Algonquin Radio Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Algonquin Radio Observatory 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	15% 11% 4 9% 6% 5% 5% 4 5% 7% 31%	150985
	Night	14% 12% 5% 11% 6% 5% 5% 3 5% 6% 29%	140744
Transparency	Day	53% 4 11% 21% 9% 1	154514
	Night	56% 4 11% 19% 9% 1	145293
Seeing	Day	24% 15% 32% 19% 8% 2	17262
	Night	23% 13% 31% 24% 8% 1	25893

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	10% 15% 7% 15% 10% 8% 6% 4 4 5% 16%	4661
	11th to 20th	Day	8% 20% 7% 20% 7% 6% 4 3 5% 5% 15%	4650
	21st to end	Day	8% 17% 8% 17% 8% 7% 5% 4 4 4 19%	5659
February	1st to 10th	Day	9% 16% 7% 15% 8% 7% 5% 4 4 5% 20%	1890
	11th to 20th	Day	10% 17% 6% 14% 7% 6% 5% 5% 5% 6% 21%	1843
	21st to end	Day	15% 16% 5% 12% 7% 6% 6% 4 4 5% 21%	1615
March	1st to 10th	Day	18% 16% 5% 12% 5% 4 4 3 4 5% 24%	4876
	11th to 20th	Day	11% 14% 5% 11% 7% 5% 4 4 6% 7% 25%	5090
	21st to end	Day	14% 13% 5% 10% 6% 5% 4 2 4 5% 33%	5676
April	1st to 10th	Day	20% 15% 5% 9% 5% 4 4 2 4 6% 27%	2520
	11th to 20th	Day	21% 13% 4 8% 4 4 3 3 4 5% 32%	2540
	21st to end	Day	20% 12% 3 7% 5% 4 4 2 3 5% 33%	2730
May	1st to 10th	Day	16% 10% 3 9% 6% 5% 5% 4 5% 7% 29%	8109
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 5% 7% 35%	8221
	21st to end	Day	19% 9% 3 7% 4 4 4 3 4 6% 38%	9060
June	1st to 10th	Day	19% 10% 3 8% 5% 5% 5% 3 6% 7% 30%	2940
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 4 6% 8% 36%	3057
	21st to end	Day	16% 7% 2 7% 6% 5% 5% 4 6% 8% 32%	3150
July	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 5% 7% 8% 36%	8761
	11th to 20th	Day	10% 5% 2 5% 4 5% 5% 4 7% 9% 46%	8280
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 10% 42%	8993
August	1st to 10th	Day	17% 7% 3 7% 5% 5% 6% 4 6% 7% 33%	6086
	11th to 20th	Day	15% 6% 2 6% 4 5% 5% 4 7% 9% 36%	5951
	21st to end	Day	12% 6% 2 7% 5% 6% 6% 5% 7% 9% 34%	6272
September	1st to 10th	Day	14% 7% 3 8% 5% 4 4 4 5% 7% 39%	2520
	11th to 20th	Day	14% 7% 3 6% 4 4 4 3 5% 7% 45%	2507
	21st to end	Day	20% 9% 3 7% 5% 4 4 4 4 7% 33%	2200
October	1st to 10th	Day	17% 11% 3 7% 5% 5% 3 3 4 6% 35%	2100
	11th to 20th	Day	21% 15% 4 9% 5% 5% 4 3 4 6% 24%	2030
	21st to end	Day	25% 16% 5% 9% 5% 4 5% 3 4 4 20%	2139
November	1st to 10th	Day	17% 15% 5% 9% 5% 4 4 3 5% 6% 28%	1705
	11th to 20th	Day	15% 18% 7% 10% 7% 5% 4 3 5% 5% 21%	1680
	21st to end	Day	19% 20% 8% 13% 7% 4 4 3 4 3 15%	1680
December	1st to 10th	Day	15% 23% 8% 14% 7% 5% 5% 4 4 3 11%	2680
	11th to 20th	Day	15% 19% 7% 15% 9% 5% 4 2 2 4 20%	3066
	21st to end	Day	18% 20% 7% 17% 6% 3 4 2 3 3 17%	4048
January	1st to 10th	Night	10% 17% 9% 19% 10% 6% 5% 3 4 4 13%	8234
	11th to 20th	Night	9% 16% 7% 19% 9% 7% 6% 4 5% 5% 15%	8235
	21st to end	Night	7% 16% 8% 16% 8% 9% 6% 5% 5% 5% 17%	8521
February	1st to 10th	Night	10% 14% 6% 12% 9% 6% 5% 4 6% 6% 21%	2730
	11th to 20th	Night	11% 15% 6% 13% 8% 6% 5% 3 5% 5% 24%	2663
	21st to end	Night	12% 16% 6% 13% 8% 6% 4 3 5% 6% 21%	2191
March	1st to 10th	Night	15% 16% 5% 10% 5% 5% 5% 4 4 4 27%	5168
	11th to 20th	Night	10% 14% 5% 11% 6% 5% 5% 4 6% 7% 25%	5089
	21st to end	Night	15% 12% 5% 11% 6% 5% 4 4 4 5% 29%	5497
April	1st to 10th	Night	19% 14% 4 9% 5% 4 4 3 4 4 30%	2100
	11th to 20th	Night	18% 12% 4 6% 5% 4 4 3 5% 5% 35%	2047
	21st to end	Night	20% 10% 3 8% 6% 5% 4 3 4 7% 31%	1890
May	1st to 10th	Night	18% 9% 3 6% 4 5% 5% 4 6% 8% 33%	4787
	11th to 20th	Night	15% 7% 3 6% 5% 4 4 3 5% 7% 39%	4639
	21st to end	Night	18% 7% 3 7% 4 4 4 4 5% 6% 38%	5114
June	1st to 10th	Night	14% 9% 4 8% 6% 4 5% 3 5% 8% 34%	1680
	11th to 20th	Night	15% 6% 2 6% 4 4 3 3 6% 8% 42%	1555
	21st to end	Night	16% 7% 2 7% 4 4 5% 4 7% 7% 36%	1470
July	1st to 10th	Night	12% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	4216
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 5% 7% 48%	4680
	21st to end	Night	12% 6% 2 7% 4 4 4 3 5% 7% 45%	5084
August	1st to 10th	Night	13% 5% 2 6% 4 4 5% 4 7% 8% 41%	4059
	11th to 20th	Night	15% 6% 2 6% 4 4 4 4 6% 8% 42%	4095
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 8% 41%	4805
September	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 8% 46%	2100
	11th to 20th	Night	14% 7% 2 6% 4 3 3 3 4 6% 48%	2110
	21st to end	Night	17% 7% 3 6% 4 3 4 3 5% 6% 42%	2420
October	1st to 10th	Night	18% 9% 3 6% 4 3 4 3 4 6% 39%	2520
	11th to 20th	Night	20% 13% 3 8% 5% 5% 5% 3 5% 5% 29%	2437
	21st to end	Night	23% 12% 4 9% 6% 4 4 4 4 5% 24%	2700
November	1st to 10th	Night	15% 14% 5% 8% 6% 5% 4 3 5% 5% 30%	2810
	11th to 20th	Night	15% 16% 5% 10% 6% 5% 5% 3 5% 5% 23%	2940
	21st to end	Night	19% 19% 6% 13% 6% 5% 4 3 4 5% 17%	2940
December	1st to 10th	Night	16% 21% 7% 16% 8% 5% 5% 3 4 5% 10%	4720
	11th to 20th	Night	15% 18% 6% 14% 7% 5% 4 3 4 4 20%	5348
	21st to end	Night	20% 19% 6% 16% 7% 4 4 3 3 4 15%	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	71% 4 9% 11% 5% 1	4662
	11th to 20th	Day	72% 3 7% 9% 8%	4680
	21st to end	Day	69% 3 6% 12% 8% 1	5659
February	1st to 10th	Day	67% 3 8% 14% 7% 1	1890
	11th to 20th	Day	64% 4 10% 13% 8% 1	1852
	21st to end	Day	66% 3 6% 15% 9% 1	1615
March	1st to 10th	Day	63% 3 9% 11% 12% 2	4879
	11th to 20th	Day	57% 4 14% 15% 8% 1	5090
	21st to end	Day	56% 3 7% 19% 13% 2	5676
April	1st to 10th	Day	60% 3 7% 19% 9% 2	2520
	11th to 20th	Day	55% 3 6% 22% 12% 1	2540
	21st to end	Day	55% 3 7% 18% 14% 2	2730
May	1st to 10th	Day	53% 5% 8% 22% 8% 4	8120
	11th to 20th	Day	49% 5% 9% 25% 11% 1	8225
	21st to end	Day	49% 3 9% 22% 14% 2	9061
June	1st to 10th	Day	53% 5% 9% 20% 13% 1	2940
	11th to 20th	Day	45% 5% 11% 24% 13% 2	3057
	21st to end	Day	48% 5% 12% 22% 11% 1	3150
July	1st to 10th	Day	43% 6% 15% 25% 11%	8689
	11th to 20th	Day	34% 4 14% 36% 10% 1	8205
	21st to end	Day	37% 5% 16% 31% 10%	8795
August	1st to 10th	Day	49% 5% 12% 24% 9% 1	6072
	11th to 20th	Day	42% 6% 19% 26% 7%	5990
	21st to end	Day	43% 6% 16% 27% 7% 1	6272
September	1st to 10th	Day	43% 6% 13% 27% 11%	2520
	11th to 20th	Day	40% 4 12% 31% 13%	2507
	21st to end	Day	51% 6% 10% 22% 11%	2200
October	1st to 10th	Day	52% 4 10% 27% 7%	3360
	11th to 20th	Day	57% 4 11% 19% 8%	3270
	21st to end	Day	65% 4 13% 13% 4 1	3429
November	1st to 10th	Day	57% 4 13% 20% 6%	1705
	11th to 20th	Day	66% 5% 10% 12% 7% 1	1680
	21st to end	Day	74% 4 9% 9% 4	1680
December	1st to 10th	Day	76% 5% 8% 9% 2	2680
	11th to 20th	Day	72% 2 5% 13% 8%	3066
	21st to end	Day	74% 3 4 14% 5%	4048
January	1st to 10th	Night	76% 3 8% 9% 4	8234
	11th to 20th	Night	72% 3 9% 8% 7%	8280
	21st to end	Night	69% 3 7% 11% 10%	8521
February	1st to 10th	Night	63% 4 11% 14% 8% 1	2730
	11th to 20th	Night	62% 4 10% 17% 6% 1	2665
	21st to end	Night	63% 4 8% 17% 7% 1	2191
March	1st to 10th	Night	61% 3 9% 14% 9% 4	5178
	11th to 20th	Night	55% 7% 15% 15% 8% 1	5090
	21st to end	Night	56% 4 8% 18% 12% 2	5497
April	1st to 10th	Night	58% 3 8% 18% 12% 2	2100
	11th to 20th	Night	51% 3 7% 24% 13% 2	2047
	21st to end	Night	54% 4 7% 18% 14% 2	1890
May	1st to 10th	Night	47% 5% 9% 25% 10% 4	4793
	11th to 20th	Night	43% 6% 11% 24% 14% 2	4640
	21st to end	Night	46% 4 10% 25% 12% 1	5115
June	1st to 10th	Night	48% 6% 10% 21% 14% 1	1680
	11th to 20th	Night	39% 5% 12% 28% 15% 2	1555
	21st to end	Night	44% 7% 14% 23% 12% 1	1470
July	1st to 10th	Night	42% 6% 15% 25% 11% 1	4180
	11th to 20th	Night	36% 5% 16% 32% 12%	4632
	21st to end	Night	38% 5% 12% 33% 12%	4967
August	1st to 10th	Night	39% 6% 16% 25% 13% 1	4049
	11th to 20th	Night	39% 6% 21% 28% 6%	4122
	21st to end	Night	41% 5% 15% 30% 8% 2	4805
September	1st to 10th	Night	36% 5% 17% 29% 12% 1	2100
	11th to 20th	Night	38% 4 14% 31% 13%	2110
	21st to end	Night	43% 5% 13% 26% 12% 1	2420
October	1st to 10th	Night	43% 4 12% 29% 12%	4040
	11th to 20th	Night	52% 4 14% 19% 11%	3936
	21st to end	Night	56% 5% 17% 15% 6%	4348
November	1st to 10th	Night	55% 4 14% 19% 7%	2810
	11th to 20th	Night	62% 4 12% 15% 6% 1	2940
	21st to end	Night	71% 5% 10% 12% 3	2940
December	1st to 10th	Night	77% 4 10% 7% 2	4720
	11th to 20th	Night	67% 4 7% 11% 10%	5348
	21st to end	Night	74% 3 6% 12% 5%	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	20% 20% 40% 15% 5%	220
	11th to 20th	Day	27% 17% 32% 18% 4 1	220
	21st to end	Day	24% 19% 34% 17% 6%	341
February	1st to 10th	Day	29% 23% 31% 12% 3 1	330
	11th to 20th	Day	27% 25% 40% 8% 1	330
	21st to end	Day	34% 17% 37% 11% 1	331
March	1st to 10th	Day	30% 19% 37% 13% 2	540
	11th to 20th	Day	30% 18% 34% 15% 4 1	540
	21st to end	Day	30% 21% 30% 15% 4 1	594
April	1st to 10th	Day	30% 21% 30% 14% 5% 1	540
	11th to 20th	Day	37% 17% 22% 15% 5% 3	532
	21st to end	Day	31% 14% 33% 14% 6% 1	540
May	1st to 10th	Day	29% 15% 30% 17% 7% 2	543
	11th to 20th	Day	23% 17% 29% 21% 8% 3	567
	21st to end	Day	24% 16% 30% 20% 7% 2	617
June	1st to 10th	Day	26% 11% 34% 23% 6% 1	570
	11th to 20th	Day	21% 14% 32% 23% 9% 2	687
	21st to end	Day	21% 14% 35% 21% 8% 2	780
July	1st to 10th	Day	13% 11% 35% 30% 10% 1	732
	11th to 20th	Day	16% 13% 34% 23% 10% 3	564
	21st to end	Day	13% 11% 35% 29% 11% 2	620
August	1st to 10th	Day	16% 8% 32% 28% 11% 4	566
	11th to 20th	Day	16% 8% 28% 28% 14% 5%	559
	21st to end	Day	15% 12% 33% 22% 12% 4	627
September	1st to 10th	Day	20% 10% 32% 19% 14% 5%	570
	11th to 20th	Day	17% 9% 25% 25% 15% 9%	570
	21st to end	Day	22% 12% 26% 22% 14% 4	570
October	1st to 10th	Day	22% 16% 28% 19% 11% 3	570
	11th to 20th	Day	31% 19% 29% 15% 4 1	542
	21st to end	Day	35% 14% 31% 16% 4	549
November	1st to 10th	Day	33% 18% 34% 10% 5%	279
	11th to 20th	Day	28% 19% 36% 10% 5%	220
	21st to end	Day	37% 19% 33% 9% 2	220
December	1st to 10th	Day	33% 15% 34% 14% 5%	220
	11th to 20th	Day	32% 25% 32% 7% 2 1	220
	21st to end	Day	36% 16% 29% 12% 6% 2	242
January	1st to 10th	Night	23% 17% 37% 18% 4	840
	11th to 20th	Night	24% 18% 33% 19% 5% 1	840
	21st to end	Night	18% 15% 35% 25% 7% 1	924
February	1st to 10th	Night	18% 21% 37% 20% 4	840
	11th to 20th	Night	20% 19% 38% 19% 4	823
	21st to end	Night	24% 18% 34% 22% 2	692
March	1st to 10th	Night	22% 20% 35% 19% 3	840
	11th to 20th	Night	25% 18% 33% 18% 5% 1	840
	21st to end	Night	22% 16% 33% 22% 6%	924
April	1st to 10th	Night	30% 15% 31% 20% 4	840
	11th to 20th	Night	28% 15% 29% 20% 8%	803
	21st to end	Night	26% 11% 27% 26% 9%	630
May	1st to 10th	Night	24% 8% 27% 33% 8%	469
	11th to 20th	Night	21% 9% 36% 26% 7% 1	414
	21st to end	Night	17% 9% 33% 30% 10%	455
June	1st to 10th	Night	18% 9% 36% 30% 7%	420
	11th to 20th	Night	19% 9% 29% 32% 11%	420
	21st to end	Night	20% 8% 29% 33% 10% 1	420
July	1st to 10th	Night	14% 6% 32% 36% 12%	410
	11th to 20th	Night	10% 7% 29% 39% 14%	408
	21st to end	Night	9% 6% 34% 33% 17%	460
August	1st to 10th	Night	15% 5% 23% 37% 19% 1	590
	11th to 20th	Night	14% 4 22% 37% 21% 2	624
	21st to end	Night	15% 7% 30% 33% 13% 3	810
September	1st to 10th	Night	16% 8% 28% 31% 15% 2	840
	11th to 20th	Night	19% 5% 25% 28% 19% 3	840
	21st to end	Night	21% 8% 24% 27% 18% 2	840
October	1st to 10th	Night	25% 10% 30% 25% 10% 1	840
	11th to 20th	Night	29% 13% 31% 19% 7% 1	813
	21st to end	Night	31% 14% 26% 24% 4	880
November	1st to 10th	Night	29% 15% 27% 22% 7%	820
	11th to 20th	Night	26% 18% 32% 16% 8%	840
	21st to end	Night	32% 17% 27% 21% 4	840
December	1st to 10th	Night	31% 15% 35% 14% 5%	840
	11th to 20th	Night	25% 21% 30% 19% 4 1	840
	21st to end	Night	34% 14% 30% 19% 3 1	924

Page generated at 2026-10-11 05:06:27. Version ac07

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