Burlington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burlington clear sky chart from 2005-11-06 to 2025-11-18.

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% 6% 2 6% 4 4 4 4 6% 8% 43%	126596
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	123716
Transparency	Day	38% 6% 12% 21% 18% 5%	130202
	Night	38% 5% 10% 20% 21% 6%	128179
Seeing	Day	16% 10% 24% 24% 18% 8%	16772
	Night	16% 8% 25% 31% 17% 2	26932

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	16% 6% 2 5% 2 2 2 2 3 4 56%	4056
	11th to 20th	Day	11% 6% 2 5% 3 3 3 2 3 5% 57%	4060
	21st to end	Day	15% 8% 3 6% 4 4 4 3 4 4 47%	4466
February	1st to 10th	Day	14% 7% 2 6% 4 4 4 4 6% 8% 42%	1800
	11th to 20th	Day	22% 7% 2 5% 4 3 4 2 3 5% 44%	1778
	21st to end	Day	18% 7% 2 6% 4 3 4 3 5% 6% 41%	1785
March	1st to 10th	Day	18% 7% 3 6% 4 3 3 3 5% 7% 42%	4935
	11th to 20th	Day	9% 5% 2 5% 3 4 3 3 5% 7% 53%	4980
	21st to end	Day	15% 6% 2 6% 4 4 4 4 4 6% 46%	5465
April	1st to 10th	Day	10% 4 2 3 3 3 4 4 5% 7% 53%	2295
	11th to 20th	Day	11% 5% 2 5% 4 3 4 3 6% 7% 49%	2374
	21st to end	Day	13% 5% 2 5% 4 4 6% 4 6% 7% 44%	2437
May	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 36%	5862
	11th to 20th	Day	19% 7% 3 7% 5% 5% 6% 4 7% 8% 29%	5861
	21st to end	Day	13% 4 2 5% 4 5% 5% 4 6% 9% 42%	6433
June	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 8% 10% 43%	2600
	11th to 20th	Day	9% 5% 2 6% 4 4 4 5% 7% 11% 44%	2600
	21st to end	Day	7% 5% 2 5% 4 4 7% 6% 7% 11% 42%	2600
July	1st to 10th	Day	9% 5% 2 7% 5% 6% 5% 5% 7% 10% 38%	5900
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 6% 9% 14% 32%	5900
	21st to end	Day	9% 6% 3 7% 6% 6% 6% 5% 7% 11% 35%	6424
August	1st to 10th	Day	19% 8% 3 7% 5% 5% 6% 5% 7% 10% 25%	4234
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 5% 7% 11% 36%	4113
	21st to end	Day	6% 4 2 5% 4 4 5% 4 6% 10% 51%	4312
September	1st to 10th	Day	11% 4 1 6% 4 4 4 4 6% 7% 48%	2400
	11th to 20th	Day	14% 5% 2 7% 4 4 4 4 5% 9% 42%	2208
	21st to end	Day	21% 7% 3 6% 4 3 4 4 5% 6% 38%	2185
October	1st to 10th	Day	14% 6% 2 5% 3 3 3 3 4 6% 52%	2000
	11th to 20th	Day	13% 4 1 5% 2 3 3 3 4 5% 57%	2000
	21st to end	Day	12% 5% 2 4 4 3 2 3 4 4 57%	2200
November	1st to 10th	Day	13% 5% 2 4 3 3 3 3 3 5% 55%	2057
	11th to 20th	Day	13% 4 2 4 3 3 3 3 5% 6% 53%	2005
	21st to end	Day	13% 5% 2 5% 4 3 4 3 6% 6% 49%	1800
December	1st to 10th	Day	13% 6% 2 5% 3 3 4 3 4 5% 52%	2632
	11th to 20th	Day	17% 6% 2 7% 4 3 4 3 4 5% 46%	3373
	21st to end	Day	18% 5% 2 5% 3 3 4 3 5% 8% 44%	4466
January	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 5% 55%	5889
	11th to 20th	Night	13% 6% 2 4 3 2 3 3 4 4 57%	5900
	21st to end	Night	15% 7% 3 5% 3 3 3 3 4 5% 48%	6490
February	1st to 10th	Night	17% 6% 2 5% 4 4 4 4 4 6% 44%	2600
	11th to 20th	Night	20% 7% 2 5% 3 4 3 3 4 6% 43%	2503
	21st to end	Night	15% 6% 2 5% 4 4 3 4 5% 6% 46%	1844
March	1st to 10th	Night	17% 7% 3 6% 4 4 4 3 4 4 44%	4918
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 7% 55%	4980
	21st to end	Night	14% 5% 2 5% 3 4 4 3 5% 6% 48%	5467
April	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 49%	2105
	11th to 20th	Night	12% 5% 2 5% 4 4 3 3 6% 7% 49%	1975
	21st to end	Night	12% 5% 2 6% 5% 4 5% 3 5% 7% 46%	1979
May	1st to 10th	Night	12% 6% 3 7% 6% 4 5% 4 6% 8% 38%	4033
	11th to 20th	Night	18% 8% 3 8% 4 4 4 3 5% 8% 37%	4032
	21st to end	Night	15% 5% 2 6% 4 3 3 3 6% 9% 44%	4421
June	1st to 10th	Night	10% 5% 2 5% 4 5% 6% 5% 8% 11% 39%	1800
	11th to 20th	Night	9% 6% 2 8% 5% 4 4 4 7% 10% 42%	1800
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 6% 8% 11% 42%	1800
July	1st to 10th	Night	11% 6% 2 8% 5% 6% 6% 4 8% 9% 33%	4058
	11th to 20th	Night	11% 7% 3 8% 6% 6% 7% 6% 8% 10% 28%	4057
	21st to end	Night	11% 8% 2 8% 5% 5% 5% 6% 8% 11% 33%	4427
August	1st to 10th	Night	21% 7% 2 7% 5% 6% 6% 4 8% 10% 24%	2915
	11th to 20th	Night	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 41%	2902
	21st to end	Night	7% 4 2 5% 4 4 5% 5% 6% 8% 50%	3586
September	1st to 10th	Night	10% 5% 3 6% 4 3 4 4 6% 7% 48%	2000
	11th to 20th	Night	14% 7% 2 6% 3 4 4 4 5% 7% 44%	2188
	21st to end	Night	19% 7% 3 7% 4 5% 4 4 6% 5% 37%	2213
October	1st to 10th	Night	14% 6% 2 6% 4 4 3 3 3 6% 49%	2400
	11th to 20th	Night	14% 6% 2 5% 3 3 3 2 4 5% 55%	2400
	21st to end	Night	13% 5% 2 4 3 3 3 3 4 4 56%	2640
November	1st to 10th	Night	15% 6% 2 5% 3 3 3 2 3 4 54%	2461
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 4 6% 52%	2545
	21st to end	Night	13% 5% 2 4 3 3 4 3 5% 7% 52%	2600
December	1st to 10th	Night	12% 5% 2 6% 4 3 3 3 4 5% 53%	4476
	11th to 20th	Night	19% 8% 2 7% 4 4 4 3 4 5% 40%	4822
	21st to end	Night	18% 5% 2 5% 2 3 3 3 5% 7% 47%	6490

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	35% 2 4 21% 32% 7%	4057
	11th to 20th	Day	32% 3 4 17% 36% 8%	4060
	21st to end	Day	42% 3 5% 22% 22% 6%	4466
February	1st to 10th	Day	40% 4 10% 21% 20% 5%	1800
	11th to 20th	Day	45% 3 6% 20% 19% 7%	1787
	21st to end	Day	44% 4 10% 16% 20% 6%	1785
March	1st to 10th	Day	44% 3 6% 18% 18% 12%	4935
	11th to 20th	Day	31% 4 7% 19% 23% 16%	4980
	21st to end	Day	41% 4 8% 22% 20% 6%	5465
April	1st to 10th	Day	29% 4 11% 24% 24% 8%	2295
	11th to 20th	Day	34% 4 11% 23% 21% 7%	2374
	21st to end	Day	38% 5% 11% 24% 17% 4	2437
May	1st to 10th	Day	41% 8% 18% 21% 11% 2	5897
	11th to 20th	Day	51% 7% 12% 21% 9% 1	5865
	21st to end	Day	38% 6% 14% 22% 18% 3	6447
June	1st to 10th	Day	35% 8% 16% 25% 16% 1	2600
	11th to 20th	Day	33% 7% 18% 25% 15% 2	2600
	21st to end	Day	33% 10% 17% 24% 14% 2	2600
July	1st to 10th	Day	39% 10% 18% 19% 12% 2	5835
	11th to 20th	Day	39% 13% 28% 16% 4 1	5831
	21st to end	Day	41% 10% 17% 23% 9%	6240
August	1st to 10th	Day	52% 8% 17% 17% 5%	4221
	11th to 20th	Day	40% 9% 21% 21% 8% 1	4152
	21st to end	Day	28% 7% 15% 34% 14% 2	4312
September	1st to 10th	Day	33% 7% 14% 21% 20% 5%	2400
	11th to 20th	Day	40% 7% 11% 18% 21% 2	2208
	21st to end	Day	47% 5% 10% 20% 15% 4	2185
October	1st to 10th	Day	34% 4 8% 19% 26% 10%	3260
	11th to 20th	Day	21% 2 5% 22% 26% 24%	3240
	21st to end	Day	24% 3 8% 25% 25% 15%	3538
November	1st to 10th	Day	33% 4 8% 22% 27% 7%	2057
	11th to 20th	Day	33% 3 7% 23% 27% 7%	2005
	21st to end	Day	35% 3 8% 22% 27% 5%	1800
December	1st to 10th	Day	35% 3 7% 21% 27% 7%	2632
	11th to 20th	Day	42% 3 10% 17% 22% 6%	3370
	21st to end	Day	39% 5% 11% 26% 18% 1	4466
January	1st to 10th	Night	31% 4 5% 18% 32% 11%	5889
	11th to 20th	Night	32% 3 5% 17% 35% 7%	5900
	21st to end	Night	39% 2 6% 21% 26% 5%	6490
February	1st to 10th	Night	41% 4 9% 22% 20% 5%	2600
	11th to 20th	Night	43% 3 8% 17% 21% 7%	2505
	21st to end	Night	38% 4 9% 20% 21% 8%	1844
March	1st to 10th	Night	43% 4 6% 15% 23% 10%	4918
	11th to 20th	Night	30% 4 6% 16% 25% 18%	4980
	21st to end	Night	37% 4 7% 24% 23% 5%	5467
April	1st to 10th	Night	36% 4 9% 18% 25% 6%	2105
	11th to 20th	Night	34% 3 10% 24% 22% 8%	1975
	21st to end	Night	37% 5% 13% 24% 17% 4	1979
May	1st to 10th	Night	42% 7% 15% 20% 14% 1	4060
	11th to 20th	Night	47% 7% 12% 19% 14% 1	4033
	21st to end	Night	36% 6% 14% 26% 15% 2	4429
June	1st to 10th	Night	37% 9% 17% 21% 16% 1	1800
	11th to 20th	Night	38% 7% 18% 22% 14% 2	1800
	21st to end	Night	33% 10% 17% 23% 13% 3	1800
July	1st to 10th	Night	44% 11% 16% 16% 13% 1	4015
	11th to 20th	Night	48% 14% 20% 12% 3 1	4006
	21st to end	Night	43% 9% 18% 21% 9%	4297
August	1st to 10th	Night	53% 8% 17% 15% 5% 1	2904
	11th to 20th	Night	35% 9% 22% 25% 9% 1	2929
	21st to end	Night	29% 7% 13% 30% 19% 2	3586
September	1st to 10th	Night	34% 8% 13% 24% 17% 6%	2000
	11th to 20th	Night	39% 7% 11% 18% 22% 3	2188
	21st to end	Night	47% 7% 10% 18% 14% 4	2213
October	1st to 10th	Night	38% 5% 7% 19% 25% 6%	3920
	11th to 20th	Night	25% 2 6% 22% 28% 18%	3899
	21st to end	Night	25% 2 6% 26% 25% 16%	4252
November	1st to 10th	Night	35% 3 8% 21% 25% 9%	2461
	11th to 20th	Night	35% 3 6% 18% 26% 11%	2545
	21st to end	Night	32% 4 7% 24% 27% 6%	2600
December	1st to 10th	Night	35% 3 6% 21% 30% 6%	4476
	11th to 20th	Night	47% 4 7% 17% 16% 8%	4824
	21st to end	Night	38% 3 12% 23% 22% 2	6490

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	26% 22% 35% 15% 3	300
	11th to 20th	Day	24% 25% 31% 14% 4 1	300
	21st to end	Day	21% 18% 44% 15% 3	330
February	1st to 10th	Day	19% 19% 41% 16% 4 1	300
	11th to 20th	Day	38% 21% 31% 7% 3	300
	21st to end	Day	27% 17% 35% 18% 3 1	384
March	1st to 10th	Day	23% 15% 34% 22% 6%	500
	11th to 20th	Day	18% 16% 43% 17% 6% 1	500
	21st to end	Day	23% 15% 37% 19% 5% 1	550
April	1st to 10th	Day	20% 17% 32% 21% 9% 1	500
	11th to 20th	Day	13% 18% 27% 24% 14% 3	492
	21st to end	Day	17% 9% 28% 29% 14% 3	500
May	1st to 10th	Day	17% 13% 29% 25% 13% 4	503
	11th to 20th	Day	16% 7% 22% 27% 22% 7%	527
	21st to end	Day	18% 6% 18% 26% 23% 10%	573
June	1st to 10th	Day	10% 4 21% 31% 25% 9%	530
	11th to 20th	Day	9% 3 19% 28% 28% 13%	530
	21st to end	Day	7% 4 14% 33% 31% 11%	530
July	1st to 10th	Day	11% 2 9% 27% 33% 18%	525
	11th to 20th	Day	6% 2 10% 27% 36% 19%	524
	21st to end	Day	8% 2 11% 30% 33% 15%	576
August	1st to 10th	Day	17% 3 13% 25% 27% 14%	526
	11th to 20th	Day	10% 4 12% 26% 31% 17%	519
	21st to end	Day	9% 3 10% 29% 27% 21%	583
September	1st to 10th	Day	13% 2 14% 25% 27% 18%	530
	11th to 20th	Day	15% 4 12% 25% 29% 15%	530
	21st to end	Day	26% 5% 19% 28% 15% 6%	530
October	1st to 10th	Day	16% 5% 19% 25% 24% 10%	530
	11th to 20th	Day	15% 9% 22% 27% 22% 5%	530
	21st to end	Day	14% 10% 26% 28% 16% 5%	583
November	1st to 10th	Day	17% 9% 31% 26% 13% 4	535
	11th to 20th	Day	18% 13% 33% 21% 14% 2	463
	21st to end	Day	13% 18% 30% 24% 13% 2	300
December	1st to 10th	Day	22% 12% 42% 17% 6%	209
	11th to 20th	Day	18% 15% 34% 24% 8% 1	300
	21st to end	Day	25% 16% 28% 21% 9% 2	330
January	1st to 10th	Night	21% 14% 37% 24% 5%	800
	11th to 20th	Night	20% 15% 34% 27% 5%	800
	21st to end	Night	19% 13% 40% 25% 3	880
February	1st to 10th	Night	21% 12% 37% 27% 3	800
	11th to 20th	Night	25% 17% 37% 20% 1	783
	21st to end	Night	17% 16% 37% 26% 3	660
March	1st to 10th	Night	18% 14% 35% 28% 5%	800
	11th to 20th	Night	19% 15% 34% 24% 8%	800
	21st to end	Night	18% 11% 38% 28% 5%	880
April	1st to 10th	Night	17% 15% 34% 28% 6%	800
	11th to 20th	Night	15% 12% 33% 29% 11% 1	791
	21st to end	Night	15% 7% 30% 37% 11%	779
May	1st to 10th	Night	11% 10% 30% 37% 12% 1	600
	11th to 20th	Night	15% 5% 22% 36% 20% 2	591
	21st to end	Night	14% 4 14% 36% 29% 4	650
June	1st to 10th	Night	12% 3 17% 38% 29% 2	600
	11th to 20th	Night	11% 3 15% 36% 32% 4	600
	21st to end	Night	9% 2 12% 39% 36% 3	600
July	1st to 10th	Night	10% 3 8% 34% 39% 6%	585
	11th to 20th	Night	8% 2 6% 35% 42% 8%	582
	21st to end	Night	7% 2 9% 36% 38% 7%	657
August	1st to 10th	Night	16% 2 7% 35% 35% 5%	597
	11th to 20th	Night	10% 2 9% 34% 38% 6%	608
	21st to end	Night	12% 2 8% 32% 39% 7%	880
September	1st to 10th	Night	13% 2 8% 35% 36% 6%	800
	11th to 20th	Night	18% 3 10% 32% 32% 6%	800
	21st to end	Night	22% 5% 16% 34% 23% 2	800
October	1st to 10th	Night	17% 4 17% 30% 27% 6%	800
	11th to 20th	Night	16% 7% 25% 33% 17% 3	800
	21st to end	Night	14% 9% 26% 30% 19% 2	880
November	1st to 10th	Night	17% 7% 24% 34% 15% 2	820
	11th to 20th	Night	14% 11% 32% 32% 10% 1	829
	21st to end	Night	15% 10% 30% 32% 12% 1	800
December	1st to 10th	Night	21% 8% 34% 30% 7%	800
	11th to 20th	Night	18% 8% 35% 32% 7%	800
	21st to end	Night	23% 11% 27% 30% 8%	880

Page generated at 2025-11-15 00:55:54. Version ac07

Copyright © 2025 Attilla Danko.