Cape Race
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cape Race clear sky chart from 2005-11-06 to 2026-07-01.

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	25% 14% 5% 10% 6% 5% 4 3 4 5% 19%	137652
	Night	24% 15% 6% 11% 6% 4 4 3 4 5% 18%	134995
Transparency	Day	62% 9% 11% 13% 5% 1	141149
	Night	63% 8% 10% 12% 5% 1	139615
Seeing	Day	29% 13% 27% 22% 8% 1	20417
	Night	30% 13% 28% 21% 7% 1	26978

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	22% 16% 8% 12% 7% 6% 4 3 3 4 15%	4179
	11th to 20th	Day	24% 17% 9% 13% 6% 5% 4 3 4 4 12%	4681
	21st to end	Day	13% 12% 8% 18% 8% 7% 6% 4 4 4 13%	5157
February	1st to 10th	Day	22% 13% 8% 14% 9% 7% 6% 3 5% 4 10%	1875
	11th to 20th	Day	22% 16% 7% 14% 7% 5% 3 3 4 5% 13%	1864
	21st to end	Day	17% 14% 6% 14% 8% 6% 5% 4 5% 5% 17%	1730
March	1st to 10th	Day	25% 12% 5% 13% 7% 5% 6% 3 4 4 16%	4656
	11th to 20th	Day	22% 14% 6% 13% 7% 4 4 3 4 4 18%	5090
	21st to end	Day	28% 13% 6% 14% 8% 5% 4 3 3 4 11%	5588
April	1st to 10th	Day	26% 15% 6% 11% 6% 5% 4 3 4 4 17%	2510
	11th to 20th	Day	24% 13% 5% 9% 6% 5% 5% 3 4 5% 21%	2701
	21st to end	Day	26% 14% 5% 11% 5% 5% 3 3 4 4 19%	2730
May	1st to 10th	Day	22% 19% 6% 11% 5% 4 3 2 3 4 20%	7638
	11th to 20th	Day	28% 16% 4 9% 5% 4 3 2 4 5% 19%	7982
	21st to end	Day	22% 14% 5% 11% 6% 5% 5% 3 4 4 20%	9682
June	1st to 10th	Day	35% 16% 4 7% 4 4 3 2 4 5% 15%	3150
	11th to 20th	Day	27% 14% 4 8% 5% 4 4 4 5% 6% 19%	3150
	21st to end	Day	30% 15% 4 8% 5% 4 4 3 5% 6% 16%	3150
July	1st to 10th	Day	35% 14% 5% 10% 5% 5% 5% 3 3 5% 11%	6800
	11th to 20th	Day	30% 15% 4 8% 4 4 3 3 4 6% 19%	6638
	21st to end	Day	23% 12% 3 8% 5% 5% 5% 4 5% 6% 24%	6927
August	1st to 10th	Day	33% 13% 3 7% 4 3 3 3 4 6% 21%	4243
	11th to 20th	Day	24% 13% 5% 10% 6% 4 5% 3 5% 5% 20%	4176
	21st to end	Day	24% 9% 3 8% 4 5% 4 3 5% 7% 29%	4675
September	1st to 10th	Day	23% 10% 3 8% 4 4 4 4 6% 7% 26%	2370
	11th to 20th	Day	23% 9% 3 8% 5% 5% 4 4 5% 6% 28%	2200
	21st to end	Day	20% 9% 3 6% 5% 5% 4 4 7% 6% 31%	2200
October	1st to 10th	Day	20% 10% 3 10% 5% 5% 5% 4 5% 7% 25%	2097
	11th to 20th	Day	24% 11% 4 10% 6% 4 4 3 5% 6% 23%	1984
	21st to end	Day	25% 13% 4 9% 5% 4 4 3 5% 7% 21%	1980
November	1st to 10th	Day	23% 11% 3 10% 5% 4 5% 4 5% 6% 23%	1848
	11th to 20th	Day	26% 12% 4 10% 6% 6% 4 4 5% 6% 18%	1680
	21st to end	Day	26% 14% 4 10% 6% 5% 4 4 5% 6% 18%	1680
December	1st to 10th	Day	21% 13% 3 9% 5% 6% 6% 5% 7% 7% 17%	2368
	11th to 20th	Day	19% 16% 4 10% 6% 5% 4 3 5% 7% 21%	2698
	21st to end	Day	21% 23% 6% 11% 5% 4 5% 3 4 4 13%	3575
January	1st to 10th	Night	20% 16% 8% 12% 6% 6% 5% 3 4 5% 15%	8730
	11th to 20th	Night	23% 14% 11% 13% 6% 5% 4 3 4 4 13%	8234
	21st to end	Night	13% 12% 8% 19% 9% 7% 6% 4 5% 4 14%	9056
February	1st to 10th	Night	23% 14% 7% 14% 7% 5% 5% 3 4 4 13%	2743
	11th to 20th	Night	23% 15% 6% 13% 6% 5% 5% 3 5% 5% 15%	2637
	21st to end	Night	16% 13% 6% 14% 8% 5% 5% 4 4 6% 19%	2076
March	1st to 10th	Night	25% 12% 6% 11% 6% 5% 4 3 5% 6% 18%	5404
	11th to 20th	Night	21% 14% 7% 14% 6% 4 4 3 4 5% 17%	5089
	21st to end	Night	29% 16% 7% 12% 6% 4 3 2 4 4 13%	5586
April	1st to 10th	Night	27% 17% 5% 9% 4 4 4 2 3 5% 20%	2105
	11th to 20th	Night	25% 14% 4 8% 5% 3 3 3 5% 5% 24%	1868
	21st to end	Night	28% 18% 5% 9% 5% 4 4 3 2 4 18%	1890
May	1st to 10th	Night	30% 16% 5% 9% 5% 3 3 2 3 4 20%	5290
	11th to 20th	Night	30% 15% 4 9% 5% 3 4 3 3 5% 18%	4903
	21st to end	Night	25% 14% 5% 10% 6% 4 4 3 4 5% 19%	4524
June	1st to 10th	Night	37% 17% 4 6% 4 3 3 2 4 5% 15%	1470
	11th to 20th	Night	29% 17% 5% 8% 5% 3 4 3 4 5% 17%	1470
	21st to end	Night	32% 17% 4 9% 5% 4 3 3 3 4 17%	1470
July	1st to 10th	Night	42% 18% 5% 10% 4 4 3 2 3 3 7%	3180
	11th to 20th	Night	32% 21% 6% 9% 4 3 3 2 3 4 13%	3326
	21st to end	Night	24% 16% 4 8% 5% 3 3 3 4 4 25%	3948
August	1st to 10th	Night	29% 20% 4 8% 4 3 3 3 4 4 18%	2915
	11th to 20th	Night	28% 17% 5% 9% 4 4 3 3 4 5% 18%	2881
	21st to end	Night	30% 10% 3 7% 4 3 3 3 4 6% 27%	3234
September	1st to 10th	Night	25% 11% 3 8% 4 3 4 3 5% 7% 27%	2026
	11th to 20th	Night	27% 11% 3 7% 5% 5% 4 3 5% 4 25%	2200
	21st to end	Night	23% 7% 3 6% 4 4 4 4 5% 6% 34%	2200
October	1st to 10th	Night	22% 10% 3 8% 5% 4 4 4 5% 7% 27%	2302
	11th to 20th	Night	23% 13% 4 8% 5% 5% 4 4 6% 6% 22%	2414
	21st to end	Night	25% 13% 4 9% 6% 4 4 3 5% 5% 21%	2860
November	1st to 10th	Night	25% 13% 4 8% 5% 5% 4 3 5% 6% 23%	2668
	11th to 20th	Night	25% 14% 4 8% 5% 4 5% 4 5% 6% 21%	2940
	21st to end	Night	22% 14% 3 9% 5% 5% 5% 4 6% 6% 19%	2940
December	1st to 10th	Night	20% 15% 4 10% 6% 5% 5% 4 5% 6% 20%	5040
	11th to 20th	Night	23% 14% 5% 10% 5% 5% 5% 4 5% 6% 18%	5731
	21st to end	Night	21% 19% 6% 11% 5% 4 4 3 4 5% 17%	7645

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	66% 10% 8% 10% 5% 1	4180
	11th to 20th	Day	70% 7% 9% 9% 4 1	4710
	21st to end	Day	63% 10% 9% 11% 7% 1	5157
February	1st to 10th	Day	72% 9% 8% 7% 4 1	1875
	11th to 20th	Day	67% 8% 12% 10% 3 1	1871
	21st to end	Day	65% 8% 9% 8% 8% 2	1730
March	1st to 10th	Day	64% 7% 9% 11% 7% 2	4661
	11th to 20th	Day	62% 9% 12% 9% 6% 3	5090
	21st to end	Day	70% 6% 9% 10% 4 1	5588
April	1st to 10th	Day	64% 6% 12% 12% 6% 1	2510
	11th to 20th	Day	60% 8% 11% 12% 8% 1	2701
	21st to end	Day	66% 7% 8% 11% 7% 1	2730
May	1st to 10th	Day	66% 6% 8% 15% 5%	7651
	11th to 20th	Day	65% 7% 10% 14% 4	7986
	21st to end	Day	60% 10% 9% 16% 4	9683
June	1st to 10th	Day	71% 6% 8% 10% 4	3150
	11th to 20th	Day	63% 9% 11% 13% 4	3150
	21st to end	Day	65% 11% 8% 12% 3	3150
July	1st to 10th	Day	70% 11% 9% 7% 2	6725
	11th to 20th	Day	60% 10% 11% 13% 5%	6556
	21st to end	Day	52% 12% 16% 15% 5%	6730
August	1st to 10th	Day	60% 10% 12% 14% 4	4229
	11th to 20th	Day	59% 11% 13% 14% 3	4215
	21st to end	Day	50% 9% 15% 23% 2	4675
September	1st to 10th	Day	53% 8% 12% 19% 7%	2370
	11th to 20th	Day	53% 9% 12% 16% 10%	2200
	21st to end	Day	49% 8% 15% 20% 8% 1	2200
October	1st to 10th	Day	60% 10% 10% 15% 4 1	3415
	11th to 20th	Day	45% 8% 14% 20% 11% 2	3222
	21st to end	Day	55% 9% 12% 17% 7%	3191
November	1st to 10th	Day	56% 8% 16% 13% 6%	1848
	11th to 20th	Day	62% 7% 11% 12% 6% 1	1680
	21st to end	Day	65% 8% 12% 12% 4	1680
December	1st to 10th	Day	53% 12% 15% 13% 6%	2368
	11th to 20th	Day	56% 9% 16% 13% 5%	2697
	21st to end	Day	72% 7% 7% 10% 4	3575
January	1st to 10th	Night	64% 10% 9% 9% 6% 2	8730
	11th to 20th	Night	70% 8% 10% 8% 4	8280
	21st to end	Night	62% 9% 11% 9% 7% 1	9056
February	1st to 10th	Night	72% 7% 8% 8% 4 1	2743
	11th to 20th	Night	67% 10% 10% 9% 4	2641
	21st to end	Night	62% 9% 11% 12% 6% 1	2076
March	1st to 10th	Night	64% 7% 10% 13% 6%	5412
	11th to 20th	Night	66% 8% 10% 10% 5% 1	5090
	21st to end	Night	69% 8% 9% 10% 4	5586
April	1st to 10th	Night	66% 6% 8% 12% 8% 1	2105
	11th to 20th	Night	61% 6% 9% 13% 10% 1	1868
	21st to end	Night	70% 4 7% 11% 7% 1	1890
May	1st to 10th	Night	66% 7% 8% 14% 5%	5295
	11th to 20th	Night	63% 7% 9% 16% 5%	4904
	21st to end	Night	64% 7% 10% 13% 5%	4525
June	1st to 10th	Night	74% 5% 7% 9% 4	1470
	11th to 20th	Night	67% 8% 8% 12% 4	1470
	21st to end	Night	69% 9% 9% 9% 4 1	1470
July	1st to 10th	Night	74% 11% 7% 5% 2	3147
	11th to 20th	Night	66% 13% 7% 12% 3	3284
	21st to end	Night	53% 11% 13% 19% 3	3831
August	1st to 10th	Night	62% 10% 11% 13% 3	2904
	11th to 20th	Night	60% 12% 12% 12% 3	2908
	21st to end	Night	56% 7% 12% 22% 3	3233
September	1st to 10th	Night	56% 9% 10% 18% 6% 1	2026
	11th to 20th	Night	59% 8% 11% 12% 9%	2200
	21st to end	Night	49% 8% 13% 20% 9%	2200
October	1st to 10th	Night	61% 8% 12% 15% 4	3770
	11th to 20th	Night	47% 9% 14% 17% 11% 1	3925
	21st to end	Night	54% 9% 13% 17% 6%	4610
November	1st to 10th	Night	59% 7% 13% 14% 6% 1	2668
	11th to 20th	Night	63% 8% 12% 13% 4 1	2940
	21st to end	Night	60% 8% 14% 12% 6% 1	2940
December	1st to 10th	Night	59% 9% 11% 15% 7%	5040
	11th to 20th	Night	60% 10% 15% 10% 5%	5733
	21st to end	Night	69% 6% 9% 10% 5%	7645

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	29% 17% 34% 16% 4 1	430
	11th to 20th	Day	29% 17% 32% 15% 6% 1	430
	21st to end	Day	27% 21% 31% 19% 3	473
February	1st to 10th	Day	31% 17% 30% 17% 4	430
	11th to 20th	Day	28% 22% 35% 11% 4	426
	21st to end	Day	24% 20% 30% 20% 5%	355
March	1st to 10th	Day	23% 27% 32% 15% 3	430
	11th to 20th	Day	24% 14% 31% 24% 7% 1	430
	21st to end	Day	28% 19% 29% 17% 5% 1	473
April	1st to 10th	Day	31% 17% 30% 18% 4 1	553
	11th to 20th	Day	29% 14% 28% 20% 8% 1	739
	21st to end	Day	30% 14% 29% 19% 7% 1	750
May	1st to 10th	Day	29% 12% 28% 22% 7% 1	753
	11th to 20th	Day	27% 10% 28% 25% 9% 1	774
	21st to end	Day	28% 12% 27% 25% 9%	845
June	1st to 10th	Day	41% 9% 20% 21% 8% 1	780
	11th to 20th	Day	31% 7% 26% 27% 9% 1	780
	21st to end	Day	30% 8% 25% 25% 10% 1	780
July	1st to 10th	Day	32% 10% 24% 26% 8% 1	720
	11th to 20th	Day	32% 8% 18% 29% 12% 1	718
	21st to end	Day	31% 8% 22% 27% 11% 1	795
August	1st to 10th	Day	28% 7% 21% 30% 13% 2	725
	11th to 20th	Day	29% 7% 19% 27% 17% 1	717
	21st to end	Day	25% 7% 25% 29% 14% 1	803
September	1st to 10th	Day	25% 9% 23% 25% 17% 1	548
	11th to 20th	Day	27% 10% 27% 24% 10% 2	420
	21st to end	Day	22% 10% 31% 25% 10% 1	420
October	1st to 10th	Day	22% 12% 30% 25% 10%	420
	11th to 20th	Day	28% 9% 34% 19% 9% 2	420
	21st to end	Day	29% 18% 25% 20% 6% 2	462
November	1st to 10th	Day	23% 20% 29% 21% 6%	425
	11th to 20th	Day	33% 16% 28% 18% 5% 1	430
	21st to end	Day	34% 17% 26% 15% 6% 1	430
December	1st to 10th	Day	28% 19% 30% 16% 8%	430
	11th to 20th	Day	27% 24% 30% 15% 3	430
	21st to end	Day	27% 18% 30% 20% 5%	473
January	1st to 10th	Night	28% 20% 35% 14% 3	950
	11th to 20th	Night	32% 17% 29% 16% 5%	950
	21st to end	Night	26% 21% 31% 18% 3	1045
February	1st to 10th	Night	28% 21% 34% 14% 3	950
	11th to 20th	Night	29% 20% 35% 13% 3	919
	21st to end	Night	21% 16% 36% 21% 6%	692
March	1st to 10th	Night	27% 19% 35% 16% 3	809
	11th to 20th	Night	23% 15% 32% 22% 9%	630
	21st to end	Night	33% 16% 27% 20% 4 1	693
April	1st to 10th	Night	34% 15% 27% 16% 7% 1	630
	11th to 20th	Night	33% 12% 27% 22% 7%	624
	21st to end	Night	34% 12% 25% 19% 9% 1	630
May	1st to 10th	Night	33% 9% 24% 24% 9% 1	630
	11th to 20th	Night	32% 5% 26% 25% 10% 1	622
	21st to end	Night	32% 8% 26% 27% 6% 1	682
June	1st to 10th	Night	42% 6% 20% 24% 7% 1	630
	11th to 20th	Night	35% 8% 25% 21% 10% 1	630
	21st to end	Night	34% 7% 22% 26% 10% 1	630
July	1st to 10th	Night	35% 8% 21% 26% 9% 1	587
	11th to 20th	Night	32% 8% 23% 28% 9%	582
	21st to end	Night	33% 8% 20% 28% 10% 1	656
August	1st to 10th	Night	31% 5% 21% 28% 12% 2	598
	11th to 20th	Night	33% 4 19% 29% 14% 1	592
	21st to end	Night	28% 5% 23% 32% 12%	660
September	1st to 10th	Night	26% 6% 26% 28% 14% 1	600
	11th to 20th	Night	30% 8% 27% 25% 9% 1	600
	21st to end	Night	25% 7% 30% 27% 10% 1	600
October	1st to 10th	Night	25% 11% 28% 26% 9% 1	657
	11th to 20th	Night	28% 10% 34% 20% 7% 1	724
	21st to end	Night	31% 14% 27% 20% 7% 1	1001
November	1st to 10th	Night	30% 15% 30% 19% 6%	930
	11th to 20th	Night	30% 15% 30% 18% 6% 1	950
	21st to end	Night	30% 17% 32% 17% 4	950
December	1st to 10th	Night	30% 18% 29% 18% 5%	950
	11th to 20th	Night	30% 25% 28% 13% 3	950
	21st to end	Night	25% 17% 32% 20% 6%	1045

Page generated at 2026-06-28 03:10:45. Version ac07

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