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 2024-11-28.

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%	105348
	Night	7% 9% 3 7% 4 4 4 4 5% 7% 46%	102888
Transparency	Day	31% 7% 11% 20% 19% 12%	105099
	Night	35% 8% 12% 19% 16% 10%	102725
Seeing	Day	10% 10% 24% 28% 21% 7%	15277
	Night	12% 6% 21% 39% 20% 2	24914

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% 20% 6% 11% 6% 6% 5% 4 5% 6% 20%	2539
	11th to 20th	Day	9% 16% 7% 10% 6% 5% 5% 3 5% 5% 30%	2577
	21st to end	Day	15% 18% 6% 12% 5% 5% 4 3 4 5% 23%	3146
February	1st to 10th	Day	8% 14% 4 11% 7% 5% 5% 5% 7% 6% 28%	1710
	11th to 20th	Day	11% 13% 5% 9% 6% 5% 5% 3 7% 6% 31%	1703
	21st to end	Day	7% 13% 4 10% 6% 3 5% 5% 6% 7% 35%	1570
March	1st to 10th	Day	8% 13% 4 10% 6% 6% 4 4 4 6% 34%	3283
	11th to 20th	Day	6% 10% 2 5% 4 3 4 4 5% 5% 51%	3490
	21st to end	Day	10% 14% 5% 10% 6% 5% 6% 6% 6% 7% 26%	3825
April	1st to 10th	Day	9% 10% 4 6% 5% 5% 5% 5% 6% 7% 38%	2158
	11th to 20th	Day	6% 10% 3 6% 5% 4 4 4 6% 7% 44%	2437
	21st to end	Day	8% 8% 2 8% 5% 4 3 3 6% 9% 44%	2470
May	1st to 10th	Day	8% 10% 3 6% 5% 5% 4 4 5% 7% 43%	4110
	11th to 20th	Day	4 3 2 4 3 3 4 4 5% 7% 60%	4071
	21st to end	Day	7% 7% 2 6% 4 4 5% 4 5% 7% 50%	4689
June	1st to 10th	Day	6% 4 2 6% 4 4 5% 4 6% 8% 51%	2799
	11th to 20th	Day	6% 5% 2 4 4 3 4 4 6% 8% 56%	2850
	21st to end	Day	3 1 1 2 2 2 3 2 4 7% 72%	2850
July	1st to 10th	Day	1 1 2 1 1 2 2 3 5% 80%	4588
	11th to 20th	Day	1 2 1 3 3 3 3 3 4 6% 72%	4420
	21st to end	Day	2 3 1 3 3 3 3 3 5% 6% 67%	4457
August	1st to 10th	Day	3 3 1 4 3 3 4 4 6% 7% 62%	4092
	11th to 20th	Day	2 2 1 3 3 3 4 3 4 7% 70%	4028
	21st to end	Day	2 2 1 2 2 2 3 2 4 6% 74%	4521
September	1st to 10th	Day	3 3 1 2 2 2 2 2 3 5% 73%	2190
	11th to 20th	Day	4 4 2 2 3 4 3 3 5% 6% 65%	2090
	21st to end	Day	6% 4 2 3 2 2 3 2 4 6% 66%	2090
October	1st to 10th	Day	6% 4 2 4 2 2 3 2 3 4 68%	3340
	11th to 20th	Day	5% 4 2 5% 3 3 3 3 4 6% 62%	3150
	21st to end	Day	8% 7% 2 5% 4 4 5% 5% 6% 8% 46%	3258
November	1st to 10th	Day	10% 9% 3 8% 4 4 3 3 5% 7% 43%	1764
	11th to 20th	Day	9% 9% 2 7% 5% 5% 3 4 6% 8% 40%	1719
	21st to end	Day	8% 11% 3 9% 5% 4 5% 3 4 6% 39%	1576
December	1st to 10th	Day	12% 13% 5% 10% 6% 5% 4 3 5% 6% 30%	1520
	11th to 20th	Day	12% 11% 5% 12% 9% 6% 6% 5% 6% 6% 23%	1822
	21st to end	Day	8% 14% 4 10% 5% 6% 5% 4 5% 7% 31%	2446
January	1st to 10th	Night	10% 18% 7% 11% 5% 5% 5% 5% 6% 7% 23%	4429
	11th to 20th	Night	13% 19% 7% 11% 6% 4 4 3 4 6% 24%	4380
	21st to end	Night	17% 18% 4 10% 6% 6% 4 4 4 5% 22%	4521
February	1st to 10th	Night	10% 13% 4 10% 6% 5% 5% 5% 5% 7% 29%	2470
	11th to 20th	Night	11% 13% 4 8% 5% 5% 4 4 5% 7% 35%	2360
	21st to end	Night	6% 14% 4 11% 6% 6% 5% 4 7% 7% 30%	1884
March	1st to 10th	Night	7% 12% 3 8% 7% 6% 5% 5% 6% 7% 34%	3591
	11th to 20th	Night	4 7% 2 5% 4 4 4 4 6% 9% 52%	3490
	21st to end	Night	8% 9% 4 7% 5% 5% 6% 5% 7% 9% 35%	3828
April	1st to 10th	Night	8% 10% 3 7% 6% 4 4 4 5% 7% 43%	2019
	11th to 20th	Night	7% 10% 4 7% 5% 4 5% 4 6% 7% 42%	1691
	21st to end	Night	8% 8% 2 6% 4 4 4 3 6% 7% 49%	1710
May	1st to 10th	Night	10% 11% 3 7% 4 4 4 3 6% 6% 43%	2860
	11th to 20th	Night	4 4 2 5% 4 4 5% 4 6% 8% 55%	2834
	21st to end	Night	7% 5% 2 6% 4 5% 3 4 6% 8% 49%	2897
June	1st to 10th	Night	6% 4 2 4 4 5% 5% 5% 8% 8% 50%	1377
	11th to 20th	Night	6% 5% 2 4 3 3 4 3 6% 8% 55%	1330
	21st to end	Night	2 2 1 3 3 2 2 4 5% 6% 70%	1330
July	1st to 10th	Night	2 1 1 2 2 2 2 2 5% 5% 74%	2367
	11th to 20th	Night	1 1 1 2 2 3 4 4 5% 9% 69%	2540
	21st to end	Night	1 2 1 3 3 4 4 3 5% 7% 67%	3104
August	1st to 10th	Night	1 2 1 3 3 3 4 4 7% 9% 63%	2847
	11th to 20th	Night	2 2 2 4 3 3 4 3 4 6% 66%	2811
	21st to end	Night	3 3 1 3 2 2 2 2 4 5% 73%	3146
September	1st to 10th	Night	3 2 1 3 3 2 3 3 4 5% 70%	1987
	11th to 20th	Night	5% 4 1 4 3 3 4 3 5% 7% 61%	2090
	21st to end	Night	7% 4 1 3 3 2 3 3 3 5% 65%	2090
October	1st to 10th	Night	4 3 1 4 2 2 2 2 4 5% 71%	3635
	11th to 20th	Night	10% 5% 2 6% 3 4 4 3 4 5% 55%	3778
	21st to end	Night	7% 7% 3 6% 4 4 5% 4 6% 7% 46%	4298
November	1st to 10th	Night	9% 9% 3 6% 5% 3 4 3 5% 7% 46%	2535
	11th to 20th	Night	9% 10% 3 6% 5% 4 4 5% 6% 6% 41%	2659
	21st to end	Night	7% 11% 4 7% 5% 4 6% 5% 5% 6% 40%	2759
December	1st to 10th	Night	10% 15% 5% 9% 4 4 4 4 5% 7% 33%	2660
	11th to 20th	Night	12% 14% 5% 10% 6% 5% 5% 3 5% 7% 28%	3367
	21st to end	Night	10% 12% 5% 12% 6% 6% 6% 4 6% 7% 26%	5214

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	60% 11% 13% 12% 3	2539
	11th to 20th	Day	54% 10% 17% 12% 6% 1	2577
	21st to end	Day	61% 11% 12% 12% 4 1	3146
February	1st to 10th	Day	53% 11% 15% 16% 4 1	1710
	11th to 20th	Day	50% 9% 17% 17% 5% 1	1712
	21st to end	Day	47% 12% 16% 17% 8% 1	1570
March	1st to 10th	Day	46% 10% 15% 22% 6% 1	3283
	11th to 20th	Day	32% 8% 14% 32% 13% 1	3490
	21st to end	Day	52% 13% 17% 14% 4	3825
April	1st to 10th	Day	42% 8% 17% 18% 12% 2	2158
	11th to 20th	Day	36% 7% 13% 27% 15% 2	2440
	21st to end	Day	36% 8% 12% 26% 17% 1	2470
May	1st to 10th	Day	33% 9% 12% 23% 18% 4	4110
	11th to 20th	Day	20% 7% 11% 31% 23% 8%	4074
	21st to end	Day	30% 9% 11% 29% 18% 2	4689
June	1st to 10th	Day	29% 7% 14% 29% 19% 2	2799
	11th to 20th	Day	26% 6% 11% 22% 23% 13%	2850
	21st to end	Day	13% 3 7% 22% 36% 20%	2850
July	1st to 10th	Day	8% 3 4 9% 26% 50%	4518
	11th to 20th	Day	14% 3 3 9% 24% 47%	4345
	21st to end	Day	17% 4 4 12% 30% 34%	4316
August	1st to 10th	Day	21% 4 5% 14% 28% 28%	4078
	11th to 20th	Day	15% 3 4 19% 37% 22%	4067
	21st to end	Day	13% 3 4 21% 30% 29%	4520
September	1st to 10th	Day	15% 3 7% 17% 32% 26%	2190
	11th to 20th	Day	20% 5% 8% 25% 28% 14%	2090
	21st to end	Day	20% 4 8% 27% 31% 10%	2090
October	1st to 10th	Day	22% 4 7% 20% 33% 15%	3340
	11th to 20th	Day	25% 4 10% 37% 19% 6%	3150
	21st to end	Day	35% 6% 14% 27% 17% 1	3258
November	1st to 10th	Day	40% 7% 18% 22% 12% 1	1764
	11th to 20th	Day	40% 7% 21% 23% 7% 2	1719
	21st to end	Day	44% 7% 19% 21% 8% 1	1576
December	1st to 10th	Day	53% 8% 14% 16% 6% 2	1520
	11th to 20th	Day	58% 10% 15% 14% 2	1820
	21st to end	Day	47% 11% 18% 18% 6%	2446
January	1st to 10th	Night	54% 11% 17% 14% 4 1	4429
	11th to 20th	Night	58% 11% 13% 13% 4 1	4380
	21st to end	Night	58% 14% 14% 10% 3 1	4521
February	1st to 10th	Night	52% 11% 16% 16% 5% 1	2470
	11th to 20th	Night	47% 9% 18% 19% 7%	2361
	21st to end	Night	49% 10% 18% 15% 6% 2	1884
March	1st to 10th	Night	41% 13% 17% 21% 8% 1	3591
	11th to 20th	Night	26% 10% 19% 28% 16% 1	3490
	21st to end	Night	40% 12% 19% 24% 4 1	3828
April	1st to 10th	Night	39% 9% 14% 20% 15% 3	2019
	11th to 20th	Night	38% 7% 14% 23% 16% 2	1691
	21st to end	Night	34% 6% 12% 25% 22% 1	1710
May	1st to 10th	Night	34% 11% 11% 23% 17% 4	2860
	11th to 20th	Night	21% 8% 12% 24% 27% 8%	2835
	21st to end	Night	27% 9% 12% 26% 23% 3	2897
June	1st to 10th	Night	28% 8% 13% 23% 23% 4	1377
	11th to 20th	Night	25% 7% 11% 17% 28% 12%	1330
	21st to end	Night	14% 4 7% 16% 31% 29%	1330
July	1st to 10th	Night	13% 2 5% 9% 21% 49%	2328
	11th to 20th	Night	13% 2 3 9% 22% 51%	2492
	21st to end	Night	16% 3 4 13% 29% 35%	3007
August	1st to 10th	Night	16% 4 5% 12% 28% 35%	2838
	11th to 20th	Night	19% 3 4 17% 32% 25%	2838
	21st to end	Night	15% 3 5% 15% 29% 33%	3146
September	1st to 10th	Night	16% 4 7% 13% 30% 31%	1987
	11th to 20th	Night	22% 4 9% 22% 25% 17%	2090
	21st to end	Night	22% 4 7% 23% 31% 13%	2090
October	1st to 10th	Night	18% 3 7% 18% 36% 18%	3635
	11th to 20th	Night	33% 3 6% 31% 20% 7%	3778
	21st to end	Night	35% 6% 13% 27% 18% 2	4298
November	1st to 10th	Night	37% 6% 14% 25% 15% 1	2535
	11th to 20th	Night	41% 9% 17% 24% 9% 2	2659
	21st to end	Night	42% 8% 18% 22% 9% 1	2759
December	1st to 10th	Night	50% 9% 19% 14% 7% 2	2660
	11th to 20th	Night	54% 9% 18% 16% 2	3368
	21st to end	Night	51% 10% 15% 15% 8%	5214

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% 11% 20% 22% 21% 6%	180
	11th to 20th	Day	18% 9% 18% 34% 17% 4	192
	21st to end	Day	20% 9% 19% 31% 20% 1	297
February	1st to 10th	Day	15% 18% 30% 27% 10% 1	270
	11th to 20th	Day	18% 12% 31% 26% 11% 2	308
	21st to end	Day	14% 18% 31% 26% 10% 1	382
March	1st to 10th	Day	11% 17% 34% 27% 10% 1	460
	11th to 20th	Day	10% 13% 29% 30% 16% 1	460
	21st to end	Day	14% 18% 32% 26% 9%	506
April	1st to 10th	Day	17% 15% 28% 20% 16% 3	460
	11th to 20th	Day	12% 20% 33% 20% 12% 3	452
	21st to end	Day	11% 13% 27% 29% 14% 5%	460
May	1st to 10th	Day	8% 14% 29% 26% 19% 4	463
	11th to 20th	Day	9% 14% 26% 25% 18% 8%	488
	21st to end	Day	13% 8% 20% 25% 23% 11%	650
June	1st to 10th	Day	7% 8% 24% 28% 24% 10%	680
	11th to 20th	Day	11% 11% 26% 31% 17% 3	680
	21st to end	Day	5% 4 25% 32% 26% 9%	680
July	1st to 10th	Day	3 3 20% 33% 32% 9%	588
	11th to 20th	Day	2 5% 21% 36% 29% 7%	484
	21st to end	Day	3 2 18% 32% 32% 13%	531
August	1st to 10th	Day	5% 5% 20% 32% 29% 10%	487
	11th to 20th	Day	4 3 18% 35% 27% 14%	477
	21st to end	Day	4 6% 21% 28% 28% 13%	539
September	1st to 10th	Day	4 4 21% 26% 30% 14%	490
	11th to 20th	Day	6% 8% 22% 28% 24% 12%	490
	21st to end	Day	8% 7% 19% 25% 29% 12%	490
October	1st to 10th	Day	9% 7% 20% 25% 23% 16%	405
	11th to 20th	Day	7% 13% 18% 19% 25% 17%	300
	21st to end	Day	13% 12% 25% 24% 22% 3	330
November	1st to 10th	Day	16% 10% 26% 24% 17% 8%	300
	11th to 20th	Day	12% 11% 21% 36% 16% 4	300
	21st to end	Day	13% 10% 22% 31% 22% 3	291
December	1st to 10th	Day	19% 8% 18% 33% 17% 4	270
	11th to 20th	Day	23% 6% 23% 31% 16% 1	239
	21st to end	Day	20% 13% 17% 28% 17% 5%	198
January	1st to 10th	Night	18% 9% 19% 35% 17% 1	770
	11th to 20th	Night	20% 7% 18% 34% 17% 3	760
	21st to end	Night	19% 4 19% 37% 17% 3	836
February	1st to 10th	Night	17% 7% 30% 33% 13% 1	760
	11th to 20th	Night	15% 8% 25% 37% 13% 2	744
	21st to end	Night	10% 12% 28% 36% 12% 2	628
March	1st to 10th	Night	13% 8% 24% 41% 13% 1	760
	11th to 20th	Night	9% 6% 28% 41% 17% 1	760
	21st to end	Night	13% 9% 24% 40% 13% 1	836
April	1st to 10th	Night	13% 7% 27% 36% 16% 1	736
	11th to 20th	Night	12% 9% 31% 36% 10% 1	563
	21st to end	Night	11% 6% 25% 40% 16% 2	570
May	1st to 10th	Night	10% 9% 25% 38% 17% 1	570
	11th to 20th	Night	9% 5% 22% 37% 23% 3	561
	21st to end	Night	11% 6% 20% 38% 23% 2	617
June	1st to 10th	Night	9% 5% 20% 36% 26% 3	427
	11th to 20th	Night	7% 7% 26% 43% 17% 1	380
	21st to end	Night	3 2 17% 46% 27% 4	380
July	1st to 10th	Night	2 2 14% 44% 35% 3	370
	11th to 20th	Night	2 1 13% 56% 27% 1	368
	21st to end	Night	2 15% 48% 33% 3	619
August	1st to 10th	Night	4 2 14% 49% 30% 2	567
	11th to 20th	Night	2 2 13% 46% 34% 2	564
	21st to end	Night	4 2 16% 44% 31% 3	627
September	1st to 10th	Night	4 3 17% 40% 32% 5%	695
	11th to 20th	Night	6% 3 16% 39% 30% 6%	760
	21st to end	Night	9% 3 15% 38% 28% 6%	760
October	1st to 10th	Night	10% 4 17% 41% 26% 2	760
	11th to 20th	Night	10% 6% 19% 35% 26% 4	760
	21st to end	Night	9% 6% 22% 42% 18% 3	836
November	1st to 10th	Night	14% 6% 24% 36% 18% 2	780
	11th to 20th	Night	13% 7% 27% 36% 15% 2	859
	21st to end	Night	11% 7% 22% 38% 19% 2	986
December	1st to 10th	Night	18% 7% 22% 40% 12% 1	950
	11th to 20th	Night	21% 7% 20% 37% 14% 1	950
	21st to end	Night	22% 9% 25% 32% 11% 1	1045

Page generated at 2024-11-24 22:22:21. Version ac07

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