Burnsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burnsville clear sky chart from 2005-11-06 to 2025-07-06.

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	13% 9% 3 8% 5% 4 4 4 5% 7% 38%	120365
	Night	12% 9% 4 9% 5% 4 4 4 5% 6% 38%	118691
Transparency	Day	44% 6% 13% 24% 11% 1	123987
	Night	45% 5% 12% 23% 13% 1	123212
Seeing	Day	16% 12% 32% 26% 12% 3	16923
	Night	15% 10% 34% 30% 10% 1	26829

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	8% 13% 6% 19% 8% 6% 4 2 5% 5% 23%	3617
	11th to 20th	Day	5% 12% 7% 12% 7% 7% 7% 8% 10% 5% 19%	3684
	21st to end	Day	6% 16% 7% 13% 5% 5% 5% 3 4 5% 31%	4488
February	1st to 10th	Day	9% 12% 5% 9% 7% 6% 5% 5% 6% 6% 30%	1800
	11th to 20th	Day	8% 11% 5% 10% 6% 5% 4 5% 5% 6% 35%	1754
	21st to end	Day	12% 10% 4 10% 5% 5% 5% 4 6% 6% 32%	1548
March	1st to 10th	Day	12% 8% 3 6% 4 3 4 3 5% 7% 45%	4840
	11th to 20th	Day	10% 10% 3 6% 4 5% 4 3 6% 8% 41%	4980
	21st to end	Day	23% 11% 4 10% 5% 4 4 3 4 6% 26%	5522
April	1st to 10th	Day	17% 11% 3 6% 5% 4 4 3 5% 7% 34%	2400
	11th to 20th	Day	20% 12% 4 8% 5% 5% 4 3 4 5% 31%	2381
	21st to end	Day	21% 12% 3 6% 5% 4 5% 4 5% 6% 30%	2600
May	1st to 10th	Day	14% 6% 2 5% 3 3 4 3 4 6% 49%	6092
	11th to 20th	Day	16% 8% 2 5% 3 4 3 3 5% 7% 43%	6319
	21st to end	Day	17% 8% 3 6% 4 4 4 3 5% 7% 38%	6935
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 46%	2800
	11th to 20th	Day	13% 7% 2 7% 5% 5% 4 4 6% 10% 36%	2800
	21st to end	Day	11% 5% 2 6% 5% 6% 6% 5% 8% 8% 38%	2800
July	1st to 10th	Day	10% 5% 2 7% 5% 6% 5% 4 8% 10% 37%	4511
	11th to 20th	Day	5% 3 1 4 3 4 4 3 5% 8% 60%	4440
	21st to end	Day	6% 4 2 5% 5% 4 5% 5% 7% 8% 48%	4736
August	1st to 10th	Day	12% 7% 2 6% 4 5% 5% 4 7% 8% 41%	4104
	11th to 20th	Day	12% 5% 2 5% 4 4 4 4 6% 9% 44%	4041
	21st to end	Day	10% 5% 2 7% 5% 4 4 4 5% 8% 46%	4322
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 5% 6% 48%	2280
	11th to 20th	Day	12% 5% 2 5% 3 3 5% 4 5% 7% 48%	2252
	21st to end	Day	14% 7% 2 6% 4 3 4 4 5% 7% 44%	2000
October	1st to 10th	Day	16% 7% 2 5% 4 4 3 3 5% 6% 45%	1900
	11th to 20th	Day	14% 9% 2 7% 5% 4 4 3 5% 7% 40%	1900
	21st to end	Day	18% 11% 3 7% 4 3 4 2 5% 6% 37%	2071
November	1st to 10th	Day	12% 10% 4 8% 6% 4 4 3 6% 6% 38%	1648
	11th to 20th	Day	10% 15% 6% 11% 6% 4 5% 3 6% 5% 30%	1600
	21st to end	Day	13% 11% 4 9% 6% 4 3 4 5% 7% 35%	1600
December	1st to 10th	Day	8% 9% 4 14% 11% 8% 6% 4 5% 7% 24%	2610
	11th to 20th	Day	11% 16% 6% 11% 7% 5% 5% 3 5% 6% 26%	3008
	21st to end	Day	20% 18% 9% 19% 5% 3 3 2 3 4 14%	3982
January	1st to 10th	Night	7% 11% 6% 15% 8% 6% 4 4 5% 6% 28%	6348
	11th to 20th	Night	7% 10% 5% 12% 8% 7% 10% 8% 8% 5% 20%	6294
	21st to end	Night	8% 17% 6% 9% 6% 5% 4 3 4 5% 33%	6490
February	1st to 10th	Night	8% 12% 5% 11% 6% 6% 5% 4 5% 6% 34%	2600
	11th to 20th	Night	6% 9% 4 9% 5% 6% 6% 4 5% 7% 39%	2533
	21st to end	Night	12% 10% 3 9% 5% 6% 4 3 5% 6% 38%	2081
March	1st to 10th	Night	10% 7% 2 7% 4 4 4 3 5% 7% 47%	5057
	11th to 20th	Night	10% 6% 3 7% 5% 5% 6% 4 6% 10% 40%	4980
	21st to end	Night	25% 12% 4 9% 4 3 3 3 4 5% 28%	5406
April	1st to 10th	Night	16% 12% 3 6% 3 4 4 3 5% 6% 38%	2000
	11th to 20th	Night	21% 9% 4 6% 4 4 4 3 5% 6% 35%	1965
	21st to end	Night	19% 10% 2 7% 4 4 4 4 5% 7% 35%	1800
May	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 5% 50%	3823
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 5% 6% 51%	3596
	21st to end	Night	16% 8% 4 6% 4 4 4 3 4 6% 40%	3942
June	1st to 10th	Night	10% 5% 2 5% 4 3 5% 4 6% 9% 49%	1600
	11th to 20th	Night	9% 5% 2 5% 5% 5% 5% 5% 6% 7% 45%	1600
	21st to end	Night	9% 3 2 5% 4 3 4 4 6% 9% 52%	1600
July	1st to 10th	Night	11% 3 2 5% 4 4 4 5% 7% 10% 46%	2570
	11th to 20th	Night	4 2 1 5% 3 4 4 4 6% 9% 58%	2530
	21st to end	Night	6% 3 2 5% 3 4 4 3 5% 7% 57%	2812
August	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 5% 6% 47%	2836
	11th to 20th	Night	13% 5% 1 4 3 3 3 3 5% 8% 52%	2798
	21st to end	Night	9% 6% 3 7% 4 4 4 3 5% 7% 47%	3338
September	1st to 10th	Night	9% 4 2 4 4 3 3 3 5% 8% 54%	1900
	11th to 20th	Night	10% 5% 2 4 3 4 4 2 5% 8% 53%	1926
	21st to end	Night	13% 6% 2 6% 3 3 4 3 4 5% 52%	2161
October	1st to 10th	Night	14% 6% 3 6% 2 3 3 3 4 6% 50%	2280
	11th to 20th	Night	14% 9% 2 6% 4 4 4 3 5% 6% 42%	2280
	21st to end	Night	18% 10% 3 7% 4 3 4 2 5% 6% 37%	2525
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 3 5% 6% 42%	2645
	11th to 20th	Night	12% 11% 4 10% 5% 5% 4 4 5% 5% 34%	2800
	21st to end	Night	14% 10% 4 9% 6% 4 5% 3 4 6% 37%	2800
December	1st to 10th	Night	6% 7% 4 14% 8% 8% 6% 4 6% 6% 31%	4580
	11th to 20th	Night	10% 16% 6% 14% 7% 5% 4 4 4 5% 24%	5199
	21st to end	Night	22% 15% 8% 14% 6% 4 4 3 3 4 16%	6996

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	63% 5% 10% 18% 5%	3618
	11th to 20th	Day	60% 5% 8% 17% 10%	3684
	21st to end	Day	56% 5% 15% 16% 7%	4488
February	1st to 10th	Day	52% 6% 14% 18% 8% 1	1800
	11th to 20th	Day	50% 5% 12% 25% 8% 1	1763
	21st to end	Day	50% 7% 14% 18% 11%	1548
March	1st to 10th	Day	38% 5% 17% 26% 11% 2	4840
	11th to 20th	Day	41% 5% 15% 29% 9% 1	4980
	21st to end	Day	60% 6% 10% 17% 7%	5524
April	1st to 10th	Day	49% 6% 13% 21% 11% 1	2400
	11th to 20th	Day	54% 5% 11% 17% 11% 2	2381
	21st to end	Day	54% 7% 11% 19% 8% 1	2600
May	1st to 10th	Day	34% 6% 12% 29% 17% 2	6130
	11th to 20th	Day	39% 6% 10% 24% 15% 5%	6323
	21st to end	Day	45% 6% 9% 30% 9% 1	6949
June	1st to 10th	Day	33% 8% 15% 30% 13% 1	2800
	11th to 20th	Day	43% 8% 13% 21% 13% 1	2800
	21st to end	Day	38% 10% 17% 24% 10% 2	2800
July	1st to 10th	Day	38% 9% 20% 22% 10% 1	4442
	11th to 20th	Day	22% 6% 16% 35% 19% 2	4365
	21st to end	Day	29% 9% 15% 28% 18% 1	4587
August	1st to 10th	Day	39% 7% 12% 28% 12% 2	4090
	11th to 20th	Day	36% 7% 13% 33% 10%	4080
	21st to end	Day	35% 7% 16% 28% 14% 1	4321
September	1st to 10th	Day	35% 7% 13% 30% 14%	2280
	11th to 20th	Day	34% 7% 18% 32% 9%	2252
	21st to end	Day	39% 6% 13% 31% 11% 1	2000
October	1st to 10th	Day	30% 4 8% 35% 23%	3160
	11th to 20th	Day	39% 4 11% 27% 18% 1	3140
	21st to end	Day	44% 4 14% 29% 9%	3397
November	1st to 10th	Day	46% 6% 14% 19% 13% 2	1648
	11th to 20th	Day	55% 6% 13% 17% 9% 1	1600
	21st to end	Day	48% 7% 17% 21% 7% 1	1600
December	1st to 10th	Day	58% 7% 16% 13% 6%	2610
	11th to 20th	Day	60% 5% 14% 16% 5%	3005
	21st to end	Day	75% 5% 8% 9% 3	3982
January	1st to 10th	Night	58% 5% 11% 20% 7%	6348
	11th to 20th	Night	61% 6% 11% 13% 10%	6294
	21st to end	Night	55% 4 10% 23% 8%	6490
February	1st to 10th	Night	51% 4 13% 21% 10% 1	2600
	11th to 20th	Night	45% 5% 14% 25% 9% 1	2534
	21st to end	Night	48% 5% 13% 22% 12% 1	2081
March	1st to 10th	Night	36% 5% 13% 27% 16% 2	5057
	11th to 20th	Night	38% 5% 15% 28% 14% 1	4980
	21st to end	Night	59% 4 9% 18% 9% 1	5406
April	1st to 10th	Night	47% 5% 10% 23% 14% 1	2000
	11th to 20th	Night	50% 5% 10% 19% 15% 2	1965
	21st to end	Night	48% 7% 10% 20% 14% 2	1800
May	1st to 10th	Night	34% 6% 10% 26% 21% 2	3850
	11th to 20th	Night	34% 5% 11% 22% 20% 7%	3597
	21st to end	Night	44% 5% 10% 28% 12% 1	3950
June	1st to 10th	Night	31% 7% 14% 29% 18% 2	1600
	11th to 20th	Night	37% 7% 15% 21% 18% 3	1600
	21st to end	Night	27% 7% 16% 30% 16% 3	1600
July	1st to 10th	Night	32% 8% 21% 25% 13% 1	2530
	11th to 20th	Night	21% 6% 14% 39% 18% 2	2482
	21st to end	Night	25% 6% 16% 31% 19% 3	2722
August	1st to 10th	Night	37% 6% 11% 28% 14% 4	2826
	11th to 20th	Night	32% 5% 14% 31% 16% 1	2825
	21st to end	Night	35% 7% 16% 27% 13% 2	3338
September	1st to 10th	Night	28% 6% 13% 34% 18% 1	1900
	11th to 20th	Night	29% 6% 17% 31% 17% 1	1926
	21st to end	Night	34% 5% 12% 30% 17% 1	2161
October	1st to 10th	Night	24% 3 7% 35% 27% 4	3800
	11th to 20th	Night	32% 5% 12% 25% 22% 4	3779
	21st to end	Night	43% 4 12% 28% 13%	4149
November	1st to 10th	Night	42% 6% 13% 23% 14% 1	2645
	11th to 20th	Night	52% 6% 12% 19% 11% 1	2800
	21st to end	Night	50% 5% 16% 22% 7% 1	2800
December	1st to 10th	Night	52% 7% 18% 19% 4	4580
	11th to 20th	Night	62% 5% 11% 17% 5% 1	5201
	21st to end	Night	71% 5% 9% 12% 3	6996

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% 13% 37% 26% 11% 2	300
	11th to 20th	Day	15% 15% 41% 24% 4	300
	21st to end	Day	17% 12% 39% 22% 9% 2	330
February	1st to 10th	Day	17% 16% 43% 20% 4 1	300
	11th to 20th	Day	13% 19% 39% 22% 5% 1	300
	21st to end	Day	18% 14% 42% 24% 2	249
March	1st to 10th	Day	18% 15% 41% 20% 5%	300
	11th to 20th	Day	20% 14% 37% 23% 6% 1	300
	21st to end	Day	26% 20% 26% 20% 7% 1	352
April	1st to 10th	Day	24% 16% 35% 20% 5% 1	500
	11th to 20th	Day	28% 17% 25% 20% 9% 1	499
	21st to end	Day	26% 14% 31% 20% 7% 2	700
May	1st to 10th	Day	18% 15% 33% 24% 9% 1	703
	11th to 20th	Day	20% 14% 29% 23% 13% 3	725
	21st to end	Day	17% 12% 28% 28% 12% 3	789
June	1st to 10th	Day	9% 11% 28% 33% 17% 2	730
	11th to 20th	Day	15% 9% 38% 27% 9% 2	730
	21st to end	Day	14% 12% 31% 25% 15% 3	730
July	1st to 10th	Day	9% 6% 25% 32% 22% 7%	697
	11th to 20th	Day	9% 7% 28% 29% 21% 5%	668
	21st to end	Day	6% 5% 28% 37% 19% 5%	739
August	1st to 10th	Day	10% 6% 25% 34% 21% 4	676
	11th to 20th	Day	14% 5% 23% 31% 21% 5%	665
	21st to end	Day	11% 7% 28% 33% 16% 5%	629
September	1st to 10th	Day	14% 10% 29% 29% 13% 5%	490
	11th to 20th	Day	12% 8% 29% 31% 16% 3	462
	21st to end	Day	17% 14% 31% 21% 12% 4	300
October	1st to 10th	Day	18% 13% 27% 27% 11% 4	300
	11th to 20th	Day	16% 23% 36% 20% 4 1	300
	21st to end	Day	25% 17% 38% 14% 6% 1	330
November	1st to 10th	Day	20% 16% 38% 17% 8% 1	300
	11th to 20th	Day	17% 23% 41% 17% 3	300
	21st to end	Day	23% 14% 43% 16% 3	300
December	1st to 10th	Day	15% 13% 40% 26% 6% 1	300
	11th to 20th	Day	19% 19% 35% 22% 4	300
	21st to end	Day	28% 15% 38% 16% 4	330
January	1st to 10th	Night	11% 13% 40% 28% 7% 1	1000
	11th to 20th	Night	16% 13% 38% 28% 5% 1	1000
	21st to end	Night	17% 12% 38% 27% 5% 1	1100
February	1st to 10th	Night	14% 13% 40% 28% 6% 1	1000
	11th to 20th	Night	11% 13% 43% 26% 6% 1	979
	21st to end	Night	15% 14% 36% 27% 7% 1	761
March	1st to 10th	Night	15% 10% 40% 27% 8% 1	665
	11th to 20th	Night	17% 12% 38% 27% 6%	600
	21st to end	Night	23% 12% 30% 24% 10% 1	660
April	1st to 10th	Night	20% 14% 35% 27% 5%	600
	11th to 20th	Night	25% 12% 30% 26% 6% 1	593
	21st to end	Night	22% 10% 33% 25% 8% 1	600
May	1st to 10th	Night	19% 10% 34% 30% 7% 1	600
	11th to 20th	Night	16% 9% 32% 31% 11% 1	591
	21st to end	Night	16% 9% 26% 36% 13%	650
June	1st to 10th	Night	11% 6% 31% 40% 12%	600
	11th to 20th	Night	11% 5% 36% 40% 8%	600
	21st to end	Night	11% 3 27% 45% 14% 1	600
July	1st to 10th	Night	6% 3 25% 39% 26% 1	570
	11th to 20th	Night	5% 5% 29% 43% 17% 2	552
	21st to end	Night	5% 2 24% 48% 18% 1	624
August	1st to 10th	Night	7% 5% 21% 46% 21% 1	567
	11th to 20th	Night	12% 2 21% 39% 22% 3	564
	21st to end	Night	7% 4 29% 35% 23% 2	627
September	1st to 10th	Night	10% 6% 25% 38% 17% 3	570
	11th to 20th	Night	10% 7% 35% 31% 15% 2	570
	21st to end	Night	13% 11% 33% 29% 14%	641
October	1st to 10th	Night	18% 11% 29% 28% 13% 1	760
	11th to 20th	Night	19% 12% 37% 25% 7% 1	760
	21st to end	Night	25% 11% 30% 27% 6%	836
November	1st to 10th	Night	18% 13% 36% 26% 7%	889
	11th to 20th	Night	18% 15% 37% 25% 6%	1000
	21st to end	Night	18% 16% 37% 23% 7%	1000
December	1st to 10th	Night	15% 12% 39% 28% 7%	1000
	11th to 20th	Night	19% 13% 38% 25% 5% 1	1000
	21st to end	Night	25% 13% 33% 25% 4 1	1100

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