North Cape
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Cape clear sky chart from 2005-11-06 to 2026-04-17.

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% 4 9% 5% 5% 4 3 5% 6% 32%	131699
	Night	18% 13% 5% 11% 6% 5% 4 3 5% 6% 26%	130608
Transparency	Day	54% 5% 13% 19% 8% 1	135207
	Night	60% 5% 11% 16% 7% 1	135190
Seeing	Day	22% 8% 26% 28% 13% 3	18772
	Night	25% 10% 27% 26% 10% 1	26361

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	15% 22% 7% 16% 8% 7% 4 3 4 4 9%	4093
	11th to 20th	Day	17% 16% 11% 17% 6% 5% 4 2 3 3 16%	4280
	21st to end	Day	6% 11% 5% 10% 9% 7% 8% 3 5% 8% 29%	5667
February	1st to 10th	Day	15% 13% 4 9% 5% 5% 5% 4 5% 5% 31%	1890
	11th to 20th	Day	14% 14% 5% 9% 6% 5% 4 4 5% 5% 31%	1843
	21st to end	Day	10% 12% 3 8% 6% 5% 4 5% 5% 6% 36%	1557
March	1st to 10th	Day	17% 13% 5% 11% 5% 8% 4 3 4 5% 26%	4948
	11th to 20th	Day	15% 13% 4 11% 6% 5% 5% 4 5% 7% 25%	5090
	21st to end	Day	24% 14% 4 8% 5% 4 4 3 5% 7% 23%	5604
April	1st to 10th	Day	19% 11% 3 8% 5% 4 4 3 5% 6% 33%	2520
	11th to 20th	Day	19% 9% 2 6% 4 4 4 3 5% 8% 36%	2571
	21st to end	Day	21% 11% 4 8% 4 3 4 3 4 6% 32%	2600
May	1st to 10th	Day	22% 10% 4 8% 4 4 4 3 4 6% 30%	6207
	11th to 20th	Day	19% 9% 2 6% 4 4 4 3 5% 6% 36%	6318
	21st to end	Day	18% 8% 3 6% 4 4 4 3 5% 7% 37%	6948
June	1st to 10th	Day	23% 9% 3 8% 4 5% 4 3 6% 6% 29%	2974
	11th to 20th	Day	16% 10% 2 6% 5% 4 5% 4 5% 7% 37%	3000
	21st to end	Day	22% 8% 3 6% 4 4 4 4 5% 7% 32%	3000
July	1st to 10th	Day	12% 8% 3 8% 5% 5% 5% 4 7% 9% 33%	6820
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	6733
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 44%	6927
August	1st to 10th	Day	14% 7% 3 8% 4 5% 5% 4 6% 8% 36%	4273
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 5% 8% 42%	4175
	21st to end	Day	15% 5% 1 5% 3 3 3 3 6% 7% 48%	4549
September	1st to 10th	Day	15% 6% 2 4 4 4 5% 4 6% 7% 44%	2400
	11th to 20th	Day	18% 6% 3 6% 3 4 3 3 4 6% 45%	2335
	21st to end	Day	16% 6% 3 5% 4 3 4 3 5% 6% 44%	2130
October	1st to 10th	Day	19% 8% 2 6% 4 3 4 4 5% 7% 38%	2000
	11th to 20th	Day	20% 12% 4 8% 6% 4 4 3 5% 8% 29%	2000
	21st to end	Day	22% 14% 3 8% 5% 4 4 3 4 7% 25%	2132
November	1st to 10th	Day	19% 18% 4 8% 5% 4 3 3 6% 5% 25%	1645
	11th to 20th	Day	20% 20% 7% 10% 6% 5% 3 3 4 5% 16%	1680
	21st to end	Day	20% 18% 8% 13% 5% 4 4 4 5% 5% 15%	1680
December	1st to 10th	Day	18% 17% 9% 19% 6% 4 3 2 3 3 17%	2690
	11th to 20th	Day	17% 17% 6% 19% 7% 4 3 2 2 3 20%	2867
	21st to end	Day	16% 14% 8% 21% 7% 5% 3 2 3 4 16%	3553
January	1st to 10th	Night	17% 20% 7% 17% 7% 7% 3 2 3 4 13%	8831
	11th to 20th	Night	18% 18% 8% 15% 6% 4 3 3 4 4 18%	8619
	21st to end	Night	6% 12% 5% 10% 9% 8% 7% 4 6% 8% 25%	8503
February	1st to 10th	Night	14% 14% 4 9% 6% 4 5% 4 6% 5% 30%	2730
	11th to 20th	Night	15% 14% 5% 8% 5% 5% 5% 3 4 6% 29%	2663
	21st to end	Night	12% 14% 3 8% 6% 4 5% 4 5% 6% 34%	2249
March	1st to 10th	Night	20% 13% 4 10% 6% 5% 4 3 4 5% 26%	5094
	11th to 20th	Night	20% 16% 5% 10% 5% 5% 4 2 4 5% 23%	5089
	21st to end	Night	26% 13% 4 10% 5% 4 3 3 4 4 23%	5556
April	1st to 10th	Night	23% 12% 3 8% 5% 5% 4 3 5% 5% 28%	2100
	11th to 20th	Night	22% 11% 3 7% 4 3 3 3 5% 6% 33%	1907
	21st to end	Night	21% 12% 4 8% 4 4 4 2 4 5% 32%	1800
May	1st to 10th	Night	27% 11% 3 8% 5% 4 3 3 4 5% 27%	3747
	11th to 20th	Night	20% 8% 3 7% 5% 4 5% 4 5% 6% 35%	3596
	21st to end	Night	17% 9% 3 7% 5% 4 5% 4 6% 7% 32%	3948
June	1st to 10th	Night	23% 12% 3 7% 5% 4 4 3 6% 7% 28%	1442
	11th to 20th	Night	18% 7% 3 6% 5% 4 4 5% 6% 7% 35%	1400
	21st to end	Night	22% 9% 3 8% 6% 5% 4 4 6% 7% 28%	1400
July	1st to 10th	Night	15% 8% 3 9% 6% 5% 6% 4 7% 8% 29%	3160
	11th to 20th	Night	11% 6% 2 8% 6% 6% 5% 4 6% 9% 38%	3200
	21st to end	Night	12% 6% 3 6% 4 5% 5% 5% 7% 8% 39%	3948
August	1st to 10th	Night	16% 7% 3 9% 6% 6% 6% 5% 6% 7% 30%	2875
	11th to 20th	Night	11% 6% 3 8% 5% 5% 5% 4 7% 8% 39%	2872
	21st to end	Night	14% 5% 2 5% 4 4 5% 4 6% 7% 44%	3347
September	1st to 10th	Night	17% 7% 2 6% 3 4 4 3 5% 7% 44%	2000
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 4 6% 45%	2062
	21st to end	Night	17% 7% 2 7% 3 4 3 3 5% 6% 42%	2270
October	1st to 10th	Night	20% 7% 2 7% 5% 4 4 4 5% 6% 37%	2400
	11th to 20th	Night	20% 12% 3 9% 4 4 3 3 5% 6% 31%	2400
	21st to end	Night	24% 13% 4 8% 5% 4 4 3 5% 6% 24%	2703
November	1st to 10th	Night	21% 16% 4 9% 4 4 3 3 4 5% 26%	2873
	11th to 20th	Night	22% 19% 5% 9% 6% 4 4 3 4 6% 18%	2940
	21st to end	Night	24% 19% 6% 12% 5% 4 3 3 4 5% 16%	2940
December	1st to 10th	Night	17% 15% 8% 18% 6% 4 4 3 4 5% 16%	4720
	11th to 20th	Night	17% 16% 7% 20% 5% 3 3 2 3 3 20%	5557
	21st to end	Night	22% 14% 7% 17% 6% 5% 3 2 3 4 16%	7667

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	81% 4 8% 4 3	4094
	11th to 20th	Day	76% 3 10% 5% 6% 1	4307
	21st to end	Day	59% 4 15% 13% 8%	5667
February	1st to 10th	Day	57% 4 13% 16% 10% 1	1890
	11th to 20th	Day	56% 5% 11% 19% 8% 1	1851
	21st to end	Day	50% 4 10% 20% 14% 2	1557
March	1st to 10th	Day	62% 4 9% 18% 8%	4952
	11th to 20th	Day	59% 6% 14% 13% 6% 2	5090
	21st to end	Day	62% 3 8% 16% 9% 1	5604
April	1st to 10th	Day	53% 4 11% 16% 15% 2	2520
	11th to 20th	Day	47% 5% 12% 21% 13% 1	2571
	21st to end	Day	54% 4 10% 16% 13% 3	2600
May	1st to 10th	Day	56% 5% 10% 19% 9% 1	6219
	11th to 20th	Day	49% 6% 13% 26% 6%	6322
	21st to end	Day	46% 7% 12% 25% 10%	6948
June	1st to 10th	Day	55% 6% 10% 20% 8% 1	2974
	11th to 20th	Day	47% 6% 12% 23% 11% 1	3000
	21st to end	Day	53% 7% 13% 17% 9% 1	3000
July	1st to 10th	Day	46% 6% 19% 20% 8%	6745
	11th to 20th	Day	39% 6% 17% 30% 8%	6652
	21st to end	Day	38% 7% 20% 29% 7%	6730
August	1st to 10th	Day	46% 7% 14% 24% 8%	4259
	11th to 20th	Day	40% 7% 14% 26% 12%	4214
	21st to end	Day	37% 5% 17% 29% 11% 1	4549
September	1st to 10th	Day	39% 7% 16% 26% 12%	2400
	11th to 20th	Day	43% 5% 13% 26% 12% 1	2335
	21st to end	Day	41% 6% 12% 28% 12%	2130
October	1st to 10th	Day	46% 5% 15% 25% 8% 1	3260
	11th to 20th	Day	55% 3 11% 24% 6%	3240
	21st to end	Day	52% 5% 19% 17% 8%	3413
November	1st to 10th	Day	62% 4 12% 16% 6% 1	1645
	11th to 20th	Day	73% 4 11% 8% 4	1680
	21st to end	Day	73% 5% 13% 6% 3	1680
December	1st to 10th	Day	76% 4 6% 11% 2	2690
	11th to 20th	Day	74% 2 9% 7% 6%	2866
	21st to end	Day	74% 5% 9% 9% 3	3553
January	1st to 10th	Night	78% 4 8% 9% 1	8831
	11th to 20th	Night	72% 3 11% 9% 5%	8667
	21st to end	Night	62% 5% 12% 14% 6% 1	8503
February	1st to 10th	Night	56% 5% 10% 15% 12% 2	2730
	11th to 20th	Night	57% 4 10% 17% 11% 1	2666
	21st to end	Night	52% 4 9% 19% 15% 2	2249
March	1st to 10th	Night	61% 3 8% 14% 12% 1	5103
	11th to 20th	Night	64% 5% 10% 13% 8% 1	5090
	21st to end	Night	65% 3 6% 15% 10% 1	5556
April	1st to 10th	Night	59% 4 9% 14% 12% 2	2100
	11th to 20th	Night	53% 4 7% 23% 11% 2	1907
	21st to end	Night	56% 4 8% 15% 14% 3	1800
May	1st to 10th	Night	61% 4 6% 15% 13% 1	3752
	11th to 20th	Night	49% 6% 13% 22% 10% 1	3597
	21st to end	Night	48% 8% 13% 22% 8%	3949
June	1st to 10th	Night	56% 6% 12% 19% 8%	1442
	11th to 20th	Night	47% 6% 10% 24% 11% 1	1400
	21st to end	Night	55% 8% 11% 16% 9% 1	1400
July	1st to 10th	Night	52% 6% 14% 19% 9%	3125
	11th to 20th	Night	43% 6% 17% 28% 6%	3158
	21st to end	Night	41% 8% 21% 23% 8%	3831
August	1st to 10th	Night	53% 7% 13% 20% 7%	2864
	11th to 20th	Night	41% 6% 17% 24% 10% 1	2899
	21st to end	Night	39% 7% 16% 25% 12% 1	3346
September	1st to 10th	Night	41% 6% 12% 30% 11%	2000
	11th to 20th	Night	41% 4 13% 29% 12%	2062
	21st to end	Night	42% 6% 11% 28% 12% 1	2270
October	1st to 10th	Night	51% 5% 14% 23% 8%	3920
	11th to 20th	Night	53% 4 10% 24% 8%	3899
	21st to end	Night	57% 4 13% 18% 8%	4375
November	1st to 10th	Night	61% 5% 12% 15% 6% 1	2873
	11th to 20th	Night	70% 4 11% 11% 4	2940
	21st to end	Night	73% 6% 10% 7% 3	2940
December	1st to 10th	Night	73% 5% 10% 10% 2	4720
	11th to 20th	Night	73% 3 7% 13% 4 1	5559
	21st to end	Night	73% 4 9% 10% 3	7667

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	26% 17% 30% 22% 5%	220
	11th to 20th	Day	28% 20% 25% 19% 6% 2	287
	21st to end	Day	15% 12% 40% 26% 7%	473
February	1st to 10th	Day	24% 12% 33% 23% 6% 2	430
	11th to 20th	Day	20% 16% 35% 20% 7% 1	426
	21st to end	Day	17% 11% 34% 28% 9% 1	355
March	1st to 10th	Day	20% 11% 38% 23% 8% 1	518
	11th to 20th	Day	16% 12% 34% 24% 12% 2	540
	21st to end	Day	26% 12% 29% 22% 9% 1	594
April	1st to 10th	Day	27% 11% 31% 23% 8%	540
	11th to 20th	Day	23% 10% 29% 28% 9% 2	516
	21st to end	Day	25% 9% 25% 25% 13% 2	500
May	1st to 10th	Day	29% 5% 26% 26% 12% 2	643
	11th to 20th	Day	22% 5% 22% 31% 16% 4	724
	21st to end	Day	23% 5% 26% 31% 14% 2	790
June	1st to 10th	Day	27% 5% 24% 29% 12% 3	730
	11th to 20th	Day	20% 4 20% 36% 17% 3	730
	21st to end	Day	27% 3 18% 33% 17% 3	730
July	1st to 10th	Day	17% 3 21% 33% 23% 4	720
	11th to 20th	Day	14% 3 17% 39% 24% 3	718
	21st to end	Day	17% 4 18% 35% 22% 4	795
August	1st to 10th	Day	12% 4 16% 35% 27% 6%	551
	11th to 20th	Day	16% 3 15% 32% 27% 8%	519
	21st to end	Day	18% 5% 19% 30% 22% 6%	583
September	1st to 10th	Day	16% 3 22% 38% 15% 4	530
	11th to 20th	Day	22% 7% 22% 26% 18% 4	530
	21st to end	Day	19% 7% 28% 28% 15% 3	491
October	1st to 10th	Day	24% 7% 20% 30% 17% 2	420
	11th to 20th	Day	27% 9% 28% 23% 12% 2	420
	21st to end	Day	28% 12% 31% 20% 8% 1	462
November	1st to 10th	Day	28% 13% 32% 21% 4 1	425
	11th to 20th	Day	37% 14% 25% 17% 6% 1	430
	21st to end	Day	31% 17% 29% 19% 4	430
December	1st to 10th	Day	31% 13% 35% 17% 3	430
	11th to 20th	Day	29% 22% 28% 18% 3	330
	21st to end	Day	19% 22% 33% 19% 7%	242
January	1st to 10th	Night	28% 14% 32% 20% 5%	950
	11th to 20th	Night	28% 12% 32% 20% 7% 1	950
	21st to end	Night	18% 15% 37% 22% 8% 1	943
February	1st to 10th	Night	23% 12% 33% 23% 8% 2	840
	11th to 20th	Night	23% 13% 35% 21% 6% 2	823
	21st to end	Night	19% 10% 30% 30% 9% 1	692
March	1st to 10th	Night	24% 10% 33% 28% 6%	840
	11th to 20th	Night	24% 9% 30% 26% 9% 1	840
	21st to end	Night	26% 11% 29% 24% 10% 1	918
April	1st to 10th	Night	29% 10% 27% 26% 7%	630
	11th to 20th	Night	26% 7% 27% 28% 9% 2	613
	21st to end	Night	27% 9% 26% 27% 11% 1	600
May	1st to 10th	Night	31% 4 24% 26% 12% 3	600
	11th to 20th	Night	22% 3 23% 32% 17% 4	592
	21st to end	Night	18% 5% 29% 35% 11% 2	649
June	1st to 10th	Night	29% 3 21% 34% 13%	442
	11th to 20th	Night	19% 2 24% 34% 19% 2	400
	21st to end	Night	26% 2 17% 39% 15% 2	400
July	1st to 10th	Night	18% 2 22% 39% 16% 3	390
	11th to 20th	Night	15% 3 20% 38% 23% 1	402
	21st to end	Night	19% 3 18% 39% 19% 2	656
August	1st to 10th	Night	18% 1 18% 40% 21% 3	598
	11th to 20th	Night	19% 2 17% 34% 26% 2	592
	21st to end	Night	16% 3 20% 34% 23% 3	660
September	1st to 10th	Night	21% 5% 26% 34% 13% 3	600
	11th to 20th	Night	21% 7% 20% 34% 16% 1	662
	21st to end	Night	21% 7% 26% 32% 12% 1	800
October	1st to 10th	Night	25% 7% 28% 27% 12% 1	800
	11th to 20th	Night	27% 9% 26% 24% 11% 2	800
	21st to end	Night	35% 13% 26% 21% 6%	904
November	1st to 10th	Night	32% 16% 28% 19% 4 1	930
	11th to 20th	Night	32% 15% 28% 17% 6% 2	950
	21st to end	Night	34% 15% 27% 20% 4 1	950
December	1st to 10th	Night	32% 14% 32% 18% 4	950
	11th to 20th	Night	31% 22% 29% 15% 3 1	950
	21st to end	Night	31% 17% 25% 20% 5% 1	1045

Page generated at 2026-04-14 03:44:30. Version ac07

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