North Frontenac Astronomy Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Frontenac Astronomy Park clear sky chart from 2005-11-06 to 2025-06-10.

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	16% 11% 4 9% 5% 5% 4 4 5% 6% 31%	119889
	Night	16% 12% 4 9% 5% 5% 4 3 5% 6% 31%	118327
Transparency	Day	52% 6% 11% 20% 11% 1	123451
	Night	52% 6% 12% 19% 10% 1	122926
Seeing	Day	23% 17% 31% 18% 8% 2	15145
	Night	22% 14% 32% 23% 8% 1	24395

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% 15% 6% 13% 7% 4 5% 4 5% 6% 22%	3597
	11th to 20th	Day	11% 19% 8% 14% 5% 6% 4 4 4 4 20%	3570
	21st to end	Day	13% 18% 7% 16% 6% 5% 4 3 4 4 19%	4327
February	1st to 10th	Day	14% 17% 5% 12% 7% 5% 4 4 6% 5% 22%	1800
	11th to 20th	Day	12% 16% 5% 10% 7% 4 4 4 4 5% 28%	1753
	21st to end	Day	19% 15% 4 9% 6% 6% 4 4 4 5% 24%	1609
March	1st to 10th	Day	18% 14% 5% 10% 5% 4 4 3 4 5% 28%	4650
	11th to 20th	Day	11% 14% 4 9% 5% 5% 6% 4 5% 7% 31%	4980
	21st to end	Day	18% 12% 4 7% 4 3 3 3 3 4 38%	5648
April	1st to 10th	Day	20% 13% 4 7% 5% 4 4 3 5% 6% 31%	2400
	11th to 20th	Day	21% 11% 3 7% 3 4 3 2 5% 5% 36%	2374
	21st to end	Day	21% 10% 4 7% 5% 5% 4 3 4 5% 32%	2545
May	1st to 10th	Day	23% 8% 3 8% 5% 4 4 4 5% 6% 29%	6300
	11th to 20th	Day	17% 9% 3 8% 5% 5% 4 4 5% 7% 33%	6318
	21st to end	Day	19% 9% 3 6% 5% 5% 4 4 6% 7% 33%	6949
June	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 6% 30%	2786
	11th to 20th	Day	15% 6% 3 5% 5% 5% 5% 5% 8% 8% 36%	2660
	21st to end	Day	17% 7% 3 8% 5% 5% 5% 4 6% 7% 33%	2660
July	1st to 10th	Day	12% 7% 3 7% 6% 6% 5% 4 6% 9% 34%	4440
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 5% 7% 9% 39%	4440
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 7% 8% 41%	4814
August	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 4 5% 7% 34%	4201
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 8% 35%	4044
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 6% 9% 38%	4194
September	1st to 10th	Day	14% 7% 2 7% 5% 4 4 4 5% 7% 41%	2280
	11th to 20th	Day	12% 5% 3 6% 4 4 4 4 5% 7% 47%	2280
	21st to end	Day	19% 6% 3 6% 5% 4 4 4 4 7% 38%	2004
October	1st to 10th	Day	21% 9% 3 8% 5% 3 3 3 5% 6% 35%	1900
	11th to 20th	Day	21% 10% 2 8% 5% 6% 4 3 5% 7% 28%	1900
	21st to end	Day	25% 11% 4 8% 5% 5% 5% 3 4 6% 25%	2000
November	1st to 10th	Day	14% 9% 3 9% 4 5% 5% 5% 5% 7% 34%	1720
	11th to 20th	Day	16% 14% 5% 8% 5% 6% 4 4 4 5% 29%	1600
	21st to end	Day	21% 16% 5% 11% 5% 6% 4 3 4 6% 19%	1600
December	1st to 10th	Day	21% 20% 5% 11% 7% 4 4 3 4 4 17%	2600
	11th to 20th	Day	17% 19% 6% 13% 5% 4 3 3 4 4 23%	2986
	21st to end	Day	23% 19% 5% 11% 5% 3 3 2 3 5% 22%	3960
January	1st to 10th	Night	14% 14% 9% 14% 6% 5% 4 3 4 4 21%	6349
	11th to 20th	Night	10% 16% 6% 15% 8% 6% 6% 4 5% 5% 19%	6315
	21st to end	Night	14% 16% 8% 14% 6% 6% 4 3 4 4 21%	6628
February	1st to 10th	Night	12% 17% 5% 10% 6% 6% 4 4 6% 7% 23%	2600
	11th to 20th	Night	13% 13% 5% 10% 6% 5% 5% 3 5% 5% 29%	2533
	21st to end	Night	12% 15% 5% 7% 6% 5% 5% 5% 6% 7% 28%	2020
March	1st to 10th	Night	20% 14% 4 9% 5% 5% 4 2 3 5% 29%	5187
	11th to 20th	Night	11% 12% 3 8% 5% 5% 5% 5% 8% 8% 30%	4979
	21st to end	Night	18% 10% 4 7% 5% 4 4 3 5% 5% 35%	5284
April	1st to 10th	Night	19% 12% 4 7% 5% 3 4 4 4 6% 33%	2000
	11th to 20th	Night	18% 10% 3 5% 6% 5% 3 3 4 5% 38%	1975
	21st to end	Night	19% 9% 3 7% 4 4 4 5% 5% 6% 34%	1872
May	1st to 10th	Night	24% 8% 3 7% 4 4 4 4 6% 7% 29%	3640
	11th to 20th	Night	15% 7% 3 7% 4 3 3 3 5% 7% 42%	3575
	21st to end	Night	18% 8% 2 6% 4 4 5% 4 5% 7% 35%	3926
June	1st to 10th	Night	14% 7% 2 8% 6% 5% 5% 3 7% 8% 35%	1598
	11th to 20th	Night	12% 6% 3 6% 4 3 4 4 6% 7% 43%	1520
	21st to end	Night	17% 7% 3 7% 4 4 5% 3 7% 7% 36%	1520
July	1st to 10th	Night	10% 6% 3 8% 6% 6% 6% 4 6% 7% 39%	2520
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 5% 7% 45%	2520
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 7% 46%	2739
August	1st to 10th	Night	13% 6% 2 6% 4 4 3 4 6% 7% 44%	2724
	11th to 20th	Night	14% 6% 2 6% 3 4 4 3 5% 8% 44%	2785
	21st to end	Night	11% 5% 2 6% 4 4 5% 4 7% 8% 44%	3430
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 4 5% 7% 48%	1900
	11th to 20th	Night	13% 4 2 4 4 4 4 4 5% 5% 51%	1900
	21st to end	Night	18% 5% 2 6% 4 3 4 3 5% 6% 43%	2171
October	1st to 10th	Night	18% 8% 3 7% 4 4 4 3 5% 6% 39%	2280
	11th to 20th	Night	20% 11% 3 7% 5% 4 5% 3 5% 6% 32%	2280
	21st to end	Night	22% 12% 3 7% 5% 4 4 3 5% 6% 29%	2596
November	1st to 10th	Night	16% 11% 3 6% 4 4 5% 4 5% 6% 35%	2577
	11th to 20th	Night	17% 12% 4 8% 5% 4 5% 4 5% 6% 30%	2800
	21st to end	Night	20% 15% 5% 8% 5% 5% 5% 4 5% 6% 23%	2800
December	1st to 10th	Night	19% 18% 5% 11% 6% 5% 5% 4 5% 6% 17%	4580
	11th to 20th	Night	21% 17% 5% 10% 6% 4 4 3 4 4 24%	5208
	21st to end	Night	25% 18% 4 11% 6% 4 3 2 3 4 20%	6996

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% 10% 16% 7% 1	3598
	11th to 20th	Day	67% 5% 9% 11% 7% 1	3600
	21st to end	Day	68% 4 7% 11% 8% 2	4327
February	1st to 10th	Day	63% 6% 9% 16% 6% 1	1800
	11th to 20th	Day	59% 4 11% 15% 10% 1	1762
	21st to end	Day	62% 5% 10% 11% 11% 1	1609
March	1st to 10th	Day	59% 4 10% 11% 15% 2	4653
	11th to 20th	Day	52% 5% 16% 15% 10% 2	4980
	21st to end	Day	49% 4 6% 20% 17% 3	5648
April	1st to 10th	Day	55% 5% 7% 18% 13% 3	2400
	11th to 20th	Day	50% 5% 7% 20% 16% 2	2374
	21st to end	Day	54% 5% 8% 16% 14% 3	2545
May	1st to 10th	Day	54% 6% 9% 18% 10% 3	6311
	11th to 20th	Day	49% 6% 11% 17% 15% 1	6322
	21st to end	Day	49% 6% 12% 21% 11% 2	6949
June	1st to 10th	Day	52% 7% 9% 18% 12% 1	2786
	11th to 20th	Day	42% 7% 13% 23% 12% 2	2660
	21st to end	Day	49% 6% 13% 19% 12% 1	2660
July	1st to 10th	Day	44% 6% 13% 24% 12% 1	4370
	11th to 20th	Day	37% 8% 15% 30% 10%	4365
	21st to end	Day	38% 7% 11% 31% 12%	4661
August	1st to 10th	Day	47% 6% 13% 22% 11%	4187
	11th to 20th	Day	45% 6% 14% 26% 8% 1	4083
	21st to end	Day	40% 7% 13% 30% 10% 1	4194
September	1st to 10th	Day	41% 6% 12% 28% 12% 1	2280
	11th to 20th	Day	36% 6% 13% 30% 15%	2280
	21st to end	Day	45% 6% 12% 26% 10%	2004
October	1st to 10th	Day	44% 5% 11% 30% 9%	3160
	11th to 20th	Day	47% 5% 13% 23% 12% 1	3140
	21st to end	Day	54% 5% 14% 20% 7%	3277
November	1st to 10th	Day	48% 6% 17% 20% 8% 1	1720
	11th to 20th	Day	56% 6% 12% 16% 9% 2	1600
	21st to end	Day	66% 6% 11% 9% 7% 1	1600
December	1st to 10th	Day	70% 5% 14% 8% 3	2600
	11th to 20th	Day	65% 4 10% 13% 6%	2986
	21st to end	Day	67% 3 7% 15% 8%	3960
January	1st to 10th	Night	65% 5% 10% 13% 6%	6349
	11th to 20th	Night	65% 5% 12% 10% 6%	6360
	21st to end	Night	67% 4 8% 8% 12% 1	6628
February	1st to 10th	Night	58% 6% 12% 17% 6% 1	2600
	11th to 20th	Night	56% 5% 11% 19% 8% 1	2535
	21st to end	Night	54% 6% 11% 18% 10% 1	2020
March	1st to 10th	Night	59% 4 7% 15% 11% 4	5197
	11th to 20th	Night	48% 7% 18% 17% 8% 2	4980
	21st to end	Night	49% 5% 9% 21% 14% 2	5284
April	1st to 10th	Night	52% 4 8% 20% 14% 2	2000
	11th to 20th	Night	48% 5% 8% 21% 16% 1	1975
	21st to end	Night	50% 7% 8% 17% 16% 3	1872
May	1st to 10th	Night	54% 5% 9% 18% 10% 3	3646
	11th to 20th	Night	41% 6% 14% 23% 14% 2	3576
	21st to end	Night	47% 6% 13% 18% 14% 1	3927
June	1st to 10th	Night	46% 7% 12% 21% 13% 1	1598
	11th to 20th	Night	37% 7% 13% 25% 17% 2	1520
	21st to end	Night	45% 6% 15% 20% 13% 1	1520
July	1st to 10th	Night	41% 7% 14% 22% 15% 1	2480
	11th to 20th	Night	37% 6% 12% 34% 11%	2472
	21st to end	Night	36% 7% 15% 29% 13% 1	2651
August	1st to 10th	Night	37% 6% 15% 27% 13% 2	2714
	11th to 20th	Night	38% 6% 15% 31% 9% 1	2812
	21st to end	Night	35% 7% 16% 30% 11% 1	3430
September	1st to 10th	Night	34% 7% 15% 29% 14% 1	1900
	11th to 20th	Night	33% 5% 14% 35% 12% 1	1900
	21st to end	Night	41% 6% 12% 30% 10% 1	2171
October	1st to 10th	Night	40% 4 12% 28% 16%	3800
	11th to 20th	Night	43% 5% 17% 24% 10%	3779
	21st to end	Night	50% 6% 15% 22% 7%	4269
November	1st to 10th	Night	48% 6% 14% 22% 10% 1	2577
	11th to 20th	Night	53% 6% 12% 19% 9% 1	2800
	21st to end	Night	60% 7% 13% 15% 5%	2800
December	1st to 10th	Night	67% 6% 13% 11% 3	4580
	11th to 20th	Night	64% 5% 8% 13% 9%	5208
	21st to end	Night	69% 4 6% 11% 9%	6996

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	23% 22% 37% 15% 4	200
	11th to 20th	Day	33% 17% 35% 11% 5%	200
	21st to end	Day	26% 23% 36% 11% 3 1	300
February	1st to 10th	Day	34% 26% 28% 11% 1	300
	11th to 20th	Day	29% 29% 36% 5%	300
	21st to end	Day	36% 18% 34% 11% 1	373
March	1st to 10th	Day	26% 24% 32% 15% 3	500
	11th to 20th	Day	26% 23% 33% 15% 3 1	500
	21st to end	Day	34% 20% 28% 12% 5% 1	550
April	1st to 10th	Day	30% 25% 27% 13% 5%	500
	11th to 20th	Day	32% 24% 23% 14% 6% 1	492
	21st to end	Day	30% 22% 31% 11% 7% 1	500
May	1st to 10th	Day	25% 18% 31% 17% 5% 3	503
	11th to 20th	Day	16% 18% 37% 19% 8% 2	527
	21st to end	Day	20% 15% 34% 19% 9% 3	573
June	1st to 10th	Day	24% 14% 36% 19% 6% 1	526
	11th to 20th	Day	15% 18% 32% 23% 10% 2	490
	21st to end	Day	20% 15% 35% 18% 9% 2	490
July	1st to 10th	Day	13% 9% 31% 31% 13% 3	485
	11th to 20th	Day	13% 11% 32% 26% 14% 3	484
	21st to end	Day	14% 10% 36% 27% 11% 3	532
August	1st to 10th	Day	16% 8% 30% 29% 13% 3	486
	11th to 20th	Day	15% 8% 28% 29% 16% 5%	479
	21st to end	Day	14% 11% 33% 24% 12% 5%	539
September	1st to 10th	Day	16% 11% 31% 23% 13% 6%	490
	11th to 20th	Day	13% 11% 24% 24% 17% 12%	490
	21st to end	Day	18% 14% 29% 22% 12% 5%	490
October	1st to 10th	Day	24% 19% 26% 15% 12% 3	490
	11th to 20th	Day	25% 22% 31% 16% 5% 1	490
	21st to end	Day	31% 20% 27% 18% 4	492
November	1st to 10th	Day	26% 18% 31% 18% 6%	354
	11th to 20th	Day	28% 22% 35% 10% 5% 2	200
	21st to end	Day	32% 24% 30% 11% 4 1	200
December	1st to 10th	Day	32% 20% 35% 11% 3 1	200
	11th to 20th	Day	34% 26% 28% 10% 2 1	200
	21st to end	Day	32% 22% 30% 10% 5%	220
January	1st to 10th	Night	27% 19% 34% 17% 4	800
	11th to 20th	Night	29% 17% 33% 16% 5% 1	800
	21st to end	Night	21% 18% 35% 22% 5%	880
February	1st to 10th	Night	22% 20% 37% 19% 2	800
	11th to 20th	Night	22% 21% 40% 15% 3	783
	21st to end	Night	22% 22% 35% 19% 2	660
March	1st to 10th	Night	24% 19% 35% 20% 3	800
	11th to 20th	Night	24% 20% 30% 21% 3 1	800
	21st to end	Night	22% 16% 35% 19% 7% 1	880
April	1st to 10th	Night	26% 17% 34% 21% 3	800
	11th to 20th	Night	23% 21% 30% 19% 6% 1	791
	21st to end	Night	22% 15% 30% 24% 8%	672
May	1st to 10th	Night	25% 9% 27% 29% 9% 1	420
	11th to 20th	Night	15% 11% 35% 31% 7%	394
	21st to end	Night	14% 8% 37% 28% 11%	433
June	1st to 10th	Night	17% 9% 35% 32% 8%	400
	11th to 20th	Night	12% 13% 31% 31% 11% 1	380
	21st to end	Night	19% 7% 29% 35% 11%	380
July	1st to 10th	Night	7% 6% 33% 39% 15% 1	370
	11th to 20th	Night	11% 5% 30% 38% 15% 1	368
	21st to end	Night	10% 4 31% 42% 12% 1	416
August	1st to 10th	Night	13% 3 28% 34% 20% 1	505
	11th to 20th	Night	13% 4 23% 36% 23% 2	564
	21st to end	Night	13% 6% 30% 30% 17% 3	803
September	1st to 10th	Night	13% 7% 33% 28% 17% 2	760
	11th to 20th	Night	14% 6% 23% 29% 24% 4	760
	21st to end	Night	20% 11% 23% 26% 17% 3	760
October	1st to 10th	Night	22% 11% 29% 21% 14% 2	760
	11th to 20th	Night	26% 16% 29% 21% 8% 1	760
	21st to end	Night	28% 16% 31% 20% 5%	836
November	1st to 10th	Night	24% 17% 31% 22% 7%	780
	11th to 20th	Night	25% 17% 33% 17% 7% 1	800
	21st to end	Night	30% 19% 27% 19% 5%	800
December	1st to 10th	Night	29% 19% 32% 17% 4	800
	11th to 20th	Night	26% 20% 34% 19% 1 1	800
	21st to end	Night	34% 15% 32% 15% 3	880

Page generated at 2025-06-07 10:28:16. Version ac07

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