Ore Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ore Lake Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	14% 10% 4 8% 5% 5% 5% 4 5% 7% 34%	126665
	Night	14% 11% 4 9% 5% 4 4 3 5% 6% 34%	125449
Transparency	Day	49% 4 11% 22% 13% 1	130234
	Night	50% 3 11% 22% 13% 1	129949
Seeing	Day	18% 12% 29% 22% 13% 5%	17132
	Night	19% 10% 29% 28% 12% 1	27262

By Month

Percentage Cloud Cover SE (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	12% 18% 6% 17% 5% 4 4 3 4 5% 22%	3697
	11th to 20th	Day	14% 16% 6% 17% 9% 8% 6% 3 5% 4 10%	3700
	21st to end	Day	22% 19% 5% 12% 6% 4 4 3 4 4 17%	4408
February	1st to 10th	Day	14% 14% 5% 13% 9% 5% 5% 3 6% 5% 21%	1800
	11th to 20th	Day	14% 14% 5% 14% 9% 4 5% 3 4 5% 23%	1915
	21st to end	Day	15% 17% 4 11% 5% 5% 4 3 4 6% 26%	1650
March	1st to 10th	Day	15% 13% 5% 10% 5% 4 4 3 5% 5% 30%	4544
	11th to 20th	Day	12% 12% 4 8% 4 4 4 4 5% 7% 36%	4980
	21st to end	Day	18% 14% 4 9% 6% 4 4 3 4 6% 28%	5465
April	1st to 10th	Day	17% 13% 3 7% 6% 4 5% 4 5% 6% 31%	2353
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 3 5% 7% 35%	2517
	21st to end	Day	17% 9% 4 8% 5% 4 4 4 4 7% 36%	2600
May	1st to 10th	Day	19% 9% 3 7% 4 4 4 3 5% 6% 34%	5862
	11th to 20th	Day	16% 7% 3 7% 6% 5% 5% 4 6% 8% 33%	5861
	21st to end	Day	14% 7% 3 7% 4 4 4 3 6% 8% 41%	6496
June	1st to 10th	Day	10% 6% 3 6% 5% 4 5% 5% 7% 8% 42%	2800
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	2800
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 4 8% 10% 39%	2800
July	1st to 10th	Day	9% 6% 2 6% 4 5% 6% 5% 7% 11% 39%	6360
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 4 7% 9% 46%	6360
	21st to end	Day	8% 6% 2 6% 5% 5% 4 4 6% 9% 45%	6607
August	1st to 10th	Day	12% 4 2 6% 4 5% 6% 5% 6% 9% 42%	4234
	11th to 20th	Day	11% 6% 2 7% 4 5% 5% 4 7% 9% 41%	4174
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 5% 8% 9% 41%	4578
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 5% 9% 42%	2279
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 9% 48%	2200
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 6% 7% 38%	2200
October	1st to 10th	Day	13% 6% 3 7% 5% 4 4 4 5% 6% 44%	2165
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 3 5% 7% 33%	2000
	21st to end	Day	19% 11% 4 7% 6% 4 4 3 5% 7% 31%	2012
November	1st to 10th	Day	13% 10% 3 8% 4 4 4 4 5% 7% 38%	1852
	11th to 20th	Day	15% 14% 3 9% 6% 5% 4 3 4 6% 30%	1890
	21st to end	Day	19% 13% 5% 8% 5% 5% 5% 3 5% 6% 27%	1864
December	1st to 10th	Day	12% 15% 7% 16% 7% 5% 5% 4 5% 5% 20%	2680
	11th to 20th	Day	18% 21% 6% 10% 6% 5% 4 3 4 5% 17%	2892
	21st to end	Day	26% 20% 8% 10% 5% 4 3 2 3 4 14%	4070
January	1st to 10th	Night	14% 15% 7% 13% 6% 5% 4 3 5% 5% 24%	6488
	11th to 20th	Night	12% 15% 7% 15% 8% 6% 6% 4 6% 6% 15%	6500
	21st to end	Night	18% 16% 8% 11% 5% 4 4 3 4 5% 21%	6794
February	1st to 10th	Night	17% 16% 5% 11% 6% 5% 4 3 5% 4 24%	2601
	11th to 20th	Night	14% 14% 5% 10% 7% 5% 4 3 5% 6% 27%	2368
	21st to end	Night	18% 11% 4 11% 5% 4 4 3 5% 7% 28%	1980
March	1st to 10th	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 36%	5309
	11th to 20th	Night	9% 9% 3 6% 4 4 5% 4 6% 8% 42%	4980
	21st to end	Night	17% 10% 3 8% 4 4 4 3 4 6% 36%	5467
April	1st to 10th	Night	17% 10% 3 6% 6% 5% 3 4 4 7% 36%	2064
	11th to 20th	Night	18% 9% 2 5% 5% 4 4 4 5% 7% 37%	1832
	21st to end	Night	17% 9% 2 6% 5% 4 5% 3 4 6% 38%	1800
May	1st to 10th	Night	20% 10% 3 8% 5% 5% 4 3 5% 6% 32%	4033
	11th to 20th	Night	18% 8% 3 7% 4 4 3 3 4 6% 40%	4032
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 8% 45%	4344
June	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 6% 8% 47%	1600
	11th to 20th	Night	11% 6% 2 5% 4 4 4 5% 7% 9% 43%	1600
	21st to end	Night	9% 5% 3 6% 3 4 3 4 7% 10% 47%	1600
July	1st to 10th	Night	7% 4 2 5% 4 5% 5% 4 7% 10% 46%	3618
	11th to 20th	Night	8% 4 2 6% 4 3 4 4 6% 8% 50%	3617
	21st to end	Night	8% 5% 2 6% 5% 4 4 3 6% 8% 48%	4248
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 9% 48%	2915
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 6% 7% 49%	2875
	21st to end	Night	8% 6% 2 6% 4 5% 4 4 5% 7% 49%	3316
September	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 5% 6% 50%	2100
	11th to 20th	Night	9% 5% 1 4 3 3 3 3 5% 7% 56%	2200
	21st to end	Night	14% 6% 2 6% 4 5% 5% 3 6% 6% 44%	2200
October	1st to 10th	Night	12% 7% 3 6% 4 4 4 3 4 6% 48%	2235
	11th to 20th	Night	18% 9% 4 7% 5% 4 3 3 4 6% 36%	2400
	21st to end	Night	20% 9% 3 7% 4 4 4 4 5% 6% 35%	2825
November	1st to 10th	Night	13% 10% 3 6% 4 4 4 3 4 6% 42%	2666
	11th to 20th	Night	15% 11% 3 8% 5% 5% 5% 4 6% 7% 31%	2730
	21st to end	Night	19% 16% 5% 9% 5% 4 4 3 5% 6% 27%	2748
December	1st to 10th	Night	12% 13% 5% 16% 6% 5% 5% 4 5% 6% 23%	4720
	11th to 20th	Night	15% 19% 6% 12% 7% 5% 5% 3 5% 5% 19%	5494
	21st to end	Night	25% 22% 6% 11% 4 4 3 3 3 4 14%	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	66% 3 10% 15% 6%	3698
	11th to 20th	Day	76% 4 8% 7% 5% 1	3700
	21st to end	Day	73% 2 10% 10% 5%	4408
February	1st to 10th	Day	63% 6% 9% 14% 7%	1800
	11th to 20th	Day	63% 4 7% 16% 8% 1	1925
	21st to end	Day	60% 4 11% 16% 8% 2	1650
March	1st to 10th	Day	57% 3 11% 17% 9% 2	4544
	11th to 20th	Day	48% 3 15% 23% 9% 2	4980
	21st to end	Day	59% 3 10% 15% 12% 1	5465
April	1st to 10th	Day	54% 4 10% 19% 12%	2353
	11th to 20th	Day	49% 4 11% 21% 13% 2	2517
	21st to end	Day	48% 5% 12% 19% 14% 1	2600
May	1st to 10th	Day	50% 4 10% 20% 13% 3	5897
	11th to 20th	Day	48% 5% 11% 22% 12% 2	5865
	21st to end	Day	42% 3 9% 23% 19% 3	6510
June	1st to 10th	Day	37% 6% 12% 28% 14% 3	2800
	11th to 20th	Day	40% 6% 12% 24% 16% 2	2800
	21st to end	Day	38% 6% 14% 23% 17% 2	2800
July	1st to 10th	Day	40% 3 13% 27% 16% 2	6291
	11th to 20th	Day	35% 3 12% 30% 19% 1	6285
	21st to end	Day	36% 4 14% 24% 22% 1	6419
August	1st to 10th	Day	38% 4 13% 26% 17% 1	4221
	11th to 20th	Day	39% 5% 10% 34% 12% 1	4213
	21st to end	Day	39% 4 13% 30% 13% 2	4577
September	1st to 10th	Day	39% 7% 12% 25% 15% 2	2279
	11th to 20th	Day	32% 6% 11% 34% 16% 1	2200
	21st to end	Day	43% 5% 11% 24% 15%	2200
October	1st to 10th	Day	32% 3 10% 32% 22% 1	3529
	11th to 20th	Day	41% 3 10% 26% 19%	3240
	21st to end	Day	46% 3 13% 24% 13% 2	3224
November	1st to 10th	Day	45% 5% 11% 24% 14% 1	1852
	11th to 20th	Day	56% 3 11% 20% 8% 2	1890
	21st to end	Day	59% 4 11% 18% 7%	1864
December	1st to 10th	Day	67% 3 13% 12% 4	2680
	11th to 20th	Day	70% 2 10% 13% 4	2888
	21st to end	Day	77% 2 7% 8% 5%	4070
January	1st to 10th	Night	62% 2 8% 19% 7% 1	6488
	11th to 20th	Night	69% 3 11% 10% 6% 1	6500
	21st to end	Night	66% 2 11% 12% 7%	6794
February	1st to 10th	Night	63% 5% 10% 14% 7% 1	2601
	11th to 20th	Night	58% 4 10% 18% 9% 1	2369
	21st to end	Night	56% 3 12% 18% 8% 2	1980
March	1st to 10th	Night	50% 3 12% 23% 11% 1	5309
	11th to 20th	Night	39% 4 13% 27% 16% 1	4980
	21st to end	Night	50% 3 11% 20% 15% 2	5467
April	1st to 10th	Night	49% 4 10% 21% 14% 2	2064
	11th to 20th	Night	46% 4 11% 19% 19% 1	1832
	21st to end	Night	46% 4 11% 19% 16% 3	1800
May	1st to 10th	Night	54% 4 9% 17% 12% 4	4060
	11th to 20th	Night	47% 5% 9% 26% 11% 3	4033
	21st to end	Night	39% 4 12% 23% 19% 4	4352
June	1st to 10th	Night	35% 4 11% 28% 20% 3	1600
	11th to 20th	Night	37% 6% 13% 26% 16% 2	1600
	21st to end	Night	32% 5% 15% 27% 20% 1	1600
July	1st to 10th	Night	34% 3 13% 29% 16% 5%	3580
	11th to 20th	Night	32% 2 14% 30% 20% 1	3572
	21st to end	Night	35% 4 14% 22% 24% 2	4123
August	1st to 10th	Night	35% 4 14% 29% 18% 1	2904
	11th to 20th	Night	35% 4 10% 38% 12% 2	2902
	21st to end	Night	36% 4 11% 32% 15% 1	3316
September	1st to 10th	Night	33% 6% 12% 29% 18% 2	2100
	11th to 20th	Night	29% 4 10% 32% 22% 2	2200
	21st to end	Night	40% 5% 11% 28% 15% 1	2200
October	1st to 10th	Night	27% 3 9% 33% 28% 1	3651
	11th to 20th	Night	44% 2 10% 24% 19%	3899
	21st to end	Night	40% 2 10% 33% 14% 1	4563
November	1st to 10th	Night	43% 4 11% 26% 16% 1	2666
	11th to 20th	Night	52% 4 13% 21% 9% 1	2730
	21st to end	Night	59% 4 11% 19% 7%	2748
December	1st to 10th	Night	63% 3 14% 15% 4	4720
	11th to 20th	Night	68% 3 10% 13% 5% 1	5496
	21st to end	Night	75% 3 8% 8% 6%	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	25% 18% 37% 14% 5% 1	330
	11th to 20th	Day	28% 18% 39% 13% 1 1	330
	21st to end	Day	29% 19% 33% 14% 4 1	363
February	1st to 10th	Day	25% 23% 35% 12% 3 1	300
	11th to 20th	Day	27% 22% 36% 14% 2	300
	21st to end	Day	30% 26% 31% 12% 1	249
March	1st to 10th	Day	26% 23% 34% 15% 2	325
	11th to 20th	Day	24% 14% 34% 22% 6%	500
	21st to end	Day	29% 15% 32% 19% 5% 1	550
April	1st to 10th	Day	23% 16% 33% 20% 7% 1	500
	11th to 20th	Day	25% 20% 32% 12% 7% 4	492
	21st to end	Day	24% 14% 30% 20% 10% 2	500
May	1st to 10th	Day	25% 13% 31% 19% 10% 3	503
	11th to 20th	Day	20% 10% 29% 22% 12% 7%	527
	21st to end	Day	15% 11% 23% 25% 18% 8%	597
June	1st to 10th	Day	12% 7% 32% 29% 16% 4	730
	11th to 20th	Day	13% 7% 33% 26% 17% 4	730
	21st to end	Day	12% 9% 29% 30% 16% 5%	730
July	1st to 10th	Day	8% 6% 23% 29% 24% 10%	721
	11th to 20th	Day	10% 7% 28% 27% 19% 9%	718
	21st to end	Day	10% 4 23% 32% 23% 9%	655
August	1st to 10th	Day	7% 4 19% 29% 26% 15%	526
	11th to 20th	Day	13% 4 19% 27% 26% 11%	519
	21st to end	Day	10% 4 21% 28% 24% 12%	583
September	1st to 10th	Day	13% 7% 22% 23% 22% 13%	530
	11th to 20th	Day	9% 3 16% 26% 28% 17%	530
	21st to end	Day	16% 9% 23% 23% 19% 9%	530
October	1st to 10th	Day	16% 9% 26% 25% 17% 7%	530
	11th to 20th	Day	19% 15% 29% 27% 9% 1	530
	21st to end	Day	29% 18% 31% 17% 4	395
November	1st to 10th	Day	18% 19% 35% 20% 7% 1	330
	11th to 20th	Day	24% 22% 32% 16% 6%	330
	21st to end	Day	26% 20% 37% 13% 4	316
December	1st to 10th	Day	24% 19% 34% 15% 8%	220
	11th to 20th	Day	28% 22% 35% 10% 4	250
	21st to end	Day	29% 23% 32% 14% 2	363
January	1st to 10th	Night	22% 16% 36% 21% 5% 1	1050
	11th to 20th	Night	26% 15% 34% 21% 4 1	1050
	21st to end	Night	21% 14% 35% 25% 5%	994
February	1st to 10th	Night	26% 13% 34% 23% 3	801
	11th to 20th	Night	23% 15% 35% 23% 4	783
	21st to end	Night	25% 13% 40% 20% 2	660
March	1st to 10th	Night	21% 13% 36% 23% 6%	800
	11th to 20th	Night	18% 17% 36% 24% 5% 1	800
	21st to end	Night	23% 13% 30% 26% 7% 1	880
April	1st to 10th	Night	20% 14% 35% 26% 4 1	664
	11th to 20th	Night	22% 11% 34% 24% 7% 1	593
	21st to end	Night	20% 10% 32% 29% 8%	600
May	1st to 10th	Night	21% 8% 32% 30% 9% 1	600
	11th to 20th	Night	22% 5% 28% 32% 12% 1	591
	21st to end	Night	13% 5% 25% 36% 20% 2	650
June	1st to 10th	Night	12% 5% 25% 43% 14% 1	600
	11th to 20th	Night	13% 4 23% 43% 18%	600
	21st to end	Night	10% 4 22% 43% 21% 1	600
July	1st to 10th	Night	8% 3 16% 42% 28% 4	585
	11th to 20th	Night	10% 3 19% 39% 25% 4	582
	21st to end	Night	6% 2 19% 48% 25% 2	657
August	1st to 10th	Night	9% 2 16% 43% 29% 2	597
	11th to 20th	Night	9% 2 19% 37% 28% 4	594
	21st to end	Night	9% 2 17% 39% 30% 3	660
September	1st to 10th	Night	12% 5% 20% 32% 26% 4	700
	11th to 20th	Night	11% 3 17% 32% 32% 5%	800
	21st to end	Night	15% 7% 21% 31% 21% 5%	800
October	1st to 10th	Night	15% 6% 28% 31% 17% 3	800
	11th to 20th	Night	22% 12% 30% 26% 9% 1	800
	21st to end	Night	24% 12% 33% 25% 5%	880
November	1st to 10th	Night	19% 11% 32% 27% 10% 1	820
	11th to 20th	Night	22% 16% 34% 21% 7% 1	840
	21st to end	Night	26% 14% 35% 20% 5%	840
December	1st to 10th	Night	23% 17% 33% 21% 6%	840
	11th to 20th	Night	23% 15% 38% 20% 3	996
	21st to end	Night	34% 12% 34% 18% 2	1155

Page generated at 2026-01-29 01:21:44. Version ac07

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