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 2026-10-14.

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% 10% 4 8% 5% 5% 4 4 5% 7% 32%	150129
	Night	15% 11% 4 9% 5% 5% 4 3 5% 6% 32%	141605
Transparency	Day	50% 6% 11% 21% 11% 1	153648
	Night	51% 5% 12% 20% 11% 1	146175
Seeing	Day	23% 18% 32% 18% 8% 2	16914
	Night	22% 14% 32% 23% 8% 1	26015

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% 5% 13% 8% 5% 6% 4 5% 6% 20%	4661
	11th to 20th	Day	11% 22% 9% 14% 6% 6% 4 3 3 4 17%	4650
	21st to end	Day	10% 16% 7% 17% 7% 7% 5% 3 4 5% 18%	5599
February	1st to 10th	Day	13% 16% 5% 12% 6% 5% 4 4 6% 5% 22%	1890
	11th to 20th	Day	12% 16% 5% 10% 7% 4 4 4 5% 5% 28%	1843
	21st to end	Day	19% 15% 4 10% 6% 6% 4 3 4 5% 24%	1687
March	1st to 10th	Day	18% 14% 5% 10% 5% 4 4 3 5% 5% 28%	4753
	11th to 20th	Day	11% 14% 4 9% 5% 5% 6% 4 5% 7% 30%	5090
	21st to end	Day	18% 12% 4 7% 4 3 3 3 3 4 38%	5773
April	1st to 10th	Day	20% 13% 4 7% 5% 4 4 3 4 6% 30%	2520
	11th to 20th	Day	21% 11% 3 7% 3 4 3 2 5% 5% 35%	2494
	21st to end	Day	21% 10% 4 7% 5% 5% 4 3 4 5% 32%	2672
May	1st to 10th	Day	21% 8% 3 8% 5% 5% 5% 4 5% 6% 30%	8177
	11th to 20th	Day	16% 9% 3 7% 5% 5% 5% 4 5% 7% 34%	8221
	21st to end	Day	19% 8% 3 6% 4 4 4 3 5% 7% 36%	9060
June	1st to 10th	Day	19% 9% 2 8% 5% 5% 5% 4 5% 6% 31%	2940
	11th to 20th	Day	15% 6% 3 6% 5% 5% 5% 5% 8% 8% 36%	2940
	21st to end	Day	16% 7% 3 8% 5% 5% 5% 4 6% 8% 34%	2940
July	1st to 10th	Day	12% 7% 2 7% 5% 6% 5% 4 6% 10% 37%	8280
	11th to 20th	Day	9% 4 2 5% 4 5% 5% 4 6% 10% 46%	8280
	21st to end	Day	11% 6% 2 6% 4 5% 5% 5% 7% 10% 40%	8993
August	1st to 10th	Day	17% 9% 3 8% 5% 5% 5% 4 5% 6% 34%	6156
	11th to 20th	Day	14% 6% 2 7% 4 5% 5% 5% 6% 9% 36%	5951
	21st to end	Day	13% 6% 3 7% 5% 5% 5% 5% 7% 9% 34%	6108
September	1st to 10th	Day	14% 7% 2 6% 5% 4 4 4 5% 7% 41%	2520
	11th to 20th	Day	11% 5% 3 6% 4 4 4 4 5% 7% 48%	2520
	21st to end	Day	19% 6% 3 6% 5% 4 5% 4 4 7% 39%	2214
October	1st to 10th	Day	20% 8% 3 7% 4 3 3 3 5% 6% 37%	2100
	11th to 20th	Day	21% 10% 2 8% 5% 6% 4 3 5% 7% 28%	2030
	21st to end	Day	25% 11% 3 8% 5% 5% 5% 3 4 6% 25%	2105
November	1st to 10th	Day	15% 9% 3 9% 5% 5% 5% 5% 5% 6% 33%	1808
	11th to 20th	Day	16% 14% 6% 8% 5% 6% 4 4 4 5% 28%	1680
	21st to end	Day	21% 16% 6% 11% 5% 5% 4 3 4 6% 19%	1680
December	1st to 10th	Day	21% 21% 5% 11% 7% 5% 4 3 4 4 17%	2680
	11th to 20th	Day	17% 19% 6% 13% 5% 4 3 3 4 4 23%	3066
	21st to end	Day	23% 19% 5% 11% 5% 3 3 2 3 5% 22%	4048
January	1st to 10th	Night	14% 14% 9% 15% 7% 6% 4 3 4 5% 20%	8234
	11th to 20th	Night	11% 19% 7% 15% 8% 6% 5% 3 4 5% 17%	8235
	21st to end	Night	11% 15% 7% 13% 6% 6% 5% 3 5% 5% 23%	8581
February	1st to 10th	Night	12% 16% 5% 10% 6% 6% 5% 4 6% 7% 24%	2730
	11th to 20th	Night	13% 13% 6% 10% 6% 5% 5% 3 6% 5% 29%	2663
	21st to end	Night	12% 15% 5% 8% 6% 5% 5% 5% 6% 7% 27%	2118
March	1st to 10th	Night	20% 14% 4 9% 5% 5% 4 2 3 5% 29%	5303
	11th to 20th	Night	11% 13% 3 8% 5% 5% 5% 5% 7% 8% 29%	5089
	21st to end	Night	18% 10% 4 7% 5% 4 4 3 5% 5% 35%	5401
April	1st to 10th	Night	20% 11% 4 7% 5% 3 4 4 4 6% 32%	2100
	11th to 20th	Night	19% 10% 3 6% 5% 4 3 3 4 5% 37%	2075
	21st to end	Night	19% 9% 3 7% 4 4 4 4 5% 6% 34%	1966
May	1st to 10th	Night	21% 8% 3 7% 4 5% 4 4 6% 8% 29%	4720
	11th to 20th	Night	14% 8% 3 7% 4 4 4 3 5% 7% 41%	4639
	21st to end	Night	18% 6% 2 6% 4 4 5% 4 6% 8% 37%	5114
June	1st to 10th	Night	14% 7% 2 7% 6% 5% 5% 3 7% 8% 35%	1680
	11th to 20th	Night	12% 6% 3 6% 4 4 4 4 6% 7% 43%	1680
	21st to end	Night	16% 7% 3 7% 5% 5% 5% 3 6% 8% 36%	1680
July	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 4 6% 9% 41%	4680
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 6% 7% 50%	4680
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 7% 46%	5084
August	1st to 10th	Night	15% 7% 2 7% 4 4 4 4 6% 7% 40%	3989
	11th to 20th	Night	12% 5% 2 6% 3 4 4 3 5% 8% 47%	4095
	21st to end	Night	11% 6% 2 7% 4 4 5% 4 7% 9% 41%	4971
September	1st to 10th	Night	11% 5% 2 6% 5% 3 4 4 5% 7% 48%	2100
	11th to 20th	Night	12% 4 2 4 4 4 4 4 5% 6% 52%	2100
	21st to end	Night	17% 6% 2 6% 4 3 4 3 5% 6% 44%	2401
October	1st to 10th	Night	17% 8% 2 6% 4 4 4 3 5% 6% 41%	2520
	11th to 20th	Night	20% 11% 3 7% 6% 4 5% 3 5% 6% 32%	2437
	21st to end	Night	22% 12% 3 7% 5% 4 4 3 5% 6% 30%	2733
November	1st to 10th	Night	16% 11% 3 6% 4 4 5% 4 5% 6% 35%	2709
	11th to 20th	Night	17% 13% 4 8% 5% 4 5% 4 5% 6% 30%	2940
	21st to end	Night	20% 15% 5% 8% 5% 5% 5% 3 5% 5% 23%	2940
December	1st to 10th	Night	19% 18% 5% 11% 6% 5% 5% 4 5% 6% 17%	4720
	11th to 20th	Night	21% 16% 5% 10% 6% 4 4 3 4 4 24%	5348
	21st to end	Night	25% 18% 4 11% 6% 4 3 2 3 4 20%	7150

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	63% 5% 10% 15% 6% 1	4662
	11th to 20th	Day	71% 4 7% 9% 8% 1	4680
	21st to end	Day	68% 4 7% 11% 8% 1	5599
February	1st to 10th	Day	62% 6% 8% 16% 6% 1	1890
	11th to 20th	Day	59% 4 11% 16% 10% 1	1852
	21st to end	Day	62% 5% 10% 12% 10% 1	1687
March	1st to 10th	Day	58% 4 10% 11% 14% 2	4756
	11th to 20th	Day	53% 5% 15% 15% 10% 2	5090
	21st to end	Day	50% 4 6% 20% 17% 3	5773
April	1st to 10th	Day	55% 4 7% 17% 13% 3	2520
	11th to 20th	Day	51% 5% 7% 20% 16% 2	2494
	21st to end	Day	54% 5% 8% 16% 14% 3	2672
May	1st to 10th	Day	52% 6% 8% 19% 11% 2	8189
	11th to 20th	Day	48% 6% 11% 20% 14% 1	8225
	21st to end	Day	48% 5% 10% 24% 12% 1	9061
June	1st to 10th	Day	52% 7% 9% 18% 13% 1	2940
	11th to 20th	Day	43% 7% 13% 23% 12% 2	2940
	21st to end	Day	47% 6% 13% 20% 12% 1	2940
July	1st to 10th	Day	41% 6% 16% 26% 11%	8210
	11th to 20th	Day	32% 7% 13% 32% 16% 1	8205
	21st to end	Day	37% 7% 14% 33% 9%	8795
August	1st to 10th	Day	50% 6% 12% 18% 12% 2	6142
	11th to 20th	Day	42% 7% 16% 28% 7% 1	5990
	21st to end	Day	43% 7% 17% 25% 8%	6108
September	1st to 10th	Day	41% 6% 12% 29% 12%	2520
	11th to 20th	Day	35% 6% 12% 32% 15%	2520
	21st to end	Day	45% 6% 12% 25% 12%	2214
October	1st to 10th	Day	44% 5% 11% 30% 10% 1	3360
	11th to 20th	Day	47% 5% 13% 22% 12% 1	3270
	21st to end	Day	54% 5% 14% 20% 7%	3382
November	1st to 10th	Day	49% 6% 16% 20% 8% 1	1808
	11th to 20th	Day	57% 5% 12% 16% 9% 1	1680
	21st to end	Day	66% 6% 10% 10% 7%	1680
December	1st to 10th	Day	70% 5% 13% 8% 3	2680
	11th to 20th	Day	65% 4 10% 13% 6%	3066
	21st to end	Day	67% 3 7% 15% 8%	4048
January	1st to 10th	Night	67% 5% 10% 12% 6%	8234
	11th to 20th	Night	68% 4 10% 10% 7%	8280
	21st to end	Night	63% 5% 7% 12% 13% 1	8581
February	1st to 10th	Night	57% 6% 12% 17% 7% 1	2730
	11th to 20th	Night	56% 5% 11% 19% 8% 1	2665
	21st to end	Night	55% 6% 11% 18% 10% 1	2118
March	1st to 10th	Night	59% 4 7% 15% 11% 4	5313
	11th to 20th	Night	48% 7% 17% 17% 8% 2	5090
	21st to end	Night	50% 5% 8% 21% 14% 2	5401
April	1st to 10th	Night	52% 4 8% 20% 13% 2	2100
	11th to 20th	Night	49% 5% 8% 21% 16% 1	2075
	21st to end	Night	50% 6% 7% 18% 16% 3	1966
May	1st to 10th	Night	52% 6% 9% 20% 10% 3	4726
	11th to 20th	Night	42% 6% 13% 24% 14% 2	4640
	21st to end	Night	44% 6% 12% 20% 16% 1	5115
June	1st to 10th	Night	45% 7% 12% 21% 14% 1	1680
	11th to 20th	Night	38% 6% 13% 25% 16% 2	1680
	21st to end	Night	45% 6% 14% 21% 12% 1	1680
July	1st to 10th	Night	39% 6% 18% 23% 14% 1	4640
	11th to 20th	Night	32% 5% 13% 33% 15% 1	4632
	21st to end	Night	37% 6% 11% 31% 14%	4967
August	1st to 10th	Night	43% 6% 14% 21% 13% 4	3979
	11th to 20th	Night	35% 6% 16% 34% 8% 1	4122
	21st to end	Night	37% 7% 18% 28% 8% 1	4971
September	1st to 10th	Night	34% 7% 14% 30% 13% 1	2100
	11th to 20th	Night	32% 5% 14% 36% 12% 1	2100
	21st to end	Night	41% 6% 11% 29% 12% 1	2401
October	1st to 10th	Night	39% 4 11% 28% 17%	4040
	11th to 20th	Night	44% 5% 17% 24% 10%	3936
	21st to end	Night	49% 6% 15% 23% 8%	4406
November	1st to 10th	Night	48% 6% 14% 22% 10% 1	2709
	11th to 20th	Night	53% 6% 12% 19% 9% 1	2940
	21st to end	Night	60% 7% 12% 15% 5%	2940
December	1st to 10th	Night	66% 6% 13% 11% 3	4720
	11th to 20th	Night	64% 4 8% 14% 9%	5348
	21st to end	Night	69% 4 6% 11% 9%	7150

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% 21% 38% 15% 3	220
	11th to 20th	Day	35% 16% 33% 10% 5%	220
	21st to end	Day	25% 24% 35% 12% 3 1	330
February	1st to 10th	Day	32% 25% 29% 12% 2	330
	11th to 20th	Day	28% 28% 38% 6%	330
	21st to end	Day	35% 19% 35% 10% 1	403
March	1st to 10th	Day	26% 24% 33% 14% 3	540
	11th to 20th	Day	28% 22% 32% 14% 3 1	540
	21st to end	Day	34% 21% 28% 12% 5% 1	594
April	1st to 10th	Day	31% 25% 27% 13% 4	540
	11th to 20th	Day	32% 24% 23% 14% 5% 1	532
	21st to end	Day	29% 21% 31% 11% 6% 1	540
May	1st to 10th	Day	26% 19% 32% 16% 5% 3	543
	11th to 20th	Day	17% 19% 37% 18% 8% 1	567
	21st to end	Day	21% 16% 33% 18% 9% 3	617
June	1st to 10th	Day	23% 15% 35% 19% 6% 1	570
	11th to 20th	Day	15% 19% 34% 22% 9% 1	570
	21st to end	Day	19% 15% 36% 19% 9% 2	570
July	1st to 10th	Day	13% 9% 33% 30% 12% 2	565
	11th to 20th	Day	13% 12% 33% 25% 13% 2	564
	21st to end	Day	14% 12% 35% 27% 10% 3	620
August	1st to 10th	Day	15% 9% 30% 30% 13% 3	566
	11th to 20th	Day	15% 8% 29% 28% 16% 5%	559
	21st to end	Day	15% 11% 33% 24% 12% 5%	627
September	1st to 10th	Day	17% 11% 31% 23% 11% 6%	570
	11th to 20th	Day	12% 11% 25% 26% 16% 11%	570
	21st to end	Day	18% 13% 31% 21% 12% 5%	570
October	1st to 10th	Day	24% 19% 26% 16% 12% 3	570
	11th to 20th	Day	25% 23% 32% 15% 4 1	542
	21st to end	Day	30% 21% 27% 18% 3	531
November	1st to 10th	Day	27% 19% 31% 17% 6%	382
	11th to 20th	Day	27% 24% 33% 10% 5% 1	220
	21st to end	Day	34% 22% 30% 10% 3	220
December	1st to 10th	Day	31% 20% 36% 10% 3	220
	11th to 20th	Day	34% 25% 29% 9% 2 1	220
	21st to end	Day	33% 22% 31% 10% 4	242
January	1st to 10th	Night	26% 19% 34% 17% 3	840
	11th to 20th	Night	30% 17% 33% 16% 4	840
	21st to end	Night	21% 18% 35% 22% 5%	924
February	1st to 10th	Night	21% 20% 37% 20% 2	840
	11th to 20th	Night	22% 20% 41% 15% 3	823
	21st to end	Night	22% 22% 35% 19% 2	692
March	1st to 10th	Night	24% 19% 35% 20% 2	840
	11th to 20th	Night	25% 20% 30% 20% 3 1	840
	21st to end	Night	23% 17% 35% 18% 7% 1	924
April	1st to 10th	Night	26% 17% 34% 20% 3	840
	11th to 20th	Night	24% 21% 30% 20% 5% 1	831
	21st to end	Night	22% 15% 31% 23% 8%	706
May	1st to 10th	Night	24% 10% 28% 28% 9% 1	441
	11th to 20th	Night	16% 12% 35% 30% 7%	414
	21st to end	Night	15% 9% 38% 27% 11%	455
June	1st to 10th	Night	17% 9% 34% 32% 8%	420
	11th to 20th	Night	13% 14% 33% 30% 10% 1	420
	21st to end	Night	18% 7% 28% 36% 10%	420
July	1st to 10th	Night	7% 6% 33% 39% 14%	410
	11th to 20th	Night	10% 7% 30% 38% 14% 1	408
	21st to end	Night	10% 5% 32% 41% 12% 1	460
August	1st to 10th	Night	13% 4 27% 36% 19% 1	559
	11th to 20th	Night	13% 3 24% 36% 22% 2	624
	21st to end	Night	13% 7% 30% 30% 17% 2	887
September	1st to 10th	Night	13% 7% 33% 29% 17% 2	840
	11th to 20th	Night	14% 6% 23% 30% 23% 4	840
	21st to end	Night	20% 11% 24% 25% 17% 2	840
October	1st to 10th	Night	21% 12% 30% 22% 13% 2	840
	11th to 20th	Night	25% 16% 30% 20% 8%	813
	21st to end	Night	27% 16% 31% 21% 5%	880
November	1st to 10th	Night	25% 17% 31% 21% 6%	820
	11th to 20th	Night	25% 17% 33% 17% 7% 1	840
	21st to end	Night	30% 19% 27% 19% 5%	840
December	1st to 10th	Night	29% 19% 31% 18% 3	840
	11th to 20th	Night	27% 20% 34% 18% 1	840
	21st to end	Night	34% 15% 32% 15% 3	924

Page generated at 2026-10-11 05:06:28. Version ac07

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