Wrights Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wrights Lake Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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	21% 12% 4 8% 5% 4 4 3 5% 6% 28%	144895
	Night	21% 12% 4 9% 5% 4 4 3 5% 6% 27%	137163
Transparency	Day	56% 4 11% 19% 10% 1	148480
	Night	57% 4 10% 19% 10% 1	141668
Seeing	Day	30% 18% 30% 15% 5% 1	19840
	Night	29% 15% 29% 21% 6%	27221

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	14% 17% 5% 17% 9% 5% 4 3 4 4 18%	4690
	11th to 20th	Day	18% 18% 8% 17% 7% 6% 4 2 4 4 12%	4864
	21st to end	Day	14% 10% 4 10% 9% 7% 6% 4 6% 6% 25%	5781
February	1st to 10th	Day	19% 14% 5% 11% 8% 5% 5% 4 5% 5% 20%	1890
	11th to 20th	Day	16% 15% 5% 12% 6% 4 4 4 5% 5% 23%	1843
	21st to end	Day	13% 15% 4 8% 7% 5% 4 3 4 7% 31%	1592
March	1st to 10th	Day	23% 14% 4 12% 6% 5% 3 2 3 4 23%	5027
	11th to 20th	Day	17% 17% 5% 9% 4 3 4 3 4 5% 29%	5090
	21st to end	Day	28% 16% 4 9% 5% 4 4 3 4 4 20%	5587
April	1st to 10th	Day	26% 16% 4 8% 4 3 3 2 3 5% 25%	2514
	11th to 20th	Day	22% 13% 3 6% 4 4 4 4 5% 6% 30%	2559
	21st to end	Day	22% 13% 3 6% 5% 4 4 3 5% 6% 29%	2730
May	1st to 10th	Day	29% 12% 3 8% 5% 4 4 3 4 5% 22%	7817
	11th to 20th	Day	22% 12% 4 7% 4 4 4 3 5% 6% 30%	8220
	21st to end	Day	23% 12% 3 8% 4 4 4 3 5% 6% 27%	9059
June	1st to 10th	Day	23% 11% 3 8% 5% 5% 4 4 5% 7% 26%	2940
	11th to 20th	Day	21% 9% 3 7% 5% 4 4 3 5% 7% 32%	2991
	21st to end	Day	29% 10% 2 6% 5% 4 4 3 5% 7% 25%	3150
July	1st to 10th	Day	19% 10% 3 7% 5% 4 5% 4 6% 8% 28%	8502
	11th to 20th	Day	17% 10% 3 6% 4 5% 4 3 6% 8% 34%	8280
	21st to end	Day	19% 7% 2 6% 4 4 4 4 7% 8% 36%	8723
August	1st to 10th	Day	26% 10% 3 7% 4 4 4 4 5% 7% 27%	4365
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 5% 6% 8% 32%	4227
	21st to end	Day	10% 6% 3 6% 3 4 5% 4 7% 8% 44%	4481
September	1st to 10th	Day	18% 7% 2 6% 4 4 4 3 5% 8% 39%	2400
	11th to 20th	Day	19% 7% 2 6% 3 3 3 3 4 6% 42%	2330
	21st to end	Day	19% 7% 3 5% 4 4 3 3 4 7% 41%	2131
October	1st to 10th	Day	18% 7% 3 6% 4 4 4 4 6% 6% 39%	2000
	11th to 20th	Day	20% 9% 3 7% 5% 4 4 3 6% 7% 33%	2000
	21st to end	Day	21% 10% 3 7% 5% 4 4 4 5% 6% 31%	2200
November	1st to 10th	Day	23% 11% 3 8% 5% 4 3 3 5% 6% 29%	1716
	11th to 20th	Day	23% 14% 4 9% 5% 4 4 3 5% 6% 24%	1680
	21st to end	Day	20% 15% 5% 9% 6% 5% 4 3 4 5% 24%	1680
December	1st to 10th	Day	22% 12% 6% 13% 5% 5% 4 3 4 6% 20%	2690
	11th to 20th	Day	30% 11% 3 8% 5% 5% 5% 3 4 4 24%	3076
	21st to end	Day	20% 13% 7% 12% 5% 3 3 3 4 6% 23%	4070
January	1st to 10th	Night	14% 16% 5% 15% 8% 7% 5% 3 4 5% 18%	8234
	11th to 20th	Night	22% 15% 6% 17% 6% 5% 4 3 4 4 14%	8037
	21st to end	Night	12% 12% 4 12% 9% 7% 6% 5% 6% 6% 21%	8400
February	1st to 10th	Night	19% 14% 4 11% 7% 7% 4 4 5% 5% 21%	2730
	11th to 20th	Night	17% 13% 4 10% 7% 5% 6% 4 6% 6% 23%	2663
	21st to end	Night	14% 13% 3 10% 8% 5% 5% 4 5% 6% 27%	2213
March	1st to 10th	Night	24% 13% 4 11% 7% 5% 4 3 3 4 21%	5031
	11th to 20th	Night	20% 15% 7% 8% 4 4 3 3 4 4 27%	5089
	21st to end	Night	29% 14% 5% 10% 4 3 3 2 3 4 24%	5587
April	1st to 10th	Night	25% 13% 3 7% 5% 4 4 3 4 5% 27%	2105
	11th to 20th	Night	24% 12% 3 7% 5% 4 4 2 4 5% 31%	2008
	21st to end	Night	24% 11% 3 6% 5% 4 3 3 5% 6% 31%	1890
May	1st to 10th	Night	27% 17% 4 8% 4 4 3 3 4 6% 20%	5090
	11th to 20th	Night	25% 13% 3 6% 3 3 4 3 4 6% 29%	4670
	21st to end	Night	18% 16% 4 9% 4 4 4 3 4 5% 29%	5147
June	1st to 10th	Night	27% 11% 2 6% 4 4 3 3 5% 6% 29%	1680
	11th to 20th	Night	21% 11% 3 7% 4 3 5% 3 5% 5% 34%	1639
	21st to end	Night	27% 13% 3 7% 5% 5% 4 3 5% 4 25%	1470
July	1st to 10th	Night	17% 11% 4 9% 5% 6% 6% 4 6% 8% 25%	4405
	11th to 20th	Night	18% 10% 3 8% 5% 4 4 4 4 6% 35%	4710
	21st to end	Night	19% 7% 2 7% 5% 5% 5% 3 5% 7% 35%	5358
August	1st to 10th	Night	24% 11% 3 6% 4 3 4 3 4 6% 34%	3005
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 3 6% 8% 33%	2909
	21st to end	Night	11% 7% 2 6% 3 3 4 3 5% 6% 50%	3416
September	1st to 10th	Night	19% 7% 2 5% 3 3 4 3 4 6% 43%	2000
	11th to 20th	Night	19% 7% 2 6% 3 3 3 2 4 6% 45%	2067
	21st to end	Night	20% 8% 3 7% 3 3 3 3 5% 6% 39%	2268
October	1st to 10th	Night	19% 7% 2 5% 4 4 4 3 5% 6% 42%	2400
	11th to 20th	Night	20% 8% 2 7% 3 4 4 3 5% 7% 37%	2400
	21st to end	Night	26% 9% 2 5% 4 3 4 3 5% 6% 33%	2640
November	1st to 10th	Night	21% 10% 3 6% 4 4 4 3 5% 7% 33%	2799
	11th to 20th	Night	22% 12% 3 9% 6% 4 4 4 4 6% 26%	2940
	21st to end	Night	20% 11% 5% 8% 6% 4 5% 4 4 6% 26%	2940
December	1st to 10th	Night	17% 11% 4 13% 6% 5% 5% 4 5% 6% 24%	4720
	11th to 20th	Night	27% 12% 3 8% 4 4 4 3 4 5% 26%	5353
	21st to end	Night	25% 11% 4 10% 5% 3 3 3 4 5% 27%	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	69% 4 10% 11% 6%	4691
	11th to 20th	Day	74% 5% 6% 12% 3	4894
	21st to end	Day	57% 3 8% 15% 14% 2	5781
February	1st to 10th	Day	66% 4 8% 13% 9% 2	1890
	11th to 20th	Day	63% 5% 8% 16% 8% 1	1851
	21st to end	Day	55% 3 8% 18% 12% 3	1592
March	1st to 10th	Day	66% 3 7% 12% 8% 3	5031
	11th to 20th	Day	58% 3 11% 20% 7% 1	5090
	21st to end	Day	68% 3 4 14% 9% 1	5587
April	1st to 10th	Day	62% 3 6% 14% 13% 2	2514
	11th to 20th	Day	54% 3 8% 20% 13% 1	2559
	21st to end	Day	55% 3 9% 19% 11% 2	2730
May	1st to 10th	Day	65% 2 10% 15% 7% 1	7829
	11th to 20th	Day	56% 4 11% 21% 8%	8224
	21st to end	Day	57% 3 11% 16% 11% 1	9060
June	1st to 10th	Day	58% 4 10% 20% 8% 1	2940
	11th to 20th	Day	52% 4 12% 21% 11% 1	2991
	21st to end	Day	60% 4 11% 15% 9% 1	3150
July	1st to 10th	Day	53% 5% 14% 18% 9% 1	8432
	11th to 20th	Day	46% 5% 13% 26% 10%	8204
	21st to end	Day	45% 4 15% 25% 10%	8531
August	1st to 10th	Day	56% 4 12% 19% 8% 1	4352
	11th to 20th	Day	48% 5% 14% 26% 7%	4266
	21st to end	Day	36% 4 12% 30% 17% 1	4481
September	1st to 10th	Day	44% 4 11% 26% 14% 2	2400
	11th to 20th	Day	44% 3 10% 26% 16% 1	2330
	21st to end	Day	44% 3 8% 26% 18% 1	2131
October	1st to 10th	Day	44% 6% 10% 27% 13% 1	3260
	11th to 20th	Day	43% 4 9% 26% 17% 1	3240
	21st to end	Day	46% 3 13% 24% 13% 2	3538
November	1st to 10th	Day	57% 3 9% 21% 9% 1	1716
	11th to 20th	Day	60% 4 10% 18% 7% 1	1680
	21st to end	Day	62% 5% 11% 15% 7%	1680
December	1st to 10th	Day	64% 4 10% 18% 4	2690
	11th to 20th	Day	62% 4 8% 15% 11%	3075
	21st to end	Day	61% 4 12% 15% 8%	4070
January	1st to 10th	Night	66% 4 9% 16% 4	8234
	11th to 20th	Night	72% 4 8% 12% 4	8082
	21st to end	Night	59% 5% 9% 15% 10% 2	8400
February	1st to 10th	Night	64% 4 9% 13% 9% 1	2730
	11th to 20th	Night	59% 5% 10% 17% 8% 1	2666
	21st to end	Night	57% 3 9% 21% 9% 1	2213
March	1st to 10th	Night	66% 4 6% 13% 11% 1	5040
	11th to 20th	Night	61% 3 8% 19% 8% 1	5090
	21st to end	Night	66% 2 5% 16% 9% 1	5587
April	1st to 10th	Night	60% 4 8% 14% 13% 3	2105
	11th to 20th	Night	56% 4 6% 19% 14% 1	2008
	21st to end	Night	54% 3 9% 20% 12% 3	1890
May	1st to 10th	Night	67% 3 9% 14% 7%	5096
	11th to 20th	Night	58% 3 9% 21% 7% 2	4671
	21st to end	Night	59% 3 11% 18% 9% 1	5148
June	1st to 10th	Night	57% 3 9% 23% 8% 1	1680
	11th to 20th	Night	53% 3 9% 23% 12% 1	1639
	21st to end	Night	63% 4 9% 15% 8% 1	1470
July	1st to 10th	Night	57% 6% 12% 16% 8% 1	4366
	11th to 20th	Night	51% 4 9% 22% 14% 1	4662
	21st to end	Night	49% 4 11% 22% 13% 1	5237
August	1st to 10th	Night	53% 4 12% 24% 7% 1	2993
	11th to 20th	Night	49% 5% 17% 23% 7%	2936
	21st to end	Night	34% 3 15% 29% 18%	3415
September	1st to 10th	Night	42% 3 11% 26% 16% 2	2000
	11th to 20th	Night	42% 3 9% 30% 16% 1	2067
	21st to end	Night	47% 3 8% 27% 14% 1	2268
October	1st to 10th	Night	45% 4 11% 26% 13% 1	3920
	11th to 20th	Night	38% 4 11% 29% 18%	3899
	21st to end	Night	43% 4 12% 23% 17% 1	4252
November	1st to 10th	Night	52% 4 12% 20% 12% 1	2799
	11th to 20th	Night	57% 4 10% 18% 10% 1	2940
	21st to end	Night	58% 5% 13% 16% 7% 1	2940
December	1st to 10th	Night	57% 4 11% 23% 5%	4720
	11th to 20th	Night	59% 4 8% 17% 11% 1	5355
	21st to end	Night	59% 4 9% 18% 9% 1	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	35% 22% 28% 13% 2	430
	11th to 20th	Day	38% 19% 27% 12% 4	430
	21st to end	Day	26% 24% 35% 12% 3	473
February	1st to 10th	Day	32% 22% 28% 15% 2	430
	11th to 20th	Day	33% 26% 28% 11% 2	426
	21st to end	Day	31% 22% 30% 12% 5%	355
March	1st to 10th	Day	30% 26% 32% 10% 2	535
	11th to 20th	Day	33% 29% 26% 9% 4 1	540
	21st to end	Day	38% 24% 25% 10% 2 1	594
April	1st to 10th	Day	44% 24% 24% 6% 2	540
	11th to 20th	Day	37% 25% 27% 8% 3	532
	21st to end	Day	33% 21% 29% 13% 4	540
May	1st to 10th	Day	36% 22% 28% 11% 3 1	606
	11th to 20th	Day	26% 20% 29% 18% 5% 1	774
	21st to end	Day	33% 15% 33% 16% 3 1	845
June	1st to 10th	Day	33% 13% 31% 18% 6%	780
	11th to 20th	Day	27% 16% 32% 18% 6% 1	780
	21st to end	Day	36% 11% 28% 17% 7% 1	780
July	1st to 10th	Day	26% 9% 33% 24% 7% 1	770
	11th to 20th	Day	26% 9% 32% 23% 10% 1	768
	21st to end	Day	29% 7% 34% 21% 7% 2	757
August	1st to 10th	Day	22% 7% 37% 23% 9% 1	566
	11th to 20th	Day	24% 8% 34% 22% 9% 2	535
	21st to end	Day	21% 13% 32% 23% 7% 4	583
September	1st to 10th	Day	20% 13% 38% 20% 7% 2	530
	11th to 20th	Day	25% 16% 31% 16% 9% 2	530
	21st to end	Day	23% 14% 33% 21% 7% 2	491
October	1st to 10th	Day	22% 14% 36% 16% 11% 1	420
	11th to 20th	Day	26% 20% 30% 16% 6% 2	420
	21st to end	Day	28% 23% 32% 11% 5% 2	462
November	1st to 10th	Day	31% 19% 30% 13% 6% 1	425
	11th to 20th	Day	35% 20% 27% 13% 5% 1	430
	21st to end	Day	33% 24% 27% 13% 2	430
December	1st to 10th	Day	36% 20% 29% 14% 2	430
	11th to 20th	Day	42% 22% 26% 9% 2	430
	21st to end	Day	33% 24% 30% 10% 3 1	473
January	1st to 10th	Night	30% 22% 32% 14% 3	950
	11th to 20th	Night	33% 19% 29% 15% 3	914
	21st to end	Night	26% 24% 32% 15% 3	924
February	1st to 10th	Night	30% 19% 30% 18% 2	840
	11th to 20th	Night	30% 24% 30% 14% 2	823
	21st to end	Night	24% 22% 32% 19% 4	692
March	1st to 10th	Night	28% 24% 32% 15% 2	840
	11th to 20th	Night	26% 20% 30% 19% 5%	840
	21st to end	Night	29% 21% 29% 15% 5%	924
April	1st to 10th	Night	35% 18% 30% 15% 3	635
	11th to 20th	Night	30% 19% 33% 15% 3	624
	21st to end	Night	31% 14% 31% 19% 5% 1	630
May	1st to 10th	Night	34% 13% 30% 18% 5%	630
	11th to 20th	Night	30% 12% 27% 23% 7% 1	622
	21st to end	Night	26% 12% 35% 23% 5%	682
June	1st to 10th	Night	34% 8% 31% 23% 5%	630
	11th to 20th	Night	26% 8% 36% 23% 6%	589
	21st to end	Night	34% 5% 21% 30% 9%	420
July	1st to 10th	Night	24% 5% 30% 32% 9%	506
	11th to 20th	Night	25% 6% 28% 31% 10%	612
	21st to end	Night	24% 4 27% 33% 12%	689
August	1st to 10th	Night	21% 5% 25% 35% 14% 1	628
	11th to 20th	Night	22% 5% 24% 35% 13% 1	605
	21st to end	Night	21% 6% 28% 30% 14% 1	660
September	1st to 10th	Night	22% 7% 30% 28% 12% 1	600
	11th to 20th	Night	23% 9% 24% 30% 14% 1	667
	21st to end	Night	26% 11% 27% 26% 9% 1	800
October	1st to 10th	Night	23% 10% 30% 27% 10% 1	800
	11th to 20th	Night	26% 15% 29% 22% 9% 1	800
	21st to end	Night	33% 16% 28% 20% 4	880
November	1st to 10th	Night	30% 14% 30% 21% 5% 1	920
	11th to 20th	Night	31% 20% 27% 18% 5%	950
	21st to end	Night	31% 22% 26% 16% 5%	950
December	1st to 10th	Night	33% 18% 30% 16% 3	950
	11th to 20th	Night	37% 20% 28% 12% 3	950
	21st to end	Night	32% 20% 29% 16% 3	1045

Page generated at 2026-08-12 04:37:16. Version ac07

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