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 2024-10-25.

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	17% 11% 4 9% 5% 5% 4 4 5% 6% 31%	101494
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 30%	97290
Transparency	Day	53% 5% 12% 21% 9% 1	101252
	Night	55% 4 11% 19% 9% 1	97152
Seeing	Day	25% 13% 30% 20% 9% 3	14391
	Night	24% 11% 27% 26% 10% 1	23431

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% 19% 8% 16% 8% 4 4 2 3 3 17%	2517
	11th to 20th	Day	13% 14% 7% 18% 7% 5% 4 3 4 5% 20%	2520
	21st to end	Day	13% 19% 7% 15% 6% 6% 4 3 4 4 18%	2867
February	1st to 10th	Day	11% 18% 6% 14% 8% 5% 4 4 5% 5% 21%	1710
	11th to 20th	Day	12% 18% 6% 12% 6% 5% 3 3 4 5% 27%	1663
	21st to end	Day	17% 17% 5% 9% 7% 4 4 3 3 4 26%	1556
March	1st to 10th	Day	17% 17% 4 9% 6% 4 4 3 3 5% 26%	3116
	11th to 20th	Day	12% 19% 6% 11% 6% 4 4 3 4 5% 26%	3480
	21st to end	Day	12% 8% 3 8% 6% 4 4 3 5% 6% 40%	4024
April	1st to 10th	Day	23% 14% 3 7% 5% 4 3 2 4 5% 30%	2280
	11th to 20th	Day	22% 10% 4 7% 4 3 3 3 4 5% 34%	2254
	21st to end	Day	22% 12% 3 7% 5% 4 4 3 4 4 31%	2451
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 3 6% 7% 30%	4426
	11th to 20th	Day	17% 8% 3 8% 5% 4 4 4 5% 7% 35%	4398
	21st to end	Day	17% 7% 2 7% 5% 5% 5% 4 6% 6% 36%	4837
June	1st to 10th	Day	22% 9% 3 7% 5% 5% 5% 4 6% 6% 29%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 4 6% 8% 38%	2660
	21st to end	Day	19% 7% 4 7% 6% 5% 5% 4 6% 7% 31%	2660
July	1st to 10th	Day	13% 7% 3 7% 6% 5% 5% 4 8% 9% 32%	4440
	11th to 20th	Day	14% 7% 3 7% 5% 4 5% 5% 6% 8% 37%	4440
	21st to end	Day	11% 7% 2 6% 4 4 4 3 6% 8% 45%	4814
August	1st to 10th	Day	14% 7% 2 8% 6% 6% 6% 4 7% 8% 32%	4376
	11th to 20th	Day	17% 7% 3 7% 4 6% 5% 4 5% 7% 36%	4022
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	4180
September	1st to 10th	Day	16% 6% 2 6% 5% 4 4 3 6% 7% 42%	2280
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 5% 6% 44%	2280
	21st to end	Day	21% 7% 2 6% 4 4 4 4 6% 7% 37%	2024
October	1st to 10th	Day	21% 10% 2 7% 4 4 4 4 6% 6% 34%	1900
	11th to 20th	Day	24% 12% 3 7% 5% 5% 4 3 4 6% 27%	1900
	21st to end	Day	26% 12% 2 8% 5% 4 5% 3 5% 6% 24%	1873
November	1st to 10th	Day	16% 12% 3 7% 5% 5% 3 4 5% 7% 32%	1648
	11th to 20th	Day	18% 17% 4 10% 5% 5% 4 4 5% 5% 22%	1520
	21st to end	Day	22% 17% 5% 13% 5% 4 4 3 3 5% 18%	1520
December	1st to 10th	Day	22% 20% 5% 12% 6% 5% 3 3 4 5% 15%	1520
	11th to 20th	Day	19% 16% 7% 11% 5% 4 5% 3 5% 5% 19%	1906
	21st to end	Day	26% 21% 6% 13% 4 3 3 2 2 3 18%	2772
January	1st to 10th	Night	17% 19% 7% 12% 6% 4 4 2 4 4 21%	4429
	11th to 20th	Night	13% 14% 6% 15% 7% 5% 5% 3 5% 5% 22%	4440
	21st to end	Night	14% 18% 8% 13% 6% 7% 4 3 4 4 19%	4788
February	1st to 10th	Night	12% 16% 6% 13% 8% 6% 4 3 4 4 23%	2470
	11th to 20th	Night	13% 16% 5% 13% 7% 5% 6% 3 4 5% 25%	2403
	21st to end	Night	13% 16% 5% 11% 6% 5% 4 3 5% 6% 27%	1896
March	1st to 10th	Night	20% 15% 3 8% 5% 4 3 3 3 5% 30%	3707
	11th to 20th	Night	16% 19% 5% 10% 5% 4 4 3 4 5% 24%	3479
	21st to end	Night	13% 9% 4 10% 5% 4 3 3 4 6% 39%	3607
April	1st to 10th	Night	21% 12% 3 8% 5% 4 4 3 5% 5% 30%	1900
	11th to 20th	Night	19% 10% 3 7% 4 3 4 3 6% 5% 36%	1875
	21st to end	Night	22% 11% 3 8% 3 4 4 2 4 4 34%	1745
May	1st to 10th	Night	20% 10% 4 8% 5% 4 5% 4 5% 6% 29%	2514
	11th to 20th	Night	17% 9% 3 7% 4 5% 4 4 5% 7% 36%	2495
	21st to end	Night	15% 8% 3 6% 5% 5% 5% 4 5% 7% 36%	2738
June	1st to 10th	Night	17% 8% 3 6% 5% 5% 5% 4 6% 9% 33%	1520
	11th to 20th	Night	16% 6% 3 6% 5% 4 4 4 5% 7% 41%	1520
	21st to end	Night	18% 7% 2 6% 5% 5% 4 4 6% 8% 34%	1520
July	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 5% 6% 8% 35%	2520
	11th to 20th	Night	14% 7% 2 7% 4 4 5% 3 6% 8% 39%	2520
	21st to end	Night	8% 6% 2 6% 4 4 5% 5% 7% 8% 45%	2739
August	1st to 10th	Night	12% 7% 3 8% 5% 5% 5% 4 7% 7% 37%	2537
	11th to 20th	Night	16% 7% 3 7% 4 5% 4 3 6% 7% 39%	2785
	21st to end	Night	16% 6% 3 7% 5% 4 5% 4 6% 7% 39%	3465
September	1st to 10th	Night	13% 5% 3 7% 4 4 4 3 5% 6% 45%	1900
	11th to 20th	Night	16% 5% 2 4 4 3 3 3 5% 8% 46%	1900
	21st to end	Night	18% 8% 3 6% 3 3 4 3 4 6% 41%	2152
October	1st to 10th	Night	20% 8% 2 6% 4 4 5% 3 5% 5% 38%	2280
	11th to 20th	Night	22% 11% 3 8% 5% 4 4 3 4 6% 30%	2280
	21st to end	Night	24% 11% 3 8% 5% 4 5% 3 5% 6% 26%	2588
November	1st to 10th	Night	18% 12% 4 9% 5% 4 4 3 5% 5% 31%	2426
	11th to 20th	Night	19% 13% 5% 10% 6% 5% 5% 3 4 5% 26%	2660
	21st to end	Night	23% 17% 4 10% 6% 4 4 4 5% 5% 19%	2660
December	1st to 10th	Night	21% 21% 6% 12% 6% 4 4 3 4 4 17%	2660
	11th to 20th	Night	21% 17% 5% 10% 5% 3 3 2 3 5% 24%	3288
	21st to end	Night	25% 22% 6% 11% 5% 3 2 2 3 4 16%	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	62% 2 9% 15% 10% 1	1556
March	1st to 10th	Day	62% 4 8% 16% 10% 1	3119
	11th to 20th	Day	62% 3 9% 15% 8% 2	3480
	21st to end	Day	45% 4 8% 24% 17% 2	4024
April	1st to 10th	Day	58% 4 6% 19% 11% 3	2280
	11th to 20th	Day	54% 3 6% 22% 13% 2	2254
	21st to end	Day	57% 3 7% 16% 12% 4	2451
May	1st to 10th	Day	52% 5% 9% 23% 10% 2	4440
	11th to 20th	Day	48% 5% 15% 21% 10% 1	4402
	21st to end	Day	48% 5% 11% 20% 15% 2	4837
June	1st to 10th	Day	55% 4 10% 20% 11% 1	2660
	11th to 20th	Day	43% 5% 11% 27% 11% 2	2660
	21st to end	Day	51% 5% 14% 20% 10%	2660
July	1st to 10th	Day	45% 7% 14% 26% 8%	4370
	11th to 20th	Day	42% 6% 16% 28% 7%	4365
	21st to end	Day	37% 5% 15% 33% 10%	4661
August	1st to 10th	Day	48% 6% 16% 23% 7%	4362
	11th to 20th	Day	45% 6% 15% 27% 6% 1	4061
	21st to end	Day	39% 7% 16% 24% 12% 1	4180
September	1st to 10th	Day	42% 4 14% 29% 12%	2280
	11th to 20th	Day	40% 4 14% 30% 12% 1	2280
	21st to end	Day	45% 6% 14% 25% 9%	2024
October	1st to 10th	Day	51% 5% 12% 23% 9% 1	1900
	11th to 20th	Day	60% 5% 13% 17% 5% 1	1900
	21st to end	Day	62% 4 12% 15% 6% 1	1873
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 9% 19% 10% 1	1896
March	1st to 10th	Night	58% 3 11% 17% 9% 2	3717
	11th to 20th	Night	61% 5% 10% 14% 7% 1	3480
	21st to end	Night	47% 4 8% 22% 15% 4	3607
April	1st to 10th	Night	56% 3 8% 18% 13% 2	1900
	11th to 20th	Night	49% 3 7% 25% 14% 2	1875
	21st to end	Night	54% 3 7% 18% 15% 3	1745
May	1st to 10th	Night	54% 5% 9% 20% 9% 2	2520
	11th to 20th	Night	47% 5% 13% 22% 11% 2	2496
	21st to end	Night	47% 5% 11% 22% 14% 2	2739
June	1st to 10th	Night	47% 7% 13% 22% 10% 1	1520
	11th to 20th	Night	43% 5% 11% 27% 12% 2	1520
	21st to end	Night	47% 5% 13% 22% 11%	1520
July	1st to 10th	Night	45% 7% 16% 20% 11% 1	2480
	11th to 20th	Night	42% 7% 16% 27% 8%	2472
	21st to end	Night	34% 7% 16% 32% 11%	2651
August	1st to 10th	Night	44% 7% 14% 27% 8%	2527
	11th to 20th	Night	43% 6% 17% 28% 7%	2812
	21st to end	Night	43% 6% 15% 24% 11% 2	3465
September	1st to 10th	Night	40% 5% 13% 29% 13%	1900
	11th to 20th	Night	36% 5% 15% 34% 9%	1900
	21st to end	Night	43% 5% 13% 29% 10%	2152
October	1st to 10th	Night	47% 6% 10% 25% 11%	2280
	11th to 20th	Night	56% 5% 11% 20% 7% 1	2280
	21st to end	Night	59% 4 13% 17% 6%	2588
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% 14% 2 1	368
March	1st to 10th	Day	26% 17% 34% 17% 6%	460
	11th to 20th	Day	27% 17% 33% 18% 4 1	460
	21st to end	Day	31% 17% 29% 17% 5% 1	506
April	1st to 10th	Day	32% 17% 27% 17% 6% 1	460
	11th to 20th	Day	36% 15% 22% 13% 10% 2	452
	21st to end	Day	33% 15% 31% 14% 6% 1	460
May	1st to 10th	Day	30% 12% 31% 17% 8% 3	463
	11th to 20th	Day	22% 16% 31% 21% 7% 3	487
	21st to end	Day	24% 14% 32% 19% 10% 2	529
June	1st to 10th	Day	25% 12% 32% 22% 7% 2	490
	11th to 20th	Day	18% 15% 30% 21% 12% 3	490
	21st to end	Day	22% 12% 30% 22% 10% 2	490
July	1st to 10th	Day	15% 7% 31% 34% 10% 3	485
	11th to 20th	Day	15% 9% 34% 25% 14% 3	484
	21st to end	Day	15% 7% 32% 29% 14% 3	532
August	1st to 10th	Day	18% 6% 28% 31% 15% 3	486
	11th to 20th	Day	20% 5% 22% 28% 16% 8%	479
	21st to end	Day	17% 10% 30% 22% 14% 7%	539
September	1st to 10th	Day	18% 10% 30% 22% 12% 8%	490
	11th to 20th	Day	16% 10% 23% 22% 19% 10%	490
	21st to end	Day	23% 11% 26% 18% 14% 8%	490
October	1st to 10th	Day	27% 14% 23% 21% 12% 3	490
	11th to 20th	Day	31% 17% 30% 14% 7% 1	490
	21st to end	Day	34% 12% 30% 19% 6%	436
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% 29% 25% 5%	628
March	1st to 10th	Night	26% 15% 29% 24% 5%	760
	11th to 20th	Night	26% 13% 31% 24% 6%	760
	21st to end	Night	22% 15% 29% 24% 9%	836
April	1st to 10th	Night	28% 14% 24% 26% 7%	760
	11th to 20th	Night	27% 13% 28% 22% 9% 1	751
	21st to end	Night	29% 11% 26% 25% 9%	605
May	1st to 10th	Night	24% 8% 29% 28% 9% 1	380
	11th to 20th	Night	24% 8% 27% 32% 9%	374
	21st to end	Night	16% 10% 34% 30% 10%	411
June	1st to 10th	Night	19% 8% 32% 32% 8% 1	380
	11th to 20th	Night	19% 8% 23% 36% 13% 1	380
	21st to end	Night	22% 4 23% 37% 14% 1	380
July	1st to 10th	Night	11% 4 27% 42% 16%	370
	11th to 20th	Night	15% 4 20% 42% 18% 1	368
	21st to end	Night	11% 4 24% 43% 17% 2	416
August	1st to 10th	Night	11% 4 21% 38% 25% 1	396
	11th to 20th	Night	15% 3 16% 37% 26% 3	564
	21st to end	Night	17% 5% 24% 32% 20% 2	825
September	1st to 10th	Night	18% 5% 25% 32% 18% 1	760
	11th to 20th	Night	19% 4 21% 30% 22% 4	760
	21st to end	Night	22% 8% 22% 27% 19% 2	760
October	1st to 10th	Night	26% 10% 25% 25% 14% 1	760
	11th to 20th	Night	30% 9% 27% 24% 8% 1	760
	21st to end	Night	31% 10% 26% 24% 7%	812
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 2024-10-22 20:21:05. Version ac07

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