% 37% 23% 3	692
March	1st to 10th	Night	23% 12% 32% 27% 5% 1	840
	11th to 20th	Night	20% 14% 34% 27% 5% 1	840
	21st to end	Night	25% 11% 30% 26% 7%	924
April	1st to 10th	Night	22% 12% 32% 27% 6% 1	677
	11th to 20th	Night	19% 12% 33% 25% 10% 1	623
	21st to end	Night	19% 7% 38% 24% 11% 1	630
May	1st to 10th	Night	23% 6% 30% 30% 9% 1	630
	11th to 20th	Night	20% 5% 24% 33% 15% 1	621
	21st to end	Night	11% 3 22% 38% 23% 3	683
June	1st to 10th	Night	11% 3 23% 40% 23% 1	630
	11th to 20th	Night	10% 4 18% 43% 23% 1	615
	21st to end	Night	8% 3 21% 38% 29% 2	600
July	1st to 10th	Night	10% 3 13% 35% 32% 7%	585
	11th to 20th	Night	9% 2 13% 40% 30% 6%	582
	21st to end	Night	11% 3 9% 40% 36% 2	657
August	1st to 10th	Night	7% 2 12% 39% 37% 4	597
	11th to 20th	Night	7% 1 11% 42% 35% 4	594
	21st to end	Night	6% 2 12% 35% 39% 6%	660
September	1st to 10th	Night	14% 4 13% 33% 33% 4	692
	11th to 20th	Night	9% 3 11% 36% 37% 5%	800
	21st to end	Night	17% 4 20% 32% 24% 4	800
October	1st to 10th	Night	12% 3 24% 33% 23% 5%	800
	11th to 20th	Night	18% 10% 27% 30% 13% 1	800
	21st to end	Night	22% 10% 32% 27% 9%	880
November	1st to 10th	Night	16% 8% 33% 27% 14% 1	820
	11th to 20th	Night	20% 14% 31% 27% 7% 1	840
	21st to end	Night	24% 13% 28% 28% 6% 1	840
December	1st to 10th	Night	24% 13% 33% 25% 5% 1	840
	11th to 20th	Night	25% 11% 35% 25% 5% 1	840
	21st to end	Night	30% 13% 30% 22% 4	1150

Page generated at 2026-06-13 02:31:45. Version ac07

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