North Point Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Point Observatory clear sky chart from 2005-11-06 to 2026-03-18.

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	6% 4 2 5% 3 3 3 3 5% 7% 60%	140014
	Night	8% 5% 2 6% 3 3 4 3 5% 7% 54%	138971
Transparency	Day	25% 4 8% 21% 24% 18%	134924
	Night	28% 4 9% 21% 22% 16%	135050
Seeing	Day	8% 10% 23% 31% 22% 7%	17097
	Night	10% 6% 16% 34% 29% 5%	26504

By Month

Percentage Cloud Cover SW (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% 7% 2 7% 4 4 5% 4 6% 8% 40%	5059
	11th to 20th	Day	9% 7% 2 6% 3 3 3 2 4 7% 53%	5340
	21st to end	Day	13% 7% 3 9% 5% 5% 4 4 5% 8% 38%	5843
February	1st to 10th	Day	15% 7% 2 6% 3 4 4 4 5% 6% 44%	1890
	11th to 20th	Day	12% 8% 3 7% 5% 5% 3 4 5% 8% 40%	1905
	21st to end	Day	13% 5% 2 6% 5% 4 4 4 5% 6% 45%	1730
March	1st to 10th	Day	10% 8% 3 9% 6% 5% 5% 4 6% 7% 36%	5019
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 3 6% 7% 49%	5078
	21st to end	Day	11% 7% 2 6% 4 5% 6% 5% 8% 9% 37%	5528
April	1st to 10th	Day	9% 7% 3 6% 4 4 4 4 6% 8% 44%	2400
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 5% 8% 53%	2369
	21st to end	Day	3 4 2 4 3 4 3 3 6% 9% 59%	2400
May	1st to 10th	Day	3 2 1 2 1 1 1 1 3 5% 78%	5734
	11th to 20th	Day	2 2 1 3 2 2 2 2 4 7% 74%	5959
	21st to end	Day	1 2 1 2 1 2 2 2 3 6% 77%	6902
June	1st to 10th	Day	4 4 2 4 3 3 3 3 4 8% 61%	2800
	11th to 20th	Day	1 2 1 3 2 1 2 2 5% 7% 74%	2800
	21st to end	Day	2 3 1 3 3 2 2 2 3 5% 74%	2800
July	1st to 10th	Day	2 1 3 2 2 2 2 2 5% 81%	6319
	11th to 20th	Day	2 1 3 2 3 3 2 4 6% 73%	5890
	21st to end	Day	3 2 5% 3 2 2 2 3 6% 71%	6402
August	1st to 10th	Day	1 2 1 3 2 3 3 3 5% 6% 71%	5777
	11th to 20th	Day	1 2 1 3 2 1 2 2 3 5% 80%	5587
	21st to end	Day	1 3 1 3 3 3 3 3 4 7% 70%	5984
September	1st to 10th	Day	1 3 1 4 2 2 2 2 3 6% 74%	2400
	11th to 20th	Day	2 6% 1 5% 3 3 3 2 4 7% 64%	2400
	21st to end	Day	3 3 1 3 2 2 2 2 3 6% 73%	2105
October	1st to 10th	Day	2 2 1 3 3 2 2 2 4 7% 72%	3280
	11th to 20th	Day	4 4 2 6% 3 3 3 2 4 6% 63%	3261
	21st to end	Day	5% 4 2 5% 4 3 4 4 5% 8% 57%	3558
November	1st to 10th	Day	8% 4 1 4 4 3 4 3 6% 8% 55%	2033
	11th to 20th	Day	9% 8% 3 8% 5% 4 4 3 6% 7% 44%	1882
	21st to end	Day	10% 7% 2 4 4 3 4 4 5% 7% 50%	1680
December	1st to 10th	Day	9% 4 2 5% 3 3 3 4 7% 10% 50%	2700
	11th to 20th	Day	19% 10% 4 11% 7% 4 5% 3 6% 5% 26%	3108
	21st to end	Day	23% 8% 3 8% 4 4 4 4 6% 8% 27%	4092
January	1st to 10th	Night	15% 6% 3 7% 4 3 4 4 6% 9% 40%	7847
	11th to 20th	Night	9% 5% 2 6% 3 3 3 3 5% 10% 50%	7650
	21st to end	Night	13% 8% 3 8% 4 4 5% 4 5% 8% 39%	8371
February	1st to 10th	Night	14% 6% 2 6% 4 3 4 3 5% 7% 47%	2730
	11th to 20th	Night	12% 6% 3 5% 4 4 5% 4 5% 8% 44%	2600
	21st to end	Night	11% 5% 2 4 4 3 4 3 5% 7% 51%	2076
March	1st to 10th	Night	10% 7% 3 7% 5% 5% 5% 4 5% 7% 41%	5081
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 52%	5077
	21st to end	Night	11% 7% 2 6% 4 4 4 3 5% 8% 45%	5446
April	1st to 10th	Night	7% 5% 2 6% 4 4 3 3 6% 8% 52%	2000
	11th to 20th	Night	7% 4 2 5% 3 3 3 3 5% 6% 58%	1979
	21st to end	Night	4 4 2 4 3 3 3 3 6% 8% 62%	2000
May	1st to 10th	Night	2 3 2 3 2 2 2 2 3 5% 75%	4248
	11th to 20th	Night	1 2 1 4 4 3 3 2 4 8% 68%	3946
	21st to end	Night	2 2 1 2 2 2 2 2 2 4 80%	3972
June	1st to 10th	Night	3 3 1 4 3 4 3 4 6% 9% 60%	1600
	11th to 20th	Night	1 1 1 2 2 2 2 2 5% 7% 75%	1600
	21st to end	Night	1 2 1 4 2 3 2 2 4 7% 71%	1600
July	1st to 10th	Night	1 1 3 2 2 3 2 3 5% 79%	3640
	11th to 20th	Night	1 3 1 6% 3 4 4 4 7% 8% 58%	4072
	21st to end	Night	5% 3 11% 4 4 5% 4 6% 7% 51%	4472
August	1st to 10th	Night	2 3 1 5% 4 3 3 3 5% 7% 64%	4035
	11th to 20th	Night	2 2 4 3 2 3 2 4 6% 72%	4272
	21st to end	Night	1 2 1 3 3 3 4 3 5% 8% 66%	5015
September	1st to 10th	Night	1 2 1 3 2 3 3 3 4 9% 70%	2000
	11th to 20th	Night	2 5% 2 6% 3 3 3 3 6% 7% 61%	2000
	21st to end	Night	1 3 2 5% 3 3 3 3 4 7% 67%	2290
October	1st to 10th	Night	3 2 1 3 2 2 3 2 4 6% 71%	3920
	11th to 20th	Night	3 4 2 5% 3 3 4 3 5% 7% 61%	3897
	21st to end	Night	5% 3 1 5% 3 3 3 3 5% 7% 61%	4253
November	1st to 10th	Night	7% 4 2 4 4 4 3 4 4 9% 55%	2485
	11th to 20th	Night	10% 6% 3 6% 4 3 4 3 5% 8% 49%	2735
	21st to end	Night	8% 5% 2 6% 4 4 2 3 5% 8% 53%	2940
December	1st to 10th	Night	8% 4 2 5% 3 4 4 4 6% 9% 50%	4700
	11th to 20th	Night	21% 9% 3 8% 4 4 4 4 7% 8% 26%	5316
	21st to end	Night	22% 9% 4 8% 4 4 4 3 5% 6% 30%	7106

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	41% 7% 14% 23% 11% 4	5060
	11th to 20th	Day	33% 2 7% 16% 22% 19%	5340
	21st to end	Day	45% 4 8% 18% 11% 14%	5843
February	1st to 10th	Day	41% 3 7% 21% 20% 8%	1890
	11th to 20th	Day	42% 5% 10% 19% 18% 6%	1914
	21st to end	Day	39% 5% 9% 24% 16% 7%	1730
March	1st to 10th	Day	45% 3 9% 21% 19% 2	5019
	11th to 20th	Day	31% 5% 15% 29% 11% 8%	5078
	21st to end	Day	39% 7% 17% 26% 9% 2	5528
April	1st to 10th	Day	36% 5% 14% 22% 19% 4	2400
	11th to 20th	Day	30% 4 15% 25% 21% 6%	2372
	21st to end	Day	23% 4 14% 31% 24% 4	2400
May	1st to 10th	Day	12% 2 7% 31% 31% 17%	5734
	11th to 20th	Day	11% 3 6% 34% 35% 11%	5962
	21st to end	Day	11% 2 7% 36% 41% 3	6904
June	1st to 10th	Day	22% 3 10% 29% 29% 7%	2800
	11th to 20th	Day	12% 2 9% 22% 38% 17%	2800
	21st to end	Day	13% 3 3 15% 36% 30%	2800
July	1st to 10th	Day	8% 2 2 9% 23% 57%	6251
	11th to 20th	Day	9% 4 2 6% 22% 57%	5820
	21st to end	Day	13% 3 5% 17% 28% 33%	6217
August	1st to 10th	Day	15% 4 3 12% 31% 35%	4206
	11th to 20th	Day	9% 2 2 11% 44% 32%	4046
	21st to end	Day	13% 3 3 15% 37% 28%	4311
September	1st to 10th	Day	13% 2 3 11% 32% 39%	2400
	11th to 20th	Day	21% 3 5% 25% 34% 13%	2400
	21st to end	Day	15% 2 4 23% 34% 23%	2105
October	1st to 10th	Day	15% 3 4 13% 29% 37%	3280
	11th to 20th	Day	22% 3 7% 24% 25% 19%	3261
	21st to end	Day	23% 4 8% 27% 26% 12%	3558
November	1st to 10th	Day	28% 5% 9% 28% 19% 10%	2033
	11th to 20th	Day	40% 6% 10% 22% 17% 6%	1882
	21st to end	Day	33% 4 10% 22% 21% 10%	1680
December	1st to 10th	Day	28% 6% 8% 30% 22% 6%	2700
	11th to 20th	Day	59% 4 8% 14% 12% 2	3108
	21st to end	Day	53% 5% 13% 18% 8% 2	4092
January	1st to 10th	Night	40% 5% 19% 21% 11% 3	7847
	11th to 20th	Night	32% 4 10% 19% 21% 15%	7650
	21st to end	Night	42% 4 9% 17% 16% 11%	8371
February	1st to 10th	Night	37% 4 9% 20% 20% 11%	2730
	11th to 20th	Night	38% 4 10% 21% 19% 7%	2602
	21st to end	Night	33% 4 11% 27% 19% 6%	2076
March	1st to 10th	Night	40% 4 13% 21% 19% 3	5081
	11th to 20th	Night	31% 4 13% 25% 20% 8%	5077
	21st to end	Night	38% 4 15% 28% 12% 2	5446
April	1st to 10th	Night	31% 4 14% 24% 22% 5%	2000
	11th to 20th	Night	28% 3 12% 28% 20% 9%	1979
	21st to end	Night	21% 3 11% 33% 26% 7%	2000
May	1st to 10th	Night	15% 1 7% 26% 34% 17%	4245
	11th to 20th	Night	15% 6% 7% 28% 29% 14%	3947
	21st to end	Night	10% 2 7% 32% 44% 5%	3972
June	1st to 10th	Night	20% 5% 11% 24% 32% 9%	1600
	11th to 20th	Night	11% 2 7% 22% 37% 20%	1600
	21st to end	Night	14% 2 3 14% 35% 32%	1600
July	1st to 10th	Night	8% 2 1 9% 25% 55%	3600
	11th to 20th	Night	11% 5% 3 7% 23% 51%	4019
	21st to end	Night	19% 4 6% 14% 24% 32%	4345
August	1st to 10th	Night	21% 4 3 14% 30% 29%	2929
	11th to 20th	Night	11% 3 2 9% 41% 33%	3084
	21st to end	Night	14% 3 4 14% 35% 31%	3608
September	1st to 10th	Night	12% 3 3 11% 32% 39%	2000
	11th to 20th	Night	21% 4 5% 23% 31% 17%	2000
	21st to end	Night	17% 3 4 20% 30% 27%	2290
October	1st to 10th	Night	15% 3 4 11% 25% 42%	3920
	11th to 20th	Night	20% 3 6% 26% 22% 22%	3897
	21st to end	Night	23% 2 7% 23% 28% 17%	4253
November	1st to 10th	Night	27% 4 10% 28% 19% 12%	2485
	11th to 20th	Night	33% 4 12% 25% 18% 8%	2735
	21st to end	Night	30% 5% 9% 23% 22% 11%	2940
December	1st to 10th	Night	30% 6% 8% 27% 20% 9%	4700
	11th to 20th	Night	53% 5% 10% 18% 12% 3	5316
	21st to end	Night	56% 3 12% 18% 9% 2	7106

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	25% 10% 29% 20% 14% 3	336
	11th to 20th	Day	17% 11% 20% 25% 23% 5%	430
	21st to end	Day	13% 9% 24% 30% 20% 4	473
February	1st to 10th	Day	18% 13% 18% 28% 19% 4	430
	11th to 20th	Day	18% 15% 27% 24% 13% 3	457
	21st to end	Day	12% 17% 24% 27% 18% 3	446
March	1st to 10th	Day	17% 16% 30% 23% 11% 3	540
	11th to 20th	Day	17% 14% 26% 20% 16% 6%	529
	21st to end	Day	13% 21% 29% 22% 12% 3	550
April	1st to 10th	Day	12% 16% 29% 27% 13% 4	500
	11th to 20th	Day	11% 18% 29% 23% 14% 6%	492
	21st to end	Day	5% 19% 28% 26% 15% 7%	500
May	1st to 10th	Day	5% 17% 29% 29% 17% 3	503
	11th to 20th	Day	6% 16% 27% 29% 17% 5%	528
	21st to end	Day	5% 11% 25% 31% 22% 5%	573
June	1st to 10th	Day	7% 10% 27% 31% 19% 6%	530
	11th to 20th	Day	3 9% 30% 38% 17% 3	530
	21st to end	Day	1 5% 23% 39% 25% 7%	530
July	1st to 10th	Day	2 3 20% 46% 22% 7%	526
	11th to 20th	Day	1 15% 41% 32% 10%	524
	21st to end	Day	1 1 15% 46% 28% 8%	575
August	1st to 10th	Day	2 3 18% 43% 23% 9%	527
	11th to 20th	Day	2 1 22% 41% 26% 9%	517
	21st to end	Day	2 2 17% 40% 29% 11%	583
September	1st to 10th	Day	1 4 17% 39% 28% 11%	530
	11th to 20th	Day	3 7% 20% 35% 25% 9%	530
	21st to end	Day	4 7% 20% 30% 29% 9%	530
October	1st to 10th	Day	5% 7% 22% 29% 23% 15%	530
	11th to 20th	Day	6% 8% 20% 23% 31% 12%	530
	21st to end	Day	9% 7% 20% 27% 25% 12%	583
November	1st to 10th	Day	9% 9% 18% 21% 33% 10%	509
	11th to 20th	Day	9% 11% 16% 33% 24% 6%	324
	21st to end	Day	11% 7% 20% 31% 25% 5%	220
December	1st to 10th	Day	16% 11% 16% 27% 22% 8%	220
	11th to 20th	Day	17% 16% 20% 23% 22% 3	220
	21st to end	Day	23% 13% 23% 29% 12% 1	242
January	1st to 10th	Night	19% 9% 13% 30% 24% 5%	840
	11th to 20th	Night	16% 6% 14% 34% 25% 5%	840
	21st to end	Night	16% 7% 14% 33% 26% 4	924
February	1st to 10th	Night	16% 8% 15% 35% 23% 3	840
	11th to 20th	Night	14% 10% 20% 30% 21% 5%	824
	21st to end	Night	14% 11% 20% 34% 20% 3	692
March	1st to 10th	Night	16% 11% 21% 30% 20% 3	840
	11th to 20th	Night	15% 9% 18% 32% 23% 3	828
	21st to end	Night	14% 10% 25% 32% 18% 2	880
April	1st to 10th	Night	10% 9% 27% 31% 20% 3	800
	11th to 20th	Night	10% 13% 23% 27% 22% 5%	791
	21st to end	Night	5% 11% 27% 28% 25% 3	800
May	1st to 10th	Night	5% 7% 27% 31% 27% 4	670
	11th to 20th	Night	3 4 23% 35% 33% 3	542
	21st to end	Night	4 8% 18% 37% 30% 3	433
June	1st to 10th	Night	3 5% 22% 39% 30% 2	400
	11th to 20th	Night	1 5% 18% 51% 24% 2	400
	21st to end	Night	2 2 15% 45% 36% 2	400
July	1st to 10th	Night	2 1 9% 44% 42% 3	390
	11th to 20th	Night	2 1 4 38% 45% 11%	568
	21st to end	Night	2 1 5% 40% 46% 6%	657
August	1st to 10th	Night	4 2 8% 37% 42% 7%	597
	11th to 20th	Night	1 10% 43% 39% 7%	684
	21st to end	Night	3 1 8% 38% 43% 8%	880
September	1st to 10th	Night	1 1 8% 39% 43% 8%	800
	11th to 20th	Night	4 3 13% 36% 37% 7%	800
	21st to end	Night	3 4 12% 34% 39% 8%	800
October	1st to 10th	Night	5% 4 16% 30% 36% 10%	800
	11th to 20th	Night	5% 5% 15% 32% 34% 9%	800
	21st to end	Night	8% 4 11% 32% 34% 11%	880
November	1st to 10th	Night	7% 6% 16% 27% 35% 10%	820
	11th to 20th	Night	13% 4 14% 35% 28% 6%	840
	21st to end	Night	11% 5% 15% 37% 27% 6%	840
December	1st to 10th	Night	15% 6% 15% 33% 25% 6%	840
	11th to 20th	Night	22% 8% 14% 31% 22% 3	840
	21st to end	Night	20% 9% 20% 31% 18% 1	924

Page generated at 2026-03-14 23:23:57. Version ac07

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