Burkman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burkman Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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% 6% 52%	136077
	Night	7% 9% 3 7% 4 4 4 4 6% 7% 45%	133360
Transparency	Day	32% 6% 10% 21% 19% 12%	130785
	Night	36% 7% 12% 19% 16% 9%	129654
Seeing	Day	10% 9% 24% 28% 21% 7%	16773
	Night	12% 6% 22% 39% 20% 2	26515

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	11% 22% 6% 10% 6% 5% 5% 4 5% 5% 21%	3719
	11th to 20th	Day	7% 13% 6% 13% 7% 5% 4 3 4 5% 33%	3787
	21st to end	Day	10% 13% 5% 11% 5% 4 4 4 6% 5% 33%	4609
February	1st to 10th	Day	9% 14% 4 11% 7% 5% 5% 5% 7% 6% 27%	1800
	11th to 20th	Day	12% 13% 5% 9% 6% 5% 5% 3 7% 6% 30%	1796
	21st to end	Day	7% 12% 4 10% 6% 3 4 5% 6% 7% 36%	1650
March	1st to 10th	Day	8% 13% 3 9% 6% 5% 4 4 5% 7% 35%	4728
	11th to 20th	Day	7% 12% 3 6% 4 4 4 4 6% 6% 45%	5000
	21st to end	Day	8% 12% 4 9% 6% 6% 6% 6% 6% 8% 31%	5486
April	1st to 10th	Day	8% 10% 3 6% 5% 5% 5% 5% 6% 7% 39%	2272
	11th to 20th	Day	6% 10% 3 6% 5% 4 4 4 5% 7% 45%	2567
	21st to end	Day	8% 8% 2 8% 5% 4 4 4 6% 9% 44%	2600
May	1st to 10th	Day	7% 8% 2 5% 4 4 3 3 5% 7% 52%	5880
	11th to 20th	Day	8% 6% 2 6% 4 4 5% 4 5% 7% 49%	5841
	21st to end	Day	5% 5% 1 4 3 3 4 3 5% 6% 59%	6733
June	1st to 10th	Day	6% 4 2 6% 4 4 4 4 6% 8% 52%	2947
	11th to 20th	Day	6% 4 2 5% 4 3 4 4 6% 8% 56%	3000
	21st to end	Day	3 2 1 2 2 2 3 2 5% 7% 72%	3000
July	1st to 10th	Day	1 1 1 3 2 2 3 3 4 5% 76%	6557
	11th to 20th	Day	1 1 1 2 2 3 3 3 4 6% 74%	6320
	21st to end	Day	2 2 1 3 3 3 3 3 5% 7% 69%	6404
August	1st to 10th	Day	3 3 1 4 3 3 3 3 5% 7% 64%	5779
	11th to 20th	Day	2 1 1 3 3 3 4 3 4 7% 71%	5798
	21st to end	Day	3 3 2 4 2 3 3 3 4 6% 66%	6468
September	1st to 10th	Day	3 3 1 2 2 2 2 2 3 5% 72%	2305
	11th to 20th	Day	4 4 2 3 3 3 3 3 5% 6% 65%	2200
	21st to end	Day	6% 4 2 3 2 2 3 2 4 6% 66%	2200
October	1st to 10th	Day	6% 4 2 4 2 2 2 2 3 4 68%	3445
	11th to 20th	Day	5% 4 2 6% 3 3 3 3 4 6% 61%	3250
	21st to end	Day	8% 7% 2 5% 4 4 5% 5% 6% 8% 47%	3362
November	1st to 10th	Day	10% 9% 3 7% 4 4 3 3 5% 7% 44%	1854
	11th to 20th	Day	9% 9% 2 7% 5% 5% 3 4 6% 9% 40%	1805
	21st to end	Day	8% 11% 4 9% 5% 4 5% 4 4 6% 39%	1680
December	1st to 10th	Day	7% 9% 4 9% 6% 4 6% 4 5% 5% 40%	2700
	11th to 20th	Day	12% 16% 6% 11% 7% 6% 5% 4 5% 5% 22%	2942
	21st to end	Day	13% 15% 4 11% 5% 6% 5% 4 5% 6% 25%	3593
January	1st to 10th	Night	10% 17% 6% 12% 6% 5% 5% 4 6% 7% 22%	6469
	11th to 20th	Night	9% 15% 6% 14% 7% 5% 4 4 6% 6% 24%	6392
	21st to end	Night	11% 13% 3 8% 5% 5% 4 4 7% 7% 33%	6611
February	1st to 10th	Night	11% 13% 4 10% 6% 5% 5% 5% 5% 7% 28%	2600
	11th to 20th	Night	11% 13% 4 8% 5% 5% 4 4 5% 7% 34%	2487
	21st to end	Night	6% 13% 4 10% 6% 6% 5% 5% 7% 7% 31%	1980
March	1st to 10th	Night	8% 13% 3 7% 5% 5% 5% 5% 6% 6% 36%	5166
	11th to 20th	Night	5% 10% 3 7% 4 4 4 4 7% 9% 43%	5000
	21st to end	Night	7% 8% 4 7% 5% 5% 5% 5% 7% 9% 38%	5489
April	1st to 10th	Night	7% 9% 3 7% 6% 4 4 4 5% 7% 43%	2124
	11th to 20th	Night	7% 10% 4 7% 5% 4 5% 4 6% 7% 43%	1781
	21st to end	Night	8% 8% 2 6% 4 4 4 3 6% 7% 48%	1800
May	1st to 10th	Night	9% 9% 2 6% 4 3 4 3 6% 7% 49%	4100
	11th to 20th	Night	7% 5% 2 5% 4 5% 5% 4 6% 8% 48%	4074
	21st to end	Night	5% 4 2 5% 4 4 4 4 6% 9% 54%	4163
June	1st to 10th	Night	6% 4 2 4 4 5% 5% 5% 7% 8% 50%	1449
	11th to 20th	Night	6% 5% 2 4 3 3 4 3 5% 8% 56%	1400
	21st to end	Night	3 2 1 3 3 2 2 4 5% 6% 70%	1400
July	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 5% 71%	3397
	11th to 20th	Night	1 1 2 2 2 3 3 5% 8% 72%	3640
	21st to end	Night	1 2 1 3 2 3 4 3 5% 8% 68%	4467
August	1st to 10th	Night	2 2 1 3 2 3 4 4 7% 9% 63%	4033
	11th to 20th	Night	1 2 1 3 3 3 4 4 5% 7% 67%	4051
	21st to end	Night	5% 4 2 4 3 3 4 3 5% 6% 62%	4509
September	1st to 10th	Night	3 2 1 3 3 2 3 3 4 5% 70%	2092
	11th to 20th	Night	5% 4 1 4 3 3 4 3 5% 7% 61%	2200
	21st to end	Night	7% 4 1 3 3 3 3 3 3 5% 65%	2200
October	1st to 10th	Night	5% 3 1 4 2 2 2 2 3 5% 70%	3750
	11th to 20th	Night	10% 5% 2 6% 3 4 4 3 4 5% 55%	3898
	21st to end	Night	7% 7% 3 6% 4 4 5% 4 6% 7% 47%	4436
November	1st to 10th	Night	9% 8% 3 6% 5% 3 4 3 5% 8% 46%	2665
	11th to 20th	Night	9% 10% 3 7% 5% 4 4 5% 6% 6% 40%	2792
	21st to end	Night	6% 11% 4 8% 5% 4 6% 5% 5% 6% 40%	2940
December	1st to 10th	Night	7% 10% 3 8% 4 4 5% 5% 6% 7% 40%	4710
	11th to 20th	Night	12% 15% 4 9% 5% 5% 5% 4 6% 7% 28%	5472
	21st to end	Night	14% 14% 5% 11% 6% 6% 6% 4 6% 6% 23%	7623

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% 8% 12% 13% 4	3719
	11th to 20th	Day	53% 7% 17% 14% 7% 3	3787
	21st to end	Day	51% 8% 11% 21% 8% 1	4609
February	1st to 10th	Day	54% 11% 14% 16% 4 1	1800
	11th to 20th	Day	51% 9% 18% 17% 5% 1	1805
	21st to end	Day	46% 11% 15% 18% 8% 2	1650
March	1st to 10th	Day	45% 8% 15% 22% 7% 3	4728
	11th to 20th	Day	37% 6% 10% 32% 12% 1	5000
	21st to end	Day	48% 10% 18% 20% 5%	5486
April	1st to 10th	Day	41% 8% 17% 19% 13% 2	2272
	11th to 20th	Day	36% 7% 12% 27% 16% 3	2570
	21st to end	Day	36% 8% 12% 26% 17% 1	2600
May	1st to 10th	Day	28% 7% 11% 26% 23% 5%	5880
	11th to 20th	Day	32% 6% 9% 26% 21% 6%	5844
	21st to end	Day	24% 7% 8% 33% 26% 3	6734
June	1st to 10th	Day	29% 6% 13% 29% 20% 3	2947
	11th to 20th	Day	25% 5% 11% 22% 23% 13%	3000
	21st to end	Day	13% 3 6% 22% 37% 20%	3000
July	1st to 10th	Day	12% 3 3 10% 26% 45%	6488
	11th to 20th	Day	12% 3 2 8% 30% 45%	6245
	21st to end	Day	15% 3 3 11% 35% 32%	6219
August	1st to 10th	Day	21% 4 5% 15% 29% 28%	4208
	11th to 20th	Day	15% 3 4 19% 37% 22%	4197
	21st to end	Day	14% 3 4 21% 30% 28%	4663
September	1st to 10th	Day	16% 3 7% 17% 32% 25%	2305
	11th to 20th	Day	19% 5% 8% 25% 29% 14%	2200
	21st to end	Day	21% 4 8% 26% 31% 10%	2200
October	1st to 10th	Day	22% 4 7% 20% 33% 14%	3445
	11th to 20th	Day	25% 4 10% 37% 19% 6%	3250
	21st to end	Day	35% 6% 14% 28% 16% 1	3362
November	1st to 10th	Day	39% 7% 18% 23% 11% 1	1854
	11th to 20th	Day	41% 7% 21% 23% 7% 1	1805
	21st to end	Day	44% 7% 20% 21% 8% 1	1680
December	1st to 10th	Day	45% 6% 21% 22% 4 1	2700
	11th to 20th	Day	62% 7% 16% 13% 2	2940
	21st to end	Day	56% 8% 16% 16% 4	3593
January	1st to 10th	Night	57% 9% 15% 14% 5%	6469
	11th to 20th	Night	58% 9% 14% 14% 4 1	6392
	21st to end	Night	45% 11% 13% 20% 9% 2	6611
February	1st to 10th	Night	52% 10% 15% 15% 6% 1	2600
	11th to 20th	Night	48% 9% 18% 19% 7%	2488
	21st to end	Night	48% 10% 18% 16% 7% 2	1980
March	1st to 10th	Night	43% 9% 15% 23% 8% 2	5166
	11th to 20th	Night	35% 8% 14% 28% 15% 1	5000
	21st to end	Night	38% 9% 19% 26% 7%	5489
April	1st to 10th	Night	39% 8% 13% 21% 15% 3	2124
	11th to 20th	Night	39% 6% 13% 22% 17% 2	1781
	21st to end	Night	35% 6% 12% 24% 22% 1	1800
May	1st to 10th	Night	30% 8% 10% 25% 21% 5%	4097
	11th to 20th	Night	30% 7% 11% 24% 23% 6%	4075
	21st to end	Night	24% 7% 9% 26% 29% 6%	4163
June	1st to 10th	Night	28% 8% 13% 23% 24% 4	1449
	11th to 20th	Night	24% 7% 11% 18% 28% 12%	1400
	21st to end	Night	14% 4 7% 16% 32% 28%	1400
July	1st to 10th	Night	16% 2 4 9% 21% 47%	3358
	11th to 20th	Night	11% 2 3 8% 26% 50%	3592
	21st to end	Night	15% 3 3 10% 32% 36%	4340
August	1st to 10th	Night	16% 4 5% 12% 28% 34%	2928
	11th to 20th	Night	19% 3 4 17% 33% 24%	2928
	21st to end	Night	16% 3 5% 15% 29% 32%	3245
September	1st to 10th	Night	16% 3 7% 13% 30% 30%	2092
	11th to 20th	Night	22% 4 9% 22% 25% 17%	2200
	21st to end	Night	22% 4 7% 23% 32% 13%	2200
October	1st to 10th	Night	18% 3 7% 18% 36% 17%	3750
	11th to 20th	Night	33% 3 6% 32% 19% 7%	3898
	21st to end	Night	35% 6% 13% 28% 17% 2	4436
November	1st to 10th	Night	37% 6% 15% 26% 15% 1	2665
	11th to 20th	Night	42% 9% 17% 23% 8% 2	2792
	21st to end	Night	43% 7% 18% 22% 9% 1	2940
December	1st to 10th	Night	43% 6% 22% 23% 5% 1	4710
	11th to 20th	Night	56% 7% 22% 14% 2	5473
	21st to end	Night	57% 7% 15% 14% 6%	7623

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% 10% 23% 22% 18% 5%	220
	11th to 20th	Day	15% 7% 18% 36% 20% 4	236
	21st to end	Day	16% 8% 18% 33% 22% 2	363
February	1st to 10th	Day	17% 17% 30% 26% 9% 1	300
	11th to 20th	Day	18% 13% 30% 26% 11% 2	341
	21st to end	Day	14% 17% 30% 27% 11% 2	414
March	1st to 10th	Day	11% 16% 33% 27% 11% 2	500
	11th to 20th	Day	13% 13% 29% 29% 15% 1	500
	21st to end	Day	14% 17% 33% 25% 9% 1	550
April	1st to 10th	Day	16% 15% 28% 21% 17% 4	500
	11th to 20th	Day	12% 19% 32% 20% 12% 4	492
	21st to end	Day	11% 13% 28% 29% 14% 5%	500
May	1st to 10th	Day	8% 13% 27% 27% 20% 5%	503
	11th to 20th	Day	10% 14% 27% 25% 17% 7%	528
	21st to end	Day	13% 8% 19% 25% 24% 11%	701
June	1st to 10th	Day	7% 7% 23% 29% 24% 10%	730
	11th to 20th	Day	11% 10% 26% 31% 18% 4	730
	21st to end	Day	5% 4 25% 31% 26% 9%	730
July	1st to 10th	Day	3 3 20% 34% 31% 9%	633
	11th to 20th	Day	2 6% 21% 35% 29% 7%	524
	21st to end	Day	3 2 19% 33% 31% 13%	575
August	1st to 10th	Day	5% 5% 21% 31% 28% 10%	527
	11th to 20th	Day	3 3 19% 34% 27% 14%	517
	21st to end	Day	4 6% 21% 28% 27% 14%	583
September	1st to 10th	Day	5% 4 20% 26% 31% 15%	530
	11th to 20th	Day	6% 7% 22% 28% 25% 12%	530
	21st to end	Day	8% 6% 18% 25% 28% 13%	530
October	1st to 10th	Day	9% 7% 20% 26% 23% 15%	440
	11th to 20th	Day	7% 13% 20% 20% 23% 16%	330
	21st to end	Day	13% 12% 24% 24% 23% 4	363
November	1st to 10th	Day	16% 10% 25% 23% 18% 8%	330
	11th to 20th	Day	12% 11% 20% 37% 16% 5%	330
	21st to end	Day	12% 9% 22% 32% 22% 3	330
December	1st to 10th	Day	19% 9% 18% 31% 17% 6%	330
	11th to 20th	Day	24% 8% 23% 30% 15% 1	291
	21st to end	Day	24% 11% 19% 26% 17% 4	242
January	1st to 10th	Night	18% 8% 21% 35% 16% 1	850
	11th to 20th	Night	18% 7% 18% 36% 18% 3	840
	21st to end	Night	18% 5% 20% 39% 16% 2	924
February	1st to 10th	Night	18% 8% 30% 32% 13% 1	800
	11th to 20th	Night	16% 8% 25% 37% 13% 2	784
	21st to end	Night	10% 12% 27% 37% 13% 2	660
March	1st to 10th	Night	13% 8% 24% 40% 14% 1	800
	11th to 20th	Night	10% 6% 28% 40% 16% 1	800
	21st to end	Night	13% 9% 25% 39% 13% 1	880
April	1st to 10th	Night	13% 7% 26% 37% 16% 1	774
	11th to 20th	Night	12% 9% 31% 36% 10% 1	593
	21st to end	Night	11% 6% 26% 39% 15% 2	600
May	1st to 10th	Night	10% 8% 24% 38% 18% 1	600
	11th to 20th	Night	10% 6% 24% 36% 22% 3	591
	21st to end	Night	10% 6% 20% 39% 23% 2	650
June	1st to 10th	Night	8% 5% 20% 37% 26% 3	449
	11th to 20th	Night	7% 6% 25% 44% 17% 1	400
	21st to end	Night	4 2 17% 46% 27% 4	400
July	1st to 10th	Night	3 2 14% 45% 34% 3	390
	11th to 20th	Night	2 1 14% 55% 27% 1	388
	21st to end	Night	2 15% 48% 32% 3	652
August	1st to 10th	Night	3 2 15% 49% 29% 2	597
	11th to 20th	Night	2 2 14% 45% 34% 3	594
	21st to end	Night	5% 2 16% 44% 30% 3	660
September	1st to 10th	Night	4 3 17% 40% 33% 5%	732
	11th to 20th	Night	6% 3 16% 39% 30% 6%	800
	21st to end	Night	9% 3 15% 38% 29% 6%	800
October	1st to 10th	Night	10% 4 18% 41% 26% 2	800
	11th to 20th	Night	10% 7% 19% 35% 24% 4	800
	21st to end	Night	9% 6% 21% 42% 18% 3	880
November	1st to 10th	Night	14% 5% 24% 36% 18% 2	820
	11th to 20th	Night	13% 6% 26% 37% 16% 1	902
	21st to end	Night	11% 7% 21% 39% 20% 2	1050
December	1st to 10th	Night	18% 7% 23% 38% 12% 2	1050
	11th to 20th	Night	21% 7% 21% 37% 13% 1	1050
	21st to end	Night	21% 9% 26% 32% 10% 1	1155

Page generated at 2026-01-28 23:21:43. Version ac07

Copyright © 2026 Attilla Danko.