Observatoire Magenta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Magenta clear sky chart from 2005-11-06 to 2025-02-06.

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	18% 11% 4 9% 5% 5% 5% 4 5% 7% 29%	108431
	Night	19% 14% 5% 10% 5% 4 4 3 4 5% 27%	109829
Transparency	Day	55% 6% 13% 19% 7% 1	111935
	Night	59% 5% 11% 16% 8% 1	114476
Seeing	Day	25% 14% 28% 22% 10% 2	14846
	Night	26% 11% 27% 26% 9% 1	23921

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	19% 24% 8% 15% 4 5% 3 2 3 3 14%	3597
	11th to 20th	Day	12% 17% 8% 20% 8% 5% 5% 3 4 4 13%	3570
	21st to end	Day	12% 18% 6% 12% 6% 7% 6% 4 4 5% 19%	3960
February	1st to 10th	Day	16% 18% 5% 11% 7% 5% 5% 3 5% 4 20%	1675
	11th to 20th	Day	15% 18% 6% 12% 5% 4 4 3 5% 5% 22%	1805
	21st to end	Day	17% 18% 4 8% 7% 6% 4 3 4 6% 23%	1570
March	1st to 10th	Day	20% 14% 5% 10% 6% 5% 5% 3 4 6% 24%	3116
	11th to 20th	Day	16% 20% 5% 10% 5% 4 4 3 3 5% 24%	3261
	21st to end	Day	17% 13% 5% 9% 4 4 3 3 3 5% 35%	4166
April	1st to 10th	Day	24% 13% 3 7% 5% 4 4 3 5% 5% 27%	2280
	11th to 20th	Day	21% 10% 3 7% 4 4 4 3 4 5% 35%	2254
	21st to end	Day	24% 10% 3 6% 5% 4 4 3 4 6% 31%	2465
May	1st to 10th	Day	24% 10% 3 7% 5% 4 4 4 5% 6% 28%	4262
	11th to 20th	Day	18% 7% 3 8% 5% 6% 6% 5% 6% 7% 29%	4398
	21st to end	Day	15% 7% 2 7% 5% 5% 5% 4 6% 9% 34%	4837
June	1st to 10th	Day	24% 8% 2 6% 4 4 5% 4 6% 7% 30%	2660
	11th to 20th	Day	17% 5% 2 6% 4 5% 5% 4 6% 9% 36%	2660
	21st to end	Day	23% 8% 2 8% 4 5% 4 4 5% 6% 30%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 9% 34%	4440
	21st to end	Day	14% 6% 2 6% 4 4 4 4 7% 8% 41%	4814
August	1st to 10th	Day	17% 7% 3 8% 6% 5% 5% 4 7% 9% 29%	4423
	11th to 20th	Day	16% 7% 3 7% 5% 4 5% 4 6% 8% 35%	3995
	21st to end	Day	16% 7% 2 7% 3 4 4 4 5% 8% 39%	4180
September	1st to 10th	Day	15% 6% 2 6% 4 4 5% 4 5% 7% 42%	2280
	11th to 20th	Day	17% 5% 2 5% 3 3 4 3 5% 7% 46%	2166
	21st to end	Day	17% 7% 2 6% 4 3 4 3 7% 8% 38%	2090
October	1st to 10th	Day	24% 8% 3 7% 5% 4 5% 3 5% 7% 29%	2013
	11th to 20th	Day	21% 9% 3 7% 6% 5% 5% 3 5% 6% 29%	1826
	21st to end	Day	26% 13% 2 7% 4 5% 4 3 4 6% 26%	1881
November	1st to 10th	Day	20% 13% 3 6% 5% 4 5% 4 5% 5% 31%	1761
	11th to 20th	Day	19% 14% 5% 10% 6% 3 4 4 4 6% 25%	1780
	21st to end	Day	23% 16% 5% 9% 5% 4 4 4 6% 5% 20%	1600
December	1st to 10th	Day	19% 24% 6% 14% 6% 4 4 3 3 3 14%	2600
	11th to 20th	Day	21% 15% 7% 11% 5% 4 5% 3 5% 5% 21%	2986
	21st to end	Day	22% 16% 5% 11% 6% 5% 5% 4 6% 5% 16%	3960
January	1st to 10th	Night	16% 26% 9% 13% 5% 4 3 2 3 3 16%	6349
	11th to 20th	Night	11% 20% 9% 18% 8% 6% 4 3 4 4 13%	6315
	21st to end	Night	14% 17% 6% 13% 8% 5% 4 3 4 4 21%	6996
February	1st to 10th	Night	17% 17% 5% 14% 7% 4 5% 3 4 5% 19%	2614
	11th to 20th	Night	15% 16% 5% 12% 8% 5% 5% 3 4 5% 23%	2261
	21st to end	Night	17% 16% 5% 10% 7% 5% 4 2 3 5% 28%	1884
March	1st to 10th	Night	23% 12% 4 8% 4 4 4 3 4 4 31%	3724
	11th to 20th	Night	19% 21% 5% 9% 5% 4 3 2 3 4 25%	3692
	21st to end	Night	15% 16% 5% 10% 4 4 3 3 3 4 34%	3466
April	1st to 10th	Night	24% 12% 3 8% 5% 4 4 3 5% 5% 27%	1900
	11th to 20th	Night	24% 11% 3 7% 5% 3 3 3 3 5% 33%	1875
	21st to end	Night	22% 10% 3 7% 4 3 4 2 4 6% 34%	1715
May	1st to 10th	Night	24% 9% 3 8% 5% 4 5% 3 5% 6% 27%	2706
	11th to 20th	Night	22% 9% 2 8% 5% 4 4 3 5% 5% 32%	2495
	21st to end	Night	17% 7% 3 6% 5% 4 4 4 5% 8% 36%	2738
June	1st to 10th	Night	25% 7% 2 5% 5% 3 5% 3 7% 6% 31%	1520
	11th to 20th	Night	18% 6% 2 6% 4 4 5% 3 6% 7% 38%	1520
	21st to end	Night	19% 8% 3 6% 6% 4 4 4 5% 7% 33%	1520
July	1st to 10th	Night	14% 8% 3 9% 5% 5% 5% 5% 6% 7% 33%	2520
	11th to 20th	Night	15% 7% 2 6% 5% 4 5% 4 7% 8% 38%	2520
	21st to end	Night	14% 7% 2 8% 5% 5% 5% 4 6% 7% 38%	2739
August	1st to 10th	Night	21% 9% 3 7% 5% 4 3 4 6% 6% 32%	2506
	11th to 20th	Night	16% 8% 3 8% 6% 4 5% 4 5% 7% 34%	2799
	21st to end	Night	17% 6% 2 6% 4 4 4 4 6% 6% 40%	3476
September	1st to 10th	Night	16% 6% 3 7% 5% 3 3 4 6% 6% 41%	1900
	11th to 20th	Night	15% 5% 2 6% 4 3 4 4 5% 7% 47%	2014
	21st to end	Night	19% 7% 2 6% 5% 4 4 3 4 7% 41%	2090
October	1st to 10th	Night	21% 7% 3 7% 4 3 4 3 5% 7% 35%	2165
	11th to 20th	Night	23% 9% 3 9% 4 4 4 3 5% 5% 30%	2353
	21st to end	Night	26% 11% 3 7% 4 5% 4 3 4 5% 27%	2717
November	1st to 10th	Night	21% 14% 3 6% 4 5% 5% 3 5% 6% 29%	2537
	11th to 20th	Night	21% 13% 4 8% 5% 4 4 4 4 5% 29%	2619
	21st to end	Night	23% 17% 4 9% 5% 4 3 3 4 5% 24%	2800
December	1st to 10th	Night	19% 24% 9% 13% 6% 4 3 2 3 4 12%	4580
	11th to 20th	Night	24% 17% 5% 13% 5% 4 3 2 3 3 21%	5208
	21st to end	Night	23% 18% 5% 10% 4 4 3 3 6% 6% 18%	6996

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	76% 5% 9% 8% 1	3598
	11th to 20th	Day	75% 6% 9% 7% 3	3600
	21st to end	Day	66% 7% 9% 11% 7%	3960
February	1st to 10th	Day	68% 6% 9% 12% 4 1	1675
	11th to 20th	Day	65% 5% 14% 11% 4 1	1814
	21st to end	Day	63% 6% 11% 13% 7% 1	1570
March	1st to 10th	Day	61% 7% 10% 16% 6% 1	3119
	11th to 20th	Day	62% 7% 12% 11% 8% 1	3261
	21st to end	Day	52% 5% 9% 18% 14% 1	4166
April	1st to 10th	Day	60% 6% 9% 17% 8% 1	2280
	11th to 20th	Day	52% 5% 10% 20% 12% 1	2254
	21st to end	Day	56% 6% 10% 17% 9% 2	2465
May	1st to 10th	Day	55% 7% 10% 19% 8% 1	4276
	11th to 20th	Day	51% 10% 16% 15% 8% 1	4402
	21st to end	Day	44% 9% 13% 22% 11% 1	4837
June	1st to 10th	Day	52% 7% 12% 18% 9% 1	2660
	11th to 20th	Day	44% 7% 13% 23% 11% 2	2660
	21st to end	Day	54% 7% 11% 19% 8% 1	2660
July	1st to 10th	Day	44% 5% 15% 27% 8%	4370
	11th to 20th	Day	45% 6% 16% 29% 4	4365
	21st to end	Day	41% 7% 14% 30% 7%	4661
August	1st to 10th	Day	51% 6% 16% 20% 6%	4409
	11th to 20th	Day	47% 6% 20% 22% 6%	4035
	21st to end	Day	43% 5% 18% 20% 13% 1	4180
September	1st to 10th	Day	41% 7% 14% 26% 11%	2280
	11th to 20th	Day	39% 5% 13% 31% 12%	2166
	21st to end	Day	43% 7% 15% 25% 9%	2090
October	1st to 10th	Day	47% 5% 14% 28% 6%	3338
	11th to 20th	Day	50% 6% 16% 24% 5%	3016
	21st to end	Day	51% 4 17% 21% 6% 1	3081
November	1st to 10th	Day	56% 7% 12% 19% 7%	1761
	11th to 20th	Day	61% 6% 12% 13% 8% 1	1780
	21st to end	Day	66% 6% 15% 9% 3	1600
December	1st to 10th	Day	77% 4 9% 9% 1	2600
	11th to 20th	Day	66% 5% 8% 16% 5%	2986
	21st to end	Day	69% 5% 9% 10% 7%	3960
January	1st to 10th	Night	75% 5% 10% 8% 2	6349
	11th to 20th	Night	75% 5% 10% 7% 2	6360
	21st to end	Night	68% 4 9% 9% 10%	6996
February	1st to 10th	Night	69% 6% 8% 12% 5%	2614
	11th to 20th	Night	65% 6% 9% 15% 5%	2263
	21st to end	Night	61% 5% 9% 14% 10% 1	1884
March	1st to 10th	Night	56% 5% 10% 18% 8% 2	3734
	11th to 20th	Night	63% 6% 8% 13% 10% 1	3693
	21st to end	Night	54% 6% 8% 19% 11% 2	3466
April	1st to 10th	Night	59% 5% 9% 17% 10% 1	1900
	11th to 20th	Night	55% 5% 8% 19% 12% 1	1875
	21st to end	Night	53% 5% 10% 17% 12% 3	1715
May	1st to 10th	Night	55% 8% 10% 17% 8% 2	2712
	11th to 20th	Night	50% 8% 12% 20% 9% 2	2496
	21st to end	Night	45% 9% 9% 20% 16% 1	2739
June	1st to 10th	Night	51% 7% 10% 20% 9% 1	1520
	11th to 20th	Night	44% 7% 13% 20% 13% 3	1520
	21st to end	Night	50% 8% 13% 18% 11% 1	1520
July	1st to 10th	Night	48% 6% 13% 21% 11%	2480
	11th to 20th	Night	42% 7% 15% 28% 8%	2472
	21st to end	Night	45% 7% 14% 21% 12%	2651
August	1st to 10th	Night	51% 6% 13% 22% 7%	2496
	11th to 20th	Night	51% 6% 17% 20% 7%	2825
	21st to end	Night	44% 5% 13% 22% 14% 2	3476
September	1st to 10th	Night	42% 7% 12% 25% 13% 1	1900
	11th to 20th	Night	37% 6% 16% 29% 12%	2014
	21st to end	Night	44% 6% 12% 24% 14% 1	2090
October	1st to 10th	Night	51% 5% 11% 24% 9%	3607
	11th to 20th	Night	50% 4 11% 27% 8%	3902
	21st to end	Night	53% 5% 12% 18% 11% 1	4467
November	1st to 10th	Night	56% 6% 13% 18% 6% 1	2537
	11th to 20th	Night	58% 5% 11% 15% 8% 2	2619
	21st to end	Night	65% 5% 12% 14% 4	2800
December	1st to 10th	Night	79% 4 8% 7% 2	4580
	11th to 20th	Night	71% 4 7% 11% 7%	5208
	21st to end	Night	66% 4 9% 13% 8%	6996

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	31% 16% 30% 16% 7% 1	200
	11th to 20th	Day	29% 21% 35% 13% 4 1	200
	21st to end	Day	23% 19% 35% 16% 6%	220
February	1st to 10th	Day	33% 25% 27% 13% 1	245
	11th to 20th	Day	26% 23% 33% 15% 3	413
	21st to end	Day	26% 21% 29% 21% 3	382
March	1st to 10th	Day	28% 18% 27% 22% 5%	460
	11th to 20th	Day	27% 18% 33% 15% 5% 1	460
	21st to end	Day	30% 20% 22% 21% 7% 1	506
April	1st to 10th	Day	33% 15% 27% 17% 7% 1	460
	11th to 20th	Day	32% 18% 24% 14% 8% 3	452
	21st to end	Day	32% 13% 32% 13% 9% 2	460
May	1st to 10th	Day	29% 14% 29% 19% 7% 2	463
	11th to 20th	Day	20% 13% 28% 26% 11% 2	487
	21st to end	Day	19% 12% 33% 24% 9% 2	529
June	1st to 10th	Day	26% 13% 28% 23% 8% 2	490
	11th to 20th	Day	19% 11% 30% 28% 11% 1	490
	21st to end	Day	26% 9% 31% 21% 10% 2	490
July	1st to 10th	Day	15% 7% 28% 33% 13% 3	485
	11th to 20th	Day	18% 7% 30% 30% 11% 4	484
	21st to end	Day	19% 7% 28% 31% 13% 2	532
August	1st to 10th	Day	17% 8% 25% 30% 17% 3	486
	11th to 20th	Day	18% 7% 24% 29% 17% 5%	479
	21st to end	Day	19% 10% 24% 25% 15% 7%	539
September	1st to 10th	Day	17% 10% 30% 23% 14% 6%	490
	11th to 20th	Day	16% 9% 21% 24% 19% 11%	490
	21st to end	Day	18% 11% 25% 23% 17% 6%	490
October	1st to 10th	Day	23% 13% 29% 19% 13% 4	490
	11th to 20th	Day	28% 18% 23% 19% 11% 1	450
	21st to end	Day	35% 15% 24% 20% 6%	429
November	1st to 10th	Day	31% 18% 28% 17% 6%	395
	11th to 20th	Day	30% 20% 24% 15% 9% 1	380
	21st to end	Day	32% 22% 29% 15% 3	200
December	1st to 10th	Day	38% 14% 24% 20% 5% 1	200
	11th to 20th	Day	28% 25% 30% 13% 4 1	200
	21st to end	Day	32% 22% 26% 14% 5% 1	220
January	1st to 10th	Night	30% 15% 30% 21% 4	800
	11th to 20th	Night	27% 16% 32% 19% 6%	800
	21st to end	Night	23% 13% 32% 25% 7%	880
February	1st to 10th	Night	28% 12% 34% 22% 4	781
	11th to 20th	Night	24% 16% 34% 23% 4	743
	21st to end	Night	27% 14% 30% 26% 3	628
March	1st to 10th	Night	26% 14% 30% 25% 4	760
	11th to 20th	Night	30% 14% 27% 23% 6%	760
	21st to end	Night	28% 14% 27% 24% 7% 1	836
April	1st to 10th	Night	29% 13% 28% 24% 5%	760
	11th to 20th	Night	29% 15% 27% 22% 7%	751
	21st to end	Night	27% 15% 27% 23% 7%	575
May	1st to 10th	Night	27% 9% 32% 23% 9% 1	494
	11th to 20th	Night	23% 9% 31% 27% 10% 1	374
	21st to end	Night	20% 7% 32% 33% 7% 1	411
June	1st to 10th	Night	29% 7% 26% 28% 9% 1	380
	11th to 20th	Night	20% 6% 27% 33% 14%	380
	21st to end	Night	19% 8% 25% 36% 12% 1	380
July	1st to 10th	Night	14% 5% 29% 40% 11% 1	370
	11th to 20th	Night	13% 3 24% 42% 17% 1	368
	21st to end	Night	15% 4 25% 41% 15%	416
August	1st to 10th	Night	19% 4 17% 40% 19% 1	378
	11th to 20th	Night	16% 5% 20% 36% 22% 1	564
	21st to end	Night	17% 6% 21% 35% 19% 2	836
September	1st to 10th	Night	17% 7% 24% 35% 15% 1	760
	11th to 20th	Night	17% 8% 18% 32% 23% 3	760
	21st to end	Night	23% 6% 27% 26% 16% 3	760
October	1st to 10th	Night	24% 9% 25% 28% 13% 1	760
	11th to 20th	Night	29% 10% 25% 26% 9% 1	760
	21st to end	Night	34% 10% 29% 22% 5%	836
November	1st to 10th	Night	30% 14% 29% 21% 5% 1	780
	11th to 20th	Night	27% 16% 27% 20% 9% 1	800
	21st to end	Night	33% 16% 27% 18% 5% 1	800
December	1st to 10th	Night	35% 14% 27% 20% 4	800
	11th to 20th	Night	33% 13% 30% 17% 6% 1	800
	21st to end	Night	34% 15% 27% 19% 5%	880

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