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 2025-02-25.

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 5% 5% 18%	108181
	Night	24% 15% 5% 11% 6% 4 4 3 4 5% 18%	110675
Transparency	Day	62% 9% 11% 12% 5%	111723
	Night	63% 8% 11% 12% 5% 1	115324
Seeing	Day	29% 13% 27% 22% 8% 1	18468
	Night	30% 13% 28% 21% 7% 1	25217

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	20% 17% 7% 11% 6% 5% 5% 4 4 4 18%	3220
	11th to 20th	Day	20% 17% 6% 14% 7% 5% 4 3 4 4 15%	3591
	21st to end	Day	15% 14% 8% 15% 7% 7% 6% 4 4 4 15%	3982
February	1st to 10th	Day	22% 12% 8% 13% 9% 7% 5% 4 5% 4 10%	1785
	11th to 20th	Day	21% 16% 7% 14% 7% 5% 3 3 4 6% 14%	1773
	21st to end	Day	16% 14% 6% 14% 8% 6% 6% 4 5% 5% 17%	1610
March	1st to 10th	Day	25% 13% 5% 12% 6% 5% 5% 3 4 4 18%	3167
	11th to 20th	Day	21% 13% 6% 16% 8% 5% 5% 3 5% 5% 13%	3480
	21st to end	Day	26% 14% 5% 14% 8% 5% 4 3 4 5% 11%	3817
April	1st to 10th	Day	26% 15% 5% 11% 6% 5% 4 3 4 4 17%	2270
	11th to 20th	Day	25% 13% 4 9% 6% 5% 4 3 4 5% 21%	2441
	21st to end	Day	26% 14% 5% 11% 5% 5% 3 3 4 5% 20%	2470
May	1st to 10th	Day	21% 19% 5% 12% 6% 4 4 3 5% 6% 17%	4105
	11th to 20th	Day	31% 18% 4 8% 5% 4 4 3 4 5% 15%	4279
	21st to end	Day	24% 15% 5% 13% 6% 5% 4 3 4 4 17%	5173
June	1st to 10th	Day	36% 16% 4 8% 4 4 3 2 4 5% 13%	2850
	11th to 20th	Day	27% 15% 4 8% 5% 4 4 4 5% 6% 18%	2850
	21st to end	Day	32% 15% 4 8% 5% 4 4 3 4 6% 14%	2850
July	1st to 10th	Day	38% 13% 4 8% 4 4 3 3 4 5% 14%	4750
	11th to 20th	Day	32% 18% 4 9% 5% 5% 4 3 3 5% 14%	4640
	21st to end	Day	24% 12% 3 9% 5% 5% 5% 4 5% 6% 23%	4815
August	1st to 10th	Day	33% 13% 3 7% 4 4 3 3 4 6% 19%	4113
	11th to 20th	Day	25% 13% 4 10% 6% 4 5% 3 5% 5% 20%	4046
	21st to end	Day	24% 9% 3 8% 4 4 4 3 5% 7% 29%	4532
September	1st to 10th	Day	23% 10% 3 8% 4 4 4 4 6% 7% 26%	2252
	11th to 20th	Day	23% 9% 3 9% 6% 5% 4 3 5% 6% 28%	2090
	21st to end	Day	20% 9% 3 6% 5% 5% 4 3 7% 6% 31%	2090
October	1st to 10th	Day	21% 10% 3 9% 5% 5% 4 4 5% 7% 24%	1992
	11th to 20th	Day	24% 11% 4 10% 6% 4 4 4 5% 6% 22%	1885
	21st to end	Day	25% 13% 4 9% 5% 4 4 3 5% 7% 21%	1881
November	1st to 10th	Day	23% 12% 3 10% 5% 4 4 4 4 6% 24%	1758
	11th to 20th	Day	26% 12% 4 10% 6% 6% 3 4 5% 7% 18%	1600
	21st to end	Day	27% 14% 4 10% 5% 5% 4 4 5% 6% 18%	1600
December	1st to 10th	Day	21% 13% 3 9% 5% 6% 6% 5% 7% 7% 17%	2298
	11th to 20th	Day	18% 16% 4 10% 5% 4 4 3 6% 8% 21%	2628
	21st to end	Day	21% 23% 6% 12% 5% 4 5% 3 4 4 13%	3498
January	1st to 10th	Night	19% 17% 7% 11% 6% 5% 5% 3 4 5% 17%	6730
	11th to 20th	Night	18% 15% 8% 16% 7% 5% 5% 3 5% 4 14%	6314
	21st to end	Night	14% 12% 9% 17% 7% 6% 5% 4 5% 5% 16%	6996
February	1st to 10th	Night	23% 14% 6% 13% 7% 6% 5% 3 4 5% 13%	2613
	11th to 20th	Night	24% 14% 5% 13% 6% 5% 5% 3 5% 5% 15%	2508
	21st to end	Night	16% 12% 6% 13% 8% 5% 5% 4 4 6% 19%	1939
March	1st to 10th	Night	25% 13% 6% 10% 5% 4 3 3 4 6% 22%	3673
	11th to 20th	Night	17% 13% 8% 17% 7% 4 4 4 5% 5% 17%	3479
	21st to end	Night	29% 15% 5% 10% 5% 4 4 3 5% 4 16%	3815
April	1st to 10th	Night	27% 17% 5% 9% 5% 5% 4 2 3 5% 19%	1905
	11th to 20th	Night	26% 14% 4 9% 5% 4 3 3 5% 5% 22%	1688
	21st to end	Night	28% 18% 5% 8% 5% 4 4 3 3 4 19%	1710
May	1st to 10th	Night	24% 19% 5% 10% 6% 3 3 3 3 5% 18%	2845
	11th to 20th	Night	35% 17% 4 8% 5% 3 3 3 3 5% 14%	2620
	21st to end	Night	26% 17% 5% 12% 5% 4 4 3 4 5% 16%	2412
June	1st to 10th	Night	38% 16% 4 6% 4 3 3 2 4 5% 14%	1330
	11th to 20th	Night	30% 17% 5% 8% 5% 3 4 3 4 5% 16%	1330
	21st to end	Night	33% 17% 4 9% 5% 4 3 3 3 4 14%	1330
July	1st to 10th	Night	47% 14% 4 9% 4 3 2 2 3 4 9%	2220
	11th to 20th	Night	34% 25% 6% 10% 4 3 3 2 2 3 8%	2327
	21st to end	Night	26% 17% 4 9% 6% 4 3 3 3 3 21%	2750
August	1st to 10th	Night	29% 21% 4 8% 4 3 3 3 4 4 17%	2825
	11th to 20th	Night	29% 17% 5% 8% 4 4 4 3 5% 5% 17%	2791
	21st to end	Night	30% 10% 3 7% 4 3 3 3 4 6% 27%	3135
September	1st to 10th	Night	26% 11% 3 8% 4 3 4 3 5% 7% 27%	1924
	11th to 20th	Night	27% 11% 3 7% 5% 5% 4 3 5% 4 25%	2090
	21st to end	Night	23% 7% 3 6% 4 5% 3 4 6% 6% 32%	2090
October	1st to 10th	Night	23% 10% 3 8% 5% 4 4 4 5% 7% 27%	2187
	11th to 20th	Night	23% 12% 4 8% 5% 4 4 5% 5% 6% 23%	2293
	21st to end	Night	24% 13% 4 9% 6% 4 4 3 5% 5% 22%	2717
November	1st to 10th	Night	25% 13% 4 8% 5% 5% 4 3 5% 6% 23%	2538
	11th to 20th	Night	25% 14% 4 8% 4 4 5% 4 5% 6% 21%	2800
	21st to end	Night	22% 13% 3 9% 5% 5% 5% 4 6% 6% 20%	2800
December	1st to 10th	Night	20% 15% 4 10% 5% 5% 5% 4 5% 7% 20%	4890
	11th to 20th	Night	22% 14% 5% 10% 6% 5% 5% 4 5% 6% 19%	5581
	21st to end	Night	21% 19% 6% 11% 5% 4 4 3 4 5% 17%	7480

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	62% 11% 9% 11% 7% 1	3221
	11th to 20th	Day	68% 8% 9% 10% 5% 1	3620
	21st to end	Day	63% 9% 9% 12% 7% 1	3982
February	1st to 10th	Day	71% 9% 8% 6% 4 1	1785
	11th to 20th	Day	66% 8% 12% 10% 3 1	1780
	21st to end	Day	65% 8% 9% 8% 8% 2	1610
March	1st to 10th	Day	65% 6% 9% 12% 6% 1	3172
	11th to 20th	Day	67% 8% 12% 9% 4	3480
	21st to end	Day	70% 5% 10% 10% 3 1	3817
April	1st to 10th	Day	65% 6% 12% 11% 6% 1	2270
	11th to 20th	Day	61% 8% 11% 11% 8% 1	2441
	21st to end	Day	65% 7% 8% 11% 8% 1	2470
May	1st to 10th	Day	68% 8% 9% 11% 4	4120
	11th to 20th	Day	72% 8% 7% 9% 4	4283
	21st to end	Day	63% 11% 9% 12% 3	5173
June	1st to 10th	Day	74% 6% 8% 9% 3	2850
	11th to 20th	Day	65% 9% 10% 11% 4	2850
	21st to end	Day	68% 11% 7% 11% 3	2850
July	1st to 10th	Day	70% 8% 9% 9% 3	4675
	11th to 20th	Day	65% 12% 10% 8% 5%	4558
	21st to end	Day	51% 14% 15% 13% 7%	4662
August	1st to 10th	Day	61% 10% 12% 14% 3	4099
	11th to 20th	Day	59% 11% 13% 14% 3	4085
	21st to end	Day	50% 9% 14% 24% 3	4532
September	1st to 10th	Day	53% 8% 12% 19% 7%	2252
	11th to 20th	Day	54% 8% 11% 16% 10%	2090
	21st to end	Day	50% 8% 15% 19% 8% 1	2090
October	1st to 10th	Day	61% 10% 10% 15% 4 1	3310
	11th to 20th	Day	45% 7% 14% 20% 12% 2	3123
	21st to end	Day	54% 9% 12% 17% 7%	3092
November	1st to 10th	Day	57% 8% 16% 13% 6%	1758
	11th to 20th	Day	63% 8% 12% 12% 6% 1	1600
	21st to end	Day	65% 8% 12% 11% 4	1600
December	1st to 10th	Day	54% 12% 15% 13% 6%	2298
	11th to 20th	Day	56% 9% 16% 13% 5%	2627
	21st to end	Day	72% 7% 7% 10% 4	3498
January	1st to 10th	Night	63% 9% 9% 10% 7% 3	6730
	11th to 20th	Night	70% 8% 11% 8% 4	6360
	21st to end	Night	62% 9% 11% 10% 6% 1	6996
February	1st to 10th	Night	71% 7% 8% 8% 4 1	2613
	11th to 20th	Night	66% 10% 10% 9% 4 1	2512
	21st to end	Night	62% 9% 11% 11% 6% 1	1939
March	1st to 10th	Night	64% 6% 10% 15% 5%	3681
	11th to 20th	Night	66% 9% 10% 10% 4	3480
	21st to end	Night	69% 5% 10% 11% 5%	3815
April	1st to 10th	Night	66% 6% 8% 12% 7% 1	1905
	11th to 20th	Night	62% 6% 9% 12% 9% 1	1688
	21st to end	Night	70% 4 7% 11% 7% 1	1710
May	1st to 10th	Night	66% 8% 9% 12% 4	2850
	11th to 20th	Night	73% 5% 7% 10% 4	2621
	21st to end	Night	67% 7% 9% 13% 4	2413
June	1st to 10th	Night	75% 5% 7% 9% 3	1330
	11th to 20th	Night	68% 8% 8% 11% 4	1330
	21st to end	Night	72% 9% 8% 7% 4 1	1330
July	1st to 10th	Night	77% 7% 6% 6% 3	2186
	11th to 20th	Night	71% 15% 6% 6% 2	2285
	21st to end	Night	56% 13% 12% 16% 4	2663
August	1st to 10th	Night	64% 11% 11% 12% 3	2814
	11th to 20th	Night	61% 12% 12% 11% 3	2818
	21st to end	Night	56% 7% 12% 22% 3	3134
September	1st to 10th	Night	55% 9% 10% 19% 6% 1	1924
	11th to 20th	Night	59% 8% 11% 12% 9%	2090
	21st to end	Night	50% 9% 14% 19% 8%	2090
October	1st to 10th	Night	61% 8% 12% 14% 4	3655
	11th to 20th	Night	47% 9% 15% 17% 11% 1	3804
	21st to end	Night	54% 9% 14% 17% 6%	4467
November	1st to 10th	Night	60% 7% 13% 14% 6% 1	2538
	11th to 20th	Night	63% 8% 12% 13% 4 1	2800
	21st to end	Night	59% 8% 14% 12% 6% 1	2800
December	1st to 10th	Night	59% 9% 11% 15% 7%	4890
	11th to 20th	Night	60% 10% 15% 10% 5%	5583
	21st to end	Night	69% 6% 9% 10% 5%	7480

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	28% 18% 34% 16% 5% 1	400
	11th to 20th	Day	27% 17% 32% 16% 7% 1	400
	21st to end	Day	28% 19% 31% 19% 3	440
February	1st to 10th	Day	31% 19% 31% 16% 4 1	400
	11th to 20th	Day	28% 23% 36% 11% 3	396
	21st to end	Day	23% 20% 30% 22% 5%	319
March	1st to 10th	Day	23% 27% 32% 15% 3	370
	11th to 20th	Day	23% 15% 31% 24% 8% 1	370
	21st to end	Day	27% 20% 29% 16% 6% 1	407
April	1st to 10th	Day	32% 16% 30% 18% 4 1	473
	11th to 20th	Day	30% 15% 27% 19% 8% 1	639
	21st to end	Day	30% 14% 30% 19% 6% 1	650
May	1st to 10th	Day	29% 13% 29% 21% 7% 2	653
	11th to 20th	Day	28% 9% 28% 25% 8% 1	674
	21st to end	Day	29% 12% 26% 24% 8%	735
June	1st to 10th	Day	43% 9% 21% 19% 7% 1	680
	11th to 20th	Day	33% 7% 26% 27% 7% 1	680
	21st to end	Day	33% 9% 24% 24% 9% 1	680
July	1st to 10th	Day	33% 10% 25% 25% 8% 1	670
	11th to 20th	Day	32% 9% 19% 28% 11% 1	668
	21st to end	Day	32% 8% 22% 26% 11% 1	740
August	1st to 10th	Day	29% 8% 22% 29% 11% 1	675
	11th to 20th	Day	30% 7% 19% 27% 16% 1	667
	21st to end	Day	25% 6% 25% 28% 15% 1	748
September	1st to 10th	Day	25% 9% 23% 25% 16% 2	510
	11th to 20th	Day	28% 11% 27% 24% 9% 1	390
	21st to end	Day	24% 10% 31% 25% 10% 1	390
October	1st to 10th	Day	23% 12% 31% 25% 10%	390
	11th to 20th	Day	28% 9% 33% 19% 9% 2	390
	21st to end	Day	28% 19% 26% 20% 5% 1	429
November	1st to 10th	Day	24% 20% 28% 21% 7%	395
	11th to 20th	Day	33% 16% 28% 17% 5% 1	400
	21st to end	Day	35% 17% 27% 15% 6% 1	400
December	1st to 10th	Day	29% 18% 29% 16% 8%	400
	11th to 20th	Day	27% 24% 30% 16% 4	400
	21st to end	Day	26% 18% 30% 19% 5%	440
January	1st to 10th	Night	28% 20% 35% 13% 3	900
	11th to 20th	Night	31% 17% 29% 16% 5%	900
	21st to end	Night	27% 20% 31% 19% 3	990
February	1st to 10th	Night	28% 22% 35% 14% 2	900
	11th to 20th	Night	29% 20% 36% 12% 3	870
	21st to end	Night	21% 16% 35% 21% 6%	647
March	1st to 10th	Night	28% 18% 34% 16% 3	732
	11th to 20th	Night	22% 14% 31% 22% 9% 1	570
	21st to end	Night	33% 15% 27% 20% 4 1	627
April	1st to 10th	Night	34% 14% 27% 17% 7% 1	570
	11th to 20th	Night	34% 13% 25% 21% 7%	564
	21st to end	Night	34% 11% 26% 20% 8% 1	570
May	1st to 10th	Night	33% 9% 23% 24% 9% 1	570
	11th to 20th	Night	33% 5% 26% 25% 10% 1	562
	21st to end	Night	32% 9% 26% 26% 7% 1	616
June	1st to 10th	Night	44% 6% 20% 23% 6% 1	570
	11th to 20th	Night	36% 8% 25% 21% 9% 1	570
	21st to end	Night	36% 7% 22% 24% 9% 1	570
July	1st to 10th	Night	36% 8% 21% 26% 8% 1	556
	11th to 20th	Night	32% 8% 24% 27% 9%	552
	21st to end	Night	34% 8% 20% 27% 10% 1	623
August	1st to 10th	Night	32% 5% 23% 27% 11% 2	568
	11th to 20th	Night	34% 4 20% 29% 13% 1	562
	21st to end	Night	28% 5% 23% 31% 12%	627
September	1st to 10th	Night	27% 5% 27% 27% 13% 1	570
	11th to 20th	Night	30% 8% 27% 25% 9% 1	570
	21st to end	Night	26% 7% 29% 27% 10% 1	570
October	1st to 10th	Night	26% 11% 29% 25% 9% 1	622
	11th to 20th	Night	28% 10% 34% 20% 8% 1	683
	21st to end	Night	31% 15% 29% 20% 6% 1	946
November	1st to 10th	Night	30% 15% 30% 19% 6%	880
	11th to 20th	Night	30% 15% 30% 18% 6% 1	900
	21st to end	Night	31% 17% 32% 16% 4	900
December	1st to 10th	Night	30% 17% 30% 17% 5%	900
	11th to 20th	Night	31% 24% 28% 14% 3	900
	21st to end	Night	25% 17% 31% 20% 6%	990

Page generated at 2025-02-22 07:51:33. Version ac07

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