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 2024-01-22.

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	17% 10% 4 7% 6% 4 5% 5% 5% 7% 30%	74636
	Night	17% 11% 4 8% 7% 4 5% 5% 5% 6% 30%	75298
Transparency	Day	52% 6% 11% 19% 10% 1	74340
	Night	52% 6% 11% 20% 10% 1	75129
Seeing	Day	25% 17% 30% 18% 8% 2	14460
	Night	24% 16% 28% 23% 8% 1	22988

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	13% 13% 6% 12% 10% 4 5% 6% 4 6% 21%	1517
	11th to 20th	Day	16% 14% 7% 8% 8% 5% 6% 5% 4 6% 22%	1520
	21st to end	Day	10% 11% 6% 9% 9% 4 6% 4 6% 7% 28%	1592
February	1st to 10th	Day	14% 14% 5% 10% 9% 6% 6% 6% 4 6% 20%	1565
	11th to 20th	Day	12% 12% 7% 12% 10% 5% 6% 4 4 5% 23%	1687
	21st to end	Day	11% 12% 5% 11% 8% 6% 6% 5% 5% 6% 25%	1480
March	1st to 10th	Day	15% 12% 5% 8% 7% 4 5% 5% 5% 5% 29%	1797
	11th to 20th	Day	14% 11% 6% 7% 7% 3 5% 4 4 6% 32%	1956
	21st to end	Day	14% 10% 6% 10% 8% 3 5% 4 4 6% 30%	2210
April	1st to 10th	Day	18% 13% 4 8% 8% 3 4 5% 5% 6% 26%	2160
	11th to 20th	Day	17% 10% 4 6% 5% 3 4 5% 5% 6% 34%	2270
	21st to end	Day	20% 12% 4 7% 5% 3 4 4 4 6% 31%	2340
May	1st to 10th	Day	19% 11% 4 6% 5% 3 5% 5% 4 6% 33%	2340
	11th to 20th	Day	21% 9% 3 6% 5% 3 4 4 5% 6% 33%	2374
	21st to end	Day	15% 8% 3 7% 7% 4 5% 6% 6% 9% 30%	2805
June	1st to 10th	Day	24% 9% 2 5% 6% 4 4 5% 6% 8% 27%	2700
	11th to 20th	Day	18% 6% 3 6% 6% 3 5% 5% 6% 7% 35%	2700
	21st to end	Day	19% 8% 4 8% 6% 3 5% 5% 6% 9% 26%	2700
July	1st to 10th	Day	15% 6% 3 5% 6% 4 5% 5% 6% 9% 35%	2604
	11th to 20th	Day	14% 7% 3 7% 7% 4 5% 5% 6% 8% 34%	2520
	21st to end	Day	14% 7% 3 7% 7% 4 6% 6% 6% 8% 31%	2744
August	1st to 10th	Day	16% 6% 2 6% 6% 4 6% 6% 6% 8% 33%	2372
	11th to 20th	Day	13% 7% 3 6% 7% 4 6% 6% 6% 8% 35%	2304
	21st to end	Day	13% 6% 4 6% 5% 4 5% 6% 5% 7% 39%	2538
September	1st to 10th	Day	12% 7% 2 5% 6% 3 4 6% 6% 9% 41%	2108
	11th to 20th	Day	17% 6% 3 5% 4 3 3 4 4 5% 48%	1980
	21st to end	Day	16% 8% 3 6% 4 3 5% 5% 6% 7% 38%	1980
October	1st to 10th	Day	16% 9% 3 6% 5% 3 4 4 4 8% 36%	1954
	11th to 20th	Day	17% 13% 3 6% 6% 3 5% 5% 5% 6% 29%	1728
	21st to end	Day	23% 16% 4 8% 6% 3 4 4 4 5% 24%	1782
November	1st to 10th	Day	19% 12% 4 7% 5% 3 4 5% 4 6% 31%	1671
	11th to 20th	Day	17% 13% 6% 9% 7% 2 4 5% 5% 6% 25%	1685
	21st to end	Day	20% 12% 5% 9% 5% 4 4 5% 5% 8% 23%	1497
December	1st to 10th	Day	21% 16% 7% 10% 7% 4 5% 4 4 4 18%	1330
	11th to 20th	Day	19% 14% 6% 7% 5% 4 5% 4 5% 6% 24%	1668
	21st to end	Day	22% 13% 4 9% 7% 4 5% 4 5% 5% 23%	2458
January	1st to 10th	Night	14% 14% 5% 12% 10% 5% 6% 5% 4 5% 19%	2649
	11th to 20th	Night	15% 13% 6% 11% 9% 5% 6% 5% 5% 5% 19%	2660
	21st to end	Night	9% 10% 5% 10% 11% 4 6% 7% 6% 6% 25%	2798
February	1st to 10th	Night	12% 14% 5% 9% 8% 4 8% 6% 5% 6% 22%	2394
	11th to 20th	Night	11% 12% 8% 9% 10% 5% 7% 6% 4 6% 22%	2156
	21st to end	Night	13% 12% 5% 10% 6% 4 6% 5% 4 6% 29%	1776
March	1st to 10th	Night	13% 14% 6% 9% 7% 4 5% 4 4 5% 30%	2150
	11th to 20th	Night	15% 10% 5% 8% 7% 4 4 5% 5% 5% 31%	2003
	21st to end	Night	15% 12% 5% 9% 5% 3 5% 5% 4 6% 31%	2142
April	1st to 10th	Night	21% 13% 5% 7% 4 3 4 5% 6% 5% 29%	1800
	11th to 20th	Night	18% 10% 3 5% 6% 3 5% 4 5% 6% 35%	1638
	21st to end	Night	21% 11% 4 7% 6% 3 5% 5% 5% 5% 28%	1620
May	1st to 10th	Night	21% 11% 4 6% 5% 3 4 4 4 6% 32%	1620
	11th to 20th	Night	19% 7% 4 7% 7% 3 6% 6% 4 6% 30%	1535
	21st to end	Night	18% 9% 3 5% 5% 4 4 5% 5% 7% 34%	1467
June	1st to 10th	Night	22% 9% 4 7% 6% 3 4 5% 6% 5% 29%	1260
	11th to 20th	Night	18% 7% 3 5% 7% 2 5% 6% 4 7% 37%	1260
	21st to end	Night	18% 8% 4 7% 4 3 5% 5% 6% 7% 32%	1260
July	1st to 10th	Night	14% 7% 3 5% 5% 3 4 5% 7% 8% 37%	1351
	11th to 20th	Night	14% 7% 3 6% 5% 3 5% 5% 7% 9% 38%	1440
	21st to end	Night	13% 7% 3 6% 7% 2 6% 5% 7% 7% 37%	1574
August	1st to 10th	Night	16% 6% 2 5% 5% 3 4 5% 7% 7% 40%	1548
	11th to 20th	Night	13% 7% 3 6% 6% 4 6% 5% 6% 8% 37%	1596
	21st to end	Night	13% 5% 2 5% 5% 2 4 5% 5% 7% 47%	1815
September	1st to 10th	Night	13% 5% 2 5% 4 2 5% 5% 5% 8% 47%	1850
	11th to 20th	Night	15% 5% 2 5% 5% 3 4 4 5% 7% 45%	1980
	21st to end	Night	17% 7% 3 5% 5% 3 4 4 5% 7% 40%	1980
October	1st to 10th	Night	17% 7% 3 6% 5% 3 5% 4 5% 7% 37%	2006
	11th to 20th	Night	19% 11% 4 6% 5% 3 4 4 5% 6% 32%	2231
	21st to end	Night	23% 14% 4 7% 6% 3 4 4 4 5% 26%	2574
November	1st to 10th	Night	18% 11% 4 8% 6% 3 4 4 5% 6% 29%	2407
	11th to 20th	Night	16% 10% 6% 10% 6% 3 4 4 4 7% 28%	2493
	21st to end	Night	16% 12% 5% 11% 8% 4 6% 4 6% 6% 23%	2680
December	1st to 10th	Night	22% 14% 6% 10% 8% 4 5% 5% 4 6% 17%	2850
	11th to 20th	Night	20% 13% 5% 10% 8% 5% 6% 4 5% 5% 20%	3531
	21st to end	Night	21% 14% 5% 10% 6% 3 4 3 5% 4 25%	5204

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	60% 6% 9% 15% 9% 1	1518
	11th to 20th	Day	60% 7% 7% 15% 9% 1	1520
	21st to end	Day	52% 5% 10% 17% 14% 2	1592
February	1st to 10th	Day	62% 5% 7% 13% 10% 2	1565
	11th to 20th	Day	61% 5% 9% 14% 9% 1	1695
	21st to end	Day	58% 6% 7% 16% 9% 4	1480
March	1st to 10th	Day	55% 6% 9% 16% 12% 3	1800
	11th to 20th	Day	53% 4 9% 17% 15% 2	1956
	21st to end	Day	54% 6% 7% 17% 12% 3	2210
April	1st to 10th	Day	58% 5% 9% 14% 11% 3	2160
	11th to 20th	Day	51% 5% 9% 20% 14% 1	2270
	21st to end	Day	57% 4 8% 18% 10% 4	2340
May	1st to 10th	Day	53% 5% 8% 19% 13% 3	2340
	11th to 20th	Day	52% 5% 9% 21% 12% 1	2378
	21st to end	Day	50% 7% 13% 19% 10% 1	2805
June	1st to 10th	Day	55% 5% 13% 20% 7%	2700
	11th to 20th	Day	48% 6% 11% 22% 13% 1	2700
	21st to end	Day	55% 6% 13% 18% 8% 1	2700
July	1st to 10th	Day	45% 6% 16% 22% 10%	2534
	11th to 20th	Day	46% 6% 15% 23% 9%	2445
	21st to end	Day	48% 8% 14% 22% 7% 1	2591
August	1st to 10th	Day	47% 8% 17% 22% 6%	2358
	11th to 20th	Day	47% 6% 15% 22% 9%	2304
	21st to end	Day	44% 6% 12% 25% 12% 1	2538
September	1st to 10th	Day	39% 7% 15% 25% 14% 1	2108
	11th to 20th	Day	39% 4 11% 29% 15% 2	1980
	21st to end	Day	45% 6% 11% 26% 13% 1	1980
October	1st to 10th	Day	47% 4 12% 24% 13%	1954
	11th to 20th	Day	54% 5% 14% 21% 7%	1728
	21st to end	Day	63% 4 9% 14% 9% 1	1782
November	1st to 10th	Day	54% 6% 11% 18% 10% 1	1671
	11th to 20th	Day	55% 7% 9% 17% 9% 2	1685
	21st to end	Day	57% 6% 13% 19% 5%	1497
December	1st to 10th	Day	68% 5% 7% 14% 7%	1330
	11th to 20th	Day	56% 7% 8% 16% 12% 1	1668
	21st to end	Day	59% 8% 9% 16% 7% 2	2458
January	1st to 10th	Night	62% 8% 7% 15% 7%	2649
	11th to 20th	Night	62% 7% 9% 14% 6% 1	2660
	21st to end	Night	53% 7% 8% 19% 10% 2	2798
February	1st to 10th	Night	57% 7% 8% 17% 9% 2	2394
	11th to 20th	Night	56% 9% 9% 15% 10% 1	2159
	21st to end	Night	54% 7% 7% 18% 11% 2	1776
March	1st to 10th	Night	55% 6% 6% 20% 11% 2	2160
	11th to 20th	Night	53% 6% 10% 15% 14% 2	2004
	21st to end	Night	50% 6% 9% 21% 11% 2	2142
April	1st to 10th	Night	55% 4 7% 15% 15% 3	1800
	11th to 20th	Night	48% 6% 9% 22% 14% 2	1638
	21st to end	Night	56% 5% 8% 17% 10% 3	1620
May	1st to 10th	Night	52% 5% 8% 19% 14% 1	1620
	11th to 20th	Night	54% 4 9% 20% 11% 1	1536
	21st to end	Night	48% 7% 13% 21% 10% 1	1468
June	1st to 10th	Night	55% 6% 11% 19% 9%	1260
	11th to 20th	Night	46% 6% 12% 22% 12% 2	1260
	21st to end	Night	50% 5% 15% 20% 9%	1260
July	1st to 10th	Night	44% 6% 16% 24% 10%	1311
	11th to 20th	Night	41% 7% 16% 28% 9%	1392
	21st to end	Night	44% 7% 17% 21% 10%	1486
August	1st to 10th	Night	42% 7% 19% 28% 6%	1538
	11th to 20th	Night	44% 7% 16% 25% 8%	1596
	21st to end	Night	35% 7% 16% 29% 13%	1815
September	1st to 10th	Night	35% 6% 15% 31% 13% 1	1850
	11th to 20th	Night	38% 5% 13% 28% 16%	1980
	21st to end	Night	42% 5% 13% 27% 12% 1	1980
October	1st to 10th	Night	45% 6% 10% 25% 13%	2006
	11th to 20th	Night	51% 6% 13% 23% 7% 1	2231
	21st to end	Night	59% 5% 10% 17% 10%	2574
November	1st to 10th	Night	54% 5% 11% 20% 10% 1	2407
	11th to 20th	Night	54% 7% 10% 17% 11% 1	2493
	21st to end	Night	57% 8% 13% 16% 7%	2680
December	1st to 10th	Night	65% 6% 8% 15% 6%	2850
	11th to 20th	Night	58% 8% 7% 16% 11%	3532
	21st to end	Night	59% 6% 9% 18% 8% 1	5204

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% 21% 33% 12% 3	180
	11th to 20th	Day	31% 28% 28% 9% 3 1	180
	21st to end	Day	26% 19% 40% 12% 3 1	178
February	1st to 10th	Day	30% 23% 30% 16% 2	285
	11th to 20th	Day	28% 28% 33% 9% 2	388
	21st to end	Day	28% 22% 33% 15% 2	346
March	1st to 10th	Day	30% 21% 33% 13% 3	420
	11th to 20th	Day	28% 23% 29% 15% 4 1	420
	21st to end	Day	29% 20% 27% 15% 7% 2	462
April	1st to 10th	Day	34% 23% 22% 14% 6% 1	420
	11th to 20th	Day	29% 22% 27% 14% 6% 2	412
	21st to end	Day	31% 18% 31% 13% 5% 2	420
May	1st to 10th	Day	31% 15% 33% 14% 4 1	423
	11th to 20th	Day	28% 15% 34% 17% 5% 1	447
	21st to end	Day	22% 19% 32% 20% 6% 1	565
June	1st to 10th	Day	28% 14% 31% 18% 7% 1	630
	11th to 20th	Day	22% 13% 29% 23% 10% 2	630
	21st to end	Day	22% 10% 32% 24% 10% 2	630
July	1st to 10th	Day	18% 11% 36% 22% 12% 1	529
	11th to 20th	Day	17% 10% 39% 20% 11% 2	444
	21st to end	Day	15% 9% 36% 28% 10% 2	488
August	1st to 10th	Day	17% 11% 28% 28% 13% 2	446
	11th to 20th	Day	17% 12% 26% 26% 16% 4	439
	21st to end	Day	19% 13% 26% 23% 15% 3	495
September	1st to 10th	Day	14% 13% 32% 22% 13% 4	450
	11th to 20th	Day	24% 12% 26% 17% 14% 7%	450
	21st to end	Day	18% 14% 30% 21% 10% 6%	450
October	1st to 10th	Day	21% 16% 29% 17% 13% 4	437
	11th to 20th	Day	28% 16% 30% 14% 9% 2	360
	21st to end	Day	33% 21% 26% 15% 5%	396
November	1st to 10th	Day	28% 18% 24% 22% 7% 1	365
	11th to 20th	Day	28% 23% 27% 16% 5% 1	370
	21st to end	Day	33% 22% 24% 16% 5% 1	347
December	1st to 10th	Day	27% 23% 30% 17% 3	180
	11th to 20th	Day	36% 29% 24% 9% 2 1	180
	21st to end	Day	37% 22% 26% 11% 4 1	198
January	1st to 10th	Night	25% 24% 28% 20% 3	760
	11th to 20th	Night	27% 23% 29% 18% 4	760
	21st to end	Night	19% 25% 35% 17% 4	800
February	1st to 10th	Night	23% 25% 33% 17% 3	720
	11th to 20th	Night	23% 26% 32% 17% 2	703
	21st to end	Night	24% 22% 33% 19% 3	592
March	1st to 10th	Night	25% 20% 33% 20% 2	720
	11th to 20th	Night	25% 22% 27% 20% 6%	720
	21st to end	Night	24% 21% 26% 22% 6%	792
April	1st to 10th	Night	31% 18% 27% 20% 5%	720
	11th to 20th	Night	24% 17% 28% 23% 7%	574
	21st to end	Night	31% 14% 27% 21% 8%	540
May	1st to 10th	Night	29% 12% 26% 27% 6% 1	540
	11th to 20th	Night	25% 14% 30% 25% 6% 1	474
	21st to end	Night	22% 9% 30% 29% 9% 1	389
June	1st to 10th	Night	25% 9% 28% 30% 7% 1	360
	11th to 20th	Night	19% 9% 24% 32% 15%	360
	21st to end	Night	22% 3 29% 35% 11% 1	360
July	1st to 10th	Night	16% 5% 28% 39% 11% 1	350
	11th to 20th	Night	18% 5% 24% 37% 17% 1	348
	21st to end	Night	17% 4 25% 38% 15% 1	394
August	1st to 10th	Night	19% 5% 20% 38% 16% 1	474
	11th to 20th	Night	16% 9% 21% 35% 18% 1	532
	21st to end	Night	17% 7% 25% 33% 18% 2	627
September	1st to 10th	Night	14% 8% 28% 32% 16% 2	720
	11th to 20th	Night	19% 10% 23% 31% 16% 2	720
	21st to end	Night	21% 9% 29% 26% 13% 2	720
October	1st to 10th	Night	22% 11% 25% 27% 14% 1	720
	11th to 20th	Night	24% 16% 29% 20% 10% 2	720
	21st to end	Night	32% 17% 27% 19% 5%	792
November	1st to 10th	Night	26% 18% 25% 22% 8% 1	740
	11th to 20th	Night	26% 20% 25% 19% 9% 1	771
	21st to end	Night	27% 21% 26% 21% 4 1	850
December	1st to 10th	Night	30% 19% 31% 16% 4	850
	11th to 20th	Night	30% 21% 28% 17% 4 1	850
	21st to end	Night	31% 22% 28% 16% 3	926

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