Observatoire Maucar de La Motte
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Maucar de La Motte clear sky chart from 2005-11-06 to 2025-07-21.

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% 13% 4 10% 6% 5% 5% 4 5% 6% 26%	120197
	Night	16% 15% 6% 12% 6% 5% 5% 4 4 5% 23%	118990
Transparency	Day	58% 6% 10% 17% 8% 1	123721
	Night	63% 5% 9% 15% 7% 1	123628
Seeing	Day	24% 16% 33% 19% 7% 2	15978
	Night	25% 13% 31% 23% 8% 1	24824

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	12% 23% 10% 20% 7% 7% 6% 3 4 3 6%	3158
	11th to 20th	Day	9% 17% 8% 19% 10% 5% 5% 4 7% 5% 11%	3202
	21st to end	Day	9% 16% 8% 17% 7% 6% 5% 4 4 6% 18%	4162
February	1st to 10th	Day	9% 16% 6% 14% 8% 10% 6% 3 5% 7% 16%	1800
	11th to 20th	Day	10% 20% 5% 13% 7% 6% 7% 4 5% 4 18%	1753
	21st to end	Day	13% 16% 6% 13% 8% 5% 4 4 5% 5% 21%	1502
March	1st to 10th	Day	19% 16% 5% 10% 6% 4 5% 3 4 4 22%	4723
	11th to 20th	Day	16% 17% 5% 14% 7% 4 3 2 3 4 24%	4980
	21st to end	Day	13% 15% 6% 13% 7% 7% 4 3 3 4 26%	5589
April	1st to 10th	Day	19% 16% 5% 10% 5% 4 4 4 4 5% 24%	2400
	11th to 20th	Day	21% 12% 4 8% 4 4 3 3 4 5% 31%	2482
	21st to end	Day	22% 13% 4 7% 5% 4 3 3 4 5% 30%	2620
May	1st to 10th	Day	17% 11% 3 7% 5% 4 5% 4 5% 6% 34%	6346
	11th to 20th	Day	14% 9% 3 8% 6% 6% 5% 4 7% 7% 32%	6318
	21st to end	Day	19% 11% 3 7% 4 4 4 3 4 6% 35%	6949
June	1st to 10th	Day	21% 8% 3 8% 5% 5% 5% 3 6% 7% 29%	2995
	11th to 20th	Day	16% 8% 3 8% 5% 5% 5% 4 5% 7% 34%	3000
	21st to end	Day	20% 8% 3 6% 5% 5% 5% 5% 5% 7% 31%	3000
July	1st to 10th	Day	17% 7% 2 7% 6% 5% 6% 5% 7% 9% 29%	4910
	11th to 20th	Day	16% 7% 3 6% 5% 5% 4 5% 7% 8% 34%	4910
	21st to end	Day	16% 7% 2 7% 5% 4 5% 4 6% 8% 35%	4825
August	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 6% 8% 31%	4307
	11th to 20th	Day	19% 7% 3 7% 4 5% 5% 4 6% 8% 32%	4044
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 3 6% 8% 38%	4384
September	1st to 10th	Day	20% 7% 3 6% 4 5% 5% 4 6% 7% 32%	2280
	11th to 20th	Day	21% 9% 2 6% 5% 4 4 4 6% 7% 32%	2269
	21st to end	Day	24% 11% 3 6% 5% 4 4 4 4 5% 31%	1990
October	1st to 10th	Day	22% 13% 2 8% 4 4 4 4 4 5% 30%	1900
	11th to 20th	Day	30% 21% 4 8% 3 3 3 3 4 4 18%	1900
	21st to end	Day	28% 19% 4 8% 5% 5% 4 3 4 5% 15%	1962
November	1st to 10th	Day	21% 21% 6% 11% 5% 5% 3 2 4 5% 17%	1566
	11th to 20th	Day	21% 20% 7% 14% 7% 6% 3 3 3 4 12%	1600
	21st to end	Day	24% 25% 9% 14% 7% 4 4 3 2 3 7%	1600
December	1st to 10th	Day	13% 28% 10% 17% 8% 5% 3 2 4 3 7%	2600
	11th to 20th	Day	14% 20% 8% 14% 10% 7% 4 3 3 3 15%	2695
	21st to end	Day	18% 22% 6% 16% 9% 6% 4 3 3 3 10%	3476
January	1st to 10th	Night	11% 20% 11% 21% 9% 5% 4 3 3 3 10%	6808
	11th to 20th	Night	9% 17% 7% 20% 9% 6% 6% 5% 4 4 11%	6698
	21st to end	Night	7% 15% 10% 17% 7% 7% 8% 5% 5% 5% 15%	6790
February	1st to 10th	Night	10% 16% 6% 11% 9% 7% 7% 5% 5% 6% 18%	2600
	11th to 20th	Night	11% 18% 6% 14% 8% 6% 5% 3 3 5% 19%	2533
	21st to end	Night	10% 17% 6% 13% 8% 7% 7% 4 4 6% 19%	2126
March	1st to 10th	Night	16% 18% 5% 11% 6% 3 4 5% 4 4 23%	5116
	11th to 20th	Night	16% 19% 6% 13% 7% 6% 5% 3 4 4 18%	4979
	21st to end	Night	13% 14% 5% 11% 6% 7% 5% 3 4 5% 26%	5342
April	1st to 10th	Night	19% 16% 4 10% 5% 4 3 3 4 5% 28%	2000
	11th to 20th	Night	18% 10% 3 8% 4 5% 4 4 6% 6% 31%	1886
	21st to end	Night	20% 11% 4 7% 4 4 3 3 4 6% 33%	1779
May	1st to 10th	Night	17% 10% 5% 7% 4 4 4 3 5% 6% 35%	3594
	11th to 20th	Night	16% 8% 3 8% 4 3 4 4 5% 6% 38%	3575
	21st to end	Night	19% 8% 3 6% 5% 4 4 4 6% 7% 33%	3926
June	1st to 10th	Night	20% 7% 4 7% 6% 5% 5% 4 5% 6% 31%	1400
	11th to 20th	Night	17% 8% 2 7% 5% 4 4 4 5% 6% 37%	1400
	21st to end	Night	16% 6% 2 8% 6% 5% 5% 4 7% 7% 36%	1400
July	1st to 10th	Night	18% 8% 3 6% 4 4 4 5% 5% 8% 35%	2280
	11th to 20th	Night	17% 9% 3 7% 5% 5% 5% 4 6% 7% 33%	2280
	21st to end	Night	17% 6% 2 5% 4 4 4 4 5% 7% 41%	2725
August	1st to 10th	Night	12% 5% 3 7% 6% 5% 6% 4 6% 9% 38%	2619
	11th to 20th	Night	16% 8% 3 7% 5% 4 5% 3 5% 6% 36%	2785
	21st to end	Night	15% 7% 3 8% 4 4 4 4 5% 6% 39%	3239
September	1st to 10th	Night	19% 7% 3 7% 5% 4 4 3 5% 6% 38%	1900
	11th to 20th	Night	20% 8% 3 6% 4 3 4 2 5% 6% 39%	1909
	21st to end	Night	22% 9% 3 5% 4 3 3 3 5% 6% 36%	2190
October	1st to 10th	Night	22% 9% 3 8% 5% 5% 4 4 5% 6% 31%	2280
	11th to 20th	Night	28% 17% 4 9% 4 4 3 3 4 4 20%	2280
	21st to end	Night	25% 19% 4 8% 4 4 4 3 4 5% 19%	2632
November	1st to 10th	Night	20% 18% 6% 11% 5% 5% 4 3 4 5% 21%	2732
	11th to 20th	Night	20% 18% 6% 14% 7% 4 4 3 4 4 16%	2800
	21st to end	Night	23% 21% 7% 14% 7% 4 4 3 3 4 10%	2800
December	1st to 10th	Night	14% 24% 9% 18% 9% 7% 4 3 3 3 8%	4580
	11th to 20th	Night	16% 19% 7% 14% 9% 8% 6% 3 3 3 12%	5505
	21st to end	Night	19% 21% 9% 16% 7% 4 4 2 2 3 13%	7502

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	83% 4 6% 5% 1	3159
	11th to 20th	Day	72% 4 6% 11% 7%	3229
	21st to end	Day	69% 3 6% 16% 6%	4162
February	1st to 10th	Day	68% 5% 6% 14% 7%	1800
	11th to 20th	Day	69% 4 7% 13% 6%	1762
	21st to end	Day	65% 4 7% 16% 6% 1	1502
March	1st to 10th	Day	65% 4 6% 14% 10% 1	4726
	11th to 20th	Day	65% 4 8% 15% 7% 1	4980
	21st to end	Day	63% 4 6% 18% 7% 1	5589
April	1st to 10th	Day	62% 5% 9% 13% 10% 1	2400
	11th to 20th	Day	56% 5% 8% 18% 12% 1	2482
	21st to end	Day	56% 4 8% 16% 14% 2	2620
May	1st to 10th	Day	49% 7% 9% 16% 16% 4	6357
	11th to 20th	Day	47% 8% 14% 20% 8% 2	6322
	21st to end	Day	51% 5% 8% 19% 15% 2	6949
June	1st to 10th	Day	52% 7% 10% 19% 10% 1	2995
	11th to 20th	Day	48% 7% 9% 23% 12% 2	3000
	21st to end	Day	51% 7% 12% 21% 8% 1	3000
July	1st to 10th	Day	49% 7% 15% 23% 5%	4836
	11th to 20th	Day	44% 8% 16% 22% 9%	4829
	21st to end	Day	46% 7% 12% 28% 6%	4672
August	1st to 10th	Day	48% 8% 16% 24% 4	4293
	11th to 20th	Day	47% 8% 15% 22% 8%	4083
	21st to end	Day	43% 7% 12% 28% 10%	4384
September	1st to 10th	Day	49% 8% 13% 20% 8% 1	2280
	11th to 20th	Day	50% 8% 16% 21% 5%	2269
	21st to end	Day	55% 7% 11% 20% 7%	1990
October	1st to 10th	Day	59% 4 10% 20% 6% 1	3160
	11th to 20th	Day	64% 5% 12% 14% 5%	3140
	21st to end	Day	70% 6% 13% 6% 5%	3214
November	1st to 10th	Day	71% 6% 11% 9% 4	1566
	11th to 20th	Day	77% 5% 7% 8% 3	1600
	21st to end	Day	85% 4 5% 4 1	1600
December	1st to 10th	Day	83% 4 6% 6% 1	2600
	11th to 20th	Day	76% 3 5% 13% 2	2695
	21st to end	Day	81% 3 5% 9% 2	3476
January	1st to 10th	Night	81% 4 7% 5% 3	6808
	11th to 20th	Night	76% 4 5% 8% 6%	6746
	21st to end	Night	71% 4 5% 14% 6%	6790
February	1st to 10th	Night	65% 6% 8% 13% 8%	2600
	11th to 20th	Night	68% 4 7% 14% 6%	2535
	21st to end	Night	66% 4 8% 14% 7% 1	2126
March	1st to 10th	Night	63% 4 7% 11% 11% 4	5126
	11th to 20th	Night	71% 4 7% 10% 6% 1	4980
	21st to end	Night	59% 4 8% 17% 10% 3	5342
April	1st to 10th	Night	60% 4 8% 15% 13% 1	2000
	11th to 20th	Night	51% 6% 10% 20% 12% 1	1886
	21st to end	Night	52% 5% 7% 18% 16% 2	1779
May	1st to 10th	Night	49% 6% 10% 17% 16% 2	3600
	11th to 20th	Night	44% 7% 13% 21% 12% 3	3576
	21st to end	Night	48% 7% 10% 19% 14% 2	3927
June	1st to 10th	Night	52% 7% 9% 20% 11% 1	1400
	11th to 20th	Night	47% 5% 10% 21% 14% 3	1400
	21st to end	Night	45% 8% 12% 23% 11% 1	1400
July	1st to 10th	Night	45% 7% 14% 26% 8%	2245
	11th to 20th	Night	48% 7% 16% 20% 8%	2238
	21st to end	Night	44% 7% 14% 29% 7%	2638
August	1st to 10th	Night	42% 7% 18% 29% 5%	2609
	11th to 20th	Night	46% 7% 16% 24% 6%	2812
	21st to end	Night	45% 7% 14% 25% 8% 2	3239
September	1st to 10th	Night	46% 7% 16% 21% 9% 1	1900
	11th to 20th	Night	46% 8% 17% 22% 7%	1909
	21st to end	Night	50% 7% 14% 23% 6%	2190
October	1st to 10th	Night	54% 6% 12% 20% 8% 1	3800
	11th to 20th	Night	63% 5% 10% 20% 2	3779
	21st to end	Night	63% 6% 14% 10% 6% 1	4330
November	1st to 10th	Night	67% 6% 12% 12% 2	2732
	11th to 20th	Night	72% 5% 9% 9% 4	2800
	21st to end	Night	80% 5% 7% 7% 1	2800
December	1st to 10th	Night	83% 4 6% 6% 1	4580
	11th to 20th	Night	78% 4 6% 9% 2	5504
	21st to end	Night	79% 3 4 11% 3	7502

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	19% 23% 44% 10% 4 1	200
	11th to 20th	Day	18% 17% 38% 21% 6% 2	200
	21st to end	Day	18% 12% 39% 24% 7% 1	263
February	1st to 10th	Day	20% 26% 36% 14% 3	300
	11th to 20th	Day	18% 27% 39% 13% 3	300
	21st to end	Day	24% 22% 37% 14% 2	266
March	1st to 10th	Day	21% 19% 40% 15% 5%	500
	11th to 20th	Day	25% 19% 35% 16% 4	500
	21st to end	Day	25% 20% 35% 15% 5% 1	550
April	1st to 10th	Day	27% 20% 29% 15% 8% 1	500
	11th to 20th	Day	30% 17% 30% 15% 6% 2	492
	21st to end	Day	30% 19% 29% 15% 6% 1	500
May	1st to 10th	Day	25% 16% 32% 19% 6% 1	503
	11th to 20th	Day	25% 16% 32% 18% 7% 2	527
	21st to end	Day	24% 17% 29% 23% 5% 1	573
June	1st to 10th	Day	23% 16% 35% 20% 6% 1	725
	11th to 20th	Day	21% 16% 33% 20% 6% 2	730
	21st to end	Day	22% 12% 32% 25% 8% 1	730
July	1st to 10th	Day	17% 13% 35% 24% 9% 1	721
	11th to 20th	Day	17% 13% 37% 23% 9% 1	718
	21st to end	Day	19% 10% 31% 26% 11% 2	543
August	1st to 10th	Day	21% 9% 31% 26% 10% 3	486
	11th to 20th	Day	20% 7% 26% 26% 14% 6%	479
	21st to end	Day	21% 12% 29% 20% 12% 6%	539
September	1st to 10th	Day	22% 13% 35% 18% 9% 3	490
	11th to 20th	Day	22% 9% 32% 24% 10% 3	490
	21st to end	Day	28% 13% 27% 19% 10% 2	490
October	1st to 10th	Day	28% 16% 27% 19% 8% 2	490
	11th to 20th	Day	38% 19% 28% 11% 3 1	490
	21st to end	Day	35% 17% 31% 14% 3	463
November	1st to 10th	Day	34% 24% 33% 9% 1	200
	11th to 20th	Day	29% 20% 33% 17% 2 1	200
	21st to end	Day	41% 23% 28% 6% 3 1	200
December	1st to 10th	Day	25% 17% 33% 17% 8% 1	200
	11th to 20th	Day	22% 18% 44% 12% 3 2	200
	21st to end	Day	33% 14% 32% 14% 5% 2	220
January	1st to 10th	Night	27% 12% 37% 19% 5% 1	1000
	11th to 20th	Night	24% 14% 34% 22% 6%	965
	21st to end	Night	16% 12% 33% 27% 10% 1	880
February	1st to 10th	Night	17% 18% 36% 23% 6%	800
	11th to 20th	Night	21% 14% 35% 25% 5%	783
	21st to end	Night	20% 20% 35% 20% 5%	660
March	1st to 10th	Night	22% 19% 30% 23% 5% 1	800
	11th to 20th	Night	27% 18% 30% 20% 4 1	800
	21st to end	Night	21% 14% 38% 21% 5% 1	880
April	1st to 10th	Night	27% 16% 29% 21% 6%	800
	11th to 20th	Night	24% 16% 28% 23% 8% 1	702
	21st to end	Night	25% 12% 32% 25% 6% 1	579
May	1st to 10th	Night	23% 12% 31% 26% 9%	400
	11th to 20th	Night	24% 9% 30% 29% 7% 2	394
	21st to end	Night	24% 11% 31% 27% 7%	433
June	1st to 10th	Night	23% 9% 34% 26% 9%	400
	11th to 20th	Night	21% 10% 32% 30% 7%	400
	21st to end	Night	17% 9% 29% 33% 12%	400
July	1st to 10th	Night	17% 9% 30% 34% 8% 1	390
	11th to 20th	Night	16% 9% 27% 36% 12%	388
	21st to end	Night	16% 6% 27% 37% 13% 1	416
August	1st to 10th	Night	20% 5% 26% 31% 16% 2	439
	11th to 20th	Night	16% 6% 26% 30% 20% 1	564
	21st to end	Night	23% 9% 25% 27% 14% 3	690
September	1st to 10th	Night	23% 9% 30% 25% 12% 1	760
	11th to 20th	Night	24% 10% 26% 26% 13% 1	760
	21st to end	Night	28% 9% 25% 26% 11% 1	760
October	1st to 10th	Night	27% 12% 29% 23% 8% 1	760
	11th to 20th	Night	38% 13% 27% 17% 5% 1	760
	21st to end	Night	37% 11% 31% 16% 4 1	836
November	1st to 10th	Night	31% 15% 34% 15% 5% 1	780
	11th to 20th	Night	30% 18% 30% 17% 5%	800
	21st to end	Night	35% 16% 30% 16% 3	800
December	1st to 10th	Night	31% 16% 30% 18% 5% 1	800
	11th to 20th	Night	27% 17% 31% 18% 6% 1	945
	21st to end	Night	30% 18% 26% 19% 6% 1	1100

Page generated at 2025-07-18 01:10:00. Version ac07

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