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 2025-03-12.

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	6% 7% 2 6% 4 4 4 3 5% 7% 52%	112678
	Night	7% 7% 3 6% 4 4 4 3 5% 7% 49%	115056
Transparency	Day	33% 4 9% 21% 19% 14%	112420
	Night	36% 4 11% 22% 18% 10%	114903
Seeing	Day	9% 7% 20% 28% 24% 12%	14936
	Night	10% 4 22% 40% 22% 3	24267

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	9% 13% 5% 13% 7% 6% 6% 5% 6% 8% 23%	3639
	11th to 20th	Day	8% 10% 4 9% 5% 5% 6% 4 5% 8% 37%	3640
	21st to end	Day	9% 11% 3 9% 6% 4 4 3 4 6% 41%	4068
February	1st to 10th	Day	7% 10% 2 10% 7% 6% 6% 5% 8% 8% 31%	1800
	11th to 20th	Day	8% 11% 4 9% 6% 6% 5% 4 6% 8% 34%	1889
	21st to end	Day	5% 9% 4 8% 6% 6% 7% 5% 7% 8% 34%	1650
March	1st to 10th	Day	5% 12% 4 9% 6% 5% 5% 4 7% 11% 30%	3238
	11th to 20th	Day	5% 7% 2 6% 4 4 4 3 5% 7% 53%	3315
	21st to end	Day	6% 11% 4 11% 7% 7% 7% 5% 7% 8% 29%	4151
April	1st to 10th	Day	7% 10% 3 8% 6% 6% 5% 4 6% 6% 39%	2280
	11th to 20th	Day	8% 9% 2 6% 5% 5% 4 4 7% 8% 43%	2249
	21st to end	Day	6% 8% 3 6% 5% 5% 4 3 5% 7% 48%	2375
May	1st to 10th	Day	8% 8% 2 5% 4 3 4 4 5% 7% 49%	4251
	11th to 20th	Day	5% 4 2 4 3 3 3 3 4 6% 64%	4377
	21st to end	Day	4 6% 2 6% 5% 5% 4 4 6% 8% 49%	4813
June	1st to 10th	Day	8% 7% 2 6% 5% 5% 4 4 6% 8% 46%	2660
	11th to 20th	Day	5% 3 1 5% 5% 4 3 3 5% 7% 58%	2660
	21st to end	Day	3 3 1 4 2 2 3 3 4 5% 70%	2660
July	1st to 10th	Day	1 1 1 2 2 1 1 2 2 3 84%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 78%	4420
	21st to end	Day	1 1 2 2 2 2 3 3 4 78%	4790
August	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 7% 66%	4400
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 5% 78%	3803
	21st to end	Day	2 2 1 3 2 2 2 2 3 5% 77%	4180
September	1st to 10th	Day	2 2 1 3 2 3 2 2 3 5% 75%	2280
	11th to 20th	Day	4 3 1 4 4 4 3 3 5% 6% 64%	2223
	21st to end	Day	5% 4 1 5% 3 3 3 3 4 5% 63%	2090
October	1st to 10th	Day	4 3 2 4 3 3 2 2 3 5% 70%	3260
	11th to 20th	Day	5% 6% 2 6% 4 4 4 4 5% 7% 55%	3161
	21st to end	Day	8% 8% 3 7% 4 5% 5% 4 6% 8% 42%	3136
November	1st to 10th	Day	11% 8% 3 6% 5% 4 5% 4 6% 8% 40%	1764
	11th to 20th	Day	11% 8% 2 9% 5% 5% 6% 4 7% 10% 33%	1784
	21st to end	Day	7% 9% 2 7% 6% 6% 5% 4 6% 9% 38%	1600
December	1st to 10th	Day	5% 6% 3 7% 5% 5% 4 3 6% 10% 47%	2620
	11th to 20th	Day	11% 14% 5% 11% 7% 6% 6% 5% 6% 8% 21%	3028
	21st to end	Day	11% 12% 5% 14% 8% 7% 7% 5% 6% 7% 20%	4004
January	1st to 10th	Night	11% 13% 5% 12% 8% 6% 5% 4 5% 8% 23%	6306
	11th to 20th	Night	11% 11% 3 6% 5% 5% 4 3 4 7% 42%	6320
	21st to end	Night	10% 10% 3 8% 6% 5% 4 3 4 6% 42%	6886
February	1st to 10th	Night	7% 10% 3 9% 6% 5% 6% 5% 7% 8% 34%	2600
	11th to 20th	Night	7% 11% 3 7% 4 5% 5% 4 7% 7% 39%	2398
	21st to end	Night	6% 10% 3 8% 7% 5% 6% 4 7% 8% 37%	1980
March	1st to 10th	Night	5% 13% 4 9% 6% 6% 6% 6% 7% 9% 30%	3856
	11th to 20th	Night	6% 8% 2 5% 4 4 4 3 5% 8% 52%	3679
	21st to end	Night	6% 10% 3 9% 6% 6% 6% 5% 7% 9% 33%	3502
April	1st to 10th	Night	9% 9% 2 7% 4 4 4 4 7% 8% 42%	1900
	11th to 20th	Night	6% 7% 2 7% 5% 5% 4 4 6% 5% 48%	1879
	21st to end	Night	5% 6% 2 5% 4 3 5% 4 7% 8% 50%	1803
May	1st to 10th	Night	6% 6% 3 5% 4 4 4 4 5% 7% 53%	2710
	11th to 20th	Night	3 4 1 3 3 2 4 3 4 6% 67%	2516
	21st to end	Night	6% 5% 2 5% 4 4 4 4 5% 6% 55%	2762
June	1st to 10th	Night	7% 6% 2 6% 4 4 4 4 7% 6% 48%	1520
	11th to 20th	Night	7% 4 2 4 3 2 4 2 5% 7% 61%	1520
	21st to end	Night	3 3 1 4 2 3 3 3 4 5% 68%	1520
July	1st to 10th	Night	1 1 1 2 1 2 1 2 3 3 82%	2540
	11th to 20th	Night	1 1 1 3 2 2 2 2 4 4 78%	2540
	21st to end	Night	2 2 1 3 3 2 3 2 4 5% 74%	2761
August	1st to 10th	Night	3 3 1 6% 3 4 4 3 6% 8% 59%	2529
	11th to 20th	Night	2 2 1 3 2 2 2 2 5% 6% 74%	3043
	21st to end	Night	1 2 1 3 2 2 2 2 3 5% 76%	3498
September	1st to 10th	Night	2 2 1 2 2 2 2 2 3 4 79%	1900
	11th to 20th	Night	4 3 1 3 2 2 2 3 5% 5% 69%	1957
	21st to end	Night	3 4 1 4 3 2 3 3 4 5% 67%	2090
October	1st to 10th	Night	3 3 1 3 3 3 2 2 3 4 73%	3705
	11th to 20th	Night	4 4 2 5% 4 3 3 3 5% 7% 62%	3777
	21st to end	Night	5% 5% 2 6% 4 4 5% 5% 6% 7% 51%	4422
November	1st to 10th	Night	11% 9% 2 6% 4 4 5% 3 6% 7% 43%	2535
	11th to 20th	Night	10% 8% 3 7% 5% 5% 5% 4 7% 8% 37%	2614
	21st to end	Night	9% 9% 3 6% 4 5% 4 3 5% 9% 43%	2800
December	1st to 10th	Night	6% 5% 2 5% 4 3 3 3 5% 8% 55%	4560
	11th to 20th	Night	12% 14% 4 10% 7% 7% 6% 5% 6% 7% 22%	5176
	21st to end	Night	11% 12% 4 12% 7% 6% 5% 4 6% 7% 26%	6952

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	62% 5% 11% 16% 5%	3639
	11th to 20th	Day	49% 5% 15% 20% 9% 1	3640
	21st to end	Day	45% 6% 10% 18% 17% 4	4068
February	1st to 10th	Day	48% 7% 20% 18% 7%	1800
	11th to 20th	Day	47% 6% 15% 21% 10% 1	1899
	21st to end	Day	44% 7% 16% 21% 11% 1	1650
March	1st to 10th	Day	47% 6% 12% 23% 11% 1	3238
	11th to 20th	Day	31% 6% 13% 38% 12%	3315
	21st to end	Day	49% 10% 13% 21% 7%	4151
April	1st to 10th	Day	44% 5% 14% 21% 14% 3	2280
	11th to 20th	Day	38% 4 11% 24% 19% 4	2252
	21st to end	Day	34% 6% 11% 27% 18% 3	2375
May	1st to 10th	Day	32% 5% 8% 29% 20% 4	4251
	11th to 20th	Day	21% 4 5% 28% 31% 11%	4380
	21st to end	Day	30% 6% 12% 29% 21% 2	4814
June	1st to 10th	Day	36% 5% 9% 27% 21% 2	2660
	11th to 20th	Day	26% 4 7% 25% 28% 10%	2660
	21st to end	Day	17% 3 6% 21% 33% 20%	2660
July	1st to 10th	Day	8% 1 2 9% 20% 59%	4351
	11th to 20th	Day	13% 1 2 8% 18% 58%	4345
	21st to end	Day	12% 1 1 10% 29% 47%	4639
August	1st to 10th	Day	19% 2 2 11% 28% 39%	4384
	11th to 20th	Day	11% 1 2 15% 37% 34%	3840
	21st to end	Day	13% 1 3 22% 32% 30%	4179
September	1st to 10th	Day	14% 2 2 20% 31% 32%	2280
	11th to 20th	Day	22% 3 6% 21% 28% 20%	2223
	21st to end	Day	24% 2 8% 25% 26% 15%	2090
October	1st to 10th	Day	20% 2 7% 21% 33% 16%	3260
	11th to 20th	Day	30% 2 11% 30% 22% 4	3161
	21st to end	Day	41% 3 9% 27% 19% 2	3136
November	1st to 10th	Day	41% 5% 14% 24% 15% 1	1764
	11th to 20th	Day	47% 6% 17% 22% 7% 1	1784
	21st to end	Day	43% 5% 17% 22% 11% 2	1600
December	1st to 10th	Day	37% 4 11% 36% 10%	2620
	11th to 20th	Day	62% 5% 14% 15% 3	3028
	21st to end	Day	64% 5% 10% 16% 5%	4004
January	1st to 10th	Night	62% 6% 14% 12% 6%	6306
	11th to 20th	Night	46% 4 14% 23% 13% 1	6320
	21st to end	Night	46% 5% 10% 19% 13% 7%	6886
February	1st to 10th	Night	47% 7% 18% 19% 9% 1	2600
	11th to 20th	Night	43% 6% 16% 21% 11% 2	2399
	21st to end	Night	44% 6% 16% 20% 12% 2	1980
March	1st to 10th	Night	51% 7% 11% 20% 9% 2	3856
	11th to 20th	Night	33% 5% 12% 37% 13% 1	3679
	21st to end	Night	44% 9% 17% 22% 7% 2	3502
April	1st to 10th	Night	40% 5% 17% 23% 14% 2	1900
	11th to 20th	Night	36% 5% 14% 27% 16% 3	1879
	21st to end	Night	30% 5% 16% 30% 17% 2	1803
May	1st to 10th	Night	30% 5% 8% 28% 27% 2	2710
	11th to 20th	Night	19% 3 7% 27% 37% 6%	2516
	21st to end	Night	29% 6% 14% 32% 18% 1	2762
June	1st to 10th	Night	35% 6% 14% 27% 18% 2	1520
	11th to 20th	Night	24% 4 8% 27% 27% 8%	1520
	21st to end	Night	18% 4 6% 24% 33% 15%	1520
July	1st to 10th	Night	9% 2 2 11% 20% 57%	2500
	11th to 20th	Night	12% 1 2 10% 19% 56%	2492
	21st to end	Night	16% 1 2 8% 30% 44%	2674
August	1st to 10th	Night	24% 2 2 11% 25% 34%	2521
	11th to 20th	Night	14% 1 3 14% 38% 30%	3072
	21st to end	Night	15% 1 2 21% 31% 29%	3498
September	1st to 10th	Night	12% 2 3 16% 33% 34%	1900
	11th to 20th	Night	17% 3 7% 21% 30% 22%	1957
	21st to end	Night	20% 3 5% 23% 30% 19%	2090
October	1st to 10th	Night	18% 2 6% 18% 33% 23%	3705
	11th to 20th	Night	24% 2 12% 29% 29% 4	3777
	21st to end	Night	33% 3 11% 30% 20% 4	4422
November	1st to 10th	Night	40% 5% 13% 22% 18% 1	2535
	11th to 20th	Night	44% 5% 16% 23% 12%	2614
	21st to end	Night	41% 5% 16% 22% 14% 2	2800
December	1st to 10th	Night	31% 5% 12% 37% 15%	4560
	11th to 20th	Night	63% 4 12% 17% 3	5176
	21st to end	Night	60% 5% 12% 15% 8%	6952

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	22% 5% 24% 26% 19% 5%	200
	11th to 20th	Day	16% 8% 19% 29% 22% 7%	200
	21st to end	Day	11% 3 20% 36% 24% 7%	245
February	1st to 10th	Day	12% 11% 30% 28% 15% 5%	400
	11th to 20th	Day	14% 11% 29% 29% 15% 3	465
	21st to end	Day	11% 11% 29% 27% 19% 3	414
March	1st to 10th	Day	12% 12% 33% 27% 14% 2	500
	11th to 20th	Day	12% 11% 25% 29% 16% 6%	465
	21st to end	Day	14% 14% 23% 32% 15% 2	506
April	1st to 10th	Day	14% 14% 26% 21% 20% 6%	460
	11th to 20th	Day	12% 15% 27% 25% 15% 6%	452
	21st to end	Day	10% 11% 26% 28% 20% 5%	460
May	1st to 10th	Day	9% 11% 23% 29% 20% 8%	463
	11th to 20th	Day	14% 9% 22% 23% 21% 11%	488
	21st to end	Day	9% 7% 17% 26% 24% 17%	529
June	1st to 10th	Day	8% 8% 20% 24% 21% 19%	490
	11th to 20th	Day	8% 11% 22% 27% 23% 9%	490
	21st to end	Day	3 4 18% 30% 25% 19%	490
July	1st to 10th	Day	5% 2 17% 30% 33% 14%	486
	11th to 20th	Day	2 1 18% 30% 34% 15%	484
	21st to end	Day	2 2 15% 27% 34% 20%	531
August	1st to 10th	Day	5% 2 15% 29% 30% 21%	487
	11th to 20th	Day	2 3 12% 26% 32% 26%	477
	21st to end	Day	3 3 14% 27% 32% 21%	539
September	1st to 10th	Day	2 3 13% 27% 33% 21%	490
	11th to 20th	Day	8% 5% 14% 26% 30% 17%	490
	21st to end	Day	7% 6% 15% 25% 32% 14%	490
October	1st to 10th	Day	10% 8% 16% 26% 23% 17%	490
	11th to 20th	Day	10% 6% 20% 25% 27% 12%	490
	21st to end	Day	11% 7% 20% 32% 21% 9%	353
November	1st to 10th	Day	15% 8% 20% 30% 21% 6%	300
	11th to 20th	Day	14% 6% 20% 32% 22% 7%	292
	21st to end	Day	11% 8% 17% 31% 26% 9%	200
December	1st to 10th	Day	12% 6% 17% 29% 21% 17%	200
	11th to 20th	Day	21% 8% 21% 34% 15% 3	200
	21st to end	Day	16% 9% 19% 32% 20% 4	220
January	1st to 10th	Night	15% 6% 24% 34% 19% 2	800
	11th to 20th	Night	15% 6% 20% 34% 22% 3	800
	21st to end	Night	14% 3 19% 40% 22% 3	880
February	1st to 10th	Night	14% 4 29% 36% 17% 1	800
	11th to 20th	Night	13% 4 25% 38% 17% 2	784
	21st to end	Night	11% 7% 28% 38% 15% 1	660
March	1st to 10th	Night	14% 4 27% 36% 17% 2	800
	11th to 20th	Night	12% 5% 22% 38% 21% 2	766
	21st to end	Night	12% 7% 29% 36% 16%	836
April	1st to 10th	Night	14% 6% 23% 38% 17% 2	760
	11th to 20th	Night	9% 7% 29% 35% 17% 3	751
	21st to end	Night	9% 5% 28% 39% 18% 1	663
May	1st to 10th	Night	7% 7% 30% 35% 20% 1	485
	11th to 20th	Night	8% 4 20% 40% 24% 4	374
	21st to end	Night	8% 4 23% 38% 23% 3	411
June	1st to 10th	Night	9% 5% 22% 41% 22% 1	380
	11th to 20th	Night	7% 4 29% 40% 18% 1	380
	21st to end	Night	4 3 22% 47% 23% 1	380
July	1st to 10th	Night	3 2 18% 55% 22% 1	370
	11th to 20th	Night	1 1 23% 56% 17% 1	368
	21st to end	Night	2 1 20% 52% 24% 1	416
August	1st to 10th	Night	3 2 18% 49% 25% 3	378
	11th to 20th	Night	2 1 12% 45% 36% 4	693
	21st to end	Night	2 2 14% 49% 31% 2	836
September	1st to 10th	Night	2 1 12% 45% 35% 4	760
	11th to 20th	Night	4 1 14% 38% 35% 7%	760
	21st to end	Night	6% 3 17% 39% 28% 7%	760
October	1st to 10th	Night	7% 2 20% 39% 28% 4	760
	11th to 20th	Night	6% 4 20% 39% 26% 5%	760
	21st to end	Night	8% 3 21% 43% 21% 5%	836
November	1st to 10th	Night	15% 3 19% 40% 21% 2	780
	11th to 20th	Night	15% 6% 22% 38% 18% 2	800
	21st to end	Night	14% 4 20% 37% 21% 4	800
December	1st to 10th	Night	15% 4 22% 38% 19% 4	800
	11th to 20th	Night	18% 5% 23% 35% 18% 2	800
	21st to end	Night	19% 7% 25% 36% 12% 2	880

Page generated at 2025-03-09 05:08:43. Version ac07

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