Barton Warnock Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Barton Warnock Visitor Center clear sky chart from 2005-11-06 to 2025-09-19.

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	3 2 1 3 2 3 3 3 5% 7% 67%	133904
	Night	3 2 1 3 3 3 4 3 5% 8% 64%	132581
Transparency	Day	12% 23% 6% 15% 21% 23%	129016
	Night	13% 24% 6% 15% 19% 23%	128472
Seeing	Day	5% 5% 19% 33% 29% 9%	15497
	Night	5% 3 19% 46% 25% 1	25663

By Month

Percentage Cloud Cover SW (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	3 2 1 3 2 2 2 2 3 6% 74%	4537
	11th to 20th	Day	3 2 1 2 2 2 2 3 4 6% 74%	4540
	21st to end	Day	3 4 1 4 3 3 3 3 4 5% 66%	4994
February	1st to 10th	Day	3 4 1 5% 3 2 4 3 5% 5% 65%	2000
	11th to 20th	Day	4 4 2 4 3 3 3 3 4 6% 64%	1949
	21st to end	Day	3 4 1 2 2 2 3 3 5% 6% 69%	1650
March	1st to 10th	Day	2 2 1 4 2 3 3 4 5% 7% 67%	4500
	11th to 20th	Day	6% 2 1 2 2 2 3 3 4 5% 70%	4810
	21st to end	Day	2 3 1 3 3 3 3 3 5% 8% 67%	5955
April	1st to 10th	Day	2 2 1 3 2 3 4 3 5% 6% 68%	2400
	11th to 20th	Day	2 3 1 3 2 2 3 3 5% 6% 72%	2371
	21st to end	Day	3 3 1 3 3 2 3 2 5% 6% 71%	2400
May	1st to 10th	Day	2 2 1 2 1 2 2 2 3 5% 80%	5440
	11th to 20th	Day	3 2 1 2 2 3 4 3 5% 7% 67%	5405
	21st to end	Day	3 1 1 2 2 2 3 3 6% 7% 69%	6118
June	1st to 10th	Day	1 1 2 1 3 3 4 6% 8% 71%	2600
	11th to 20th	Day	2 2 1 3 3 3 4 4 5% 8% 67%	2600
	21st to end	Day	2 3 1 3 3 3 4 4 7% 10% 59%	2468
July	1st to 10th	Day	3 2 1 3 3 3 4 4 6% 10% 61%	5439
	11th to 20th	Day	2 2 1 3 3 3 4 5% 8% 12% 58%	5440
	21st to end	Day	2 2 1 3 3 4 5% 5% 7% 11% 58%	5922
August	1st to 10th	Day	1 1 1 2 2 3 3 6% 11% 71%	5348
	11th to 20th	Day	2 2 1 4 3 3 4 5% 7% 12% 56%	5366
	21st to end	Day	2 1 1 3 3 3 4 4 7% 9% 64%	5984
September	1st to 10th	Day	5% 5% 2 6% 5% 4 5% 4 7% 10% 47%	2400
	11th to 20th	Day	7% 5% 2 4 4 4 4 4 6% 10% 50%	2242
	21st to end	Day	5% 3 1 4 3 3 4 3 5% 7% 62%	2090
October	1st to 10th	Day	2 1 1 2 2 1 2 2 3 5% 79%	3480
	11th to 20th	Day	4 2 1 2 2 2 3 3 4 7% 72%	3320
	21st to end	Day	3 2 1 1 1 1 1 1 2 3 83%	3438
November	1st to 10th	Day	6% 2 1 2 2 2 2 2 3 5% 72%	1939
	11th to 20th	Day	4 3 1 2 2 2 3 3 5% 5% 70%	1800
	21st to end	Day	5% 3 1 3 3 4 3 3 5% 6% 65%	1800
December	1st to 10th	Day	8% 6% 2 5% 4 3 2 3 4 7% 57%	2940
	11th to 20th	Day	2 3 1 3 3 3 3 2 5% 6% 69%	3391
	21st to end	Day	2 2 1 2 2 2 3 3 4 6% 74%	4828
January	1st to 10th	Night	2 2 1 2 1 2 2 2 3 5% 77%	5428
	11th to 20th	Night	3 1 1 2 2 2 3 3 3 5% 75%	5440
	21st to end	Night	4 4 1 4 3 3 4 3 5% 7% 62%	5984
February	1st to 10th	Night	3 4 1 4 2 3 3 3 5% 5% 66%	2400
	11th to 20th	Night	5% 4 1 4 3 3 4 3 5% 7% 61%	2338
	21st to end	Night	4 3 1 2 3 3 4 3 4 6% 67%	1980
March	1st to 10th	Night	3 3 1 4 2 3 3 3 5% 7% 64%	5374
	11th to 20th	Night	8% 3 1 3 2 1 2 2 4 5% 70%	5176
	21st to end	Night	3 3 1 3 3 3 3 3 5% 6% 67%	4995
April	1st to 10th	Night	3 4 1 4 3 4 4 3 4 6% 65%	2000
	11th to 20th	Night	4 2 1 3 2 3 3 3 5% 7% 68%	1977
	21st to end	Night	3 3 1 2 2 2 4 3 4 5% 71%	2000
May	1st to 10th	Night	2 1 1 2 1 2 2 2 3 5% 80%	4540
	11th to 20th	Night	7% 3 1 4 3 3 4 4 5% 7% 59%	4510
	21st to end	Night	3 2 1 3 3 3 4 3 5% 7% 65%	4769
June	1st to 10th	Night	2 2 1 4 3 3 5% 5% 9% 11% 56%	1800
	11th to 20th	Night	2 2 1 4 4 5% 5% 5% 8% 10% 55%	1800
	21st to end	Night	3 3 1 5% 4 3 4 4 8% 10% 54%	1920
July	1st to 10th	Night	4 3 2 4 4 4 5% 5% 8% 12% 49%	4540
	11th to 20th	Night	2 1 1 4 3 4 4 4 8% 13% 55%	4540
	21st to end	Night	2 2 1 4 4 5% 5% 6% 9% 11% 51%	4951
August	1st to 10th	Night	1 1 2 2 3 3 4 8% 12% 64%	4464
	11th to 20th	Night	2 2 1 3 3 4 5% 5% 8% 14% 53%	4483
	21st to end	Night	1 2 1 3 3 4 5% 5% 8% 13% 56%	4993
September	1st to 10th	Night	5% 4 2 5% 5% 5% 6% 4 7% 10% 49%	2000
	11th to 20th	Night	5% 4 2 7% 5% 4 6% 6% 7% 10% 43%	2113
	21st to end	Night	5% 4 2 5% 4 4 4 4 6% 10% 53%	2090
October	1st to 10th	Night	2 1 1 2 2 2 3 3 4 6% 73%	3480
	11th to 20th	Night	5% 2 1 3 2 2 4 2 5% 6% 69%	3584
	21st to end	Night	3 2 2 1 1 1 1 2 4 82%	4120
November	1st to 10th	Night	6% 2 1 2 2 1 1 2 3 4 76%	2340
	11th to 20th	Night	4 2 1 2 2 2 3 2 5% 5% 71%	2595
	21st to end	Night	5% 3 1 3 2 3 4 3 4 6% 66%	2600
December	1st to 10th	Night	8% 3 2 5% 4 4 6% 4 6% 6% 53%	4250
	11th to 20th	Night	2 3 1 3 2 2 2 3 4 7% 72%	4816
	21st to end	Night	2 2 1 2 2 2 3 3 4 7% 72%	6191

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	8% 19% 3 17% 27% 26%	4538
	11th to 20th	Day	8% 20% 3 17% 28% 23%	4540
	21st to end	Day	16% 19% 3 22% 23% 17%	4994
February	1st to 10th	Day	12% 37% 4 7% 15% 26%	2000
	11th to 20th	Day	13% 38% 3 9% 20% 18%	1959
	21st to end	Day	9% 35% 3 9% 20% 25%	1650
March	1st to 10th	Day	12% 16% 4 7% 20% 41%	4500
	11th to 20th	Day	12% 16% 4 8% 15% 45%	4810
	21st to end	Day	13% 15% 5% 6% 21% 40%	5955
April	1st to 10th	Day	10% 32% 5% 8% 14% 31%	2400
	11th to 20th	Day	8% 31% 4 9% 16% 32%	2374
	21st to end	Day	10% 32% 4 8% 15% 31%	2400
May	1st to 10th	Day	8% 15% 2 10% 19% 46%	5440
	11th to 20th	Day	13% 18% 4 8% 23% 34%	5408
	21st to end	Day	10% 17% 6% 15% 17% 34%	6119
June	1st to 10th	Day	6% 33% 6% 16% 21% 19%	2600
	11th to 20th	Day	8% 33% 6% 10% 22% 21%	2600
	21st to end	Day	15% 34% 9% 14% 17% 11%	2468
July	1st to 10th	Day	16% 19% 15% 25% 19% 6%	5381
	11th to 20th	Day	14% 18% 14% 35% 14% 4	5377
	21st to end	Day	17% 18% 15% 22% 19% 9%	5752
August	1st to 10th	Day	9% 22% 7% 26% 28% 8%	3892
	11th to 20th	Day	13% 22% 10% 31% 20% 4	3882
	21st to end	Day	14% 25% 12% 23% 20% 6%	4311
September	1st to 10th	Day	22% 36% 10% 12% 11% 10%	2400
	11th to 20th	Day	20% 35% 8% 14% 16% 8%	2242
	21st to end	Day	12% 35% 5% 14% 18% 16%	2090
October	1st to 10th	Day	6% 22% 4 9% 22% 38%	3480
	11th to 20th	Day	8% 21% 8% 17% 15% 31%	3320
	21st to end	Day	5% 21% 2 9% 35% 29%	3438
November	1st to 10th	Day	4 40% 3 10% 21% 22%	1939
	11th to 20th	Day	6% 42% 5% 11% 20% 16%	1800
	21st to end	Day	11% 43% 6% 14% 12% 15%	1800
December	1st to 10th	Day	22% 27% 6% 12% 20% 13%	2940
	11th to 20th	Day	12% 23% 3 22% 27% 13%	3389
	21st to end	Day	8% 19% 3 12% 32% 27%	4828
January	1st to 10th	Night	6% 19% 2 15% 32% 25%	5428
	11th to 20th	Night	9% 19% 4 12% 23% 32%	5440
	21st to end	Night	17% 19% 4 20% 23% 18%	5984
February	1st to 10th	Night	12% 36% 4 7% 15% 27%	2400
	11th to 20th	Night	14% 38% 4 8% 16% 19%	2338
	21st to end	Night	9% 36% 2 7% 19% 26%	1980
March	1st to 10th	Night	15% 17% 3 6% 19% 41%	5374
	11th to 20th	Night	14% 16% 4 8% 15% 43%	5176
	21st to end	Night	15% 15% 5% 7% 18% 40%	4995
April	1st to 10th	Night	13% 33% 4 9% 13% 29%	2000
	11th to 20th	Night	10% 31% 5% 9% 13% 31%	1977
	21st to end	Night	11% 32% 4 10% 15% 28%	2000
May	1st to 10th	Night	7% 15% 4 14% 18% 41%	4537
	11th to 20th	Night	21% 18% 5% 9% 16% 31%	4511
	21st to end	Night	15% 17% 7% 14% 16% 30%	4770
June	1st to 10th	Night	11% 35% 10% 19% 13% 12%	1800
	11th to 20th	Night	13% 34% 7% 12% 17% 16%	1800
	21st to end	Night	18% 35% 9% 14% 15% 9%	1920
July	1st to 10th	Night	22% 18% 17% 25% 15% 3	4490
	11th to 20th	Night	16% 18% 16% 32% 14% 4	4480
	21st to end	Night	22% 19% 15% 21% 16% 6%	4808
August	1st to 10th	Night	10% 23% 7% 29% 26% 4	3244
	11th to 20th	Night	13% 22% 13% 33% 16% 2	3243
	21st to end	Night	16% 25% 14% 24% 19% 3	3597
September	1st to 10th	Night	21% 36% 12% 14% 9% 8%	2000
	11th to 20th	Night	24% 36% 9% 12% 13% 6%	2113
	21st to end	Night	15% 36% 8% 13% 14% 14%	2090
October	1st to 10th	Night	7% 22% 5% 8% 18% 39%	3480
	11th to 20th	Night	13% 22% 7% 15% 12% 31%	3584
	21st to end	Night	6% 21% 2 11% 33% 27%	4120
November	1st to 10th	Night	4 39% 2 9% 23% 23%	2340
	11th to 20th	Night	7% 42% 5% 9% 16% 21%	2595
	21st to end	Night	10% 42% 6% 12% 13% 17%	2600
December	1st to 10th	Night	25% 27% 6% 13% 13% 16%	4250
	11th to 20th	Night	9% 23% 3 20% 28% 17%	4817
	21st to end	Night	9% 19% 3 11% 32% 25%	6191

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	11% 4 27% 36% 18% 3	300
	11th to 20th	Day	6% 6% 25% 41% 21% 1	300
	21st to end	Day	4 12% 28% 35% 19% 2	330
February	1st to 10th	Day	7% 9% 22% 28% 29% 6%	300
	11th to 20th	Day	9% 12% 25% 36% 17% 2	300
	21st to end	Day	6% 11% 30% 39% 11% 2	249
March	1st to 10th	Day	8% 7% 31% 35% 18% 1	300
	11th to 20th	Day	9% 14% 33% 29% 12% 4	414
	21st to end	Day	8% 14% 33% 32% 11% 1	550
April	1st to 10th	Day	6% 14% 36% 31% 11% 2	500
	11th to 20th	Day	4 14% 39% 30% 10% 2	492
	21st to end	Day	6% 11% 32% 40% 10%	500
May	1st to 10th	Day	4 9% 34% 38% 13% 3	503
	11th to 20th	Day	3 11% 31% 38% 16% 2	528
	21st to end	Day	3 4 26% 43% 22% 2	643
June	1st to 10th	Day	1 2 15% 39% 37% 5%	730
	11th to 20th	Day	2 12% 40% 41% 5%	730
	21st to end	Day	4 1 10% 34% 42% 9%	598
July	1st to 10th	Day	4 1 8% 27% 39% 21%	526
	11th to 20th	Day	2 6% 34% 41% 17%	524
	21st to end	Day	2 1 4 36% 42% 15%	575
August	1st to 10th	Day	2 1 5% 23% 51% 20%	527
	11th to 20th	Day	5% 1 7% 27% 39% 22%	517
	21st to end	Day	3 1 7% 27% 40% 22%	583
September	1st to 10th	Day	7% 1 7% 32% 37% 15%	530
	11th to 20th	Day	5% 5% 21% 49% 19%	388
	21st to end	Day	7% 8% 23% 40% 22%	300
October	1st to 10th	Day	4 2 8% 27% 42% 17%	300
	11th to 20th	Day	9% 1 12% 29% 32% 16%	300
	21st to end	Day	8% 3 13% 28% 34% 13%	330
November	1st to 10th	Day	6% 5% 15% 29% 34% 10%	300
	11th to 20th	Day	8% 7% 18% 25% 31% 11%	300
	21st to end	Day	7% 9% 22% 32% 26% 5%	300
December	1st to 10th	Day	8% 5% 17% 31% 33% 5%	300
	11th to 20th	Day	4 8% 23% 37% 25% 3	300
	21st to end	Day	5% 6% 22% 43% 22% 2	330
January	1st to 10th	Night	7% 3 22% 51% 17% 1	800
	11th to 20th	Night	8% 3 21% 51% 18%	800
	21st to end	Night	7% 5% 25% 48% 14% 1	880
February	1st to 10th	Night	6% 5% 25% 44% 20% 1	800
	11th to 20th	Night	7% 5% 25% 52% 11% 1	784
	21st to end	Night	7% 6% 31% 48% 8%	660
March	1st to 10th	Night	7% 6% 33% 43% 10% 1	800
	11th to 20th	Night	8% 8% 27% 43% 14% 1	800
	21st to end	Night	5% 7% 35% 44% 10%	671
April	1st to 10th	Night	4 8% 33% 46% 9%	600
	11th to 20th	Night	4 7% 38% 44% 6%	593
	21st to end	Night	4 7% 36% 48% 7%	600
May	1st to 10th	Night	4 5% 32% 51% 9%	600
	11th to 20th	Night	6% 5% 29% 50% 10%	591
	21st to end	Night	3 2 28% 53% 14%	650
June	1st to 10th	Night	2 2 17% 59% 19% 1	600
	11th to 20th	Night	2 1 18% 58% 22%	600
	21st to end	Night	4 1 13% 47% 34% 1	600
July	1st to 10th	Night	5% 1 12% 41% 39% 3	585
	11th to 20th	Night	3 5% 42% 47% 2	582
	21st to end	Night	4 6% 40% 48% 2	657
August	1st to 10th	Night	2 1 4 32% 59% 2	597
	11th to 20th	Night	3 1 5% 32% 55% 4	594
	21st to end	Night	3 1 6% 34% 52% 3	660
September	1st to 10th	Night	6% 1 6% 36% 49% 2	600
	11th to 20th	Night	7% 1 8% 37% 46% 1	594
	21st to end	Night	6% 1 9% 43% 39% 2	570
October	1st to 10th	Night	4 1 10% 47% 37% 1	570
	11th to 20th	Night	8% 1 12% 50% 27% 2	644
	21st to end	Night	5% 3 13% 43% 32% 4	836
November	1st to 10th	Night	7% 2 10% 46% 32% 3	780
	11th to 20th	Night	4 4 14% 49% 28% 1	995
	21st to end	Night	6% 4 22% 46% 20% 2	1000
December	1st to 10th	Night	8% 2 15% 51% 23% 1	1000
	11th to 20th	Night	5% 3 22% 50% 19% 1	1000
	21st to end	Night	5% 4 22% 53% 15% 2	970

Page generated at 2025-09-16 00:49:13. Version ac07

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