Burk Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burk Astronomical Observatory clear sky chart from 2005-11-06 to 2024-04-25.

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	4 5% 2 5% 5% 3 5% 5% 6% 8% 51%	83395
	Night	4 5% 2 4 4 2 4 4 5% 8% 58%	85828
Transparency	Day	27% 9% 14% 23% 19% 7%	83100
	Night	23% 8% 15% 26% 21% 7%	85646
Seeing	Day	13% 25% 31% 20% 8% 2	14851
	Night	10% 30% 26% 23% 10% 1	25046

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	1 4 3 7% 5% 3 3 4 4 7% 60%	2538
	11th to 20th	Day	2 2 6% 6% 3 6% 6% 7% 10% 51%	2572
	21st to end	Day	1 4 2 4 4 3 4 4 5% 8% 61%	3146
February	1st to 10th	Day	1 6% 2 6% 5% 3 4 5% 6% 8% 55%	1710
	11th to 20th	Day	1 4 3 4 5% 3 5% 5% 5% 9% 57%	1780
	21st to end	Day	1 6% 3 6% 5% 2 3 2 5% 9% 57%	1570
March	1st to 10th	Day	2 9% 4 6% 4 2 4 4 5% 8% 52%	3130
	11th to 20th	Day	4 11% 5% 6% 5% 3 4 4 5% 6% 48%	3477
	21st to end	Day	3 8% 3 6% 5% 3 5% 5% 7% 10% 44%	4036
April	1st to 10th	Day	4 6% 3 4 4 3 5% 5% 6% 9% 51%	2280
	11th to 20th	Day	7% 9% 4 6% 5% 3 5% 5% 6% 8% 43%	2251
	21st to end	Day	8% 8% 2 5% 5% 3 6% 6% 7% 9% 41%	2209
May	1st to 10th	Day	12% 8% 3 5% 5% 3 6% 6% 6% 7% 38%	2348
	11th to 20th	Day	13% 10% 3 5% 5% 3 4 5% 7% 8% 36%	2478
	21st to end	Day	9% 6% 2 5% 6% 4 7% 7% 8% 9% 37%	2724
June	1st to 10th	Day	5% 4 2 4 4 4 6% 8% 8% 9% 46%	2520
	11th to 20th	Day	6% 4 2 4 4 3 5% 6% 7% 9% 50%	2520
	21st to end	Day	4 3 2 4 5% 3 6% 6% 8% 9% 52%	2520
July	1st to 10th	Day	7% 4 2 4 5% 3 6% 7% 8% 9% 45%	2520
	11th to 20th	Day	3 3 2 5% 5% 4 6% 6% 8% 9% 50%	2520
	21st to end	Day	6% 4 2 6% 6% 4 6% 7% 7% 10% 42%	2724
August	1st to 10th	Day	6% 4 2 5% 6% 5% 7% 8% 8% 9% 41%	2328
	11th to 20th	Day	5% 3 2 4 6% 4 5% 5% 6% 9% 51%	2170
	21st to end	Day	4 4 2 5% 5% 4 5% 5% 6% 9% 50%	2376
September	1st to 10th	Day	6% 5% 2 3 3 2 4 4 6% 7% 58%	2160
	11th to 20th	Day	6% 3 1 4 4 3 4 5% 6% 7% 56%	2156
	21st to end	Day	6% 5% 2 3 4 2 3 3 3 6% 63%	1964
October	1st to 10th	Day	7% 6% 2 4 4 2 3 4 4 6% 56%	1800
	11th to 20th	Day	3 4 2 4 4 2 3 4 5% 6% 65%	1800
	21st to end	Day	4 6% 2 3 4 1 4 4 5% 7% 60%	1906
November	1st to 10th	Day	2 3 1 2 3 2 3 4 6% 8% 65%	1673
	11th to 20th	Day	1 5% 2 2 3 2 3 4 5% 9% 64%	1710
	21st to end	Day	1 5% 2 4 4 2 4 4 6% 8% 59%	1539
December	1st to 10th	Day	1 4 2 4 3 3 4 5% 5% 9% 59%	1520
	11th to 20th	Day	3 5% 3 4 4 2 3 3 6% 9% 59%	1926
	21st to end	Day	1 6% 3 6% 5% 3 4 4 5% 6% 55%	2794
January	1st to 10th	Night	1 5% 3 6% 6% 3 4 4 5% 7% 56%	4417
	11th to 20th	Night	1 4 3 5% 4 2 3 4 5% 9% 60%	4426
	21st to end	Night	1 6% 3 5% 5% 2 3 3 5% 7% 60%	4521
February	1st to 10th	Night	1 5% 2 5% 4 2 4 5% 5% 8% 59%	2470
	11th to 20th	Night	1 5% 3 5% 5% 3 4 5% 5% 6% 59%	2286
	21st to end	Night	1 7% 3 4 5% 4 3 3 4 6% 60%	1884
March	1st to 10th	Night	1 8% 4 6% 4 3 3 4 4 7% 56%	3734
	11th to 20th	Night	5% 10% 3 5% 4 2 3 3 4 7% 55%	3500
	21st to end	Night	4 8% 3 5% 4 3 4 4 5% 8% 52%	3609
April	1st to 10th	Night	4 7% 2 4 4 2 3 4 6% 8% 55%	1900
	11th to 20th	Night	7% 8% 3 5% 4 2 3 4 4 7% 52%	1877
	21st to end	Night	10% 9% 3 4 4 2 3 4 5% 8% 49%	1850
May	1st to 10th	Night	11% 8% 2 4 4 2 4 5% 6% 7% 46%	1608
	11th to 20th	Night	15% 8% 2 5% 4 2 3 4 4 8% 45%	1417
	21st to end	Night	7% 6% 2 5% 4 3 4 5% 6% 7% 51%	1552
June	1st to 10th	Night	5% 3 2 3 4 2 4 5% 6% 11% 56%	1440
	11th to 20th	Night	6% 3 1 3 3 2 4 4 5% 7% 61%	1440
	21st to end	Night	5% 3 1 3 3 2 3 4 6% 9% 63%	1440
July	1st to 10th	Night	6% 3 2 4 3 2 5% 6% 6% 10% 52%	1440
	11th to 20th	Night	2 3 1 3 3 3 4 4 6% 10% 60%	1440
	21st to end	Night	4 3 1 4 4 3 5% 6% 7% 9% 54%	1591
August	1st to 10th	Night	4 4 2 4 4 4 5% 6% 7% 10% 51%	1611
	11th to 20th	Night	4 3 2 3 4 2 3 5% 5% 9% 59%	1731
	21st to end	Night	3 4 1 3 4 3 4 5% 7% 8% 58%	1980
September	1st to 10th	Night	7% 4 1 3 4 2 4 4 4 7% 59%	1800
	11th to 20th	Night	6% 3 1 3 3 2 3 3 4 7% 64%	1804
	21st to end	Night	6% 4 1 2 4 2 3 3 5% 6% 64%	1993
October	1st to 10th	Night	8% 7% 1 3 3 2 3 4 5% 6% 58%	2160
	11th to 20th	Night	4 4 2 3 3 2 2 3 4 6% 68%	2160
	21st to end	Night	4 8% 2 4 3 2 3 3 3 6% 60%	2430
November	1st to 10th	Night	2 4 1 3 3 2 3 4 4 8% 67%	2405
	11th to 20th	Night	2 4 2 3 3 2 3 3 5% 8% 65%	2470
	21st to end	Night	2 5% 3 4 3 2 3 4 6% 8% 61%	2638
December	1st to 10th	Night	1 4 2 4 4 2 3 4 5% 7% 63%	2660
	11th to 20th	Night	2 5% 2 4 4 2 3 4 6% 10% 58%	3271
	21st to end	Night	2 5% 3 5% 5% 3 4 4 5% 8% 56%	4873

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	22% 8% 17% 26% 20% 7%	2539
	11th to 20th	Day	22% 12% 22% 24% 16% 4	2572
	21st to end	Day	19% 9% 19% 29% 19% 5%	3146
February	1st to 10th	Day	26% 8% 19% 26% 17% 5%	1710
	11th to 20th	Day	23% 8% 15% 28% 21% 5%	1789
	21st to end	Day	25% 7% 14% 26% 22% 7%	1570
March	1st to 10th	Day	25% 9% 14% 24% 23% 5%	3130
	11th to 20th	Day	30% 13% 16% 27% 12% 3	3477
	21st to end	Day	28% 13% 16% 31% 11% 2	4036
April	1st to 10th	Day	27% 8% 15% 25% 17% 8%	2280
	11th to 20th	Day	36% 9% 14% 19% 16% 5%	2254
	21st to end	Day	35% 11% 14% 25% 14% 1	2209
May	1st to 10th	Day	41% 11% 12% 20% 13% 2	2348
	11th to 20th	Day	43% 10% 13% 22% 11% 1	2482
	21st to end	Day	37% 13% 15% 19% 13% 3	2724
June	1st to 10th	Day	27% 14% 17% 21% 15% 6%	2520
	11th to 20th	Day	27% 9% 13% 18% 21% 12%	2520
	21st to end	Day	23% 10% 13% 21% 21% 12%	2520
July	1st to 10th	Day	30% 11% 14% 16% 20% 9%	2451
	11th to 20th	Day	25% 9% 14% 19% 19% 14%	2445
	21st to end	Day	32% 11% 14% 21% 15% 7%	2573
August	1st to 10th	Day	33% 13% 14% 19% 14% 8%	2313
	11th to 20th	Day	28% 8% 13% 18% 21% 12%	2170
	21st to end	Day	28% 9% 12% 19% 24% 8%	2376
September	1st to 10th	Day	23% 7% 10% 18% 26% 15%	2160
	11th to 20th	Day	23% 8% 12% 20% 24% 12%	2156
	21st to end	Day	24% 6% 7% 20% 35% 8%	1964
October	1st to 10th	Day	29% 6% 11% 22% 24% 8%	1800
	11th to 20th	Day	20% 6% 11% 27% 28% 9%	1800
	21st to end	Day	22% 7% 13% 26% 24% 8%	1906
November	1st to 10th	Day	17% 7% 15% 27% 27% 8%	1673
	11th to 20th	Day	18% 6% 13% 32% 26% 6%	1710
	21st to end	Day	22% 7% 14% 27% 23% 8%	1539
December	1st to 10th	Day	21% 7% 19% 29% 17% 7%	1520
	11th to 20th	Day	22% 5% 15% 32% 24% 2	1924
	21st to end	Day	25% 9% 14% 24% 20% 8%	2794
January	1st to 10th	Night	23% 9% 14% 29% 19% 5%	4417
	11th to 20th	Night	17% 12% 19% 24% 20% 8%	4426
	21st to end	Night	22% 8% 19% 30% 17% 4	4521
February	1st to 10th	Night	23% 7% 19% 28% 18% 4	2470
	11th to 20th	Night	24% 8% 14% 30% 21% 4	2287
	21st to end	Night	25% 4 12% 25% 25% 8%	1884
March	1st to 10th	Night	23% 9% 11% 26% 25% 5%	3734
	11th to 20th	Night	26% 10% 15% 25% 21% 3	3500
	21st to end	Night	27% 10% 17% 32% 12% 2	3609
April	1st to 10th	Night	26% 8% 13% 26% 20% 7%	1900
	11th to 20th	Night	30% 7% 15% 26% 16% 5%	1877
	21st to end	Night	34% 7% 12% 27% 19% 1	1850
May	1st to 10th	Night	35% 9% 16% 24% 13% 2	1608
	11th to 20th	Night	37% 9% 16% 25% 13%	1418
	21st to end	Night	29% 10% 19% 24% 14% 4	1552
June	1st to 10th	Night	22% 9% 23% 26% 14% 6%	1440
	11th to 20th	Night	21% 8% 14% 21% 21% 15%	1440
	21st to end	Night	17% 8% 11% 28% 25% 12%	1440
July	1st to 10th	Night	24% 9% 15% 26% 19% 7%	1400
	11th to 20th	Night	18% 7% 16% 26% 19% 15%	1392
	21st to end	Night	23% 9% 17% 28% 15% 7%	1503
August	1st to 10th	Night	25% 11% 19% 22% 16% 7%	1602
	11th to 20th	Night	20% 7% 13% 26% 23% 12%	1731
	21st to end	Night	21% 7% 13% 24% 25% 9%	1980
September	1st to 10th	Night	24% 6% 12% 17% 24% 18%	1800
	11th to 20th	Night	20% 6% 11% 26% 24% 13%	1804
	21st to end	Night	21% 6% 8% 25% 31% 9%	1993
October	1st to 10th	Night	25% 8% 12% 22% 25% 8%	2160
	11th to 20th	Night	18% 5% 11% 27% 26% 12%	2160
	21st to end	Night	26% 5% 11% 25% 25% 8%	2430
November	1st to 10th	Night	17% 6% 16% 25% 27% 9%	2405
	11th to 20th	Night	17% 6% 14% 30% 25% 7%	2470
	21st to end	Night	21% 6% 12% 27% 26% 7%	2638
December	1st to 10th	Night	21% 7% 18% 27% 21% 7%	2660
	11th to 20th	Night	20% 6% 17% 32% 22% 3	3272
	21st to end	Night	22% 10% 15% 25% 20% 7%	4873

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	20% 35% 24% 15% 4 1	270
	11th to 20th	Day	19% 47% 18% 16%	270
	21st to end	Day	13% 49% 26% 8% 2	297
February	1st to 10th	Day	16% 56% 20% 6% 1 1	270
	11th to 20th	Day	15% 51% 26% 5% 3	270
	21st to end	Day	25% 42% 26% 7%	225
March	1st to 10th	Day	18% 38% 29% 13% 2	270
	11th to 20th	Day	17% 36% 31% 13% 4	447
	21st to end	Day	16% 40% 32% 9% 2	506
April	1st to 10th	Day	21% 37% 29% 11% 2	460
	11th to 20th	Day	24% 36% 28% 9% 2 1	452
	21st to end	Day	21% 30% 29% 15% 3 1	437
May	1st to 10th	Day	21% 26% 29% 16% 7% 1	549
	11th to 20th	Day	22% 17% 31% 18% 10% 2	625
	21st to end	Day	13% 20% 28% 24% 12% 2	679
June	1st to 10th	Day	9% 13% 32% 26% 17% 4	630
	11th to 20th	Day	10% 17% 40% 21% 10% 2	630
	21st to end	Day	8% 11% 37% 27% 14% 3	630
July	1st to 10th	Day	8% 4 28% 35% 20% 5%	621
	11th to 20th	Day	4 7% 35% 33% 17% 4	618
	21st to end	Day	6% 6% 28% 35% 19% 6%	666
August	1st to 10th	Day	9% 9% 37% 34% 9% 2	447
	11th to 20th	Day	6% 8% 38% 32% 14% 3	437
	21st to end	Day	6% 13% 35% 34% 10% 3	495
September	1st to 10th	Day	7% 14% 36% 31% 10% 2	450
	11th to 20th	Day	8% 17% 36% 27% 10% 2	446
	21st to end	Day	10% 20% 32% 22% 11% 4	270
October	1st to 10th	Day	12% 20% 30% 23% 13% 3	270
	11th to 20th	Day	13% 36% 31% 12% 6% 2	270
	21st to end	Day	11% 42% 30% 12% 4 1	297
November	1st to 10th	Day	14% 36% 30% 11% 7% 2	270
	11th to 20th	Day	14% 46% 26% 11% 2	270
	21st to end	Day	17% 43% 29% 10% 1 1	270
December	1st to 10th	Day	21% 42% 28% 6% 3	270
	11th to 20th	Day	20% 51% 23% 5% 1	270
	21st to end	Day	22% 47% 18% 11% 1 1	297
January	1st to 10th	Night	12% 46% 23% 14% 4 1	950
	11th to 20th	Night	15% 52% 19% 10% 3 1	946
	21st to end	Night	8% 52% 24% 12% 3 1	836
February	1st to 10th	Night	10% 52% 24% 10% 4	760
	11th to 20th	Night	11% 43% 31% 13% 1	744
	21st to end	Night	14% 46% 29% 9% 1	628
March	1st to 10th	Night	9% 40% 33% 14% 4	760
	11th to 20th	Night	10% 33% 27% 24% 5% 1	760
	21st to end	Night	12% 33% 31% 20% 4 1	707
April	1st to 10th	Night	15% 28% 34% 20% 3	570
	11th to 20th	Night	17% 26% 33% 19% 5% 1	563
	21st to end	Night	16% 23% 28% 25% 7% 1	555
May	1st to 10th	Night	16% 17% 33% 23% 9% 1	540
	11th to 20th	Night	18% 10% 27% 28% 15% 1	531
	21st to end	Night	10% 13% 26% 30% 18% 2	584
June	1st to 10th	Night	6% 8% 27% 39% 19% 2	540
	11th to 20th	Night	8% 11% 33% 38% 10%	540
	21st to end	Night	6% 7% 27% 37% 21% 2	540
July	1st to 10th	Night	8% 3 15% 41% 31% 3	525
	11th to 20th	Night	3 3 20% 43% 28% 3	522
	21st to end	Night	5% 3 13% 45% 31% 3	591
August	1st to 10th	Night	6% 4 17% 47% 25% 2	537
	11th to 20th	Night	5% 3 20% 47% 22% 3	534
	21st to end	Night	4 4 19% 41% 28% 4	594
September	1st to 10th	Night	9% 6% 21% 40% 21% 4	540
	11th to 20th	Night	9% 6% 24% 39% 18% 3	540
	21st to end	Night	8% 14% 26% 34% 16% 2	553
October	1st to 10th	Night	12% 20% 26% 27% 14% 2	720
	11th to 20th	Night	8% 35% 26% 21% 9% 1	720
	21st to end	Night	11% 32% 33% 17% 6% 2	846
November	1st to 10th	Night	8% 34% 33% 18% 6% 1	925
	11th to 20th	Night	11% 46% 27% 14% 2 1	950
	21st to end	Night	10% 41% 32% 15% 3	950
December	1st to 10th	Night	12% 49% 24% 13% 2	950
	11th to 20th	Night	11% 50% 23% 13% 3 1	950
	21st to end	Night	13% 50% 22% 10% 4	1045

Page generated at 2024-04-22 07:25:40. Version ac07

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