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 2024-12-06.

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% 3 8% 5% 5% 5% 4 5% 7% 33%	101830
	Night	16% 10% 3 8% 5% 4 4 3 5% 6% 34%	97894
Transparency	Day	48% 7% 13% 21% 10% 1	105293
	Night	49% 6% 13% 21% 10% 1	102520
Seeing	Day	21% 16% 32% 20% 8% 2	14607
	Night	21% 11% 33% 26% 8% 1	23585

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% 14% 5% 12% 6% 5% 5% 3 4 4 27%	2517
	11th to 20th	Day	13% 14% 6% 11% 7% 4 5% 3 4 4 29%	2520
	21st to end	Day	11% 14% 7% 13% 7% 5% 5% 3 5% 5% 24%	2772
February	1st to 10th	Day	13% 17% 5% 10% 6% 5% 5% 3 5% 5% 27%	1653
	11th to 20th	Day	11% 15% 5% 11% 6% 5% 4 4 4 5% 29%	1751
	21st to end	Day	16% 16% 5% 9% 6% 5% 4 3 3 4 28%	1570
March	1st to 10th	Day	18% 13% 4 11% 6% 6% 4 3 4 4 26%	3116
	11th to 20th	Day	10% 16% 6% 12% 6% 5% 4 4 4 6% 28%	3278
	21st to end	Day	14% 10% 3 7% 5% 4 5% 3 5% 6% 38%	4163
April	1st to 10th	Day	20% 13% 3 8% 5% 4 3 3 4 5% 31%	2280
	11th to 20th	Day	22% 7% 3 6% 5% 3 5% 3 5% 6% 36%	2254
	21st to end	Day	21% 10% 4 7% 5% 4 4 3 4 5% 33%	2443
May	1st to 10th	Day	21% 9% 3 7% 5% 4 4 3 5% 6% 32%	4394
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	4398
	21st to end	Day	16% 5% 2 7% 5% 5% 5% 5% 6% 8% 35%	4837
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 4 6% 7% 30%	2660
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 5% 7% 8% 35%	2660
	21st to end	Day	22% 7% 4 8% 5% 5% 6% 3 6% 6% 28%	2660
July	1st to 10th	Day	12% 6% 2 8% 6% 6% 5% 5% 7% 8% 35%	4440
	11th to 20th	Day	13% 5% 2 6% 5% 5% 6% 6% 8% 8% 35%	4440
	21st to end	Day	11% 5% 2 5% 5% 5% 5% 4 6% 8% 44%	4814
August	1st to 10th	Day	14% 5% 2 7% 5% 6% 7% 6% 7% 9% 31%	4423
	11th to 20th	Day	15% 6% 3 7% 5% 4 5% 5% 6% 9% 36%	4049
	21st to end	Day	15% 5% 2 7% 5% 4 5% 4 6% 8% 39%	4180
September	1st to 10th	Day	14% 5% 2 5% 4 4 5% 4 5% 8% 43%	2280
	11th to 20th	Day	14% 4 2 5% 3 3 3 3 5% 8% 48%	2201
	21st to end	Day	19% 6% 3 5% 4 4 4 4 4 6% 42%	2090
October	1st to 10th	Day	21% 7% 2 7% 4 4 5% 4 6% 6% 36%	1957
	11th to 20th	Day	19% 8% 4 8% 6% 6% 4 5% 4 7% 30%	1852
	21st to end	Day	22% 11% 3 7% 4 5% 4 3 4 6% 32%	1881
November	1st to 10th	Day	15% 10% 2 7% 5% 5% 4 4 5% 7% 36%	1761
	11th to 20th	Day	17% 10% 4 8% 5% 5% 5% 4 5% 6% 31%	1698
	21st to end	Day	20% 14% 3 8% 5% 4 5% 4 4 6% 27%	1600
December	1st to 10th	Day	22% 18% 5% 9% 5% 4 3 3 4 6% 23%	1560
	11th to 20th	Day	21% 15% 5% 8% 4 3 3 3 4 4 29%	1906
	21st to end	Day	25% 16% 5% 10% 4 3 3 3 4 4 24%	2772
January	1st to 10th	Night	15% 14% 5% 9% 5% 4 5% 4 5% 6% 28%	4429
	11th to 20th	Night	10% 12% 5% 13% 8% 5% 6% 3 5% 6% 28%	4440
	21st to end	Night	11% 13% 5% 12% 7% 6% 5% 4 5% 5% 26%	4884
February	1st to 10th	Night	12% 13% 4 10% 7% 6% 5% 4 5% 6% 27%	2526
	11th to 20th	Night	12% 11% 4 11% 6% 4 6% 4 5% 5% 32%	2314
	21st to end	Night	14% 12% 4 9% 5% 4 5% 3 4 6% 33%	1884
March	1st to 10th	Night	20% 13% 4 7% 4 4 4 3 4 4 32%	3724
	11th to 20th	Night	13% 19% 5% 9% 5% 4 4 3 4 4 29%	3677
	21st to end	Night	14% 9% 4 8% 6% 5% 4 3 4 5% 38%	3468
April	1st to 10th	Night	21% 11% 3 7% 5% 4 4 4 4 6% 33%	1900
	11th to 20th	Night	21% 6% 2 7% 5% 4 4 3 5% 5% 38%	1875
	21st to end	Night	20% 10% 3 6% 3 4 4 3 5% 6% 36%	1736
May	1st to 10th	Night	21% 10% 3 8% 5% 4 5% 3 5% 6% 31%	2562
	11th to 20th	Night	21% 6% 2 6% 5% 4 4 4 5% 7% 37%	2495
	21st to end	Night	17% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	2738
June	1st to 10th	Night	19% 7% 2 6% 5% 5% 5% 3 6% 8% 34%	1520
	11th to 20th	Night	18% 6% 3 6% 3 5% 4 4 6% 6% 38%	1520
	21st to end	Night	20% 6% 2 6% 5% 4 5% 4 6% 7% 35%	1520
July	1st to 10th	Night	12% 6% 3 8% 6% 4 6% 5% 7% 8% 36%	2520
	11th to 20th	Night	14% 5% 2 6% 4 4 5% 4 6% 6% 45%	2520
	21st to end	Night	11% 5% 2 5% 4 4 4 5% 7% 7% 47%	2739
August	1st to 10th	Night	12% 5% 3 8% 5% 5% 4 4 6% 8% 40%	2506
	11th to 20th	Night	16% 7% 2 6% 4 4 4 3 5% 8% 42%	2743
	21st to end	Night	17% 6% 3 6% 4 4 4 3 5% 7% 42%	3476
September	1st to 10th	Night	10% 4 2 6% 4 5% 4 4 5% 6% 50%	1900
	11th to 20th	Night	13% 5% 2 5% 3 4 3 2 5% 6% 51%	1978
	21st to end	Night	18% 6% 2 5% 3 4 4 3 4 6% 46%	2090
October	1st to 10th	Night	17% 7% 3 7% 4 4 3 3 4 5% 42%	2220
	11th to 20th	Night	20% 7% 3 7% 4 4 4 4 5% 6% 38%	2327
	21st to end	Night	21% 8% 3 8% 5% 4 4 3 5% 6% 33%	2717
November	1st to 10th	Night	16% 9% 3 8% 5% 5% 4 3 5% 7% 35%	2537
	11th to 20th	Night	17% 9% 3 8% 5% 4 4 5% 4 5% 35%	2700
	21st to end	Night	20% 12% 4 8% 5% 4 4 3 4 5% 31%	2800
December	1st to 10th	Night	19% 13% 4 10% 6% 5% 5% 4 6% 6% 23%	2737
	11th to 20th	Night	21% 14% 4 8% 5% 3 4 3 3 5% 29%	3288
	21st to end	Night	24% 19% 5% 9% 4 3 3 2 3 4 25%	4884

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% 7% 12% 17% 5% 1	2518
	11th to 20th	Day	55% 8% 10% 17% 8% 1	2520
	21st to end	Day	60% 6% 10% 16% 7% 1	2772
February	1st to 10th	Day	59% 5% 7% 19% 8% 2	1653
	11th to 20th	Day	57% 5% 10% 15% 12% 1	1760
	21st to end	Day	59% 5% 8% 17% 9% 3	1570
March	1st to 10th	Day	60% 7% 6% 15% 10% 1	3119
	11th to 20th	Day	56% 6% 10% 13% 11% 4	3278
	21st to end	Day	46% 5% 8% 20% 17% 3	4163
April	1st to 10th	Day	56% 4 8% 17% 12% 3	2280
	11th to 20th	Day	49% 5% 9% 22% 13% 2	2254
	21st to end	Day	53% 6% 7% 18% 12% 3	2443
May	1st to 10th	Day	52% 6% 9% 21% 10% 2	4408
	11th to 20th	Day	48% 7% 19% 16% 9% 1	4402
	21st to end	Day	44% 8% 11% 22% 14% 1	4837
June	1st to 10th	Day	51% 7% 10% 19% 11% 2	2660
	11th to 20th	Day	44% 8% 12% 22% 12% 3	2660
	21st to end	Day	54% 7% 12% 16% 9% 1	2660
July	1st to 10th	Day	42% 9% 16% 23% 10%	4370
	11th to 20th	Day	39% 11% 17% 25% 7%	4365
	21st to end	Day	36% 8% 15% 31% 10%	4661
August	1st to 10th	Day	44% 9% 17% 21% 8%	4409
	11th to 20th	Day	42% 9% 18% 25% 6%	4091
	21st to end	Day	41% 9% 16% 20% 14% 1	4180
September	1st to 10th	Day	37% 7% 15% 28% 13%	2280
	11th to 20th	Day	35% 6% 14% 31% 13% 1	2201
	21st to end	Day	43% 5% 14% 26% 11%	2090
October	1st to 10th	Day	41% 8% 16% 25% 9%	3256
	11th to 20th	Day	43% 6% 15% 28% 8%	3055
	21st to end	Day	41% 6% 22% 20% 10% 1	3081
November	1st to 10th	Day	46% 7% 14% 22% 10% 1	1761
	11th to 20th	Day	51% 6% 11% 19% 11% 1	1698
	21st to end	Day	57% 7% 13% 16% 7% 1	1600
December	1st to 10th	Day	64% 4 11% 14% 6%	1560
	11th to 20th	Day	58% 5% 10% 19% 8%	1906
	21st to end	Day	66% 3 9% 15% 7%	2772
January	1st to 10th	Night	57% 7% 16% 16% 5%	4429
	11th to 20th	Night	55% 7% 14% 18% 5% 1	4440
	21st to end	Night	57% 7% 13% 13% 8% 1	4884
February	1st to 10th	Night	57% 5% 9% 20% 8% 1	2526
	11th to 20th	Night	53% 5% 10% 20% 11% 1	2316
	21st to end	Night	53% 4 9% 18% 13% 2	1884
March	1st to 10th	Night	55% 5% 10% 16% 10% 4	3734
	11th to 20th	Night	57% 6% 9% 14% 13% 2	3678
	21st to end	Night	48% 5% 7% 22% 14% 4	3468
April	1st to 10th	Night	53% 5% 7% 18% 14% 2	1900
	11th to 20th	Night	48% 5% 9% 22% 15% 2	1875
	21st to end	Night	49% 5% 9% 20% 14% 3	1736
May	1st to 10th	Night	52% 7% 11% 19% 8% 3	2568
	11th to 20th	Night	46% 7% 16% 18% 11% 2	2496
	21st to end	Night	46% 7% 10% 20% 15% 2	2739
June	1st to 10th	Night	48% 5% 13% 20% 13% 1	1520
	11th to 20th	Night	45% 6% 11% 21% 14% 3	1520
	21st to end	Night	48% 7% 12% 20% 13% 1	1520
July	1st to 10th	Night	42% 8% 19% 20% 11% 1	2480
	11th to 20th	Night	37% 8% 20% 29% 7%	2472
	21st to end	Night	34% 7% 19% 28% 12%	2651
August	1st to 10th	Night	42% 8% 14% 27% 9%	2496
	11th to 20th	Night	40% 6% 20% 26% 8%	2767
	21st to end	Night	42% 7% 15% 23% 13% 1	3476
September	1st to 10th	Night	34% 6% 17% 27% 15% 1	1900
	11th to 20th	Night	34% 5% 16% 33% 11% 1	1978
	21st to end	Night	39% 6% 12% 30% 14%	2090
October	1st to 10th	Night	43% 7% 15% 24% 11% 1	3701
	11th to 20th	Night	39% 6% 13% 30% 11%	3863
	21st to end	Night	42% 6% 19% 19% 13% 2	4467
November	1st to 10th	Night	48% 6% 14% 23% 8% 1	2537
	11th to 20th	Night	50% 6% 12% 19% 11% 1	2700
	21st to end	Night	57% 5% 11% 19% 8% 1	2800
December	1st to 10th	Night	61% 6% 13% 16% 5%	2737
	11th to 20th	Night	58% 5% 9% 19% 9% 1	3288
	21st to end	Night	64% 4 8% 17% 6% 1	4884

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	17% 22% 36% 22% 3	180
	11th to 20th	Day	27% 14% 37% 18% 3 1	180
	21st to end	Day	16% 20% 40% 19% 5% 1	198
February	1st to 10th	Day	28% 24% 40% 8% 1	243
	11th to 20th	Day	20% 22% 42% 15% 2	358
	21st to end	Day	27% 21% 32% 18% 3	382
March	1st to 10th	Day	24% 18% 33% 20% 5%	460
	11th to 20th	Day	19% 25% 36% 16% 3 1	460
	21st to end	Day	27% 21% 31% 14% 6% 1	506
April	1st to 10th	Day	27% 19% 31% 16% 5% 1	460
	11th to 20th	Day	30% 19% 30% 13% 6% 2	452
	21st to end	Day	30% 16% 33% 16% 4 1	460
May	1st to 10th	Day	25% 20% 35% 14% 4 1	463
	11th to 20th	Day	18% 20% 35% 19% 7% 1	487
	21st to end	Day	19% 20% 34% 21% 5% 1	529
June	1st to 10th	Day	22% 15% 34% 21% 7% 1	490
	11th to 20th	Day	17% 18% 32% 21% 11% 1	490
	21st to end	Day	25% 12% 33% 20% 9% 1	490
July	1st to 10th	Day	13% 10% 35% 27% 12% 3	485
	11th to 20th	Day	14% 11% 35% 27% 11% 2	484
	21st to end	Day	13% 9% 31% 32% 13% 2	532
August	1st to 10th	Day	13% 9% 30% 30% 16% 2	486
	11th to 20th	Day	13% 8% 27% 29% 15% 7%	479
	21st to end	Day	15% 14% 29% 24% 13% 6%	539
September	1st to 10th	Day	16% 9% 35% 23% 11% 6%	490
	11th to 20th	Day	12% 13% 24% 29% 15% 8%	490
	21st to end	Day	18% 13% 28% 22% 13% 5%	490
October	1st to 10th	Day	23% 14% 28% 21% 11% 2	490
	11th to 20th	Day	22% 19% 29% 20% 8% 2	464
	21st to end	Day	28% 16% 31% 21% 4	429
November	1st to 10th	Day	25% 18% 32% 18% 6% 1	395
	11th to 20th	Day	22% 21% 33% 16% 7%	298
	21st to end	Day	28% 19% 34% 14% 5% 1	200
December	1st to 10th	Day	26% 16% 29% 21% 7% 1	190
	11th to 20th	Day	25% 23% 36% 13% 3 1	180
	21st to end	Day	33% 22% 28% 10% 7% 1	198
January	1st to 10th	Night	24% 13% 36% 23% 4	760
	11th to 20th	Night	22% 15% 35% 23% 6%	760
	21st to end	Night	15% 12% 40% 27% 6% 1	836
February	1st to 10th	Night	19% 13% 41% 23% 4 1	760
	11th to 20th	Night	18% 15% 42% 20% 4	743
	21st to end	Night	20% 16% 37% 24% 2	628
March	1st to 10th	Night	25% 14% 35% 22% 4	760
	11th to 20th	Night	23% 16% 34% 20% 6%	760
	21st to end	Night	21% 13% 35% 25% 5%	836
April	1st to 10th	Night	27% 14% 33% 22% 4	760
	11th to 20th	Night	24% 14% 32% 24% 5% 1	751
	21st to end	Night	27% 14% 32% 21% 6%	596
May	1st to 10th	Night	22% 12% 35% 24% 6% 1	415
	11th to 20th	Night	22% 10% 30% 30% 6% 1	374
	21st to end	Night	21% 9% 38% 24% 8%	411
June	1st to 10th	Night	24% 8% 32% 29% 7%	380
	11th to 20th	Night	22% 7% 29% 30% 12% 1	380
	21st to end	Night	21% 6% 27% 33% 12% 1	380
July	1st to 10th	Night	13% 7% 33% 34% 12% 2	370
	11th to 20th	Night	12% 4 29% 43% 11% 1	368
	21st to end	Night	13% 5% 27% 42% 13% 1	416
August	1st to 10th	Night	12% 4 21% 44% 17% 1	378
	11th to 20th	Night	14% 4 26% 34% 21% 2	532
	21st to end	Night	15% 6% 28% 32% 17% 2	836
September	1st to 10th	Night	12% 6% 32% 36% 12% 1	760
	11th to 20th	Night	15% 7% 26% 31% 20% 2	760
	21st to end	Night	19% 8% 29% 28% 14% 2	760
October	1st to 10th	Night	20% 10% 30% 28% 11% 1	760
	11th to 20th	Night	23% 11% 32% 23% 10% 1	760
	21st to end	Night	27% 8% 35% 24% 6%	836
November	1st to 10th	Night	22% 13% 33% 24% 7% 1	780
	11th to 20th	Night	22% 14% 32% 22% 9% 1	800
	21st to end	Night	25% 17% 31% 20% 6% 1	800
December	1st to 10th	Night	26% 12% 33% 21% 7%	783
	11th to 20th	Night	26% 16% 31% 22% 4 1	760
	21st to end	Night	31% 15% 31% 20% 3	836

Page generated at 2024-12-03 06:45:11. Version ac07

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