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 2024-11-05.

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% 4 4 5% 4 6% 8% 52%	105232
	Night	4 6% 2 5% 3 3 3 3 5% 8% 58%	102518
Transparency	Day	26% 9% 13% 23% 20% 9%	104975
	Night	23% 8% 14% 26% 21% 8%	102366
Seeing	Day	13% 25% 31% 20% 8% 2	15667
	Night	10% 29% 26% 23% 10% 1	25674

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 8% 5% 4 3 3 4 7% 60%	2538
	11th to 20th	Day	3 1 7% 5% 5% 6% 5% 8% 10% 51%	2572
	21st to end	Day	1 4 2 5% 4 4 3 3 6% 8% 60%	3146
February	1st to 10th	Day	1 6% 2 7% 4 4 4 4 6% 8% 55%	1710
	11th to 20th	Day	1 4 2 5% 4 4 4 4 6% 9% 57%	1780
	21st to end	Day	1 7% 2 7% 4 3 3 2 6% 8% 57%	1570
March	1st to 10th	Day	1 10% 4 7% 3 3 4 3 5% 8% 52%	3130
	11th to 20th	Day	4 11% 5% 7% 4 4 4 2 5% 6% 48%	3477
	21st to end	Day	3 8% 3 6% 4 5% 5% 4 7% 10% 44%	4036
April	1st to 10th	Day	4 7% 2 4 4 4 4 4 6% 8% 51%	2280
	11th to 20th	Day	7% 10% 4 7% 4 4 4 4 6% 7% 43%	2251
	21st to end	Day	8% 8% 2 6% 5% 5% 5% 5% 8% 9% 40%	2280
May	1st to 10th	Day	10% 9% 3 7% 4 5% 5% 5% 6% 7% 37%	4138
	11th to 20th	Day	8% 8% 2 6% 5% 5% 6% 5% 8% 8% 39%	4388
	21st to end	Day	6% 5% 2 5% 5% 5% 6% 5% 8% 9% 44%	4825
June	1st to 10th	Day	5% 4 2 5% 4 5% 7% 6% 8% 10% 46%	2660
	11th to 20th	Day	6% 4 2 5% 4 4 5% 5% 7% 9% 49%	2660
	21st to end	Day	3 4 1 4 4 4 6% 5% 8% 9% 51%	2660
July	1st to 10th	Day	6% 4 1 4 4 3 4 5% 7% 8% 53%	4430
	11th to 20th	Day	2 3 1 5% 5% 6% 7% 5% 9% 9% 48%	4430
	21st to end	Day	4 4 2 6% 5% 5% 5% 5% 7% 8% 51%	4758
August	1st to 10th	Day	10% 4 1 5% 4 6% 6% 6% 8% 9% 41%	4092
	11th to 20th	Day	3 3 2 6% 5% 6% 6% 5% 7% 8% 50%	3797
	21st to end	Day	4 4 2 5% 4 4 5% 4 7% 9% 52%	4180
September	1st to 10th	Day	5% 5% 2 4 3 3 4 4 6% 7% 57%	2280
	11th to 20th	Day	6% 3 1 4 4 4 4 4 5% 7% 57%	2275
	21st to end	Day	6% 5% 1 4 3 3 3 3 3 5% 64%	2073
October	1st to 10th	Day	4 4 1 3 2 2 2 2 3 4 72%	3170
	11th to 20th	Day	5% 4 2 5% 3 4 3 3 5% 7% 59%	3150
	21st to end	Day	4 6% 2 4 3 2 3 3 5% 7% 63%	3298
November	1st to 10th	Day	2 3 1 3 3 2 3 3 6% 8% 64%	1709
	11th to 20th	Day	1 5% 1 2 3 3 3 3 5% 9% 64%	1710
	21st to end	Day	1 5% 2 5% 4 4 4 3 6% 7% 59%	1539
December	1st to 10th	Day	1 5% 2 5% 3 3 5% 4 6% 9% 58%	1520
	11th to 20th	Day	3 5% 2 4 4 3 3 3 6% 9% 59%	1926
	21st to end	Day	1 6% 3 7% 5% 4 5% 3 6% 6% 55%	2794
January	1st to 10th	Night	1 5% 3 7% 5% 4 4 3 5% 7% 56%	4417
	11th to 20th	Night	1 5% 3 5% 3 3 3 3 6% 8% 60%	4426
	21st to end	Night	1 6% 2 6% 4 3 3 3 5% 7% 60%	4521
February	1st to 10th	Night	1 5% 2 6% 3 4 4 4 5% 8% 58%	2470
	11th to 20th	Night	1 6% 3 5% 5% 4 3 4 5% 6% 58%	2286
	21st to end	Night	1 8% 3 5% 4 4 3 3 4 6% 60%	1884
March	1st to 10th	Night	1 8% 4 6% 3 3 3 3 5% 7% 56%	3734
	11th to 20th	Night	5% 11% 3 5% 3 2 3 3 4 7% 55%	3500
	21st to end	Night	3 8% 3 6% 4 4 4 3 5% 8% 52%	3609
April	1st to 10th	Night	3 8% 2 4 3 3 3 4 6% 8% 55%	1900
	11th to 20th	Night	7% 9% 3 5% 3 3 3 4 4 7% 52%	1877
	21st to end	Night	10% 10% 2 5% 3 3 2 3 5% 7% 48%	1900
May	1st to 10th	Night	9% 8% 2 5% 4 4 5% 4 6% 6% 47%	2814
	11th to 20th	Night	10% 6% 2 5% 3 3 4 5% 5% 9% 47%	2517
	21st to end	Night	7% 5% 2 5% 3 4 4 4 5% 6% 55%	2762
June	1st to 10th	Night	5% 4 1 4 3 2 4 4 6% 11% 56%	1520
	11th to 20th	Night	5% 3 1 4 3 3 4 4 6% 7% 61%	1520
	21st to end	Night	5% 3 1 3 2 2 3 3 6% 8% 63%	1520
July	1st to 10th	Night	4 3 1 4 3 3 4 4 5% 8% 59%	2540
	11th to 20th	Night	2 2 1 4 3 4 5% 4 8% 10% 56%	2540
	21st to end	Night	3 2 1 4 3 4 5% 4 7% 8% 60%	2789
August	1st to 10th	Night	11% 5% 1 3 3 4 4 5% 7% 10% 48%	2847
	11th to 20th	Night	3 4 2 5% 4 4 5% 5% 7% 9% 51%	3042
	21st to end	Night	2 3 1 3 3 4 4 3 7% 10% 60%	3487
September	1st to 10th	Night	7% 4 1 4 3 3 4 2 4 7% 60%	1900
	11th to 20th	Night	6% 3 1 3 3 2 3 3 4 7% 65%	1905
	21st to end	Night	6% 4 1 3 3 3 3 2 5% 6% 64%	2104
October	1st to 10th	Night	5% 4 1 2 2 2 2 2 3 5% 73%	3800
	11th to 20th	Night	6% 6% 2 4 3 3 3 3 4 6% 59%	3778
	21st to end	Night	4 6% 2 4 2 2 3 3 4 7% 64%	4227
November	1st to 10th	Night	2 4 1 4 2 3 3 3 5% 7% 66%	2470
	11th to 20th	Night	2 4 1 3 3 3 3 3 5% 8% 64%	2470
	21st to end	Night	2 5% 3 5% 2 3 3 4 6% 7% 61%	2638
December	1st to 10th	Night	1 4 2 5% 3 3 3 3 5% 7% 63%	2660
	11th to 20th	Night	2 6% 2 4 4 3 3 3 6% 10% 58%	3271
	21st to end	Night	2 6% 3 6% 4 4 4 3 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	2280
May	1st to 10th	Day	36% 14% 12% 19% 13% 6%	4138
	11th to 20th	Day	30% 16% 15% 22% 13% 3	4392
	21st to end	Day	24% 15% 16% 21% 19% 4	4825
June	1st to 10th	Day	27% 14% 17% 21% 16% 5%	2660
	11th to 20th	Day	27% 9% 13% 19% 21% 12%	2660
	21st to end	Day	24% 10% 12% 21% 20% 13%	2660
July	1st to 10th	Day	25% 8% 9% 14% 25% 19%	4361
	11th to 20th	Day	26% 8% 11% 19% 19% 18%	4355
	21st to end	Day	27% 8% 10% 17% 21% 18%	4608
August	1st to 10th	Day	34% 10% 14% 19% 15% 8%	4078
	11th to 20th	Day	29% 8% 12% 16% 19% 16%	3834
	21st to end	Day	26% 7% 12% 18% 25% 12%	4179
September	1st to 10th	Day	23% 7% 10% 18% 27% 15%	2280
	11th to 20th	Day	23% 7% 12% 20% 26% 12%	2275
	21st to end	Day	23% 6% 7% 19% 35% 10%	2073
October	1st to 10th	Day	17% 4 6% 16% 35% 22%	3170
	11th to 20th	Day	25% 5% 9% 31% 23% 7%	3150
	21st to end	Day	21% 5% 8% 33% 27% 6%	3298
November	1st to 10th	Day	17% 6% 15% 27% 27% 7%	1709
	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	35% 7% 12% 27% 18% 1	1900
May	1st to 10th	Night	29% 13% 14% 24% 14% 7%	2814
	11th to 20th	Night	27% 14% 18% 26% 12% 3	2518
	21st to end	Night	23% 11% 18% 25% 19% 4	2762
June	1st to 10th	Night	21% 10% 22% 26% 14% 6%	1520
	11th to 20th	Night	20% 8% 14% 22% 21% 15%	1520
	21st to end	Night	17% 8% 11% 27% 25% 12%	1520
July	1st to 10th	Night	21% 7% 10% 23% 25% 14%	2500
	11th to 20th	Night	20% 6% 15% 26% 20% 13%	2492
	21st to end	Night	20% 6% 13% 27% 18% 15%	2702
August	1st to 10th	Night	30% 7% 18% 21% 19% 5%	2838
	11th to 20th	Night	27% 8% 16% 21% 17% 12%	3071
	21st to end	Night	19% 6% 15% 24% 26% 10%	3487
September	1st to 10th	Night	23% 6% 11% 18% 25% 17%	1900
	11th to 20th	Night	20% 5% 10% 26% 25% 14%	1905
	21st to end	Night	21% 6% 8% 24% 31% 10%	2104
October	1st to 10th	Night	16% 4 7% 20% 31% 21%	3800
	11th to 20th	Night	27% 4 9% 29% 24% 7%	3778
	21st to end	Night	22% 4 8% 29% 29% 8%	4227
November	1st to 10th	Night	17% 6% 16% 26% 27% 9%	2470
	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% 30% 15% 3 1	460
May	1st to 10th	Day	23% 27% 28% 15% 6% 1	596
	11th to 20th	Day	21% 16% 33% 19% 9% 2	675
	21st to end	Day	13% 22% 28% 23% 12% 2	734
June	1st to 10th	Day	9% 14% 32% 26% 16% 4	680
	11th to 20th	Day	10% 17% 41% 21% 9% 2	680
	21st to end	Day	8% 13% 37% 26% 13% 3	680
July	1st to 10th	Day	9% 5% 28% 34% 20% 4	671
	11th to 20th	Day	3 7% 34% 35% 17% 4	668
	21st to end	Day	6% 7% 28% 36% 18% 6%	719
August	1st to 10th	Day	9% 9% 37% 34% 8% 3	487
	11th to 20th	Day	6% 8% 37% 32% 14% 2	477
	21st to end	Day	5% 13% 37% 33% 10% 2	539
September	1st to 10th	Day	7% 13% 37% 30% 11% 3	490
	11th to 20th	Day	9% 18% 35% 26% 11% 2	485
	21st to end	Day	10% 21% 32% 22% 11% 4	300
October	1st to 10th	Day	11% 20% 31% 23% 13% 3	300
	11th to 20th	Day	12% 34% 32% 13% 7% 3	300
	21st to end	Day	12% 40% 30% 13% 4 1	330
November	1st to 10th	Day	14% 35% 32% 11% 6% 2	282
	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	17% 24% 27% 25% 7% 1	570
May	1st to 10th	Night	17% 17% 34% 22% 9% 1	570
	11th to 20th	Night	17% 11% 28% 29% 15% 1	561
	21st to end	Night	11% 13% 27% 30% 18% 1	617
June	1st to 10th	Night	6% 9% 27% 39% 18% 2	570
	11th to 20th	Night	7% 11% 35% 37% 10%	570
	21st to end	Night	6% 7% 28% 36% 20% 2	570
July	1st to 10th	Night	7% 4 16% 41% 29% 3	555
	11th to 20th	Night	3 3 21% 44% 27% 3	552
	21st to end	Night	5% 3 14% 46% 30% 3	624
August	1st to 10th	Night	6% 3 17% 48% 24% 2	567
	11th to 20th	Night	5% 3 21% 46% 22% 3	564
	21st to end	Night	4 4 21% 41% 27% 3	627
September	1st to 10th	Night	9% 5% 20% 41% 20% 4	570
	11th to 20th	Night	9% 7% 26% 39% 17% 3	570
	21st to end	Night	8% 14% 27% 34% 15% 2	584
October	1st to 10th	Night	11% 19% 28% 27% 13% 1	760
	11th to 20th	Night	8% 33% 26% 23% 9% 1	760
	21st to end	Night	11% 31% 34% 17% 5% 2	894
November	1st to 10th	Night	8% 34% 34% 18% 5% 1	950
	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 2024-11-03 00:11:08. Version ac07

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