White Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the White Lake Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	13% 6% 3 5% 5% 3 5% 5% 6% 8% 41%	74891
	Night	12% 6% 3 5% 5% 3 4 5% 5% 8% 44%	74924
Transparency	Day	40% 8% 12% 19% 17% 4	74614
	Night	38% 7% 11% 19% 19% 5%	74720
Seeing	Day	16% 11% 23% 23% 18% 10%	13713
	Night	16% 10% 23% 27% 20% 4	23804

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	18% 8% 3 5% 4 2 4 4 4 7% 41%	1706
	11th to 20th	Day	17% 9% 3 6% 5% 2 4 4 3 6% 42%	1665
	21st to end	Day	16% 9% 4 5% 4 2 4 4 4 5% 43%	1876
February	1st to 10th	Day	17% 8% 3 6% 5% 2 4 5% 5% 8% 37%	1800
	11th to 20th	Day	22% 6% 3 5% 4 3 4 4 4 6% 39%	1748
	21st to end	Day	23% 7% 3 5% 4 2 4 4 5% 5% 38%	1480
March	1st to 10th	Day	15% 5% 2 6% 5% 3 4 3 5% 7% 45%	1831
	11th to 20th	Day	18% 8% 3 5% 4 4 4 5% 5% 7% 37%	1980
	21st to end	Day	15% 6% 3 6% 6% 3 6% 5% 5% 7% 38%	2178
April	1st to 10th	Day	12% 6% 2 5% 5% 3 5% 5% 5% 7% 45%	2065
	11th to 20th	Day	12% 5% 3 6% 4 4 4 4 5% 5% 46%	2134
	21st to end	Day	10% 4 2 5% 4 4 5% 5% 6% 9% 49%	2281
May	1st to 10th	Day	10% 5% 2 4 5% 2 5% 4 6% 9% 48%	2340
	11th to 20th	Day	10% 5% 3 6% 6% 4 6% 5% 7% 9% 39%	2301
	21st to end	Day	8% 6% 3 5% 5% 4 5% 6% 7% 10% 42%	2531
June	1st to 10th	Day	10% 6% 3 7% 7% 4 6% 5% 7% 10% 35%	2340
	11th to 20th	Day	5% 3 2 5% 5% 3 6% 7% 9% 12% 42%	2340
	21st to end	Day	7% 4 2 6% 7% 4 7% 6% 9% 10% 38%	2340
July	1st to 10th	Day	9% 5% 3 6% 7% 4 8% 8% 9% 11% 30%	2340
	11th to 20th	Day	8% 4 3 7% 7% 5% 8% 9% 8% 11% 30%	2340
	21st to end	Day	6% 5% 3 6% 7% 5% 8% 8% 10% 11% 30%	2547
August	1st to 10th	Day	6% 5% 2 7% 7% 5% 8% 9% 10% 11% 30%	2327
	11th to 20th	Day	11% 6% 3 6% 8% 4 7% 6% 7% 9% 33%	2131
	21st to end	Day	12% 7% 3 5% 8% 5% 7% 7% 7% 10% 29%	2376
September	1st to 10th	Day	11% 6% 2 5% 6% 3 6% 6% 6% 9% 40%	2008
	11th to 20th	Day	14% 7% 2 4 5% 3 4 5% 6% 7% 43%	1980
	21st to end	Day	12% 5% 2 5% 5% 3 4 4 5% 6% 48%	1980
October	1st to 10th	Day	11% 5% 2 4 4 3 4 3 4 6% 54%	1980
	11th to 20th	Day	12% 5% 2 3 3 3 3 4 4 6% 54%	1900
	21st to end	Day	13% 6% 2 5% 4 2 3 3 3 5% 54%	1967
November	1st to 10th	Day	12% 6% 3 3 3 2 4 3 4 5% 56%	1672
	11th to 20th	Day	13% 6% 2 4 4 3 4 3 5% 5% 52%	1710
	21st to end	Day	14% 6% 2 6% 4 3 4 4 5% 7% 45%	1710
December	1st to 10th	Day	20% 8% 2 6% 5% 3 4 4 5% 6% 38%	1710
	11th to 20th	Day	17% 7% 3 6% 6% 3 4 4 4 6% 41%	2153
	21st to end	Day	21% 8% 4 5% 5% 2 4 5% 5% 6% 35%	3124
January	1st to 10th	Night	19% 8% 3 5% 3 2 4 3 4 6% 43%	2459
	11th to 20th	Night	17% 8% 4 6% 4 3 5% 4 5% 6% 38%	2417
	21st to end	Night	17% 7% 4 5% 4 2 3 4 4 5% 46%	2477
February	1st to 10th	Night	16% 7% 3 5% 5% 3 3 4 5% 7% 42%	2160
	11th to 20th	Night	21% 7% 3 5% 4 2 4 4 3 5% 42%	2098
	21st to end	Night	21% 7% 3 5% 4 3 4 4 6% 6% 37%	1776
March	1st to 10th	Night	14% 7% 3 5% 3 2 4 3 5% 5% 48%	2128
	11th to 20th	Night	14% 7% 3 5% 6% 2 4 5% 5% 8% 41%	1980
	21st to end	Night	13% 6% 3 6% 6% 2 5% 4 5% 6% 44%	2178
April	1st to 10th	Night	11% 4 2 4 5% 2 5% 5% 6% 7% 48%	1908
	11th to 20th	Night	12% 6% 3 4 4 3 3 4 6% 7% 50%	1775
	21st to end	Night	8% 5% 2 5% 4 2 4 4 5% 8% 52%	1676
May	1st to 10th	Night	9% 4 2 5% 4 3 5% 5% 5% 8% 51%	1620
	11th to 20th	Night	9% 6% 3 5% 6% 3 6% 6% 7% 8% 42%	1592
	21st to end	Night	7% 6% 3 4 5% 4 5% 6% 6% 10% 44%	1744
June	1st to 10th	Night	5% 5% 3 6% 6% 4 6% 8% 9% 12% 37%	1620
	11th to 20th	Night	4 3 3 5% 5% 3 5% 5% 8% 12% 47%	1620
	21st to end	Night	6% 4 2 4 6% 3 5% 6% 9% 12% 43%	1620
July	1st to 10th	Night	7% 7% 4 6% 6% 3 7% 7% 8% 11% 36%	1620
	11th to 20th	Night	6% 4 3 6% 5% 4 8% 7% 9% 11% 36%	1620
	21st to end	Night	6% 6% 3 6% 6% 4 6% 7% 8% 11% 36%	1771
August	1st to 10th	Night	6% 5% 2 6% 7% 4 5% 8% 7% 14% 36%	1611
	11th to 20th	Night	8% 6% 4 6% 6% 4 6% 5% 6% 9% 40%	1767
	21st to end	Night	12% 6% 3 7% 5% 4 6% 6% 6% 9% 36%	1980
September	1st to 10th	Night	8% 4 3 6% 6% 4 4 6% 7% 9% 43%	1934
	11th to 20th	Night	12% 6% 2 5% 5% 3 4 5% 5% 7% 45%	1980
	21st to end	Night	11% 4 2 4 4 2 4 4 5% 7% 52%	1980
October	1st to 10th	Night	10% 4 2 3 4 2 4 3 4 7% 58%	1980
	11th to 20th	Night	11% 5% 2 4 4 2 4 3 3 5% 56%	2057
	21st to end	Night	12% 6% 3 4 4 2 2 4 4 5% 55%	2386
November	1st to 10th	Night	11% 5% 2 3 3 2 3 4 4 5% 56%	2406
	11th to 20th	Night	12% 6% 3 4 4 2 3 3 4 6% 53%	2470
	21st to end	Night	15% 6% 2 4 4 2 4 5% 5% 6% 45%	2470
December	1st to 10th	Night	18% 7% 3 6% 5% 3 4 4 5% 6% 39%	2470
	11th to 20th	Night	16% 9% 2 4 3 2 3 3 4 6% 46%	3042
	21st to end	Night	19% 10% 4 5% 6% 3 4 4 5% 7% 33%	4532

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	43% 6% 8% 19% 21% 4	1707
	11th to 20th	Day	45% 4 8% 18% 21% 4	1665
	21st to end	Day	43% 5% 6% 19% 21% 6%	1876
February	1st to 10th	Day	46% 4 9% 18% 20% 3	1800
	11th to 20th	Day	46% 5% 7% 18% 19% 5%	1758
	21st to end	Day	48% 5% 8% 14% 18% 7%	1480
March	1st to 10th	Day	39% 5% 10% 16% 21% 9%	1831
	11th to 20th	Day	46% 6% 11% 14% 17% 5%	1980
	21st to end	Day	44% 7% 10% 20% 16% 3	2178
April	1st to 10th	Day	38% 5% 11% 21% 18% 6%	2065
	11th to 20th	Day	38% 7% 7% 18% 23% 7%	2134
	21st to end	Day	32% 6% 12% 27% 21% 3	2281
May	1st to 10th	Day	32% 7% 13% 22% 22% 4	2340
	11th to 20th	Day	39% 10% 15% 21% 13% 1	2305
	21st to end	Day	35% 9% 13% 24% 17% 2	2531
June	1st to 10th	Day	41% 10% 16% 20% 11% 1	2340
	11th to 20th	Day	29% 11% 21% 26% 12% 1	2340
	21st to end	Day	37% 12% 17% 21% 11% 2	2340
July	1st to 10th	Day	41% 13% 20% 16% 8% 1	2275
	11th to 20th	Day	42% 14% 19% 14% 8% 2	2271
	21st to end	Day	39% 16% 18% 18% 8%	2405
August	1st to 10th	Day	39% 15% 20% 19% 5% 1	2314
	11th to 20th	Day	44% 12% 17% 17% 9% 2	2131
	21st to end	Day	47% 12% 15% 14% 10% 2	2376
September	1st to 10th	Day	39% 9% 15% 16% 16% 5%	2008
	11th to 20th	Day	38% 9% 12% 19% 20% 2	1980
	21st to end	Day	37% 5% 11% 17% 23% 7%	1980
October	1st to 10th	Day	32% 6% 9% 18% 27% 8%	1980
	11th to 20th	Day	31% 5% 9% 23% 24% 9%	1900
	21st to end	Day	34% 4 6% 18% 28% 9%	1967
November	1st to 10th	Day	33% 3 7% 16% 32% 10%	1672
	11th to 20th	Day	35% 3 7% 18% 27% 10%	1710
	21st to end	Day	39% 5% 8% 17% 25% 6%	1710
December	1st to 10th	Day	47% 5% 7% 19% 17% 5%	1710
	11th to 20th	Day	45% 4 6% 17% 22% 6%	2150
	21st to end	Day	46% 7% 10% 18% 17% 2	3124
January	1st to 10th	Night	43% 4 8% 18% 22% 5%	2459
	11th to 20th	Night	47% 6% 7% 18% 19% 4	2417
	21st to end	Night	41% 4 5% 21% 25% 5%	2477
February	1st to 10th	Night	42% 4 8% 19% 19% 7%	2160
	11th to 20th	Night	46% 5% 6% 17% 20% 7%	2099
	21st to end	Night	47% 5% 8% 16% 17% 8%	1776
March	1st to 10th	Night	38% 4 8% 18% 20% 11%	2128
	11th to 20th	Night	41% 7% 11% 17% 19% 6%	1980
	21st to end	Night	40% 6% 9% 23% 19% 3	2178
April	1st to 10th	Night	34% 6% 10% 19% 24% 6%	1908
	11th to 20th	Night	33% 5% 8% 21% 24% 9%	1775
	21st to end	Night	30% 5% 11% 29% 20% 5%	1676
May	1st to 10th	Night	31% 7% 13% 23% 22% 4	1620
	11th to 20th	Night	37% 10% 17% 21% 15% 1	1593
	21st to end	Night	33% 11% 12% 24% 18% 3	1745
June	1st to 10th	Night	34% 14% 19% 19% 13% 2	1620
	11th to 20th	Night	28% 9% 24% 25% 13% 2	1620
	21st to end	Night	31% 10% 21% 19% 14% 4	1620
July	1st to 10th	Night	39% 11% 19% 19% 10% 1	1575
	11th to 20th	Night	35% 15% 21% 17% 9% 3	1566
	21st to end	Night	37% 13% 21% 20% 8% 2	1672
August	1st to 10th	Night	35% 14% 20% 24% 7% 1	1600
	11th to 20th	Night	39% 12% 17% 17% 14% 1	1767
	21st to end	Night	42% 12% 16% 17% 11% 2	1980
September	1st to 10th	Night	35% 11% 16% 18% 15% 5%	1934
	11th to 20th	Night	37% 10% 11% 20% 20% 2	1980
	21st to end	Night	32% 7% 12% 21% 21% 8%	1980
October	1st to 10th	Night	28% 5% 11% 20% 29% 7%	1980
	11th to 20th	Night	32% 5% 8% 20% 26% 9%	2057
	21st to end	Night	32% 4 5% 18% 29% 12%	2386
November	1st to 10th	Night	31% 4 8% 18% 27% 12%	2406
	11th to 20th	Night	33% 4 6% 18% 27% 11%	2470
	21st to end	Night	39% 5% 6% 19% 25% 6%	2470
December	1st to 10th	Night	45% 6% 8% 19% 18% 4	2470
	11th to 20th	Night	40% 5% 7% 16% 27% 6%	3044
	21st to end	Night	48% 6% 8% 21% 15% 2	4532

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% 27% 36% 11% 2	270
	11th to 20th	Day	29% 20% 31% 14% 5% 1	255
	21st to end	Day	22% 28% 36% 10% 3 1	264
February	1st to 10th	Day	25% 23% 35% 16% 2	240
	11th to 20th	Day	36% 22% 32% 10%	240
	21st to end	Day	30% 23% 35% 10% 2	198
March	1st to 10th	Day	23% 17% 37% 18% 4 1	271
	11th to 20th	Day	22% 21% 31% 19% 7%	420
	21st to end	Day	19% 20% 34% 19% 6% 1	462
April	1st to 10th	Day	17% 17% 32% 20% 13% 2	420
	11th to 20th	Day	13% 17% 33% 21% 14% 1	412
	21st to end	Day	15% 11% 30% 24% 17% 3	420
May	1st to 10th	Day	13% 10% 33% 24% 15% 5%	423
	11th to 20th	Day	13% 5% 21% 29% 20% 11%	447
	21st to end	Day	13% 5% 15% 31% 23% 14%	485
June	1st to 10th	Day	14% 3 16% 28% 26% 13%	450
	11th to 20th	Day	7% 3 15% 25% 27% 22%	450
	21st to end	Day	10% 3 17% 28% 25% 17%	450
July	1st to 10th	Day	11% 2 8% 24% 29% 25%	445
	11th to 20th	Day	8% 1 9% 20% 32% 29%	444
	21st to end	Day	8% 2 7% 19% 40% 24%	488
August	1st to 10th	Day	11% 3 13% 23% 26% 23%	446
	11th to 20th	Day	13% 1 10% 31% 27% 19%	439
	21st to end	Day	15% 2 10% 25% 28% 20%	495
September	1st to 10th	Day	12% 4 11% 26% 29% 18%	450
	11th to 20th	Day	14% 7% 13% 24% 30% 12%	450
	21st to end	Day	12% 4 19% 27% 27% 11%	450
October	1st to 10th	Day	15% 4 22% 30% 19% 9%	450
	11th to 20th	Day	13% 11% 24% 26% 22% 4	450
	21st to end	Day	19% 13% 22% 25% 19% 2	482
November	1st to 10th	Day	19% 13% 27% 23% 13% 4	270
	11th to 20th	Day	17% 20% 35% 20% 7% 2	270
	21st to end	Day	8% 21% 39% 21% 10% 1	270
December	1st to 10th	Day	28% 21% 28% 17% 4 1	270
	11th to 20th	Day	24% 19% 31% 19% 7%	270
	21st to end	Day	28% 18% 35% 16% 4	297
January	1st to 10th	Night	23% 22% 30% 20% 5%	760
	11th to 20th	Night	23% 18% 30% 23% 6%	744
	21st to end	Night	20% 19% 33% 24% 3	792
February	1st to 10th	Night	22% 15% 32% 26% 6%	720
	11th to 20th	Night	25% 19% 33% 22% 1	703
	21st to end	Night	24% 18% 35% 19% 3	592
March	1st to 10th	Night	17% 18% 33% 26% 5%	720
	11th to 20th	Night	18% 14% 34% 24% 11%	720
	21st to end	Night	18% 14% 33% 27% 8% 1	792
April	1st to 10th	Night	13% 14% 31% 28% 13%	648
	11th to 20th	Night	16% 13% 28% 30% 13% 1	533
	21st to end	Night	12% 9% 25% 35% 17% 1	540
May	1st to 10th	Night	9% 11% 25% 32% 22% 1	540
	11th to 20th	Night	12% 6% 23% 31% 24% 4	531
	21st to end	Night	11% 4 13% 33% 33% 7%	584
June	1st to 10th	Night	8% 2 13% 38% 33% 6%	540
	11th to 20th	Night	4 3 12% 30% 37% 14%	540
	21st to end	Night	7% 1 8% 35% 39% 9%	540
July	1st to 10th	Night	9% 2 8% 22% 44% 14%	525
	11th to 20th	Night	6% 2 8% 20% 50% 14%	522
	21st to end	Night	8% 2 9% 25% 45% 12%	591
August	1st to 10th	Night	8% 1 7% 30% 41% 13%	537
	11th to 20th	Night	10% 2 9% 28% 43% 8%	534
	21st to end	Night	15% 2 11% 25% 36% 11%	594
September	1st to 10th	Night	10% 2 11% 27% 39% 11%	674
	11th to 20th	Night	15% 3 15% 26% 37% 4	720
	21st to end	Night	14% 3 17% 31% 34% 2	720
October	1st to 10th	Night	11% 4 23% 31% 23% 7%	720
	11th to 20th	Night	13% 8% 25% 30% 21% 3	720
	21st to end	Night	15% 10% 22% 35% 16% 3	792
November	1st to 10th	Night	14% 8% 26% 29% 22% 1	740
	11th to 20th	Night	15% 13% 31% 27% 12% 1	760
	21st to end	Night	20% 13% 27% 28% 12% 1	760
December	1st to 10th	Night	22% 17% 29% 23% 8% 1	760
	11th to 20th	Night	24% 13% 30% 24% 8%	760
	21st to end	Night	27% 16% 26% 26% 5%	836

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