Observatoire Les Trois Étangs - La Patrie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Les Trois Étangs - La Patrie clear sky chart from 2005-11-06 to 2026-05-17.

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% 13% 5% 10% 6% 5% 5% 3 5% 6% 23%	131055
	Night	17% 15% 6% 12% 7% 5% 5% 3 4 5% 22%	131685
Transparency	Day	61% 6% 10% 16% 7% 1	134523
	Night	65% 5% 9% 14% 7% 1	136292
Seeing	Day	29% 20% 28% 15% 6% 1	16603
	Night	27% 18% 27% 21% 7% 1	25738

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	11% 16% 10% 18% 12% 9% 8% 3 3 2 8%	4661
	11th to 20th	Day	7% 16% 8% 27% 17% 7% 3 2 2 2 8%	4650
	21st to end	Day	6% 15% 8% 16% 9% 15% 8% 3 5% 3 12%	5124
February	1st to 10th	Day	12% 19% 6% 16% 11% 6% 5% 3 3 3 15%	1749
	11th to 20th	Day	12% 19% 9% 18% 9% 5% 4 2 3 4 15%	2048
	21st to end	Day	10% 21% 5% 14% 8% 7% 5% 4 4 5% 18%	1730
March	1st to 10th	Day	16% 17% 7% 15% 7% 5% 5% 3 3 4 19%	4576
	11th to 20th	Day	14% 18% 6% 11% 5% 5% 4 3 5% 5% 24%	4869
	21st to end	Day	20% 18% 6% 13% 5% 4 3 2 3 4 22%	5914
April	1st to 10th	Day	21% 21% 4 9% 5% 3 3 3 4 4 24%	2520
	11th to 20th	Day	19% 17% 5% 7% 4 3 3 2 3 5% 31%	2571
	21st to end	Day	22% 17% 4 8% 4 4 4 3 4 4 26%	2730
May	1st to 10th	Day	29% 14% 4 8% 5% 5% 4 4 4 5% 19%	6016
	11th to 20th	Day	21% 9% 3 9% 6% 6% 5% 4 5% 6% 26%	6396
	21st to end	Day	22% 10% 3 7% 5% 5% 5% 4 5% 7% 27%	6949
June	1st to 10th	Day	30% 8% 2 7% 4 5% 4 4 6% 7% 23%	2800
	11th to 20th	Day	21% 8% 2 6% 5% 5% 5% 4 6% 8% 31%	2807
	21st to end	Day	25% 9% 3 7% 5% 5% 5% 4 6% 6% 25%	2800
July	1st to 10th	Day	18% 8% 3 9% 6% 6% 6% 5% 7% 8% 23%	6360
	11th to 20th	Day	17% 8% 2 8% 5% 5% 5% 4 7% 8% 30%	6360
	21st to end	Day	17% 8% 2 5% 4 5% 5% 4 6% 8% 36%	6926
August	1st to 10th	Day	21% 8% 3 8% 5% 6% 5% 4 6% 8% 26%	4466
	11th to 20th	Day	21% 9% 3 7% 5% 5% 5% 5% 6% 8% 23%	4175
	21st to end	Day	22% 8% 2 6% 4 4 5% 4 5% 7% 33%	4416
September	1st to 10th	Day	20% 7% 2 6% 5% 4 4 3 5% 7% 37%	2400
	11th to 20th	Day	21% 7% 1 5% 3 3 4 3 5% 7% 41%	2212
	21st to end	Day	20% 10% 2 6% 4 4 4 3 5% 8% 33%	2200
October	1st to 10th	Day	21% 12% 3 5% 4 4 4 4 5% 7% 30%	2200
	11th to 20th	Day	20% 17% 4 8% 3 5% 4 3 5% 6% 25%	1864
	21st to end	Day	24% 24% 4 8% 4 4 3 3 4 4 21%	1980
November	1st to 10th	Day	20% 22% 6% 7% 4 3 3 3 3 4 25%	1851
	11th to 20th	Day	17% 20% 8% 13% 5% 4 3 3 3 4 20%	1890
	21st to end	Day	18% 22% 8% 13% 5% 4 3 2 4 5% 16%	1736
December	1st to 10th	Day	14% 24% 9% 19% 11% 5% 3 2 2 3 9%	2350
	11th to 20th	Day	16% 19% 8% 15% 6% 4 4 2 3 3 19%	2711
	21st to end	Day	17% 20% 6% 14% 6% 4 5% 3 3 4 17%	4048
January	1st to 10th	Night	10% 18% 9% 21% 11% 8% 7% 3 3 3 7%	8234
	11th to 20th	Night	9% 19% 10% 25% 14% 7% 4 2 2 2 7%	8235
	21st to end	Night	7% 13% 7% 17% 11% 14% 7% 4 4 4 12%	9057
February	1st to 10th	Night	11% 18% 7% 16% 10% 6% 5% 2 4 4 17%	2866
	11th to 20th	Night	11% 20% 7% 18% 8% 7% 5% 2 3 4 15%	2458
	21st to end	Night	12% 19% 7% 12% 7% 7% 4 3 3 4 22%	2076
March	1st to 10th	Night	18% 18% 6% 14% 5% 5% 6% 2 3 4 19%	5484
	11th to 20th	Night	13% 21% 6% 11% 6% 5% 4 3 4 5% 22%	5309
	21st to end	Night	17% 19% 6% 11% 6% 4 3 2 3 3 24%	5243
April	1st to 10th	Night	22% 18% 5% 8% 4 3 4 3 3 4 25%	2100
	11th to 20th	Night	21% 17% 4 6% 4 3 4 3 4 5% 29%	1998
	21st to end	Night	23% 15% 3 6% 4 4 4 4 4 5% 29%	1890
May	1st to 10th	Night	29% 12% 4 9% 4 4 4 4 4 6% 21%	4144
	11th to 20th	Night	23% 10% 3 8% 5% 4 4 3 5% 6% 28%	3673
	21st to end	Night	22% 9% 3 7% 4 4 5% 3 5% 7% 31%	3926
June	1st to 10th	Night	28% 10% 3 6% 5% 3 4 3 6% 7% 26%	1600
	11th to 20th	Night	21% 8% 2 7% 5% 3 4 4 6% 7% 33%	1494
	21st to end	Night	22% 8% 3 7% 6% 5% 5% 3 5% 7% 30%	1600
July	1st to 10th	Night	19% 9% 4 10% 5% 6% 5% 4 5% 7% 26%	3600
	11th to 20th	Night	22% 8% 3 6% 4 4 5% 4 5% 7% 34%	3600
	21st to end	Night	15% 8% 2 7% 5% 4 5% 4 7% 7% 35%	3926
August	1st to 10th	Night	26% 8% 3 7% 4 4 4 3 5% 6% 29%	2650
	11th to 20th	Night	20% 8% 3 8% 5% 5% 6% 5% 5% 7% 28%	2872
	21st to end	Night	20% 9% 2 6% 4 4 3 4 4 6% 38%	3478
September	1st to 10th	Night	20% 7% 3 6% 4 3 4 3 5% 5% 39%	2000
	11th to 20th	Night	19% 6% 2 5% 3 4 4 4 5% 5% 44%	2187
	21st to end	Night	22% 7% 2 5% 4 4 4 2 5% 7% 39%	2200
October	1st to 10th	Night	21% 10% 2 6% 5% 4 3 3 4 6% 35%	2200
	11th to 20th	Night	23% 15% 3 8% 5% 4 3 3 4 5% 27%	2533
	21st to end	Night	26% 18% 3 7% 4 3 4 3 4 5% 23%	2860
November	1st to 10th	Night	22% 19% 6% 9% 4 4 2 2 4 5% 23%	2667
	11th to 20th	Night	18% 18% 7% 13% 4 3 3 2 4 4 23%	2730
	21st to end	Night	18% 21% 8% 14% 6% 4 3 2 4 4 17%	2873
December	1st to 10th	Night	14% 21% 11% 23% 9% 4 3 2 2 2 8%	5060
	11th to 20th	Night	16% 22% 7% 17% 8% 5% 4 2 3 3 14%	5712
	21st to end	Night	17% 21% 6% 12% 6% 4 5% 2 3 4 20%	7150

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	81% 5% 7% 6% 2	4662
	11th to 20th	Day	84% 3 3 7% 2	4680
	21st to end	Day	74% 5% 6% 7% 7% 1	5124
February	1st to 10th	Day	75% 4 4 10% 6% 1	1749
	11th to 20th	Day	75% 3 7% 10% 4 1	2057
	21st to end	Day	68% 5% 7% 12% 6% 2	1730
March	1st to 10th	Day	70% 4 6% 9% 7% 3	4579
	11th to 20th	Day	61% 5% 12% 12% 9% 1	4869
	21st to end	Day	67% 4 5% 12% 12% 1	5914
April	1st to 10th	Day	65% 3 8% 14% 8% 2	2520
	11th to 20th	Day	58% 4 7% 19% 11% 1	2571
	21st to end	Day	61% 4 7% 16% 9% 2	2730
May	1st to 10th	Day	68% 6% 8% 14% 5%	6027
	11th to 20th	Day	57% 9% 13% 14% 6% 2	6400
	21st to end	Day	53% 8% 11% 18% 9% 1	6949
June	1st to 10th	Day	60% 6% 10% 18% 5% 1	2800
	11th to 20th	Day	50% 7% 12% 22% 8% 1	2807
	21st to end	Day	58% 7% 11% 17% 6%	2800
July	1st to 10th	Day	54% 8% 15% 17% 6%	6290
	11th to 20th	Day	47% 9% 14% 25% 5%	6285
	21st to end	Day	45% 7% 14% 27% 6%	6728
August	1st to 10th	Day	55% 8% 14% 19% 4	4452
	11th to 20th	Day	55% 9% 16% 16% 4	4214
	21st to end	Day	48% 7% 14% 18% 11% 2	4416
September	1st to 10th	Day	46% 6% 13% 25% 9% 1	2400
	11th to 20th	Day	45% 4 12% 27% 12% 1	2212
	21st to end	Day	50% 6% 11% 21% 11% 1	2200
October	1st to 10th	Day	51% 6% 14% 20% 9%	3590
	11th to 20th	Day	58% 4 10% 21% 6%	3002
	21st to end	Day	58% 4 13% 17% 8%	3180
November	1st to 10th	Day	63% 6% 9% 14% 7% 1	1851
	11th to 20th	Day	68% 5% 8% 11% 7% 2	1890
	21st to end	Day	71% 6% 10% 11% 2	1736
December	1st to 10th	Day	82% 3 5% 6% 3	2350
	11th to 20th	Day	71% 4 6% 12% 7%	2711
	21st to end	Day	71% 4 6% 9% 8% 2	4048
January	1st to 10th	Night	83% 4 6% 5% 2	8234
	11th to 20th	Night	85% 3 4 4 2	8280
	21st to end	Night	74% 5% 6% 8% 7% 1	9057
February	1st to 10th	Night	73% 4 6% 12% 5% 1	2866
	11th to 20th	Night	75% 4 6% 9% 5% 1	2460
	21st to end	Night	68% 4 6% 13% 8% 1	2076
March	1st to 10th	Night	72% 3 8% 11% 5% 2	5494
	11th to 20th	Night	65% 5% 12% 11% 6% 1	5310
	21st to end	Night	66% 3 5% 12% 12% 1	5243
April	1st to 10th	Night	63% 4 7% 15% 10% 1	2100
	11th to 20th	Night	57% 6% 8% 18% 11% 1	1998
	21st to end	Night	57% 6% 9% 16% 10% 2	1890
May	1st to 10th	Night	63% 7% 12% 12% 6% 1	4150
	11th to 20th	Night	55% 10% 10% 19% 5% 1	3674
	21st to end	Night	51% 8% 13% 16% 12%	3927
June	1st to 10th	Night	57% 5% 11% 19% 7%	1600
	11th to 20th	Night	48% 8% 11% 21% 10% 2	1494
	21st to end	Night	54% 8% 12% 19% 8%	1600
July	1st to 10th	Night	55% 7% 15% 18% 5%	3560
	11th to 20th	Night	48% 8% 14% 25% 5%	3552
	21st to end	Night	45% 9% 14% 25% 6%	3809
August	1st to 10th	Night	55% 7% 12% 22% 4	2640
	11th to 20th	Night	52% 10% 16% 16% 6%	2899
	21st to end	Night	46% 7% 13% 21% 13%	3478
September	1st to 10th	Night	46% 6% 13% 25% 10%	2000
	11th to 20th	Night	41% 6% 13% 29% 11% 1	2187
	21st to end	Night	45% 6% 12% 24% 11% 2	2200
October	1st to 10th	Night	50% 6% 12% 21% 11%	3590
	11th to 20th	Night	58% 5% 9% 20% 8%	4121
	21st to end	Night	58% 5% 13% 15% 8% 2	4610
November	1st to 10th	Night	65% 5% 10% 14% 6%	2667
	11th to 20th	Night	66% 4 8% 12% 7% 2	2730
	21st to end	Night	72% 4 10% 10% 3	2873
December	1st to 10th	Night	86% 3 4 6% 1	5060
	11th to 20th	Night	77% 4 5% 9% 6%	5713
	21st to end	Night	69% 4 7% 10% 7% 1	7150

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	30% 27% 33% 9%	220
	11th to 20th	Day	32% 30% 25% 12% 1	220
	21st to end	Day	28% 26% 34% 10% 2	242
February	1st to 10th	Day	35% 30% 22% 10% 3	277
	11th to 20th	Day	32% 27% 32% 7% 1	536
	21st to end	Day	31% 27% 28% 12% 1	446
March	1st to 10th	Day	32% 26% 29% 11% 2	540
	11th to 20th	Day	32% 30% 24% 10% 4	540
	21st to end	Day	37% 23% 21% 13% 5% 1	594
April	1st to 10th	Day	40% 20% 24% 11% 4	540
	11th to 20th	Day	36% 23% 24% 11% 4 2	532
	21st to end	Day	36% 21% 27% 11% 4 1	540
May	1st to 10th	Day	43% 16% 26% 10% 3 1	543
	11th to 20th	Day	27% 19% 31% 17% 5% 1	551
	21st to end	Day	23% 24% 31% 17% 5% 1	573
June	1st to 10th	Day	32% 19% 29% 15% 4 1	530
	11th to 20th	Day	24% 19% 30% 20% 7% 1	537
	21st to end	Day	27% 18% 32% 15% 7% 1	530
July	1st to 10th	Day	23% 14% 36% 20% 6% 1	525
	11th to 20th	Day	20% 14% 38% 21% 7% 1	524
	21st to end	Day	24% 13% 33% 23% 6% 1	576
August	1st to 10th	Day	22% 11% 31% 25% 11% 1	526
	11th to 20th	Day	20% 11% 30% 24% 11% 4	519
	21st to end	Day	24% 15% 26% 21% 10% 4	583
September	1st to 10th	Day	24% 12% 29% 20% 11% 3	530
	11th to 20th	Day	22% 11% 24% 23% 13% 8%	530
	21st to end	Day	22% 15% 26% 23% 11% 3	530
October	1st to 10th	Day	27% 18% 23% 19% 10% 3	530
	11th to 20th	Day	30% 20% 26% 15% 8% 1	445
	21st to end	Day	37% 26% 20% 14% 3	462
November	1st to 10th	Day	39% 21% 25% 12% 3	425
	11th to 20th	Day	29% 24% 29% 11% 5% 1	430
	21st to end	Day	36% 24% 26% 11% 2 1	295
December	1st to 10th	Day	32% 25% 28% 14% 2	220
	11th to 20th	Day	38% 26% 28% 5% 2	220
	21st to end	Day	36% 24% 29% 7% 4	242
January	1st to 10th	Night	25% 28% 34% 11% 2	840
	11th to 20th	Night	25% 28% 29% 16% 2	840
	21st to end	Night	20% 26% 35% 16% 3	924
February	1st to 10th	Night	21% 27% 34% 15% 3	840
	11th to 20th	Night	25% 26% 33% 14% 2	823
	21st to end	Night	25% 23% 33% 17% 2	692
March	1st to 10th	Night	28% 22% 33% 16% 2	840
	11th to 20th	Night	29% 23% 27% 16% 4	840
	21st to end	Night	29% 21% 26% 18% 6% 1	924
April	1st to 10th	Night	34% 20% 25% 17% 4	840
	11th to 20th	Night	34% 18% 25% 17% 5% 1	754
	21st to end	Night	32% 19% 26% 18% 4 1	630
May	1st to 10th	Night	30% 15% 29% 19% 6% 1	630
	11th to 20th	Night	26% 11% 29% 26% 7% 1	430
	21st to end	Night	25% 11% 30% 27% 7%	433
June	1st to 10th	Night	32% 7% 27% 25% 9%	400
	11th to 20th	Night	25% 9% 22% 32% 13% 1	400
	21st to end	Night	21% 11% 27% 33% 9%	400
July	1st to 10th	Night	21% 6% 27% 35% 9% 1	390
	11th to 20th	Night	18% 7% 27% 35% 13% 1	388
	21st to end	Night	19% 7% 24% 38% 12%	438
August	1st to 10th	Night	20% 3 17% 39% 19% 1	436
	11th to 20th	Night	19% 7% 21% 35% 18% 1	592
	21st to end	Night	22% 7% 23% 30% 15% 2	811
September	1st to 10th	Night	23% 8% 24% 32% 13% 1	800
	11th to 20th	Night	23% 7% 20% 28% 21% 2	800
	21st to end	Night	24% 10% 25% 24% 15% 1	800
October	1st to 10th	Night	27% 11% 25% 24% 13% 1	800
	11th to 20th	Night	32% 15% 22% 22% 7% 2	800
	21st to end	Night	36% 18% 26% 17% 4	880
November	1st to 10th	Night	36% 18% 24% 17% 5%	820
	11th to 20th	Night	29% 20% 28% 15% 6% 2	840
	21st to end	Night	31% 25% 23% 15% 4 1	847
December	1st to 10th	Night	32% 24% 26% 14% 3	950
	11th to 20th	Night	31% 26% 24% 14% 4	942
	21st to end	Night	34% 23% 27% 14% 3	924

Page generated at 2026-05-14 01:58:56. Version ac07

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