Burkes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burkes Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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	18% 8% 3 7% 4 4 4 4 5% 7% 35%	130584
	Night	18% 9% 3 7% 4 4 4 4 5% 7% 35%	131568
Transparency	Day	47% 6% 12% 21% 13% 2	134091
	Night	47% 5% 12% 21% 13% 2	136149
Seeing	Day	24% 16% 31% 20% 7% 2	17342
	Night	23% 12% 32% 26% 7%	25942

By Month

Percentage Cloud Cover NE (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% 10% 3 8% 6% 5% 4 4 5% 5% 35%	4661
	11th to 20th	Day	15% 11% 4 8% 5% 3 3 3 4 6% 37%	4650
	21st to end	Day	10% 8% 3 7% 5% 4 5% 4 5% 5% 44%	5124
February	1st to 10th	Day	16% 10% 2 7% 5% 4 5% 4 6% 5% 35%	1868
	11th to 20th	Day	12% 10% 4 10% 5% 6% 4 4 5% 6% 35%	1989
	21st to end	Day	13% 12% 3 8% 4 4 6% 5% 5% 5% 35%	1730
March	1st to 10th	Day	24% 12% 3 8% 5% 4 4 3 4 4 29%	4576
	11th to 20th	Day	20% 11% 3 7% 5% 4 4 3 4 5% 33%	5059
	21st to end	Day	27% 9% 3 7% 4 3 3 3 6% 6% 30%	5633
April	1st to 10th	Day	22% 12% 3 7% 5% 4 3 2 5% 5% 32%	2520
	11th to 20th	Day	20% 9% 2 6% 5% 4 3 3 5% 7% 37%	2596
	21st to end	Day	23% 9% 3 6% 4 3 4 3 4 6% 35%	2600
May	1st to 10th	Day	30% 9% 3 8% 4 4 4 4 5% 6% 24%	5886
	11th to 20th	Day	22% 8% 3 8% 5% 5% 5% 4 5% 6% 30%	5942
	21st to end	Day	19% 7% 2 7% 5% 5% 5% 4 6% 7% 32%	7013
June	1st to 10th	Day	24% 8% 2 7% 4 4 4 3 6% 8% 30%	3000
	11th to 20th	Day	18% 7% 2 6% 4 4 5% 5% 6% 8% 36%	3000
	21st to end	Day	24% 7% 3 6% 5% 4 5% 4 6% 7% 30%	3000
July	1st to 10th	Day	15% 7% 2 7% 6% 6% 6% 5% 7% 10% 30%	6389
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 4 6% 9% 36%	6360
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 8% 41%	6926
August	1st to 10th	Day	16% 6% 2 8% 5% 5% 5% 4 6% 9% 34%	4242
	11th to 20th	Day	16% 8% 3 7% 5% 4 5% 4 5% 8% 34%	4175
	21st to end	Day	12% 6% 2 6% 3 4 4 5% 6% 9% 43%	4586
September	1st to 10th	Day	11% 4 3 7% 5% 4 4 3 5% 7% 47%	2330
	11th to 20th	Day	12% 6% 2 5% 3 4 4 3 5% 6% 51%	2200
	21st to end	Day	16% 6% 2 5% 4 4 4 3 6% 7% 43%	2200
October	1st to 10th	Day	18% 6% 2 6% 4 4 4 3 5% 6% 40%	2171
	11th to 20th	Day	19% 7% 2 6% 4 4 4 3 5% 7% 39%	1942
	21st to end	Day	23% 9% 3 7% 4 4 4 3 4 5% 34%	1980
November	1st to 10th	Day	17% 6% 2 6% 4 4 5% 5% 5% 6% 39%	1851
	11th to 20th	Day	19% 7% 2 5% 3 4 4 4 5% 6% 40%	1890
	21st to end	Day	21% 8% 2 6% 4 4 3 3 3 6% 39%	1697
December	1st to 10th	Day	18% 9% 3 6% 3 4 5% 4 6% 7% 36%	2394
	11th to 20th	Day	19% 8% 2 5% 3 3 3 3 5% 6% 42%	2688
	21st to end	Day	22% 12% 3 6% 4 3 4 3 5% 5% 34%	3716
January	1st to 10th	Night	12% 11% 3 9% 5% 5% 4 3 5% 6% 34%	8234
	11th to 20th	Night	15% 13% 5% 10% 5% 5% 6% 5% 5% 6% 26%	8235
	21st to end	Night	10% 10% 3 8% 5% 5% 5% 4 6% 7% 38%	9057
February	1st to 10th	Night	14% 10% 3 9% 6% 5% 5% 4 6% 7% 32%	2751
	11th to 20th	Night	13% 10% 4 8% 5% 4 4 3 5% 6% 37%	2515
	21st to end	Night	15% 12% 3 7% 5% 5% 4 3 4 5% 38%	2076
March	1st to 10th	Night	26% 11% 4 7% 4 5% 4 3 4 5% 28%	5484
	11th to 20th	Night	18% 11% 3 7% 4 4 5% 4 5% 7% 31%	5119
	21st to end	Night	25% 10% 2 7% 4 5% 4 3 6% 6% 28%	5524
April	1st to 10th	Night	23% 12% 3 5% 4 3 3 4 4 5% 34%	2100
	11th to 20th	Night	21% 7% 3 7% 5% 5% 4 3 6% 7% 34%	1885
	21st to end	Night	25% 10% 2 6% 3 4 3 3 4 6% 33%	1800
May	1st to 10th	Night	28% 10% 3 7% 4 4 3 4 5% 7% 25%	4054
	11th to 20th	Night	22% 7% 3 8% 5% 4 5% 4 6% 8% 28%	3994
	21st to end	Night	17% 7% 3 8% 5% 4 4 4 5% 8% 35%	3848
June	1st to 10th	Night	20% 10% 2 8% 5% 4 4 4 5% 7% 31%	1400
	11th to 20th	Night	16% 7% 3 6% 5% 4 5% 3 6% 8% 38%	1400
	21st to end	Night	22% 9% 2 6% 4 5% 4 4 6% 8% 30%	1400
July	1st to 10th	Night	13% 6% 3 7% 5% 5% 6% 5% 7% 9% 35%	3554
	11th to 20th	Night	17% 8% 2 7% 5% 4 4 4 6% 8% 35%	3600
	21st to end	Night	10% 4 2 5% 4 4 4 5% 7% 10% 45%	3926
August	1st to 10th	Night	19% 7% 3 7% 6% 5% 5% 4 6% 7% 31%	2874
	11th to 20th	Night	15% 9% 2 7% 5% 5% 6% 4 6% 7% 33%	2872
	21st to end	Night	12% 6% 2 7% 4 3 4 3 6% 7% 45%	3307
September	1st to 10th	Night	14% 4 2 4 3 3 4 4 5% 7% 50%	2070
	11th to 20th	Night	15% 5% 2 5% 2 3 4 3 3 6% 53%	2200
	21st to end	Night	17% 6% 2 5% 4 3 4 3 4 6% 45%	2200
October	1st to 10th	Night	18% 7% 2 6% 4 4 5% 3 4 6% 41%	2228
	11th to 20th	Night	18% 5% 2 6% 4 4 5% 4 5% 7% 40%	2455
	21st to end	Night	24% 10% 2 5% 4 4 4 3 5% 6% 34%	2860
November	1st to 10th	Night	18% 7% 2 6% 4 3 4 3 5% 6% 41%	2667
	11th to 20th	Night	18% 6% 2 6% 4 5% 4 3 5% 8% 39%	2730
	21st to end	Night	17% 8% 3 6% 5% 4 4 3 6% 7% 37%	2919
December	1st to 10th	Night	17% 10% 3 7% 4 4 5% 4 6% 6% 34%	5010
	11th to 20th	Night	23% 8% 2 5% 3 4 3 3 4 5% 38%	5741
	21st to end	Night	22% 11% 3 6% 3 3 4 3 4 5% 36%	7479

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	50% 3 12% 22% 12% 1	4662
	11th to 20th	Day	48% 5% 10% 25% 11% 2	4680
	21st to end	Day	42% 4 11% 21% 19% 5%	5124
February	1st to 10th	Day	48% 5% 11% 20% 14% 2	1868
	11th to 20th	Day	49% 5% 11% 19% 13% 3	1998
	21st to end	Day	48% 6% 11% 19% 12% 5%	1730
March	1st to 10th	Day	60% 4 7% 9% 14% 6%	4579
	11th to 20th	Day	52% 6% 13% 18% 10% 2	5059
	21st to end	Day	54% 4 6% 17% 16% 3	5633
April	1st to 10th	Day	54% 4 9% 16% 13% 4	2520
	11th to 20th	Day	46% 5% 10% 22% 15% 2	2596
	21st to end	Day	51% 4 9% 19% 13% 4	2600
May	1st to 10th	Day	60% 7% 11% 14% 7% 1	5897
	11th to 20th	Day	53% 7% 13% 17% 7% 3	5946
	21st to end	Day	47% 7% 13% 18% 12% 2	7013
June	1st to 10th	Day	51% 6% 12% 20% 10% 1	3000
	11th to 20th	Day	45% 7% 12% 20% 15% 2	3000
	21st to end	Day	52% 6% 13% 17% 10% 2	3000
July	1st to 10th	Day	47% 7% 15% 22% 9%	6319
	11th to 20th	Day	42% 7% 15% 22% 13% 1	6285
	21st to end	Day	40% 6% 13% 27% 14% 1	6728
August	1st to 10th	Day	47% 6% 14% 26% 7%	4228
	11th to 20th	Day	46% 7% 16% 22% 8%	4214
	21st to end	Day	35% 6% 14% 26% 17% 1	4586
September	1st to 10th	Day	35% 6% 14% 27% 17% 1	2330
	11th to 20th	Day	33% 5% 10% 28% 21% 2	2200
	21st to end	Day	38% 6% 11% 28% 16% 1	2200
October	1st to 10th	Day	52% 5% 9% 21% 12% 1	3535
	11th to 20th	Day	38% 4 12% 29% 17% 1	3145
	21st to end	Day	38% 4 15% 22% 19% 1	3180
November	1st to 10th	Day	44% 6% 14% 21% 14% 2	1851
	11th to 20th	Day	43% 6% 11% 20% 17% 3	1890
	21st to end	Day	47% 4 15% 23% 10% 1	1697
December	1st to 10th	Day	46% 5% 17% 19% 13% 1	2394
	11th to 20th	Day	42% 4 13% 18% 17% 6%	2688
	21st to end	Day	52% 5% 9% 19% 13% 3	3716
January	1st to 10th	Night	49% 5% 11% 21% 12% 1	8234
	11th to 20th	Night	56% 6% 11% 15% 10% 2	8280
	21st to end	Night	45% 4 9% 21% 17% 4	9057
February	1st to 10th	Night	50% 5% 11% 20% 12% 2	2751
	11th to 20th	Night	47% 4 10% 20% 15% 2	2517
	21st to end	Night	48% 4 9% 20% 14% 4	2076
March	1st to 10th	Night	59% 3 7% 12% 13% 6%	5494
	11th to 20th	Night	49% 7% 18% 17% 8% 1	5120
	21st to end	Night	54% 4 7% 17% 16% 2	5524
April	1st to 10th	Night	53% 4 8% 16% 16% 3	2100
	11th to 20th	Night	48% 6% 9% 20% 15% 1	1885
	21st to end	Night	52% 5% 11% 16% 14% 3	1800
May	1st to 10th	Night	57% 6% 15% 14% 7% 1	4060
	11th to 20th	Night	52% 7% 13% 19% 8% 1	3995
	21st to end	Night	46% 7% 16% 21% 10% 1	3849
June	1st to 10th	Night	51% 6% 14% 19% 9% 1	1400
	11th to 20th	Night	43% 6% 15% 21% 13% 2	1400
	21st to end	Night	51% 6% 13% 18% 9% 2	1400
July	1st to 10th	Night	44% 7% 16% 24% 9%	3514
	11th to 20th	Night	46% 7% 12% 25% 9%	3552
	21st to end	Night	33% 7% 17% 31% 11% 1	3809
August	1st to 10th	Night	51% 8% 13% 22% 6%	2864
	11th to 20th	Night	47% 8% 16% 19% 9%	2899
	21st to end	Night	37% 6% 14% 24% 16% 2	3307
September	1st to 10th	Night	33% 7% 14% 30% 15% 1	2070
	11th to 20th	Night	34% 4 11% 30% 19% 1	2200
	21st to end	Night	40% 5% 11% 28% 15% 1	2200
October	1st to 10th	Night	43% 6% 13% 23% 14% 1	3644
	11th to 20th	Night	36% 5% 11% 29% 18% 1	3991
	21st to end	Night	40% 4 12% 27% 14% 2	4610
November	1st to 10th	Night	43% 6% 12% 24% 14% 1	2667
	11th to 20th	Night	43% 5% 11% 23% 16% 2	2730
	21st to end	Night	46% 5% 16% 18% 13% 2	2919
December	1st to 10th	Night	49% 5% 11% 24% 10%	5010
	11th to 20th	Night	48% 4 10% 19% 18% 2	5742
	21st to end	Night	51% 4 11% 17% 16% 1	7479

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	30% 18% 32% 15% 5%	220
	11th to 20th	Day	28% 23% 32% 12% 4 1	220
	21st to end	Day	20% 26% 33% 18% 3	242
February	1st to 10th	Day	27% 15% 32% 22% 4	408
	11th to 20th	Day	25% 25% 35% 13% 3	506
	21st to end	Day	24% 22% 33% 17% 4	446
March	1st to 10th	Day	31% 21% 31% 14% 3	540
	11th to 20th	Day	28% 22% 33% 14% 3 1	540
	21st to end	Day	31% 23% 26% 13% 5% 2	594
April	1st to 10th	Day	35% 22% 26% 12% 4 1	540
	11th to 20th	Day	33% 23% 27% 11% 5% 1	516
	21st to end	Day	32% 20% 29% 14% 4 1	500
May	1st to 10th	Day	34% 16% 31% 16% 3 1	503
	11th to 20th	Day	25% 18% 32% 17% 6% 2	527
	21st to end	Day	24% 17% 35% 18% 7%	598
June	1st to 10th	Day	26% 14% 33% 19% 8% 1	730
	11th to 20th	Day	22% 15% 27% 22% 12% 1	730
	21st to end	Day	26% 11% 28% 25% 8% 1	730
July	1st to 10th	Day	18% 11% 36% 26% 8% 1	541
	11th to 20th	Day	16% 9% 38% 23% 10% 3	524
	21st to end	Day	15% 9% 37% 28% 9% 2	576
August	1st to 10th	Day	13% 8% 35% 30% 12% 2	526
	11th to 20th	Day	16% 8% 29% 27% 15% 4	519
	21st to end	Day	17% 11% 34% 24% 12% 3	583
September	1st to 10th	Day	14% 12% 33% 24% 13% 4	530
	11th to 20th	Day	18% 10% 27% 24% 13% 8%	530
	21st to end	Day	17% 13% 29% 23% 12% 5%	530
October	1st to 10th	Day	20% 16% 24% 24% 13% 3	513
	11th to 20th	Day	26% 14% 29% 20% 10% 2	420
	21st to end	Day	31% 15% 29% 19% 5% 1	462
November	1st to 10th	Day	26% 16% 29% 20% 8% 1	425
	11th to 20th	Day	28% 15% 32% 18% 6% 1	430
	21st to end	Day	30% 17% 28% 20% 5%	430
December	1st to 10th	Day	27% 16% 35% 16% 6%	251
	11th to 20th	Day	34% 21% 33% 9% 3	220
	21st to end	Day	33% 18% 29% 15% 5% 1	242
January	1st to 10th	Night	22% 16% 35% 24% 3	840
	11th to 20th	Night	24% 16% 35% 20% 4	840
	21st to end	Night	17% 17% 40% 22% 4	924
February	1st to 10th	Night	22% 15% 34% 24% 4	840
	11th to 20th	Night	21% 18% 38% 19% 3	823
	21st to end	Night	21% 14% 36% 26% 3	692
March	1st to 10th	Night	27% 15% 35% 22% 1	840
	11th to 20th	Night	22% 18% 34% 21% 5%	840
	21st to end	Night	26% 16% 31% 22% 5%	924
April	1st to 10th	Night	30% 16% 33% 19% 3	840
	11th to 20th	Night	25% 15% 34% 21% 4	665
	21st to end	Night	32% 13% 31% 21% 4	600
May	1st to 10th	Night	26% 12% 32% 26% 4	600
	11th to 20th	Night	22% 13% 37% 22% 5%	579
	21st to end	Night	20% 7% 33% 34% 5%	433
June	1st to 10th	Night	24% 8% 31% 31% 6%	400
	11th to 20th	Night	20% 5% 29% 37% 10%	400
	21st to end	Night	25% 4 28% 37% 6%	400
July	1st to 10th	Night	17% 4 32% 37% 10%	390
	11th to 20th	Night	16% 4 26% 41% 13% 1	388
	21st to end	Night	15% 4 25% 42% 13%	438
August	1st to 10th	Night	13% 6% 28% 39% 13%	569
	11th to 20th	Night	16% 6% 27% 38% 13% 1	592
	21st to end	Night	15% 7% 26% 37% 13% 1	705
September	1st to 10th	Night	17% 5% 30% 35% 13% 1	800
	11th to 20th	Night	17% 7% 27% 31% 16% 3	800
	21st to end	Night	19% 7% 31% 29% 13% 2	800
October	1st to 10th	Night	21% 8% 27% 31% 13%	800
	11th to 20th	Night	22% 10% 30% 29% 9% 1	800
	21st to end	Night	29% 14% 29% 23% 5%	880
November	1st to 10th	Night	25% 12% 30% 25% 7% 1	820
	11th to 20th	Night	22% 15% 31% 24% 7% 1	840
	21st to end	Night	25% 17% 30% 23% 5%	939
December	1st to 10th	Night	27% 12% 35% 20% 5%	950
	11th to 20th	Night	26% 16% 35% 20% 3	950
	21st to end	Night	29% 15% 32% 20% 4	1001

Page generated at 2026-04-14 02:44:26. Version ac07

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