Cheboygan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cheboygan clear sky chart from 2005-11-06 to 2026-03-18.

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% 11% 4 10% 5% 5% 4 3 5% 7% 33%	130615
	Night	14% 12% 5% 11% 6% 5% 5% 4 5% 6% 28%	131101
Transparency	Day	32% 38% 8% 15% 7% 1	134106
	Night	37% 37% 8% 12% 6% 1	135697
Seeing	Day	17% 7% 24% 30% 18% 4	17301
	Night	20% 9% 27% 29% 14% 2	26980

By Month

Percentage Cloud Cover NE (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% 17% 10% 24% 9% 6% 4 3 4 3 8%	4691
	11th to 20th	Day	10% 20% 7% 22% 12% 8% 4 3 3 3 8%	4679
	21st to end	Day	9% 15% 7% 18% 8% 8% 7% 4 5% 5% 14%	5156
February	1st to 10th	Day	9% 16% 6% 12% 9% 6% 5% 3 5% 6% 21%	1828
	11th to 20th	Day	13% 14% 7% 13% 8% 5% 4 3 4 5% 23%	1970
	21st to end	Day	11% 16% 6% 12% 8% 5% 4 4 4 7% 23%	1730
March	1st to 10th	Day	14% 10% 3 10% 5% 4 4 3 6% 7% 33%	4578
	11th to 20th	Day	12% 12% 4 11% 6% 6% 5% 4 6% 6% 28%	5007
	21st to end	Day	19% 12% 8% 11% 6% 5% 4 3 4 5% 23%	5547
April	1st to 10th	Day	17% 14% 4 8% 5% 5% 3 3 5% 6% 30%	2400
	11th to 20th	Day	18% 11% 3 7% 4 4 4 4 5% 5% 34%	2532
	21st to end	Day	16% 11% 3 7% 4 5% 4 4 5% 7% 33%	2600
May	1st to 10th	Day	16% 9% 3 6% 4 4 4 3 5% 7% 41%	5888
	11th to 20th	Day	12% 8% 3 7% 4 4 4 3 5% 6% 44%	6015
	21st to end	Day	13% 9% 2 6% 4 4 4 3 4 7% 44%	7215
June	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 6% 7% 44%	3000
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 4 7% 8% 40%	3000
	21st to end	Day	16% 7% 2 5% 4 4 4 4 5% 8% 42%	3000
July	1st to 10th	Day	15% 6% 2 5% 3 3 4 3 5% 8% 45%	6617
	11th to 20th	Day	9% 5% 2 5% 3 4 4 4 6% 8% 51%	6360
	21st to end	Day	9% 5% 2 6% 4 3 4 4 5% 9% 49%	6926
August	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	4337
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 8% 45%	4174
	21st to end	Day	12% 6% 3 7% 4 4 4 4 4 7% 45%	4617
September	1st to 10th	Day	15% 7% 3 6% 4 4 4 4 5% 8% 41%	2339
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 3 6% 8% 43%	2200
	21st to end	Day	16% 9% 3 7% 4 3 4 4 5% 8% 38%	2200
October	1st to 10th	Day	19% 8% 2 6% 5% 5% 4 2 5% 8% 35%	2165
	11th to 20th	Day	23% 13% 4 11% 5% 5% 4 3 4 7% 21%	1921
	21st to end	Day	22% 15% 4 9% 5% 5% 5% 3 6% 6% 20%	1980
November	1st to 10th	Day	18% 15% 4 9% 5% 4 5% 3 5% 8% 24%	1852
	11th to 20th	Day	14% 16% 7% 11% 7% 6% 6% 5% 6% 6% 17%	1843
	21st to end	Day	19% 19% 8% 14% 6% 4 4 4 5% 5% 13%	1654
December	1st to 10th	Day	11% 24% 10% 15% 8% 6% 6% 4 4 4 8%	2350
	11th to 20th	Day	14% 18% 8% 17% 10% 6% 6% 4 4 4 9%	2691
	21st to end	Day	22% 22% 8% 16% 5% 4 5% 3 4 4 7%	3553
January	1st to 10th	Night	11% 15% 7% 22% 9% 6% 5% 4 4 5% 11%	8233
	11th to 20th	Night	10% 18% 8% 19% 11% 7% 6% 4 5% 4 8%	8236
	21st to end	Night	8% 14% 6% 16% 8% 7% 7% 4 6% 7% 18%	9058
February	1st to 10th	Night	10% 17% 5% 12% 8% 7% 5% 4 6% 5% 21%	2790
	11th to 20th	Night	11% 15% 5% 12% 8% 5% 5% 4 4 6% 25%	2534
	21st to end	Night	14% 15% 5% 10% 7% 6% 4 4 4 6% 25%	2076
March	1st to 10th	Night	16% 10% 4 7% 5% 4 4 3 5% 7% 37%	5482
	11th to 20th	Night	11% 12% 4 10% 5% 4 5% 4 5% 7% 32%	5105
	21st to end	Night	21% 12% 5% 7% 4 4 3 3 5% 6% 30%	5427
April	1st to 10th	Night	19% 12% 2 7% 5% 5% 5% 4 5% 5% 30%	2000
	11th to 20th	Night	19% 10% 3 7% 4 3 4 3 5% 5% 36%	1817
	21st to end	Night	17% 10% 3 8% 5% 4 5% 4 4 5% 35%	1800
May	1st to 10th	Night	15% 8% 3 7% 5% 4 4 4 5% 6% 39%	4053
	11th to 20th	Night	14% 7% 3 7% 4 5% 4 3 5% 7% 41%	3871
	21st to end	Night	17% 9% 3 6% 4 3 3 3 5% 6% 42%	3679
June	1st to 10th	Night	13% 6% 2 7% 5% 4 4 4 7% 8% 40%	1400
	11th to 20th	Night	10% 6% 2 6% 5% 4 6% 4 7% 9% 40%	1400
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	1400
July	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 6% 7% 45%	3344
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 5% 6% 52%	3620
	21st to end	Night	8% 5% 2 5% 4 4 4 3 6% 8% 53%	3948
August	1st to 10th	Night	10% 6% 2 6% 4 5% 4 3 6% 8% 45%	2813
	11th to 20th	Night	13% 6% 2 4 2 3 4 3 5% 8% 51%	2875
	21st to end	Night	10% 5% 2 5% 3 4 4 3 5% 7% 52%	3279
September	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 7% 47%	2040
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 8% 46%	2200
	21st to end	Night	17% 7% 3 6% 4 4 4 4 5% 7% 40%	2200
October	1st to 10th	Night	16% 8% 2 6% 4 4 3 3 6% 7% 40%	2235
	11th to 20th	Night	21% 12% 4 8% 5% 5% 4 4 5% 7% 24%	2475
	21st to end	Night	24% 13% 3 8% 5% 5% 4 4 5% 6% 23%	2860
November	1st to 10th	Night	16% 14% 5% 9% 5% 4 5% 4 5% 7% 27%	2666
	11th to 20th	Night	14% 17% 5% 11% 7% 5% 6% 4 5% 5% 20%	2775
	21st to end	Night	19% 21% 6% 12% 7% 4 4 4 5% 4 15%	2965
December	1st to 10th	Night	11% 20% 8% 15% 8% 6% 6% 4 5% 5% 11%	5060
	11th to 20th	Night	13% 20% 7% 17% 8% 5% 5% 3 4 5% 13%	5736
	21st to end	Night	22% 20% 9% 15% 7% 5% 4 3 3 3 9%	7649

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% 25% 6% 4 2 1	4692
	11th to 20th	Day	67% 22% 5% 5% 1	4710
	21st to end	Day	54% 25% 8% 10% 3	5156
February	1st to 10th	Day	23% 59% 6% 8% 3	1828
	11th to 20th	Day	26% 59% 5% 6% 4	1979
	21st to end	Day	24% 59% 5% 8% 4	1730
March	1st to 10th	Day	34% 29% 12% 12% 11% 2	4580
	11th to 20th	Day	42% 31% 9% 12% 5% 1	5007
	21st to end	Day	45% 32% 6% 11% 6%	5547
April	1st to 10th	Day	21% 62% 4 9% 4	2400
	11th to 20th	Day	18% 63% 3 9% 6% 1	2532
	21st to end	Day	18% 62% 4 9% 6% 1	2600
May	1st to 10th	Day	29% 30% 7% 16% 15% 2	5897
	11th to 20th	Day	29% 31% 7% 19% 13% 1	6019
	21st to end	Day	29% 29% 8% 17% 12% 4	7215
June	1st to 10th	Day	15% 62% 4 11% 7% 1	3000
	11th to 20th	Day	18% 62% 6% 8% 5% 1	3000
	21st to end	Day	16% 61% 5% 12% 6% 1	3000
July	1st to 10th	Day	29% 26% 11% 24% 9% 1	6548
	11th to 20th	Day	22% 27% 14% 31% 6%	6285
	21st to end	Day	22% 27% 10% 29% 12%	6728
August	1st to 10th	Day	20% 39% 10% 23% 8%	4322
	11th to 20th	Day	26% 38% 10% 20% 6%	4213
	21st to end	Day	25% 37% 11% 22% 4	4616
September	1st to 10th	Day	18% 58% 7% 12% 4	2339
	11th to 20th	Day	14% 58% 6% 15% 6%	2200
	21st to end	Day	18% 57% 8% 12% 5%	2200
October	1st to 10th	Day	20% 36% 8% 23% 13%	3529
	11th to 20th	Day	32% 37% 7% 18% 6%	3111
	21st to end	Day	38% 36% 9% 13% 4	3180
November	1st to 10th	Day	30% 54% 5% 9% 2	1852
	11th to 20th	Day	31% 55% 7% 6% 2	1843
	21st to end	Day	37% 55% 4 3 1	1654
December	1st to 10th	Day	51% 37% 8% 3 1	2350
	11th to 20th	Day	55% 33% 7% 4 1	2691
	21st to end	Day	62% 27% 3 5% 3	3553
January	1st to 10th	Night	60% 23% 9% 5% 2	8233
	11th to 20th	Night	64% 24% 7% 4 2	8280
	21st to end	Night	50% 25% 9% 10% 5%	9058
February	1st to 10th	Night	24% 60% 5% 6% 4	2790
	11th to 20th	Night	24% 58% 5% 10% 2	2536
	21st to end	Night	22% 60% 5% 7% 5%	2076
March	1st to 10th	Night	36% 28% 13% 14% 8% 1	5493
	11th to 20th	Night	37% 30% 14% 13% 5% 1	5106
	21st to end	Night	42% 30% 7% 13% 8%	5427
April	1st to 10th	Night	23% 62% 2 8% 4	2000
	11th to 20th	Night	20% 62% 2 9% 5% 2	1817
	21st to end	Night	21% 62% 3 7% 6% 1	1800
May	1st to 10th	Night	32% 30% 6% 17% 12% 3	4060
	11th to 20th	Night	31% 31% 5% 20% 12% 1	3872
	21st to end	Night	34% 30% 8% 15% 8% 4	3680
June	1st to 10th	Night	16% 61% 4 10% 8% 1	1400
	11th to 20th	Night	18% 62% 4 10% 5% 2	1400
	21st to end	Night	17% 61% 4 11% 5% 2	1400
July	1st to 10th	Night	31% 27% 11% 18% 12% 1	3305
	11th to 20th	Night	23% 26% 13% 26% 12%	3572
	21st to end	Night	21% 27% 11% 26% 15%	3832
August	1st to 10th	Night	25% 38% 9% 18% 9%	2804
	11th to 20th	Night	24% 37% 9% 22% 7% 1	2902
	21st to end	Night	20% 37% 9% 24% 10%	3279
September	1st to 10th	Night	16% 58% 7% 12% 6%	2040
	11th to 20th	Night	15% 58% 7% 13% 7%	2200
	21st to end	Night	18% 58% 7% 12% 5%	2200
October	1st to 10th	Night	24% 37% 7% 23% 9%	3651
	11th to 20th	Night	26% 36% 13% 16% 10%	4024
	21st to end	Night	34% 37% 10% 15% 4	4610
November	1st to 10th	Night	30% 54% 5% 8% 3	2666
	11th to 20th	Night	29% 55% 7% 6% 3	2775
	21st to end	Night	36% 55% 4 3 2	2965
December	1st to 10th	Night	50% 38% 7% 5% 1	5060
	11th to 20th	Night	53% 33% 6% 5% 2	5735
	21st to end	Night	63% 27% 3 5% 2	7649

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	18% 14% 34% 27% 8%	330
	11th to 20th	Day	19% 12% 33% 28% 7% 2	330
	21st to end	Day	20% 9% 27% 31% 12% 1	363
February	1st to 10th	Day	16% 13% 35% 24% 10% 1	330
	11th to 20th	Day	19% 9% 38% 23% 9% 1	330
	21st to end	Day	19% 14% 34% 28% 5%	273
March	1st to 10th	Day	15% 10% 34% 30% 12%	330
	11th to 20th	Day	18% 10% 31% 29% 10% 2	504
	21st to end	Day	24% 9% 28% 28% 10% 2	550
April	1st to 10th	Day	21% 10% 28% 31% 9% 2	500
	11th to 20th	Day	23% 8% 28% 26% 12% 3	492
	21st to end	Day	20% 7% 31% 28% 12% 2	500
May	1st to 10th	Day	22% 3 28% 29% 15% 3	503
	11th to 20th	Day	16% 3 22% 37% 18% 4	590
	21st to end	Day	12% 5% 21% 36% 21% 5%	789
June	1st to 10th	Day	12% 2 25% 36% 20% 4	730
	11th to 20th	Day	12% 3 25% 35% 21% 4	730
	21st to end	Day	18% 5% 18% 36% 20% 3	730
July	1st to 10th	Day	9% 2 16% 41% 26% 7%	721
	11th to 20th	Day	11% 3 18% 34% 27% 7%	718
	21st to end	Day	11% 2 16% 35% 28% 7%	794
August	1st to 10th	Day	11% 3 13% 33% 32% 9%	591
	11th to 20th	Day	11% 3 13% 29% 31% 13%	519
	21st to end	Day	14% 4 15% 32% 28% 7%	583
September	1st to 10th	Day	16% 4 18% 26% 25% 10%	530
	11th to 20th	Day	12% 4 14% 28% 29% 13%	530
	21st to end	Day	18% 6% 17% 28% 25% 6%	530
October	1st to 10th	Day	21% 8% 25% 23% 18% 5%	530
	11th to 20th	Day	24% 10% 27% 27% 12% 1	451
	21st to end	Day	31% 6% 23% 29% 9% 2	363
November	1st to 10th	Day	20% 15% 26% 27% 9% 2	330
	11th to 20th	Day	21% 16% 33% 23% 6% 1	305
	21st to end	Day	27% 19% 32% 20% 2	220
December	1st to 10th	Day	24% 15% 34% 18% 8% 1	220
	11th to 20th	Day	20% 20% 37% 17% 6%	220
	21st to end	Day	30% 13% 37% 14% 5% 1	242
January	1st to 10th	Night	21% 12% 36% 24% 6% 1	1050
	11th to 20th	Night	22% 12% 33% 24% 8%	1050
	21st to end	Night	17% 10% 34% 31% 7% 1	1155
February	1st to 10th	Night	16% 11% 38% 26% 8% 1	900
	11th to 20th	Night	18% 10% 34% 29% 9%	823
	21st to end	Night	20% 9% 34% 30% 7%	692
March	1st to 10th	Night	18% 8% 34% 30% 9% 1	840
	11th to 20th	Night	17% 10% 34% 30% 8% 1	829
	21st to end	Night	19% 6% 29% 33% 11% 1	865
April	1st to 10th	Night	23% 9% 28% 31% 8% 1	600
	11th to 20th	Night	23% 5% 26% 31% 12% 2	593
	21st to end	Night	21% 6% 26% 34% 13% 1	600
May	1st to 10th	Night	18% 3 24% 37% 18% 1	600
	11th to 20th	Night	18% 4 17% 38% 21% 2	591
	21st to end	Night	15% 3 19% 35% 24% 3	536
June	1st to 10th	Night	13% 5% 19% 39% 24% 1	400
	11th to 20th	Night	13% 2 20% 39% 25% 2	400
	21st to end	Night	17% 4 17% 36% 24% 3	400
July	1st to 10th	Night	11% 1 14% 41% 30% 3	466
	11th to 20th	Night	9% 2 14% 38% 30% 8%	582
	21st to end	Night	10% 2 15% 42% 27% 4	657
August	1st to 10th	Night	11% 3 15% 39% 28% 5%	597
	11th to 20th	Night	11% 2 17% 32% 30% 9%	594
	21st to end	Night	15% 4 14% 38% 27% 3	660
September	1st to 10th	Night	15% 5% 18% 30% 26% 6%	640
	11th to 20th	Night	15% 3 17% 30% 27% 8%	800
	21st to end	Night	20% 6% 17% 29% 22% 6%	800
October	1st to 10th	Night	20% 7% 22% 31% 18% 2	800
	11th to 20th	Night	28% 10% 24% 30% 7% 1	800
	21st to end	Night	31% 11% 24% 27% 7% 1	880
November	1st to 10th	Night	24% 12% 30% 24% 9% 1	820
	11th to 20th	Night	22% 16% 32% 23% 6%	840
	21st to end	Night	31% 15% 30% 19% 4	865
December	1st to 10th	Night	21% 15% 37% 20% 6%	1050
	11th to 20th	Night	23% 17% 37% 17% 5% 1	1050
	21st to end	Night	32% 13% 32% 19% 5%	1155

Page generated at 2026-03-15 02:23:53. Version ac07

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