Oak Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Lake Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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% 10% 3 8% 5% 4 4 4 5% 7% 33%	101570
	Night	17% 11% 4 8% 5% 4 4 4 5% 6% 33%	97528
Transparency	Day	49% 6% 12% 21% 11% 1	105142
	Night	49% 7% 12% 20% 10% 1	102045
Seeing	Day	23% 16% 31% 19% 8% 3	14450
	Night	22% 13% 30% 24% 10% 1	23679

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	16% 18% 6% 11% 5% 3 4 3 4 5% 25%	2517
	11th to 20th	Day	12% 18% 8% 14% 7% 5% 5% 3 4 5% 20%	2528
	21st to end	Day	20% 20% 7% 12% 6% 4 3 2 3 4 19%	3124
February	1st to 10th	Day	13% 18% 4 14% 6% 5% 5% 5% 4 5% 22%	1710
	11th to 20th	Day	13% 16% 5% 13% 6% 5% 3 3 3 4 28%	1663
	21st to end	Day	17% 16% 5% 10% 6% 5% 5% 3 4 4 25%	1491
March	1st to 10th	Day	21% 13% 4 8% 5% 4 3 3 4 5% 30%	3330
	11th to 20th	Day	12% 17% 5% 9% 6% 5% 4 3 6% 7% 28%	3480
	21st to end	Day	14% 9% 3 6% 4 4 3 3 5% 5% 45%	3874
April	1st to 10th	Day	21% 13% 3 7% 4 3 4 3 5% 6% 31%	2280
	11th to 20th	Day	24% 8% 2 6% 3 4 4 3 5% 5% 37%	2254
	21st to end	Day	22% 10% 3 8% 5% 4 4 3 4 6% 31%	2467
May	1st to 10th	Day	21% 7% 3 7% 5% 4 4 4 5% 6% 35%	4295
	11th to 20th	Day	17% 10% 3 7% 5% 4 4 4 6% 8% 32%	4398
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 8% 42%	4837
June	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 5% 7% 32%	2660
	11th to 20th	Day	15% 6% 2 6% 4 5% 6% 5% 6% 9% 36%	2660
	21st to end	Day	17% 8% 2 7% 5% 5% 5% 4 6% 7% 36%	2660
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 5% 7% 9% 37%	4440
	11th to 20th	Day	12% 5% 2 5% 4 5% 4 4 6% 9% 44%	4440
	21st to end	Day	8% 6% 2 6% 5% 5% 6% 5% 6% 9% 42%	4768
August	1st to 10th	Day	16% 9% 3 6% 4 5% 5% 4 6% 8% 35%	4104
	11th to 20th	Day	16% 7% 3 7% 5% 4 5% 4 7% 9% 34%	4044
	21st to end	Day	11% 5% 2 7% 5% 4 5% 4 7% 9% 40%	4258
September	1st to 10th	Day	14% 7% 3 6% 5% 4 5% 4 5% 6% 41%	2280
	11th to 20th	Day	12% 5% 2 6% 3 4 4 4 5% 7% 49%	2275
	21st to end	Day	16% 7% 3 7% 4 4 4 3 5% 7% 39%	1986
October	1st to 10th	Day	20% 8% 2 7% 5% 5% 4 3 5% 7% 33%	1900
	11th to 20th	Day	21% 10% 3 9% 5% 5% 4 3 5% 7% 27%	1900
	21st to end	Day	26% 12% 3 8% 5% 5% 4 3 4 5% 25%	2057
November	1st to 10th	Day	17% 10% 2 7% 5% 5% 5% 4 5% 6% 33%	1652
	11th to 20th	Day	17% 13% 3 8% 6% 4 4 4 5% 7% 28%	1520
	21st to end	Day	22% 16% 5% 8% 4 4 5% 4 5% 6% 21%	1520
December	1st to 10th	Day	19% 20% 6% 12% 5% 5% 4 3 4 4 19%	1520
	11th to 20th	Day	18% 17% 6% 8% 5% 4 3 4 4 3 27%	1906
	21st to end	Day	27% 18% 5% 11% 5% 4 3 2 3 5% 18%	2772
January	1st to 10th	Night	18% 18% 7% 12% 6% 4 4 3 4 4 19%	4429
	11th to 20th	Night	14% 14% 6% 13% 8% 6% 6% 4 6% 5% 18%	4431
	21st to end	Night	20% 15% 7% 12% 6% 5% 4 4 4 5% 19%	4532
February	1st to 10th	Night	13% 16% 5% 10% 7% 5% 6% 4 4 6% 23%	2470
	11th to 20th	Night	13% 14% 6% 10% 6% 5% 4 4 5% 5% 29%	2403
	21st to end	Night	16% 12% 4 8% 5% 5% 5% 4 5% 7% 28%	1962
March	1st to 10th	Night	19% 12% 4 8% 4 5% 5% 3 4 5% 31%	3505
	11th to 20th	Night	15% 15% 6% 9% 5% 4 4 4 5% 6% 28%	3479
	21st to end	Night	15% 8% 3 6% 4 4 4 4 5% 7% 40%	3756
April	1st to 10th	Night	20% 11% 3 7% 4 4 3 3 5% 7% 33%	1900
	11th to 20th	Night	18% 8% 3 7% 5% 3 4 3 5% 6% 37%	1875
	21st to end	Night	18% 10% 3 6% 5% 5% 4 4 5% 7% 33%	1729
May	1st to 10th	Night	20% 8% 3 7% 4 4 4 4 5% 6% 36%	2645
	11th to 20th	Night	16% 8% 3 6% 5% 5% 4 4 6% 7% 36%	2495
	21st to end	Night	11% 6% 2 6% 4 5% 4 3 5% 7% 46%	2738
June	1st to 10th	Night	14% 7% 2 7% 5% 5% 4 5% 5% 9% 38%	1520
	11th to 20th	Night	11% 6% 3 5% 4 5% 4 4 5% 8% 44%	1520
	21st to end	Night	14% 8% 2 7% 4 4 5% 4 5% 7% 40%	1520
July	1st to 10th	Night	9% 4 2 7% 5% 5% 5% 5% 6% 8% 45%	2520
	11th to 20th	Night	13% 5% 2 4 4 4 3 3 5% 7% 49%	2520
	21st to end	Night	10% 5% 2 5% 3 4 4 4 6% 8% 49%	2769
August	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 5% 8% 46%	2825
	11th to 20th	Night	15% 6% 2 5% 4 3 4 3 5% 7% 45%	2785
	21st to end	Night	10% 5% 2 5% 3 4 5% 3 7% 8% 47%	3366
September	1st to 10th	Night	10% 6% 3 5% 4 4 4 3 7% 8% 46%	1900
	11th to 20th	Night	12% 4 1 5% 4 3 3 4 4 7% 53%	1901
	21st to end	Night	18% 6% 3 5% 4 4 4 3 5% 5% 42%	2194
October	1st to 10th	Night	18% 6% 3 6% 4 4 4 3 5% 7% 39%	2280
	11th to 20th	Night	22% 10% 3 7% 4 4 4 4 4 6% 32%	2280
	21st to end	Night	22% 12% 3 7% 5% 5% 5% 3 5% 5% 28%	2540
November	1st to 10th	Night	19% 10% 3 6% 4 5% 4 3 5% 6% 36%	2587
	11th to 20th	Night	19% 12% 3 7% 5% 5% 4 3 5% 6% 30%	2660
	21st to end	Night	20% 12% 3 8% 6% 5% 5% 4 6% 6% 24%	2660
December	1st to 10th	Night	21% 16% 6% 10% 6% 5% 4 4 5% 6% 19%	2660
	11th to 20th	Night	18% 18% 5% 9% 5% 4 4 3 4 5% 25%	3288
	21st to end	Night	28% 18% 4 11% 5% 4 4 3 4 4 15%	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	60% 8% 12% 12% 7% 1	2518
	11th to 20th	Day	67% 7% 11% 9% 6% 1	2528
	21st to end	Day	71% 4 8% 10% 5% 1	3124
February	1st to 10th	Day	64% 6% 10% 15% 5% 1	1710
	11th to 20th	Day	60% 5% 10% 14% 10% 1	1672
	21st to end	Day	62% 4 10% 13% 10% 1	1491
March	1st to 10th	Day	56% 4 13% 15% 10% 1	3333
	11th to 20th	Day	54% 6% 14% 16% 9% 2	3480
	21st to end	Day	40% 5% 10% 25% 17% 3	3874
April	1st to 10th	Day	55% 5% 8% 19% 10% 3	2280
	11th to 20th	Day	49% 4 9% 21% 16% 1	2254
	21st to end	Day	54% 4 9% 18% 12% 3	2467
May	1st to 10th	Day	48% 6% 10% 23% 11% 2	4307
	11th to 20th	Day	48% 9% 12% 19% 11% 1	4402
	21st to end	Day	39% 7% 13% 22% 16% 3	4837
June	1st to 10th	Day	50% 7% 12% 17% 13% 1	2660
	11th to 20th	Day	42% 8% 12% 23% 13% 2	2660
	21st to end	Day	46% 7% 12% 21% 12% 1	2660
July	1st to 10th	Day	40% 7% 15% 23% 14% 1	4370
	11th to 20th	Day	34% 7% 16% 33% 10%	4365
	21st to end	Day	36% 8% 13% 31% 12%	4616
August	1st to 10th	Day	46% 6% 15% 22% 11%	4091
	11th to 20th	Day	45% 7% 14% 25% 8% 1	4083
	21st to end	Day	37% 7% 13% 32% 10% 1	4258
September	1st to 10th	Day	41% 7% 12% 27% 12% 1	2280
	11th to 20th	Day	34% 6% 15% 29% 15% 1	2275
	21st to end	Day	44% 7% 14% 24% 11%	1986
October	1st to 10th	Day	44% 6% 12% 29% 10% 1	3160
	11th to 20th	Day	47% 5% 15% 20% 12% 1	3140
	21st to end	Day	56% 5% 12% 19% 7%	3371
November	1st to 10th	Day	50% 7% 15% 19% 8% 1	1652
	11th to 20th	Day	55% 6% 14% 15% 8% 2	1520
	21st to end	Day	63% 7% 11% 12% 6%	1520
December	1st to 10th	Day	70% 5% 10% 10% 5%	1520
	11th to 20th	Day	61% 8% 11% 11% 8%	1906
	21st to end	Day	71% 4 7% 13% 5%	2772
January	1st to 10th	Night	67% 6% 10% 12% 4	4429
	11th to 20th	Night	64% 7% 14% 10% 4 1	4431
	21st to end	Night	67% 6% 10% 11% 6% 1	4532
February	1st to 10th	Night	60% 7% 12% 15% 6% 1	2470
	11th to 20th	Night	56% 5% 10% 19% 8%	2405
	21st to end	Night	54% 5% 11% 19% 9% 1	1962
March	1st to 10th	Night	54% 6% 9% 20% 10% 1	3515
	11th to 20th	Night	54% 7% 15% 16% 7% 1	3480
	21st to end	Night	40% 6% 12% 24% 16% 2	3756
April	1st to 10th	Night	51% 5% 8% 20% 13% 2	1900
	11th to 20th	Night	47% 6% 9% 21% 15% 1	1875
	21st to end	Night	49% 6% 11% 16% 16% 2	1729
May	1st to 10th	Night	47% 7% 11% 18% 15% 2	2652
	11th to 20th	Night	44% 9% 13% 22% 10% 2	2496
	21st to end	Night	36% 7% 13% 22% 19% 2	2739
June	1st to 10th	Night	42% 7% 14% 22% 13% 1	1520
	11th to 20th	Night	37% 7% 12% 23% 19% 2	1520
	21st to end	Night	43% 7% 14% 21% 13% 1	1520
July	1st to 10th	Night	35% 7% 16% 24% 16% 2	2480
	11th to 20th	Night	35% 6% 13% 32% 14%	2472
	21st to end	Night	33% 6% 16% 32% 13%	2681
August	1st to 10th	Night	36% 6% 15% 26% 16% 1	2814
	11th to 20th	Night	37% 7% 18% 25% 11% 1	2812
	21st to end	Night	32% 8% 14% 34% 11% 2	3366
September	1st to 10th	Night	35% 9% 14% 27% 14% 1	1900
	11th to 20th	Night	31% 6% 15% 32% 15% 1	1901
	21st to end	Night	42% 6% 13% 27% 11%	2194
October	1st to 10th	Night	36% 6% 11% 28% 19%	3800
	11th to 20th	Night	44% 6% 15% 26% 9%	3779
	21st to end	Night	48% 7% 14% 23% 7%	4176
November	1st to 10th	Night	48% 6% 13% 22% 10%	2587
	11th to 20th	Night	53% 6% 13% 17% 8% 2	2660
	21st to end	Night	57% 9% 15% 14% 4	2660
December	1st to 10th	Night	65% 8% 10% 13% 4	2660
	11th to 20th	Night	62% 6% 11% 14% 6% 1	3288
	21st to end	Night	73% 6% 8% 10% 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	25% 21% 32% 18% 3 1	180
	11th to 20th	Day	29% 21% 32% 15% 3 1	184
	21st to end	Day	25% 22% 35% 13% 4	297
February	1st to 10th	Day	30% 24% 33% 9% 3	270
	11th to 20th	Day	30% 23% 40% 5% 1	270
	21st to end	Day	37% 20% 32% 11% 1	303
March	1st to 10th	Day	27% 20% 35% 15% 3	460
	11th to 20th	Day	27% 19% 34% 17% 3 1	460
	21st to end	Day	32% 21% 28% 12% 6% 1	506
April	1st to 10th	Day	28% 20% 33% 12% 6%	460
	11th to 20th	Day	33% 23% 20% 14% 8% 2	452
	21st to end	Day	28% 20% 33% 12% 6% 2	460
May	1st to 10th	Day	27% 15% 29% 20% 4 5%	463
	11th to 20th	Day	20% 14% 35% 18% 9% 3	487
	21st to end	Day	18% 15% 36% 18% 10% 3	529
June	1st to 10th	Day	22% 12% 34% 24% 7% 1	490
	11th to 20th	Day	17% 13% 34% 22% 11% 3	490
	21st to end	Day	20% 13% 33% 21% 9% 3	490
July	1st to 10th	Day	12% 10% 32% 30% 13% 3	485
	11th to 20th	Day	14% 10% 32% 25% 14% 5%	484
	21st to end	Day	12% 10% 35% 27% 12% 4	532
August	1st to 10th	Day	15% 9% 30% 27% 14% 5%	486
	11th to 20th	Day	13% 8% 27% 29% 17% 6%	479
	21st to end	Day	14% 10% 32% 24% 12% 8%	539
September	1st to 10th	Day	14% 11% 31% 23% 13% 7%	490
	11th to 20th	Day	10% 11% 26% 21% 19% 12%	490
	21st to end	Day	18% 15% 26% 26% 11% 5%	490
October	1st to 10th	Day	26% 16% 24% 16% 14% 4	490
	11th to 20th	Day	25% 22% 30% 15% 6% 2	490
	21st to end	Day	32% 19% 27% 17% 3 1	522
November	1st to 10th	Day	26% 18% 29% 19% 7%	304
	11th to 20th	Day	29% 25% 29% 11% 4 1	180
	21st to end	Day	28% 21% 37% 11% 4	180
December	1st to 10th	Day	32% 19% 34% 13% 2	180
	11th to 20th	Day	34% 20% 30% 12% 2 1	180
	21st to end	Day	36% 21% 29% 13% 2	198
January	1st to 10th	Night	29% 20% 29% 18% 4	760
	11th to 20th	Night	29% 17% 30% 20% 4	760
	21st to end	Night	20% 16% 34% 23% 6% 1	836
February	1st to 10th	Night	24% 20% 34% 20% 2	760
	11th to 20th	Night	22% 18% 40% 17% 4	743
	21st to end	Night	25% 21% 30% 20% 3	628
March	1st to 10th	Night	24% 18% 36% 20% 3	760
	11th to 20th	Night	24% 19% 33% 20% 4 1	760
	21st to end	Night	21% 15% 33% 22% 8% 1	836
April	1st to 10th	Night	25% 15% 33% 21% 5%	760
	11th to 20th	Night	25% 18% 29% 20% 8% 1	751
	21st to end	Night	23% 11% 32% 24% 10%	589
May	1st to 10th	Night	23% 7% 32% 25% 12% 1	460
	11th to 20th	Night	15% 10% 36% 30% 9%	374
	21st to end	Night	12% 7% 36% 31% 13%	411
June	1st to 10th	Night	15% 8% 36% 30% 11%	380
	11th to 20th	Night	12% 11% 28% 37% 11% 1	380
	21st to end	Night	17% 9% 26% 35% 12%	380
July	1st to 10th	Night	7% 5% 31% 40% 16%	370
	11th to 20th	Night	11% 6% 28% 35% 20% 1	368
	21st to end	Night	12% 3 29% 40% 15% 1	434
August	1st to 10th	Night	12% 4 24% 33% 25% 2	567
	11th to 20th	Night	12% 4 21% 34% 26% 2	564
	21st to end	Night	13% 5% 28% 32% 21% 2	765
September	1st to 10th	Night	13% 6% 31% 30% 18% 2	760
	11th to 20th	Night	13% 5% 23% 30% 24% 5%	760
	21st to end	Night	20% 11% 23% 26% 18% 3	760
October	1st to 10th	Night	21% 11% 27% 24% 15% 2	760
	11th to 20th	Night	26% 14% 28% 22% 8% 1	760
	21st to end	Night	28% 16% 29% 22% 6%	836
November	1st to 10th	Night	24% 14% 28% 26% 8% 1	771
	11th to 20th	Night	26% 17% 31% 19% 6% 1	760
	21st to end	Night	29% 16% 29% 21% 5%	760
December	1st to 10th	Night	30% 18% 33% 16% 3	760
	11th to 20th	Night	26% 19% 34% 19% 3	760
	21st to end	Night	34% 16% 30% 17% 3	836

Page generated at 2024-11-05 08:15:53. Version ac07

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