Observatoire du Lac Rouge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Lac Rouge clear sky chart from 2005-11-06 to 2024-01-16.

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% 10% 4 7% 6% 3 5% 5% 5% 6% 32%	74794
	Night	17% 10% 4 7% 5% 3 4 4 5% 6% 35%	75018
Transparency	Day	51% 6% 11% 19% 11% 1	74499
	Night	50% 6% 11% 21% 11% 1	74847
Seeing	Day	24% 14% 32% 20% 8% 2	13422
	Night	23% 12% 29% 27% 9% 1	22495

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	15% 16% 6% 9% 8% 4 5% 5% 4 4 24%	1517
	11th to 20th	Day	17% 16% 6% 8% 7% 3 4 4 4 5% 27%	1486
	21st to end	Day	11% 12% 6% 10% 7% 4 5% 4 5% 6% 31%	1584
February	1st to 10th	Day	11% 19% 6% 10% 8% 3 5% 4 5% 5% 25%	1560
	11th to 20th	Day	12% 16% 6% 10% 6% 4 5% 4 4 5% 29%	1655
	21st to end	Day	16% 16% 6% 8% 7% 4 5% 3 3 6% 27%	1480
March	1st to 10th	Day	14% 12% 6% 8% 9% 4 4 4 4 5% 30%	1797
	11th to 20th	Day	15% 12% 4 7% 8% 3 4 4 5% 6% 31%	1861
	21st to end	Day	17% 11% 3 6% 5% 3 5% 4 4 6% 34%	2376
April	1st to 10th	Day	19% 13% 5% 7% 6% 3 4 4 4 5% 31%	2160
	11th to 20th	Day	21% 9% 3 6% 5% 3 4 5% 4 6% 35%	2134
	21st to end	Day	22% 11% 3 7% 5% 4 4 3 4 4 32%	2318
May	1st to 10th	Day	21% 9% 3 7% 5% 3 4 4 5% 7% 33%	2504
	11th to 20th	Day	20% 7% 3 6% 6% 3 4 5% 5% 7% 34%	2478
	21st to end	Day	19% 6% 3 6% 6% 3 5% 5% 6% 7% 34%	2725
June	1st to 10th	Day	23% 6% 3 6% 6% 3 5% 6% 5% 7% 29%	2520
	11th to 20th	Day	16% 6% 3 6% 6% 4 5% 5% 7% 8% 34%	2520
	21st to end	Day	23% 7% 4 7% 6% 4 5% 5% 6% 7% 27%	2520
July	1st to 10th	Day	14% 5% 3 5% 7% 4 7% 6% 6% 8% 37%	2520
	11th to 20th	Day	15% 6% 3 5% 6% 4 6% 6% 7% 8% 34%	2520
	21st to end	Day	13% 6% 3 7% 6% 4 6% 6% 7% 8% 35%	2744
August	1st to 10th	Day	14% 7% 2 7% 6% 4 7% 7% 7% 10% 31%	2506
	11th to 20th	Day	12% 6% 2 6% 6% 4 6% 6% 7% 8% 36%	2321
	21st to end	Day	13% 5% 2 7% 5% 3 5% 4 6% 9% 41%	2376
September	1st to 10th	Day	15% 5% 2 5% 5% 3 4 5% 6% 8% 41%	2160
	11th to 20th	Day	16% 5% 3 4 4 3 4 5% 5% 6% 46%	2085
	21st to end	Day	20% 7% 2 5% 5% 2 4 4 4 7% 41%	1980
October	1st to 10th	Day	23% 7% 2 5% 5% 3 5% 3 5% 6% 35%	1854
	11th to 20th	Day	22% 10% 3 8% 7% 3 4 5% 5% 7% 26%	1751
	21st to end	Day	25% 10% 3 6% 5% 2 4 4 4 6% 29%	1782
November	1st to 10th	Day	16% 10% 3 6% 6% 3 5% 5% 5% 6% 35%	1671
	11th to 20th	Day	19% 10% 4 9% 6% 2 4 5% 6% 6% 28%	1611
	21st to end	Day	20% 14% 4 7% 5% 4 5% 4 4 6% 26%	1520
December	1st to 10th	Day	23% 15% 6% 8% 7% 2 3 4 4 4 24%	1520
	11th to 20th	Day	20% 14% 5% 8% 6% 2 3 4 4 5% 28%	1906
	21st to end	Day	23% 17% 5% 7% 5% 3 4 3 4 4 26%	2772
January	1st to 10th	Night	15% 17% 6% 9% 6% 3 5% 5% 5% 5% 25%	2649
	11th to 20th	Night	14% 15% 6% 9% 6% 3 4 4 5% 6% 26%	2602
	21st to end	Night	10% 12% 5% 8% 7% 4 6% 5% 5% 5% 34%	2772
February	1st to 10th	Night	12% 12% 5% 10% 7% 4 7% 4 5% 5% 29%	2398
	11th to 20th	Night	12% 12% 5% 9% 7% 4 5% 4 5% 6% 31%	2190
	21st to end	Night	14% 13% 4 8% 6% 3 5% 4 4 6% 33%	1776
March	1st to 10th	Night	15% 13% 5% 8% 7% 4 4 4 4 5% 31%	2150
	11th to 20th	Night	15% 14% 5% 7% 5% 3 4 4 4 6% 32%	2097
	21st to end	Night	15% 9% 4 6% 6% 3 4 5% 4 5% 39%	1980
April	1st to 10th	Night	21% 10% 4 7% 5% 4 4 4 4 6% 32%	1800
	11th to 20th	Night	19% 6% 2 6% 5% 3 4 4 5% 6% 40%	1775
	21st to end	Night	21% 10% 4 5% 4 3 3 4 5% 6% 35%	1640
May	1st to 10th	Night	21% 9% 4 5% 4 3 4 3 4 7% 36%	1472
	11th to 20th	Night	20% 7% 2 5% 5% 3 4 4 5% 7% 39%	1415
	21st to end	Night	18% 6% 2 5% 5% 4 5% 5% 5% 7% 39%	1550
June	1st to 10th	Night	19% 6% 3 5% 6% 3 4 5% 6% 8% 34%	1440
	11th to 20th	Night	18% 6% 3 5% 5% 3 6% 5% 5% 7% 37%	1440
	21st to end	Night	19% 5% 3 5% 6% 4 5% 5% 5% 8% 36%	1440
July	1st to 10th	Night	12% 5% 2 4 5% 3 5% 5% 6% 8% 45%	1440
	11th to 20th	Night	12% 4 2 5% 5% 3 5% 6% 5% 8% 44%	1440
	21st to end	Night	12% 6% 2 4 5% 3 4 5% 7% 8% 44%	1574
August	1st to 10th	Night	11% 5% 2 5% 5% 3 5% 5% 6% 9% 43%	1432
	11th to 20th	Night	14% 4 2 5% 5% 3 5% 5% 5% 7% 45%	1560
	21st to end	Night	15% 5% 2 4 5% 2 4 4 5% 7% 47%	1980
September	1st to 10th	Night	12% 4 2 5% 5% 3 4 5% 5% 7% 49%	1800
	11th to 20th	Night	15% 5% 2 4 4 2 3 4 5% 6% 49%	1874
	21st to end	Night	18% 6% 2 4 3 2 4 4 4 6% 47%	1980
October	1st to 10th	Night	18% 8% 3 5% 5% 3 4 4 4 5% 42%	2102
	11th to 20th	Night	22% 8% 2 5% 5% 2 5% 4 5% 7% 36%	2209
	21st to end	Night	22% 9% 4 6% 5% 3 5% 4 5% 6% 31%	2574
November	1st to 10th	Night	16% 10% 3 6% 5% 4 4 4 6% 7% 34%	2407
	11th to 20th	Night	18% 9% 4 7% 6% 3 5% 5% 5% 5% 33%	2568
	21st to end	Night	19% 15% 4 7% 5% 3 4 4 4 6% 30%	2660
December	1st to 10th	Night	19% 13% 6% 9% 6% 3 4 5% 5% 6% 22%	2660
	11th to 20th	Night	20% 14% 5% 7% 6% 3 4 3 4 5% 28%	3288
	21st to end	Night	23% 18% 5% 7% 5% 3 2 3 4 4 25%	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	63% 5% 8% 16% 8%	1518
	11th to 20th	Day	61% 4 8% 14% 12% 1	1486
	21st to end	Day	54% 4 7% 19% 13% 3	1584
February	1st to 10th	Day	61% 4 6% 17% 9% 3	1560
	11th to 20th	Day	58% 5% 10% 14% 12% 1	1664
	21st to end	Day	61% 4 6% 17% 10% 3	1480
March	1st to 10th	Day	58% 4 7% 16% 12% 3	1800
	11th to 20th	Day	53% 4 11% 14% 14% 3	1861
	21st to end	Day	51% 5% 9% 17% 14% 4	2376
April	1st to 10th	Day	56% 3 10% 16% 12% 3	2160
	11th to 20th	Day	50% 3 10% 21% 13% 2	2134
	21st to end	Day	55% 5% 7% 18% 12% 3	2318
May	1st to 10th	Day	51% 5% 8% 20% 13% 3	2504
	11th to 20th	Day	50% 4 9% 18% 17% 3	2482
	21st to end	Day	49% 6% 11% 18% 14% 2	2725
June	1st to 10th	Day	52% 7% 10% 18% 10% 2	2520
	11th to 20th	Day	46% 6% 11% 21% 12% 3	2520
	21st to end	Day	56% 8% 10% 17% 9% 1	2520
July	1st to 10th	Day	42% 8% 13% 25% 11%	2450
	11th to 20th	Day	44% 9% 13% 24% 10%	2445
	21st to end	Day	45% 8% 14% 22% 9%	2591
August	1st to 10th	Day	46% 10% 17% 21% 6%	2492
	11th to 20th	Day	42% 10% 15% 23% 9%	2321
	21st to end	Day	39% 7% 16% 25% 13% 1	2376
September	1st to 10th	Day	40% 7% 14% 26% 14%	2160
	11th to 20th	Day	37% 6% 13% 30% 13% 1	2085
	21st to end	Day	44% 6% 13% 25% 12%	1980
October	1st to 10th	Day	49% 6% 10% 22% 12% 1	1854
	11th to 20th	Day	57% 6% 12% 19% 6%	1751
	21st to end	Day	58% 4 11% 16% 9% 1	1782
November	1st to 10th	Day	49% 5% 14% 21% 10% 1	1671
	11th to 20th	Day	55% 5% 12% 16% 11% 1	1611
	21st to end	Day	58% 6% 12% 15% 7% 1	1520
December	1st to 10th	Day	64% 4 10% 15% 7%	1520
	11th to 20th	Day	59% 4 10% 17% 9%	1906
	21st to end	Day	64% 4 10% 14% 8%	2772
January	1st to 10th	Night	61% 5% 10% 16% 8% 1	2649
	11th to 20th	Night	59% 6% 10% 14% 9% 2	2602
	21st to end	Night	51% 5% 10% 17% 15% 2	2772
February	1st to 10th	Night	58% 5% 7% 19% 9% 1	2398
	11th to 20th	Night	54% 5% 10% 19% 12% 1	2192
	21st to end	Night	53% 5% 7% 19% 14% 2	1776
March	1st to 10th	Night	56% 4 9% 17% 12% 2	2160
	11th to 20th	Night	54% 5% 9% 15% 15% 3	2098
	21st to end	Night	47% 5% 8% 20% 15% 4	1980
April	1st to 10th	Night	54% 4 9% 16% 15% 2	1800
	11th to 20th	Night	44% 6% 9% 23% 15% 3	1775
	21st to end	Night	50% 6% 9% 19% 14% 3	1640
May	1st to 10th	Night	50% 4 8% 18% 15% 5%	1472
	11th to 20th	Night	45% 5% 10% 19% 17% 4	1416
	21st to end	Night	45% 6% 11% 21% 15% 2	1551
June	1st to 10th	Night	47% 8% 12% 21% 12% 1	1440
	11th to 20th	Night	46% 6% 11% 21% 13% 3	1440
	21st to end	Night	47% 6% 13% 20% 13%	1440
July	1st to 10th	Night	36% 8% 15% 27% 13% 1	1400
	11th to 20th	Night	38% 9% 14% 28% 11% 1	1392
	21st to end	Night	36% 8% 18% 26% 12%	1486
August	1st to 10th	Night	37% 9% 18% 27% 9%	1422
	11th to 20th	Night	38% 8% 18% 26% 12%	1560
	21st to end	Night	37% 7% 14% 29% 13%	1980
September	1st to 10th	Night	35% 7% 15% 28% 15%	1800
	11th to 20th	Night	34% 6% 15% 33% 11% 1	1874
	21st to end	Night	39% 6% 11% 32% 13%	1980
October	1st to 10th	Night	46% 6% 9% 25% 14% 1	2102
	11th to 20th	Night	48% 6% 14% 23% 9%	2209
	21st to end	Night	54% 6% 12% 18% 10% 1	2574
November	1st to 10th	Night	48% 5% 14% 22% 9% 1	2407
	11th to 20th	Night	51% 6% 12% 18% 11% 1	2568
	21st to end	Night	56% 5% 11% 19% 9% 1	2660
December	1st to 10th	Night	61% 6% 11% 16% 5%	2660
	11th to 20th	Night	59% 4 8% 18% 9% 1	3288
	21st to end	Night	64% 4 8% 17% 7% 1	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	23% 16% 34% 23% 3 1	180
	11th to 20th	Day	29% 10% 37% 17% 5% 1	172
	21st to end	Day	18% 20% 36% 18% 6% 1	176
February	1st to 10th	Day	36% 20% 34% 7% 3	214
	11th to 20th	Day	24% 21% 41% 11% 2	322
	21st to end	Day	29% 18% 32% 16% 4	346
March	1st to 10th	Day	26% 18% 36% 16% 3 1	420
	11th to 20th	Day	26% 20% 33% 18% 3 1	420
	21st to end	Day	31% 19% 26% 16% 6% 2	462
April	1st to 10th	Day	33% 14% 30% 16% 7% 1	420
	11th to 20th	Day	32% 18% 26% 15% 8% 1	412
	21st to end	Day	32% 13% 36% 12% 6% 1	420
May	1st to 10th	Day	29% 17% 36% 14% 3 2	423
	11th to 20th	Day	25% 17% 35% 15% 6% 2	447
	21st to end	Day	23% 19% 35% 16% 5% 2	485
June	1st to 10th	Day	24% 13% 36% 18% 7% 1	450
	11th to 20th	Day	21% 17% 32% 19% 9% 2	450
	21st to end	Day	26% 11% 30% 22% 8% 2	450
July	1st to 10th	Day	15% 8% 36% 28% 9% 4	445
	11th to 20th	Day	16% 7% 39% 27% 9% 1	444
	21st to end	Day	15% 7% 34% 29% 12% 4	488
August	1st to 10th	Day	15% 9% 28% 34% 14% 1	446
	11th to 20th	Day	13% 8% 28% 31% 13% 7%	439
	21st to end	Day	16% 13% 28% 24% 13% 5%	495
September	1st to 10th	Day	17% 10% 33% 24% 10% 6%	450
	11th to 20th	Day	16% 10% 30% 26% 11% 7%	450
	21st to end	Day	21% 14% 26% 22% 12% 5%	450
October	1st to 10th	Day	28% 14% 24% 21% 10% 2	450
	11th to 20th	Day	27% 17% 28% 18% 8% 2	426
	21st to end	Day	34% 14% 27% 20% 5%	396
November	1st to 10th	Day	28% 15% 30% 20% 7% 1	365
	11th to 20th	Day	28% 15% 34% 14% 7%	271
	21st to end	Day	31% 19% 30% 16% 3 1	180
December	1st to 10th	Day	31% 12% 33% 16% 7% 2	180
	11th to 20th	Day	29% 17% 34% 16% 4 1	180
	21st to end	Day	32% 20% 27% 15% 5% 1	198
January	1st to 10th	Night	26% 12% 33% 23% 5%	760
	11th to 20th	Night	24% 15% 31% 25% 6%	744
	21st to end	Night	16% 14% 35% 28% 6%	792
February	1st to 10th	Night	19% 13% 40% 22% 5% 1	720
	11th to 20th	Night	19% 18% 35% 23% 4 1	703
	21st to end	Night	21% 17% 32% 26% 4	592
March	1st to 10th	Night	26% 15% 34% 21% 4	720
	11th to 20th	Night	26% 17% 30% 20% 6% 1	720
	21st to end	Night	22% 14% 32% 24% 7% 1	792
April	1st to 10th	Night	29% 13% 29% 23% 5%	720
	11th to 20th	Night	25% 13% 32% 24% 6% 1	711
	21st to end	Night	27% 14% 30% 22% 6% 1	560
May	1st to 10th	Night	26% 15% 29% 22% 7% 1	392
	11th to 20th	Night	24% 11% 30% 27% 8%	354
	21st to end	Night	22% 11% 34% 24% 9%	389
June	1st to 10th	Night	24% 8% 29% 31% 8%	360
	11th to 20th	Night	24% 7% 24% 33% 12% 1	360
	21st to end	Night	19% 6% 25% 36% 13% 1	360
July	1st to 10th	Night	13% 7% 29% 37% 13% 1	350
	11th to 20th	Night	11% 5% 25% 44% 14% 1	348
	21st to end	Night	14% 5% 23% 42% 15% 1	394
August	1st to 10th	Night	13% 4 18% 47% 17% 1	358
	11th to 20th	Night	15% 3 23% 38% 18% 3	496
	21st to end	Night	16% 6% 26% 30% 19% 3	792
September	1st to 10th	Night	14% 6% 30% 34% 15% 1	720
	11th to 20th	Night	17% 6% 25% 31% 19% 1	720
	21st to end	Night	21% 8% 25% 29% 15% 2	720
October	1st to 10th	Night	22% 11% 27% 27% 12% 1	720
	11th to 20th	Night	27% 12% 26% 24% 10% 1	720
	21st to end	Night	30% 10% 29% 24% 7%	792
November	1st to 10th	Night	24% 14% 27% 26% 9% 1	740
	11th to 20th	Night	25% 13% 31% 21% 10% 1	760
	21st to end	Night	27% 18% 24% 23% 6% 1	760
December	1st to 10th	Night	27% 12% 30% 24% 6%	760
	11th to 20th	Night	28% 14% 29% 23% 5% 1	760
	21st to end	Night	32% 13% 31% 20% 4	836

Page generated at 2024-01-13 19:28:30. Version ac07

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