St. Clair Shores
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. Clair Shores clear sky chart from 2005-11-06 to 2025-12-03.

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% 9% 3 8% 6% 5% 5% 4 6% 8% 34%	126388
	Night	14% 10% 4 8% 5% 5% 4 4 5% 7% 34%	124395
Transparency	Day	45% 6% 14% 21% 12% 1	129972
	Night	47% 6% 12% 21% 12% 1	128880
Seeing	Day	14% 7% 26% 29% 18% 6%	16743
	Night	18% 8% 28% 31% 14% 2	26373

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	11% 12% 6% 15% 7% 5% 5% 3 4 6% 26%	3617
	11th to 20th	Day	13% 15% 4 15% 9% 9% 7% 4 6% 6% 12%	3687
	21st to end	Day	22% 14% 5% 10% 7% 6% 5% 4 5% 6% 17%	4466
February	1st to 10th	Day	14% 13% 4 10% 8% 5% 5% 5% 6% 6% 23%	1800
	11th to 20th	Day	13% 12% 3 11% 7% 6% 6% 4 5% 6% 26%	1862
	21st to end	Day	14% 11% 4 9% 6% 6% 6% 4 6% 6% 28%	1650
March	1st to 10th	Day	14% 11% 4 10% 6% 5% 5% 4 5% 6% 31%	4654
	11th to 20th	Day	10% 10% 4 9% 5% 6% 5% 3 5% 7% 35%	4980
	21st to end	Day	16% 10% 3 11% 7% 6% 5% 3 5% 6% 29%	5465
April	1st to 10th	Day	14% 10% 4 8% 6% 4 4 4 6% 8% 32%	2290
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 5% 6% 7% 34%	2562
	21st to end	Day	16% 8% 3 8% 5% 5% 4 4 6% 7% 36%	2600
May	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 4 5% 6% 34%	5862
	11th to 20th	Day	14% 8% 2 7% 5% 5% 6% 4 6% 8% 34%	5861
	21st to end	Day	13% 6% 2 7% 5% 4 5% 4 6% 7% 41%	6433
June	1st to 10th	Day	8% 6% 2 6% 6% 5% 6% 4 7% 9% 41%	2895
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 5% 6% 9% 42%	3000
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	2930
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 10% 40%	6360
	11th to 20th	Day	6% 5% 2 6% 4 4 5% 5% 7% 11% 45%	6345
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	6424
August	1st to 10th	Day	11% 5% 2 5% 4 5% 5% 4 6% 10% 42%	4234
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 5% 9% 10% 38%	4174
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	4675
September	1st to 10th	Day	9% 7% 2 6% 5% 4 5% 4 6% 9% 44%	2247
	11th to 20th	Day	8% 4 1 5% 4 4 4 4 7% 9% 50%	2200
	21st to end	Day	14% 7% 3 7% 5% 4 3 4 6% 8% 39%	2200
October	1st to 10th	Day	11% 6% 3 6% 4 4 4 4 7% 8% 44%	2120
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	2000
	21st to end	Day	16% 9% 3 7% 6% 5% 4 4 6% 7% 31%	2070
November	1st to 10th	Day	11% 8% 2 7% 6% 5% 5% 4 6% 8% 38%	1852
	11th to 20th	Day	13% 10% 3 7% 6% 5% 5% 5% 7% 7% 32%	1890
	21st to end	Day	16% 11% 5% 11% 6% 5% 5% 4 5% 7% 26%	1712
December	1st to 10th	Day	13% 12% 5% 11% 8% 6% 6% 4 6% 6% 24%	2616
	11th to 20th	Day	20% 17% 4 10% 5% 5% 5% 4 5% 5% 20%	2880
	21st to end	Day	24% 17% 6% 13% 7% 4 4 2 3 5% 13%	3775
January	1st to 10th	Night	13% 14% 6% 11% 6% 5% 4 4 5% 6% 28%	6348
	11th to 20th	Night	12% 16% 7% 13% 8% 6% 6% 4 8% 6% 16%	6286
	21st to end	Night	18% 15% 7% 11% 5% 5% 4 4 4 5% 24%	6490
February	1st to 10th	Night	14% 14% 4 11% 8% 5% 5% 4 6% 5% 23%	2600
	11th to 20th	Night	15% 13% 4 10% 6% 6% 4 4 6% 7% 26%	2420
	21st to end	Night	17% 12% 3 9% 5% 5% 4 4 5% 6% 29%	1980
March	1st to 10th	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 34%	5199
	11th to 20th	Night	9% 7% 3 8% 5% 5% 5% 5% 6% 7% 41%	4980
	21st to end	Night	14% 9% 3 9% 5% 5% 5% 3 5% 5% 37%	5467
April	1st to 10th	Night	17% 10% 3 6% 5% 4 4 4 6% 6% 35%	2129
	11th to 20th	Night	16% 9% 3 7% 3 5% 4 4 6% 7% 37%	1787
	21st to end	Night	16% 8% 3 6% 4 5% 4 4 5% 8% 38%	1800
May	1st to 10th	Night	18% 10% 3 9% 5% 4 5% 3 4 6% 33%	4033
	11th to 20th	Night	15% 9% 3 7% 5% 4 4 4 5% 7% 38%	4032
	21st to end	Night	13% 6% 2 7% 5% 4 4 4 5% 7% 44%	4421
June	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 6% 9% 46%	1493
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 4 6% 9% 44%	1400
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 4 9% 49%	1462
July	1st to 10th	Night	7% 5% 2 5% 4 4 5% 4 7% 10% 47%	3618
	11th to 20th	Night	8% 5% 1 5% 4 4 5% 4 7% 10% 46%	3617
	21st to end	Night	6% 5% 2 5% 4 4 4 4 7% 9% 48%	4427
August	1st to 10th	Night	10% 7% 2 6% 4 4 4 4 6% 8% 45%	2915
	11th to 20th	Night	8% 6% 3 7% 4 4 4 4 5% 8% 46%	2875
	21st to end	Night	6% 6% 2 7% 4 5% 4 4 6% 8% 46%	3223
September	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 5% 7% 48%	2128
	11th to 20th	Night	8% 4 2 4 3 4 3 4 6% 8% 54%	2200
	21st to end	Night	15% 6% 2 8% 4 4 4 3 5% 8% 42%	2200
October	1st to 10th	Night	12% 6% 3 7% 3 3 4 2 5% 6% 48%	2279
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 4 5% 6% 37%	2400
	21st to end	Night	20% 9% 2 6% 5% 5% 4 3 5% 6% 34%	2765
November	1st to 10th	Night	12% 8% 3 7% 5% 4 4 4 5% 8% 41%	2666
	11th to 20th	Night	14% 10% 3 8% 5% 6% 5% 3 6% 8% 32%	2730
	21st to end	Night	19% 13% 5% 9% 5% 4 4 3 6% 5% 27%	2903
December	1st to 10th	Night	13% 13% 5% 13% 6% 5% 5% 4 6% 6% 23%	4609
	11th to 20th	Night	16% 18% 6% 11% 6% 5% 5% 3 5% 5% 20%	5315
	21st to end	Night	25% 19% 6% 11% 6% 4 3 3 4 4 16%	7198

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	59% 6% 12% 15% 7% 1	3618
	11th to 20th	Day	69% 6% 9% 8% 7% 1	3687
	21st to end	Day	68% 4 12% 9% 6%	4466
February	1st to 10th	Day	58% 8% 13% 14% 7%	1800
	11th to 20th	Day	57% 6% 10% 17% 8% 1	1871
	21st to end	Day	54% 7% 14% 18% 7% 1	1650
March	1st to 10th	Day	52% 6% 16% 17% 8% 1	4654
	11th to 20th	Day	47% 6% 16% 22% 8% 1	4980
	21st to end	Day	54% 6% 13% 17% 10% 1	5465
April	1st to 10th	Day	48% 6% 13% 19% 12% 1	2290
	11th to 20th	Day	47% 6% 12% 21% 13% 2	2562
	21st to end	Day	47% 6% 13% 21% 12% 2	2600
May	1st to 10th	Day	47% 7% 10% 20% 12% 3	5897
	11th to 20th	Day	45% 8% 13% 21% 11% 2	5865
	21st to end	Day	40% 6% 11% 21% 17% 5%	6447
June	1st to 10th	Day	38% 6% 13% 27% 14% 2	2895
	11th to 20th	Day	37% 8% 14% 23% 16% 2	3000
	21st to end	Day	35% 8% 15% 23% 17% 1	2930
July	1st to 10th	Day	35% 7% 14% 26% 16% 2	6291
	11th to 20th	Day	30% 7% 16% 29% 17% 1	6270
	21st to end	Day	32% 7% 16% 23% 21% 1	6240
August	1st to 10th	Day	35% 7% 15% 27% 15% 1	4221
	11th to 20th	Day	36% 9% 14% 31% 9% 1	4213
	21st to end	Day	35% 8% 14% 27% 14% 1	4674
September	1st to 10th	Day	35% 7% 17% 26% 15% 1	2247
	11th to 20th	Day	29% 5% 15% 34% 16% 1	2200
	21st to end	Day	42% 6% 14% 25% 13%	2200
October	1st to 10th	Day	29% 6% 13% 32% 19% 1	3458
	11th to 20th	Day	38% 5% 14% 26% 17%	3240
	21st to end	Day	43% 5% 14% 24% 13% 1	3320
November	1st to 10th	Day	43% 7% 13% 25% 11% 2	1852
	11th to 20th	Day	48% 6% 15% 20% 9% 1	1890
	21st to end	Day	58% 6% 12% 17% 6% 1	1712
December	1st to 10th	Day	59% 7% 17% 13% 4	2616
	11th to 20th	Day	64% 5% 12% 12% 6%	2876
	21st to end	Day	74% 5% 8% 8% 4	3775
January	1st to 10th	Night	56% 6% 11% 20% 7% 2	6348
	11th to 20th	Night	64% 6% 13% 11% 5%	6286
	21st to end	Night	62% 4 10% 14% 9%	6490
February	1st to 10th	Night	61% 6% 11% 14% 6% 1	2600
	11th to 20th	Night	56% 6% 12% 18% 9% 1	2422
	21st to end	Night	55% 5% 13% 18% 8% 1	1980
March	1st to 10th	Night	50% 4 15% 21% 10% 1	5199
	11th to 20th	Night	39% 6% 16% 25% 14% 1	4980
	21st to end	Night	47% 5% 11% 20% 15% 1	5467
April	1st to 10th	Night	48% 6% 11% 21% 12% 2	2129
	11th to 20th	Night	45% 6% 11% 19% 17% 2	1787
	21st to end	Night	44% 5% 12% 20% 16% 4	1800
May	1st to 10th	Night	52% 5% 9% 16% 15% 3	4060
	11th to 20th	Night	44% 6% 11% 25% 10% 3	4033
	21st to end	Night	39% 6% 12% 22% 17% 4	4429
June	1st to 10th	Night	35% 5% 11% 27% 18% 3	1493
	11th to 20th	Night	35% 9% 13% 25% 16% 2	1400
	21st to end	Night	33% 6% 12% 26% 22% 1	1462
July	1st to 10th	Night	30% 6% 15% 29% 15% 5%	3580
	11th to 20th	Night	32% 7% 15% 30% 16% 2	3572
	21st to end	Night	30% 8% 14% 22% 24% 2	4297
August	1st to 10th	Night	36% 6% 14% 26% 17% 1	2904
	11th to 20th	Night	35% 7% 10% 33% 13% 1	2902
	21st to end	Night	33% 8% 13% 31% 14% 1	3223
September	1st to 10th	Night	34% 7% 12% 29% 16% 2	2128
	11th to 20th	Night	27% 7% 12% 32% 20% 2	2200
	21st to end	Night	40% 6% 13% 26% 13% 1	2200
October	1st to 10th	Night	26% 4 10% 33% 27% 1	3721
	11th to 20th	Night	42% 4 13% 22% 19%	3899
	21st to end	Night	41% 4 12% 27% 14% 1	4465
November	1st to 10th	Night	41% 5% 13% 26% 14% 1	2666
	11th to 20th	Night	49% 6% 13% 21% 10% 1	2730
	21st to end	Night	57% 5% 13% 19% 6%	2903
December	1st to 10th	Night	60% 5% 18% 14% 4	4609
	11th to 20th	Night	63% 6% 12% 12% 6%	5318
	21st to end	Night	72% 5% 10% 8% 5%	7198

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	17% 12% 36% 26% 7% 1	300
	11th to 20th	Day	18% 13% 41% 21% 6% 1	300
	21st to end	Day	23% 8% 34% 29% 6%	330
February	1st to 10th	Day	20% 11% 39% 26% 3 1	300
	11th to 20th	Day	17% 13% 38% 29% 4	300
	21st to end	Day	16% 16% 42% 21% 4	249
March	1st to 10th	Day	17% 15% 34% 28% 6%	370
	11th to 20th	Day	15% 13% 33% 30% 8% 2	500
	21st to end	Day	20% 13% 32% 25% 9% 1	550
April	1st to 10th	Day	16% 8% 34% 31% 9% 2	500
	11th to 20th	Day	22% 10% 29% 24% 8% 5%	492
	21st to end	Day	20% 9% 30% 27% 12% 2	500
May	1st to 10th	Day	19% 7% 28% 31% 13% 3	503
	11th to 20th	Day	16% 5% 27% 26% 20% 6%	527
	21st to end	Day	13% 3 23% 30% 24% 8%	573
June	1st to 10th	Day	12% 5% 22% 36% 20% 5%	660
	11th to 20th	Day	9% 3 22% 38% 25% 3	730
	21st to end	Day	8% 4 24% 35% 24% 6%	730
July	1st to 10th	Day	8% 3 16% 32% 27% 14%	721
	11th to 20th	Day	9% 3 17% 35% 26% 10%	716
	21st to end	Day	6% 3 14% 34% 31% 11%	576
August	1st to 10th	Day	8% 3 13% 32% 29% 16%	526
	11th to 20th	Day	9% 2 13% 31% 32% 12%	519
	21st to end	Day	10% 3 13% 29% 32% 13%	583
September	1st to 10th	Day	11% 3 19% 25% 27% 15%	530
	11th to 20th	Day	8% 2 15% 23% 35% 19%	530
	21st to end	Day	18% 6% 19% 24% 21% 12%	530
October	1st to 10th	Day	12% 6% 23% 24% 23% 12%	530
	11th to 20th	Day	17% 11% 29% 29% 10% 4	530
	21st to end	Day	23% 10% 31% 26% 9% 1	453
November	1st to 10th	Day	14% 11% 33% 28% 12% 2	330
	11th to 20th	Day	17% 18% 31% 25% 7% 1	330
	21st to end	Day	21% 15% 36% 23% 5%	236
December	1st to 10th	Day	18% 16% 35% 19% 11% 1	204
	11th to 20th	Day	27% 12% 40% 20% 1 1	200
	21st to end	Day	23% 12% 39% 22% 3 1	285
January	1st to 10th	Night	21% 12% 37% 23% 6% 1	1000
	11th to 20th	Night	24% 10% 34% 27% 4	965
	21st to end	Night	19% 9% 35% 31% 6%	880
February	1st to 10th	Night	21% 10% 37% 28% 4	800
	11th to 20th	Night	20% 10% 34% 31% 5%	783
	21st to end	Night	23% 11% 37% 26% 3	660
March	1st to 10th	Night	20% 9% 34% 30% 7%	800
	11th to 20th	Night	17% 9% 38% 30% 7% 1	800
	21st to end	Night	20% 10% 31% 29% 9% 1	880
April	1st to 10th	Night	20% 12% 30% 33% 5% 1	729
	11th to 20th	Night	19% 8% 33% 29% 9% 2	593
	21st to end	Night	19% 5% 32% 33% 10% 1	600
May	1st to 10th	Night	19% 6% 28% 34% 12% 2	600
	11th to 20th	Night	19% 4 24% 34% 17% 2	591
	21st to end	Night	12% 2 20% 40% 23% 3	650
June	1st to 10th	Night	13% 3 21% 45% 18% 1	428
	11th to 20th	Night	11% 3 19% 47% 20% 1	400
	21st to end	Night	10% 3 19% 44% 23% 1	462
July	1st to 10th	Night	8% 2 13% 40% 31% 6%	585
	11th to 20th	Night	8% 2 15% 40% 29% 5%	582
	21st to end	Night	5% 2 12% 46% 30% 4	657
August	1st to 10th	Night	9% 2 13% 37% 35% 4	597
	11th to 20th	Night	8% 3 14% 36% 34% 6%	594
	21st to end	Night	9% 1 15% 37% 33% 5%	660
September	1st to 10th	Night	12% 5% 16% 33% 28% 7%	743
	11th to 20th	Night	9% 4 15% 29% 34% 9%	800
	21st to end	Night	17% 6% 18% 32% 21% 7%	800
October	1st to 10th	Night	13% 6% 25% 31% 21% 4	800
	11th to 20th	Night	22% 10% 27% 29% 11% 2	800
	21st to end	Night	23% 10% 28% 31% 6%	880
November	1st to 10th	Night	15% 10% 34% 26% 14% 1	820
	11th to 20th	Night	20% 13% 35% 24% 7% 1	840
	21st to end	Night	25% 12% 35% 22% 5%	840
December	1st to 10th	Night	24% 12% 34% 23% 5% 1	809
	11th to 20th	Night	23% 12% 37% 24% 4	845
	21st to end	Night	28% 10% 34% 24% 4	1100

Page generated at 2025-11-30 01:00:55. Version ac07

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