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 2024-01-22.

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	20% 13% 5% 8% 6% 3 5% 4 4 6% 25%	74430
	Night	19% 15% 6% 9% 7% 3 5% 4 4 5% 24%	75405
Transparency	Day	61% 6% 10% 16% 7% 1	74135
	Night	63% 5% 9% 15% 7% 1	75235
Seeing	Day	29% 20% 28% 16% 6% 1	13648
	Night	27% 17% 27% 21% 7% 1	22789

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	16% 20% 10% 13% 11% 5% 5% 4 3 2 10%	1517
	11th to 20th	Day	16% 18% 7% 14% 11% 4 4 4 3 3 15%	1520
	21st to end	Day	9% 15% 9% 13% 12% 5% 7% 5% 4 4 18%	1592
February	1st to 10th	Day	14% 19% 7% 14% 13% 5% 6% 3 3 3 13%	1498
	11th to 20th	Day	14% 18% 10% 16% 9% 4 4 4 3 4 14%	1748
	21st to end	Day	12% 21% 5% 12% 9% 5% 6% 4 4 5% 18%	1480
March	1st to 10th	Day	13% 18% 8% 12% 7% 5% 3 4 3 4 22%	1797
	11th to 20th	Day	16% 15% 7% 9% 8% 5% 3 4 3 5% 25%	1890
	21st to end	Day	18% 19% 6% 11% 6% 3 4 3 3 3 25%	2304
April	1st to 10th	Day	22% 18% 6% 8% 6% 2 3 3 4 4 24%	2160
	11th to 20th	Day	19% 15% 5% 6% 5% 3 3 3 4 5% 33%	2199
	21st to end	Day	24% 16% 4 7% 5% 3 4 3 4 5% 25%	2340
May	1st to 10th	Day	25% 13% 4 5% 5% 3 4 4 4 4 30%	2340
	11th to 20th	Day	22% 10% 3 6% 6% 3 4 4 5% 6% 31%	2472
	21st to end	Day	22% 8% 3 7% 5% 3 5% 5% 5% 8% 27%	2725
June	1st to 10th	Day	31% 8% 3 6% 5% 3 4 5% 6% 7% 23%	2520
	11th to 20th	Day	22% 7% 3 5% 6% 3 5% 5% 5% 8% 31%	2527
	21st to end	Day	26% 8% 4 7% 5% 4 5% 5% 6% 7% 24%	2520
July	1st to 10th	Day	20% 7% 3 6% 6% 3 5% 5% 5% 8% 31%	2520
	11th to 20th	Day	18% 8% 3 6% 6% 3 6% 6% 6% 8% 28%	2520
	21st to end	Day	22% 8% 3 5% 5% 4 5% 6% 6% 8% 26%	2744
August	1st to 10th	Day	23% 6% 3 6% 6% 4 6% 5% 6% 8% 27%	2453
	11th to 20th	Day	20% 8% 3 5% 5% 3 5% 6% 6% 9% 29%	2304
	21st to end	Day	23% 7% 2 5% 5% 3 5% 5% 6% 6% 33%	2435
September	1st to 10th	Day	21% 7% 2 6% 5% 3 4 4 5% 7% 35%	2160
	11th to 20th	Day	24% 6% 2 4 4 2 4 4 5% 6% 39%	1992
	21st to end	Day	21% 9% 3 6% 4 3 4 4 5% 8% 33%	1980
October	1st to 10th	Day	24% 12% 3 5% 5% 3 4 6% 5% 7% 27%	1980
	11th to 20th	Day	21% 15% 4 7% 5% 4 5% 5% 5% 6% 24%	1679
	21st to end	Day	26% 23% 4 6% 4 3 3 3 4 4 20%	1782
November	1st to 10th	Day	21% 19% 6% 6% 5% 2 3 4 4 4 26%	1671
	11th to 20th	Day	18% 17% 9% 11% 6% 3 4 4 3 5% 20%	1710
	21st to end	Day	18% 20% 7% 11% 6% 4 3 4 4 6% 17%	1572
December	1st to 10th	Day	20% 24% 11% 12% 6% 3 3 3 3 3 13%	1330
	11th to 20th	Day	18% 19% 9% 12% 7% 3 5% 3 3 3 19%	1677
	21st to end	Day	22% 21% 8% 12% 9% 3 4 3 2 3 15%	2772
January	1st to 10th	Night	14% 23% 10% 14% 11% 4 5% 4 4 3 10%	2649
	11th to 20th	Night	15% 18% 8% 15% 10% 5% 6% 4 3 3 12%	2660
	21st to end	Night	10% 15% 7% 14% 11% 6% 8% 5% 3 4 15%	2798
February	1st to 10th	Night	12% 18% 8% 14% 11% 5% 6% 3 3 4 15%	2458
	11th to 20th	Night	12% 18% 9% 14% 10% 5% 6% 4 3 4 16%	2098
	21st to end	Night	12% 18% 7% 12% 8% 4 7% 3 2 4 22%	1776
March	1st to 10th	Night	14% 18% 9% 10% 8% 4 5% 3 3 4 23%	2150
	11th to 20th	Night	16% 16% 6% 10% 7% 3 4 4 4 5% 26%	2068
	21st to end	Night	18% 18% 6% 9% 5% 3 4 2 4 4 28%	2049
April	1st to 10th	Night	23% 17% 5% 8% 4 3 4 4 3 4 25%	1800
	11th to 20th	Night	21% 15% 4 5% 4 2 4 4 4 6% 32%	1710
	21st to end	Night	24% 14% 3 5% 5% 3 4 4 4 5% 28%	1620
May	1st to 10th	Night	25% 12% 3 6% 4 3 4 5% 5% 5% 28%	1620
	11th to 20th	Night	22% 10% 3 7% 5% 3 5% 3 4 5% 33%	1436
	21st to end	Night	23% 7% 3 5% 6% 3 5% 4 5% 8% 32%	1550
June	1st to 10th	Night	29% 9% 4 5% 5% 3 3 4 5% 7% 26%	1440
	11th to 20th	Night	21% 6% 3 6% 5% 3 5% 4 6% 7% 35%	1344
	21st to end	Night	22% 7% 3 6% 7% 4 5% 4 5% 6% 30%	1440
July	1st to 10th	Night	18% 7% 3 6% 5% 3 5% 5% 5% 8% 34%	1440
	11th to 20th	Night	16% 6% 3 5% 6% 3 6% 6% 7% 10% 31%	1440
	21st to end	Night	18% 7% 3 5% 6% 3 6% 5% 6% 7% 34%	1574
August	1st to 10th	Night	19% 5% 3 4 6% 3 5% 5% 7% 8% 35%	1466
	11th to 20th	Night	19% 7% 3 8% 6% 3 4 5% 4 8% 34%	1596
	21st to end	Night	19% 9% 2 5% 5% 2 4 4 4 7% 39%	1917
September	1st to 10th	Night	21% 7% 3 6% 5% 2 4 4 5% 6% 38%	1800
	11th to 20th	Night	21% 6% 2 4 3 3 4 4 5% 6% 41%	1967
	21st to end	Night	23% 7% 2 3 4 2 4 3 5% 7% 40%	1980
October	1st to 10th	Night	22% 10% 3 6% 5% 3 4 4 4 7% 33%	1980
	11th to 20th	Night	24% 14% 4 7% 6% 3 4 4 4 5% 25%	2279
	21st to end	Night	28% 17% 3 6% 5% 2 4 4 4 5% 23%	2574
November	1st to 10th	Night	22% 18% 5% 8% 6% 3 3 2 4 5% 23%	2407
	11th to 20th	Night	19% 16% 7% 11% 6% 3 4 3 4 5% 24%	2470
	21st to end	Night	18% 19% 8% 11% 7% 3 4 3 3 5% 19%	2598
December	1st to 10th	Night	21% 22% 9% 13% 8% 4 3 3 3 3 12%	2850
	11th to 20th	Night	18% 21% 9% 14% 9% 4 4 3 2 3 12%	3517
	21st to end	Night	21% 21% 7% 11% 7% 3 4 2 3 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	80% 4 6% 7% 3	1518
	11th to 20th	Day	74% 5% 5% 10% 5% 1	1520
	21st to end	Day	68% 6% 7% 11% 7% 2	1592
February	1st to 10th	Day	78% 4 5% 8% 5% 1	1498
	11th to 20th	Day	76% 3 7% 9% 4 1	1757
	21st to end	Day	69% 4 7% 12% 6% 2	1480
March	1st to 10th	Day	67% 4 7% 13% 5% 3	1800
	11th to 20th	Day	63% 5% 8% 11% 10% 2	1890
	21st to end	Day	66% 3 6% 14% 9% 2	2304
April	1st to 10th	Day	66% 3 9% 13% 7% 2	2160
	11th to 20th	Day	56% 4 8% 20% 11% 1	2199
	21st to end	Day	63% 4 8% 14% 9% 3	2340
May	1st to 10th	Day	58% 4 7% 18% 11% 1	2340
	11th to 20th	Day	55% 6% 11% 17% 10% 1	2476
	21st to end	Day	55% 8% 12% 16% 9% 1	2725
June	1st to 10th	Day	61% 5% 10% 18% 5% 1	2520
	11th to 20th	Day	51% 7% 11% 21% 8% 1	2527
	21st to end	Day	58% 7% 12% 17% 6%	2520
July	1st to 10th	Day	50% 7% 15% 21% 7%	2450
	11th to 20th	Day	52% 8% 14% 20% 6%	2445
	21st to end	Day	56% 7% 13% 18% 5%	2591
August	1st to 10th	Day	53% 9% 15% 20% 3	2439
	11th to 20th	Day	50% 8% 17% 18% 7%	2304
	21st to end	Day	49% 7% 13% 20% 11%	2435
September	1st to 10th	Day	48% 6% 13% 23% 9% 1	2160
	11th to 20th	Day	47% 4 11% 26% 12% 1	1992
	21st to end	Day	50% 6% 11% 22% 10% 1	1980
October	1st to 10th	Day	56% 6% 12% 17% 9%	1980
	11th to 20th	Day	61% 6% 13% 14% 5%	1679
	21st to end	Day	69% 4 8% 11% 6% 1	1782
November	1st to 10th	Day	62% 6% 10% 15% 7% 1	1671
	11th to 20th	Day	67% 5% 8% 11% 6% 2	1710
	21st to end	Day	68% 6% 11% 12% 2	1572
December	1st to 10th	Day	78% 4 5% 8% 4	1330
	11th to 20th	Day	72% 4 4 13% 6% 1	1677
	21st to end	Day	77% 4 5% 8% 6%	2772
January	1st to 10th	Night	80% 4 6% 6% 3	2649
	11th to 20th	Night	78% 5% 5% 7% 3 1	2660
	21st to end	Night	72% 5% 7% 10% 5% 1	2798
February	1st to 10th	Night	75% 4 5% 10% 5% 1	2458
	11th to 20th	Night	74% 5% 6% 10% 5% 1	2100
	21st to end	Night	69% 4 5% 13% 9% 1	1776
March	1st to 10th	Night	67% 4 7% 14% 6% 2	2160
	11th to 20th	Night	63% 6% 9% 11% 10% 2	2069
	21st to end	Night	62% 3 6% 18% 8% 3	2049
April	1st to 10th	Night	63% 4 7% 14% 10% 1	1800
	11th to 20th	Night	54% 6% 8% 19% 11% 1	1710
	21st to end	Night	59% 6% 9% 15% 9% 2	1620
May	1st to 10th	Night	56% 5% 8% 16% 12% 1	1620
	11th to 20th	Night	53% 7% 11% 18% 10% 2	1437
	21st to end	Night	51% 8% 12% 19% 10% 1	1551
June	1st to 10th	Night	57% 5% 12% 19% 7%	1440
	11th to 20th	Night	47% 8% 10% 22% 10% 2	1344
	21st to end	Night	54% 8% 12% 20% 7%	1440
July	1st to 10th	Night	47% 9% 14% 21% 9%	1400
	11th to 20th	Night	45% 10% 15% 23% 7%	1392
	21st to end	Night	49% 9% 13% 22% 7%	1486
August	1st to 10th	Night	44% 9% 18% 24% 5%	1456
	11th to 20th	Night	48% 9% 15% 20% 8%	1596
	21st to end	Night	45% 6% 15% 24% 9%	1917
September	1st to 10th	Night	47% 6% 13% 24% 10%	1800
	11th to 20th	Night	44% 6% 14% 27% 9% 1	1967
	21st to end	Night	45% 5% 13% 24% 11% 2	1980
October	1st to 10th	Night	53% 5% 11% 20% 11%	1980
	11th to 20th	Night	61% 6% 12% 16% 5%	2279
	21st to end	Night	66% 6% 9% 12% 6% 1	2574
November	1st to 10th	Night	64% 5% 10% 15% 6% 1	2407
	11th to 20th	Night	65% 4 9% 13% 7% 2	2470
	21st to end	Night	71% 4 11% 11% 4	2598
December	1st to 10th	Night	80% 4 6% 8% 2	2850
	11th to 20th	Night	79% 3 5% 8% 5%	3518
	21st to end	Night	74% 4 8% 10% 4	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	31% 26% 32% 11%	180
	11th to 20th	Day	32% 30% 23% 13% 1 1	180
	21st to end	Day	23% 28% 37% 11% 2 1	178
February	1st to 10th	Day	42% 29% 20% 8% 2	206
	11th to 20th	Day	31% 30% 31% 6% 2	416
	21st to end	Day	33% 27% 26% 13% 2	346
March	1st to 10th	Day	29% 26% 30% 11% 3	420
	11th to 20th	Day	30% 30% 25% 11% 4	420
	21st to end	Day	34% 23% 21% 16% 6% 1	462
April	1st to 10th	Day	40% 20% 23% 12% 5%	420
	11th to 20th	Day	33% 22% 25% 12% 5% 2	412
	21st to end	Day	37% 20% 27% 10% 4 1	420
May	1st to 10th	Day	41% 16% 26% 12% 4 1	423
	11th to 20th	Day	27% 19% 32% 16% 4 1	447
	21st to end	Day	23% 24% 29% 18% 5% 1	485
June	1st to 10th	Day	35% 19% 28% 14% 4	450
	11th to 20th	Day	24% 19% 29% 20% 7% 1	457
	21st to end	Day	26% 16% 33% 16% 8% 1	450
July	1st to 10th	Day	22% 13% 35% 22% 7% 1	445
	11th to 20th	Day	21% 13% 37% 20% 8% 1	444
	21st to end	Day	25% 13% 32% 23% 6% 1	488
August	1st to 10th	Day	23% 11% 30% 24% 11% 1	446
	11th to 20th	Day	21% 11% 30% 24% 11% 3	439
	21st to end	Day	26% 15% 24% 20% 10% 4	495
September	1st to 10th	Day	25% 12% 29% 20% 12% 3	450
	11th to 20th	Day	25% 12% 23% 21% 12% 7%	450
	21st to end	Day	22% 15% 26% 22% 11% 4	450
October	1st to 10th	Day	29% 18% 21% 19% 10% 3	450
	11th to 20th	Day	30% 19% 27% 14% 8% 1	381
	21st to end	Day	39% 24% 20% 15% 3	396
November	1st to 10th	Day	37% 20% 26% 14% 4	365
	11th to 20th	Day	29% 24% 28% 11% 6% 1	370
	21st to end	Day	33% 24% 27% 12% 3 1	249
December	1st to 10th	Day	34% 26% 24% 14% 2	180
	11th to 20th	Day	38% 27% 26% 6% 3 1	180
	21st to end	Day	38% 26% 27% 7% 2	198
January	1st to 10th	Night	26% 27% 34% 11% 2	760
	11th to 20th	Night	26% 28% 28% 15% 3	760
	21st to end	Night	19% 25% 36% 16% 4 1	800
February	1st to 10th	Night	22% 28% 34% 14% 2	720
	11th to 20th	Night	25% 25% 34% 14% 2	703
	21st to end	Night	26% 23% 32% 18% 2	592
March	1st to 10th	Night	26% 21% 32% 18% 2	720
	11th to 20th	Night	28% 23% 28% 16% 5%	720
	21st to end	Night	28% 20% 26% 20% 6% 1	792
April	1st to 10th	Night	33% 21% 24% 17% 5%	720
	11th to 20th	Night	33% 16% 26% 19% 6% 1	646
	21st to end	Night	32% 20% 25% 19% 5% 1	540
May	1st to 10th	Night	30% 14% 30% 18% 7% 1	540
	11th to 20th	Night	26% 11% 29% 27% 6% 1	375
	21st to end	Night	24% 11% 30% 27% 7% 1	389
June	1st to 10th	Night	32% 7% 27% 25% 9%	360
	11th to 20th	Night	25% 7% 22% 33% 14% 1	360
	21st to end	Night	20% 10% 26% 34% 9%	360
July	1st to 10th	Night	21% 6% 28% 34% 10% 1	350
	11th to 20th	Night	16% 7% 27% 34% 14% 1	348
	21st to end	Night	20% 6% 23% 38% 13% 1	394
August	1st to 10th	Night	20% 3 19% 38% 20% 1	392
	11th to 20th	Night	19% 7% 21% 35% 17% 1	532
	21st to end	Night	23% 7% 23% 30% 16% 2	729
September	1st to 10th	Night	23% 7% 24% 32% 13% 1	720
	11th to 20th	Night	25% 8% 21% 27% 18% 2	720
	21st to end	Night	25% 10% 25% 24% 15% 1	720
October	1st to 10th	Night	28% 10% 25% 23% 13% 1	720
	11th to 20th	Night	33% 14% 22% 21% 8% 2	720
	21st to end	Night	37% 18% 25% 17% 4	792
November	1st to 10th	Night	34% 18% 25% 18% 5% 1	740
	11th to 20th	Night	29% 20% 28% 14% 7% 2	760
	21st to end	Night	31% 23% 24% 16% 4 1	765
December	1st to 10th	Night	33% 24% 24% 14% 4	850
	11th to 20th	Night	30% 26% 24% 14% 5%	844
	21st to end	Night	35% 23% 27% 13% 2	836

Page generated at 2024-01-19 09:28:33. Version ac07

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