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 2024-11-05.

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%	101093
	Night	15% 10% 4 8% 5% 4 4 4 5% 7% 35%	97939
Transparency	Day	25% 47% 8% 13% 7% 1	104708
	Night	26% 47% 7% 13% 7% 1	102450
Seeing	Day	16% 4 21% 30% 21% 8%	15314
	Night	19% 5% 26% 32% 15% 2	24889

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	16% 14% 6% 11% 6% 5% 5% 4 5% 6% 23%	2527
	11th to 20th	Day	14% 17% 5% 14% 7% 9% 7% 4 6% 5% 12%	2588
	21st to end	Day	28% 15% 5% 10% 5% 5% 5% 3 4 5% 15%	3124
February	1st to 10th	Day	14% 14% 5% 10% 7% 6% 6% 4 5% 6% 23%	1710
	11th to 20th	Day	13% 12% 5% 10% 7% 6% 6% 4 6% 6% 26%	1760
	21st to end	Day	14% 12% 4 11% 5% 5% 5% 4 5% 7% 29%	1570
March	1st to 10th	Day	17% 13% 4 9% 5% 5% 4 4 4 5% 29%	3240
	11th to 20th	Day	12% 11% 3 8% 6% 6% 5% 4 5% 7% 33%	3480
	21st to end	Day	18% 10% 3 9% 6% 5% 5% 4 5% 6% 30%	3815
April	1st to 10th	Day	13% 11% 3 8% 6% 4 4 4 6% 7% 33%	2170
	11th to 20th	Day	17% 7% 3 7% 6% 4 5% 4 5% 7% 34%	2437
	21st to end	Day	17% 9% 3 7% 5% 4 4 4 5% 7% 35%	2470
May	1st to 10th	Day	16% 7% 3 7% 5% 5% 4 4 6% 7% 36%	4082
	11th to 20th	Day	14% 8% 2 6% 5% 5% 5% 4 6% 9% 35%	4081
	21st to end	Day	8% 5% 2 7% 5% 4 5% 4 6% 8% 46%	4476
June	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	2776
	11th to 20th	Day	8% 5% 2 7% 4 5% 5% 5% 7% 8% 43%	2850
	21st to end	Day	8% 6% 2 6% 5% 6% 5% 5% 7% 11% 40%	2811
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 7% 10% 39%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 7% 10% 47%	4422
	21st to end	Day	6% 5% 2 6% 5% 6% 6% 5% 8% 10% 42%	4466
August	1st to 10th	Day	12% 5% 2 5% 4 5% 5% 5% 7% 10% 41%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 5% 8% 11% 39%	4044
	21st to end	Day	8% 5% 2 7% 5% 6% 7% 5% 7% 10% 40%	4532
September	1st to 10th	Day	10% 6% 2 5% 5% 4 5% 4 6% 9% 44%	2141
	11th to 20th	Day	8% 5% 2 4 5% 4 4 4 7% 9% 49%	2090
	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% 9% 38%	1708
	11th to 20th	Day	14% 11% 3 8% 4 5% 5% 4 6% 8% 33%	1710
	21st to end	Day	19% 10% 5% 10% 4 4 5% 4 5% 6% 27%	1535
December	1st to 10th	Day	16% 13% 5% 11% 7% 5% 7% 4 5% 5% 21%	1520
	11th to 20th	Day	17% 15% 4 9% 5% 5% 4 4 7% 6% 24%	1844
	21st to end	Day	25% 17% 7% 12% 6% 5% 4 3 4 6% 12%	2600
January	1st to 10th	Night	16% 16% 6% 9% 6% 4 4 3 4 6% 26%	4428
	11th to 20th	Night	15% 18% 6% 13% 6% 5% 5% 4 9% 5% 14%	4376
	21st to end	Night	25% 16% 7% 10% 5% 4 3 3 4 4 19%	4532
February	1st to 10th	Night	16% 14% 4 11% 6% 5% 5% 4 5% 6% 24%	2470
	11th to 20th	Night	14% 14% 4 9% 7% 5% 4 4 5% 6% 28%	2305
	21st to end	Night	18% 12% 3 10% 5% 5% 5% 3 5% 5% 29%	1884
March	1st to 10th	Night	16% 12% 5% 8% 4 5% 4 3 4 6% 33%	3612
	11th to 20th	Night	9% 8% 3 8% 4 4 5% 4 6% 8% 40%	3480
	21st to end	Night	16% 8% 3 8% 5% 4 4 4 5% 5% 38%	3817
April	1st to 10th	Night	17% 10% 2 6% 4 4 4 4 6% 6% 36%	2027
	11th to 20th	Night	18% 9% 3 6% 4 4 4 4 5% 7% 37%	1692
	21st to end	Night	17% 8% 2 6% 5% 4 4 3 6% 7% 38%	1710
May	1st to 10th	Night	16% 9% 2 7% 5% 4 4 3 6% 7% 37%	2813
	11th to 20th	Night	14% 8% 3 8% 4 4 4 3 6% 7% 39%	2812
	21st to end	Night	9% 5% 2 6% 4 4 4 3 6% 8% 49%	3079
June	1st to 10th	Night	12% 5% 2 6% 3 3 4 4 6% 9% 46%	1395
	11th to 20th	Night	10% 4 2 6% 5% 6% 5% 5% 6% 8% 44%	1330
	21st to end	Night	9% 5% 2 4 4 5% 4 3 5% 8% 49%	1360
July	1st to 10th	Night	8% 4 2 5% 4 4 4 3 6% 11% 50%	2530
	11th to 20th	Night	10% 3 1 4 3 4 4 3 6% 9% 52%	2546
	21st to end	Night	4 5% 1 5% 4 5% 6% 5% 8% 10% 47%	3087
August	1st to 10th	Night	11% 6% 2 6% 4 4 3 4 6% 8% 46%	2825
	11th to 20th	Night	9% 7% 2 6% 5% 4 4 4 5% 8% 46%	2785
	21st to end	Night	7% 5% 3 7% 4 4 5% 4 7% 8% 47%	3124
September	1st to 10th	Night	9% 6% 3 5% 5% 4 4 3 6% 7% 47%	2014
	11th to 20th	Night	9% 5% 2 4 3 3 4 3 6% 8% 54%	2090
	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	12% 7% 2 7% 5% 5% 5% 4 5% 8% 41%	2470
	11th to 20th	Night	16% 11% 3 7% 6% 5% 5% 4 5% 7% 32%	2470
	21st to end	Night	19% 14% 4 8% 4 4 3 4 5% 6% 28%	2643
December	1st to 10th	Night	19% 14% 5% 10% 7% 5% 4 4 6% 6% 21%	2660
	11th to 20th	Night	15% 15% 4 9% 6% 4 5% 4 5% 6% 26%	3349
	21st to end	Night	27% 19% 6% 11% 5% 4 4 3 3 4 14%	5062

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	39% 41% 7% 9% 4	2528
	11th to 20th	Day	48% 39% 6% 5% 3	2588
	21st to end	Day	47% 42% 6% 3 2	3124
February	1st to 10th	Day	21% 66% 4 6% 3	1710
	11th to 20th	Day	20% 63% 3 9% 4	1769
	21st to end	Day	16% 65% 5% 9% 3 1	1570
March	1st to 10th	Day	36% 42% 7% 13% 3	3240
	11th to 20th	Day	30% 42% 12% 13% 4	3480
	21st to end	Day	31% 42% 10% 8% 8% 1	3815
April	1st to 10th	Day	19% 65% 5% 8% 4	2170
	11th to 20th	Day	18% 65% 4 9% 5% 1	2437
	21st to end	Day	18% 64% 4 7% 5%	2470
May	1st to 10th	Day	26% 42% 10% 14% 6% 2	4120
	11th to 20th	Day	25% 44% 12% 15% 3	4085
	21st to end	Day	20% 42% 7% 10% 16% 5%	4489
June	1st to 10th	Day	14% 65% 4 11% 6%	2776
	11th to 20th	Day	16% 65% 5% 7% 6% 1	2850
	21st to end	Day	13% 63% 6% 11% 6%	2811
July	1st to 10th	Day	29% 36% 10% 14% 10% 1	4371
	11th to 20th	Day	19% 36% 9% 27% 8%	4347
	21st to end	Day	22% 36% 13% 11% 16% 1	4324
August	1st to 10th	Day	25% 37% 9% 17% 11% 1	4091
	11th to 20th	Day	25% 38% 7% 26% 4	4083
	21st to end	Day	27% 37% 10% 18% 7%	4531
September	1st to 10th	Day	14% 61% 8% 13% 5%	2141
	11th to 20th	Day	13% 60% 5% 12% 10% 1	2090
	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	21% 59% 6% 9% 4 1	1708
	11th to 20th	Day	19% 60% 6% 10% 6%	1710
	21st to end	Day	25% 60% 5% 7% 3 1	1535
December	1st to 10th	Day	26% 60% 3 8% 3	1520
	11th to 20th	Day	31% 49% 7% 9% 4	1840
	21st to end	Day	49% 39% 7% 4 2	2600
January	1st to 10th	Night	38% 39% 8% 10% 4 1	4428
	11th to 20th	Night	44% 41% 7% 6% 2	4376
	21st to end	Night	47% 40% 4 7% 2	4532
February	1st to 10th	Night	23% 65% 3 6% 3	2470
	11th to 20th	Night	18% 64% 4 9% 5%	2307
	21st to end	Night	21% 65% 4 7% 4 1	1884
March	1st to 10th	Night	33% 42% 8% 14% 3	3612
	11th to 20th	Night	22% 43% 12% 11% 13% 1	3480
	21st to end	Night	26% 42% 8% 13% 10% 1	3817
April	1st to 10th	Night	20% 65% 4 7% 4 1	2027
	11th to 20th	Night	18% 65% 3 7% 5% 1	1692
	21st to end	Night	16% 65% 3 9% 5% 2	1710
May	1st to 10th	Night	27% 41% 7% 12% 10% 3	2840
	11th to 20th	Night	25% 43% 8% 19% 4	2813
	21st to end	Night	21% 42% 6% 12% 14% 5%	3087
June	1st to 10th	Night	11% 65% 3 13% 7% 1	1395
	11th to 20th	Night	16% 65% 3 10% 5% 1	1330
	21st to end	Night	13% 64% 4 11% 8%	1360
July	1st to 10th	Night	18% 36% 9% 25% 7% 5%	2490
	11th to 20th	Night	19% 36% 9% 24% 11%	2498
	21st to end	Night	20% 37% 13% 15% 14% 2	2988
August	1st to 10th	Night	25% 37% 9% 16% 12% 1	2814
	11th to 20th	Night	26% 38% 7% 22% 7%	2812
	21st to end	Night	25% 37% 8% 22% 8%	3124
September	1st to 10th	Night	12% 61% 6% 13% 7% 1	2014
	11th to 20th	Night	11% 61% 4 12% 11% 1	2090
	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	23% 58% 5% 9% 5% 1	2470
	11th to 20th	Night	20% 60% 5% 10% 6%	2470
	21st to end	Night	23% 60% 6% 7% 4	2643
December	1st to 10th	Night	24% 61% 4 7% 4	2660
	11th to 20th	Night	28% 50% 8% 9% 5%	3352
	21st to end	Night	49% 39% 6% 4 2	5062

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	20% 9% 32% 26% 10% 2	270
	11th to 20th	Day	21% 6% 41% 21% 9% 1	270
	21st to end	Day	28% 2 29% 30% 10% 2	297
February	1st to 10th	Day	21% 4 40% 27% 6% 1	270
	11th to 20th	Day	18% 5% 38% 34% 5%	270
	21st to end	Day	16% 7% 41% 29% 7%	225
March	1st to 10th	Day	19% 6% 34% 31% 10%	338
	11th to 20th	Day	16% 7% 29% 34% 12% 2	460
	21st to end	Day	25% 4 27% 31% 11% 1	506
April	1st to 10th	Day	15% 3 32% 35% 13% 2	460
	11th to 20th	Day	23% 4 26% 27% 12% 8%	452
	21st to end	Day	23% 3 22% 32% 17% 3	460
May	1st to 10th	Day	21% 3 21% 33% 18% 4	463
	11th to 20th	Day	17% 1 19% 29% 26% 8%	487
	21st to end	Day	13% 1 15% 29% 31% 12%	529
June	1st to 10th	Day	11% 2 18% 35% 26% 8%	611
	11th to 20th	Day	10% 2 15% 39% 28% 6%	680
	21st to end	Day	11% 3 16% 34% 29% 7%	680
July	1st to 10th	Day	9% 2 10% 31% 30% 17%	671
	11th to 20th	Day	10% 1 10% 36% 29% 13%	663
	21st to end	Day	8% 2 8% 33% 35% 14%	532
August	1st to 10th	Day	10% 2 6% 34% 30% 18%	486
	11th to 20th	Day	11% 2 8% 31% 34% 14%	479
	21st to end	Day	11% 2 9% 30% 34% 14%	539
September	1st to 10th	Day	12% 1 16% 26% 29% 16%	490
	11th to 20th	Day	8% 3 9% 23% 34% 23%	490
	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	15% 6% 33% 30% 13% 3	282
	11th to 20th	Day	19% 15% 29% 24% 10% 2	270
	21st to end	Day	27% 7% 37% 25% 5%	187
December	1st to 10th	Day	21% 9% 36% 24% 9% 1	180
	11th to 20th	Day	27% 9% 35% 22% 6% 1	180
	21st to end	Day	24% 7% 36% 26% 6% 1	247
January	1st to 10th	Night	23% 9% 36% 24% 8% 1	950
	11th to 20th	Night	26% 8% 31% 30% 5% 1	912
	21st to end	Night	21% 6% 31% 34% 7%	836
February	1st to 10th	Night	21% 5% 37% 31% 6%	760
	11th to 20th	Night	20% 8% 32% 33% 6%	743
	21st to end	Night	24% 6% 39% 28% 3	628
March	1st to 10th	Night	21% 5% 33% 34% 7%	760
	11th to 20th	Night	17% 4 39% 31% 8% 1	760
	21st to end	Night	23% 4 30% 31% 11% 1	836
April	1st to 10th	Night	20% 6% 32% 34% 7% 1	697
	11th to 20th	Night	21% 5% 32% 28% 12% 2	563
	21st to end	Night	20% 4 26% 37% 12% 1	570
May	1st to 10th	Night	17% 3 26% 38% 15% 2	570
	11th to 20th	Night	20% 3 20% 33% 20% 2	561
	21st to end	Night	11% 2 15% 38% 29% 5%	617
June	1st to 10th	Night	13% 2 17% 44% 21% 2	380
	11th to 20th	Night	11% 2 15% 47% 22% 3	380
	21st to end	Night	10% 3 16% 44% 24% 4	410
July	1st to 10th	Night	8% 2 8% 39% 34% 8%	555
	11th to 20th	Night	9% 2 13% 38% 31% 7%	552
	21st to end	Night	7% 1 11% 43% 34% 4	624
August	1st to 10th	Night	8% 2 12% 36% 35% 7%	567
	11th to 20th	Night	8% 1 11% 40% 35% 6%	564
	21st to end	Night	9% 1 12% 39% 33% 6%	627
September	1st to 10th	Night	12% 3 15% 32% 30% 8%	708
	11th to 20th	Night	11% 2 14% 31% 33% 8%	760
	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	15% 9% 31% 29% 15% 1	760
	11th to 20th	Night	22% 10% 35% 24% 8% 1	760
	21st to end	Night	27% 10% 34% 23% 6%	760
December	1st to 10th	Night	28% 9% 34% 23% 6% 1	760
	11th to 20th	Night	23% 9% 36% 27% 5%	798
	21st to end	Night	30% 8% 32% 26% 5%	1045

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