Lac Heney
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Heney clear sky chart from 2005-11-06 to 2024-02-25.

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% 11% 4 8% 6% 3 4 4 5% 6% 30%	78242
	Night	17% 12% 5% 8% 6% 3 4 4 5% 6% 30%	81051
Transparency	Day	55% 4 11% 20% 9% 1	77947
	Night	56% 4 11% 19% 9% 1	80880
Seeing	Day	25% 13% 30% 20% 9% 3	13418
	Night	24% 11% 27% 26% 10% 1	22680

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	17% 18% 8% 14% 10% 3 4 3 3 3 17%	2517
	11th to 20th	Day	14% 14% 7% 15% 9% 4 4 4 4 5% 20%	2520
	21st to end	Day	13% 18% 7% 13% 8% 5% 5% 4 4 4 18%	2867
February	1st to 10th	Day	12% 17% 6% 12% 9% 3 5% 4 5% 6% 21%	1710
	11th to 20th	Day	12% 16% 7% 11% 7% 3 4 4 4 5% 27%	1663
	21st to end	Day	18% 15% 7% 7% 8% 3 4 4 3 4 26%	1506
March	1st to 10th	Day	15% 14% 5% 9% 8% 4 4 5% 3 5% 27%	1797
	11th to 20th	Day	15% 14% 5% 9% 8% 3 5% 4 4 5% 28%	1980
	21st to end	Day	18% 9% 4 6% 6% 3 4 4 4 6% 36%	2290
April	1st to 10th	Day	24% 13% 3 7% 6% 3 3 3 4 4 30%	2160
	11th to 20th	Day	22% 10% 4 7% 5% 3 3 3 4 5% 35%	2134
	21st to end	Day	23% 11% 3 7% 5% 3 4 4 5% 4 31%	2321
May	1st to 10th	Day	22% 8% 3 6% 5% 3 4 4 4 6% 34%	2520
	11th to 20th	Day	19% 8% 3 7% 5% 3 4 5% 4 6% 37%	2478
	21st to end	Day	17% 6% 3 6% 6% 3 5% 4 5% 6% 37%	2725
June	1st to 10th	Day	22% 8% 3 7% 6% 4 5% 5% 6% 6% 29%	2520
	11th to 20th	Day	16% 5% 2 5% 5% 3 5% 5% 6% 9% 39%	2520
	21st to end	Day	18% 6% 4 6% 7% 4 5% 5% 6% 7% 31%	2520
July	1st to 10th	Day	14% 5% 3 6% 6% 4 5% 5% 7% 9% 36%	2520
	11th to 20th	Day	14% 6% 3 5% 6% 3 6% 6% 6% 9% 36%	2520
	21st to end	Day	12% 6% 2 7% 6% 4 6% 6% 7% 9% 36%	2744
August	1st to 10th	Day	14% 6% 2 6% 7% 4 6% 5% 6% 8% 35%	2487
	11th to 20th	Day	15% 6% 3 6% 5% 4 5% 5% 4 7% 39%	2295
	21st to end	Day	15% 7% 2 5% 5% 3 6% 5% 6% 8% 38%	2376
September	1st to 10th	Day	16% 6% 2 6% 5% 3 4 4 6% 7% 42%	2160
	11th to 20th	Day	16% 6% 2 6% 5% 3 4 4 5% 6% 43%	2160
	21st to end	Day	21% 6% 2 5% 5% 3 4 5% 6% 8% 36%	1918
October	1st to 10th	Day	21% 9% 2 6% 5% 3 4 5% 5% 6% 34%	1800
	11th to 20th	Day	25% 11% 4 6% 7% 4 4 4 4 6% 26%	1800
	21st to end	Day	28% 11% 2 7% 6% 3 5% 4 5% 6% 24%	1828
November	1st to 10th	Day	16% 11% 4 6% 6% 4 4 5% 5% 8% 32%	1648
	11th to 20th	Day	19% 15% 5% 8% 7% 4 4 5% 5% 5% 22%	1520
	21st to end	Day	23% 16% 6% 11% 6% 3 5% 4 3 5% 18%	1520
December	1st to 10th	Day	23% 18% 6% 11% 7% 4 3 4 4 5% 15%	1520
	11th to 20th	Day	20% 15% 7% 10% 6% 3 5% 5% 5% 5% 19%	1906
	21st to end	Day	26% 20% 6% 11% 6% 2 3 2 2 3 18%	2772
January	1st to 10th	Night	17% 18% 7% 11% 8% 3 4 3 4 4 21%	4429
	11th to 20th	Night	13% 14% 6% 13% 9% 4 5% 4 5% 5% 22%	4440
	21st to end	Night	14% 18% 8% 11% 8% 5% 5% 4 4 4 19%	4788
February	1st to 10th	Night	12% 14% 7% 12% 9% 4 5% 4 4 4 23%	2470
	11th to 20th	Night	13% 14% 6% 11% 8% 4 6% 5% 4 5% 25%	2403
	21st to end	Night	13% 15% 6% 10% 7% 4 5% 4 5% 5% 28%	1843
March	1st to 10th	Night	17% 15% 5% 8% 8% 3 5% 4 4 5% 27%	2147
	11th to 20th	Night	16% 15% 5% 8% 6% 3 4 4 4 5% 31%	1979
	21st to end	Night	16% 10% 5% 6% 6% 3 3 4 4 4 40%	2065
April	1st to 10th	Night	22% 10% 4 7% 5% 3 4 4 5% 6% 30%	1800
	11th to 20th	Night	19% 9% 3 6% 5% 2 4 4 5% 6% 37%	1775
	21st to end	Night	22% 10% 4 7% 5% 3 5% 3 4 4 33%	1654
May	1st to 10th	Night	21% 8% 3 6% 5% 2 3 4 5% 6% 36%	1440
	11th to 20th	Night	19% 7% 3 6% 4 3 4 4 4 7% 38%	1415
	21st to end	Night	13% 6% 3 5% 6% 3 6% 4 5% 7% 42%	1550
June	1st to 10th	Night	18% 7% 3 5% 6% 3 5% 5% 6% 9% 33%	1440
	11th to 20th	Night	16% 6% 3 5% 6% 3 4 5% 5% 7% 41%	1440
	21st to end	Night	17% 7% 2 5% 5% 3 5% 4 6% 8% 36%	1440
July	1st to 10th	Night	11% 5% 2 4 5% 3 4 6% 6% 9% 44%	1440
	11th to 20th	Night	14% 6% 1 5% 4 3 6% 4 6% 8% 43%	1440
	21st to end	Night	9% 5% 2 5% 5% 3 6% 6% 7% 10% 42%	1574
August	1st to 10th	Night	11% 5% 3 6% 6% 4 5% 6% 7% 8% 40%	1449
	11th to 20th	Night	11% 6% 2 5% 6% 4 5% 5% 6% 7% 45%	1598
	21st to end	Night	14% 5% 2 5% 5% 3 4 5% 6% 7% 43%	1969
September	1st to 10th	Night	13% 5% 3 6% 5% 3 4 4 5% 6% 45%	1800
	11th to 20th	Night	17% 5% 2 4 5% 2 4 4 4 8% 45%	1800
	21st to end	Night	19% 7% 3 5% 4 3 4 4 4 7% 41%	2038
October	1st to 10th	Night	21% 8% 2 5% 5% 3 4 4 4 6% 37%	2160
	11th to 20th	Night	23% 10% 4 7% 6% 3 4 4 4 6% 29%	2160
	21st to end	Night	24% 10% 4 7% 6% 3 4 4 5% 6% 26%	2527
November	1st to 10th	Night	18% 11% 4 8% 7% 3 4 4 5% 5% 31%	2426
	11th to 20th	Night	19% 12% 5% 8% 8% 4 5% 4 4 5% 26%	2660
	21st to end	Night	23% 16% 5% 9% 6% 3 4 4 5% 5% 19%	2660
December	1st to 10th	Night	21% 19% 6% 10% 7% 3 4 4 4 4 17%	2660
	11th to 20th	Night	22% 16% 6% 9% 6% 2 3 3 3 5% 24%	3288
	21st to end	Night	25% 22% 6% 10% 6% 3 3 3 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	73% 4 9% 10% 5%	2518
	11th to 20th	Day	68% 3 9% 13% 6%	2520
	21st to end	Day	71% 3 9% 10% 6% 1	2867
February	1st to 10th	Day	65% 4 8% 16% 5% 1	1710
	11th to 20th	Day	62% 2 11% 14% 9% 1	1672
	21st to end	Day	63% 2 8% 15% 10% 1	1506
March	1st to 10th	Day	60% 4 8% 17% 10% 1	1800
	11th to 20th	Day	59% 3 9% 16% 10% 3	1980
	21st to end	Day	51% 3 8% 20% 13% 4	2290
April	1st to 10th	Day	59% 3 6% 18% 11% 3	2160
	11th to 20th	Day	53% 3 6% 22% 13% 2	2134
	21st to end	Day	57% 3 8% 16% 12% 4	2321
May	1st to 10th	Day	52% 4 7% 21% 13% 3	2520
	11th to 20th	Day	49% 4 8% 20% 17% 3	2482
	21st to end	Day	48% 5% 11% 20% 14% 2	2725
June	1st to 10th	Day	54% 4 10% 20% 11% 1	2520
	11th to 20th	Day	43% 5% 11% 28% 11% 2	2520
	21st to end	Day	51% 5% 14% 20% 10% 1	2520
July	1st to 10th	Day	41% 6% 13% 27% 12%	2450
	11th to 20th	Day	43% 6% 14% 26% 11% 1	2445
	21st to end	Day	43% 6% 16% 26% 9%	2591
August	1st to 10th	Day	47% 6% 16% 23% 8%	2473
	11th to 20th	Day	44% 6% 16% 26% 8% 1	2295
	21st to end	Day	43% 6% 14% 25% 11% 1	2376
September	1st to 10th	Day	42% 4 14% 28% 12%	2160
	11th to 20th	Day	42% 4 13% 29% 11% 1	2160
	21st to end	Day	45% 6% 15% 26% 8%	1918
October	1st to 10th	Day	51% 5% 12% 23% 9% 1	1800
	11th to 20th	Day	61% 5% 13% 16% 4 1	1800
	21st to end	Day	62% 4 12% 15% 6% 1	1828
November	1st to 10th	Day	50% 5% 14% 23% 6% 1	1648
	11th to 20th	Day	64% 3 12% 13% 7%	1520
	21st to end	Day	70% 4 11% 9% 6%	1520
December	1st to 10th	Day	72% 4 10% 10% 3	1520
	11th to 20th	Day	66% 4 10% 14% 5%	1906
	21st to end	Day	74% 3 6% 15% 3	2772
January	1st to 10th	Night	68% 4 15% 10% 3	4429
	11th to 20th	Night	65% 4 14% 12% 5%	4440
	21st to end	Night	70% 4 9% 10% 7%	4788
February	1st to 10th	Night	64% 4 8% 16% 6% 1	2470
	11th to 20th	Night	63% 4 8% 18% 7% 1	2405
	21st to end	Night	58% 4 8% 19% 10% 1	1843
March	1st to 10th	Night	61% 3 8% 18% 9% 1	2157
	11th to 20th	Night	56% 4 9% 17% 11% 3	1980
	21st to end	Night	49% 4 8% 21% 14% 5%	2065
April	1st to 10th	Night	56% 3 8% 18% 14% 2	1800
	11th to 20th	Night	49% 3 7% 25% 15% 2	1775
	21st to end	Night	55% 3 6% 18% 15% 3	1654
May	1st to 10th	Night	50% 3 6% 21% 16% 4	1440
	11th to 20th	Night	47% 4 7% 21% 17% 4	1416
	21st to end	Night	42% 5% 13% 22% 16% 3	1551
June	1st to 10th	Night	46% 6% 14% 23% 9% 1	1440
	11th to 20th	Night	44% 5% 11% 26% 12% 2	1440
	21st to end	Night	46% 5% 14% 22% 12%	1440
July	1st to 10th	Night	35% 6% 15% 27% 16% 1	1400
	11th to 20th	Night	39% 6% 12% 29% 13%	1392
	21st to end	Night	36% 7% 19% 27% 11%	1486
August	1st to 10th	Night	40% 7% 18% 25% 10%	1439
	11th to 20th	Night	38% 6% 18% 27% 11%	1598
	21st to end	Night	40% 5% 17% 28% 9%	1969
September	1st to 10th	Night	41% 5% 13% 28% 13%	1800
	11th to 20th	Night	37% 5% 15% 34% 9% 1	1800
	21st to end	Night	43% 5% 13% 30% 9%	2038
October	1st to 10th	Night	48% 6% 10% 24% 11% 1	2160
	11th to 20th	Night	57% 4 11% 20% 7% 1	2160
	21st to end	Night	60% 4 12% 17% 6%	2527
November	1st to 10th	Night	55% 4 14% 19% 8%	2426
	11th to 20th	Night	62% 3 11% 15% 7% 1	2660
	21st to end	Night	68% 4 11% 14% 3	2660
December	1st to 10th	Night	71% 3 9% 13% 4	2660
	11th to 20th	Night	65% 3 9% 16% 7%	3288
	21st to end	Night	74% 3 6% 13% 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	27% 16% 34% 18% 4 1	180
	11th to 20th	Day	29% 13% 36% 14% 7% 1	180
	21st to end	Day	24% 14% 35% 20% 6% 1	225
February	1st to 10th	Day	30% 21% 34% 11% 3 1	270
	11th to 20th	Day	25% 27% 38% 10%	270
	21st to end	Day	30% 20% 33% 15% 2 1	348
March	1st to 10th	Day	26% 17% 34% 16% 6%	420
	11th to 20th	Day	27% 17% 32% 18% 4 1	420
	21st to end	Day	32% 16% 27% 17% 6% 1	462
April	1st to 10th	Day	31% 16% 28% 17% 6% 1	420
	11th to 20th	Day	35% 15% 22% 14% 11% 3	412
	21st to end	Day	33% 15% 31% 15% 6% 1	420
May	1st to 10th	Day	30% 13% 30% 16% 8% 3	423
	11th to 20th	Day	23% 17% 32% 19% 6% 3	447
	21st to end	Day	24% 14% 32% 19% 9% 2	485
June	1st to 10th	Day	24% 13% 33% 22% 6% 2	450
	11th to 20th	Day	19% 15% 29% 22% 12% 3	450
	21st to end	Day	20% 12% 30% 24% 11% 3	450
July	1st to 10th	Day	14% 5% 32% 36% 10% 3	445
	11th to 20th	Day	16% 8% 33% 25% 15% 3	444
	21st to end	Day	15% 7% 33% 29% 14% 2	488
August	1st to 10th	Day	18% 5% 28% 31% 15% 3	446
	11th to 20th	Day	20% 4 23% 29% 16% 8%	439
	21st to end	Day	18% 11% 29% 21% 14% 7%	495
September	1st to 10th	Day	18% 10% 30% 22% 13% 8%	450
	11th to 20th	Day	17% 10% 25% 22% 17% 8%	450
	21st to end	Day	23% 12% 26% 18% 13% 8%	450
October	1st to 10th	Day	27% 13% 24% 21% 12% 4	450
	11th to 20th	Day	32% 16% 30% 13% 7% 1	450
	21st to end	Day	34% 12% 29% 19% 6%	419
November	1st to 10th	Day	29% 14% 29% 22% 5% 1	342
	11th to 20th	Day	31% 17% 34% 11% 6% 2	180
	21st to end	Day	29% 20% 33% 14% 2 2	180
December	1st to 10th	Day	36% 7% 36% 16% 5%	180
	11th to 20th	Day	30% 24% 31% 12% 3 1	180
	21st to end	Day	28% 17% 34% 16% 4 1	198
January	1st to 10th	Night	29% 12% 33% 21% 5%	760
	11th to 20th	Night	30% 14% 26% 23% 7%	760
	21st to end	Night	20% 10% 33% 27% 9% 1	836
February	1st to 10th	Night	21% 15% 38% 23% 4 1	760
	11th to 20th	Night	23% 15% 36% 20% 5%	743
	21st to end	Night	23% 18% 28% 26% 4	611
March	1st to 10th	Night	26% 15% 29% 25% 5%	720
	11th to 20th	Night	26% 13% 31% 23% 6%	720
	21st to end	Night	23% 15% 28% 24% 10% 1	792
April	1st to 10th	Night	28% 14% 24% 27% 6%	720
	11th to 20th	Night	27% 13% 28% 22% 10% 1	711
	21st to end	Night	29% 12% 25% 25% 9%	574
May	1st to 10th	Night	25% 8% 30% 27% 9% 1	360
	11th to 20th	Night	24% 8% 28% 32% 8%	354
	21st to end	Night	15% 10% 34% 30% 11%	389
June	1st to 10th	Night	20% 8% 32% 32% 7% 1	360
	11th to 20th	Night	19% 8% 23% 36% 13% 1	360
	21st to end	Night	20% 4 24% 37% 15% 1	360
July	1st to 10th	Night	11% 4 27% 41% 17%	350
	11th to 20th	Night	15% 4 20% 43% 18% 1	348
	21st to end	Night	11% 4 25% 42% 16% 2	394
August	1st to 10th	Night	11% 4 21% 38% 25% 1	375
	11th to 20th	Night	14% 3 16% 38% 25% 4	534
	21st to end	Night	17% 5% 25% 32% 19% 3	781
September	1st to 10th	Night	17% 5% 25% 32% 19% 1	720
	11th to 20th	Night	20% 4 23% 31% 19% 3	720
	21st to end	Night	22% 8% 23% 27% 19% 2	720
October	1st to 10th	Night	27% 10% 24% 25% 13% 1	720
	11th to 20th	Night	31% 9% 28% 23% 8% 1	720
	21st to end	Night	32% 11% 26% 24% 7%	792
November	1st to 10th	Night	27% 13% 27% 24% 8% 1	740
	11th to 20th	Night	28% 15% 28% 19% 9% 1	760
	21st to end	Night	34% 14% 24% 22% 6%	760
December	1st to 10th	Night	32% 14% 28% 21% 4 1	760
	11th to 20th	Night	29% 16% 28% 20% 6% 1	760
	21st to end	Night	34% 13% 28% 20% 4 1	836

Page generated at 2024-02-22 06:05:48. Version ac07

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