Les Coteaux
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Les Coteaux clear sky chart from 2005-11-06 to 2025-02-06.

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	16% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	108478
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 29%	109777
Transparency	Day	30% 43% 8% 14% 5%	111970
	Night	34% 41% 7% 12% 6%	114449
Seeing	Day	20% 12% 28% 25% 12% 3	14774
	Night	23% 10% 29% 28% 10% 1	23923

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% 21% 5% 12% 6% 4 4 4 3 5% 21%	3597
	11th to 20th	Day	12% 16% 6% 12% 6% 6% 5% 4 5% 5% 23%	3570
	21st to end	Day	12% 14% 6% 11% 6% 6% 5% 4 6% 7% 23%	3960
February	1st to 10th	Day	15% 15% 5% 11% 6% 5% 5% 4 5% 6% 24%	1747
	11th to 20th	Day	14% 12% 4 10% 6% 5% 6% 4 7% 6% 27%	1743
	21st to end	Day	19% 14% 4 8% 5% 6% 5% 3 5% 5% 26%	1570
March	1st to 10th	Day	19% 13% 4 9% 6% 4 4 3 4 6% 27%	3116
	11th to 20th	Day	11% 14% 4 12% 6% 5% 5% 4 5% 5% 28%	3335
	21st to end	Day	15% 7% 3 8% 5% 5% 4 3 5% 6% 40%	4129
April	1st to 10th	Day	21% 10% 3 7% 5% 4 4 3 5% 6% 33%	2280
	11th to 20th	Day	20% 7% 2 6% 5% 4 4 4 5% 6% 36%	2254
	21st to end	Day	22% 9% 3 7% 4 4 4 3 5% 6% 33%	2403
May	1st to 10th	Day	20% 9% 3 8% 5% 4 4 4 6% 6% 31%	4409
	11th to 20th	Day	18% 8% 3 8% 5% 4 4 4 5% 7% 35%	4398
	21st to end	Day	14% 7% 2 6% 4 5% 5% 5% 7% 9% 37%	4837
June	1st to 10th	Day	21% 7% 3 7% 5% 4 4 4 6% 8% 31%	2660
	11th to 20th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	19% 8% 3 7% 4 4 6% 4 6% 8% 32%	2660
July	1st to 10th	Day	11% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	4440
	11th to 20th	Day	13% 5% 2 6% 5% 5% 6% 5% 7% 9% 39%	4440
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 7% 9% 44%	4814
August	1st to 10th	Day	15% 6% 3 8% 5% 5% 5% 4 6% 9% 34%	4423
	11th to 20th	Day	14% 6% 3 6% 5% 4 5% 4 6% 8% 40%	3957
	21st to end	Day	15% 6% 2 5% 4 4 5% 4 7% 8% 40%	4180
September	1st to 10th	Day	13% 5% 3 5% 5% 4 5% 4 5% 8% 44%	2280
	11th to 20th	Day	13% 4 2 5% 4 4 4 3 5% 6% 49%	2218
	21st to end	Day	16% 6% 3 7% 4 4 5% 3 5% 8% 40%	2090
October	1st to 10th	Day	19% 8% 3 6% 5% 4 5% 4 5% 6% 35%	1933
	11th to 20th	Day	18% 9% 3 10% 5% 5% 5% 4 5% 6% 30%	1886
	21st to end	Day	24% 10% 3 8% 4 4 4 4 5% 7% 27%	1881
November	1st to 10th	Day	16% 11% 3 7% 5% 4 5% 3 6% 7% 34%	1761
	11th to 20th	Day	16% 12% 2 9% 5% 5% 5% 5% 6% 6% 30%	1701
	21st to end	Day	21% 12% 5% 9% 6% 5% 5% 4 6% 7% 21%	1600
December	1st to 10th	Day	21% 18% 6% 10% 6% 5% 5% 4 5% 5% 16%	2600
	11th to 20th	Day	18% 13% 4 10% 6% 5% 6% 4 5% 5% 24%	2986
	21st to end	Day	23% 14% 4 10% 5% 5% 5% 5% 6% 5% 18%	3960
January	1st to 10th	Night	14% 21% 8% 14% 6% 4 3 3 4 4 18%	6349
	11th to 20th	Night	10% 16% 7% 17% 8% 6% 6% 4 5% 5% 16%	6315
	21st to end	Night	13% 18% 5% 12% 7% 5% 5% 3 5% 6% 22%	6996
February	1st to 10th	Night	14% 16% 5% 12% 7% 6% 5% 4 5% 5% 21%	2541
	11th to 20th	Night	14% 12% 5% 10% 6% 5% 6% 3 6% 6% 27%	2322
	21st to end	Night	15% 14% 5% 9% 6% 5% 4 3 5% 5% 30%	1884
March	1st to 10th	Night	20% 10% 3 8% 5% 4 4 3 4 5% 32%	3724
	11th to 20th	Night	20% 17% 4 9% 5% 5% 4 3 4 5% 26%	3621
	21st to end	Night	14% 10% 4 8% 5% 4 4 3 5% 5% 38%	3502
April	1st to 10th	Night	23% 9% 3 8% 5% 5% 4 3 5% 5% 30%	1900
	11th to 20th	Night	22% 10% 3 6% 4 3 4 3 5% 6% 33%	1875
	21st to end	Night	20% 10% 4 8% 4 3 4 3 4 5% 34%	1776
May	1st to 10th	Night	22% 11% 3 7% 5% 4 4 3 5% 6% 30%	2560
	11th to 20th	Night	21% 9% 3 6% 4 4 5% 3 4 6% 36%	2495
	21st to end	Night	15% 6% 3 7% 5% 4 5% 4 6% 8% 38%	2738
June	1st to 10th	Night	19% 9% 2 7% 5% 4 5% 5% 7% 9% 29%	1520
	11th to 20th	Night	17% 6% 2 7% 3 3 5% 3 5% 8% 40%	1520
	21st to end	Night	18% 7% 3 7% 5% 5% 4 3 5% 8% 34%	1520
July	1st to 10th	Night	13% 8% 3 8% 5% 4 5% 5% 7% 7% 35%	2520
	11th to 20th	Night	14% 5% 2 5% 5% 5% 5% 4 6% 8% 40%	2520
	21st to end	Night	12% 7% 2 6% 5% 4 4 4 6% 7% 43%	2739
August	1st to 10th	Night	16% 8% 3 7% 5% 3 4 4 5% 7% 40%	2506
	11th to 20th	Night	17% 7% 2 7% 5% 5% 5% 3 5% 6% 39%	2836
	21st to end	Night	14% 6% 2 7% 4 4 4 4 5% 8% 41%	3476
September	1st to 10th	Night	11% 6% 2 7% 4 4 5% 4 6% 7% 42%	1900
	11th to 20th	Night	15% 6% 2 4 4 3 3 3 5% 7% 49%	1962
	21st to end	Night	16% 6% 2 5% 5% 4 5% 3 5% 7% 41%	2090
October	1st to 10th	Night	19% 7% 2 7% 5% 4 5% 4 5% 7% 35%	2243
	11th to 20th	Night	19% 8% 3 8% 5% 6% 4 3 5% 6% 33%	2294
	21st to end	Night	22% 9% 3 9% 6% 5% 4 3 5% 6% 29%	2717
November	1st to 10th	Night	19% 10% 4 7% 5% 5% 4 4 5% 6% 32%	2537
	11th to 20th	Night	18% 11% 3 9% 5% 4 4 3 5% 5% 32%	2695
	21st to end	Night	21% 12% 5% 10% 5% 5% 4 4 5% 6% 23%	2800
December	1st to 10th	Night	18% 19% 6% 12% 7% 5% 5% 3 4 4 16%	4580
	11th to 20th	Night	23% 15% 4 9% 5% 4 4 4 5% 5% 22%	5208
	21st to end	Night	24% 16% 4 10% 5% 4 3 3 5% 5% 19%	6996

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	52% 26% 9% 11% 3	3598
	11th to 20th	Day	48% 26% 8% 12% 5% 1	3600
	21st to end	Day	48% 28% 9% 9% 7% 1	3960
February	1st to 10th	Day	23% 63% 4 8% 2 1	1747
	11th to 20th	Day	20% 64% 3 8% 4	1752
	21st to end	Day	20% 65% 3 5% 6% 1	1570
March	1st to 10th	Day	37% 40% 5% 13% 4	3119
	11th to 20th	Day	37% 40% 7% 8% 6% 1	3335
	21st to end	Day	28% 41% 5% 14% 12% 1	4129
April	1st to 10th	Day	18% 65% 4 7% 5% 1	2280
	11th to 20th	Day	18% 65% 2 8% 5% 1	2254
	21st to end	Day	19% 65% 4 7% 6%	2403
May	1st to 10th	Day	35% 40% 7% 14% 4	4423
	11th to 20th	Day	34% 39% 11% 12% 4	4402
	21st to end	Day	27% 40% 8% 18% 7%	4837
June	1st to 10th	Day	18% 65% 3 9% 5% 1	2660
	11th to 20th	Day	16% 65% 5% 8% 5% 1	2660
	21st to end	Day	18% 63% 4 9% 5% 1	2660
July	1st to 10th	Day	30% 35% 9% 19% 7%	4370
	11th to 20th	Day	27% 35% 11% 22% 4	4365
	21st to end	Day	23% 36% 9% 26% 6%	4661
August	1st to 10th	Day	31% 37% 11% 15% 6%	4409
	11th to 20th	Day	31% 37% 11% 18% 3	3999
	21st to end	Day	26% 36% 13% 15% 8%	4180
September	1st to 10th	Day	14% 61% 7% 12% 6%	2280
	11th to 20th	Day	13% 60% 6% 13% 7% 1	2218
	21st to end	Day	14% 60% 6% 12% 7% 1	2090
October	1st to 10th	Day	30% 36% 7% 22% 5%	3206
	11th to 20th	Day	24% 36% 14% 21% 4	3114
	21st to end	Day	27% 36% 15% 17% 4	3081
November	1st to 10th	Day	26% 56% 6% 9% 3	1761
	11th to 20th	Day	20% 58% 5% 12% 5% 1	1701
	21st to end	Day	26% 59% 7% 6% 3	1600
December	1st to 10th	Day	46% 35% 8% 10% 1	2600
	11th to 20th	Day	44% 32% 6% 11% 7%	2986
	21st to end	Day	50% 26% 6% 15% 4	3960
January	1st to 10th	Night	55% 25% 9% 9% 2	6349
	11th to 20th	Night	55% 26% 7% 9% 3	6360
	21st to end	Night	50% 27% 6% 8% 9% 1	6996
February	1st to 10th	Night	24% 63% 4 7% 1	2541
	11th to 20th	Night	20% 64% 3 8% 4	2324
	21st to end	Night	18% 64% 3 7% 7%	1884
March	1st to 10th	Night	31% 40% 5% 15% 7% 2	3734
	11th to 20th	Night	40% 39% 5% 8% 5% 2	3622
	21st to end	Night	30% 41% 2 15% 11% 1	3502
April	1st to 10th	Night	21% 64% 3 6% 6%	1900
	11th to 20th	Night	20% 65% 3 7% 5% 1	1875
	21st to end	Night	20% 65% 3 6% 6% 1	1776
May	1st to 10th	Night	35% 40% 9% 12% 3	2566
	11th to 20th	Night	33% 39% 9% 13% 5%	2496
	21st to end	Night	29% 40% 7% 13% 11%	2739
June	1st to 10th	Night	18% 66% 3 8% 6%	1520
	11th to 20th	Night	14% 65% 5% 8% 8% 1	1520
	21st to end	Night	19% 64% 4 8% 6% 1	1520
July	1st to 10th	Night	34% 36% 9% 12% 9%	2480
	11th to 20th	Night	27% 35% 12% 22% 4	2472
	21st to end	Night	26% 36% 11% 17% 10%	2651
August	1st to 10th	Night	31% 37% 10% 18% 5%	2496
	11th to 20th	Night	34% 36% 12% 15% 3	2860
	21st to end	Night	28% 36% 10% 15% 10% 1	3476
September	1st to 10th	Night	14% 60% 6% 12% 8%	1900
	11th to 20th	Night	14% 60% 6% 15% 5% 1	1962
	21st to end	Night	15% 60% 5% 12% 7%	2090
October	1st to 10th	Night	29% 36% 9% 21% 5%	3750
	11th to 20th	Night	26% 37% 9% 23% 6%	3805
	21st to end	Night	29% 37% 12% 14% 8%	4467
November	1st to 10th	Night	26% 56% 6% 8% 4 1	2537
	11th to 20th	Night	24% 57% 4 9% 5%	2695
	21st to end	Night	27% 57% 6% 7% 2	2800
December	1st to 10th	Night	47% 35% 9% 7% 2	4580
	11th to 20th	Night	47% 32% 4 9% 8%	5208
	21st to end	Night	50% 26% 4 11% 8%	6996

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	27% 11% 32% 24% 6% 1	200
	11th to 20th	Day	26% 17% 33% 18% 5% 2	200
	21st to end	Day	18% 15% 36% 24% 6% 1	220
February	1st to 10th	Day	27% 18% 37% 14% 4	282
	11th to 20th	Day	23% 11% 42% 21% 3	350
	21st to end	Day	28% 12% 30% 27% 2	382
March	1st to 10th	Day	22% 13% 35% 23% 7%	460
	11th to 20th	Day	19% 19% 35% 20% 7% 1	460
	21st to end	Day	24% 15% 30% 17% 12% 2	506
April	1st to 10th	Day	27% 13% 28% 22% 9% 1	460
	11th to 20th	Day	24% 17% 27% 20% 10% 2	452
	21st to end	Day	25% 15% 27% 21% 10% 2	460
May	1st to 10th	Day	21% 11% 31% 26% 9% 2	463
	11th to 20th	Day	16% 11% 32% 23% 15% 3	487
	21st to end	Day	17% 11% 29% 26% 13% 4	529
June	1st to 10th	Day	20% 11% 25% 29% 12% 4	490
	11th to 20th	Day	14% 10% 27% 31% 17% 2	490
	21st to end	Day	21% 9% 28% 23% 14% 4	490
July	1st to 10th	Day	12% 6% 27% 31% 18% 6%	485
	11th to 20th	Day	15% 6% 26% 31% 18% 5%	484
	21st to end	Day	13% 6% 25% 35% 17% 4	532
August	1st to 10th	Day	15% 7% 20% 33% 19% 6%	486
	11th to 20th	Day	11% 4 22% 33% 21% 8%	479
	21st to end	Day	14% 9% 23% 26% 20% 8%	539
September	1st to 10th	Day	15% 7% 26% 26% 18% 8%	490
	11th to 20th	Day	13% 8% 21% 24% 20% 14%	490
	21st to end	Day	17% 9% 27% 24% 19% 6%	490
October	1st to 10th	Day	22% 12% 25% 21% 15% 5%	490
	11th to 20th	Day	20% 16% 28% 23% 11% 2	483
	21st to end	Day	29% 14% 26% 23% 9%	429
November	1st to 10th	Day	27% 15% 26% 22% 10% 1	395
	11th to 20th	Day	23% 18% 31% 21% 6% 1	301
	21st to end	Day	26% 20% 30% 18% 7%	200
December	1st to 10th	Day	29% 13% 27% 24% 7%	200
	11th to 20th	Day	28% 16% 39% 15% 4 1	200
	21st to end	Day	30% 16% 29% 19% 5% 2	220
January	1st to 10th	Night	25% 14% 32% 25% 4	800
	11th to 20th	Night	28% 13% 29% 23% 5% 1	800
	21st to end	Night	20% 10% 36% 27% 6%	880
February	1st to 10th	Night	21% 13% 36% 26% 4	781
	11th to 20th	Night	20% 14% 35% 26% 5%	743
	21st to end	Night	21% 11% 35% 29% 4	628
March	1st to 10th	Night	23% 12% 33% 27% 5%	760
	11th to 20th	Night	25% 14% 31% 25% 4 1	760
	21st to end	Night	23% 10% 29% 28% 9%	836
April	1st to 10th	Night	27% 12% 29% 28% 5% 1	760
	11th to 20th	Night	24% 13% 31% 25% 6%	751
	21st to end	Night	26% 10% 29% 25% 9%	636
May	1st to 10th	Night	25% 8% 28% 29% 8% 1	413
	11th to 20th	Night	21% 7% 29% 31% 11% 1	374
	21st to end	Night	17% 5% 34% 34% 10%	411
June	1st to 10th	Night	22% 7% 29% 33% 10% 1	380
	11th to 20th	Night	17% 8% 27% 33% 14% 1	380
	21st to end	Night	19% 5% 29% 29% 17% 1	380
July	1st to 10th	Night	12% 4 25% 40% 18% 1	370
	11th to 20th	Night	12% 2 27% 40% 17% 1	368
	21st to end	Night	15% 3 23% 43% 15% 2	416
August	1st to 10th	Night	15% 3 17% 44% 19% 1	378
	11th to 20th	Night	15% 3 21% 34% 24% 3	586
	21st to end	Night	14% 4 25% 34% 20% 2	836
September	1st to 10th	Night	14% 5% 25% 38% 17% 1	760
	11th to 20th	Night	18% 5% 18% 34% 21% 3	760
	21st to end	Night	18% 8% 23% 30% 18% 3	760
October	1st to 10th	Night	23% 7% 26% 28% 15% 1	760
	11th to 20th	Night	24% 10% 29% 27% 10% 1	760
	21st to end	Night	28% 11% 30% 26% 5%	836
November	1st to 10th	Night	24% 14% 28% 25% 8%	780
	11th to 20th	Night	23% 15% 31% 21% 9% 1	800
	21st to end	Night	27% 14% 31% 20% 8%	800
December	1st to 10th	Night	30% 14% 30% 22% 4	800
	11th to 20th	Night	30% 14% 31% 20% 4 1	800
	21st to end	Night	34% 13% 29% 20% 5%	880

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