Burnt Jacket Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burnt Jacket Mountain Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	15% 11% 4 9% 6% 5% 5% 4 5% 6% 29%	131033
	Night	15% 12% 4 10% 6% 6% 5% 4 5% 6% 27%	131503
Transparency	Day	52% 8% 11% 18% 10% 1	134513
	Night	52% 8% 11% 18% 10% 1	136098
Seeing	Day	26% 18% 30% 17% 7% 2	17436
	Night	24% 17% 28% 23% 8% 1	25937

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	9% 14% 6% 16% 8% 7% 4 4 4 5% 22%	4661
	11th to 20th	Day	9% 13% 7% 17% 11% 8% 5% 3 4 4 19%	4650
	21st to end	Day	7% 8% 5% 12% 7% 8% 9% 5% 6% 6% 26%	5124
February	1st to 10th	Day	12% 13% 5% 11% 9% 8% 5% 4 5% 6% 22%	1826
	11th to 20th	Day	11% 12% 7% 13% 9% 7% 4 3 4 5% 24%	1977
	21st to end	Day	11% 13% 4 12% 8% 7% 5% 4 5% 6% 27%	1730
March	1st to 10th	Day	16% 16% 5% 13% 6% 6% 4 3 4 3 24%	4576
	11th to 20th	Day	14% 15% 4 10% 6% 5% 5% 4 5% 6% 26%	5037
	21st to end	Day	19% 14% 5% 11% 5% 5% 4 3 4 6% 25%	5675
April	1st to 10th	Day	17% 15% 3 9% 6% 4 4 4 5% 5% 27%	2520
	11th to 20th	Day	17% 12% 3 8% 5% 4 4 4 5% 5% 32%	2654
	21st to end	Day	19% 12% 4 8% 5% 4 4 3 4 6% 32%	2730
May	1st to 10th	Day	22% 12% 3 9% 6% 6% 5% 4 5% 5% 23%	5899
	11th to 20th	Day	20% 11% 4 8% 5% 5% 5% 5% 5% 6% 27%	6060
	21st to end	Day	17% 9% 3 8% 6% 5% 5% 5% 6% 7% 30%	7169
June	1st to 10th	Day	23% 9% 2 6% 5% 5% 4 4 6% 8% 28%	3000
	11th to 20th	Day	17% 7% 3 7% 6% 5% 5% 4 6% 7% 34%	3000
	21st to end	Day	19% 10% 3 9% 6% 4 4 4 6% 9% 27%	3000
July	1st to 10th	Day	13% 7% 3 9% 5% 6% 7% 5% 7% 9% 28%	6556
	11th to 20th	Day	14% 7% 3 8% 5% 5% 5% 4 6% 9% 36%	6360
	21st to end	Day	11% 8% 3 7% 5% 4 5% 5% 6% 8% 40%	6926
August	1st to 10th	Day	15% 7% 2 8% 5% 6% 6% 5% 7% 8% 31%	4310
	11th to 20th	Day	14% 9% 4 9% 6% 6% 6% 4 6% 8% 29%	4175
	21st to end	Day	14% 8% 3 7% 5% 4 5% 4 5% 7% 37%	4609
September	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 6% 9% 42%	2342
	11th to 20th	Day	15% 6% 3 6% 3 3 3 4 4 6% 48%	2200
	21st to end	Day	15% 8% 3 7% 4 4 5% 4 6% 7% 38%	2200
October	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 4 8% 37%	2170
	11th to 20th	Day	16% 14% 3 8% 5% 4 5% 4 4 6% 30%	1919
	21st to end	Day	21% 16% 3 9% 4 5% 4 3 4 5% 25%	1980
November	1st to 10th	Day	17% 14% 4 8% 5% 4 4 4 4 5% 30%	1851
	11th to 20th	Day	16% 16% 5% 11% 6% 3 4 4 5% 6% 25%	1861
	21st to end	Day	20% 14% 5% 11% 4 5% 4 4 5% 7% 21%	1654
December	1st to 10th	Day	15% 16% 5% 15% 8% 7% 5% 3 4 4 18%	2350
	11th to 20th	Day	16% 14% 5% 9% 5% 4 4 3 5% 6% 28%	2688
	21st to end	Day	16% 14% 5% 11% 6% 6% 5% 4 5% 5% 24%	3594
January	1st to 10th	Night	10% 13% 7% 16% 10% 8% 5% 3 4 4 18%	8234
	11th to 20th	Night	11% 15% 7% 16% 11% 7% 6% 4 5% 4 14%	8235
	21st to end	Night	6% 8% 4 13% 8% 9% 9% 5% 6% 5% 25%	9057
February	1st to 10th	Night	10% 14% 5% 11% 7% 7% 6% 4 5% 6% 24%	2793
	11th to 20th	Night	10% 13% 7% 12% 8% 7% 7% 4 4 6% 23%	2526
	21st to end	Night	13% 13% 4 10% 6% 7% 5% 4 4 6% 30%	2076
March	1st to 10th	Night	20% 15% 5% 12% 5% 4 5% 3 4 4 23%	5484
	11th to 20th	Night	15% 14% 5% 10% 5% 5% 5% 4 6% 6% 26%	5142
	21st to end	Night	20% 15% 4 9% 6% 4 4 3 5% 7% 25%	5495
April	1st to 10th	Night	20% 14% 5% 7% 4 3 3 4 5% 5% 30%	2100
	11th to 20th	Night	19% 12% 2 7% 5% 4 4 3 5% 6% 33%	1914
	21st to end	Night	19% 12% 3 8% 5% 4 5% 4 5% 5% 30%	1890
May	1st to 10th	Night	22% 12% 5% 9% 5% 5% 5% 3 5% 6% 24%	4064
	11th to 20th	Night	20% 10% 3 8% 5% 4 5% 4 6% 6% 27%	3863
	21st to end	Night	18% 8% 2 5% 4 4 4 3 6% 8% 37%	3713
June	1st to 10th	Night	20% 11% 4 8% 5% 4 4 4 6% 6% 29%	1400
	11th to 20th	Night	16% 8% 3 6% 6% 4 5% 5% 5% 8% 35%	1400
	21st to end	Night	18% 9% 4 7% 5% 5% 5% 4 7% 7% 31%	1400
July	1st to 10th	Night	13% 9% 3 9% 5% 5% 5% 4 6% 7% 34%	3394
	11th to 20th	Night	15% 9% 3 8% 5% 4 4 4 5% 7% 37%	3600
	21st to end	Night	9% 7% 3 7% 5% 5% 6% 4 7% 8% 39%	3926
August	1st to 10th	Night	19% 8% 3 8% 5% 6% 4 4 6% 6% 32%	2807
	11th to 20th	Night	13% 9% 4 9% 6% 7% 7% 3 6% 7% 30%	2872
	21st to end	Night	13% 8% 2 6% 5% 3 4 3 5% 7% 44%	3286
September	1st to 10th	Night	12% 6% 2 5% 3 3 4 4 5% 8% 47%	2056
	11th to 20th	Night	14% 5% 2 6% 4 4 3 3 5% 7% 47%	2200
	21st to end	Night	16% 7% 2 6% 5% 5% 4 4 5% 7% 40%	2200
October	1st to 10th	Night	16% 8% 3 7% 5% 4 4 3 5% 6% 39%	2230
	11th to 20th	Night	18% 13% 3 7% 4 4 4 3 5% 6% 33%	2479
	21st to end	Night	21% 14% 4 8% 5% 4 4 3 4 6% 27%	2860
November	1st to 10th	Night	18% 13% 5% 9% 4 4 4 3 5% 6% 28%	2667
	11th to 20th	Night	15% 13% 7% 11% 5% 5% 4 3 4 6% 27%	2756
	21st to end	Night	16% 13% 5% 13% 6% 6% 5% 3 6% 6% 22%	2963
December	1st to 10th	Night	14% 13% 6% 20% 9% 7% 5% 4 4 4 14%	5060
	11th to 20th	Night	17% 14% 4 11% 8% 6% 5% 3 5% 5% 21%	5741
	21st to end	Night	17% 14% 5% 11% 6% 5% 4 3 4 4 27%	7620

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	54% 11% 10% 16% 7% 1	4662
	11th to 20th	Day	58% 12% 7% 15% 7% 1	4680
	21st to end	Day	49% 10% 11% 13% 16% 2	5124
February	1st to 10th	Day	59% 6% 7% 15% 11% 2	1826
	11th to 20th	Day	59% 6% 9% 15% 10% 1	1985
	21st to end	Day	55% 7% 8% 17% 10% 4	1730
March	1st to 10th	Day	63% 5% 6% 9% 12% 4	4579
	11th to 20th	Day	56% 8% 13% 13% 9% 1	5037
	21st to end	Day	58% 6% 5% 15% 13% 3	5675
April	1st to 10th	Day	57% 5% 9% 15% 12% 3	2520
	11th to 20th	Day	52% 6% 8% 20% 13% 1	2654
	21st to end	Day	54% 5% 8% 19% 11% 3	2730
May	1st to 10th	Day	61% 7% 8% 15% 7% 1	5910
	11th to 20th	Day	56% 7% 12% 17% 6% 2	6064
	21st to end	Day	50% 8% 12% 17% 12% 2	7169
June	1st to 10th	Day	54% 5% 12% 21% 8%	3000
	11th to 20th	Day	47% 6% 11% 21% 13% 1	3000
	21st to end	Day	55% 6% 12% 19% 8% 1	3000
July	1st to 10th	Day	47% 9% 18% 17% 8%	6486
	11th to 20th	Day	44% 8% 14% 27% 6%	6285
	21st to end	Day	40% 8% 13% 29% 9%	6728
August	1st to 10th	Day	48% 9% 15% 22% 6%	4296
	11th to 20th	Day	50% 8% 16% 21% 6%	4214
	21st to end	Day	43% 9% 13% 21% 14%	4609
September	1st to 10th	Day	37% 6% 15% 27% 14% 1	2342
	11th to 20th	Day	37% 4 12% 29% 16% 1	2200
	21st to end	Day	44% 6% 10% 26% 13% 1	2200
October	1st to 10th	Day	49% 9% 12% 20% 10%	3534
	11th to 20th	Day	50% 7% 11% 24% 9%	3096
	21st to end	Day	45% 6% 17% 19% 14%	3180
November	1st to 10th	Day	55% 6% 11% 18% 10% 1	1851
	11th to 20th	Day	55% 9% 9% 16% 9% 2	1861
	21st to end	Day	59% 7% 12% 18% 5%	1654
December	1st to 10th	Day	65% 8% 10% 10% 7%	2350
	11th to 20th	Day	51% 8% 11% 14% 13% 3	2688
	21st to end	Day	55% 8% 9% 14% 9% 4	3594
January	1st to 10th	Night	58% 12% 11% 13% 7%	8234
	11th to 20th	Night	64% 10% 8% 10% 6% 1	8280
	21st to end	Night	50% 10% 8% 16% 15% 1	9057
February	1st to 10th	Night	56% 7% 8% 17% 10% 2	2793
	11th to 20th	Night	54% 10% 9% 16% 11% 1	2529
	21st to end	Night	52% 7% 8% 18% 12% 3	2076
March	1st to 10th	Night	62% 5% 7% 13% 10% 3	5494
	11th to 20th	Night	54% 10% 14% 13% 8% 1	5143
	21st to end	Night	57% 6% 6% 17% 13% 1	5495
April	1st to 10th	Night	55% 4 7% 15% 15% 3	2100
	11th to 20th	Night	51% 5% 9% 20% 13% 2	1914
	21st to end	Night	53% 6% 8% 19% 11% 3	1890
May	1st to 10th	Night	61% 6% 11% 14% 8% 1	4070
	11th to 20th	Night	56% 6% 12% 20% 5%	3864
	21st to end	Night	44% 7% 17% 20% 13%	3714
June	1st to 10th	Night	54% 6% 11% 20% 9%	1400
	11th to 20th	Night	46% 6% 13% 22% 11% 2	1400
	21st to end	Night	51% 5% 15% 20% 9%	1400
July	1st to 10th	Night	47% 8% 16% 22% 8%	3354
	11th to 20th	Night	45% 8% 12% 29% 5%	3552
	21st to end	Night	37% 11% 16% 28% 8%	3809
August	1st to 10th	Night	51% 7% 14% 23% 4	2797
	11th to 20th	Night	50% 9% 15% 17% 8% 1	2899
	21st to end	Night	37% 10% 14% 23% 15% 1	3286
September	1st to 10th	Night	34% 6% 15% 31% 13%	2056
	11th to 20th	Night	36% 4 13% 29% 16%	2200
	21st to end	Night	41% 6% 13% 26% 12% 1	2200
October	1st to 10th	Night	46% 9% 12% 22% 12%	3646
	11th to 20th	Night	43% 10% 11% 26% 10%	4028
	21st to end	Night	45% 6% 18% 19% 10% 1	4610
November	1st to 10th	Night	55% 6% 11% 20% 9% 1	2667
	11th to 20th	Night	54% 8% 9% 16% 11% 2	2756
	21st to end	Night	57% 8% 13% 15% 6%	2963
December	1st to 10th	Night	65% 11% 8% 12% 4	5060
	11th to 20th	Night	56% 9% 7% 15% 13% 1	5742
	21st to end	Night	56% 6% 10% 17% 10% 2	7620

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	31% 23% 33% 10% 3	220
	11th to 20th	Day	32% 26% 28% 10% 3	220
	21st to end	Day	28% 21% 38% 10% 4	242
February	1st to 10th	Day	30% 21% 30% 16% 2 1	366
	11th to 20th	Day	29% 28% 33% 8% 2	498
	21st to end	Day	29% 23% 33% 13% 2	446
March	1st to 10th	Day	31% 23% 31% 12% 2	540
	11th to 20th	Day	31% 24% 29% 13% 3 1	540
	21st to end	Day	33% 21% 27% 12% 6% 1	594
April	1st to 10th	Day	36% 22% 24% 12% 5% 1	540
	11th to 20th	Day	33% 23% 26% 12% 5% 2	532
	21st to end	Day	32% 19% 31% 11% 5% 2	540
May	1st to 10th	Day	33% 16% 31% 14% 5% 1	507
	11th to 20th	Day	28% 14% 32% 17% 7% 1	527
	21st to end	Day	23% 19% 32% 20% 6% 1	663
June	1st to 10th	Day	27% 14% 31% 19% 7% 2	730
	11th to 20th	Day	22% 15% 30% 21% 10% 2	730
	21st to end	Day	23% 12% 32% 22% 8% 2	730
July	1st to 10th	Day	18% 13% 36% 21% 11% 1	617
	11th to 20th	Day	16% 12% 40% 20% 10% 2	524
	21st to end	Day	15% 11% 37% 26% 9% 1	576
August	1st to 10th	Day	17% 12% 29% 28% 13% 3	526
	11th to 20th	Day	16% 13% 25% 26% 16% 4	519
	21st to end	Day	18% 14% 29% 23% 14% 3	583
September	1st to 10th	Day	16% 14% 31% 22% 12% 4	530
	11th to 20th	Day	21% 12% 25% 18% 15% 7%	530
	21st to end	Day	19% 14% 30% 22% 10% 6%	530
October	1st to 10th	Day	20% 18% 29% 17% 13% 4	513
	11th to 20th	Day	28% 17% 30% 14% 9% 2	420
	21st to end	Day	32% 21% 26% 15% 5%	462
November	1st to 10th	Day	30% 21% 24% 19% 6%	425
	11th to 20th	Day	28% 26% 26% 14% 5% 1	430
	21st to end	Day	35% 22% 24% 15% 4	404
December	1st to 10th	Day	28% 24% 29% 16% 3	220
	11th to 20th	Day	36% 29% 24% 9% 2	220
	21st to end	Day	35% 21% 28% 12% 3 1	242
January	1st to 10th	Night	25% 25% 28% 19% 3	840
	11th to 20th	Night	26% 23% 30% 18% 4	840
	21st to end	Night	19% 24% 35% 17% 4	924
February	1st to 10th	Night	22% 25% 32% 17% 3	840
	11th to 20th	Night	23% 26% 32% 17% 2	823
	21st to end	Night	23% 21% 35% 18% 2	692
March	1st to 10th	Night	26% 20% 33% 19% 2	840
	11th to 20th	Night	26% 22% 26% 20% 6%	840
	21st to end	Night	27% 20% 26% 22% 5%	924
April	1st to 10th	Night	32% 19% 26% 19% 4	840
	11th to 20th	Night	26% 18% 26% 22% 7%	670
	21st to end	Night	30% 15% 28% 20% 8%	630
May	1st to 10th	Night	29% 12% 26% 26% 6% 1	604
	11th to 20th	Night	25% 14% 29% 25% 8% 1	526
	21st to end	Night	22% 9% 30% 30% 9%	433
June	1st to 10th	Night	25% 9% 28% 30% 8% 1	400
	11th to 20th	Night	18% 11% 25% 32% 15%	400
	21st to end	Night	22% 5% 30% 33% 10% 1	400
July	1st to 10th	Night	16% 6% 27% 39% 11% 1	390
	11th to 20th	Night	19% 6% 23% 36% 16% 1	388
	21st to end	Night	17% 5% 26% 38% 14% 1	438
August	1st to 10th	Night	19% 5% 20% 39% 16% 1	528
	11th to 20th	Night	16% 10% 21% 34% 19% 1	592
	21st to end	Night	16% 8% 25% 32% 18% 1	697
September	1st to 10th	Night	14% 10% 27% 31% 17% 2	800
	11th to 20th	Night	17% 10% 22% 31% 18% 2	800
	21st to end	Night	20% 10% 29% 27% 13% 2	800
October	1st to 10th	Night	22% 12% 24% 27% 15% 1	800
	11th to 20th	Night	26% 15% 28% 20% 9% 2	800
	21st to end	Night	30% 18% 28% 20% 5%	880
November	1st to 10th	Night	28% 18% 25% 20% 7% 1	820
	11th to 20th	Night	26% 22% 25% 17% 8% 1	854
	21st to end	Night	28% 21% 26% 20% 4 1	950
December	1st to 10th	Night	29% 19% 31% 17% 3	950
	11th to 20th	Night	31% 22% 27% 16% 4 1	950
	21st to end	Night	30% 22% 27% 16% 3	1034

Page generated at 2026-04-29 02:21:45. Version ac07

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