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 2024-11-10.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	101112
	Night	14% 10% 4 8% 5% 4 4 4 5% 7% 35%	98012
Transparency	Day	45% 7% 14% 22% 12% 1	104740
	Night	47% 6% 12% 22% 12% 1	102523
Seeing	Day	14% 7% 26% 28% 18% 7%	15344
	Night	18% 8% 28% 31% 14% 2	24967

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	15% 14% 6% 13% 7% 5% 5% 3 5% 6% 22%	2527
	11th to 20th	Day	14% 18% 5% 12% 8% 9% 7% 5% 6% 5% 12%	2571
	21st to end	Day	27% 16% 5% 10% 6% 5% 4 3 3 4 15%	3124
February	1st to 10th	Day	14% 13% 4 10% 8% 5% 5% 5% 6% 6% 23%	1710
	11th to 20th	Day	13% 13% 3 10% 6% 6% 6% 4 5% 6% 26%	1766
	21st to end	Day	14% 11% 3 9% 6% 5% 5% 4 6% 6% 29%	1570
March	1st to 10th	Day	16% 13% 4 9% 5% 5% 5% 4 5% 5% 29%	3238
	11th to 20th	Day	12% 10% 4 9% 6% 6% 6% 4 6% 6% 32%	3480
	21st to end	Day	17% 9% 3 9% 6% 6% 5% 4 5% 6% 29%	3815
April	1st to 10th	Day	13% 11% 4 8% 6% 4 4 4 6% 8% 32%	2175
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 5% 6% 7% 34%	2432
	21st to end	Day	16% 8% 3 7% 5% 5% 4 4 6% 7% 35%	2470
May	1st to 10th	Day	16% 7% 3 7% 6% 4 5% 4 6% 7% 35%	4082
	11th to 20th	Day	14% 8% 2 6% 5% 5% 6% 4 6% 9% 34%	4081
	21st to end	Day	8% 5% 2 7% 5% 4 5% 4 6% 8% 46%	4476
June	1st to 10th	Day	8% 6% 2 6% 6% 5% 6% 4 7% 9% 40%	2750
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 5% 6% 9% 43%	2850
	21st to end	Day	7% 6% 2 6% 5% 5% 6% 5% 8% 10% 40%	2784
July	1st to 10th	Day	9% 5% 3 7% 5% 5% 6% 5% 8% 10% 38%	4440
	11th to 20th	Day	6% 4 1 5% 4 5% 5% 5% 7% 12% 45%	4425
	21st to end	Day	5% 5% 2 6% 6% 6% 6% 5% 8% 10% 41%	4466
August	1st to 10th	Day	11% 5% 2 5% 4 5% 5% 4 7% 10% 41%	4104
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 5% 9% 10% 38%	4044
	21st to end	Day	7% 5% 2 6% 6% 5% 7% 5% 8% 10% 39%	4532
September	1st to 10th	Day	9% 7% 2 6% 4 4 5% 4 6% 9% 43%	2135
	11th to 20th	Day	8% 4 1 5% 4 5% 4 4 7% 9% 49%	2090
	21st to end	Day	14% 7% 3 7% 4 4 3 4 6% 8% 39%	2090
October	1st to 10th	Day	11% 6% 3 6% 5% 4 5% 4 7% 7% 43%	2014
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 6% 7% 34%	1900
	21st to end	Day	17% 10% 3 8% 6% 5% 4 4 6% 7% 31%	1967
November	1st to 10th	Day	10% 8% 2 7% 6% 5% 5% 4 6% 8% 39%	1753
	11th to 20th	Day	13% 10% 3 7% 6% 5% 5% 5% 6% 7% 33%	1710
	21st to end	Day	18% 10% 5% 10% 6% 5% 5% 4 5% 7% 27%	1550
December	1st to 10th	Day	15% 13% 5% 12% 8% 6% 5% 4 5% 6% 20%	1520
	11th to 20th	Day	16% 15% 5% 10% 6% 5% 5% 4 6% 6% 23%	1839
	21st to end	Day	25% 17% 7% 13% 6% 4 5% 2 4 6% 11%	2632
January	1st to 10th	Night	15% 16% 6% 10% 5% 5% 4 4 4 6% 26%	4428
	11th to 20th	Night	14% 18% 7% 13% 6% 5% 6% 4 8% 5% 14%	4394
	21st to end	Night	24% 17% 7% 11% 5% 5% 3 3 3 4 18%	4532
February	1st to 10th	Night	15% 15% 4 11% 8% 5% 5% 4 6% 5% 24%	2470
	11th to 20th	Night	14% 13% 4 10% 6% 6% 4 4 6% 7% 26%	2296
	21st to end	Night	18% 12% 4 9% 5% 5% 4 4 5% 6% 29%	1884
March	1st to 10th	Night	16% 13% 4 9% 4 4 4 3 5% 6% 33%	3615
	11th to 20th	Night	9% 7% 2 8% 5% 5% 5% 5% 7% 7% 40%	3480
	21st to end	Night	15% 8% 3 9% 5% 4 5% 3 5% 5% 37%	3817
April	1st to 10th	Night	16% 10% 3 6% 5% 4 4 4 6% 6% 36%	2023
	11th to 20th	Night	17% 9% 3 7% 3 4 4 3 6% 7% 37%	1697
	21st to end	Night	16% 8% 3 6% 4 5% 4 4 5% 7% 38%	1710
May	1st to 10th	Night	16% 9% 3 8% 4 4 5% 3 5% 7% 36%	2813
	11th to 20th	Night	14% 8% 3 7% 4 4 4 4 5% 7% 39%	2812
	21st to end	Night	9% 5% 2 7% 4 4 4 4 5% 8% 48%	3079
June	1st to 10th	Night	11% 6% 3 5% 4 3 4 3 6% 9% 46%	1419
	11th to 20th	Night	9% 5% 2 7% 5% 5% 5% 4 6% 9% 44%	1330
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 4 9% 49%	1389
July	1st to 10th	Night	8% 4 1 4 4 4 4 4 6% 10% 50%	2530
	11th to 20th	Night	9% 4 1 4 3 4 4 4 6% 9% 51%	2530
	21st to end	Night	5% 4 2 5% 4 5% 5% 5% 9% 10% 46%	3087
August	1st to 10th	Night	11% 7% 2 6% 4 4 4 4 6% 8% 45%	2825
	11th to 20th	Night	8% 6% 3 7% 4 4 4 4 5% 8% 46%	2785
	21st to end	Night	7% 6% 2 7% 4 5% 4 4 6% 8% 46%	3124
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 5% 7% 48%	2022
	11th to 20th	Night	9% 5% 2 4 3 4 3 4 6% 8% 53%	2090
	21st to end	Night	15% 6% 2 8% 4 4 4 3 5% 7% 42%	2090
October	1st to 10th	Night	12% 6% 3 7% 3 3 4 2 5% 6% 47%	2165
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 5% 6% 36%	2280
	21st to end	Night	21% 9% 3 6% 5% 5% 4 3 5% 6% 33%	2627
November	1st to 10th	Night	12% 7% 3 7% 5% 4 4 4 5% 8% 42%	2530
	11th to 20th	Night	15% 10% 3 8% 6% 6% 5% 3 6% 8% 31%	2470
	21st to end	Night	19% 13% 4 8% 5% 4 4 3 6% 5% 28%	2626
December	1st to 10th	Night	18% 15% 5% 10% 6% 5% 5% 4 6% 5% 21%	2660
	11th to 20th	Night	14% 15% 5% 10% 6% 5% 5% 3 5% 6% 26%	3353
	21st to end	Night	26% 20% 6% 11% 6% 4 4 3 3 4 13%	5030

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	63% 6% 13% 12% 5%	2528
	11th to 20th	Day	71% 7% 10% 8% 4	2571
	21st to end	Day	74% 4 11% 7% 3	3124
February	1st to 10th	Day	58% 8% 13% 14% 7%	1710
	11th to 20th	Day	57% 6% 10% 18% 8% 1	1775
	21st to end	Day	54% 7% 14% 18% 7% 1	1570
March	1st to 10th	Day	55% 7% 14% 19% 5% 1	3238
	11th to 20th	Day	49% 7% 16% 20% 7% 1	3480
	21st to end	Day	53% 6% 14% 16% 9% 1	3815
April	1st to 10th	Day	48% 7% 13% 19% 12% 1	2175
	11th to 20th	Day	47% 6% 12% 21% 13% 2	2432
	21st to end	Day	47% 6% 13% 20% 12% 2	2470
May	1st to 10th	Day	44% 8% 12% 23% 11% 2	4120
	11th to 20th	Day	44% 7% 16% 22% 9% 1	4085
	21st to end	Day	34% 6% 13% 19% 21% 7%	4489
June	1st to 10th	Day	38% 6% 13% 26% 14% 2	2750
	11th to 20th	Day	36% 7% 14% 23% 17% 3	2850
	21st to end	Day	35% 8% 16% 23% 17% 1	2784
July	1st to 10th	Day	38% 7% 14% 23% 16% 2	4371
	11th to 20th	Day	28% 7% 15% 34% 15% 1	4350
	21st to end	Day	34% 8% 17% 18% 21% 2	4324
August	1st to 10th	Day	35% 7% 14% 27% 15% 1	4091
	11th to 20th	Day	36% 9% 14% 31% 9% 1	4083
	21st to end	Day	36% 9% 15% 26% 14% 1	4531
September	1st to 10th	Day	35% 7% 17% 24% 15% 2	2135
	11th to 20th	Day	30% 6% 15% 33% 16% 1	2090
	21st to end	Day	42% 6% 14% 25% 12%	2090
October	1st to 10th	Day	29% 6% 14% 32% 18% 1	3352
	11th to 20th	Day	39% 5% 14% 25% 17%	3140
	21st to end	Day	44% 5% 15% 24% 12% 1	3217
November	1st to 10th	Day	42% 7% 13% 25% 11% 2	1753
	11th to 20th	Day	48% 6% 15% 20% 10% 1	1710
	21st to end	Day	57% 6% 13% 17% 7% 1	1550
December	1st to 10th	Day	63% 6% 12% 14% 5%	1520
	11th to 20th	Day	60% 6% 15% 15% 5%	1835
	21st to end	Day	75% 6% 10% 7% 3	2632
January	1st to 10th	Night	60% 5% 12% 16% 6% 1	4428
	11th to 20th	Night	68% 7% 13% 10% 3	4394
	21st to end	Night	70% 4 9% 13% 3	4532
February	1st to 10th	Night	61% 6% 11% 14% 6% 1	2470
	11th to 20th	Night	55% 6% 11% 18% 9% 1	2298
	21st to end	Night	55% 4 13% 18% 8% 1	1884
March	1st to 10th	Night	52% 4 14% 23% 7%	3615
	11th to 20th	Night	38% 7% 16% 20% 17% 1	3480
	21st to end	Night	47% 6% 11% 23% 12% 1	3817
April	1st to 10th	Night	47% 6% 11% 22% 13% 2	2023
	11th to 20th	Night	45% 5% 11% 19% 17% 2	1697
	21st to end	Night	45% 5% 11% 19% 16% 4	1710
May	1st to 10th	Night	46% 5% 10% 21% 15% 3	2840
	11th to 20th	Night	42% 7% 12% 25% 12% 2	2813
	21st to end	Night	34% 6% 12% 22% 21% 6%	3087
June	1st to 10th	Night	35% 5% 12% 29% 17% 3	1419
	11th to 20th	Night	35% 9% 13% 24% 17% 2	1330
	21st to end	Night	33% 6% 12% 27% 21% 1	1389
July	1st to 10th	Night	28% 6% 13% 32% 15% 6%	2490
	11th to 20th	Night	28% 6% 14% 34% 17% 1	2482
	21st to end	Night	28% 9% 18% 22% 20% 3	2988
August	1st to 10th	Night	36% 6% 13% 26% 17% 1	2814
	11th to 20th	Night	35% 7% 10% 33% 13% 1	2812
	21st to end	Night	33% 8% 13% 31% 15% 1	3124
September	1st to 10th	Night	35% 7% 12% 27% 17% 2	2022
	11th to 20th	Night	28% 7% 12% 31% 20% 2	2090
	21st to end	Night	41% 6% 12% 27% 13% 1	2090
October	1st to 10th	Night	26% 4 10% 33% 27% 1	3607
	11th to 20th	Night	42% 4 13% 22% 18%	3779
	21st to end	Night	42% 4 12% 27% 14% 1	4327
November	1st to 10th	Night	41% 5% 13% 26% 14% 1	2530
	11th to 20th	Night	50% 6% 14% 21% 10% 1	2470
	21st to end	Night	56% 5% 13% 19% 6%	2626
December	1st to 10th	Night	62% 6% 12% 14% 5%	2660
	11th to 20th	Night	57% 7% 15% 14% 7%	3356
	21st to end	Night	75% 5% 10% 7% 3	5030

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% 13% 37% 23% 7% 1	270
	11th to 20th	Day	18% 14% 41% 19% 7% 1	270
	21st to end	Day	24% 8% 32% 30% 6%	297
February	1st to 10th	Day	20% 12% 39% 24% 3 1	270
	11th to 20th	Day	16% 14% 37% 29% 3	270
	21st to end	Day	16% 16% 44% 19% 4	225
March	1st to 10th	Day	17% 15% 35% 27% 6%	336
	11th to 20th	Day	16% 12% 33% 30% 7% 2	460
	21st to end	Day	21% 12% 33% 25% 9% 1	506
April	1st to 10th	Day	14% 8% 36% 31% 9% 2	460
	11th to 20th	Day	23% 10% 30% 23% 8% 6%	452
	21st to end	Day	21% 8% 31% 26% 12% 2	460
May	1st to 10th	Day	19% 7% 28% 30% 13% 3	463
	11th to 20th	Day	16% 5% 27% 26% 20% 7%	487
	21st to end	Day	12% 2 22% 29% 26% 9%	529
June	1st to 10th	Day	11% 5% 23% 34% 21% 6%	613
	11th to 20th	Day	9% 3 23% 37% 25% 3	680
	21st to end	Day	9% 4 25% 34% 22% 6%	680
July	1st to 10th	Day	8% 3 16% 31% 27% 15%	671
	11th to 20th	Day	9% 3 17% 35% 26% 10%	666
	21st to end	Day	6% 3 14% 34% 31% 11%	532
August	1st to 10th	Day	8% 3 14% 32% 26% 16%	486
	11th to 20th	Day	9% 2 14% 32% 32% 12%	479
	21st to end	Day	10% 3 13% 29% 31% 14%	539
September	1st to 10th	Day	12% 2 20% 26% 27% 14%	490
	11th to 20th	Day	8% 2 16% 24% 32% 18%	490
	21st to end	Day	18% 6% 20% 25% 21% 10%	490
October	1st to 10th	Day	12% 6% 25% 24% 21% 11%	490
	11th to 20th	Day	17% 12% 30% 27% 10% 4	490
	21st to end	Day	22% 11% 32% 24% 9% 1	416
November	1st to 10th	Day	13% 9% 36% 27% 12% 3	297
	11th to 20th	Day	16% 19% 32% 25% 7% 1	270
	21st to end	Day	21% 15% 36% 24% 4	194
December	1st to 10th	Day	19% 16% 37% 18% 8% 1	180
	11th to 20th	Day	26% 13% 40% 19% 1 1	180
	21st to end	Day	23% 13% 39% 21% 4	256
January	1st to 10th	Night	22% 12% 37% 22% 7% 1	950
	11th to 20th	Night	25% 10% 34% 26% 4	917
	21st to end	Night	19% 9% 34% 31% 6%	836
February	1st to 10th	Night	22% 10% 37% 27% 4	760
	11th to 20th	Night	20% 10% 34% 31% 6%	743
	21st to end	Night	23% 11% 37% 25% 3	628
March	1st to 10th	Night	20% 9% 34% 30% 7%	760
	11th to 20th	Night	17% 9% 38% 29% 7% 1	760
	21st to end	Night	20% 9% 31% 30% 10% 1	836
April	1st to 10th	Night	18% 12% 30% 33% 5% 1	693
	11th to 20th	Night	19% 8% 33% 29% 9% 2	563
	21st to end	Night	20% 5% 31% 34% 10%	570
May	1st to 10th	Night	19% 5% 28% 34% 12% 2	570
	11th to 20th	Night	19% 4 23% 35% 17% 2	561
	21st to end	Night	11% 2 20% 39% 24% 3	617
June	1st to 10th	Night	13% 3 21% 44% 19% 1	407
	11th to 20th	Night	10% 3 20% 47% 20% 1	380
	21st to end	Night	10% 3 19% 45% 22% 1	439
July	1st to 10th	Night	8% 2 13% 40% 30% 6%	555
	11th to 20th	Night	8% 2 16% 40% 28% 5%	552
	21st to end	Night	5% 2 13% 46% 29% 4	624
August	1st to 10th	Night	9% 2 14% 38% 33% 4	567
	11th to 20th	Night	8% 2 15% 36% 33% 6%	564
	21st to end	Night	9% 1 15% 37% 33% 5%	627
September	1st to 10th	Night	12% 5% 15% 33% 27% 7%	706
	11th to 20th	Night	10% 4 16% 30% 32% 8%	760
	21st to end	Night	17% 6% 19% 31% 21% 6%	760
October	1st to 10th	Night	14% 6% 26% 31% 19% 4	760
	11th to 20th	Night	22% 10% 28% 27% 11% 2	760
	21st to end	Night	24% 10% 28% 30% 6%	836
November	1st to 10th	Night	15% 10% 33% 26% 15% 1	779
	11th to 20th	Night	21% 13% 35% 23% 8% 1	760
	21st to end	Night	25% 11% 35% 22% 6%	760
December	1st to 10th	Night	25% 13% 34% 22% 5% 1	760
	11th to 20th	Night	23% 11% 38% 24% 4	802
	21st to end	Night	27% 10% 35% 24% 4	1045

Page generated at 2024-11-07 06:55:47. Version ac07

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