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 2024-03-18.

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% 5% 8% 7% 4 5% 4 5% 6% 29%	78953
	Night	15% 12% 5% 9% 7% 4 5% 4 5% 6% 28%	80820
Transparency	Day	56% 4 10% 19% 9% 1	78655
	Night	57% 5% 11% 18% 9% 1	80653
Seeing	Day	24% 15% 32% 19% 8% 2	13833
	Night	23% 13% 31% 24% 8% 1	22797

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	14% 16% 8% 13% 10% 4 5% 4 4 5% 18%	2517
	11th to 20th	Day	12% 13% 6% 14% 12% 5% 5% 5% 5% 6% 18%	2520
	21st to end	Day	14% 23% 9% 12% 7% 4 4 3 3 3 18%	3059
February	1st to 10th	Day	10% 15% 8% 13% 11% 5% 6% 5% 3 5% 20%	1710
	11th to 20th	Day	10% 16% 7% 12% 8% 4 5% 6% 5% 6% 21%	1663
	21st to end	Day	16% 15% 6% 9% 8% 5% 6% 5% 3 5% 22%	1465
March	1st to 10th	Day	14% 14% 6% 10% 6% 4 4 4 4 6% 28%	2016
	11th to 20th	Day	12% 14% 6% 10% 9% 4 4 5% 4 5% 27%	2058
	21st to end	Day	17% 11% 5% 7% 6% 4 4 3 4 5% 35%	2211
April	1st to 10th	Day	22% 13% 5% 8% 6% 3 4 3 3 6% 27%	2160
	11th to 20th	Day	19% 11% 5% 7% 5% 3 4 4 4 5% 35%	2173
	21st to end	Day	21% 11% 4 6% 6% 3 4 3 3 5% 33%	2340
May	1st to 10th	Day	18% 9% 3 7% 6% 3 4 4 5% 7% 33%	2475
	11th to 20th	Day	18% 9% 4 7% 6% 3 4 4 4 6% 34%	2478
	21st to end	Day	15% 6% 4 6% 5% 3 5% 5% 5% 7% 39%	2725
June	1st to 10th	Day	20% 9% 3 6% 7% 3 5% 4 6% 7% 30%	2520
	11th to 20th	Day	16% 5% 3 6% 5% 4 6% 5% 6% 8% 37%	2619
	21st to end	Day	17% 7% 3 6% 7% 3 6% 5% 6% 8% 32%	2700
July	1st to 10th	Day	13% 5% 3 5% 6% 4 5% 6% 6% 8% 40%	2666
	11th to 20th	Day	12% 7% 3 5% 6% 4 6% 6% 6% 8% 37%	2520
	21st to end	Day	12% 6% 3 6% 6% 3 6% 7% 7% 9% 35%	2744
August	1st to 10th	Day	13% 7% 3 6% 6% 4 6% 5% 6% 8% 35%	2356
	11th to 20th	Day	14% 6% 3 6% 6% 4 5% 6% 6% 8% 36%	2303
	21st to end	Day	15% 6% 2 6% 7% 4 6% 7% 7% 7% 33%	2455
September	1st to 10th	Day	14% 7% 3 7% 6% 3 4 5% 5% 7% 40%	2160
	11th to 20th	Day	16% 7% 3 6% 5% 3 4 4 5% 6% 42%	2150
	21st to end	Day	20% 9% 3 6% 5% 3 5% 5% 4 7% 32%	1886
October	1st to 10th	Day	18% 11% 3 7% 5% 4 4 3 4 6% 34%	1800
	11th to 20th	Day	23% 14% 4 8% 7% 4 5% 4 4 6% 22%	1800
	21st to end	Day	26% 15% 5% 8% 6% 4 4 4 4 4 19%	1926
November	1st to 10th	Day	16% 14% 4 9% 5% 3 4 4 6% 6% 28%	1540
	11th to 20th	Day	17% 16% 7% 9% 8% 3 6% 4 5% 5% 22%	1520
	21st to end	Day	20% 18% 8% 12% 8% 3 4 4 4 3 15%	1520
December	1st to 10th	Day	18% 20% 9% 10% 8% 4 5% 5% 4 3 15%	1520
	11th to 20th	Day	17% 18% 8% 11% 8% 3 6% 4 3 5% 17%	1906
	21st to end	Day	22% 20% 7% 15% 8% 2 3 2 2 3 17%	2772
January	1st to 10th	Night	14% 18% 9% 14% 10% 4 5% 4 5% 5% 13%	4429
	11th to 20th	Night	10% 12% 6% 15% 12% 6% 7% 5% 5% 5% 16%	4440
	21st to end	Night	12% 20% 9% 12% 7% 5% 6% 4 4 4 16%	4596
February	1st to 10th	Night	11% 14% 7% 11% 10% 4 5% 5% 6% 6% 20%	2470
	11th to 20th	Night	11% 14% 6% 12% 9% 5% 6% 4 5% 5% 25%	2403
	21st to end	Night	13% 14% 6% 12% 9% 4 5% 4 5% 6% 23%	1989
March	1st to 10th	Night	13% 13% 6% 9% 7% 4 5% 4 4 4 30%	2149
	11th to 20th	Night	13% 14% 6% 9% 5% 3 6% 4 5% 6% 30%	2067
	21st to end	Night	14% 10% 4 8% 6% 3 4 4 4 5% 38%	2144
April	1st to 10th	Night	20% 13% 5% 7% 6% 3 4 4 5% 4 31%	1800
	11th to 20th	Night	19% 10% 4 6% 5% 3 4 3 5% 6% 35%	1752
	21st to end	Night	20% 10% 3 7% 7% 3 5% 4 3 6% 31%	1620
May	1st to 10th	Night	18% 10% 3 5% 5% 3 5% 4 5% 7% 37%	1483
	11th to 20th	Night	17% 7% 3 5% 6% 3 4 5% 5% 7% 39%	1415
	21st to end	Night	13% 6% 3 5% 5% 4 4 5% 6% 6% 43%	1550
June	1st to 10th	Night	15% 7% 4 7% 7% 3 5% 4 6% 8% 34%	1440
	11th to 20th	Night	14% 6% 2 5% 5% 3 3 4 6% 9% 42%	1333
	21st to end	Night	17% 6% 3 6% 5% 3 5% 6% 7% 7% 36%	1260
July	1st to 10th	Night	11% 5% 2 5% 4 3 4 5% 6% 7% 48%	1288
	11th to 20th	Night	10% 6% 3 6% 5% 3 5% 5% 6% 8% 45%	1440
	21st to end	Night	9% 4 2 5% 5% 4 6% 5% 6% 9% 44%	1574
August	1st to 10th	Night	11% 6% 3 5% 6% 3 5% 4 6% 8% 43%	1579
	11th to 20th	Night	10% 4 3 5% 6% 3 5% 6% 6% 9% 45%	1598
	21st to end	Night	12% 6% 2 6% 5% 3 4 5% 6% 8% 42%	1881
September	1st to 10th	Night	11% 6% 2 6% 5% 3 4 4 5% 8% 46%	1800
	11th to 20th	Night	15% 7% 3 5% 4 3 3 3 4 6% 45%	1808
	21st to end	Night	18% 7% 3 5% 5% 2 5% 4 5% 6% 41%	2074
October	1st to 10th	Night	20% 10% 3 5% 5% 2 4 4 4 6% 38%	2160
	11th to 20th	Night	21% 13% 4 7% 6% 4 5% 4 5% 5% 27%	2160
	21st to end	Night	24% 12% 5% 7% 7% 3 4 5% 5% 5% 24%	2430
November	1st to 10th	Night	16% 13% 5% 7% 6% 4 4 4 5% 5% 31%	2536
	11th to 20th	Night	16% 15% 5% 9% 8% 4 5% 5% 6% 6% 23%	2660
	21st to end	Night	20% 17% 6% 12% 8% 4 4 4 4 5% 18%	2660
December	1st to 10th	Night	19% 20% 7% 12% 8% 3 5% 4 3 5% 14%	2660
	11th to 20th	Night	15% 19% 7% 10% 8% 4 5% 5% 5% 5% 19%	3288
	21st to end	Night	22% 19% 6% 14% 9% 3 3 3 3 4 13%	4884

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	70% 4 11% 9% 6%	2518
	11th to 20th	Day	68% 4 11% 11% 6% 1	2520
	21st to end	Day	73% 3 6% 12% 5% 1	3059
February	1st to 10th	Day	68% 3 8% 14% 6% 1	1710
	11th to 20th	Day	63% 4 10% 12% 9% 1	1672
	21st to end	Day	65% 3 6% 15% 10% 1	1465
March	1st to 10th	Day	59% 4 10% 16% 10% 1	2019
	11th to 20th	Day	60% 4 8% 17% 10% 1	2058
	21st to end	Day	53% 3 8% 18% 14% 4	2211
April	1st to 10th	Day	60% 3 7% 18% 9% 3	2160
	11th to 20th	Day	53% 3 6% 23% 12% 2	2173
	21st to end	Day	55% 3 7% 17% 14% 3	2340
May	1st to 10th	Day	51% 4 9% 20% 12% 4	2475
	11th to 20th	Day	52% 4 7% 21% 14% 2	2482
	21st to end	Day	45% 5% 11% 22% 13% 4	2725
June	1st to 10th	Day	53% 5% 9% 20% 11% 1	2520
	11th to 20th	Day	45% 5% 11% 23% 14% 2	2619
	21st to end	Day	49% 6% 12% 22% 11% 1	2700
July	1st to 10th	Day	40% 6% 12% 27% 13% 1	2593
	11th to 20th	Day	42% 5% 13% 28% 11% 1	2445
	21st to end	Day	44% 6% 13% 27% 9%	2591
August	1st to 10th	Day	45% 6% 14% 24% 10% 1	2342
	11th to 20th	Day	45% 5% 16% 25% 8% 1	2303
	21st to end	Day	46% 7% 14% 24% 9% 1	2455
September	1st to 10th	Day	42% 6% 13% 27% 12%	2160
	11th to 20th	Day	43% 5% 12% 29% 11%	2150
	21st to end	Day	52% 6% 11% 24% 6%	1886
October	1st to 10th	Day	52% 4 11% 20% 12% 1	1800
	11th to 20th	Day	64% 5% 13% 13% 4	1800
	21st to end	Day	69% 4 9% 13% 5% 1	1926
November	1st to 10th	Day	56% 4 13% 20% 6%	1540
	11th to 20th	Day	65% 5% 11% 12% 7% 1	1520
	21st to end	Day	74% 4 9% 9% 3 1	1520
December	1st to 10th	Day	74% 4 8% 11% 3	1520
	11th to 20th	Day	72% 3 7% 11% 7%	1906
	21st to end	Day	76% 3 5% 14% 3	2772
January	1st to 10th	Night	74% 4 10% 9% 3	4429
	11th to 20th	Night	70% 4 11% 9% 4	4440
	21st to end	Night	73% 4 7% 10% 6%	4596
February	1st to 10th	Night	63% 4 11% 14% 7%	2470
	11th to 20th	Night	61% 4 11% 16% 7% 1	2405
	21st to end	Night	62% 4 9% 17% 8% 1	1989
March	1st to 10th	Night	57% 4 10% 17% 10% 2	2159
	11th to 20th	Night	54% 5% 12% 17% 11% 1	2068
	21st to end	Night	50% 3 9% 20% 15% 3	2144
April	1st to 10th	Night	57% 3 8% 18% 12% 2	1800
	11th to 20th	Night	50% 4 7% 24% 13% 2	1752
	21st to end	Night	55% 4 7% 16% 15% 3	1620
May	1st to 10th	Night	46% 5% 9% 21% 15% 3	1483
	11th to 20th	Night	45% 5% 7% 23% 17% 2	1416
	21st to end	Night	40% 5% 15% 20% 16% 4	1551
June	1st to 10th	Night	48% 6% 11% 22% 12% 1	1440
	11th to 20th	Night	38% 5% 13% 26% 16% 2	1333
	21st to end	Night	43% 8% 14% 22% 12% 1	1260
July	1st to 10th	Night	33% 5% 15% 28% 18% 2	1252
	11th to 20th	Night	36% 5% 15% 29% 13% 1	1392
	21st to end	Night	35% 7% 18% 29% 10%	1486
August	1st to 10th	Night	39% 7% 17% 24% 13%	1569
	11th to 20th	Night	34% 8% 22% 26% 10% 1	1598
	21st to end	Night	39% 5% 18% 29% 9% 1	1881
September	1st to 10th	Night	36% 5% 17% 28% 13% 1	1800
	11th to 20th	Night	40% 4 15% 30% 11%	1808
	21st to end	Night	44% 5% 14% 29% 8%	2074
October	1st to 10th	Night	49% 4 12% 23% 12%	2160
	11th to 20th	Night	58% 5% 13% 17% 6%	2160
	21st to end	Night	63% 5% 9% 14% 8% 1	2430
November	1st to 10th	Night	54% 5% 15% 19% 7%	2536
	11th to 20th	Night	62% 4 12% 15% 6% 1	2660
	21st to end	Night	70% 5% 11% 12% 3	2660
December	1st to 10th	Night	75% 4 9% 9% 3	2660
	11th to 20th	Night	67% 5% 7% 14% 6%	3288
	21st to end	Night	77% 3 6% 11% 3	4884

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	21% 20% 38% 16% 5% 1	180
	11th to 20th	Day	28% 14% 34% 18% 4 2	180
	21st to end	Day	25% 15% 34% 18% 7%	279
February	1st to 10th	Day	29% 23% 34% 11% 3 1	270
	11th to 20th	Day	27% 23% 41% 7% 1	270
	21st to end	Day	36% 19% 33% 12% 1	277
March	1st to 10th	Day	28% 19% 38% 14% 2	460
	11th to 20th	Day	27% 18% 34% 16% 4 1	449
	21st to end	Day	30% 20% 29% 16% 5% 1	462
April	1st to 10th	Day	28% 19% 31% 15% 6% 1	420
	11th to 20th	Day	33% 17% 23% 17% 6% 4	412
	21st to end	Day	30% 15% 32% 15% 7% 1	420
May	1st to 10th	Day	30% 14% 28% 17% 8% 2	423
	11th to 20th	Day	24% 17% 28% 21% 7% 3	447
	21st to end	Day	21% 14% 33% 21% 8% 2	485
June	1st to 10th	Day	26% 11% 34% 22% 6% 1	450
	11th to 20th	Day	20% 13% 31% 23% 10% 2	549
	21st to end	Day	21% 13% 34% 21% 10% 2	630
July	1st to 10th	Day	12% 10% 35% 32% 11% 1	588
	11th to 20th	Day	16% 11% 33% 24% 12% 4	444
	21st to end	Day	13% 10% 35% 29% 11% 2	488
August	1st to 10th	Day	16% 7% 33% 28% 11% 5%	446
	11th to 20th	Day	16% 7% 27% 27% 16% 6%	439
	21st to end	Day	17% 13% 31% 21% 13% 5%	495
September	1st to 10th	Day	16% 11% 32% 20% 15% 5%	450
	11th to 20th	Day	21% 8% 27% 23% 14% 7%	450
	21st to end	Day	22% 13% 26% 22% 13% 4	450
October	1st to 10th	Day	24% 15% 27% 20% 12% 4	450
	11th to 20th	Day	32% 18% 28% 15% 5% 1	450
	21st to end	Day	37% 13% 31% 15% 4	468
November	1st to 10th	Day	30% 19% 34% 11% 6%	234
	11th to 20th	Day	30% 17% 37% 11% 5% 1	180
	21st to end	Day	37% 19% 32% 9% 2 1	180
December	1st to 10th	Day	32% 16% 34% 14% 5%	180
	11th to 20th	Day	32% 25% 33% 7% 3 1	180
	21st to end	Day	34% 17% 30% 12% 6% 1	198
January	1st to 10th	Night	23% 16% 36% 19% 5%	760
	11th to 20th	Night	25% 17% 32% 20% 6%	760
	21st to end	Night	18% 13% 36% 25% 8% 1	836
February	1st to 10th	Night	19% 20% 38% 18% 5%	760
	11th to 20th	Night	20% 19% 38% 19% 4	743
	21st to end	Night	25% 19% 33% 21% 2	628
March	1st to 10th	Night	21% 20% 35% 20% 3	760
	11th to 20th	Night	24% 18% 32% 19% 6% 1	752
	21st to end	Night	21% 15% 33% 24% 7% 1	792
April	1st to 10th	Night	29% 15% 31% 22% 4	720
	11th to 20th	Night	27% 16% 28% 21% 8% 1	688
	21st to end	Night	27% 10% 26% 28% 9% 1	540
May	1st to 10th	Night	24% 7% 28% 32% 9%	403
	11th to 20th	Night	20% 9% 36% 25% 8% 1	354
	21st to end	Night	15% 8% 35% 31% 11%	389
June	1st to 10th	Night	18% 9% 37% 29% 6% 1	360
	11th to 20th	Night	19% 7% 30% 32% 12% 1	360
	21st to end	Night	20% 8% 28% 33% 11% 1	360
July	1st to 10th	Night	14% 5% 32% 35% 13% 1	350
	11th to 20th	Night	11% 5% 29% 38% 16%	348
	21st to end	Night	9% 5% 36% 33% 16% 1	394
August	1st to 10th	Night	15% 5% 24% 35% 20% 1	505
	11th to 20th	Night	13% 3 22% 37% 22% 2	534
	21st to end	Night	16% 7% 30% 31% 13% 3	693
September	1st to 10th	Night	15% 7% 29% 30% 17% 2	720
	11th to 20th	Night	21% 5% 27% 28% 17% 3	720
	21st to end	Night	22% 8% 24% 26% 17% 2	720
October	1st to 10th	Night	26% 9% 29% 24% 10% 1	720
	11th to 20th	Night	30% 13% 31% 17% 8% 1	720
	21st to end	Night	33% 13% 27% 23% 3	792
November	1st to 10th	Night	27% 14% 28% 23% 7%	740
	11th to 20th	Night	26% 19% 31% 16% 8%	760
	21st to end	Night	32% 15% 27% 22% 4	760
December	1st to 10th	Night	32% 15% 34% 13% 5% 1	760
	11th to 20th	Night	26% 20% 30% 19% 4 1	760
	21st to end	Night	35% 14% 30% 19% 3 1	836

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