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 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	15% 12% 4 10% 6% 5% 4 4 5% 6% 29%	120464
	Night	14% 13% 5% 11% 6% 5% 4 3 5% 6% 28%	117732
Transparency	Day	55% 4 10% 20% 9% 1	124036
	Night	57% 4 11% 18% 9% 1	122310
Seeing	Day	25% 15% 32% 19% 8% 2	15450
	Night	23% 13% 31% 24% 8% 1	24281

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	11% 16% 7% 16% 11% 8% 5% 3 4 5% 14%	3597
	11th to 20th	Day	10% 17% 6% 17% 8% 7% 5% 4 5% 5% 16%	3570
	21st to end	Day	11% 21% 9% 15% 6% 5% 4 3 4 5% 19%	4373
February	1st to 10th	Day	9% 16% 7% 15% 9% 7% 5% 4 4 5% 20%	1800
	11th to 20th	Day	10% 17% 6% 14% 7% 6% 5% 4 5% 6% 21%	1753
	21st to end	Day	16% 16% 4 11% 7% 6% 6% 4 4 5% 21%	1540
March	1st to 10th	Day	18% 16% 5% 12% 5% 4 4 3 4 5% 24%	4770
	11th to 20th	Day	11% 14% 5% 11% 7% 5% 4 4 6% 7% 26%	4980
	21st to end	Day	14% 13% 5% 10% 6% 5% 4 2 4 5% 33%	5553
April	1st to 10th	Day	21% 15% 4 9% 5% 4 4 2 4 6% 28%	2400
	11th to 20th	Day	20% 12% 4 7% 4 4 3 3 4 5% 33%	2418
	21st to end	Day	20% 12% 3 8% 5% 4 4 2 4 5% 33%	2600
May	1st to 10th	Day	19% 11% 3 8% 5% 5% 4 3 4 6% 31%	6245
	11th to 20th	Day	14% 9% 3 8% 5% 4 4 3 5% 7% 37%	6318
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 4 5% 35%	6949
June	1st to 10th	Day	19% 10% 3 8% 6% 5% 5% 3 6% 7% 29%	2786
	11th to 20th	Day	15% 5% 3 7% 5% 5% 5% 4 6% 8% 37%	2765
	21st to end	Day	17% 8% 2 7% 6% 5% 5% 4 6% 8% 31%	2850
July	1st to 10th	Day	14% 7% 3 7% 6% 5% 5% 5% 7% 8% 33%	4698
	11th to 20th	Day	12% 6% 3 6% 5% 6% 5% 4 7% 8% 38%	4440
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 7% 45%	4814
August	1st to 10th	Day	13% 7% 3 7% 6% 6% 7% 4 6% 8% 32%	4147
	11th to 20th	Day	17% 7% 2 7% 4 5% 5% 5% 6% 8% 35%	4044
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 9% 40%	4315
September	1st to 10th	Day	14% 7% 3 7% 5% 4 4 4 5% 7% 40%	2280
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 5% 6% 44%	2269
	21st to end	Day	21% 9% 3 7% 5% 4 5% 4 4 7% 32%	1990
October	1st to 10th	Day	18% 11% 3 7% 5% 5% 4 3 4 6% 34%	1900
	11th to 20th	Day	22% 15% 4 9% 5% 5% 4 3 4 6% 23%	1900
	21st to end	Day	25% 16% 5% 9% 5% 4 5% 3 4 4 19%	2032
November	1st to 10th	Day	16% 14% 5% 9% 5% 4 4 3 6% 6% 28%	1622
	11th to 20th	Day	16% 17% 7% 10% 7% 5% 4 3 5% 5% 22%	1600
	21st to end	Day	19% 19% 8% 13% 7% 4 4 4 4 3 15%	1600
December	1st to 10th	Day	15% 23% 8% 14% 7% 5% 5% 4 4 3 11%	2600
	11th to 20th	Day	15% 19% 7% 15% 8% 5% 4 2 2 4 20%	2986
	21st to end	Day	18% 20% 7% 17% 6% 3 4 2 3 3 17%	3960
January	1st to 10th	Night	11% 19% 10% 18% 9% 6% 4 2 4 4 13%	6349
	11th to 20th	Night	9% 14% 6% 18% 10% 8% 6% 4 5% 5% 15%	6315
	21st to end	Night	9% 19% 9% 15% 6% 7% 6% 4 4 4 17%	6582
February	1st to 10th	Night	11% 15% 6% 12% 9% 6% 5% 4 6% 6% 20%	2600
	11th to 20th	Night	11% 15% 6% 12% 8% 6% 5% 3 5% 5% 24%	2533
	21st to end	Night	12% 16% 5% 13% 8% 6% 4 3 5% 6% 22%	2090
March	1st to 10th	Night	15% 16% 5% 10% 5% 5% 5% 4 4 4 27%	5054
	11th to 20th	Night	10% 14% 5% 11% 6% 5% 5% 4 7% 7% 26%	4979
	21st to end	Night	15% 12% 5% 11% 6% 5% 4 4 5% 6% 29%	5378
April	1st to 10th	Night	19% 14% 4 9% 5% 4 4 3 5% 4 30%	2000
	11th to 20th	Night	18% 11% 3 6% 5% 4 3 3 5% 5% 35%	1948
	21st to end	Night	20% 10% 3 8% 6% 5% 4 3 4 7% 31%	1800
May	1st to 10th	Night	21% 9% 2 6% 4 4 5% 4 6% 7% 32%	3693
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 6% 8% 42%	3575
	21st to end	Night	18% 9% 3 8% 5% 4 4 4 5% 5% 35%	3926
June	1st to 10th	Night	14% 9% 4 8% 6% 4 5% 3 6% 8% 33%	1598
	11th to 20th	Night	14% 6% 2 7% 4 4 3 3 6% 9% 42%	1407
	21st to end	Night	17% 8% 2 7% 4 4 5% 5% 7% 6% 36%	1330
July	1st to 10th	Night	12% 7% 3 8% 4 5% 5% 4 5% 6% 40%	2264
	11th to 20th	Night	12% 7% 2 7% 4 4 4 5% 6% 7% 42%	2520
	21st to end	Night	10% 5% 2 6% 4 4 5% 3 6% 8% 48%	2739
August	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 7% 8% 44%	2779
	11th to 20th	Night	16% 6% 2 6% 4 3 4 4 5% 8% 42%	2785
	21st to end	Night	13% 5% 1 6% 4 4 4 4 6% 9% 44%	3307
September	1st to 10th	Night	12% 6% 2 6% 4 3 4 3 5% 8% 47%	1900
	11th to 20th	Night	15% 7% 3 6% 4 4 3 3 4 6% 48%	1909
	21st to end	Night	18% 7% 3 6% 4 3 4 3 5% 6% 40%	2190
October	1st to 10th	Night	19% 10% 3 6% 4 3 4 3 4 6% 38%	2280
	11th to 20th	Night	19% 13% 3 8% 5% 5% 5% 3 5% 5% 28%	2280
	21st to end	Night	23% 13% 4 9% 6% 4 4 4 4 5% 24%	2565
November	1st to 10th	Night	16% 14% 4 8% 5% 5% 4 3 5% 5% 31%	2673
	11th to 20th	Night	16% 16% 4 10% 6% 5% 5% 3 5% 5% 23%	2800
	21st to end	Night	19% 19% 6% 13% 6% 5% 4 3 4 5% 18%	2800
December	1st to 10th	Night	16% 21% 7% 16% 8% 5% 5% 3 4 5% 10%	4580
	11th to 20th	Night	15% 18% 6% 14% 6% 5% 4 3 4 4 20%	5208
	21st to end	Night	20% 19% 6% 16% 7% 4 4 3 3 4 15%	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	74% 4 8% 9% 5%	3598
	11th to 20th	Day	70% 4 9% 10% 7%	3600
	21st to end	Day	69% 3 6% 13% 8% 1	4373
February	1st to 10th	Day	68% 3 8% 14% 7% 1	1800
	11th to 20th	Day	64% 4 10% 12% 8% 1	1762
	21st to end	Day	66% 3 6% 15% 9% 1	1540
March	1st to 10th	Day	63% 3 9% 11% 12% 2	4773
	11th to 20th	Day	56% 5% 14% 15% 8% 2	4980
	21st to end	Day	56% 3 6% 19% 14% 2	5553
April	1st to 10th	Day	59% 3 7% 19% 9% 3	2400
	11th to 20th	Day	54% 3 6% 22% 13% 2	2418
	21st to end	Day	55% 3 7% 17% 15% 3	2600
May	1st to 10th	Day	54% 5% 7% 21% 8% 5%	6256
	11th to 20th	Day	47% 5% 9% 25% 13% 1	6322
	21st to end	Day	52% 4 9% 20% 13% 2	6949
June	1st to 10th	Day	53% 5% 9% 20% 11% 1	2786
	11th to 20th	Day	45% 5% 11% 24% 13% 2	2765
	21st to end	Day	49% 6% 12% 21% 11% 1	2850
July	1st to 10th	Day	46% 6% 13% 25% 9% 1	4625
	11th to 20th	Day	41% 5% 15% 29% 9%	4365
	21st to end	Day	37% 5% 13% 32% 13%	4661
August	1st to 10th	Day	48% 5% 12% 26% 8%	4133
	11th to 20th	Day	46% 5% 16% 26% 7%	4083
	21st to end	Day	37% 6% 13% 33% 10% 1	4315
September	1st to 10th	Day	42% 5% 13% 27% 12%	2280
	11th to 20th	Day	42% 4 13% 29% 12%	2269
	21st to end	Day	52% 6% 11% 23% 8%	1990
October	1st to 10th	Day	53% 4 10% 26% 7%	3160
	11th to 20th	Day	57% 4 12% 19% 8%	3140
	21st to end	Day	65% 5% 13% 13% 4	3322
November	1st to 10th	Day	56% 4 13% 20% 6%	1622
	11th to 20th	Day	65% 5% 10% 12% 7% 1	1600
	21st to end	Day	74% 4 9% 9% 4 1	1600
December	1st to 10th	Day	77% 5% 8% 9% 2	2600
	11th to 20th	Day	71% 2 5% 13% 8%	2986
	21st to end	Day	74% 3 4 14% 5%	3960
January	1st to 10th	Night	76% 3 8% 9% 4	6349
	11th to 20th	Night	70% 4 10% 9% 7%	6360
	21st to end	Night	70% 3 7% 9% 10% 1	6582
February	1st to 10th	Night	63% 4 11% 14% 8% 1	2600
	11th to 20th	Night	62% 4 11% 16% 7% 1	2535
	21st to end	Night	62% 3 8% 18% 7% 1	2090
March	1st to 10th	Night	61% 3 9% 14% 9% 4	5064
	11th to 20th	Night	54% 7% 15% 15% 8% 1	4980
	21st to end	Night	56% 4 8% 18% 12% 2	5378
April	1st to 10th	Night	58% 3 7% 18% 12% 2	2000
	11th to 20th	Night	50% 3 7% 24% 14% 2	1948
	21st to end	Night	55% 4 7% 16% 14% 3	1800
May	1st to 10th	Night	49% 5% 10% 21% 10% 5%	3699
	11th to 20th	Night	40% 7% 12% 22% 15% 3	3576
	21st to end	Night	49% 5% 11% 21% 12% 2	3927
June	1st to 10th	Night	48% 6% 11% 22% 12% 1	1598
	11th to 20th	Night	39% 5% 13% 27% 15% 2	1407
	21st to end	Night	44% 7% 14% 22% 13% 1	1330
July	1st to 10th	Night	43% 5% 14% 24% 13% 1	2228
	11th to 20th	Night	39% 6% 15% 30% 9% 1	2472
	21st to end	Night	34% 6% 13% 33% 14%	2651
August	1st to 10th	Night	37% 5% 16% 27% 14% 1	2769
	11th to 20th	Night	40% 6% 19% 27% 8%	2812
	21st to end	Night	36% 4 15% 31% 10% 3	3307
September	1st to 10th	Night	35% 5% 17% 29% 13% 1	1900
	11th to 20th	Night	38% 4 15% 30% 13%	1909
	21st to end	Night	44% 5% 14% 27% 9%	2190
October	1st to 10th	Night	44% 4 12% 29% 12%	3800
	11th to 20th	Night	52% 4 14% 19% 11%	3779
	21st to end	Night	56% 5% 17% 14% 6%	4213
November	1st to 10th	Night	55% 4 14% 19% 7%	2673
	11th to 20th	Night	62% 4 12% 15% 6% 1	2800
	21st to end	Night	70% 5% 11% 12% 3	2800
December	1st to 10th	Night	77% 5% 10% 6% 2	4580
	11th to 20th	Night	68% 4 6% 11% 10%	5208
	21st to end	Night	74% 3 6% 12% 5%	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	20% 21% 40% 15% 5% 1	200
	11th to 20th	Day	27% 15% 34% 19% 5% 2	200
	21st to end	Day	26% 17% 33% 16% 7%	310
February	1st to 10th	Day	30% 24% 32% 11% 3 1	300
	11th to 20th	Day	28% 24% 40% 7% 1	300
	21st to end	Day	34% 18% 35% 12% 1	304
March	1st to 10th	Day	30% 18% 36% 13% 2	500
	11th to 20th	Day	27% 17% 35% 15% 4 1	500
	21st to end	Day	30% 20% 31% 15% 4 1	550
April	1st to 10th	Day	29% 20% 30% 14% 6% 1	500
	11th to 20th	Day	37% 17% 22% 15% 6% 3	492
	21st to end	Day	31% 15% 33% 14% 6% 1	500
May	1st to 10th	Day	29% 15% 30% 17% 8% 2	503
	11th to 20th	Day	22% 17% 28% 22% 8% 3	527
	21st to end	Day	23% 15% 31% 21% 8% 2	573
June	1st to 10th	Day	26% 11% 34% 22% 6% 1	526
	11th to 20th	Day	19% 13% 33% 24% 10% 2	595
	21st to end	Day	22% 14% 34% 20% 9% 1	680
July	1st to 10th	Day	12% 10% 34% 31% 10% 1	636
	11th to 20th	Day	15% 11% 35% 24% 11% 4	484
	21st to end	Day	13% 10% 34% 30% 11% 2	532
August	1st to 10th	Day	17% 7% 32% 28% 11% 5%	486
	11th to 20th	Day	16% 7% 27% 28% 16% 6%	479
	21st to end	Day	16% 12% 31% 23% 12% 5%	539
September	1st to 10th	Day	17% 11% 33% 20% 14% 5%	490
	11th to 20th	Day	19% 8% 25% 23% 16% 9%	490
	21st to end	Day	23% 13% 25% 22% 14% 3	490
October	1st to 10th	Day	23% 16% 27% 19% 11% 3	490
	11th to 20th	Day	31% 19% 29% 15% 5% 1	490
	21st to end	Day	36% 14% 31% 15% 4	508
November	1st to 10th	Day	32% 18% 34% 11% 5%	256
	11th to 20th	Day	29% 18% 37% 11% 5% 1	200
	21st to end	Day	37% 20% 32% 10% 2 1	200
December	1st to 10th	Day	32% 14% 35% 14% 5%	200
	11th to 20th	Day	32% 25% 33% 7% 3 2	200
	21st to end	Day	34% 16% 29% 14% 6% 1	220
January	1st to 10th	Night	23% 17% 37% 18% 5%	800
	11th to 20th	Night	24% 17% 33% 20% 6% 1	800
	21st to end	Night	18% 14% 35% 25% 7% 1	880
February	1st to 10th	Night	18% 21% 37% 19% 4	800
	11th to 20th	Night	20% 19% 38% 19% 4	783
	21st to end	Night	24% 19% 33% 21% 2	660
March	1st to 10th	Night	22% 20% 35% 20% 3	800
	11th to 20th	Night	24% 19% 33% 18% 5% 1	800
	21st to end	Night	21% 16% 33% 23% 7%	880
April	1st to 10th	Night	30% 14% 30% 21% 4	800
	11th to 20th	Night	27% 15% 28% 21% 8% 1	764
	21st to end	Night	27% 11% 26% 27% 9% 1	600
May	1st to 10th	Night	23% 7% 28% 33% 8%	447
	11th to 20th	Night	20% 8% 37% 27% 8% 1	394
	21st to end	Night	17% 9% 33% 31% 11%	433
June	1st to 10th	Night	18% 9% 36% 31% 6% 1	400
	11th to 20th	Night	18% 8% 30% 31% 12% 1	380
	21st to end	Night	21% 8% 28% 32% 10% 1	380
July	1st to 10th	Night	15% 5% 32% 35% 13% 1	370
	11th to 20th	Night	11% 6% 29% 39% 15%	368
	21st to end	Night	9% 5% 35% 33% 17%	416
August	1st to 10th	Night	15% 5% 23% 36% 20% 1	534
	11th to 20th	Night	13% 4 22% 37% 22% 2	564
	21st to end	Night	16% 7% 30% 32% 13% 3	732
September	1st to 10th	Night	15% 7% 29% 30% 16% 2	760
	11th to 20th	Night	20% 4 25% 27% 19% 3	760
	21st to end	Night	23% 8% 24% 27% 17% 2	760
October	1st to 10th	Night	26% 9% 29% 24% 11% 1	760
	11th to 20th	Night	30% 13% 31% 18% 8% 1	760
	21st to end	Night	33% 15% 27% 22% 3	836
November	1st to 10th	Night	28% 15% 27% 22% 7%	780
	11th to 20th	Night	26% 19% 31% 16% 8%	800
	21st to end	Night	32% 16% 27% 21% 4	800
December	1st to 10th	Night	32% 15% 34% 14% 5% 1	800
	11th to 20th	Night	26% 20% 31% 19% 4 1	800
	21st to end	Night	34% 13% 30% 19% 3 1	880

Page generated at 2025-06-07 10:28:18. Version ac07

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