Observatoire de Mirabilis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Mirabilis clear sky chart from 2005-11-06 to 2024-11-05.

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% 4 4 3 5% 6% 29%	101578
	Night	18% 13% 4 9% 5% 4 4 3 5% 5% 29%	97473
Transparency	Day	55% 4 12% 19% 9% 1	105027
	Night	56% 4 12% 18% 9% 1	102113
Seeing	Day	27% 17% 30% 18% 7% 2	14493
	Night	25% 14% 28% 24% 9% 1	23465

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	17% 20% 6% 17% 7% 5% 4 2 3 3 16%	2517
	11th to 20th	Day	13% 16% 8% 19% 10% 4 3 2 3 5% 18%	2520
	21st to end	Day	11% 17% 10% 13% 6% 5% 7% 4 4 4 18%	2772
February	1st to 10th	Day	12% 18% 6% 13% 9% 4 3 3 4 5% 22%	1691
	11th to 20th	Day	12% 20% 5% 12% 6% 5% 4 3 4 4 24%	1714
	21st to end	Day	16% 19% 5% 9% 7% 5% 3 3 4 4 24%	1570
March	1st to 10th	Day	18% 16% 4 11% 5% 5% 4 3 4 5% 24%	3116
	11th to 20th	Day	13% 19% 7% 13% 5% 4 4 3 3 5% 23%	3350
	21st to end	Day	14% 10% 3 9% 6% 4 4 4 5% 6% 36%	4120
April	1st to 10th	Day	21% 16% 3 8% 5% 3 3 3 4 5% 29%	2280
	11th to 20th	Day	22% 11% 4 7% 5% 5% 3 3 4 5% 32%	2254
	21st to end	Day	22% 11% 4 9% 5% 4 4 3 4 4 30%	2436
May	1st to 10th	Day	22% 10% 4 7% 4 4 5% 4 6% 6% 27%	4426
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 4 6% 8% 30%	4398
	21st to end	Day	19% 7% 3 7% 5% 5% 4 3 6% 7% 34%	4837
June	1st to 10th	Day	24% 9% 3 6% 5% 5% 5% 4 6% 6% 26%	2660
	11th to 20th	Day	17% 7% 3 7% 5% 5% 5% 4 6% 8% 33%	2660
	21st to end	Day	24% 8% 3 7% 5% 5% 5% 4 5% 6% 26%	2660
July	1st to 10th	Day	16% 8% 3 7% 5% 5% 6% 4 6% 9% 31%	4440
	11th to 20th	Day	17% 7% 3 7% 5% 5% 5% 4 6% 8% 33%	4440
	21st to end	Day	13% 7% 3 6% 4 4 4 4 6% 7% 43%	4814
August	1st to 10th	Day	17% 8% 3 8% 5% 6% 5% 4 6% 9% 29%	4423
	11th to 20th	Day	18% 7% 2 7% 4 4 5% 4 6% 7% 34%	4023
	21st to end	Day	17% 6% 2 6% 5% 4 5% 4 5% 8% 37%	4180
September	1st to 10th	Day	19% 5% 2 6% 4 5% 4 3 5% 7% 40%	2280
	11th to 20th	Day	16% 7% 2 6% 3 4 4 3 5% 8% 43%	2233
	21st to end	Day	22% 7% 2 5% 4 3 4 3 5% 6% 38%	2090
October	1st to 10th	Day	24% 10% 3 6% 4 4 4 3 6% 6% 31%	1910
	11th to 20th	Day	26% 14% 3 9% 4 5% 4 3 5% 5% 24%	1886
	21st to end	Day	26% 14% 3 8% 4 4 4 3 4 6% 23%	1881
November	1st to 10th	Day	18% 14% 3 7% 5% 4 4 3 5% 6% 31%	1708
	11th to 20th	Day	21% 16% 5% 11% 6% 4 4 3 5% 5% 21%	1571
	21st to end	Day	22% 17% 6% 10% 6% 4 4 3 3 5% 20%	1520
December	1st to 10th	Day	23% 21% 6% 9% 6% 4 4 3 4 5% 16%	1520
	11th to 20th	Day	20% 18% 5% 13% 6% 4 4 3 4 4 19%	1906
	21st to end	Day	23% 20% 6% 11% 5% 3 4 2 4 4 18%	2772
January	1st to 10th	Night	15% 19% 8% 12% 6% 4 4 3 4 4 19%	4429
	11th to 20th	Night	12% 16% 6% 17% 11% 5% 3 3 4 5% 18%	4440
	21st to end	Night	11% 17% 8% 16% 8% 6% 5% 3 4 4 17%	4884
February	1st to 10th	Night	12% 17% 6% 11% 8% 5% 4 4 5% 5% 23%	2485
	11th to 20th	Night	13% 17% 7% 11% 7% 5% 4 3 4 4 25%	2351
	21st to end	Night	14% 17% 5% 10% 4 5% 5% 3 6% 5% 25%	1884
March	1st to 10th	Night	20% 13% 5% 8% 5% 4 4 3 4 5% 30%	3724
	11th to 20th	Night	17% 19% 6% 10% 6% 3 3 2 4 4 26%	3607
	21st to end	Night	14% 12% 4 9% 5% 4 4 3 4 5% 34%	3512
April	1st to 10th	Night	22% 12% 4 7% 5% 4 3 3 4 6% 30%	1900
	11th to 20th	Night	21% 9% 3 6% 5% 4 4 4 4 6% 35%	1875
	21st to end	Night	20% 11% 3 7% 4 4 4 3 5% 5% 34%	1760
May	1st to 10th	Night	19% 10% 3 8% 4 4 4 4 6% 7% 31%	2514
	11th to 20th	Night	20% 7% 3 6% 4 3 5% 3 5% 7% 37%	2495
	21st to end	Night	19% 7% 2 7% 5% 5% 6% 4 5% 7% 33%	2738
June	1st to 10th	Night	20% 8% 3 7% 5% 4 5% 3 7% 8% 30%	1520
	11th to 20th	Night	18% 7% 3 6% 5% 4 4 4 5% 7% 38%	1520
	21st to end	Night	22% 7% 2 6% 5% 4 4 3 6% 5% 36%	1520
July	1st to 10th	Night	16% 8% 3 8% 5% 5% 5% 4 5% 7% 34%	2520
	11th to 20th	Night	18% 8% 2 6% 3 4 4 4 6% 7% 39%	2520
	21st to end	Night	12% 5% 1 5% 4 4 4 3 7% 8% 46%	2739
August	1st to 10th	Night	15% 8% 3 7% 5% 4 4 4 5% 7% 38%	2506
	11th to 20th	Night	19% 8% 2 6% 4 4 4 3 5% 5% 40%	2770
	21st to end	Night	18% 6% 3 5% 4 4 4 4 5% 7% 41%	3476
September	1st to 10th	Night	16% 8% 2 6% 4 3 4 3 5% 6% 45%	1900
	11th to 20th	Night	16% 6% 2 4 3 3 3 3 6% 7% 47%	1947
	21st to end	Night	19% 7% 2 5% 3 3 4 3 4 7% 43%	2090
October	1st to 10th	Night	20% 8% 3 6% 4 5% 4 3 5% 6% 37%	2267
	11th to 20th	Night	23% 13% 3 6% 4 4 4 3 4 5% 29%	2294
	21st to end	Night	25% 13% 3 7% 5% 4 4 3 4 6% 26%	2717
November	1st to 10th	Night	20% 13% 4 7% 4 4 4 4 5% 6% 29%	2470
	11th to 20th	Night	18% 16% 5% 11% 5% 5% 4 3 4 6% 25%	2607
	21st to end	Night	22% 18% 6% 10% 5% 4 4 3 4 4 20%	2660
December	1st to 10th	Night	21% 20% 7% 12% 6% 4 4 3 4 4 15%	2660
	11th to 20th	Night	21% 18% 6% 11% 5% 4 3 3 3 4 21%	3288
	21st to end	Night	23% 22% 5% 12% 5% 3 3 2 4 4 17%	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	74% 2 9% 11% 4	2518
	11th to 20th	Day	72% 2 5% 14% 7% 1	2520
	21st to end	Day	68% 3 10% 11% 7% 1	2772
February	1st to 10th	Day	65% 2 7% 17% 7% 2	1691
	11th to 20th	Day	63% 3 10% 13% 10% 1	1723
	21st to end	Day	65% 2 7% 15% 9% 2	1570
March	1st to 10th	Day	63% 3 8% 13% 11% 1	3119
	11th to 20th	Day	65% 3 9% 12% 10% 2	3350
	21st to end	Day	48% 4 7% 21% 17% 2	4120
April	1st to 10th	Day	58% 3 8% 17% 11% 3	2280
	11th to 20th	Day	55% 3 8% 20% 12% 2	2254
	21st to end	Day	58% 3 8% 16% 12% 3	2436
May	1st to 10th	Day	55% 5% 9% 21% 8% 2	4440
	11th to 20th	Day	51% 4 18% 17% 9% 1	4402
	21st to end	Day	50% 4 11% 20% 14% 1	4837
June	1st to 10th	Day	57% 5% 9% 18% 11% 1	2660
	11th to 20th	Day	49% 5% 12% 20% 11% 3	2660
	21st to end	Day	57% 6% 10% 18% 8%	2660
July	1st to 10th	Day	48% 6% 15% 23% 7%	4370
	11th to 20th	Day	46% 6% 17% 24% 6%	4365
	21st to end	Day	40% 6% 15% 31% 9%	4661
August	1st to 10th	Day	52% 5% 16% 21% 6%	4409
	11th to 20th	Day	46% 6% 17% 26% 5%	4065
	21st to end	Day	45% 6% 15% 22% 12% 1	4180
September	1st to 10th	Day	44% 4 13% 26% 12%	2280
	11th to 20th	Day	40% 4 14% 30% 11% 1	2233
	21st to end	Day	46% 5% 13% 26% 10%	2090
October	1st to 10th	Day	51% 4 12% 26% 7%	3170
	11th to 20th	Day	54% 5% 13% 22% 6%	3114
	21st to end	Day	54% 5% 20% 14% 7% 1	3081
November	1st to 10th	Day	54% 4 13% 20% 7% 1	1708
	11th to 20th	Day	65% 3 11% 12% 8% 1	1571
	21st to end	Day	68% 4 11% 12% 5% 1	1520
December	1st to 10th	Day	72% 3 9% 11% 5%	1520
	11th to 20th	Day	69% 3 9% 13% 5%	1906
	21st to end	Day	71% 3 7% 13% 7%	2772
January	1st to 10th	Night	68% 3 13% 12% 3	4429
	11th to 20th	Night	68% 2 11% 13% 5% 1	4440
	21st to end	Night	70% 3 10% 10% 7% 1	4884
February	1st to 10th	Night	63% 4 8% 17% 7% 1	2485
	11th to 20th	Night	62% 3 9% 17% 8% 1	2353
	21st to end	Night	59% 3 9% 17% 10% 2	1884
March	1st to 10th	Night	58% 2 11% 14% 11% 3	3734
	11th to 20th	Night	62% 3 8% 14% 11% 1	3608
	21st to end	Night	52% 4 7% 20% 13% 4	3512
April	1st to 10th	Night	56% 3 7% 19% 13% 2	1900
	11th to 20th	Night	50% 4 8% 22% 14% 2	1875
	21st to end	Night	53% 3 9% 19% 13% 3	1760
May	1st to 10th	Night	53% 3 14% 19% 8% 2	2520
	11th to 20th	Night	47% 4 17% 17% 12% 2	2496
	21st to end	Night	50% 4 10% 19% 14% 2	2739
June	1st to 10th	Night	51% 4 12% 22% 10%	1520
	11th to 20th	Night	45% 6% 11% 23% 13% 2	1520
	21st to end	Night	49% 6% 11% 21% 12% 1	1520
July	1st to 10th	Night	49% 5% 18% 19% 9%	2480
	11th to 20th	Night	43% 6% 19% 26% 6%	2472
	21st to end	Night	35% 6% 20% 27% 12%	2651
August	1st to 10th	Night	44% 6% 16% 27% 7%	2496
	11th to 20th	Night	44% 5% 19% 25% 6%	2794
	21st to end	Night	43% 5% 16% 24% 11% 2	3476
September	1st to 10th	Night	39% 5% 14% 28% 13% 1	1900
	11th to 20th	Night	38% 4 15% 32% 11% 1	1947
	21st to end	Night	42% 5% 13% 29% 11%	2090
October	1st to 10th	Night	46% 5% 14% 23% 11%	3787
	11th to 20th	Night	53% 4 13% 21% 9%	3805
	21st to end	Night	54% 3 17% 15% 9% 1	4467
November	1st to 10th	Night	56% 4 13% 19% 7% 1	2470
	11th to 20th	Night	61% 3 10% 16% 7% 2	2607
	21st to end	Night	68% 2 10% 14% 5%	2660
December	1st to 10th	Night	73% 3 8% 12% 4	2660
	11th to 20th	Night	68% 3 7% 15% 7% 1	3288
	21st to end	Night	72% 2 7% 13% 6%	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	25% 20% 38% 13% 4	180
	11th to 20th	Day	29% 20% 33% 12% 6% 1	180
	21st to end	Day	27% 20% 35% 13% 5% 1	198
February	1st to 10th	Day	36% 25% 31% 7% 2	261
	11th to 20th	Day	28% 31% 34% 6% 1	321
	21st to end	Day	34% 23% 30% 12% 2	382
March	1st to 10th	Day	28% 21% 34% 14% 2 1	460
	11th to 20th	Day	31% 21% 31% 13% 3 1	460
	21st to end	Day	33% 22% 24% 14% 6% 1	506
April	1st to 10th	Day	33% 19% 29% 15% 3 1	460
	11th to 20th	Day	37% 18% 25% 12% 8% 1	452
	21st to end	Day	33% 18% 30% 13% 4 1	460
May	1st to 10th	Day	31% 19% 30% 15% 5%	463
	11th to 20th	Day	25% 16% 33% 19% 6% 1	487
	21st to end	Day	26% 18% 33% 18% 5%	529
June	1st to 10th	Day	29% 16% 33% 16% 6%	490
	11th to 20th	Day	21% 19% 31% 19% 9% 1	490
	21st to end	Day	29% 13% 32% 17% 7% 2	490
July	1st to 10th	Day	19% 11% 35% 24% 8% 2	485
	11th to 20th	Day	18% 13% 35% 27% 6% 1	484
	21st to end	Day	16% 11% 37% 27% 8% 2	532
August	1st to 10th	Day	19% 12% 29% 29% 10% 2	486
	11th to 20th	Day	18% 8% 28% 27% 13% 6%	479
	21st to end	Day	19% 16% 27% 22% 10% 6%	539
September	1st to 10th	Day	24% 9% 30% 21% 11% 5%	490
	11th to 20th	Day	16% 12% 26% 22% 15% 9%	490
	21st to end	Day	22% 16% 24% 22% 10% 5%	490
October	1st to 10th	Day	31% 16% 23% 17% 11% 2	490
	11th to 20th	Day	34% 18% 25% 15% 6% 1	483
	21st to end	Day	38% 12% 30% 15% 5%	429
November	1st to 10th	Day	37% 14% 26% 19% 4 1	378
	11th to 20th	Day	31% 23% 29% 13% 5%	231
	21st to end	Day	32% 25% 29% 12% 1 1	180
December	1st to 10th	Day	37% 18% 27% 13% 5%	180
	11th to 20th	Day	33% 28% 28% 8% 2 1	180
	21st to end	Day	37% 24% 25% 10% 4 1	198
January	1st to 10th	Night	29% 17% 34% 16% 4	760
	11th to 20th	Night	30% 20% 28% 17% 6%	760
	21st to end	Night	18% 19% 37% 20% 6% 1	836
February	1st to 10th	Night	22% 21% 33% 20% 4 1	760
	11th to 20th	Night	23% 23% 34% 17% 3	743
	21st to end	Night	26% 18% 32% 21% 3	628
March	1st to 10th	Night	26% 17% 33% 21% 3	760
	11th to 20th	Night	27% 20% 30% 18% 4 1	760
	21st to end	Night	27% 16% 29% 22% 6% 1	836
April	1st to 10th	Night	31% 16% 26% 22% 4	760
	11th to 20th	Night	28% 15% 28% 22% 6%	751
	21st to end	Night	29% 16% 27% 19% 8%	620
May	1st to 10th	Night	27% 11% 29% 23% 8% 1	380
	11th to 20th	Night	23% 9% 30% 28% 9% 1	374
	21st to end	Night	20% 11% 37% 24% 8%	411
June	1st to 10th	Night	23% 8% 31% 28% 9% 1	380
	11th to 20th	Night	20% 9% 25% 32% 11% 1	380
	21st to end	Night	22% 7% 22% 33% 16% 1	380
July	1st to 10th	Night	15% 7% 24% 38% 15% 1	370
	11th to 20th	Night	16% 6% 23% 37% 17% 1	368
	21st to end	Night	14% 7% 23% 40% 15% 1	416
August	1st to 10th	Night	15% 4 17% 46% 17% 1	378
	11th to 20th	Night	15% 5% 20% 33% 25% 2	546
	21st to end	Night	19% 6% 25% 31% 16% 2	836
September	1st to 10th	Night	18% 7% 27% 34% 14% 1	760
	11th to 20th	Night	20% 7% 19% 32% 21% 1	760
	21st to end	Night	21% 9% 24% 26% 17% 2	760
October	1st to 10th	Night	24% 12% 25% 26% 12% 1	760
	11th to 20th	Night	31% 12% 26% 23% 7% 1	760
	21st to end	Night	31% 13% 27% 23% 5%	836
November	1st to 10th	Night	30% 15% 26% 22% 6% 1	760
	11th to 20th	Night	28% 18% 29% 15% 9% 1	760
	21st to end	Night	33% 18% 25% 17% 6% 1	760
December	1st to 10th	Night	32% 20% 26% 17% 5%	760
	11th to 20th	Night	32% 21% 26% 16% 5% 1	760
	21st to end	Night	37% 17% 27% 16% 3	836

Page generated at 2024-11-03 02:11:12. Version ac07

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