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 2024-01-14.

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	7% 7% 3 5% 5% 3 4 5% 5% 7% 49%	74676
	Night	8% 8% 3 6% 5% 3 4 5% 5% 7% 45%	75081
Transparency	Day	33% 7% 13% 21% 17% 9%	74387
	Night	37% 8% 14% 19% 15% 8%	74890
Seeing	Day	10% 9% 24% 29% 21% 7%	14054
	Night	12% 6% 21% 39% 20% 2	23827

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	14% 13% 5% 9% 6% 4 5% 4 6% 8% 26%	1519
	11th to 20th	Day	12% 9% 5% 9% 6% 4 5% 5% 5% 6% 33%	1487
	21st to end	Day	13% 16% 6% 10% 6% 2 5% 5% 5% 6% 26%	1782
February	1st to 10th	Day	8% 12% 5% 9% 8% 4 5% 5% 7% 7% 30%	1620
	11th to 20th	Day	11% 12% 5% 8% 6% 4 5% 5% 6% 6% 32%	1611
	21st to end	Day	8% 12% 5% 9% 6% 3 4 5% 6% 7% 35%	1480
March	1st to 10th	Day	7% 9% 3 8% 8% 4 6% 6% 6% 7% 36%	1880
	11th to 20th	Day	8% 9% 3 6% 6% 3 6% 6% 7% 8% 40%	1980
	21st to end	Day	9% 12% 5% 6% 7% 3 6% 6% 5% 7% 33%	2178
April	1st to 10th	Day	10% 9% 4 6% 6% 3 5% 6% 6% 7% 39%	2043
	11th to 20th	Day	7% 9% 4 6% 5% 3 5% 5% 5% 8% 44%	2307
	21st to end	Day	8% 7% 3 6% 5% 3 4 4 5% 9% 46%	2340
May	1st to 10th	Day	6% 7% 2 5% 5% 4 4 5% 6% 7% 49%	2340
	11th to 20th	Day	7% 5% 2 5% 5% 3 5% 6% 7% 9% 46%	2301
	21st to end	Day	10% 7% 2 6% 6% 4 5% 6% 6% 8% 40%	2644
June	1st to 10th	Day	6% 4 2 5% 5% 3 5% 5% 6% 8% 51%	2651
	11th to 20th	Day	6% 5% 2 4 4 2 4 5% 5% 8% 55%	2700
	21st to end	Day	3 1 1 2 3 2 3 2 4 7% 72%	2700
July	1st to 10th	Day	2 2 1 3 2 1 3 4 5% 8% 69%	2618
	11th to 20th	Day	2 2 1 2 2 2 3 4 4 6% 73%	2520
	21st to end	Day	3 3 1 4 4 2 4 4 5% 7% 65%	2548
August	1st to 10th	Day	4 3 1 4 4 3 4 4 4 6% 63%	2328
	11th to 20th	Day	3 2 1 2 2 2 3 3 4 6% 74%	2299
	21st to end	Day	3 2 1 3 3 2 3 4 4 7% 68%	2574
September	1st to 10th	Day	4 3 1 2 3 2 2 3 3 5% 73%	2075
	11th to 20th	Day	4 3 2 2 3 2 3 4 5% 6% 66%	1980
	21st to end	Day	6% 4 2 2 2 1 3 3 4 6% 65%	1980
October	1st to 10th	Day	10% 5% 3 4 4 2 4 4 5% 6% 53%	1900
	11th to 20th	Day	7% 5% 2 5% 4 3 4 4 4 8% 55%	1800
	21st to end	Day	7% 6% 2 5% 5% 3 4 6% 5% 8% 49%	1875
November	1st to 10th	Day	11% 9% 3 7% 5% 3 3 4 5% 7% 44%	1674
	11th to 20th	Day	10% 8% 3 5% 6% 3 4 5% 6% 8% 41%	1634
	21st to end	Day	8% 10% 4 8% 6% 4 5% 5% 4 6% 40%	1520
December	1st to 10th	Day	12% 13% 5% 9% 6% 4 5% 4 4 6% 31%	1520
	11th to 20th	Day	12% 10% 5% 11% 11% 4 6% 6% 6% 6% 23%	1822
	21st to end	Day	9% 13% 4 8% 6% 4 6% 6% 5% 8% 31%	2446
January	1st to 10th	Night	13% 15% 6% 10% 6% 3 4 4 5% 7% 27%	2656
	11th to 20th	Night	13% 12% 5% 8% 7% 3 5% 4 5% 7% 30%	2547
	21st to end	Night	13% 15% 6% 11% 7% 4 4 3 4 6% 29%	2574
February	1st to 10th	Night	10% 11% 5% 9% 7% 3 6% 6% 5% 8% 30%	2340
	11th to 20th	Night	11% 11% 4 6% 6% 4 5% 5% 5% 7% 36%	2232
	21st to end	Night	7% 13% 5% 9% 7% 5% 6% 5% 7% 7% 30%	1776
March	1st to 10th	Night	7% 12% 4 7% 6% 4 6% 6% 5% 7% 36%	2080
	11th to 20th	Night	5% 8% 2 6% 5% 3 5% 6% 7% 10% 42%	1980
	21st to end	Night	9% 9% 4 6% 7% 3 6% 6% 6% 8% 35%	2178
April	1st to 10th	Night	8% 9% 4 7% 6% 3 4 5% 5% 7% 42%	1914
	11th to 20th	Night	8% 9% 4 6% 5% 3 5% 4 5% 8% 42%	1601
	21st to end	Night	9% 7% 2 5% 5% 3 4 4 5% 6% 50%	1620
May	1st to 10th	Night	7% 7% 3 5% 4 3 5% 5% 7% 7% 49%	1620
	11th to 20th	Night	6% 6% 2 5% 6% 3 5% 6% 7% 9% 44%	1594
	21st to end	Night	10% 6% 2 5% 6% 3 5% 5% 7% 9% 43%	1631
June	1st to 10th	Night	6% 4 3 3 4 3 5% 6% 7% 9% 50%	1305
	11th to 20th	Night	6% 5% 2 4 4 3 4 4 6% 8% 55%	1260
	21st to end	Night	2 2 1 2 3 2 2 4 5% 7% 70%	1260
July	1st to 10th	Night	2 1 1 2 3 1 3 4 7% 9% 65%	1337
	11th to 20th	Night	1 1 1 2 2 2 3 4 5% 8% 72%	1440
	21st to end	Night	2 2 1 3 3 3 4 4 5% 8% 66%	1768
August	1st to 10th	Night	2 3 2 4 4 2 5% 5% 6% 8% 59%	1611
	11th to 20th	Night	2 2 1 3 3 2 3 4 5% 7% 67%	1602
	21st to end	Night	3 2 1 3 3 2 3 4 5% 7% 67%	1782
September	1st to 10th	Night	3 2 1 3 3 2 3 3 4 5% 71%	1882
	11th to 20th	Night	5% 4 1 3 3 2 4 3 5% 7% 62%	1980
	21st to end	Night	8% 4 1 3 3 2 3 4 3 6% 64%	1980
October	1st to 10th	Night	8% 5% 2 5% 3 2 4 4 5% 6% 56%	2060
	11th to 20th	Night	8% 5% 2 4 3 3 4 4 4 6% 57%	2160
	21st to end	Night	6% 5% 3 5% 5% 3 4 5% 6% 7% 52%	2479
November	1st to 10th	Night	10% 9% 3 6% 5% 3 4 4 5% 7% 46%	2405
	11th to 20th	Night	9% 9% 4 6% 6% 3 4 5% 6% 7% 41%	2526
	21st to end	Night	7% 10% 4 7% 6% 3 5% 6% 5% 6% 41%	2660
December	1st to 10th	Night	10% 14% 5% 8% 5% 3 4 5% 5% 7% 33%	2660
	11th to 20th	Night	12% 14% 5% 9% 7% 3 5% 5% 5% 7% 28%	3367
	21st to end	Night	11% 12% 5% 10% 8% 4 6% 5% 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	55% 10% 17% 13% 4 1	1519
	11th to 20th	Day	51% 10% 17% 16% 5% 1	1487
	21st to end	Day	59% 9% 14% 14% 4 1	1782
February	1st to 10th	Day	52% 11% 15% 17% 4 1	1620
	11th to 20th	Day	50% 9% 18% 18% 5% 1	1620
	21st to end	Day	47% 11% 16% 17% 8% 1	1480
March	1st to 10th	Day	44% 11% 16% 21% 8% 1	1880
	11th to 20th	Day	39% 10% 17% 23% 9% 2	1980
	21st to end	Day	49% 9% 17% 17% 7% 1	2178
April	1st to 10th	Day	43% 8% 16% 17% 13% 2	2043
	11th to 20th	Day	38% 7% 13% 26% 14% 2	2310
	21st to end	Day	36% 8% 12% 26% 17% 1	2340
May	1st to 10th	Day	30% 9% 13% 25% 20% 3	2340
	11th to 20th	Day	32% 8% 13% 28% 15% 4	2304
	21st to end	Day	38% 10% 14% 25% 11% 2	2644
June	1st to 10th	Day	30% 7% 14% 28% 19% 2	2651
	11th to 20th	Day	26% 6% 12% 22% 22% 12%	2700
	21st to end	Day	13% 3 7% 22% 36% 19%	2700
July	1st to 10th	Day	13% 4 7% 16% 34% 26%	2548
	11th to 20th	Day	13% 3 5% 14% 29% 36%	2445
	21st to end	Day	18% 5% 6% 14% 24% 33%	2406
August	1st to 10th	Day	21% 5% 8% 16% 26% 23%	2313
	11th to 20th	Day	13% 4 5% 17% 36% 25%	2299
	21st to end	Day	16% 4 7% 18% 33% 21%	2574
September	1st to 10th	Day	16% 3 7% 17% 31% 26%	2075
	11th to 20th	Day	19% 5% 9% 24% 28% 15%	1980
	21st to end	Day	21% 4 8% 27% 30% 9%	1980
October	1st to 10th	Day	32% 7% 12% 26% 17% 6%	1900
	11th to 20th	Day	30% 5% 16% 32% 14% 4	1800
	21st to end	Day	31% 9% 17% 25% 17% 1	1875
November	1st to 10th	Day	40% 7% 19% 22% 11% 1	1674
	11th to 20th	Day	39% 8% 21% 23% 7% 2	1634
	21st to end	Day	44% 8% 19% 20% 8% 1	1520
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	56% 10% 17% 13% 4 1	2656
	11th to 20th	Night	51% 10% 17% 17% 4 1	2547
	21st to end	Night	57% 8% 16% 13% 5% 1	2574
February	1st to 10th	Night	51% 11% 17% 16% 5% 1	2340
	11th to 20th	Night	45% 9% 19% 20% 7%	2233
	21st to end	Night	50% 10% 17% 15% 7% 2	1776
March	1st to 10th	Night	46% 9% 15% 22% 6% 1	2080
	11th to 20th	Night	35% 10% 15% 24% 13% 2	1980
	21st to end	Night	44% 10% 17% 20% 7% 1	2178
April	1st to 10th	Night	41% 8% 14% 19% 15% 3	1914
	11th to 20th	Night	39% 6% 14% 23% 15% 2	1601
	21st to end	Night	34% 6% 12% 25% 22%	1620
May	1st to 10th	Night	31% 7% 12% 27% 20% 3	1620
	11th to 20th	Night	32% 8% 13% 21% 22% 4	1595
	21st to end	Night	35% 9% 14% 27% 13% 2	1631
June	1st to 10th	Night	28% 9% 14% 22% 23% 4	1305
	11th to 20th	Night	25% 7% 12% 18% 28% 11%	1260
	21st to end	Night	13% 4 7% 17% 31% 28%	1260
July	1st to 10th	Night	15% 4 8% 15% 28% 30%	1298
	11th to 20th	Night	10% 3 6% 12% 26% 43%	1392
	21st to end	Night	16% 3 6% 13% 23% 38%	1670
August	1st to 10th	Night	20% 5% 9% 16% 21% 27%	1602
	11th to 20th	Night	15% 3 6% 14% 32% 30%	1602
	21st to end	Night	16% 4 8% 14% 28% 29%	1782
September	1st to 10th	Night	16% 4 7% 13% 29% 32%	1882
	11th to 20th	Night	21% 4 9% 21% 25% 18%	1980
	21st to end	Night	23% 4 7% 23% 31% 13%	1980
October	1st to 10th	Night	29% 5% 12% 25% 21% 8%	2060
	11th to 20th	Night	28% 5% 11% 32% 20% 4	2160
	21st to end	Night	29% 9% 16% 25% 20% 2	2479
November	1st to 10th	Night	38% 7% 14% 25% 14% 1	2405
	11th to 20th	Night	40% 9% 16% 24% 9% 2	2526
	21st to end	Night	41% 8% 18% 22% 10% 1	2660
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	20% 7% 16% 34% 18% 5%	177
	21st to end	Day	21% 9% 20% 30% 19% 1	264
February	1st to 10th	Day	15% 15% 31% 28% 11% 1	240
	11th to 20th	Day	18% 11% 32% 26% 11% 2	276
	21st to end	Day	14% 17% 30% 27% 10% 1	346
March	1st to 10th	Day	10% 16% 35% 27% 10% 1	420
	11th to 20th	Day	11% 13% 29% 31% 15% 1	420
	21st to end	Day	15% 17% 32% 27% 9%	462
April	1st to 10th	Day	18% 15% 29% 20% 15% 3	420
	11th to 20th	Day	12% 21% 33% 20% 10% 3	412
	21st to end	Day	11% 12% 27% 29% 15% 6%	420
May	1st to 10th	Day	9% 12% 28% 27% 21% 4	423
	11th to 20th	Day	9% 13% 26% 25% 18% 8%	448
	21st to end	Day	14% 8% 19% 26% 23% 12%	599
June	1st to 10th	Day	7% 7% 23% 28% 25% 11%	630
	11th to 20th	Day	11% 11% 25% 31% 18% 3	630
	21st to end	Day	4 3 24% 32% 27% 10%	630
July	1st to 10th	Day	3 3 19% 34% 33% 9%	543
	11th to 20th	Day	2 5% 22% 37% 27% 6%	444
	21st to end	Day	3 2 17% 32% 32% 13%	487
August	1st to 10th	Day	5% 5% 19% 32% 30% 9%	447
	11th to 20th	Day	3 3 18% 33% 27% 16%	437
	21st to end	Day	4 5% 20% 29% 29% 13%	495
September	1st to 10th	Day	5% 4 22% 27% 29% 13%	450
	11th to 20th	Day	6% 8% 21% 28% 25% 13%	450
	21st to end	Day	9% 7% 18% 26% 29% 11%	450
October	1st to 10th	Day	9% 8% 21% 24% 22% 16%	370
	11th to 20th	Day	6% 14% 19% 20% 24% 15%	270
	21st to end	Day	14% 12% 24% 25% 22% 3	297
November	1st to 10th	Day	17% 11% 25% 24% 16% 7%	270
	11th to 20th	Day	12% 10% 19% 38% 17% 5%	270
	21st to end	Day	13% 10% 21% 31% 21% 3	270
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% 35% 18% 3	736
	21st to end	Night	19% 4 20% 38% 16% 3	792
February	1st to 10th	Night	16% 7% 30% 33% 14% 1	720
	11th to 20th	Night	15% 8% 25% 37% 13% 2	704
	21st to end	Night	11% 12% 27% 36% 13% 2	592
March	1st to 10th	Night	12% 8% 24% 42% 13% 1	720
	11th to 20th	Night	9% 5% 28% 41% 16% 1	720
	21st to end	Night	13% 9% 24% 40% 13% 1	792
April	1st to 10th	Night	14% 7% 26% 37% 16% 1	698
	11th to 20th	Night	13% 9% 32% 35% 11% 1	533
	21st to end	Night	11% 6% 24% 39% 17% 2	540
May	1st to 10th	Night	9% 8% 24% 40% 18% 1	540
	11th to 20th	Night	10% 5% 22% 36% 25% 3	531
	21st to end	Night	11% 5% 20% 37% 24% 3	584
June	1st to 10th	Night	9% 5% 20% 36% 27% 3	405
	11th to 20th	Night	7% 6% 26% 43% 18% 1	360
	21st to end	Night	3 2 17% 46% 28% 5%	360
July	1st to 10th	Night	3 1 14% 43% 36% 3	350
	11th to 20th	Night	2 1 14% 56% 26% 1	348
	21st to end	Night	2 1 14% 47% 34% 3	586
August	1st to 10th	Night	4 2 13% 49% 30% 2	537
	11th to 20th	Night	2 2 11% 46% 36% 3	534
	21st to end	Night	4 2 15% 44% 32% 3	594
September	1st to 10th	Night	4 3 18% 40% 31% 5%	658
	11th to 20th	Night	6% 3 16% 39% 31% 6%	720
	21st to end	Night	10% 3 16% 37% 28% 7%	720
October	1st to 10th	Night	11% 3 18% 41% 25% 2	720
	11th to 20th	Night	10% 7% 20% 35% 25% 4	720
	21st to end	Night	10% 6% 21% 42% 18% 4	792
November	1st to 10th	Night	15% 5% 24% 36% 17% 2	740
	11th to 20th	Night	13% 7% 26% 37% 16% 2	816
	21st to end	Night	12% 7% 21% 39% 20% 2	950
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

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