Observatoire POLARIS
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire POLARIS clear sky chart from 2005-11-06 to 2024-11-04.

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	17% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	101563
	Night	17% 10% 4 8% 5% 4 4 3 5% 6% 34%	97460
Transparency	Day	49% 8% 13% 19% 10% 1	105013
	Night	50% 7% 13% 20% 10% 1	102086
Seeing	Day	22% 17% 32% 20% 8% 2	14522
	Night	22% 12% 31% 26% 9% 1	23425

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	14% 14% 5% 11% 6% 4 4 3 4 5% 28%	2517
	11th to 20th	Day	12% 15% 6% 14% 7% 5% 3 3 3 4 28%	2520
	21st to end	Day	11% 13% 6% 12% 7% 5% 4 4 5% 6% 26%	2772
February	1st to 10th	Day	11% 19% 5% 10% 7% 4 4 3 4 5% 26%	1624
	11th to 20th	Day	12% 16% 5% 11% 5% 5% 5% 3 5% 4 29%	1760
	21st to end	Day	15% 17% 6% 9% 6% 4 4 3 5% 5% 27%	1570
March	1st to 10th	Day	19% 14% 4 10% 6% 5% 4 3 4 4 26%	3116
	11th to 20th	Day	11% 18% 5% 12% 5% 5% 5% 3 4 5% 27%	3269
	21st to end	Day	13% 13% 3 7% 4 4 4 3 5% 6% 37%	4166
April	1st to 10th	Day	19% 14% 4 8% 5% 4 4 3 4 5% 30%	2280
	11th to 20th	Day	22% 8% 3 7% 5% 4 4 3 4 5% 35%	2254
	21st to end	Day	20% 12% 3 8% 4 4 5% 3 5% 5% 31%	2465
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 4 4 6% 33%	4384
	11th to 20th	Day	17% 7% 3 8% 5% 4 4 3 6% 9% 34%	4398
	21st to end	Day	16% 7% 3 7% 6% 5% 6% 4 6% 7% 33%	4837
June	1st to 10th	Day	21% 8% 3 7% 5% 5% 5% 5% 6% 7% 27%	2660
	11th to 20th	Day	16% 6% 2 7% 6% 5% 5% 4 7% 8% 34%	2660
	21st to end	Day	22% 8% 3 8% 6% 5% 5% 4 6% 7% 26%	2660
July	1st to 10th	Day	13% 7% 3 8% 6% 5% 6% 5% 7% 8% 33%	4440
	11th to 20th	Day	14% 6% 2 6% 5% 5% 6% 6% 7% 8% 33%	4440
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 6% 7% 42%	4814
August	1st to 10th	Day	13% 6% 2 7% 5% 6% 8% 5% 7% 9% 31%	4423
	11th to 20th	Day	16% 6% 3 7% 5% 4 5% 4 7% 9% 33%	4072
	21st to end	Day	17% 6% 2 6% 5% 4 5% 4 5% 7% 39%	4180
September	1st to 10th	Day	15% 5% 2 5% 5% 4 4 4 6% 8% 43%	2280
	11th to 20th	Day	14% 6% 2 4 4 4 5% 3 5% 6% 47%	2190
	21st to end	Day	21% 7% 2 6% 4 3 3 3 5% 6% 40%	2090
October	1st to 10th	Day	22% 6% 3 7% 4 3 4 4 5% 7% 35%	1973
	11th to 20th	Day	21% 10% 3 9% 4 6% 5% 4 5% 6% 28%	1832
	21st to end	Day	25% 12% 3 6% 5% 4 3 3 4 5% 30%	1881
November	1st to 10th	Day	15% 12% 3 7% 5% 5% 4 3 5% 6% 35%	1698
	11th to 20th	Day	20% 12% 4 8% 5% 4 5% 4 4 7% 27%	1620
	21st to end	Day	20% 15% 4 7% 5% 4 6% 3 5% 6% 27%	1520
December	1st to 10th	Day	23% 17% 4 9% 5% 4 3 3 5% 4 23%	1520
	11th to 20th	Day	21% 15% 4 9% 5% 3 4 2 4 6% 26%	1906
	21st to end	Day	22% 17% 6% 10% 4 3 3 3 3 4 24%	2772
January	1st to 10th	Night	15% 16% 5% 10% 5% 5% 4 3 5% 5% 27%	4429
	11th to 20th	Night	10% 13% 5% 12% 8% 5% 4 3 5% 5% 29%	4440
	21st to end	Night	10% 13% 6% 13% 7% 6% 5% 4 5% 5% 25%	4884
February	1st to 10th	Night	12% 14% 6% 10% 7% 5% 5% 4 5% 5% 28%	2552
	11th to 20th	Night	11% 12% 4 11% 7% 5% 5% 4 4 5% 31%	2305
	21st to end	Night	14% 13% 4 8% 6% 4 5% 3 5% 6% 32%	1884
March	1st to 10th	Night	20% 14% 4 8% 4 4 4 3 3 5% 30%	3724
	11th to 20th	Night	14% 18% 5% 10% 5% 4 4 3 4 4 28%	3687
	21st to end	Night	13% 9% 4 10% 6% 5% 5% 4 5% 4 36%	3466
April	1st to 10th	Night	21% 12% 3 7% 5% 4 3 3 4 6% 31%	1900
	11th to 20th	Night	19% 7% 3 7% 5% 3 4 3 5% 6% 38%	1875
	21st to end	Night	21% 10% 3 6% 4 4 3 3 5% 6% 35%	1715
May	1st to 10th	Night	21% 10% 3 6% 5% 5% 4 4 6% 7% 31%	2585
	11th to 20th	Night	22% 6% 2 5% 4 4 4 3 5% 6% 39%	2495
	21st to end	Night	18% 6% 2 7% 5% 5% 5% 5% 6% 7% 33%	2738
June	1st to 10th	Night	20% 7% 2 7% 5% 4 4 4 7% 7% 35%	1520
	11th to 20th	Night	18% 7% 2 6% 5% 4 5% 5% 5% 7% 37%	1520
	21st to end	Night	19% 7% 3 6% 5% 5% 5% 4 4 8% 34%	1520
July	1st to 10th	Night	13% 5% 2 7% 6% 5% 6% 5% 7% 9% 35%	2520
	11th to 20th	Night	15% 5% 2 6% 5% 5% 4 4 6% 7% 43%	2520
	21st to end	Night	11% 5% 2 4 4 4 5% 4 6% 8% 48%	2739
August	1st to 10th	Night	13% 6% 3 7% 6% 5% 5% 4 6% 7% 40%	2506
	11th to 20th	Night	18% 6% 2 6% 4 4 4 4 5% 6% 42%	2709
	21st to end	Night	19% 6% 2 5% 4 4 4 3 4 6% 41%	3476
September	1st to 10th	Night	12% 5% 2 5% 3 5% 5% 4 5% 6% 48%	1900
	11th to 20th	Night	15% 5% 2 4 3 3 4 3 4 6% 51%	1990
	21st to end	Night	19% 5% 2 6% 4 3 3 3 4 5% 46%	2090
October	1st to 10th	Night	18% 8% 3 7% 4 4 4 3 4 6% 40%	2204
	11th to 20th	Night	22% 8% 3 6% 4 4 4 3 5% 7% 36%	2347
	21st to end	Night	23% 9% 3 7% 4 4 4 3 5% 6% 31%	2717
November	1st to 10th	Night	16% 10% 3 8% 4 4 4 3 5% 5% 36%	2453
	11th to 20th	Night	18% 12% 3 6% 6% 4 4 3 5% 6% 32%	2558
	21st to end	Night	20% 14% 3 9% 6% 4 3 3 4 5% 29%	2660
December	1st to 10th	Night	19% 16% 4 10% 6% 4 4 3 5% 5% 23%	2660
	11th to 20th	Night	22% 13% 5% 9% 5% 4 4 3 4 4 28%	3288
	21st to end	Night	22% 17% 6% 10% 4 4 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	56% 10% 12% 17% 5% 1	2518
	11th to 20th	Day	57% 9% 9% 17% 7% 1	2520
	21st to end	Day	58% 8% 9% 17% 7% 1	2772
February	1st to 10th	Day	60% 4 8% 17% 9% 2	1624
	11th to 20th	Day	57% 6% 11% 14% 11% 1	1769
	21st to end	Day	59% 6% 7% 16% 9% 3	1570
March	1st to 10th	Day	59% 9% 7% 14% 10% 2	3119
	11th to 20th	Day	56% 8% 10% 12% 11% 3	3269
	21st to end	Day	46% 6% 9% 19% 16% 4	4166
April	1st to 10th	Day	56% 6% 9% 16% 11% 2	2280
	11th to 20th	Day	50% 6% 9% 21% 12% 2	2254
	21st to end	Day	54% 7% 8% 16% 12% 3	2465
May	1st to 10th	Day	50% 7% 12% 18% 12% 1	4398
	11th to 20th	Day	44% 11% 18% 17% 8% 2	4402
	21st to end	Day	46% 10% 11% 18% 15% 2	4837
June	1st to 10th	Day	52% 10% 10% 17% 9% 1	2660
	11th to 20th	Day	44% 8% 13% 21% 11% 2	2660
	21st to end	Day	56% 8% 11% 15% 9%	2660
July	1st to 10th	Day	45% 8% 15% 23% 9%	4370
	11th to 20th	Day	43% 9% 18% 23% 7%	4365
	21st to end	Day	39% 9% 15% 27% 10%	4661
August	1st to 10th	Day	46% 9% 17% 20% 7%	4409
	11th to 20th	Day	45% 9% 18% 22% 5%	4114
	21st to end	Day	43% 7% 15% 20% 14% 1	4180
September	1st to 10th	Day	38% 7% 17% 25% 12% 1	2280
	11th to 20th	Day	37% 8% 14% 28% 12% 1	2190
	21st to end	Day	44% 6% 13% 26% 11%	2090
October	1st to 10th	Day	47% 6% 13% 26% 7% 1	3272
	11th to 20th	Day	47% 6% 16% 25% 6% 1	3022
	21st to end	Day	44% 5% 21% 19% 9% 1	3081
November	1st to 10th	Day	49% 8% 13% 19% 10% 1	1698
	11th to 20th	Day	55% 7% 12% 16% 10%	1620
	21st to end	Day	59% 8% 12% 15% 7% 1	1520
December	1st to 10th	Day	64% 5% 10% 15% 6%	1520
	11th to 20th	Day	59% 5% 10% 18% 9%	1906
	21st to end	Day	64% 5% 8% 14% 8%	2772
January	1st to 10th	Night	57% 9% 14% 14% 6%	4429
	11th to 20th	Night	55% 8% 12% 19% 5% 1	4440
	21st to end	Night	57% 10% 10% 14% 8% 1	4884
February	1st to 10th	Night	57% 6% 9% 18% 9% 1	2552
	11th to 20th	Night	53% 6% 10% 18% 11% 1	2307
	21st to end	Night	52% 6% 10% 18% 13% 2	1884
March	1st to 10th	Night	56% 7% 11% 14% 9% 3	3734
	11th to 20th	Night	57% 8% 7% 14% 12% 2	3688
	21st to end	Night	48% 6% 9% 21% 12% 4	3466
April	1st to 10th	Night	53% 6% 9% 15% 15% 2	1900
	11th to 20th	Night	46% 7% 10% 22% 13% 3	1875
	21st to end	Night	49% 6% 8% 19% 15% 2	1715
May	1st to 10th	Night	50% 9% 13% 17% 8% 2	2591
	11th to 20th	Night	43% 11% 14% 20% 11% 2	2496
	21st to end	Night	45% 10% 12% 17% 14% 1	2739
June	1st to 10th	Night	45% 8% 14% 20% 12% 1	1520
	11th to 20th	Night	45% 8% 12% 19% 13% 3	1520
	21st to end	Night	49% 8% 12% 18% 13% 1	1520
July	1st to 10th	Night	44% 7% 20% 18% 10% 1	2480
	11th to 20th	Night	40% 7% 20% 27% 6%	2472
	21st to end	Night	34% 6% 20% 28% 11%	2651
August	1st to 10th	Night	43% 7% 17% 26% 8%	2496
	11th to 20th	Night	42% 5% 21% 23% 8%	2733
	21st to end	Night	44% 6% 15% 23% 12%	3476
September	1st to 10th	Night	35% 7% 17% 26% 14% 1	1900
	11th to 20th	Night	34% 6% 16% 32% 11% 1	1990
	21st to end	Night	40% 6% 12% 29% 13%	2090
October	1st to 10th	Night	46% 4 14% 25% 10%	3672
	11th to 20th	Night	41% 6% 13% 31% 9%	3896
	21st to end	Night	45% 5% 17% 19% 12% 2	4467
November	1st to 10th	Night	49% 6% 15% 21% 8% 1	2453
	11th to 20th	Night	52% 6% 13% 17% 10% 1	2558
	21st to end	Night	58% 5% 12% 16% 8% 1	2660
December	1st to 10th	Night	62% 6% 12% 15% 5%	2660
	11th to 20th	Night	59% 7% 8% 17% 9% 1	3288
	21st to end	Night	63% 6% 7% 16% 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	21% 20% 34% 20% 4	180
	11th to 20th	Day	24% 16% 37% 17% 4 1	180
	21st to end	Day	16% 17% 45% 18% 3 1	198
February	1st to 10th	Day	28% 26% 37% 8% 1	229
	11th to 20th	Day	22% 23% 40% 13% 2	367
	21st to end	Day	25% 24% 32% 15% 4	382
March	1st to 10th	Day	23% 20% 35% 17% 5%	460
	11th to 20th	Day	22% 21% 36% 15% 4	460
	21st to end	Day	26% 24% 28% 14% 7% 2	506
April	1st to 10th	Day	27% 19% 31% 16% 6%	460
	11th to 20th	Day	29% 22% 26% 15% 7% 2	452
	21st to end	Day	29% 21% 33% 11% 5% 1	460
May	1st to 10th	Day	27% 19% 33% 15% 4 1	463
	11th to 20th	Day	19% 19% 34% 21% 6% 1	487
	21st to end	Day	21% 22% 35% 16% 5% 2	529
June	1st to 10th	Day	21% 17% 38% 17% 8%	490
	11th to 20th	Day	17% 18% 32% 21% 10% 1	490
	21st to end	Day	25% 13% 29% 24% 8% 1	490
July	1st to 10th	Day	15% 10% 36% 27% 10% 2	485
	11th to 20th	Day	15% 12% 36% 27% 8% 2	484
	21st to end	Day	14% 9% 33% 30% 13% 2	532
August	1st to 10th	Day	14% 10% 30% 30% 13% 2	486
	11th to 20th	Day	15% 8% 28% 28% 15% 6%	479
	21st to end	Day	16% 15% 27% 23% 15% 4	539
September	1st to 10th	Day	16% 13% 33% 23% 11% 5%	490
	11th to 20th	Day	14% 11% 28% 26% 15% 7%	490
	21st to end	Day	23% 11% 29% 20% 13% 4	490
October	1st to 10th	Day	24% 15% 26% 23% 10% 2	490
	11th to 20th	Day	25% 19% 29% 17% 9% 1	453
	21st to end	Day	31% 18% 27% 19% 4	429
November	1st to 10th	Day	22% 20% 30% 20% 7% 1	374
	11th to 20th	Day	23% 22% 31% 18% 6%	280
	21st to end	Day	25% 28% 27% 17% 3	180
December	1st to 10th	Day	29% 16% 29% 19% 6% 2	180
	11th to 20th	Day	30% 23% 32% 12% 3	180
	21st to end	Day	32% 20% 28% 16% 4 1	198
January	1st to 10th	Night	24% 12% 38% 23% 4	760
	11th to 20th	Night	24% 14% 35% 21% 6%	760
	21st to end	Night	15% 12% 39% 27% 6%	836
February	1st to 10th	Night	18% 14% 38% 24% 6%	760
	11th to 20th	Night	20% 17% 36% 22% 5%	743
	21st to end	Night	21% 15% 37% 23% 4	628
March	1st to 10th	Night	24% 15% 33% 24% 4	760
	11th to 20th	Night	22% 19% 33% 19% 5% 1	760
	21st to end	Night	20% 17% 33% 23% 6%	836
April	1st to 10th	Night	28% 14% 29% 24% 6%	760
	11th to 20th	Night	23% 16% 32% 23% 6%	751
	21st to end	Night	27% 16% 31% 21% 5% 1	575
May	1st to 10th	Night	25% 14% 31% 23% 6% 1	425
	11th to 20th	Night	21% 13% 31% 28% 7%	374
	21st to end	Night	21% 9% 41% 21% 8%	411
June	1st to 10th	Night	21% 9% 29% 32% 8%	380
	11th to 20th	Night	19% 8% 29% 31% 13% 1	380
	21st to end	Night	21% 6% 29% 31% 13%	380
July	1st to 10th	Night	13% 5% 31% 36% 13% 1	370
	11th to 20th	Night	13% 4 28% 41% 14% 1	368
	21st to end	Night	15% 5% 24% 40% 14% 1	416
August	1st to 10th	Night	12% 3 24% 45% 16% 1	378
	11th to 20th	Night	15% 4 24% 36% 20% 2	511
	21st to end	Night	17% 6% 27% 31% 18% 2	836
September	1st to 10th	Night	14% 6% 31% 35% 13% 1	760
	11th to 20th	Night	18% 7% 27% 27% 20% 2	760
	21st to end	Night	21% 9% 28% 25% 15% 2	760
October	1st to 10th	Night	22% 11% 30% 26% 11% 1	760
	11th to 20th	Night	24% 12% 29% 25% 8% 1	760
	21st to end	Night	28% 12% 31% 23% 6%	836
November	1st to 10th	Night	24% 13% 30% 25% 8% 1	755
	11th to 20th	Night	23% 15% 32% 20% 9% 1	760
	21st to end	Night	27% 17% 27% 23% 6% 1	760
December	1st to 10th	Night	28% 13% 30% 23% 6%	760
	11th to 20th	Night	25% 15% 32% 21% 5%	760
	21st to end	Night	29% 15% 31% 21% 4	836

Page generated at 2024-11-01 22:47:48. Version ac07

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