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 2024-01-12.

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% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	74695
	Night	17% 10% 4 7% 6% 3 5% 4 5% 6% 33%	75024
Transparency	Day	51% 6% 12% 19% 11% 1	74402
	Night	51% 6% 12% 19% 11% 1	74852
Seeing	Day	23% 16% 31% 19% 8% 3	13312
	Night	22% 13% 31% 24% 10% 1	22687

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	15% 17% 6% 9% 6% 3 4 4 4 7% 24%	1517
	11th to 20th	Day	18% 19% 6% 7% 6% 3 4 3 4 5% 24%	1462
	21st to end	Day	15% 13% 7% 11% 8% 4 4 4 4 5% 23%	1782
February	1st to 10th	Day	15% 17% 5% 12% 8% 4 5% 6% 4 5% 21%	1620
	11th to 20th	Day	13% 14% 6% 12% 7% 3 4 4 3 4 27%	1573
	21st to end	Day	18% 16% 5% 10% 7% 4 5% 4 3 4 25%	1405
March	1st to 10th	Day	15% 11% 5% 9% 8% 4 4 5% 5% 5% 30%	1913
	11th to 20th	Day	14% 14% 5% 7% 7% 3 5% 4 5% 5% 30%	1980
	21st to end	Day	20% 10% 4 6% 4 2 3 4 4 4 37%	2210
April	1st to 10th	Day	21% 11% 5% 6% 5% 2 4 4 5% 6% 31%	2160
	11th to 20th	Day	23% 7% 2 5% 4 2 4 3 5% 5% 39%	2134
	21st to end	Day	22% 10% 3 7% 6% 3 4 4 4 6% 32%	2337
May	1st to 10th	Day	19% 7% 2 6% 6% 3 5% 5% 6% 6% 35%	2443
	11th to 20th	Day	17% 8% 3 5% 6% 3 5% 5% 5% 6% 39%	2478
	21st to end	Day	14% 5% 3 5% 6% 3 5% 5% 6% 9% 40%	2725
June	1st to 10th	Day	19% 7% 3 6% 6% 4 5% 5% 5% 6% 34%	2520
	11th to 20th	Day	15% 6% 2 5% 5% 3 7% 6% 6% 9% 37%	2520
	21st to end	Day	16% 7% 3 6% 5% 3 5% 5% 6% 8% 36%	2520
July	1st to 10th	Day	12% 4 2 5% 6% 4 5% 5% 6% 9% 42%	2520
	11th to 20th	Day	12% 6% 3 5% 6% 4 5% 5% 7% 9% 39%	2520
	21st to end	Day	11% 6% 2 6% 6% 4 6% 7% 6% 9% 36%	2724
August	1st to 10th	Day	11% 7% 2 5% 6% 4 5% 7% 7% 9% 36%	2327
	11th to 20th	Day	12% 6% 3 6% 7% 3 5% 6% 6% 8% 37%	2303
	21st to end	Day	14% 6% 2 5% 6% 3 5% 5% 7% 8% 38%	2426
September	1st to 10th	Day	14% 6% 3 5% 6% 3 5% 5% 5% 6% 41%	2160
	11th to 20th	Day	12% 4 2 5% 4 3 4 5% 5% 7% 47%	2156
	21st to end	Day	16% 7% 3 5% 6% 3 4 4 6% 7% 39%	1882
October	1st to 10th	Day	21% 8% 3 6% 6% 4 4 4 4 7% 33%	1800
	11th to 20th	Day	23% 10% 3 7% 6% 3 4 5% 5% 7% 26%	1800
	21st to end	Day	28% 12% 3 7% 6% 4 4 4 4 5% 24%	1949
November	1st to 10th	Day	17% 9% 3 6% 7% 4 6% 5% 5% 7% 33%	1591
	11th to 20th	Day	17% 12% 4 7% 7% 3 4 5% 5% 7% 28%	1520
	21st to end	Day	22% 15% 5% 7% 5% 3 5% 5% 5% 6% 21%	1520
December	1st to 10th	Day	19% 19% 7% 11% 6% 4 5% 3 4 4 19%	1520
	11th to 20th	Day	19% 15% 7% 7% 5% 3 4 4 4 4 27%	1906
	21st to end	Day	28% 18% 5% 10% 5% 3 3 3 3 5% 18%	2772
January	1st to 10th	Night	18% 16% 7% 9% 7% 4 5% 4 4 5% 22%	2649
	11th to 20th	Night	19% 16% 5% 9% 7% 4 4 4 4 5% 23%	2537
	21st to end	Night	14% 13% 6% 10% 8% 3 5% 5% 4 6% 26%	2574
February	1st to 10th	Night	14% 15% 5% 10% 8% 3 7% 6% 5% 6% 22%	2340
	11th to 20th	Night	13% 13% 6% 9% 7% 4 4 5% 4 5% 29%	2273
	21st to end	Night	17% 12% 4 7% 6% 4 5% 5% 4 7% 29%	1850
March	1st to 10th	Night	15% 11% 4 7% 6% 4 5% 4 4 7% 33%	2029
	11th to 20th	Night	15% 12% 5% 7% 5% 3 4 4 4 5% 34%	1979
	21st to end	Night	15% 8% 3 6% 6% 3 4 5% 4 6% 39%	2144
April	1st to 10th	Night	20% 10% 4 6% 5% 3 4 4 5% 7% 33%	1800
	11th to 20th	Night	18% 8% 3 7% 5% 2 4 4 5% 6% 38%	1775
	21st to end	Night	18% 9% 3 5% 5% 4 5% 5% 5% 7% 33%	1638
May	1st to 10th	Night	19% 6% 3 6% 5% 3 5% 5% 5% 6% 37%	1516
	11th to 20th	Night	12% 7% 2 4 5% 4 4 5% 6% 7% 44%	1415
	21st to end	Night	11% 5% 2 4 4 4 4 5% 5% 8% 49%	1550
June	1st to 10th	Night	15% 5% 3 5% 6% 3 4 6% 5% 9% 38%	1440
	11th to 20th	Night	12% 5% 3 5% 5% 3 5% 5% 5% 8% 45%	1440
	21st to end	Night	13% 7% 2 6% 5% 3 6% 5% 5% 7% 41%	1440
July	1st to 10th	Night	8% 4 2 5% 5% 3 4 5% 5% 8% 51%	1440
	11th to 20th	Night	10% 5% 2 4 4 3 5% 4 6% 9% 47%	1440
	21st to end	Night	10% 4 2 4 4 3 5% 5% 6% 8% 49%	1591
August	1st to 10th	Night	10% 5% 2 5% 5% 3 4 5% 6% 8% 48%	1611
	11th to 20th	Night	9% 5% 2 5% 5% 3 4 5% 6% 8% 46%	1598
	21st to end	Night	10% 5% 3 5% 4 3 5% 5% 7% 8% 46%	1912
September	1st to 10th	Night	11% 6% 3 4 5% 3 5% 4 7% 8% 45%	1800
	11th to 20th	Night	13% 4 1 4 4 3 3 5% 4 7% 51%	1800
	21st to end	Night	17% 6% 3 4 5% 3 4 3 5% 6% 43%	2078
October	1st to 10th	Night	19% 6% 3 6% 5% 3 5% 4 5% 7% 37%	2160
	11th to 20th	Night	23% 10% 3 6% 5% 3 4 4 4 6% 31%	2160
	21st to end	Night	23% 12% 4 6% 6% 4 5% 4 5% 5% 27%	2406
November	1st to 10th	Night	19% 9% 3 5% 5% 4 5% 3 5% 6% 37%	2487
	11th to 20th	Night	19% 11% 4 6% 6% 3 4 5% 5% 6% 30%	2660
	21st to end	Night	21% 11% 4 8% 6% 4 5% 5% 6% 7% 24%	2660
December	1st to 10th	Night	21% 14% 7% 9% 6% 3 5% 4 5% 6% 19%	2660
	11th to 20th	Night	18% 16% 6% 8% 6% 3 4 4 4 5% 25%	3288
	21st to end	Night	29% 17% 4 10% 6% 3 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	61% 5% 12% 14% 7%	1518
	11th to 20th	Day	64% 6% 9% 10% 10% 1	1462
	21st to end	Day	64% 5% 8% 12% 9% 3	1782
February	1st to 10th	Day	66% 6% 9% 13% 5% 1	1620
	11th to 20th	Day	61% 4 9% 14% 10% 1	1582
	21st to end	Day	64% 4 8% 13% 10% 1	1405
March	1st to 10th	Day	56% 5% 14% 15% 9% 2	1916
	11th to 20th	Day	55% 6% 10% 17% 10% 2	1980
	21st to end	Day	50% 5% 7% 19% 14% 5%	2210
April	1st to 10th	Day	55% 4 9% 19% 10% 3	2160
	11th to 20th	Day	48% 4 9% 22% 16% 1	2134
	21st to end	Day	54% 4 9% 18% 12% 3	2337
May	1st to 10th	Day	49% 5% 10% 19% 14% 3	2443
	11th to 20th	Day	45% 6% 9% 23% 16% 2	2482
	21st to end	Day	41% 8% 14% 20% 14% 3	2725
June	1st to 10th	Day	50% 6% 12% 17% 14% 1	2520
	11th to 20th	Day	42% 8% 11% 24% 13% 2	2520
	21st to end	Day	46% 7% 13% 21% 12% 1	2520
July	1st to 10th	Day	38% 7% 12% 25% 16% 2	2450
	11th to 20th	Day	38% 9% 16% 27% 10%	2445
	21st to end	Day	42% 9% 14% 24% 10% 1	2572
August	1st to 10th	Day	41% 8% 16% 23% 11% 1	2314
	11th to 20th	Day	43% 7% 16% 23% 10% 1	2303
	21st to end	Day	41% 8% 13% 26% 11% 1	2426
September	1st to 10th	Day	41% 7% 12% 27% 12% 1	2160
	11th to 20th	Day	35% 6% 15% 29% 14% 1	2156
	21st to end	Day	44% 7% 14% 25% 9%	1882
October	1st to 10th	Day	51% 5% 12% 19% 12% 1	1800
	11th to 20th	Day	56% 7% 15% 14% 7% 1	1800
	21st to end	Day	63% 5% 9% 15% 7%	1949
November	1st to 10th	Day	50% 7% 15% 19% 8% 1	1591
	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	66% 5% 9% 13% 7%	2649
	11th to 20th	Night	65% 5% 8% 12% 8% 1	2537
	21st to end	Night	59% 5% 8% 16% 11% 1	2574
February	1st to 10th	Night	61% 6% 11% 14% 6% 1	2340
	11th to 20th	Night	57% 5% 10% 19% 9%	2275
	21st to end	Night	55% 6% 11% 19% 9% 1	1850
March	1st to 10th	Night	51% 6% 12% 17% 12% 2	2039
	11th to 20th	Night	52% 5% 11% 20% 11% 1	1980
	21st to end	Night	46% 5% 9% 21% 15% 3	2144
April	1st to 10th	Night	51% 5% 8% 21% 13% 2	1800
	11th to 20th	Night	47% 6% 9% 22% 15% 2	1775
	21st to end	Night	49% 6% 11% 16% 16% 2	1638
May	1st to 10th	Night	46% 5% 9% 19% 16% 4	1516
	11th to 20th	Night	38% 6% 10% 25% 17% 3	1416
	21st to end	Night	34% 7% 14% 22% 18% 4	1551
June	1st to 10th	Night	42% 7% 14% 22% 14% 1	1440
	11th to 20th	Night	37% 7% 12% 22% 20% 2	1440
	21st to end	Night	42% 7% 15% 22% 13% 2	1440
July	1st to 10th	Night	30% 8% 13% 28% 19% 3	1400
	11th to 20th	Night	33% 7% 15% 30% 14%	1392
	21st to end	Night	32% 6% 18% 32% 12% 1	1503
August	1st to 10th	Night	34% 7% 19% 28% 12% 1	1600
	11th to 20th	Night	35% 7% 17% 26% 14% 1	1598
	21st to end	Night	34% 9% 13% 29% 14% 1	1912
September	1st to 10th	Night	35% 9% 15% 26% 14% 1	1800
	11th to 20th	Night	32% 6% 15% 32% 14% 1	1800
	21st to end	Night	41% 6% 13% 28% 11%	2078
October	1st to 10th	Night	46% 8% 11% 21% 13% 1	2160
	11th to 20th	Night	54% 6% 13% 20% 7%	2160
	21st to end	Night	58% 7% 11% 13% 10%	2406
November	1st to 10th	Night	48% 6% 14% 22% 10%	2487
	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	24% 22% 32% 18% 3 1	180
	11th to 20th	Day	30% 19% 33% 15% 3 1	168
	21st to end	Day	24% 22% 36% 13% 5%	264
February	1st to 10th	Day	33% 25% 34% 6% 2	240
	11th to 20th	Day	30% 23% 41% 4 1	240
	21st to end	Day	39% 20% 30% 10% 1	271
March	1st to 10th	Day	26% 21% 35% 15% 3	420
	11th to 20th	Day	28% 18% 34% 17% 3 1	420
	21st to end	Day	32% 20% 28% 13% 6% 1	462
April	1st to 10th	Day	28% 21% 32% 12% 7%	420
	11th to 20th	Day	30% 23% 21% 16% 8% 3	412
	21st to end	Day	27% 20% 34% 12% 6% 2	420
May	1st to 10th	Day	28% 15% 29% 20% 4 5%	423
	11th to 20th	Day	21% 14% 36% 16% 9% 3	447
	21st to end	Day	19% 14% 36% 18% 10% 4	485
June	1st to 10th	Day	22% 12% 35% 23% 6% 1	450
	11th to 20th	Day	17% 13% 32% 23% 11% 3	450
	21st to end	Day	19% 12% 34% 23% 10% 3	450
July	1st to 10th	Day	11% 9% 31% 31% 14% 3	445
	11th to 20th	Day	14% 9% 32% 25% 15% 5%	444
	21st to end	Day	13% 9% 37% 27% 10% 3	488
August	1st to 10th	Day	13% 8% 31% 28% 14% 6%	446
	11th to 20th	Day	12% 8% 26% 30% 18% 7%	439
	21st to end	Day	15% 11% 31% 24% 12% 8%	495
September	1st to 10th	Day	14% 11% 31% 24% 12% 7%	450
	11th to 20th	Day	11% 12% 28% 22% 18% 9%	450
	21st to end	Day	17% 15% 27% 26% 10% 6%	450
October	1st to 10th	Day	26% 16% 23% 16% 14% 4	450
	11th to 20th	Day	26% 22% 30% 14% 6% 2	450
	21st to end	Day	34% 19% 26% 18% 3	480
November	1st to 10th	Day	25% 18% 29% 20% 8%	285
	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% 5%	728
	21st to end	Night	20% 16% 35% 22% 6% 1	792
February	1st to 10th	Night	24% 20% 34% 19% 2	720
	11th to 20th	Night	22% 17% 40% 17% 4	703
	21st to end	Night	25% 21% 31% 20% 3	592
March	1st to 10th	Night	23% 18% 36% 20% 3	720
	11th to 20th	Night	24% 18% 33% 20% 4 1	720
	21st to end	Night	21% 14% 33% 23% 8% 1	792
April	1st to 10th	Night	24% 15% 33% 22% 5%	720
	11th to 20th	Night	24% 17% 28% 21% 8% 1	711
	21st to end	Night	23% 11% 31% 24% 10%	558
May	1st to 10th	Night	24% 7% 31% 25% 12% 1	436
	11th to 20th	Night	16% 9% 36% 30% 10%	354
	21st to end	Night	12% 7% 37% 30% 13% 1	389
June	1st to 10th	Night	15% 7% 37% 29% 12%	360
	11th to 20th	Night	13% 11% 28% 36% 11% 1	360
	21st to end	Night	16% 9% 25% 37% 13%	360
July	1st to 10th	Night	7% 6% 30% 40% 17%	350
	11th to 20th	Night	11% 5% 29% 34% 20% 1	348
	21st to end	Night	11% 3 30% 40% 15% 1	411
August	1st to 10th	Night	12% 4 23% 34% 25% 2	537
	11th to 20th	Night	11% 4 21% 34% 27% 2	534
	21st to end	Night	13% 6% 28% 31% 20% 2	724
September	1st to 10th	Night	13% 6% 32% 29% 18% 2	720
	11th to 20th	Night	14% 5% 25% 30% 23% 4	720
	21st to end	Night	19% 11% 23% 25% 18% 3	720
October	1st to 10th	Night	22% 11% 27% 24% 15% 2	720
	11th to 20th	Night	27% 14% 29% 21% 7% 1	720
	21st to end	Night	29% 15% 29% 22% 5%	792
November	1st to 10th	Night	24% 14% 27% 26% 9% 1	740
	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 2024-01-09 16:24:23. Version ac07

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