Observatoire North Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire North Point 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	16% 9% 4 8% 5% 5% 5% 4 5% 7% 32%	131267
	Night	16% 10% 4 9% 5% 4 5% 4 5% 6% 33%	130242
Transparency	Day	49% 7% 12% 20% 10% 1	134712
	Night	50% 6% 12% 20% 11% 1	134884
Seeing	Day	21% 17% 33% 20% 8% 2	16142
	Night	21% 12% 33% 26% 8% 1	25229

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	12% 16% 6% 14% 5% 4 4 3 4 5% 27%	4661
	11th to 20th	Day	10% 16% 8% 15% 7% 5% 5% 3 4 5% 24%	4650
	21st to end	Day	6% 11% 6% 14% 8% 7% 6% 3 5% 6% 27%	5124
February	1st to 10th	Day	12% 16% 5% 10% 6% 5% 5% 3 5% 5% 28%	1827
	11th to 20th	Day	11% 14% 5% 12% 6% 5% 4 4 4 6% 29%	1941
	21st to end	Day	15% 16% 5% 10% 6% 5% 4 3 3 5% 29%	1730
March	1st to 10th	Day	18% 14% 5% 12% 7% 5% 4 3 4 4 24%	4576
	11th to 20th	Day	10% 13% 5% 11% 5% 5% 4 4 5% 7% 33%	4764
	21st to end	Day	17% 12% 4 8% 5% 4 4 3 4 5% 34%	5967
April	1st to 10th	Day	20% 13% 3 8% 5% 4 3 3 4 5% 32%	2400
	11th to 20th	Day	21% 8% 3 6% 5% 3 4 3 4 6% 36%	2374
	21st to end	Day	21% 10% 4 7% 5% 4 4 3 4 5% 33%	2572
May	1st to 10th	Day	26% 10% 3 8% 5% 4 4 3 5% 5% 26%	6300
	11th to 20th	Day	20% 9% 3 7% 5% 5% 4 3 5% 7% 31%	6318
	21st to end	Day	21% 7% 3 7% 5% 5% 5% 4 5% 7% 30%	6949
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 4 5% 7% 30%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 5% 7% 8% 35%	2800
	21st to end	Day	21% 7% 4 8% 5% 5% 6% 4 6% 7% 28%	2800
July	1st to 10th	Day	14% 6% 3 8% 6% 6% 6% 5% 7% 8% 33%	6360
	11th to 20th	Day	11% 5% 2 6% 4 5% 6% 6% 7% 9% 38%	6360
	21st to end	Day	10% 5% 2 5% 5% 4 5% 4 6% 10% 44%	6926
August	1st to 10th	Day	13% 5% 2 7% 5% 6% 7% 6% 7% 9% 32%	4563
	11th to 20th	Day	15% 6% 3 7% 5% 4 5% 5% 6% 9% 36%	4179
	21st to end	Day	15% 5% 2 7% 5% 4 5% 4 6% 8% 39%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 5% 4 6% 8% 44%	2400
	11th to 20th	Day	13% 4 2 5% 3 3 4 3 5% 7% 49%	2317
	21st to end	Day	19% 6% 3 5% 4 3 4 4 5% 6% 42%	2200
October	1st to 10th	Day	20% 6% 2 6% 4 4 5% 4 6% 6% 38%	2060
	11th to 20th	Day	19% 8% 4 8% 6% 6% 4 4 4 7% 31%	1949
	21st to end	Day	23% 10% 3 7% 4 4 4 3 4 6% 32%	1980
November	1st to 10th	Day	15% 11% 2 7% 5% 5% 4 4 5% 6% 35%	1851
	11th to 20th	Day	17% 11% 4 8% 5% 4 5% 4 5% 7% 31%	1783
	21st to end	Day	20% 14% 3 8% 5% 4 4 4 4 6% 27%	1680
December	1st to 10th	Day	18% 17% 6% 12% 5% 5% 4 3 4 5% 21%	2680
	11th to 20th	Day	17% 14% 5% 9% 5% 4 3 3 5% 4 30%	3066
	21st to end	Day	21% 13% 5% 11% 4 4 4 3 4 4 27%	4048
January	1st to 10th	Night	12% 16% 7% 13% 5% 4 5% 3 4 5% 26%	8234
	11th to 20th	Night	8% 16% 7% 17% 7% 5% 5% 3 5% 5% 22%	8235
	21st to end	Night	7% 11% 4 13% 8% 6% 6% 4 6% 6% 28%	9057
February	1st to 10th	Night	11% 13% 5% 11% 7% 6% 5% 4 5% 6% 28%	2791
	11th to 20th	Night	12% 12% 4 11% 6% 5% 5% 4 5% 5% 32%	2564
	21st to end	Night	14% 12% 4 9% 5% 4 5% 3 5% 6% 33%	2076
March	1st to 10th	Night	20% 14% 4 9% 5% 4 4 2 4 4 29%	5484
	11th to 20th	Night	11% 14% 4 8% 5% 5% 5% 4 6% 7% 31%	5345
	21st to end	Night	16% 10% 4 9% 6% 5% 5% 3 4 6% 33%	4964
April	1st to 10th	Night	21% 11% 3 7% 5% 4 4 4 4 5% 33%	2000
	11th to 20th	Night	20% 6% 2 7% 5% 4 4 3 5% 5% 38%	1975
	21st to end	Night	21% 10% 3 6% 3 4 4 3 5% 6% 36%	1827
May	1st to 10th	Night	25% 10% 3 8% 4 4 5% 4 5% 6% 27%	3670
	11th to 20th	Night	21% 7% 2 7% 5% 4 4 4 5% 7% 34%	3575
	21st to end	Night	21% 8% 3 7% 5% 5% 5% 4 6% 7% 29%	3926
June	1st to 10th	Night	19% 7% 2 6% 5% 5% 5% 3 6% 8% 34%	1600
	11th to 20th	Night	18% 6% 3 6% 3 5% 4 4 6% 6% 39%	1600
	21st to end	Night	20% 6% 2 6% 5% 4 5% 4 6% 7% 35%	1600
July	1st to 10th	Night	13% 6% 2 7% 5% 5% 6% 5% 8% 9% 35%	3600
	11th to 20th	Night	13% 5% 2 6% 4 4 4 4 6% 7% 45%	3600
	21st to end	Night	9% 4 2 5% 4 5% 5% 4 7% 8% 48%	3926
August	1st to 10th	Night	12% 5% 3 8% 5% 5% 4 4 5% 8% 41%	2586
	11th to 20th	Night	15% 7% 2 6% 4 4 3 4 5% 7% 43%	2832
	21st to end	Night	17% 6% 3 6% 4 4 4 3 5% 7% 42%	3586
September	1st to 10th	Night	10% 4 2 6% 4 5% 4 4 5% 7% 51%	2000
	11th to 20th	Night	13% 5% 2 5% 3 4 3 3 5% 6% 52%	2082
	21st to end	Night	18% 6% 2 5% 3 4 4 3 4 6% 46%	2200
October	1st to 10th	Night	16% 7% 3 7% 4 4 3 3 4 5% 43%	2337
	11th to 20th	Night	19% 7% 3 7% 4 4 4 4 5% 6% 39%	2450
	21st to end	Night	21% 8% 3 8% 4 5% 4 3 5% 6% 33%	2860
November	1st to 10th	Night	17% 8% 3 8% 5% 5% 4 3 5% 7% 34%	2667
	11th to 20th	Night	17% 10% 3 8% 5% 4 4 5% 4 5% 35%	2835
	21st to end	Night	20% 13% 4 8% 5% 4 4 3 4 5% 30%	2940
December	1st to 10th	Night	16% 13% 5% 10% 6% 6% 5% 4 6% 6% 22%	4720
	11th to 20th	Night	22% 12% 4 9% 5% 4 4 3 3 4 29%	5348
	21st to end	Night	21% 17% 4 9% 4 3 3 2 3 4 29%	7150

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	58% 6% 11% 19% 6% 1	4662
	11th to 20th	Day	59% 8% 8% 14% 9% 2	4680
	21st to end	Day	55% 7% 9% 16% 13% 1	5124
February	1st to 10th	Day	58% 5% 7% 19% 9% 2	1827
	11th to 20th	Day	56% 5% 10% 16% 12% 1	1950
	21st to end	Day	58% 5% 7% 17% 10% 3	1730
March	1st to 10th	Day	61% 7% 7% 12% 10% 4	4579
	11th to 20th	Day	50% 7% 16% 13% 11% 3	4764
	21st to end	Day	53% 5% 7% 16% 18% 3	5967
April	1st to 10th	Day	55% 4 8% 17% 13% 3	2400
	11th to 20th	Day	49% 5% 8% 22% 13% 2	2374
	21st to end	Day	52% 6% 8% 18% 12% 3	2572
May	1st to 10th	Day	59% 6% 8% 18% 8% 1	6311
	11th to 20th	Day	51% 7% 16% 16% 8% 2	6322
	21st to end	Day	51% 7% 11% 17% 12% 2	6949
June	1st to 10th	Day	51% 7% 10% 19% 11% 2	2800
	11th to 20th	Day	43% 8% 12% 23% 12% 3	2800
	21st to end	Day	54% 7% 12% 17% 9% 1	2800
July	1st to 10th	Day	45% 8% 15% 23% 8%	6290
	11th to 20th	Day	36% 10% 16% 28% 10%	6285
	21st to end	Day	33% 8% 17% 33% 10%	6728
August	1st to 10th	Day	43% 9% 17% 22% 8%	4549
	11th to 20th	Day	42% 9% 17% 25% 6%	4221
	21st to end	Day	40% 9% 16% 21% 13% 1	4312
September	1st to 10th	Day	36% 7% 15% 29% 12%	2400
	11th to 20th	Day	34% 6% 14% 32% 13% 1	2317
	21st to end	Day	42% 5% 14% 26% 12%	2200
October	1st to 10th	Day	40% 8% 16% 26% 10%	3359
	11th to 20th	Day	43% 6% 15% 28% 8%	3152
	21st to end	Day	42% 6% 22% 20% 10% 1	3180
November	1st to 10th	Day	47% 7% 13% 21% 10% 1	1851
	11th to 20th	Day	52% 6% 11% 19% 11% 1	1783
	21st to end	Day	57% 7% 12% 15% 7% 1	1680
December	1st to 10th	Day	65% 5% 10% 14% 5%	2680
	11th to 20th	Day	55% 6% 9% 18% 11%	3066
	21st to end	Day	60% 5% 10% 16% 10%	4048
January	1st to 10th	Night	60% 5% 11% 16% 6% 1	8234
	11th to 20th	Night	62% 6% 10% 15% 6% 1	8280
	21st to end	Night	53% 7% 11% 14% 14% 1	9057
February	1st to 10th	Night	56% 5% 9% 20% 9% 1	2791
	11th to 20th	Night	53% 5% 10% 20% 11% 1	2566
	21st to end	Night	52% 4 9% 19% 12% 2	2076
March	1st to 10th	Night	59% 4 8% 13% 12% 4	5494
	11th to 20th	Night	50% 7% 14% 15% 12% 3	5346
	21st to end	Night	51% 5% 7% 21% 13% 3	4964
April	1st to 10th	Night	54% 5% 7% 18% 15% 2	2000
	11th to 20th	Night	47% 5% 9% 22% 15% 2	1975
	21st to end	Night	49% 5% 9% 20% 14% 3	1827
May	1st to 10th	Night	57% 6% 10% 18% 7% 2	3676
	11th to 20th	Night	49% 7% 14% 18% 10% 2	3576
	21st to end	Night	52% 7% 11% 17% 12% 1	3927
June	1st to 10th	Night	48% 5% 13% 20% 14% 1	1600
	11th to 20th	Night	45% 7% 11% 21% 14% 3	1600
	21st to end	Night	47% 7% 12% 20% 13% 1	1600
July	1st to 10th	Night	41% 8% 21% 21% 8%	3560
	11th to 20th	Night	35% 8% 19% 30% 7%	3552
	21st to end	Night	32% 7% 18% 31% 12%	3809
August	1st to 10th	Night	41% 8% 15% 28% 9%	2576
	11th to 20th	Night	40% 6% 20% 26% 8%	2856
	21st to end	Night	42% 7% 15% 23% 13% 1	3586
September	1st to 10th	Night	34% 6% 17% 29% 15% 1	2000
	11th to 20th	Night	33% 5% 16% 34% 12% 1	2082
	21st to end	Night	39% 6% 12% 30% 14%	2200
October	1st to 10th	Night	42% 7% 15% 24% 12% 1	3818
	11th to 20th	Night	39% 6% 13% 30% 12%	3986
	21st to end	Night	42% 6% 19% 19% 12% 2	4610
November	1st to 10th	Night	48% 6% 14% 23% 8% 1	2667
	11th to 20th	Night	50% 6% 12% 20% 11% 1	2835
	21st to end	Night	57% 4 11% 18% 8% 1	2940
December	1st to 10th	Night	59% 7% 14% 15% 5%	4720
	11th to 20th	Night	58% 5% 8% 16% 12% 1	5348
	21st to end	Night	60% 4 7% 15% 13%	7150

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	19% 21% 36% 21% 3	220
	11th to 20th	Day	28% 15% 38% 15% 3 1	220
	21st to end	Day	15% 22% 38% 18% 6%	242
February	1st to 10th	Day	25% 24% 40% 9% 2	297
	11th to 20th	Day	20% 21% 41% 16% 2	428
	21st to end	Day	25% 20% 35% 17% 3	446
March	1st to 10th	Day	24% 21% 33% 18% 4	540
	11th to 20th	Day	21% 23% 37% 15% 3 1	528
	21st to end	Day	27% 21% 31% 13% 6% 1	550
April	1st to 10th	Day	28% 20% 30% 15% 5% 1	500
	11th to 20th	Day	31% 19% 29% 12% 7% 1	492
	21st to end	Day	30% 17% 33% 15% 4 1	500
May	1st to 10th	Day	27% 19% 35% 14% 4 1	503
	11th to 20th	Day	19% 20% 34% 19% 7% 1	527
	21st to end	Day	20% 20% 33% 20% 5% 1	573
June	1st to 10th	Day	22% 15% 35% 20% 6% 1	530
	11th to 20th	Day	17% 19% 32% 20% 11% 1	530
	21st to end	Day	24% 12% 35% 20% 8% 1	530
July	1st to 10th	Day	14% 11% 36% 25% 11% 3	525
	11th to 20th	Day	13% 11% 36% 27% 10% 2	524
	21st to end	Day	12% 10% 32% 31% 13% 2	576
August	1st to 10th	Day	12% 8% 30% 32% 16% 2	526
	11th to 20th	Day	12% 8% 28% 29% 16% 7%	519
	21st to end	Day	15% 13% 29% 24% 13% 6%	583
September	1st to 10th	Day	16% 10% 34% 23% 12% 5%	530
	11th to 20th	Day	11% 12% 24% 30% 16% 8%	530
	21st to end	Day	18% 14% 29% 22% 13% 5%	530
October	1st to 10th	Day	22% 14% 29% 22% 11% 3	530
	11th to 20th	Day	21% 19% 30% 21% 7% 1	501
	21st to end	Day	28% 15% 31% 21% 4	462
November	1st to 10th	Day	26% 19% 31% 18% 6%	425
	11th to 20th	Day	22% 21% 33% 17% 7%	323
	21st to end	Day	30% 20% 33% 13% 5%	220
December	1st to 10th	Day	25% 17% 32% 19% 6% 1	220
	11th to 20th	Day	25% 23% 35% 14% 2	220
	21st to end	Day	29% 21% 30% 12% 7% 1	242
January	1st to 10th	Night	23% 14% 37% 22% 4	840
	11th to 20th	Night	22% 15% 34% 23% 6%	840
	21st to end	Night	14% 13% 40% 26% 6% 1	924
February	1st to 10th	Night	17% 13% 40% 23% 5% 1	840
	11th to 20th	Night	18% 15% 42% 20% 4	823
	21st to end	Night	19% 15% 38% 25% 2	692
March	1st to 10th	Night	26% 14% 35% 21% 4	840
	11th to 20th	Night	23% 16% 35% 19% 6%	829
	21st to end	Night	22% 13% 34% 25% 5%	880
April	1st to 10th	Night	27% 15% 33% 21% 4	800
	11th to 20th	Night	24% 14% 32% 25% 5% 1	791
	21st to end	Night	27% 14% 33% 20% 5%	627
May	1st to 10th	Night	24% 12% 34% 23% 5% 1	437
	11th to 20th	Night	22% 11% 30% 30% 7% 1	394
	21st to end	Night	22% 9% 37% 24% 8%	433
June	1st to 10th	Night	24% 9% 33% 28% 7%	400
	11th to 20th	Night	21% 8% 30% 31% 11% 1	400
	21st to end	Night	21% 6% 28% 33% 11% 1	400
July	1st to 10th	Night	13% 7% 33% 35% 11% 2	390
	11th to 20th	Night	12% 5% 27% 44% 11% 1	388
	21st to end	Night	12% 5% 27% 42% 12% 1	438
August	1st to 10th	Night	11% 5% 20% 45% 17% 1	398
	11th to 20th	Night	14% 4 25% 34% 22% 2	561
	21st to end	Night	15% 7% 28% 32% 16% 2	880
September	1st to 10th	Night	12% 6% 32% 36% 12% 1	800
	11th to 20th	Night	14% 6% 26% 32% 20% 2	800
	21st to end	Night	19% 8% 29% 29% 14% 2	800
October	1st to 10th	Night	19% 9% 31% 29% 12% 1	800
	11th to 20th	Night	22% 11% 33% 24% 10% 1	800
	21st to end	Night	27% 8% 35% 24% 6%	880
November	1st to 10th	Night	23% 13% 32% 24% 6% 1	820
	11th to 20th	Night	23% 14% 32% 22% 9% 1	840
	21st to end	Night	25% 17% 32% 20% 5% 1	840
December	1st to 10th	Night	26% 13% 33% 22% 7%	840
	11th to 20th	Night	26% 17% 31% 21% 4 1	840
	21st to end	Night	31% 15% 30% 21% 4	924

Page generated at 2026-03-15 02:23:54. Version ac07

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