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 2024-01-13.

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 7% 6% 4 5% 5% 6% 8% 35%	74659
	Night	15% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	75062
Transparency	Day	46% 7% 13% 21% 11% 1	74370
	Night	48% 6% 12% 20% 12% 1	74871
Seeing	Day	15% 7% 26% 28% 17% 7%	14160
	Night	18% 8% 28% 31% 14% 2	23924

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% 12% 5% 10% 9% 4 5% 5% 5% 7% 23%	1517
	11th to 20th	Day	15% 15% 5% 10% 10% 5% 6% 5% 5% 6% 17%	1484
	21st to end	Day	15% 15% 6% 10% 8% 5% 5% 5% 5% 6% 20%	1782
February	1st to 10th	Day	16% 12% 5% 8% 9% 5% 5% 5% 6% 6% 22%	1620
	11th to 20th	Day	14% 11% 4 9% 8% 4 7% 5% 6% 7% 26%	1671
	21st to end	Day	15% 10% 4 8% 6% 4 6% 5% 6% 7% 29%	1480
March	1st to 10th	Day	15% 9% 5% 6% 7% 4 7% 6% 6% 7% 30%	1862
	11th to 20th	Day	13% 9% 4 7% 6% 4 6% 4 5% 7% 34%	1980
	21st to end	Day	18% 10% 4 8% 7% 4 5% 4 5% 6% 28%	2178
April	1st to 10th	Day	13% 9% 5% 7% 7% 3 5% 5% 6% 8% 32%	2060
	11th to 20th	Day	16% 8% 3 6% 6% 4 6% 5% 6% 7% 33%	2302
	21st to end	Day	17% 7% 3 7% 6% 4 5% 4 6% 7% 34%	2340
May	1st to 10th	Day	14% 7% 3 6% 7% 4 6% 5% 6% 7% 34%	2340
	11th to 20th	Day	15% 8% 3 5% 6% 4 6% 5% 5% 7% 35%	2301
	21st to end	Day	10% 5% 2 5% 6% 3 5% 5% 6% 9% 43%	2531
June	1st to 10th	Day	8% 6% 2 5% 6% 4 6% 5% 7% 9% 41%	2604
	11th to 20th	Day	8% 5% 2 6% 6% 3 6% 6% 6% 10% 43%	2700
	21st to end	Day	7% 5% 3 5% 6% 3 6% 7% 7% 10% 41%	2638
July	1st to 10th	Day	6% 4 2 5% 5% 3 6% 5% 7% 9% 48%	2520
	11th to 20th	Day	8% 4 2 5% 4 3 5% 7% 5% 11% 46%	2519
	21st to end	Day	6% 5% 2 5% 7% 4 6% 6% 7% 11% 42%	2547
August	1st to 10th	Day	7% 4 2 4 5% 4 6% 6% 8% 11% 43%	2327
	11th to 20th	Day	8% 5% 2 5% 6% 3 6% 6% 8% 11% 41%	2303
	21st to end	Day	9% 5% 2 5% 6% 4 5% 5% 7% 9% 44%	2574
September	1st to 10th	Day	10% 7% 2 5% 6% 3 4 6% 6% 9% 41%	2024
	11th to 20th	Day	9% 4 2 4 5% 3 5% 4 7% 9% 48%	1980
	21st to end	Day	14% 6% 3 6% 5% 2 4 5% 6% 9% 41%	1980
October	1st to 10th	Day	11% 6% 3 5% 6% 4 5% 5% 6% 8% 42%	1908
	11th to 20th	Day	16% 9% 3 7% 6% 4 5% 4 5% 8% 33%	1800
	21st to end	Day	17% 10% 3 7% 7% 3 4 5% 5% 7% 30%	1864
November	1st to 10th	Day	11% 7% 3 6% 6% 4 5% 4 6% 9% 38%	1672
	11th to 20th	Day	13% 9% 3 6% 7% 3 6% 5% 7% 7% 33%	1710
	21st to end	Day	18% 9% 5% 9% 6% 4 4 5% 5% 7% 27%	1550
December	1st to 10th	Day	15% 12% 6% 10% 9% 4 6% 5% 5% 6% 21%	1520
	11th to 20th	Day	17% 14% 5% 9% 6% 4 5% 5% 6% 6% 23%	1839
	21st to end	Day	25% 16% 7% 11% 8% 3 4 4 4 6% 12%	2632
January	1st to 10th	Night	16% 13% 5% 9% 7% 3 5% 5% 5% 6% 25%	2648
	11th to 20th	Night	19% 15% 6% 10% 7% 4 4 5% 5% 5% 21%	2517
	21st to end	Night	13% 13% 7% 11% 9% 4 5% 5% 4 6% 23%	2574
February	1st to 10th	Night	16% 14% 5% 10% 8% 3 6% 4 5% 5% 23%	2340
	11th to 20th	Night	15% 12% 5% 9% 7% 4 5% 5% 5% 6% 26%	2171
	21st to end	Night	19% 11% 5% 7% 6% 3 4 5% 5% 6% 29%	1776
March	1st to 10th	Night	15% 10% 4 8% 5% 4 5% 5% 6% 7% 32%	2098
	11th to 20th	Night	14% 7% 3 6% 4 3 5% 6% 7% 6% 39%	1980
	21st to end	Night	19% 8% 4 7% 6% 3 4 5% 5% 6% 33%	2178
April	1st to 10th	Night	16% 8% 4 5% 6% 3 4 5% 6% 7% 37%	1917
	11th to 20th	Night	17% 8% 3 6% 4 3 4 4 5% 7% 37%	1607
	21st to end	Night	17% 7% 3 5% 5% 3 5% 5% 5% 7% 39%	1620
May	1st to 10th	Night	15% 8% 3 8% 6% 3 6% 5% 5% 7% 34%	1620
	11th to 20th	Night	17% 7% 3 5% 4 3 4 5% 5% 7% 39%	1592
	21st to end	Night	9% 4 2 6% 5% 3 5% 5% 5% 10% 46%	1744
June	1st to 10th	Night	11% 5% 3 5% 4 2 5% 4 6% 9% 46%	1345
	11th to 20th	Night	9% 5% 2 6% 5% 4 5% 5% 5% 9% 45%	1260
	21st to end	Night	9% 5% 2 4 4 3 6% 5% 4 9% 49%	1315
July	1st to 10th	Night	7% 5% 2 4 4 3 4 5% 5% 9% 52%	1440
	11th to 20th	Night	8% 4 1 4 3 2 5% 5% 6% 10% 51%	1440
	21st to end	Night	5% 4 2 3 5% 3 5% 6% 8% 10% 48%	1771
August	1st to 10th	Night	7% 5% 2 4 5% 3 5% 5% 7% 9% 49%	1611
	11th to 20th	Night	6% 4 2 5% 5% 4 4 6% 6% 9% 49%	1598
	21st to end	Night	8% 5% 2 5% 4 3 4 5% 6% 8% 50%	1782
September	1st to 10th	Night	10% 6% 2 5% 5% 3 4 4 5% 7% 47%	1914
	11th to 20th	Night	9% 5% 2 4 4 3 3 5% 6% 8% 51%	1980
	21st to end	Night	14% 5% 2 6% 5% 3 4 5% 5% 8% 43%	1980
October	1st to 10th	Night	13% 6% 4 7% 4 3 4 3 5% 7% 45%	2051
	11th to 20th	Night	18% 8% 3 6% 6% 4 4 5% 5% 6% 35%	2160
	21st to end	Night	22% 9% 3 5% 6% 3 4 4 5% 6% 32%	2488
November	1st to 10th	Night	12% 7% 3 6% 5% 3 5% 5% 5% 8% 42%	2406
	11th to 20th	Night	15% 9% 4 7% 6% 4 6% 4 6% 8% 32%	2470
	21st to end	Night	19% 12% 5% 7% 6% 2 4 4 6% 5% 29%	2626
December	1st to 10th	Night	18% 13% 6% 9% 7% 4 5% 5% 5% 6% 22%	2660
	11th to 20th	Night	14% 14% 5% 8% 7% 4 6% 4 5% 6% 26%	3353
	21st to end	Night	27% 19% 6% 10% 7% 3 4 4 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	61% 6% 13% 13% 6% 1	1518
	11th to 20th	Day	66% 8% 12% 9% 4	1484
	21st to end	Day	65% 5% 11% 13% 6% 1	1782
February	1st to 10th	Day	60% 7% 13% 13% 7%	1620
	11th to 20th	Day	58% 6% 11% 17% 7% 1	1680
	21st to end	Day	55% 6% 13% 17% 7% 1	1480
March	1st to 10th	Day	52% 8% 16% 17% 7% 1	1862
	11th to 20th	Day	48% 5% 13% 20% 12% 2	1980
	21st to end	Day	56% 6% 11% 19% 7% 1	2178
April	1st to 10th	Day	49% 7% 13% 19% 12% 1	2060
	11th to 20th	Day	47% 6% 12% 20% 13% 2	2302
	21st to end	Day	48% 6% 14% 19% 11% 2	2340
May	1st to 10th	Day	48% 7% 11% 21% 11% 2	2340
	11th to 20th	Day	47% 7% 10% 20% 13% 2	2305
	21st to end	Day	37% 7% 16% 24% 15% 2	2531
June	1st to 10th	Day	38% 6% 14% 26% 14% 2	2604
	11th to 20th	Day	36% 8% 15% 23% 16% 3	2700
	21st to end	Day	34% 8% 16% 24% 17% 1	2638
July	1st to 10th	Day	31% 8% 10% 27% 20% 3	2451
	11th to 20th	Day	31% 8% 15% 28% 17% 2	2444
	21st to end	Day	33% 8% 17% 23% 17% 2	2405
August	1st to 10th	Day	32% 8% 15% 31% 12% 1	2314
	11th to 20th	Day	35% 9% 16% 27% 11% 2	2303
	21st to end	Day	34% 8% 13% 25% 18% 2	2574
September	1st to 10th	Day	37% 7% 17% 23% 14% 2	2024
	11th to 20th	Day	31% 6% 15% 33% 14% 1	1980
	21st to end	Day	40% 6% 15% 26% 12% 1	1980
October	1st to 10th	Day	39% 6% 13% 27% 13% 2	1908
	11th to 20th	Day	49% 5% 15% 20% 10%	1800
	21st to end	Day	53% 5% 14% 20% 8%	1864
November	1st to 10th	Day	42% 7% 13% 24% 11% 2	1672
	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	59% 5% 11% 17% 7% 1	2648
	11th to 20th	Night	65% 6% 13% 12% 5%	2517
	21st to end	Night	61% 5% 12% 16% 5% 1	2574
February	1st to 10th	Night	63% 6% 12% 13% 6% 1	2340
	11th to 20th	Night	57% 5% 11% 17% 9% 1	2173
	21st to end	Night	56% 4 13% 18% 8% 1	1776
March	1st to 10th	Night	51% 5% 12% 22% 9% 1	2098
	11th to 20th	Night	43% 6% 13% 21% 15% 2	1980
	21st to end	Night	52% 5% 10% 22% 11% 1	2178
April	1st to 10th	Night	46% 5% 11% 22% 14% 2	1917
	11th to 20th	Night	45% 5% 11% 19% 17% 2	1607
	21st to end	Night	45% 5% 11% 19% 16% 4	1620
May	1st to 10th	Night	49% 5% 11% 19% 12% 3	1620
	11th to 20th	Night	45% 6% 10% 19% 18% 3	1593
	21st to end	Night	35% 6% 14% 26% 17% 2	1745
June	1st to 10th	Night	35% 5% 12% 29% 17% 3	1345
	11th to 20th	Night	34% 9% 13% 25% 17% 2	1260
	21st to end	Night	33% 6% 12% 27% 21% 1	1315
July	1st to 10th	Night	29% 7% 11% 29% 21% 4	1400
	11th to 20th	Night	28% 7% 13% 33% 17% 2	1392
	21st to end	Night	26% 10% 17% 25% 19% 4	1672
August	1st to 10th	Night	31% 6% 15% 31% 16% 2	1600
	11th to 20th	Night	31% 8% 14% 31% 14% 3	1598
	21st to end	Night	31% 7% 14% 28% 18% 2	1782
September	1st to 10th	Night	36% 7% 12% 27% 16% 2	1914
	11th to 20th	Night	30% 7% 12% 31% 19% 1	1980
	21st to end	Night	39% 6% 13% 27% 14% 1	1980
October	1st to 10th	Night	39% 6% 11% 24% 19% 1	2051
	11th to 20th	Night	47% 5% 14% 19% 13% 1	2160
	21st to end	Night	53% 5% 12% 20% 9% 1	2488
November	1st to 10th	Night	41% 5% 13% 26% 14% 1	2406
	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% 12% 38% 23% 7% 1	270
	11th to 20th	Day	18% 11% 43% 19% 7% 2	246
	21st to end	Day	22% 8% 34% 29% 6%	264
February	1st to 10th	Day	23% 13% 40% 23% 1	240
	11th to 20th	Day	18% 13% 38% 27% 3	240
	21st to end	Day	18% 14% 45% 19% 4	198
March	1st to 10th	Day	18% 14% 36% 25% 6%	302
	11th to 20th	Day	16% 11% 34% 30% 8% 2	420
	21st to end	Day	21% 13% 32% 25% 10% 1	462
April	1st to 10th	Day	14% 9% 34% 32% 10% 2	420
	11th to 20th	Day	23% 10% 30% 23% 9% 6%	412
	21st to end	Day	22% 6% 31% 25% 13% 2	420
May	1st to 10th	Day	20% 6% 27% 30% 13% 3	423
	11th to 20th	Day	17% 5% 27% 25% 20% 6%	447
	21st to end	Day	13% 2 21% 28% 26% 9%	485
June	1st to 10th	Day	11% 4 22% 36% 21% 5%	566
	11th to 20th	Day	10% 3 23% 36% 24% 4	630
	21st to end	Day	9% 4 25% 34% 22% 7%	630
July	1st to 10th	Day	7% 3 16% 30% 28% 16%	621
	11th to 20th	Day	9% 3 18% 34% 26% 10%	617
	21st to end	Day	7% 3 16% 34% 29% 12%	488
August	1st to 10th	Day	8% 3 13% 33% 26% 18%	446
	11th to 20th	Day	9% 2 14% 31% 31% 13%	439
	21st to end	Day	11% 4 15% 28% 29% 14%	495
September	1st to 10th	Day	13% 2 20% 24% 27% 13%	450
	11th to 20th	Day	9% 2 17% 24% 31% 17%	450
	21st to end	Day	17% 6% 21% 24% 22% 11%	450
October	1st to 10th	Day	13% 7% 25% 23% 21% 12%	450
	11th to 20th	Day	18% 12% 32% 26% 9% 2	450
	21st to end	Day	24% 12% 33% 23% 7% 1	379
November	1st to 10th	Day	13% 10% 36% 25% 12% 3	270
	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% 33% 27% 4	879
	21st to end	Night	17% 9% 35% 31% 7%	792
February	1st to 10th	Night	23% 10% 37% 27% 4	720
	11th to 20th	Night	21% 10% 33% 31% 6%	703
	21st to end	Night	24% 10% 38% 25% 3	592
March	1st to 10th	Night	20% 9% 35% 30% 7%	720
	11th to 20th	Night	18% 8% 36% 30% 7% 1	720
	21st to end	Night	20% 9% 30% 29% 10% 1	792
April	1st to 10th	Night	18% 12% 30% 34% 6% 1	657
	11th to 20th	Night	19% 8% 32% 30% 10% 2	533
	21st to end	Night	20% 5% 31% 33% 10%	540
May	1st to 10th	Night	19% 5% 28% 35% 12% 2	540
	11th to 20th	Night	19% 4 23% 36% 17% 2	531
	21st to end	Night	11% 1 20% 39% 26% 4	584
June	1st to 10th	Night	12% 2 21% 45% 19% 1	386
	11th to 20th	Night	10% 3 19% 47% 20% 1	360
	21st to end	Night	10% 3 19% 44% 23% 1	415
July	1st to 10th	Night	8% 2 13% 39% 30% 6%	525
	11th to 20th	Night	9% 2 16% 40% 28% 6%	522
	21st to end	Night	5% 2 13% 47% 28% 4	591
August	1st to 10th	Night	9% 2 13% 38% 34% 4	537
	11th to 20th	Night	8% 2 15% 37% 33% 6%	534
	21st to end	Night	10% 1 15% 36% 32% 5%	594
September	1st to 10th	Night	12% 6% 15% 34% 27% 7%	668
	11th to 20th	Night	10% 5% 17% 31% 30% 7%	720
	21st to end	Night	17% 5% 19% 31% 22% 7%	720
October	1st to 10th	Night	14% 6% 25% 31% 19% 4	720
	11th to 20th	Night	22% 10% 29% 27% 11% 1	720
	21st to end	Night	25% 11% 29% 29% 6%	792
November	1st to 10th	Night	15% 9% 34% 26% 16% 1	740
	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

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