Lake St. Clair Metropark Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake St. Clair Metropark Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	125684
	Night	14% 10% 4 8% 5% 4 4 4 5% 7% 35%	123452
Transparency	Day	30% 38% 8% 14% 8% 1	129255
	Night	31% 38% 8% 14% 8% 1	127937
Seeing	Day	16% 4 21% 31% 21% 8%	16476
	Night	19% 5% 27% 32% 15% 2	26012

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	12% 13% 6% 13% 7% 5% 5% 3 5% 6% 27%	3617
	11th to 20th	Day	13% 15% 4 16% 8% 9% 7% 4 6% 6% 12%	3704
	21st to end	Day	22% 14% 5% 10% 6% 5% 5% 4 5% 6% 18%	4466
February	1st to 10th	Day	14% 14% 4 10% 7% 6% 7% 4 5% 6% 23%	1800
	11th to 20th	Day	13% 12% 5% 10% 7% 6% 5% 4 5% 6% 26%	1856
	21st to end	Day	13% 12% 4 11% 6% 5% 5% 5% 6% 7% 28%	1650
March	1st to 10th	Day	14% 11% 4 9% 6% 5% 4 4 5% 5% 31%	4656
	11th to 20th	Day	11% 10% 3 8% 6% 6% 5% 4 5% 7% 35%	4980
	21st to end	Day	16% 10% 3 9% 6% 6% 5% 4 5% 6% 30%	5465
April	1st to 10th	Day	14% 11% 3 8% 6% 4 4 4 6% 7% 33%	2284
	11th to 20th	Day	16% 7% 3 7% 6% 4 5% 4 5% 7% 34%	2567
	21st to end	Day	16% 8% 3 8% 5% 4 4 4 5% 7% 36%	2600
May	1st to 10th	Day	18% 9% 3 7% 5% 5% 4 4 5% 6% 35%	5862
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	5861
	21st to end	Day	13% 6% 2 7% 5% 4 5% 4 6% 7% 41%	6433
June	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	2923
	11th to 20th	Day	8% 5% 2 8% 4 5% 5% 5% 7% 9% 42%	3000
	21st to end	Day	7% 6% 2 6% 5% 6% 5% 5% 7% 10% 40%	2959
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 4 7% 10% 41%	6360
	11th to 20th	Day	6% 4 2 6% 5% 4 5% 5% 7% 9% 47%	6342
	21st to end	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 45%	6424
August	1st to 10th	Day	11% 5% 2 5% 4 5% 5% 5% 7% 10% 42%	4234
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 5% 8% 11% 39%	4174
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 10% 40%	4675
September	1st to 10th	Day	9% 6% 2 5% 5% 4 5% 4 6% 9% 45%	2253
	11th to 20th	Day	8% 5% 2 4 5% 4 4 3 7% 9% 50%	2178
	21st to end	Day	14% 6% 2 6% 5% 4 4 4 6% 8% 38%	2090
October	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 6% 8% 43%	2009
	11th to 20th	Day	17% 9% 3 7% 4 5% 5% 3 6% 7% 35%	1900
	21st to end	Day	18% 8% 3 9% 5% 5% 5% 4 6% 7% 31%	1971
November	1st to 10th	Day	11% 8% 3 7% 5% 5% 4 4 6% 8% 38%	1762
	11th to 20th	Day	14% 11% 3 8% 4 5% 5% 4 6% 8% 32%	1800
	21st to end	Day	18% 11% 5% 11% 5% 4 5% 4 5% 6% 26%	1615
December	1st to 10th	Day	14% 12% 5% 11% 7% 6% 6% 4 5% 5% 25%	2600
	11th to 20th	Day	20% 17% 4 9% 5% 5% 4 4 5% 5% 21%	2885
	21st to end	Day	24% 16% 6% 12% 6% 5% 4 3 4 5% 13%	3729
January	1st to 10th	Night	13% 14% 5% 10% 6% 4 4 3 5% 6% 28%	6348
	11th to 20th	Night	12% 16% 6% 13% 8% 5% 5% 4 8% 5% 16%	6268
	21st to end	Night	18% 15% 7% 10% 5% 4 4 4 5% 5% 23%	6490
February	1st to 10th	Night	15% 14% 5% 11% 6% 5% 5% 4 5% 6% 24%	2600
	11th to 20th	Night	14% 14% 4 9% 7% 5% 4 4 5% 5% 27%	2429
	21st to end	Night	18% 12% 3 10% 5% 5% 5% 3 5% 5% 29%	1980
March	1st to 10th	Night	16% 10% 4 9% 5% 5% 4 3 5% 6% 34%	5196
	11th to 20th	Night	9% 8% 3 8% 5% 4 5% 4 6% 7% 41%	4980
	21st to end	Night	15% 9% 3 8% 5% 4 4 3 5% 5% 38%	5467
April	1st to 10th	Night	17% 11% 2 6% 4 4 4 4 6% 6% 35%	2133
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 5% 7% 37%	1782
	21st to end	Night	16% 8% 2 6% 4 4 4 4 6% 7% 38%	1800
May	1st to 10th	Night	19% 9% 3 8% 5% 4 4 3 5% 6% 33%	4033
	11th to 20th	Night	15% 8% 3 7% 4 4 4 3 6% 7% 38%	4032
	21st to end	Night	14% 5% 2 6% 5% 4 4 3 5% 7% 44%	4421
June	1st to 10th	Night	12% 5% 2 6% 4 3 4 4 6% 9% 46%	1468
	11th to 20th	Night	10% 4 2 6% 5% 6% 5% 5% 6% 8% 44%	1400
	21st to end	Night	9% 5% 2 5% 4 5% 4 3 5% 8% 50%	1432
July	1st to 10th	Night	7% 4 2 6% 4 4 4 4 6% 11% 47%	3618
	11th to 20th	Night	9% 4 2 5% 4 4 4 3 7% 10% 48%	3633
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 6% 9% 49%	4427
August	1st to 10th	Night	11% 6% 2 6% 4 4 3 4 6% 8% 46%	2915
	11th to 20th	Night	8% 7% 2 6% 5% 4 4 4 5% 7% 46%	2875
	21st to end	Night	7% 5% 3 7% 4 4 5% 4 7% 8% 47%	3223
September	1st to 10th	Night	9% 6% 2 5% 5% 4 4 3 6% 7% 48%	2121
	11th to 20th	Night	8% 5% 2 4 3 3 4 3 5% 8% 55%	2179
	21st to end	Night	15% 6% 3 7% 4 3 4 4 5% 6% 43%	2090
October	1st to 10th	Night	13% 6% 3 6% 3 4 3 3 5% 7% 47%	2170
	11th to 20th	Night	19% 9% 2 7% 4 5% 4 3 5% 6% 36%	2280
	21st to end	Night	21% 8% 3 6% 5% 4 5% 3 5% 6% 33%	2622
November	1st to 10th	Night	13% 7% 2 7% 4 4 4 4 5% 7% 41%	2536
	11th to 20th	Night	16% 10% 3 7% 6% 5% 5% 4 5% 7% 32%	2600
	21st to end	Night	19% 14% 4 8% 4 4 3 4 5% 6% 27%	2783
December	1st to 10th	Night	14% 13% 5% 13% 6% 6% 5% 4 5% 6% 23%	4580
	11th to 20th	Night	16% 18% 6% 10% 6% 4 5% 3 4 6% 21%	5297
	21st to end	Night	25% 19% 6% 11% 5% 4 4 3 4 4 16%	7244

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	42% 29% 8% 13% 6% 1	3618
	11th to 20th	Day	55% 28% 5% 6% 6% 1	3704
	21st to end	Day	50% 30% 8% 6% 6%	4466
February	1st to 10th	Day	23% 63% 4 7% 3	1800
	11th to 20th	Day	23% 60% 3 9% 4	1865
	21st to end	Day	19% 62% 5% 9% 4 1	1650
March	1st to 10th	Day	40% 30% 10% 12% 7% 1	4656
	11th to 20th	Day	34% 29% 13% 17% 5%	4980
	21st to end	Day	39% 30% 10% 11% 9% 1	5465
April	1st to 10th	Day	21% 62% 5% 8% 4 1	2284
	11th to 20th	Day	19% 62% 4 9% 5% 1	2567
	21st to end	Day	19% 61% 5% 9% 6%	2600
May	1st to 10th	Day	35% 30% 10% 14% 8% 4	5897
	11th to 20th	Day	33% 32% 10% 17% 7% 1	5865
	21st to end	Day	32% 30% 6% 15% 13% 4	6447
June	1st to 10th	Day	15% 62% 4 12% 7%	2923
	11th to 20th	Day	18% 62% 6% 8% 6% 1	3000
	21st to end	Day	14% 61% 6% 12% 7% 1	2959
July	1st to 10th	Day	30% 26% 11% 21% 12% 1	6291
	11th to 20th	Day	25% 25% 11% 25% 13% 1	6267
	21st to end	Day	25% 26% 13% 19% 17% 1	6240
August	1st to 10th	Day	25% 36% 10% 17% 11% 1	4221
	11th to 20th	Day	25% 37% 7% 26% 4	4213
	21st to end	Day	27% 36% 10% 20% 7%	4674
September	1st to 10th	Day	14% 58% 8% 15% 6%	2253
	11th to 20th	Day	13% 58% 5% 14% 10% 1	2178
	21st to end	Day	18% 60% 5% 12% 4	2090
October	1st to 10th	Day	17% 37% 9% 24% 13% 1	3334
	11th to 20th	Day	22% 37% 7% 20% 14%	3140
	21st to end	Day	26% 37% 10% 17% 9% 1	3221
November	1st to 10th	Day	22% 57% 5% 10% 5% 1	1762
	11th to 20th	Day	21% 57% 6% 10% 6%	1800
	21st to end	Day	27% 57% 5% 7% 3 1	1615
December	1st to 10th	Day	39% 36% 13% 9% 3	2600
	11th to 20th	Day	47% 32% 7% 9% 6%	2881
	21st to end	Day	56% 27% 6% 6% 5%	3729
January	1st to 10th	Night	41% 27% 7% 17% 6% 2	6348
	11th to 20th	Night	51% 29% 7% 8% 4	6268
	21st to end	Night	48% 28% 6% 10% 7%	6490
February	1st to 10th	Night	25% 62% 4 6% 3	2600
	11th to 20th	Night	21% 61% 4 9% 5%	2431
	21st to end	Night	22% 61% 4 7% 4 1	1980
March	1st to 10th	Night	37% 29% 10% 15% 8% 1	5196
	11th to 20th	Night	29% 30% 12% 18% 11%	4980
	21st to end	Night	34% 30% 8% 13% 14% 1	5467
April	1st to 10th	Night	23% 61% 4 7% 3 1	2133
	11th to 20th	Night	20% 62% 4 7% 6% 1	1782
	21st to end	Night	17% 62% 4 10% 6% 2	1800
May	1st to 10th	Night	38% 29% 7% 11% 11% 4	4060
	11th to 20th	Night	33% 31% 8% 21% 6% 1	4033
	21st to end	Night	32% 29% 8% 16% 12% 4	4429
June	1st to 10th	Night	13% 62% 3 13% 9% 1	1468
	11th to 20th	Night	17% 62% 4 11% 5% 1	1400
	21st to end	Night	14% 60% 5% 12% 9% 1	1432
July	1st to 10th	Night	24% 26% 12% 24% 10% 4	3580
	11th to 20th	Night	26% 25% 12% 23% 12% 1	3588
	21st to end	Night	25% 26% 11% 18% 19% 1	4297
August	1st to 10th	Night	25% 36% 9% 16% 13% 1	2904
	11th to 20th	Night	26% 36% 7% 23% 7%	2902
	21st to end	Night	25% 36% 8% 23% 8%	3223
September	1st to 10th	Night	13% 58% 6% 15% 7% 1	2121
	11th to 20th	Night	10% 59% 4 14% 11% 1	2179
	21st to end	Night	17% 61% 5% 13% 5%	2090
October	1st to 10th	Night	14% 36% 5% 25% 20%	3625
	11th to 20th	Night	26% 37% 7% 16% 14%	3779
	21st to end	Night	24% 36% 9% 20% 11% 1	4309
November	1st to 10th	Night	24% 56% 5% 9% 5% 1	2536
	11th to 20th	Night	22% 57% 5% 10% 7%	2600
	21st to end	Night	26% 57% 6% 7% 4	2783
December	1st to 10th	Night	39% 36% 13% 9% 3	4580
	11th to 20th	Night	45% 32% 7% 10% 5% 1	5300
	21st to end	Night	54% 27% 7% 7% 5%	7244

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	19% 8% 32% 28% 11% 2	300
	11th to 20th	Day	21% 6% 41% 22% 8% 1	300
	21st to end	Day	26% 2 32% 28% 10% 2	330
February	1st to 10th	Day	21% 4 41% 28% 5% 1	300
	11th to 20th	Day	18% 6% 38% 34% 5%	300
	21st to end	Day	16% 7% 41% 29% 7%	249
March	1st to 10th	Day	19% 5% 34% 31% 10%	372
	11th to 20th	Day	16% 7% 30% 33% 12% 2	500
	21st to end	Day	24% 4 29% 30% 11% 1	550
April	1st to 10th	Day	16% 3 32% 34% 12% 2	500
	11th to 20th	Day	22% 4 26% 28% 12% 7%	492
	21st to end	Day	22% 3 22% 33% 17% 3	500
May	1st to 10th	Day	21% 2 22% 34% 17% 4	503
	11th to 20th	Day	17% 2 19% 29% 25% 8%	527
	21st to end	Day	14% 1 15% 30% 28% 11%	573
June	1st to 10th	Day	11% 2 18% 37% 25% 7%	658
	11th to 20th	Day	10% 2 15% 40% 27% 6%	730
	21st to end	Day	10% 3 16% 34% 30% 7%	730
July	1st to 10th	Day	9% 2 10% 32% 30% 16%	721
	11th to 20th	Day	10% 1 11% 37% 29% 12%	713
	21st to end	Day	8% 1 8% 34% 35% 14%	576
August	1st to 10th	Day	10% 2 6% 33% 32% 18%	526
	11th to 20th	Day	10% 2 8% 31% 34% 14%	519
	21st to end	Day	11% 2 9% 30% 35% 14%	583
September	1st to 10th	Day	11% 2 16% 26% 29% 16%	530
	11th to 20th	Day	8% 2 9% 22% 35% 24%	522
	21st to end	Day	18% 4 17% 25% 21% 14%	490
October	1st to 10th	Day	15% 5% 22% 25% 19% 14%	490
	11th to 20th	Day	23% 7% 26% 27% 13% 4	490
	21st to end	Day	25% 7% 28% 27% 11% 2	420
November	1st to 10th	Day	16% 6% 32% 30% 13% 3	300
	11th to 20th	Day	21% 14% 29% 24% 10% 2	300
	21st to end	Day	26% 6% 38% 24% 5%	207
December	1st to 10th	Day	21% 9% 34% 24% 11% 2	200
	11th to 20th	Day	29% 9% 34% 23% 6% 1	200
	21st to end	Day	25% 6% 35% 27% 6% 1	275
January	1st to 10th	Night	23% 8% 37% 24% 8% 1	1000
	11th to 20th	Night	25% 7% 32% 30% 5% 1	960
	21st to end	Night	21% 6% 32% 34% 7%	880
February	1st to 10th	Night	21% 6% 37% 31% 5%	800
	11th to 20th	Night	20% 8% 33% 33% 6%	783
	21st to end	Night	23% 6% 39% 29% 3	660
March	1st to 10th	Night	21% 5% 35% 33% 7%	800
	11th to 20th	Night	17% 4 39% 31% 8% 1	800
	21st to end	Night	23% 4 30% 31% 11% 1	880
April	1st to 10th	Night	21% 6% 32% 33% 7% 1	733
	11th to 20th	Night	20% 5% 32% 29% 12% 2	593
	21st to end	Night	19% 4 27% 38% 12% 1	600
May	1st to 10th	Night	18% 3 27% 37% 14% 2	600
	11th to 20th	Night	20% 3 21% 33% 20% 2	591
	21st to end	Night	11% 2 16% 39% 27% 5%	650
June	1st to 10th	Night	13% 2 18% 45% 21% 2	400
	11th to 20th	Night	11% 2 16% 47% 22% 3	400
	21st to end	Night	9% 3 16% 43% 26% 3	432
July	1st to 10th	Night	9% 2 9% 39% 34% 8%	585
	11th to 20th	Night	10% 2 13% 37% 32% 7%	582
	21st to end	Night	7% 1 11% 43% 34% 4	657
August	1st to 10th	Night	8% 2 12% 36% 36% 6%	597
	11th to 20th	Night	8% 1 11% 39% 35% 6%	594
	21st to end	Night	9% 2 12% 39% 33% 6%	660
September	1st to 10th	Night	12% 3 15% 31% 31% 8%	746
	11th to 20th	Night	11% 2 14% 30% 34% 9%	793
	21st to end	Night	18% 4 17% 33% 22% 7%	760
October	1st to 10th	Night	17% 4 24% 28% 21% 5%	760
	11th to 20th	Night	23% 8% 27% 28% 12% 2	760
	21st to end	Night	25% 7% 30% 30% 8%	836
November	1st to 10th	Night	16% 9% 31% 29% 14% 1	780
	11th to 20th	Night	21% 10% 35% 25% 7% 1	800
	21st to end	Night	27% 10% 35% 22% 6%	800
December	1st to 10th	Night	27% 9% 33% 24% 6% 1	800
	11th to 20th	Night	23% 9% 36% 27% 5%	840
	21st to end	Night	30% 7% 31% 27% 5%	1100

Page generated at 2025-09-16 01:49:11. Version ac07

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