Lake Ariel
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Ariel clear sky chart from 2005-11-06 to 2026-03-03.

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% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	131202
	Night	15% 9% 3 8% 5% 4 5% 4 5% 7% 35%	129955
Transparency	Day	48% 5% 12% 21% 12% 2	134718
	Night	47% 5% 13% 21% 13% 2	134526
Seeing	Day	25% 19% 28% 18% 8% 3	16447
	Night	22% 18% 28% 23% 8% 1	25791

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	11% 13% 7% 16% 7% 5% 5% 3 5% 5% 23%	4661
	11th to 20th	Day	12% 13% 5% 15% 6% 5% 4 3 4 6% 27%	4650
	21st to end	Day	14% 10% 5% 8% 6% 5% 5% 4 6% 6% 32%	5757
February	1st to 10th	Day	14% 11% 4 10% 6% 5% 6% 5% 5% 5% 29%	1890
	11th to 20th	Day	13% 11% 6% 9% 6% 5% 5% 4 6% 7% 30%	1957
	21st to end	Day	18% 12% 3 8% 6% 4 4 3 5% 5% 30%	1730
March	1st to 10th	Day	20% 11% 4 7% 6% 4 4 3 4 5% 33%	4496
	11th to 20th	Day	13% 9% 4 7% 5% 4 4 3 5% 6% 39%	4979
	21st to end	Day	17% 8% 2 6% 5% 5% 5% 4 5% 6% 35%	5782
April	1st to 10th	Day	17% 12% 3 7% 5% 5% 4 4 5% 5% 33%	2400
	11th to 20th	Day	16% 11% 3 7% 5% 4 4 4 5% 6% 36%	2374
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 6% 6% 36%	2400
May	1st to 10th	Day	29% 8% 2 6% 5% 5% 5% 3 5% 7% 26%	6060
	11th to 20th	Day	22% 8% 3 7% 5% 5% 5% 5% 6% 7% 29%	6318
	21st to end	Day	20% 7% 2 6% 4 5% 5% 5% 7% 8% 30%	6949
June	1st to 10th	Day	15% 7% 2 7% 5% 5% 6% 4 6% 9% 34%	2800
	11th to 20th	Day	16% 8% 3 7% 5% 5% 6% 5% 6% 9% 32%	2800
	21st to end	Day	13% 7% 3 7% 5% 5% 6% 5% 7% 9% 36%	2800
July	1st to 10th	Day	9% 6% 2 8% 7% 6% 6% 5% 8% 9% 36%	6360
	11th to 20th	Day	9% 6% 2 8% 6% 6% 6% 5% 8% 11% 31%	6360
	21st to end	Day	13% 6% 3 7% 4 5% 5% 5% 5% 9% 39%	6926
August	1st to 10th	Day	22% 6% 3 7% 5% 5% 5% 3 7% 7% 30%	4246
	11th to 20th	Day	15% 6% 2 7% 4 5% 6% 5% 6% 8% 36%	3923
	21st to end	Day	16% 5% 2 5% 4 4 4 4 6% 8% 42%	4312
September	1st to 10th	Day	16% 6% 2 7% 4 5% 5% 4 6% 6% 40%	2400
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 8% 46%	2376
	21st to end	Day	18% 8% 2 6% 5% 4 5% 4 7% 7% 35%	2182
October	1st to 10th	Day	16% 8% 3 6% 4 4 4 3 5% 8% 39%	2000
	11th to 20th	Day	14% 9% 2 7% 5% 4 6% 4 6% 7% 38%	2000
	21st to end	Day	18% 11% 2 7% 4 4 5% 4 5% 7% 33%	2104
November	1st to 10th	Day	12% 9% 3 7% 4 3 4 4 5% 6% 43%	1851
	11th to 20th	Day	13% 10% 4 7% 6% 6% 4 4 6% 5% 35%	1885
	21st to end	Day	17% 11% 3 7% 6% 5% 5% 4 6% 7% 30%	1680
December	1st to 10th	Day	13% 11% 5% 9% 5% 5% 5% 5% 6% 7% 28%	2680
	11th to 20th	Day	20% 12% 5% 8% 4 4 4 3 5% 5% 31%	3066
	21st to end	Day	16% 13% 6% 12% 6% 5% 5% 4 5% 6% 25%	4048
January	1st to 10th	Night	11% 10% 6% 15% 8% 6% 6% 4 6% 6% 24%	8234
	11th to 20th	Night	11% 11% 5% 15% 6% 5% 5% 4 5% 7% 25%	8235
	21st to end	Night	13% 9% 3 8% 7% 5% 5% 4 7% 7% 32%	8419
February	1st to 10th	Night	15% 10% 4 8% 5% 5% 6% 4 6% 6% 33%	2730
	11th to 20th	Night	13% 10% 5% 10% 6% 5% 6% 5% 7% 6% 28%	2548
	21st to end	Night	15% 10% 4 9% 5% 5% 5% 4 5% 5% 32%	2076
March	1st to 10th	Night	17% 10% 5% 8% 5% 4 4 3 5% 5% 35%	5374
	11th to 20th	Night	11% 9% 4 7% 5% 4 5% 4 6% 6% 39%	4979
	21st to end	Night	15% 10% 3 8% 5% 4 5% 4 5% 6% 36%	5148
April	1st to 10th	Night	16% 11% 3 9% 6% 5% 5% 4 6% 6% 30%	2000
	11th to 20th	Night	17% 10% 2 6% 4 4 4 3 6% 7% 36%	1975
	21st to end	Night	19% 9% 3 5% 4 4 3 3 5% 6% 40%	2000
May	1st to 10th	Night	32% 9% 2 6% 4 4 4 3 5% 6% 27%	3907
	11th to 20th	Night	23% 9% 3 5% 4 4 4 3 5% 6% 34%	3575
	21st to end	Night	20% 9% 2 6% 5% 4 5% 4 6% 7% 31%	3926
June	1st to 10th	Night	16% 7% 1 6% 5% 4 4 3 6% 8% 40%	1600
	11th to 20th	Night	14% 6% 2 6% 5% 4 5% 4 6% 8% 41%	1600
	21st to end	Night	11% 4 2 5% 3 4 5% 5% 8% 9% 45%	1600
July	1st to 10th	Night	10% 6% 2 8% 5% 4 5% 4 6% 9% 41%	3600
	11th to 20th	Night	10% 7% 2 7% 6% 6% 5% 4 7% 10% 35%	3600
	21st to end	Night	11% 6% 2 6% 4 4 4 3 4 7% 48%	3926
August	1st to 10th	Night	20% 6% 2 6% 4 5% 6% 4 6% 8% 34%	2899
	11th to 20th	Night	17% 5% 2 6% 4 4 4 3 5% 7% 42%	3091
	21st to end	Night	13% 5% 1 5% 4 3 4 4 5% 7% 48%	3586
September	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 5% 7% 45%	2000
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 4 6% 52%	2022
	21st to end	Night	17% 7% 3 6% 4 4 4 3 6% 6% 40%	2215
October	1st to 10th	Night	19% 7% 2 6% 3 3 3 3 5% 6% 43%	2400
	11th to 20th	Night	16% 9% 2 6% 3 4 4 3 5% 6% 43%	2400
	21st to end	Night	20% 10% 2 5% 3 4 3 3 6% 7% 37%	2735
November	1st to 10th	Night	11% 8% 3 7% 5% 4 4 3 5% 6% 44%	2667
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 4 5% 6% 38%	2730
	21st to end	Night	13% 10% 4 7% 4 5% 5% 4 6% 7% 35%	2940
December	1st to 10th	Night	13% 10% 4 9% 5% 5% 4 5% 7% 8% 31%	4720
	11th to 20th	Night	21% 11% 4 6% 5% 4 4 3 4 5% 33%	5348
	21st to end	Night	19% 13% 6% 9% 5% 4 4 3 5% 6% 26%	7150

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	61% 3 10% 18% 8% 1	4662
	11th to 20th	Day	58% 3 9% 16% 12% 3	4680
	21st to end	Day	51% 3 11% 22% 14%	5757
February	1st to 10th	Day	53% 6% 12% 17% 11% 1	1890
	11th to 20th	Day	51% 6% 10% 21% 11% 1	1966
	21st to end	Day	53% 4 11% 21% 9% 2	1730
March	1st to 10th	Day	53% 3 10% 17% 12% 6%	4499
	11th to 20th	Day	42% 7% 15% 25% 7% 4	4979
	21st to end	Day	47% 5% 10% 12% 22% 4	5782
April	1st to 10th	Day	51% 6% 9% 20% 11% 3	2400
	11th to 20th	Day	46% 6% 12% 20% 13% 2	2374
	21st to end	Day	46% 7% 9% 21% 13% 4	2400
May	1st to 10th	Day	57% 5% 12% 16% 9% 1	6071
	11th to 20th	Day	52% 7% 9% 20% 10% 1	6322
	21st to end	Day	48% 6% 12% 21% 11% 1	6949
June	1st to 10th	Day	45% 8% 13% 20% 13% 1	2800
	11th to 20th	Day	47% 8% 13% 20% 10% 1	2800
	21st to end	Day	42% 9% 14% 24% 11% 1	2800
July	1st to 10th	Day	44% 7% 13% 23% 12% 1	6290
	11th to 20th	Day	44% 6% 15% 25% 10%	6285
	21st to end	Day	42% 5% 12% 22% 18% 1	6728
August	1st to 10th	Day	51% 7% 14% 20% 8%	4232
	11th to 20th	Day	43% 6% 15% 28% 9%	3961
	21st to end	Day	39% 5% 10% 33% 11% 1	4312
September	1st to 10th	Day	43% 7% 12% 21% 16% 1	2400
	11th to 20th	Day	36% 6% 11% 24% 22% 2	2376
	21st to end	Day	46% 6% 11% 19% 15% 1	2182
October	1st to 10th	Day	46% 3 7% 22% 20% 2	3260
	11th to 20th	Day	39% 3 9% 26% 17% 6%	3240
	21st to end	Day	34% 4 17% 26% 16% 3	3381
November	1st to 10th	Day	40% 5% 14% 23% 16% 2	1851
	11th to 20th	Day	46% 6% 12% 21% 13% 2	1885
	21st to end	Day	50% 7% 14% 21% 7% 1	1680
December	1st to 10th	Day	54% 4 14% 20% 6% 1	2680
	11th to 20th	Day	54% 4 13% 17% 10% 1	3066
	21st to end	Day	59% 4 10% 15% 10% 1	4048
January	1st to 10th	Night	58% 3 11% 18% 9% 1	8234
	11th to 20th	Night	56% 4 12% 15% 9% 3	8280
	21st to end	Night	49% 3 11% 19% 17% 2	8419
February	1st to 10th	Night	48% 6% 14% 20% 11% 1	2730
	11th to 20th	Night	51% 6% 12% 18% 11% 2	2550
	21st to end	Night	51% 5% 10% 21% 11% 2	2076
March	1st to 10th	Night	50% 4 13% 17% 14% 3	5384
	11th to 20th	Night	39% 6% 20% 22% 8% 4	4980
	21st to end	Night	47% 6% 8% 16% 20% 3	5148
April	1st to 10th	Night	52% 7% 10% 17% 11% 3	2000
	11th to 20th	Night	45% 7% 11% 21% 15% 1	1975
	21st to end	Night	45% 7% 10% 20% 15% 4	2000
May	1st to 10th	Night	58% 5% 10% 17% 8% 1	3913
	11th to 20th	Night	50% 8% 13% 17% 11% 1	3576
	21st to end	Night	48% 7% 13% 21% 10% 1	3927
June	1st to 10th	Night	41% 6% 12% 24% 16% 1	1600
	11th to 20th	Night	40% 8% 16% 25% 10% 1	1600
	21st to end	Night	32% 8% 19% 27% 13% 1	1600
July	1st to 10th	Night	40% 7% 16% 20% 15% 1	3560
	11th to 20th	Night	42% 7% 17% 23% 11%	3552
	21st to end	Night	36% 4 13% 28% 18% 1	3809
August	1st to 10th	Night	46% 7% 18% 21% 8%	2889
	11th to 20th	Night	41% 6% 16% 27% 10%	3119
	21st to end	Night	35% 5% 12% 33% 15% 1	3586
September	1st to 10th	Night	38% 7% 12% 26% 17% 1	2000
	11th to 20th	Night	33% 6% 11% 25% 23% 2	2022
	21st to end	Night	42% 7% 10% 23% 17% 1	2215
October	1st to 10th	Night	46% 3 10% 23% 17% 1	3920
	11th to 20th	Night	34% 4 11% 25% 21% 5%	3899
	21st to end	Night	33% 4 17% 28% 17% 1	4408
November	1st to 10th	Night	40% 5% 12% 22% 19% 2	2667
	11th to 20th	Night	45% 4 12% 22% 14% 2	2730
	21st to end	Night	45% 6% 16% 23% 10% 1	2940
December	1st to 10th	Night	48% 4 14% 28% 6%	4720
	11th to 20th	Night	52% 4 13% 17% 12% 1	5348
	21st to end	Night	58% 5% 10% 15% 11% 1	7150

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	35% 29% 25% 11%	220
	11th to 20th	Day	42% 29% 20% 9% 1	220
	21st to end	Day	31% 34% 24% 7% 3	358
February	1st to 10th	Day	34% 31% 28% 7% 1	330
	11th to 20th	Day	39% 28% 28% 5%	445
	21st to end	Day	33% 30% 27% 8% 2	446
March	1st to 10th	Day	33% 22% 30% 13% 2	508
	11th to 20th	Day	32% 25% 28% 12% 3	500
	21st to end	Day	33% 28% 25% 9% 4 1	550
April	1st to 10th	Day	36% 25% 24% 11% 4	500
	11th to 20th	Day	30% 25% 25% 12% 6% 2	492
	21st to end	Day	29% 20% 32% 14% 3 2	500
May	1st to 10th	Day	34% 20% 26% 11% 6% 2	503
	11th to 20th	Day	25% 18% 30% 19% 6% 2	527
	21st to end	Day	21% 12% 30% 23% 11% 3	573
June	1st to 10th	Day	21% 15% 31% 22% 9% 2	530
	11th to 20th	Day	20% 16% 27% 23% 12% 1	530
	21st to end	Day	15% 15% 33% 27% 8% 2	530
July	1st to 10th	Day	13% 8% 30% 28% 16% 4	525
	11th to 20th	Day	9% 9% 32% 30% 17% 3	524
	21st to end	Day	13% 9% 37% 27% 11% 3	576
August	1st to 10th	Day	12% 9% 27% 26% 19% 6%	526
	11th to 20th	Day	15% 8% 24% 31% 17% 5%	519
	21st to end	Day	14% 11% 28% 25% 15% 7%	583
September	1st to 10th	Day	18% 13% 22% 23% 16% 7%	530
	11th to 20th	Day	12% 8% 27% 25% 17% 11%	530
	21st to end	Day	25% 12% 26% 22% 12% 3	530
October	1st to 10th	Day	23% 15% 23% 22% 12% 6%	530
	11th to 20th	Day	22% 22% 28% 19% 8% 1	530
	21st to end	Day	26% 20% 29% 17% 7% 1	530
November	1st to 10th	Day	24% 23% 24% 19% 8% 2	425
	11th to 20th	Day	28% 24% 28% 16% 4	425
	21st to end	Day	36% 21% 33% 8% 2	220
December	1st to 10th	Day	35% 29% 24% 9% 4	220
	11th to 20th	Day	41% 25% 22% 8% 3	220
	21st to end	Day	30% 26% 28% 12% 3	242
January	1st to 10th	Night	24% 29% 32% 13% 2	840
	11th to 20th	Night	27% 25% 29% 17% 2	840
	21st to end	Night	21% 30% 33% 14% 2	924
February	1st to 10th	Night	28% 21% 34% 16% 1	840
	11th to 20th	Night	29% 28% 32% 11% 1	823
	21st to end	Night	28% 26% 30% 14% 2	692
March	1st to 10th	Night	27% 25% 32% 14% 2	809
	11th to 20th	Night	25% 25% 29% 17% 4	800
	21st to end	Night	22% 26% 31% 16% 4	880
April	1st to 10th	Night	24% 24% 31% 20% 2	800
	11th to 20th	Night	25% 21% 30% 18% 6%	791
	21st to end	Night	24% 18% 30% 22% 5%	800
May	1st to 10th	Night	28% 15% 28% 22% 7%	544
	11th to 20th	Night	20% 13% 32% 28% 6% 1	394
	21st to end	Night	15% 10% 27% 36% 12%	433
June	1st to 10th	Night	17% 9% 23% 39% 12% 1	400
	11th to 20th	Night	16% 6% 29% 37% 11% 1	400
	21st to end	Night	12% 6% 27% 44% 11% 1	400
July	1st to 10th	Night	14% 5% 21% 39% 19% 2	390
	11th to 20th	Night	11% 6% 21% 44% 17% 1	388
	21st to end	Night	11% 7% 22% 44% 16%	438
August	1st to 10th	Night	14% 2 21% 41% 20% 3	581
	11th to 20th	Night	14% 5% 15% 39% 24% 2	720
	21st to end	Night	15% 7% 20% 36% 21% 1	880
September	1st to 10th	Night	16% 8% 24% 32% 19% 3	800
	11th to 20th	Night	13% 7% 23% 28% 23% 5%	800
	21st to end	Night	20% 9% 23% 30% 16% 2	800
October	1st to 10th	Night	23% 13% 21% 23% 18% 2	800
	11th to 20th	Night	22% 15% 27% 29% 8% 1	800
	21st to end	Night	26% 17% 29% 23% 5%	880
November	1st to 10th	Night	18% 19% 31% 24% 8%	820
	11th to 20th	Night	25% 23% 26% 19% 6% 1	840
	21st to end	Night	23% 22% 33% 17% 4 1	840
December	1st to 10th	Night	27% 23% 31% 15% 4	840
	11th to 20th	Night	27% 23% 30% 18% 3	840
	21st to end	Night	27% 25% 30% 16% 3	924

Page generated at 2026-02-28 01:40:25. Version ac07

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