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 2024-04-25.

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	19% 11% 4 8% 6% 3 5% 4 5% 6% 28%	83106
	Night	18% 13% 5% 8% 6% 3 4 4 4 6% 29%	86002
Transparency	Day	57% 4 10% 18% 10% 1	82811
	Night	57% 4 11% 18% 9% 1	85831
Seeing	Day	28% 17% 30% 17% 7% 2	13733
	Night	25% 14% 28% 23% 8% 1	22909

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% 19% 7% 15% 9% 4 4 3 2 3 16%	2517
	11th to 20th	Day	13% 16% 8% 17% 13% 3 3 2 3 5% 18%	2520
	21st to end	Day	11% 17% 10% 12% 8% 4 7% 5% 4 5% 18%	2772
February	1st to 10th	Day	12% 17% 7% 11% 10% 3 4 4 4 5% 22%	1691
	11th to 20th	Day	13% 19% 6% 11% 7% 3 5% 3 4 5% 24%	1714
	21st to end	Day	16% 17% 6% 9% 7% 4 5% 4 4 5% 24%	1570
March	1st to 10th	Day	18% 15% 5% 9% 7% 4 5% 4 4 5% 24%	3116
	11th to 20th	Day	13% 18% 8% 11% 6% 3 4 4 3 5% 23%	3350
	21st to end	Day	14% 10% 3 8% 6% 3 4 5% 5% 6% 36%	4120
April	1st to 10th	Day	21% 14% 4 7% 5% 3 3 4 4 5% 29%	2280
	11th to 20th	Day	22% 10% 4 6% 5% 3 4 4 4 5% 32%	2254
	21st to end	Day	22% 10% 4 8% 6% 3 4 4 4 4 30%	2359
May	1st to 10th	Day	22% 10% 4 6% 5% 3 4 5% 4 6% 30%	2520
	11th to 20th	Day	20% 8% 4 6% 6% 3 4 4 5% 6% 34%	2478
	21st to end	Day	21% 7% 3 6% 6% 4 5% 4 5% 7% 34%	2725
June	1st to 10th	Day	24% 8% 4 6% 6% 3 6% 5% 6% 6% 27%	2520
	11th to 20th	Day	18% 6% 3 6% 5% 4 6% 5% 5% 8% 33%	2520
	21st to end	Day	23% 8% 3 7% 6% 4 5% 6% 5% 6% 27%	2520
July	1st to 10th	Day	16% 6% 3 5% 4 3 6% 5% 6% 9% 36%	2520
	11th to 20th	Day	16% 6% 3 6% 7% 4 5% 5% 7% 9% 33%	2520
	21st to end	Day	15% 7% 3 5% 6% 4 6% 6% 7% 9% 33%	2744
August	1st to 10th	Day	16% 8% 3 6% 6% 4 5% 6% 6% 8% 32%	2506
	11th to 20th	Day	16% 6% 2 6% 6% 4 6% 6% 6% 8% 35%	2299
	21st to end	Day	17% 7% 2 6% 5% 3 5% 6% 5% 8% 37%	2376
September	1st to 10th	Day	19% 5% 2 5% 4 3 4 4 5% 7% 40%	2160
	11th to 20th	Day	17% 7% 2 6% 4 3 4 4 5% 8% 41%	2116
	21st to end	Day	22% 7% 3 4 4 2 4 4 5% 7% 38%	1980
October	1st to 10th	Day	24% 9% 3 5% 5% 3 4 4 6% 6% 32%	1810
	11th to 20th	Day	28% 13% 3 8% 5% 3 4 4 4 5% 24%	1787
	21st to end	Day	27% 14% 3 7% 5% 3 4 4 4 6% 22%	1782
November	1st to 10th	Day	18% 14% 4 6% 6% 3 4 4 5% 6% 31%	1671
	11th to 20th	Day	22% 15% 6% 10% 7% 3 4 4 5% 5% 21%	1571
	21st to end	Day	23% 16% 6% 10% 7% 3 5% 4 4 4 20%	1520
December	1st to 10th	Day	24% 19% 7% 8% 7% 3 4 4 3 5% 16%	1520
	11th to 20th	Day	21% 17% 6% 12% 7% 3 4 3 4 4 19%	1906
	21st to end	Day	23% 20% 6% 9% 6% 3 4 3 4 4 18%	2772
January	1st to 10th	Night	16% 18% 9% 11% 7% 3 4 4 4 4 19%	4429
	11th to 20th	Night	12% 15% 7% 15% 13% 4 3 4 4 5% 18%	4440
	21st to end	Night	11% 17% 9% 15% 9% 4 6% 4 4 4 17%	4884
February	1st to 10th	Night	12% 16% 7% 10% 8% 4 5% 5% 5% 5% 23%	2485
	11th to 20th	Night	13% 16% 8% 11% 8% 3 4 4 4 5% 25%	2351
	21st to end	Night	14% 17% 5% 9% 5% 3 6% 4 6% 6% 25%	1884
March	1st to 10th	Night	21% 12% 5% 7% 6% 3 5% 3 4 5% 31%	3724
	11th to 20th	Night	17% 18% 6% 9% 7% 2 3 3 3 4 26%	3607
	21st to end	Night	14% 11% 5% 8% 6% 3 5% 4 4 5% 34%	3512
April	1st to 10th	Night	23% 11% 4 7% 5% 3 3 3 4 6% 30%	1900
	11th to 20th	Night	21% 9% 3 5% 5% 3 3 5% 4 6% 35%	1875
	21st to end	Night	20% 10% 4 7% 5% 3 4 4 4 5% 34%	1716
May	1st to 10th	Night	20% 9% 4 6% 5% 2 4 4 4 6% 35%	1440
	11th to 20th	Night	19% 6% 4 6% 5% 2 4 4 4 7% 38%	1415
	21st to end	Night	17% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	1550
June	1st to 10th	Night	20% 7% 3 6% 6% 3 4 5% 7% 8% 31%	1440
	11th to 20th	Night	18% 6% 3 5% 6% 3 4 5% 5% 7% 38%	1440
	21st to end	Night	21% 6% 2 5% 4 3 4 5% 5% 6% 37%	1440
July	1st to 10th	Night	13% 6% 3 5% 4 3 4 5% 6% 8% 44%	1440
	11th to 20th	Night	15% 6% 2 5% 4 2 5% 6% 6% 8% 41%	1440
	21st to end	Night	13% 5% 2 5% 5% 4 5% 5% 7% 9% 41%	1574
August	1st to 10th	Night	11% 6% 3 5% 6% 3 5% 5% 6% 9% 41%	1432
	11th to 20th	Night	13% 6% 2 5% 6% 3 4 4 6% 6% 44%	1580
	21st to end	Night	16% 6% 2 4 5% 2 4 4 6% 8% 43%	1980
September	1st to 10th	Night	16% 8% 2 5% 5% 2 4 4 5% 6% 44%	1800
	11th to 20th	Night	17% 5% 2 4 4 2 4 4 6% 7% 45%	1844
	21st to end	Night	19% 7% 2 4 4 3 4 4 4 7% 43%	1980
October	1st to 10th	Night	21% 7% 3 5% 5% 4 4 4 4 6% 37%	2147
	11th to 20th	Night	24% 12% 3 6% 5% 3 4 4 5% 6% 29%	2173
	21st to end	Night	25% 13% 4 6% 6% 3 4 4 4 6% 25%	2574
November	1st to 10th	Night	21% 12% 4 7% 5% 3 4 4 5% 6% 29%	2407
	11th to 20th	Night	19% 14% 6% 10% 6% 3 4 4 4 6% 25%	2607
	21st to end	Night	22% 17% 7% 9% 6% 3 5% 4 3 4 20%	2660
December	1st to 10th	Night	21% 19% 8% 11% 7% 3 4 4 4 4 15%	2660
	11th to 20th	Night	22% 17% 7% 10% 7% 3 4 3 3 4 22%	3288
	21st to end	Night	24% 21% 5% 10% 7% 3 3 3 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% 4	2359
May	1st to 10th	Day	55% 4 6% 20% 13% 3	2520
	11th to 20th	Day	52% 4 8% 19% 15% 2	2482
	21st to end	Day	52% 4 10% 19% 13% 2	2725
June	1st to 10th	Day	57% 5% 9% 18% 11% 1	2520
	11th to 20th	Day	49% 5% 11% 21% 11% 3	2520
	21st to end	Day	57% 5% 11% 18% 9%	2520
July	1st to 10th	Day	44% 5% 15% 26% 10%	2450
	11th to 20th	Day	46% 6% 14% 24% 10%	2445
	21st to end	Day	47% 6% 16% 22% 8%	2591
August	1st to 10th	Day	50% 5% 17% 23% 5%	2492
	11th to 20th	Day	45% 5% 18% 23% 8% 1	2299
	21st to end	Day	46% 4 14% 24% 11% 1	2376
September	1st to 10th	Day	45% 4 13% 26% 13%	2160
	11th to 20th	Day	42% 4 13% 29% 11% 1	2116
	21st to end	Day	46% 4 14% 26% 10%	1980
October	1st to 10th	Day	53% 3 12% 21% 10% 1	1810
	11th to 20th	Day	63% 4 10% 17% 5% 1	1787
	21st to end	Day	64% 3 11% 14% 6% 1	1782
November	1st to 10th	Day	54% 4 13% 20% 7% 1	1671
	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	1716
May	1st to 10th	Night	52% 3 7% 20% 14% 3	1440
	11th to 20th	Night	47% 4 9% 19% 17% 3	1416
	21st to end	Night	45% 6% 12% 22% 14% 3	1551
June	1st to 10th	Night	50% 5% 13% 22% 10%	1440
	11th to 20th	Night	46% 6% 10% 23% 13% 3	1440
	21st to end	Night	48% 6% 12% 22% 12%	1440
July	1st to 10th	Night	38% 4 17% 27% 13% 1	1400
	11th to 20th	Night	40% 5% 15% 30% 10%	1392
	21st to end	Night	39% 6% 19% 26% 10%	1486
August	1st to 10th	Night	38% 7% 20% 27% 8%	1422
	11th to 20th	Night	40% 5% 17% 27% 10%	1580
	21st to end	Night	40% 5% 17% 28% 10%	1980
September	1st to 10th	Night	40% 5% 14% 28% 13% 1	1800
	11th to 20th	Night	39% 4 14% 32% 10% 1	1844
	21st to end	Night	42% 5% 13% 30% 11%	1980
October	1st to 10th	Night	49% 4 10% 24% 12% 1	2147
	11th to 20th	Night	57% 3 13% 19% 8%	2173
	21st to end	Night	61% 3 12% 16% 8% 1	2574
November	1st to 10th	Night	55% 5% 13% 19% 7% 1	2407
	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	32% 19% 30% 14% 4 1	437
May	1st to 10th	Day	31% 19% 30% 15% 5%	423
	11th to 20th	Day	27% 17% 33% 17% 6% 1	447
	21st to end	Day	25% 19% 33% 17% 5%	485
June	1st to 10th	Day	30% 16% 33% 14% 6%	450
	11th to 20th	Day	22% 18% 30% 19% 9% 1	450
	21st to end	Day	27% 12% 33% 18% 7% 2	450
July	1st to 10th	Day	19% 10% 34% 26% 9% 2	445
	11th to 20th	Day	17% 12% 35% 28% 6% 1	444
	21st to end	Day	16% 10% 38% 27% 8% 1	488
August	1st to 10th	Day	18% 12% 28% 29% 10% 2	446
	11th to 20th	Day	18% 8% 28% 27% 13% 7%	439
	21st to end	Day	20% 17% 25% 21% 10% 6%	495
September	1st to 10th	Day	23% 9% 30% 20% 12% 5%	450
	11th to 20th	Day	17% 13% 28% 20% 13% 8%	450
	21st to end	Day	22% 17% 24% 23% 10% 5%	450
October	1st to 10th	Day	31% 16% 23% 17% 11% 2	450
	11th to 20th	Day	35% 18% 24% 16% 6% 1	444
	21st to end	Day	39% 11% 30% 15% 5%	396
November	1st to 10th	Day	38% 13% 25% 19% 4 1	365
	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% 17% 27% 18% 9%	606
May	1st to 10th	Night	26% 12% 29% 23% 9% 1	360
	11th to 20th	Night	23% 9% 31% 27% 8% 1	354
	21st to end	Night	19% 12% 37% 24% 7%	389
June	1st to 10th	Night	23% 8% 32% 28% 9% 1	360
	11th to 20th	Night	20% 9% 25% 32% 11% 1	360
	21st to end	Night	20% 7% 21% 34% 16% 1	360
July	1st to 10th	Night	15% 7% 25% 37% 16% 1	350
	11th to 20th	Night	16% 6% 23% 37% 17% 1	348
	21st to end	Night	14% 7% 24% 39% 15% 1	394
August	1st to 10th	Night	15% 4 18% 45% 17% 1	358
	11th to 20th	Night	15% 5% 20% 34% 24% 2	516
	21st to end	Night	19% 6% 26% 30% 17% 3	792
September	1st to 10th	Night	18% 7% 27% 33% 14% 1	720
	11th to 20th	Night	21% 7% 20% 33% 18% 1	720
	21st to end	Night	22% 9% 24% 26% 17% 2	720
October	1st to 10th	Night	25% 12% 26% 25% 12% 1	720
	11th to 20th	Night	31% 11% 26% 23% 7% 1	720
	21st to end	Night	31% 13% 27% 23% 5%	792
November	1st to 10th	Night	29% 15% 26% 22% 6% 1	740
	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 2024-04-22 09:25:40. Version ac07

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