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 2024-12-09.

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	12% 7% 3 6% 5% 5% 5% 4 6% 8% 40%	101263
	Night	13% 7% 3 6% 4 4 4 4 6% 7% 43%	98491
Transparency	Day	38% 8% 12% 19% 18% 5%	105093
	Night	37% 7% 11% 19% 20% 6%	102799
Seeing	Day	16% 11% 23% 23% 18% 9%	14933
	Night	16% 10% 23% 28% 20% 4	24966

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	17% 11% 3 6% 4 4 4 3 5% 6% 36%	2836
	11th to 20th	Day	13% 8% 2 7% 4 4 4 3 4 5% 47%	2840
	21st to end	Day	23% 11% 3 6% 3 3 3 3 3 5% 36%	3288
February	1st to 10th	Day	17% 9% 2 7% 5% 3 4 3 6% 7% 37%	1900
	11th to 20th	Day	21% 6% 3 6% 3 4 4 3 4 6% 39%	1848
	21st to end	Day	22% 8% 3 6% 4 3 4 3 5% 5% 38%	1570
March	1st to 10th	Day	24% 10% 3 7% 4 3 3 3 5% 6% 33%	3179
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 7% 46%	3480
	21st to end	Day	17% 6% 3 7% 5% 4 5% 4 5% 7% 38%	3815
April	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 6% 7% 44%	2180
	11th to 20th	Day	12% 6% 2 7% 4 5% 4 4 5% 6% 47%	2254
	21st to end	Day	10% 4 2 5% 4 5% 4 4 6% 8% 48%	2408
May	1st to 10th	Day	10% 7% 3 7% 5% 4 4 4 6% 9% 41%	4082
	11th to 20th	Day	16% 8% 3 7% 4 5% 4 4 7% 8% 34%	4081
	21st to end	Day	8% 6% 3 6% 4 5% 5% 5% 7% 9% 43%	4476
June	1st to 10th	Day	10% 6% 3 8% 5% 6% 5% 4 7% 10% 35%	2470
	11th to 20th	Day	5% 4 1 5% 4 5% 6% 6% 9% 12% 43%	2470
	21st to end	Day	7% 4 2 7% 6% 6% 6% 5% 9% 10% 38%	2470
July	1st to 10th	Day	7% 6% 2 8% 7% 7% 8% 7% 10% 11% 28%	4120
	11th to 20th	Day	8% 5% 2 8% 6% 6% 7% 6% 7% 10% 35%	4120
	21st to end	Day	11% 9% 4 10% 8% 7% 7% 6% 9% 9% 19%	4466
August	1st to 10th	Day	5% 4 2 7% 5% 5% 6% 6% 9% 11% 40%	4104
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 4 7% 11% 43%	3735
	21st to end	Day	7% 4 2 5% 4 5% 5% 5% 6% 9% 48%	4180
September	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 6% 8% 40%	2119
	11th to 20th	Day	14% 8% 2 5% 4 4 4 4 6% 8% 42%	2090
	21st to end	Day	12% 5% 2 6% 4 4 4 4 5% 6% 47%	2090
October	1st to 10th	Day	11% 5% 2 4 3 4 3 2 4 6% 54%	2090
	11th to 20th	Day	11% 5% 2 3 3 4 3 3 4 6% 56%	2005
	21st to end	Day	13% 6% 2 5% 3 3 3 3 3 5% 54%	2076
November	1st to 10th	Day	12% 7% 3 4 3 3 3 2 4 5% 54%	1762
	11th to 20th	Day	13% 6% 2 5% 3 4 3 2 5% 6% 51%	1800
	21st to end	Day	13% 6% 2 7% 3 4 4 3 6% 7% 46%	1800
December	1st to 10th	Day	20% 8% 2 7% 4 3 4 3 5% 6% 38%	1782
	11th to 20th	Day	17% 8% 3 7% 5% 4 4 3 4 6% 41%	2153
	21st to end	Day	20% 8% 4 6% 4 3 5% 4 5% 6% 35%	3124
January	1st to 10th	Night	18% 9% 3 7% 3 3 3 3 5% 7% 39%	4109
	11th to 20th	Night	13% 9% 4 6% 3 3 4 3 4 5% 45%	4120
	21st to end	Night	23% 13% 4 6% 3 3 2 3 3 4 38%	4365
February	1st to 10th	Night	15% 8% 3 6% 5% 3 4 3 5% 7% 42%	2280
	11th to 20th	Night	21% 7% 2 6% 4 3 4 3 4 4 42%	2218
	21st to end	Night	20% 8% 2 6% 3 5% 3 3 6% 6% 38%	1884
March	1st to 10th	Night	22% 11% 3 7% 4 3 3 3 4 5% 34%	3673
	11th to 20th	Night	11% 6% 2 5% 4 3 4 4 5% 8% 49%	3480
	21st to end	Night	15% 6% 3 7% 5% 4 5% 3 5% 5% 41%	3817
April	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 7% 6% 47%	2014
	11th to 20th	Night	12% 6% 3 5% 3 3 3 3 6% 7% 49%	1875
	21st to end	Night	8% 5% 2 6% 4 3 4 3 6% 8% 51%	1769
May	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 4 6% 8% 41%	2813
	11th to 20th	Night	15% 7% 3 7% 5% 4 5% 4 7% 7% 37%	2812
	21st to end	Night	5% 4 2 5% 4 5% 4 5% 8% 11% 46%	3079
June	1st to 10th	Night	6% 5% 2 7% 5% 6% 5% 7% 9% 11% 36%	1710
	11th to 20th	Night	4 4 2 6% 4 4 5% 5% 8% 12% 46%	1710
	21st to end	Night	6% 5% 1 5% 5% 5% 4 5% 8% 12% 43%	1710
July	1st to 10th	Night	7% 7% 3 8% 6% 6% 7% 5% 8% 11% 30%	2840
	11th to 20th	Night	6% 5% 2 7% 5% 6% 7% 6% 9% 12% 35%	2840
	21st to end	Night	11% 10% 4 10% 6% 6% 7% 5% 8% 10% 23%	3087
August	1st to 10th	Night	5% 4 2 6% 5% 5% 6% 5% 8% 13% 41%	2825
	11th to 20th	Night	7% 6% 3 6% 4 4 4 3 5% 8% 48%	3091
	21st to end	Night	7% 5% 2 5% 4 4 4 4 5% 8% 52%	3476
September	1st to 10th	Night	8% 5% 3 7% 6% 6% 4 5% 7% 9% 42%	2042
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 7% 43%	2090
	21st to end	Night	12% 5% 2 5% 3 4 4 3 5% 7% 50%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 3 3 4 7% 57%	2090
	11th to 20th	Night	10% 5% 2 5% 3 3 4 2 3 5% 58%	2172
	21st to end	Night	11% 6% 2 4 3 3 3 3 3 5% 57%	2519
November	1st to 10th	Night	11% 6% 2 4 3 3 4 3 4 5% 54%	2536
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 6% 53%	2600
	21st to end	Night	14% 7% 2 5% 4 3 4 4 5% 6% 46%	2600
December	1st to 10th	Night	17% 8% 3 7% 4 4 4 4 5% 6% 40%	2581
	11th to 20th	Night	16% 9% 2 5% 3 3 3 3 4 6% 46%	3042
	21st to end	Night	18% 10% 4 7% 5% 4 4 3 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	46% 7% 7% 15% 22% 4	2837
	11th to 20th	Day	38% 6% 7% 21% 22% 4	2840
	21st to end	Day	49% 5% 5% 16% 20% 4	3288
February	1st to 10th	Day	46% 4 9% 18% 20% 4	1900
	11th to 20th	Day	46% 5% 6% 18% 19% 6%	1858
	21st to end	Day	48% 5% 7% 14% 19% 7%	1570
March	1st to 10th	Day	52% 5% 9% 11% 13% 9%	3179
	11th to 20th	Day	38% 5% 8% 17% 23% 9%	3480
	21st to end	Day	44% 6% 9% 19% 18% 4	3815
April	1st to 10th	Day	39% 5% 11% 21% 19% 6%	2180
	11th to 20th	Day	37% 7% 7% 18% 24% 8%	2254
	21st to end	Day	33% 6% 11% 27% 20% 3	2408
May	1st to 10th	Day	36% 8% 15% 22% 18% 2	4120
	11th to 20th	Day	44% 9% 13% 22% 11% 1	4085
	21st to end	Day	32% 10% 14% 23% 19% 2	4489
June	1st to 10th	Day	41% 10% 17% 20% 11% 2	2470
	11th to 20th	Day	28% 11% 20% 27% 13% 1	2470
	21st to end	Day	36% 12% 17% 21% 12% 2	2470
July	1st to 10th	Day	42% 14% 21% 18% 5% 1	4055
	11th to 20th	Day	40% 12% 20% 20% 6% 1	4051
	21st to end	Day	56% 13% 14% 12% 5%	4324
August	1st to 10th	Day	32% 9% 15% 32% 11%	4091
	11th to 20th	Day	33% 8% 18% 25% 14% 2	3771
	21st to end	Day	30% 9% 14% 23% 20% 3	4179
September	1st to 10th	Day	39% 9% 15% 15% 17% 5%	2119
	11th to 20th	Day	39% 9% 12% 19% 19% 2	2090
	21st to end	Day	37% 5% 12% 17% 22% 7%	2090
October	1st to 10th	Day	25% 4 7% 12% 38% 14%	3480
	11th to 20th	Day	20% 3 5% 16% 29% 26%	3310
	21st to end	Day	27% 3 6% 23% 29% 12%	3402
November	1st to 10th	Day	35% 3 7% 16% 30% 9%	1762
	11th to 20th	Day	35% 3 7% 17% 28% 10%	1800
	21st to end	Day	38% 5% 8% 17% 26% 6%	1800
December	1st to 10th	Day	46% 5% 7% 19% 18% 5%	1782
	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% 6% 7% 17% 24% 4	4109
	11th to 20th	Night	41% 5% 6% 22% 19% 7%	4120
	21st to end	Night	50% 4 4 12% 24% 5%	4365
February	1st to 10th	Night	42% 4 8% 19% 19% 7%	2280
	11th to 20th	Night	46% 5% 5% 17% 19% 7%	2219
	21st to end	Night	46% 5% 8% 16% 17% 8%	1884
March	1st to 10th	Night	51% 6% 9% 14% 14% 6%	3673
	11th to 20th	Night	32% 5% 10% 17% 25% 10%	3480
	21st to end	Night	41% 7% 7% 19% 20% 6%	3817
April	1st to 10th	Night	35% 6% 10% 19% 24% 6%	2014
	11th to 20th	Night	33% 5% 8% 20% 23% 9%	1875
	21st to end	Night	31% 6% 11% 28% 20% 5%	1769
May	1st to 10th	Night	36% 10% 15% 21% 16% 2	2840
	11th to 20th	Night	40% 9% 15% 23% 11% 1	2813
	21st to end	Night	26% 11% 16% 25% 19% 2	3087
June	1st to 10th	Night	35% 14% 18% 19% 13% 2	1710
	11th to 20th	Night	28% 9% 23% 25% 14% 2	1710
	21st to end	Night	31% 10% 21% 19% 14% 4	1710
July	1st to 10th	Night	44% 11% 20% 18% 6% 1	2795
	11th to 20th	Night	36% 14% 21% 22% 6% 2	2786
	21st to end	Night	53% 13% 15% 13% 5% 1	2988
August	1st to 10th	Night	32% 9% 17% 33% 9%	2814
	11th to 20th	Night	33% 8% 13% 28% 16% 1	3121
	21st to end	Night	29% 9% 13% 19% 27% 3	3476
September	1st to 10th	Night	36% 11% 15% 17% 15% 6%	2042
	11th to 20th	Night	38% 9% 11% 20% 19% 2	2090
	21st to end	Night	33% 7% 12% 20% 21% 8%	2090
October	1st to 10th	Night	23% 4 9% 13% 38% 12%	3480
	11th to 20th	Night	18% 3 5% 17% 34% 23%	3606
	21st to end	Night	22% 3 4 24% 30% 17%	4143
November	1st to 10th	Night	32% 5% 8% 18% 26% 11%	2536
	11th to 20th	Night	33% 4 6% 18% 28% 11%	2600
	21st to end	Night	38% 5% 6% 19% 26% 6%	2600
December	1st to 10th	Night	44% 6% 8% 19% 19% 4	2581
	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% 21% 31% 13% 5% 1	270
	21st to end	Day	23% 27% 36% 10% 3 1	297
February	1st to 10th	Day	25% 21% 34% 18% 2	270
	11th to 20th	Day	36% 21% 31% 11% 1	270
	21st to end	Day	30% 25% 35% 9% 2	225
March	1st to 10th	Day	27% 17% 33% 18% 4 1	303
	11th to 20th	Day	20% 20% 32% 20% 7%	460
	21st to end	Day	20% 20% 34% 20% 6% 1	506
April	1st to 10th	Day	18% 17% 32% 19% 12% 2	460
	11th to 20th	Day	13% 17% 34% 22% 13% 1	452
	21st to end	Day	15% 12% 30% 25% 17% 2	460
May	1st to 10th	Day	13% 10% 32% 24% 14% 6%	463
	11th to 20th	Day	14% 6% 21% 29% 19% 10%	487
	21st to end	Day	13% 5% 17% 31% 21% 12%	529
June	1st to 10th	Day	13% 4 17% 28% 25% 12%	490
	11th to 20th	Day	7% 3 17% 26% 28% 21%	490
	21st to end	Day	10% 2 17% 28% 26% 16%	490
July	1st to 10th	Day	11% 2 9% 24% 29% 25%	485
	11th to 20th	Day	8% 1 10% 20% 33% 29%	484
	21st to end	Day	9% 3 7% 20% 39% 22%	532
August	1st to 10th	Day	11% 3 12% 25% 27% 22%	486
	11th to 20th	Day	12% 1 11% 31% 27% 18%	479
	21st to end	Day	14% 2 9% 26% 28% 21%	539
September	1st to 10th	Day	11% 4 12% 28% 27% 17%	490
	11th to 20th	Day	15% 7% 13% 24% 29% 11%	490
	21st to end	Day	14% 4 19% 26% 26% 11%	490
October	1st to 10th	Day	14% 4 21% 32% 20% 9%	490
	11th to 20th	Day	12% 11% 24% 27% 22% 3	490
	21st to end	Day	18% 12% 22% 25% 21% 3	525
November	1st to 10th	Day	19% 14% 28% 22% 13% 4	300
	11th to 20th	Day	18% 19% 34% 20% 7% 2	300
	21st to end	Day	9% 22% 38% 21% 9% 1	300
December	1st to 10th	Day	26% 22% 30% 17% 4 1	294
	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	22% 19% 30% 23% 6%	760
	21st to end	Night	22% 19% 33% 23% 3	836
February	1st to 10th	Night	22% 15% 32% 27% 5%	760
	11th to 20th	Night	25% 19% 33% 22% 1	743
	21st to end	Night	24% 19% 36% 19% 2	628
March	1st to 10th	Night	18% 18% 32% 27% 5%	760
	11th to 20th	Night	17% 14% 35% 24% 11%	760
	21st to end	Night	18% 14% 32% 27% 8%	836
April	1st to 10th	Night	13% 15% 31% 27% 12%	684
	11th to 20th	Night	16% 13% 28% 31% 12% 1	563
	21st to end	Night	12% 9% 26% 35% 17% 1	570
May	1st to 10th	Night	9% 11% 25% 32% 22% 1	570
	11th to 20th	Night	13% 7% 22% 31% 23% 4	561
	21st to end	Night	10% 4 14% 34% 32% 7%	617
June	1st to 10th	Night	8% 3 13% 39% 32% 6%	570
	11th to 20th	Night	4 3 13% 30% 37% 14%	570
	21st to end	Night	7% 2 8% 35% 40% 9%	570
July	1st to 10th	Night	9% 3 9% 22% 44% 14%	555
	11th to 20th	Night	7% 1 7% 20% 50% 15%	552
	21st to end	Night	8% 2 9% 25% 44% 11%	624
August	1st to 10th	Night	8% 1 7% 31% 41% 12%	567
	11th to 20th	Night	10% 2 10% 29% 41% 8%	564
	21st to end	Night	14% 2 11% 26% 37% 11%	627
September	1st to 10th	Night	10% 3 12% 28% 38% 10%	712
	11th to 20th	Night	16% 3 14% 26% 36% 4	760
	21st to end	Night	14% 3 17% 30% 33% 2	760
October	1st to 10th	Night	11% 4 22% 33% 23% 7%	760
	11th to 20th	Night	13% 8% 25% 31% 21% 3	760
	21st to end	Night	14% 10% 22% 36% 16% 3	836
November	1st to 10th	Night	14% 8% 26% 29% 21% 1	780
	11th to 20th	Night	16% 13% 31% 27% 12% 1	800
	21st to end	Night	19% 14% 27% 27% 12% 1	800
December	1st to 10th	Night	21% 17% 30% 24% 7% 1	795
	11th to 20th	Night	24% 13% 30% 24% 8%	760
	21st to end	Night	27% 16% 26% 26% 5%	836

Page generated at 2024-12-06 03:54:46. Version ac07

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