Burns
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burns clear sky chart from 2005-11-06 to 2026-07-16.

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	5% 6% 2 6% 4 4 4 3 5% 7% 54%	146853
	Night	6% 7% 2 6% 4 4 4 4 5% 7% 50%	143130
Transparency	Day	31% 3 8% 22% 22% 14%	141652
	Night	35% 4 10% 22% 19% 9%	139329
Seeing	Day	9% 8% 20% 28% 24% 12%	16713
	Night	10% 4 22% 40% 21% 3	25871

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	10% 14% 5% 12% 6% 6% 6% 5% 6% 8% 23%	4722
	11th to 20th	Day	6% 8% 3 7% 4 4 4 3 4 9% 48%	4740
	21st to end	Day	7% 9% 3 8% 6% 5% 5% 3 6% 8% 41%	5265
February	1st to 10th	Day	6% 9% 2 10% 7% 6% 7% 5% 8% 9% 32%	1890
	11th to 20th	Day	7% 11% 4 9% 6% 6% 5% 5% 6% 8% 33%	1986
	21st to end	Day	5% 9% 4 8% 6% 6% 7% 5% 7% 8% 34%	1730
March	1st to 10th	Day	5% 12% 5% 10% 6% 5% 5% 4 6% 11% 32%	4618
	11th to 20th	Day	6% 8% 2 7% 5% 5% 4 4 6% 8% 45%	4840
	21st to end	Day	6% 10% 4 10% 7% 7% 7% 5% 7% 8% 31%	6073
April	1st to 10th	Day	7% 9% 3 7% 6% 6% 5% 4 6% 7% 39%	2520
	11th to 20th	Day	8% 8% 2 6% 5% 5% 4 4 7% 8% 44%	2489
	21st to end	Day	6% 8% 3 6% 4 5% 4 3 5% 7% 49%	2625
May	1st to 10th	Day	5% 5% 1 4 3 3 4 4 5% 7% 58%	7870
	11th to 20th	Day	4 4 2 4 3 3 4 3 5% 8% 60%	8160
	21st to end	Day	4 4 2 4 3 4 4 3 5% 8% 58%	8992
June	1st to 10th	Day	7% 6% 2 6% 5% 5% 4 4 6% 7% 48%	2940
	11th to 20th	Day	5% 4 1 5% 5% 4 3 3 5% 7% 59%	2940
	21st to end	Day	3 3 1 4 2 2 3 3 4 5% 69%	2940
July	1st to 10th	Day	1 1 1 2 2 2 2 2 3 4 80%	6459
	11th to 20th	Day	2 2 2 2 2 2 2 2 3 82%	6391
	21st to end	Day	2 2 1 2 2 2 3 3 4 6% 73%	6880
August	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 7% 65%	6210
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 80%	5482
	21st to end	Day	4 3 1 4 3 2 2 2 3 5% 69%	5984
September	1st to 10th	Day	2 3 1 3 2 3 3 2 3 5% 73%	2400
	11th to 20th	Day	4 3 1 4 4 4 3 3 5% 6% 64%	2340
	21st to end	Day	5% 4 1 5% 3 3 3 3 4 5% 64%	2200
October	1st to 10th	Day	4 3 2 4 3 3 2 2 3 5% 69%	3363
	11th to 20th	Day	5% 6% 2 6% 4 4 4 3 5% 7% 55%	3261
	21st to end	Day	8% 8% 2 7% 4 4 5% 4 6% 7% 42%	3236
November	1st to 10th	Day	11% 8% 3 6% 5% 4 5% 4 6% 9% 40%	1854
	11th to 20th	Day	11% 8% 2 9% 5% 5% 6% 4 7% 9% 33%	1873
	21st to end	Day	7% 9% 2 8% 6% 6% 5% 4 6% 9% 38%	1680
December	1st to 10th	Day	5% 6% 2 7% 5% 5% 4 3 7% 10% 46%	2700
	11th to 20th	Day	11% 13% 5% 11% 7% 6% 6% 5% 6% 9% 22%	3108
	21st to end	Day	11% 12% 5% 14% 8% 7% 7% 5% 6% 7% 20%	4092
January	1st to 10th	Night	10% 13% 4 11% 7% 6% 5% 4 6% 9% 24%	8172
	11th to 20th	Night	8% 8% 2 4 4 4 4 3 4 8% 52%	8220
	21st to end	Night	8% 9% 3 8% 6% 5% 5% 4 5% 7% 40%	8902
February	1st to 10th	Night	7% 10% 3 8% 5% 5% 5% 5% 7% 8% 35%	2730
	11th to 20th	Night	7% 11% 3 8% 4 5% 5% 4 7% 7% 38%	2521
	21st to end	Night	6% 10% 4 8% 6% 5% 6% 4 7% 8% 37%	2076
March	1st to 10th	Night	5% 12% 4 8% 5% 6% 6% 5% 6% 10% 34%	5496
	11th to 20th	Night	7% 10% 3 6% 4 4 4 4 6% 8% 46%	5366
	21st to end	Night	5% 9% 3 8% 6% 6% 7% 6% 8% 9% 34%	5144
April	1st to 10th	Night	8% 9% 2 7% 4 5% 4 4 7% 8% 43%	2100
	11th to 20th	Night	6% 7% 2 7% 5% 5% 4 4 6% 5% 49%	2079
	21st to end	Night	5% 7% 2 5% 4 3 5% 4 7% 8% 50%	1993
May	1st to 10th	Night	4 4 2 4 3 3 3 3 5% 6% 62%	5047
	11th to 20th	Night	3 6% 2 3 2 2 3 4 5% 7% 62%	4700
	21st to end	Night	6% 4 2 4 3 3 3 3 5% 6% 61%	5181
June	1st to 10th	Night	7% 6% 2 6% 4 4 4 3 7% 7% 50%	1680
	11th to 20th	Night	7% 4 2 4 3 2 4 2 5% 7% 61%	1680
	21st to end	Night	3 3 1 4 2 3 3 3 4 6% 67%	1680
July	1st to 10th	Night	1 2 1 3 2 3 2 2 4 4 77%	3720
	11th to 20th	Night	1 1 2 1 1 1 2 4 4 82%	3680
	21st to end	Night	4 3 2 4 3 3 3 3 4 5% 65%	3970
August	1st to 10th	Night	3 3 1 5% 3 4 5% 3 6% 8% 58%	3582
	11th to 20th	Night	2 2 1 3 2 2 2 2 4 5% 74%	4381
	21st to end	Night	3 3 2 5% 3 3 3 2 3 6% 67%	5015
September	1st to 10th	Night	2 2 1 3 2 2 2 2 3 4 76%	2000
	11th to 20th	Night	4 3 1 3 2 3 2 3 5% 6% 68%	2060
	21st to end	Night	3 4 1 4 3 2 3 3 4 5% 68%	2200
October	1st to 10th	Night	3 3 1 4 3 3 2 2 3 4 73%	3822
	11th to 20th	Night	4 4 2 5% 4 3 3 3 4 7% 62%	3897
	21st to end	Night	5% 5% 2 6% 4 4 5% 5% 6% 7% 52%	4564
November	1st to 10th	Night	11% 9% 2 6% 5% 4 5% 3 6% 7% 42%	2665
	11th to 20th	Night	10% 8% 3 8% 5% 5% 5% 4 7% 8% 37%	2745
	21st to end	Night	9% 9% 3 6% 4 5% 4 3 5% 9% 43%	2940
December	1st to 10th	Night	6% 6% 2 5% 4 3 3 3 5% 8% 54%	4700
	11th to 20th	Night	12% 14% 4 10% 7% 7% 6% 5% 6% 7% 23%	5316
	21st to end	Night	11% 12% 4 12% 7% 6% 5% 4 6% 7% 26%	7106

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	61% 5% 14% 16% 4	4723
	11th to 20th	Day	39% 4 12% 26% 17% 1	4740
	21st to end	Day	43% 5% 11% 19% 19% 3	5265
February	1st to 10th	Day	47% 7% 19% 19% 8%	1890
	11th to 20th	Day	47% 6% 14% 21% 10% 1	1996
	21st to end	Day	45% 6% 16% 21% 11% 1	1730
March	1st to 10th	Day	49% 5% 10% 25% 10% 2	4618
	11th to 20th	Day	38% 4 12% 33% 12%	4840
	21st to end	Day	48% 8% 13% 20% 9% 1	6073
April	1st to 10th	Day	43% 4 13% 23% 14% 3	2520
	11th to 20th	Day	37% 3 11% 23% 21% 4	2492
	21st to end	Day	35% 5% 11% 27% 18% 4	2625
May	1st to 10th	Day	26% 3 5% 25% 36% 6%	7870
	11th to 20th	Day	23% 2 7% 30% 29% 9%	8163
	21st to end	Day	24% 3 8% 30% 30% 4	8994
June	1st to 10th	Day	34% 5% 8% 27% 22% 3	2940
	11th to 20th	Day	26% 3 6% 24% 30% 11%	2940
	21st to end	Day	18% 3 6% 21% 33% 20%	2940
July	1st to 10th	Day	11% 1 1 12% 24% 51%	6391
	11th to 20th	Day	11% 1 2 7% 19% 60%	6316
	21st to end	Day	15% 1 1 18% 32% 33%	6681
August	1st to 10th	Day	19% 2 2 11% 28% 37%	4524
	11th to 20th	Day	11% 1 2 15% 37% 34%	3963
	21st to end	Day	14% 1 3 22% 32% 29%	4311
September	1st to 10th	Day	15% 2 2 20% 30% 30%	2400
	11th to 20th	Day	22% 3 6% 21% 28% 20%	2340
	21st to end	Day	24% 2 8% 24% 26% 16%	2200
October	1st to 10th	Day	21% 2 7% 22% 33% 16%	3363
	11th to 20th	Day	30% 2 11% 30% 23% 4	3261
	21st to end	Day	41% 3 9% 28% 18% 2	3236
November	1st to 10th	Day	41% 5% 14% 25% 15% 1	1854
	11th to 20th	Day	47% 5% 17% 22% 7% 1	1873
	21st to end	Day	43% 5% 16% 23% 11% 2	1680
December	1st to 10th	Day	38% 4 12% 35% 10%	2700
	11th to 20th	Day	61% 5% 14% 16% 4	3108
	21st to end	Day	63% 5% 10% 17% 5%	4092
January	1st to 10th	Night	59% 5% 17% 13% 5%	8172
	11th to 20th	Night	37% 3 11% 26% 19% 3	8220
	21st to end	Night	45% 4 10% 19% 16% 6%	8902
February	1st to 10th	Night	46% 7% 17% 20% 10% 1	2730
	11th to 20th	Night	44% 6% 16% 21% 11% 2	2522
	21st to end	Night	44% 6% 16% 20% 12% 2	2076
March	1st to 10th	Night	47% 5% 9% 24% 12% 3	5496
	11th to 20th	Night	39% 4 11% 31% 14% 1	5366
	21st to end	Night	44% 8% 14% 25% 7% 1	5144
April	1st to 10th	Night	39% 5% 16% 26% 14% 1	2100
	11th to 20th	Night	35% 5% 13% 26% 17% 3	2079
	21st to end	Night	31% 5% 15% 30% 18% 2	1993
May	1st to 10th	Night	23% 3 5% 24% 41% 4	5045
	11th to 20th	Night	24% 2 7% 31% 33% 4	4700
	21st to end	Night	25% 3 10% 31% 27% 3	5182
June	1st to 10th	Night	33% 5% 12% 26% 20% 3	1680
	11th to 20th	Night	24% 4 8% 26% 28% 10%	1680
	21st to end	Night	19% 3 6% 24% 33% 15%	1680
July	1st to 10th	Night	13% 1 1 12% 28% 44%	3680
	11th to 20th	Night	9% 1 2 9% 21% 59%	3632
	21st to end	Night	24% 1 2 13% 30% 31%	3857
August	1st to 10th	Night	24% 2 3 12% 26% 33%	2601
	11th to 20th	Night	14% 1 3 14% 38% 30%	3169
	21st to end	Night	16% 1 2 21% 31% 29%	3608
September	1st to 10th	Night	15% 2 3 16% 32% 32%	2000
	11th to 20th	Night	17% 3 7% 21% 30% 22%	2060
	21st to end	Night	19% 3 5% 23% 30% 20%	2200
October	1st to 10th	Night	19% 2 6% 18% 33% 22%	3822
	11th to 20th	Night	24% 2 12% 29% 29% 4	3897
	21st to end	Night	32% 3 10% 30% 20% 3	4564
November	1st to 10th	Night	40% 5% 14% 23% 17% 1	2665
	11th to 20th	Night	45% 5% 17% 23% 11%	2745
	21st to end	Night	40% 4 16% 23% 14% 2	2940
December	1st to 10th	Night	31% 5% 13% 37% 14%	4700
	11th to 20th	Night	62% 4 12% 17% 4	5316
	21st to end	Night	59% 5% 13% 15% 8%	7106

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	21% 6% 24% 25% 20% 4	220
	11th to 20th	Day	15% 7% 17% 28% 23% 10%	220
	21st to end	Day	10% 3 20% 37% 25% 6%	268
February	1st to 10th	Day	11% 11% 30% 27% 16% 5%	430
	11th to 20th	Day	13% 10% 29% 29% 15% 3	502
	21st to end	Day	12% 11% 30% 26% 18% 3	446
March	1st to 10th	Day	13% 14% 32% 26% 14% 2	540
	11th to 20th	Day	13% 13% 26% 27% 16% 5%	540
	21st to end	Day	14% 14% 25% 30% 15% 2	594
April	1st to 10th	Day	13% 13% 24% 21% 21% 7%	540
	11th to 20th	Day	11% 14% 26% 27% 16% 6%	532
	21st to end	Day	10% 10% 26% 29% 20% 5%	540
May	1st to 10th	Day	8% 10% 23% 29% 21% 9%	543
	11th to 20th	Day	14% 10% 23% 23% 20% 9%	568
	21st to end	Day	8% 8% 17% 26% 24% 17%	617
June	1st to 10th	Day	8% 8% 19% 25% 22% 18%	570
	11th to 20th	Day	7% 10% 21% 28% 23% 10%	570
	21st to end	Day	3 4 19% 30% 27% 18%	570
July	1st to 10th	Day	4 2 16% 31% 32% 15%	566
	11th to 20th	Day	3 2 18% 29% 34% 15%	545
	21st to end	Day	3 2 14% 26% 34% 21%	575
August	1st to 10th	Day	5% 2 15% 28% 30% 20%	527
	11th to 20th	Day	2 3 13% 26% 32% 25%	517
	21st to end	Day	4 3 14% 27% 32% 20%	583
September	1st to 10th	Day	2 3 13% 28% 33% 20%	530
	11th to 20th	Day	8% 5% 13% 27% 30% 17%	530
	21st to end	Day	7% 5% 15% 26% 32% 15%	530
October	1st to 10th	Day	9% 8% 17% 26% 23% 16%	530
	11th to 20th	Day	10% 7% 21% 25% 27% 12%	530
	21st to end	Day	10% 6% 20% 32% 23% 9%	387
November	1st to 10th	Day	14% 8% 21% 30% 21% 6%	330
	11th to 20th	Day	14% 7% 20% 32% 21% 6%	321
	21st to end	Day	10% 7% 17% 31% 26% 9%	220
December	1st to 10th	Day	11% 6% 18% 29% 20% 15%	220
	11th to 20th	Day	21% 8% 20% 33% 16% 3	220
	21st to end	Day	17% 10% 19% 31% 20% 3	242
January	1st to 10th	Night	15% 6% 25% 33% 19% 2	840
	11th to 20th	Night	14% 6% 20% 34% 23% 3	840
	21st to end	Night	13% 3 18% 41% 21% 3	924
February	1st to 10th	Night	13% 4 28% 36% 18% 1	840
	11th to 20th	Night	13% 4 25% 38% 17% 2	824
	21st to end	Night	11% 7% 29% 38% 14% 1	692
March	1st to 10th	Night	14% 4 27% 37% 16% 2	840
	11th to 20th	Night	12% 6% 25% 37% 19% 2	840
	21st to end	Night	11% 7% 30% 36% 15%	924
April	1st to 10th	Night	13% 6% 23% 39% 17% 2	840
	11th to 20th	Night	9% 7% 29% 35% 16% 3	831
	21st to end	Night	9% 5% 28% 40% 17% 1	733
May	1st to 10th	Night	6% 7% 30% 36% 19% 1	536
	11th to 20th	Night	8% 4 23% 40% 22% 3	414
	21st to end	Night	7% 5% 25% 39% 21% 3	455
June	1st to 10th	Night	8% 6% 23% 41% 20% 1	420
	11th to 20th	Night	7% 5% 29% 41% 17% 1	420
	21st to end	Night	4 3 24% 46% 22% 1	420
July	1st to 10th	Night	3 2 19% 54% 20% 1	410
	11th to 20th	Night	2 2 24% 56% 17% 1	398
	21st to end	Night	3 2 19% 52% 23% 1	438
August	1st to 10th	Night	4 2 18% 49% 25% 3	398
	11th to 20th	Night	2 1 13% 45% 35% 4	730
	21st to end	Night	2 2 14% 49% 31% 2	880
September	1st to 10th	Night	2 2 13% 46% 34% 4	800
	11th to 20th	Night	5% 1 14% 38% 35% 7%	800
	21st to end	Night	6% 3 17% 40% 29% 6%	800
October	1st to 10th	Night	7% 2 21% 39% 27% 3	800
	11th to 20th	Night	6% 4 22% 39% 25% 5%	800
	21st to end	Night	8% 3 21% 43% 21% 4	880
November	1st to 10th	Night	14% 4 20% 40% 20% 1	820
	11th to 20th	Night	15% 6% 21% 38% 17% 2	840
	21st to end	Night	13% 4 21% 37% 20% 4	840
December	1st to 10th	Night	14% 4 23% 37% 18% 4	840
	11th to 20th	Night	18% 5% 23% 35% 18% 1	840
	21st to end	Night	19% 7% 25% 36% 12% 2	924

Page generated at 2026-07-13 00:14:48. Version ac07

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