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 2024-01-31.

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 7% 6% 3 5% 5% 5% 7% 34%	75130
	Night	15% 9% 4 7% 6% 3 4 4 5% 7% 36%	74991
Transparency	Day	48% 5% 12% 21% 12% 2	74843
	Night	48% 5% 11% 21% 13% 2	74798
Seeing	Day	18% 9% 25% 24% 16% 8%	14369
	Night	19% 8% 27% 30% 15% 2	24289

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% 7% 9% 8% 5% 5% 5% 4 6% 21%	1517
	11th to 20th	Day	19% 14% 8% 10% 8% 3 5% 4 5% 4 20%	1555
	21st to end	Day	16% 17% 8% 12% 7% 3 5% 4 5% 4 19%	1872
February	1st to 10th	Day	21% 13% 7% 10% 7% 4 5% 4 4 5% 21%	1688
	11th to 20th	Day	15% 11% 5% 12% 9% 5% 6% 3 5% 6% 23%	1748
	21st to end	Day	17% 13% 5% 11% 6% 4 4 3 4 5% 29%	1480
March	1st to 10th	Day	18% 12% 5% 6% 6% 3 3 5% 5% 7% 29%	1805
	11th to 20th	Day	17% 11% 5% 8% 7% 3 5% 4 4 6% 30%	1980
	21st to end	Day	22% 12% 4 8% 6% 4 4 3 4 6% 27%	2178
April	1st to 10th	Day	14% 10% 4 7% 7% 4 5% 4 4 7% 33%	2134
	11th to 20th	Day	17% 8% 4 5% 5% 2 5% 5% 6% 6% 37%	2195
	21st to end	Day	19% 8% 3 7% 6% 3 4 5% 6% 7% 31%	2340
May	1st to 10th	Day	19% 9% 4 6% 6% 4 5% 4 6% 6% 32%	2340
	11th to 20th	Day	20% 7% 3 6% 6% 3 4 5% 5% 7% 33%	2301
	21st to end	Day	9% 6% 3 7% 7% 4 6% 6% 7% 10% 36%	2531
June	1st to 10th	Day	13% 5% 4 5% 5% 3 6% 5% 5% 8% 41%	2425
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 5% 6% 11% 42%	2520
	21st to end	Day	9% 5% 2 6% 6% 4 5% 7% 7% 11% 39%	2520
July	1st to 10th	Day	10% 5% 3 5% 6% 4 6% 6% 7% 10% 38%	2520
	11th to 20th	Day	8% 4 2 4 5% 3 5% 6% 6% 11% 45%	2507
	21st to end	Day	9% 4 2 5% 6% 4 6% 6% 7% 10% 42%	2547
August	1st to 10th	Day	8% 4 2 5% 6% 3 5% 6% 7% 10% 43%	2327
	11th to 20th	Day	9% 5% 2 6% 6% 4 7% 6% 7% 9% 39%	2303
	21st to end	Day	8% 5% 2 6% 6% 4 5% 5% 7% 10% 42%	2420
September	1st to 10th	Day	12% 5% 2 4 5% 3 5% 4 5% 7% 47%	2058
	11th to 20th	Day	10% 5% 3 6% 5% 2 4 5% 6% 8% 47%	1980
	21st to end	Day	14% 6% 2 5% 5% 3 4 3 5% 6% 48%	1980
October	1st to 10th	Day	12% 6% 3 5% 5% 4 5% 4 5% 7% 43%	1980
	11th to 20th	Day	14% 7% 3 4 5% 3 3 4 6% 7% 43%	1819
	21st to end	Day	19% 11% 3 7% 5% 3 4 4 5% 7% 32%	1822
November	1st to 10th	Day	9% 8% 3 4 4 2 4 4 5% 7% 49%	1672
	11th to 20th	Day	15% 12% 4 7% 6% 3 4 5% 4 6% 34%	1710
	21st to end	Day	19% 11% 5% 8% 6% 3 4 4 4 6% 31%	1710
December	1st to 10th	Day	18% 14% 9% 9% 7% 3 3 4 4 6% 23%	1710
	11th to 20th	Day	15% 13% 7% 11% 6% 4 5% 4 4 5% 24%	2153
	21st to end	Day	22% 20% 10% 9% 7% 4 4 4 4 4 11%	2783
January	1st to 10th	Night	17% 12% 7% 10% 9% 4 5% 4 4 5% 23%	2648
	11th to 20th	Night	18% 16% 7% 10% 7% 3 4 4 4 5% 22%	2621
	21st to end	Night	18% 15% 6% 10% 7% 3 4 4 4 5% 23%	2711
February	1st to 10th	Night	21% 13% 5% 9% 7% 4 4 4 3 6% 25%	2268
	11th to 20th	Night	15% 11% 6% 8% 7% 4 5% 4 5% 6% 30%	2098
	21st to end	Night	20% 11% 6% 9% 6% 4 3 4 4 5% 27%	1776
March	1st to 10th	Night	17% 8% 5% 7% 6% 3 4 4 5% 5% 35%	2154
	11th to 20th	Night	14% 9% 3 6% 6% 3 4 5% 5% 7% 37%	1980
	21st to end	Night	21% 10% 5% 6% 6% 2 4 3 4 6% 33%	2178
April	1st to 10th	Night	14% 7% 4 7% 5% 3 5% 5% 6% 7% 37%	1841
	11th to 20th	Night	16% 7% 3 5% 5% 3 5% 5% 6% 7% 37%	1712
	21st to end	Night	17% 7% 3 6% 6% 3 5% 4 5% 8% 36%	1620
May	1st to 10th	Night	18% 9% 3 7% 6% 3 5% 5% 7% 7% 30%	1620
	11th to 20th	Night	20% 6% 3 4 4 3 4 4 5% 7% 40%	1592
	21st to end	Night	7% 5% 2 4 5% 3 5% 6% 8% 12% 43%	1744
June	1st to 10th	Night	8% 4 2 5% 5% 3 5% 6% 5% 9% 48%	1530
	11th to 20th	Night	8% 4 2 5% 5% 2 4 5% 6% 8% 49%	1440
	21st to end	Night	7% 5% 1 5% 5% 3 5% 6% 7% 10% 47%	1440
July	1st to 10th	Night	9% 4 2 7% 5% 5% 6% 4 5% 8% 46%	1440
	11th to 20th	Night	7% 3 2 5% 4 2 4 6% 6% 9% 51%	1448
	21st to end	Night	8% 5% 2 5% 4 3 4 5% 6% 8% 49%	1771
August	1st to 10th	Night	6% 4 2 4 5% 5% 6% 5% 7% 9% 47%	1611
	11th to 20th	Night	6% 5% 2 5% 5% 4 5% 5% 6% 8% 49%	1598
	21st to end	Night	6% 3 2 5% 5% 4 5% 5% 7% 8% 51%	1933
September	1st to 10th	Night	13% 5% 2 4 4 2 3 5% 5% 9% 49%	1882
	11th to 20th	Night	9% 4 2 4 4 2 3 5% 5% 8% 55%	1980
	21st to end	Night	12% 5% 2 4 4 3 5% 4 5% 6% 51%	1980
October	1st to 10th	Night	10% 5% 2 4 5% 3 4 4 5% 6% 52%	1980
	11th to 20th	Night	17% 7% 3 6% 6% 3 4 4 5% 6% 40%	2140
	21st to end	Night	20% 7% 3 6% 4 3 4 5% 4 6% 38%	2531
November	1st to 10th	Night	12% 8% 3 5% 5% 3 3 3 5% 7% 46%	2406
	11th to 20th	Night	15% 9% 3 7% 6% 4 4 4 4 7% 37%	2470
	21st to end	Night	18% 11% 5% 8% 6% 4 5% 4 4 7% 28%	2470
December	1st to 10th	Night	19% 13% 6% 8% 6% 3 5% 4 4 7% 25%	2470
	11th to 20th	Night	17% 13% 7% 9% 5% 3 5% 5% 4 5% 27%	3042
	21st to end	Night	23% 18% 7% 9% 7% 3 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% 17% 8%	1518
	11th to 20th	Day	68% 3 11% 13% 5%	1555
	21st to end	Day	68% 4 9% 13% 5% 1	1872
February	1st to 10th	Day	66% 3 9% 13% 8% 1	1688
	11th to 20th	Day	62% 4 10% 17% 7%	1758
	21st to end	Day	58% 4 11% 17% 9% 1	1480
March	1st to 10th	Day	54% 4 11% 21% 8% 1	1805
	11th to 20th	Day	56% 3 12% 18% 10% 1	1980
	21st to end	Day	60% 3 12% 19% 5% 1	2178
April	1st to 10th	Day	52% 4 12% 19% 13% 1	2134
	11th to 20th	Day	47% 5% 13% 20% 13% 3	2195
	21st to end	Day	51% 5% 12% 20% 10% 2	2340
May	1st to 10th	Day	53% 5% 12% 19% 10% 1	2340
	11th to 20th	Day	50% 5% 13% 19% 11% 1	2305
	21st to end	Day	42% 8% 16% 23% 11% 1	2531
June	1st to 10th	Day	41% 5% 12% 24% 15% 3	2425
	11th to 20th	Day	37% 6% 14% 25% 17% 2	2520
	21st to end	Day	38% 7% 16% 22% 15% 3	2520
July	1st to 10th	Day	40% 6% 15% 22% 15% 3	2451
	11th to 20th	Day	32% 7% 13% 27% 19% 1	2432
	21st to end	Day	35% 6% 16% 25% 15% 3	2405
August	1st to 10th	Day	33% 7% 13% 30% 14% 2	2314
	11th to 20th	Day	38% 6% 14% 27% 13% 1	2303
	21st to end	Day	35% 6% 12% 25% 16% 5%	2420
September	1st to 10th	Day	36% 5% 13% 22% 20% 3	2058
	11th to 20th	Day	35% 5% 11% 26% 21% 2	1980
	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	64% 4 7% 17% 8%	2648
	11th to 20th	Night	67% 3 9% 15% 6%	2621
	21st to end	Night	65% 3 9% 16% 7% 1	2711
February	1st to 10th	Night	63% 3 10% 17% 6% 1	2268
	11th to 20th	Night	55% 3 11% 18% 11% 1	2099
	21st to end	Night	60% 3 9% 16% 9% 2	1776
March	1st to 10th	Night	51% 3 10% 21% 13% 1	2154
	11th to 20th	Night	47% 5% 13% 21% 12% 3	1980
	21st to end	Night	54% 3 9% 24% 8% 1	2178
April	1st to 10th	Night	46% 5% 12% 23% 13% 1	1841
	11th to 20th	Night	44% 5% 11% 18% 17% 4	1712
	21st to end	Night	47% 5% 11% 22% 12% 3	1620
May	1st to 10th	Night	52% 5% 12% 19% 9% 3	1620
	11th to 20th	Night	44% 6% 12% 22% 14% 2	1593
	21st to end	Night	32% 7% 17% 27% 13% 4	1745
June	1st to 10th	Night	33% 6% 12% 25% 22% 3	1530
	11th to 20th	Night	32% 7% 14% 26% 18% 4	1440
	21st to end	Night	32% 8% 17% 24% 17% 4	1440
July	1st to 10th	Night	37% 6% 13% 21% 18% 5%	1400
	11th to 20th	Night	29% 7% 14% 30% 18% 2	1400
	21st to end	Night	31% 6% 14% 28% 18% 3	1672
August	1st to 10th	Night	31% 8% 14% 29% 18% 2	1600
	11th to 20th	Night	32% 7% 13% 28% 20% 1	1598
	21st to end	Night	29% 7% 14% 22% 22% 5%	1933
September	1st to 10th	Night	34% 5% 14% 24% 18% 6%	1882
	11th to 20th	Night	28% 5% 10% 29% 26% 2	1980
	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	36% 12% 29% 19% 4 1	294
February	1st to 10th	Day	33% 15% 34% 14% 4	240
	11th to 20th	Day	26% 20% 34% 15% 6%	240
	21st to end	Day	25% 14% 46% 14% 2	198
March	1st to 10th	Day	28% 16% 35% 18% 3	245
	11th to 20th	Day	25% 11% 35% 19% 8% 1	420
	21st to end	Day	31% 12% 32% 18% 7%	462
April	1st to 10th	Day	21% 14% 32% 21% 10% 2	420
	11th to 20th	Day	21% 15% 27% 22% 10% 5%	412
	21st to end	Day	24% 12% 31% 21% 10% 2	420
May	1st to 10th	Day	27% 9% 28% 24% 8% 4	423
	11th to 20th	Day	22% 6% 28% 23% 13% 8%	447
	21st to end	Day	13% 6% 24% 27% 18% 13%	485
June	1st to 10th	Day	13% 4 21% 33% 20% 8%	535
	11th to 20th	Day	12% 5% 25% 29% 21% 9%	630
	21st to end	Day	12% 5% 24% 30% 18% 10%	630
July	1st to 10th	Day	12% 3 16% 24% 27% 19%	621
	11th to 20th	Day	9% 3 18% 30% 24% 16%	605
	21st to end	Day	11% 3 14% 26% 26% 20%	488
August	1st to 10th	Day	12% 3 9% 23% 33% 20%	446
	11th to 20th	Day	10% 3 16% 27% 30% 13%	439
	21st to end	Day	10% 3 12% 26% 32% 17%	495
September	1st to 10th	Day	13% 3 14% 25% 27% 18%	450
	11th to 20th	Day	10% 3 12% 26% 30% 18%	450
	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% 4	835
February	1st to 10th	Night	28% 9% 33% 27% 3	720
	11th to 20th	Night	23% 15% 35% 25% 2	703
	21st to end	Night	27% 11% 37% 21% 3	592
March	1st to 10th	Night	22% 11% 32% 28% 6% 1	720
	11th to 20th	Night	20% 13% 33% 28% 6% 1	720
	21st to end	Night	27% 9% 28% 26% 9% 1	792
April	1st to 10th	Night	19% 11% 32% 30% 7% 1	581
	11th to 20th	Night	19% 11% 32% 26% 11% 1	533
	21st to end	Night	21% 6% 38% 23% 11% 1	540
May	1st to 10th	Night	24% 6% 29% 30% 10% 1	540
	11th to 20th	Night	22% 3 24% 33% 16% 1	531
	21st to end	Night	9% 2 22% 38% 26% 3	584
June	1st to 10th	Night	9% 2 22% 43% 24% 1	540
	11th to 20th	Night	10% 4 19% 41% 25% 1	540
	21st to end	Night	9% 3 21% 38% 29% 1	540
July	1st to 10th	Night	10% 2 13% 34% 34% 7%	525
	11th to 20th	Night	9% 2 12% 40% 30% 7%	522
	21st to end	Night	11% 3 9% 40% 36% 2	591
August	1st to 10th	Night	7% 2 11% 40% 37% 4	537
	11th to 20th	Night	7% 1 11% 42% 35% 5%	534
	21st to end	Night	6% 2 13% 33% 40% 6%	594
September	1st to 10th	Night	15% 4 12% 32% 33% 5%	622
	11th to 20th	Night	9% 3 12% 35% 36% 5%	720
	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

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