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 2024-11-02.

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% 5% 5% 4 4 5% 6% 31%	102141
	Night	15% 13% 4 10% 6% 5% 4 3 5% 6% 29%	96839
Transparency	Day	54% 5% 11% 21% 9% 1	101896
	Night	56% 5% 11% 19% 9% 1	96705
Seeing	Day	24% 15% 32% 19% 8% 2	14768
	Night	23% 13% 31% 24% 9% 1	23493

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% 17% 7% 15% 8% 6% 4 3 4 5% 18%	2517
	11th to 20th	Day	12% 14% 6% 17% 9% 6% 5% 4 5% 6% 18%	2520
	21st to end	Day	14% 23% 8% 14% 6% 5% 3 2 3 3 18%	3059
February	1st to 10th	Day	9% 16% 7% 15% 9% 7% 5% 4 4 5% 20%	1710
	11th to 20th	Day	10% 17% 6% 13% 7% 5% 5% 4 5% 6% 21%	1663
	21st to end	Day	16% 17% 5% 10% 7% 6% 6% 4 4 5% 22%	1465
March	1st to 10th	Day	18% 18% 5% 9% 4 4 3 3 4 5% 26%	3326
	11th to 20th	Day	10% 18% 6% 13% 7% 5% 4 3 5% 4 25%	3480
	21st to end	Day	11% 9% 4 8% 6% 6% 4 3 5% 5% 38%	3875
April	1st to 10th	Day	21% 15% 4 9% 4 4 4 2 4 6% 28%	2280
	11th to 20th	Day	20% 12% 4 7% 4 4 3 3 4 5% 34%	2296
	21st to end	Day	21% 12% 3 8% 5% 4 3 2 4 5% 33%	2470
May	1st to 10th	Day	19% 10% 3 8% 5% 5% 4 3 5% 7% 30%	4353
	11th to 20th	Day	15% 9% 3 8% 4 4 4 4 5% 7% 36%	4398
	21st to end	Day	17% 7% 3 6% 5% 4 4 4 5% 6% 39%	4837
June	1st to 10th	Day	19% 10% 3 8% 6% 5% 5% 3 6% 7% 29%	2660
	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% 4 9% 5% 4 4 3 5% 6% 28%	1550
	11th to 20th	Day	17% 17% 6% 10% 7% 5% 4 3 5% 5% 22%	1520
	21st to end	Day	19% 20% 8% 13% 7% 4 4 3 4 3 15%	1520
December	1st to 10th	Day	17% 22% 7% 12% 7% 5% 5% 4 4 4 14%	1520
	11th to 20th	Day	17% 19% 7% 12% 7% 5% 5% 3 3 5% 17%	1906
	21st to end	Day	21% 21% 6% 17% 6% 3 3 2 2 3 17%	2772
January	1st to 10th	Night	14% 19% 8% 15% 8% 6% 4 3 5% 5% 13%	4429
	11th to 20th	Night	10% 13% 5% 18% 10% 8% 6% 4 5% 5% 16%	4440
	21st to end	Night	12% 21% 9% 13% 6% 7% 5% 3 4 4 16%	4596
February	1st to 10th	Night	11% 15% 6% 12% 9% 5% 5% 4 6% 6% 20%	2470
	11th to 20th	Night	11% 15% 6% 13% 8% 6% 5% 3 5% 5% 25%	2403
	21st to end	Night	13% 16% 5% 12% 8% 6% 4 3 5% 6% 22%	1989
March	1st to 10th	Night	15% 15% 4 9% 5% 5% 5% 3 4 5% 31%	3512
	11th to 20th	Night	13% 17% 6% 12% 6% 5% 5% 3 5% 5% 24%	3479
	21st to end	Night	12% 9% 5% 10% 7% 5% 4 4 5% 6% 33%	3756
April	1st to 10th	Night	20% 14% 4 8% 5% 4 4 3 5% 4 31%	1900
	11th to 20th	Night	19% 11% 3 6% 5% 4 4 3 5% 6% 35%	1850
	21st to end	Night	21% 11% 3 8% 6% 5% 4 3 4 6% 31%	1710
May	1st to 10th	Night	19% 10% 2 6% 4 4 5% 4 6% 7% 34%	2585
	11th to 20th	Night	16% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	2495
	21st to end	Night	12% 8% 3 8% 5% 5% 4 4 6% 6% 40%	2738
June	1st to 10th	Night	14% 8% 4 8% 6% 5% 5% 3 6% 8% 33%	1520
	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 5% 5% 24%	2565
November	1st to 10th	Night	16% 14% 4 7% 5% 5% 4 3 6% 5% 31%	2560
	11th to 20th	Night	16% 16% 4 10% 6% 5% 5% 3 6% 5% 23%	2660
	21st to end	Night	20% 18% 5% 13% 7% 5% 4 3 4 5% 18%	2660
December	1st to 10th	Night	18% 21% 7% 13% 7% 5% 5% 3 3 4 14%	2660
	11th to 20th	Night	15% 20% 6% 11% 7% 5% 4 4 5% 5% 19%	3288
	21st to end	Night	22% 20% 6% 17% 6% 4 3 2 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	60% 4 11% 14% 10% 1	3329
	11th to 20th	Day	61% 5% 9% 15% 9% 1	3480
	21st to end	Day	48% 4 8% 22% 15% 3	3875
April	1st to 10th	Day	59% 3 7% 19% 9% 3	2280
	11th to 20th	Day	54% 4 6% 23% 12% 2	2296
	21st to end	Day	55% 4 7% 17% 14% 3	2470
May	1st to 10th	Day	53% 5% 8% 23% 9% 2	4367
	11th to 20th	Day	47% 5% 11% 28% 9% 1	4402
	21st to end	Day	45% 5% 12% 20% 16% 3	4837
June	1st to 10th	Day	54% 5% 9% 20% 11% 1	2660
	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	52% 4 11% 21% 11% 1	1900
	11th to 20th	Day	63% 5% 13% 15% 5%	1900
	21st to end	Day	68% 4 9% 13% 5% 1	2032
November	1st to 10th	Day	56% 4 13% 20% 6%	1550
	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	56% 5% 12% 17% 9% 1	3522
	11th to 20th	Night	59% 6% 12% 14% 7% 1	3480
	21st to end	Night	50% 5% 9% 21% 13% 2	3756
April	1st to 10th	Night	57% 3 8% 18% 12% 2	1900
	11th to 20th	Night	50% 4 7% 24% 13% 2	1850
	21st to end	Night	55% 4 7% 16% 15% 3	1710
May	1st to 10th	Night	47% 6% 12% 23% 10% 2	2591
	11th to 20th	Night	46% 7% 10% 25% 11% 1	2496
	21st to end	Night	43% 6% 12% 23% 14% 2	2739
June	1st to 10th	Night	49% 6% 11% 21% 12% 1	1520
	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	49% 4 12% 23% 12%	2280
	11th to 20th	Night	58% 5% 13% 18% 7%	2280
	21st to end	Night	63% 5% 10% 14% 8% 1	2565
November	1st to 10th	Night	54% 5% 15% 19% 7%	2560
	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% 35% 16% 4 1	460
	21st to end	Day	29% 20% 31% 15% 4 1	506
April	1st to 10th	Day	29% 20% 30% 15% 6% 1	460
	11th to 20th	Day	37% 17% 22% 15% 6% 3	452
	21st to end	Day	31% 15% 32% 15% 7% 1	460
May	1st to 10th	Day	30% 14% 29% 17% 8% 2	463
	11th to 20th	Day	23% 16% 28% 22% 8% 3	487
	21st to end	Day	21% 15% 33% 21% 8% 2	529
June	1st to 10th	Day	26% 10% 34% 23% 6% 1	490
	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% 13% 31% 15% 4	508
November	1st to 10th	Day	31% 19% 34% 11% 6%	238
	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% 19% 33% 18% 6% 1	760
	21st to end	Night	20% 16% 33% 23% 7%	836
April	1st to 10th	Night	30% 14% 30% 22% 4	760
	11th to 20th	Night	28% 15% 28% 21% 8% 1	726
	21st to end	Night	27% 10% 26% 27% 9% 1	570
May	1st to 10th	Night	23% 7% 28% 32% 8%	425
	11th to 20th	Night	20% 9% 36% 27% 8% 1	374
	21st to end	Night	16% 9% 34% 31% 11%	411
June	1st to 10th	Night	18% 9% 37% 30% 6% 1	380
	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% 14% 27% 22% 3	836
November	1st to 10th	Night	28% 14% 28% 22% 7%	748
	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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