Muskegon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Muskegon clear sky chart from 2005-11-06 to 2026-01-17.

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	14% 10% 4 9% 5% 4 4 3 5% 6% 35%	127278
	Night	15% 13% 5% 10% 5% 4 4 3 4 6% 30%	124656
Transparency	Day	47% 6% 12% 22% 12% 1	130791
	Night	54% 5% 11% 18% 11% 1	129217
Seeing	Day	19% 14% 31% 23% 10% 3	17471
	Night	20% 11% 28% 28% 12% 1	27403

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	12% 22% 12% 23% 7% 4 3 2 2 3 9%	3697
	11th to 20th	Day	11% 16% 7% 24% 17% 9% 4 2 3 2 5%	3668
	21st to end	Day	14% 20% 8% 21% 7% 5% 6% 2 2 3 13%	3982
February	1st to 10th	Day	12% 17% 6% 15% 12% 6% 4 2 5% 4 16%	1809
	11th to 20th	Day	13% 16% 6% 16% 8% 7% 5% 3 4 5% 19%	1948
	21st to end	Day	14% 16% 6% 13% 6% 6% 5% 4 5% 4 22%	1650
March	1st to 10th	Day	13% 10% 5% 12% 5% 5% 4 3 6% 5% 33%	4480
	11th to 20th	Day	12% 8% 5% 9% 5% 5% 4 4 5% 7% 38%	4786
	21st to end	Day	21% 12% 7% 7% 4 4 3 3 4 5% 28%	5773
April	1st to 10th	Day	18% 12% 4 8% 5% 4 4 3 5% 7% 31%	2400
	11th to 20th	Day	18% 9% 3 6% 4 5% 4 3 4 6% 36%	2408
	21st to end	Day	16% 9% 3 7% 5% 5% 5% 3 5% 8% 36%	2600
May	1st to 10th	Day	16% 7% 3 5% 4 3 4 4 6% 7% 42%	5862
	11th to 20th	Day	14% 7% 2 6% 4 4 4 3 5% 8% 43%	6013
	21st to end	Day	13% 6% 2 5% 3 4 4 4 5% 7% 47%	6935
June	1st to 10th	Day	10% 5% 2 5% 5% 3 4 4 6% 8% 47%	2800
	11th to 20th	Day	11% 5% 1 5% 4 4 3 4 6% 9% 47%	2800
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 10% 46%	2800
July	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 6% 8% 46%	6360
	11th to 20th	Day	7% 5% 2 6% 3 4 4 3 6% 8% 53%	6360
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 8% 49%	6924
August	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 6% 9% 45%	4365
	11th to 20th	Day	12% 4 2 5% 4 4 4 3 6% 7% 51%	4174
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 8% 48%	4313
September	1st to 10th	Day	10% 6% 2 6% 4 4 4 4 6% 8% 47%	2395
	11th to 20th	Day	12% 5% 2 4 4 4 4 4 5% 8% 49%	2200
	21st to end	Day	12% 6% 3 7% 4 4 4 4 6% 8% 42%	2200
October	1st to 10th	Day	15% 7% 2 7% 4 4 4 4 4 6% 44%	2200
	11th to 20th	Day	22% 9% 2 9% 6% 5% 6% 4 4 7% 25%	1927
	21st to end	Day	22% 12% 4 8% 6% 4 5% 3 5% 6% 25%	1980
November	1st to 10th	Day	15% 14% 4 7% 5% 4 4 4 4 6% 33%	1852
	11th to 20th	Day	17% 22% 5% 10% 5% 5% 4 3 3 5% 21%	1890
	21st to end	Day	22% 18% 6% 10% 5% 4 4 3 4 5% 17%	1879
December	1st to 10th	Day	11% 27% 12% 15% 5% 4 4 2 4 3 12%	2690
	11th to 20th	Day	17% 25% 14% 12% 8% 4 3 3 3 3 9%	3088
	21st to end	Day	25% 24% 7% 11% 6% 4 3 2 3 3 12%	4070
January	1st to 10th	Night	12% 23% 11% 22% 6% 4 3 2 3 3 11%	6488
	11th to 20th	Night	12% 19% 10% 24% 11% 9% 3 2 2 2 6%	6445
	21st to end	Night	15% 22% 10% 17% 6% 6% 6% 2 2 3 12%	6996
February	1st to 10th	Night	12% 19% 5% 15% 10% 6% 4 3 4 4 17%	2585
	11th to 20th	Night	14% 16% 7% 14% 9% 6% 4 4 4 4 20%	2338
	21st to end	Night	15% 17% 5% 12% 7% 5% 3 4 4 5% 24%	1980
March	1st to 10th	Night	16% 8% 3 10% 5% 4 4 3 5% 6% 36%	5373
	11th to 20th	Night	10% 8% 3 7% 5% 4 4 4 6% 8% 41%	5174
	21st to end	Night	18% 11% 4 10% 5% 4 4 3 4 6% 31%	5199
April	1st to 10th	Night	17% 10% 3 7% 5% 5% 4 3 5% 7% 34%	2000
	11th to 20th	Night	19% 9% 3 6% 4 4 5% 4 5% 4 36%	1940
	21st to end	Night	16% 9% 3 7% 4 4 3 4 5% 6% 39%	1800
May	1st to 10th	Night	17% 7% 3 8% 5% 5% 4 4 5% 6% 36%	4033
	11th to 20th	Night	14% 7% 2 7% 5% 4 5% 3 5% 8% 40%	3885
	21st to end	Night	19% 7% 2 6% 4 3 4 3 4 5% 42%	3942
June	1st to 10th	Night	11% 5% 2 5% 4 5% 4 4 8% 8% 44%	1600
	11th to 20th	Night	10% 6% 3 7% 4 4 3 4 6% 9% 44%	1600
	21st to end	Night	9% 6% 2 6% 4 4 3 5% 6% 9% 46%	1600
July	1st to 10th	Night	10% 6% 2 7% 4 5% 5% 4 6% 9% 41%	3618
	11th to 20th	Night	7% 5% 2 5% 4 5% 4 3 6% 7% 52%	3617
	21st to end	Night	8% 7% 3 6% 4 3 4 3 5% 7% 49%	3947
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 5% 9% 50%	2788
	11th to 20th	Night	12% 5% 1 5% 4 4 4 4 5% 6% 51%	2875
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 5% 8% 47%	3581
September	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 6% 7% 50%	2000
	11th to 20th	Night	10% 4 2 4 3 3 3 3 5% 7% 56%	2183
	21st to end	Night	14% 6% 2 8% 5% 5% 4 4 6% 6% 41%	2200
October	1st to 10th	Night	17% 6% 2 6% 3 3 3 3 4 6% 47%	2200
	11th to 20th	Night	23% 11% 4 7% 3 3 3 3 4 6% 34%	2469
	21st to end	Night	25% 10% 2 8% 4 3 4 2 4 6% 31%	2860
November	1st to 10th	Night	16% 13% 3 7% 4 4 4 3 5% 6% 35%	2666
	11th to 20th	Night	17% 19% 5% 11% 5% 4 4 3 6% 5% 21%	2730
	21st to end	Night	19% 22% 5% 11% 5% 4 3 3 4 5% 21%	2735
December	1st to 10th	Night	14% 23% 8% 16% 6% 4 4 3 4 4 13%	4720
	11th to 20th	Night	18% 26% 9% 13% 8% 4 3 2 3 4 10%	5339
	21st to end	Night	25% 20% 7% 10% 5% 4 4 3 4 5% 14%	7150

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	82% 4 6% 7% 1	3698
	11th to 20th	Day	85% 5% 6% 3 1	3668
	21st to end	Day	78% 5% 9% 7% 1	3982
February	1st to 10th	Day	71% 5% 8% 13% 3	1809
	11th to 20th	Day	69% 5% 8% 13% 5%	1958
	21st to end	Day	63% 6% 12% 13% 5%	1650
March	1st to 10th	Day	50% 7% 15% 19% 8% 1	4480
	11th to 20th	Day	44% 6% 17% 22% 10% 1	4786
	21st to end	Day	58% 5% 10% 16% 11% 1	5775
April	1st to 10th	Day	54% 5% 9% 21% 11% 1	2400
	11th to 20th	Day	48% 6% 9% 20% 14% 2	2408
	21st to end	Day	46% 5% 12% 20% 13% 2	2600
May	1st to 10th	Day	40% 6% 12% 24% 17% 2	5897
	11th to 20th	Day	39% 6% 14% 23% 16% 2	6017
	21st to end	Day	35% 7% 11% 28% 19% 1	6949
June	1st to 10th	Day	35% 6% 12% 28% 17% 2	2800
	11th to 20th	Day	34% 7% 14% 24% 21% 1	2800
	21st to end	Day	34% 8% 14% 26% 16% 2	2800
July	1st to 10th	Day	36% 6% 13% 29% 15% 2	6291
	11th to 20th	Day	28% 7% 14% 31% 18% 1	6285
	21st to end	Day	30% 8% 15% 26% 19% 2	6728
August	1st to 10th	Day	34% 7% 13% 31% 14% 1	4350
	11th to 20th	Day	31% 7% 12% 32% 16% 1	4213
	21st to end	Day	32% 7% 16% 26% 17% 2	4312
September	1st to 10th	Day	35% 7% 13% 30% 14% 2	2395
	11th to 20th	Day	33% 6% 13% 32% 15% 2	2200
	21st to end	Day	39% 7% 12% 27% 15%	2200
October	1st to 10th	Day	28% 4 9% 40% 18% 1	3590
	11th to 20th	Day	44% 6% 12% 26% 11%	3104
	21st to end	Day	51% 6% 16% 19% 8%	3180
November	1st to 10th	Day	51% 6% 13% 20% 10%	1852
	11th to 20th	Day	66% 3 12% 13% 5%	1890
	21st to end	Day	68% 4 13% 11% 3	1879
December	1st to 10th	Day	73% 10% 9% 7% 1	2690
	11th to 20th	Day	80% 5% 10% 6% 1	3085
	21st to end	Day	77% 4 7% 9% 3	4070
January	1st to 10th	Night	77% 5% 7% 8% 2	6488
	11th to 20th	Night	87% 4 5% 3 1	6445
	21st to end	Night	80% 3 9% 6% 1	6996
February	1st to 10th	Night	71% 3 9% 11% 5%	2585
	11th to 20th	Night	68% 3 9% 15% 5%	2339
	21st to end	Night	62% 5% 14% 13% 7% 1	1980
March	1st to 10th	Night	48% 5% 15% 23% 8% 1	5373
	11th to 20th	Night	40% 4 16% 27% 10% 2	5174
	21st to end	Night	55% 5% 10% 17% 12% 1	5199
April	1st to 10th	Night	49% 5% 10% 21% 13% 1	2000
	11th to 20th	Night	49% 5% 7% 19% 17% 3	1940
	21st to end	Night	45% 5% 11% 22% 13% 4	1800
May	1st to 10th	Night	47% 5% 13% 17% 15% 3	4060
	11th to 20th	Night	42% 6% 12% 22% 15% 3	3886
	21st to end	Night	44% 5% 7% 22% 19% 3	3950
June	1st to 10th	Night	35% 6% 12% 29% 16% 3	1600
	11th to 20th	Night	35% 6% 13% 26% 19% 1	1600
	21st to end	Night	35% 6% 15% 25% 16% 3	1600
July	1st to 10th	Night	37% 6% 12% 26% 14% 5%	3580
	11th to 20th	Night	30% 6% 13% 26% 24% 2	3572
	21st to end	Night	34% 6% 12% 23% 23% 2	3832
August	1st to 10th	Night	31% 6% 14% 28% 20% 1	2779
	11th to 20th	Night	32% 6% 11% 32% 18% 1	2902
	21st to end	Night	33% 7% 11% 26% 21% 2	3581
September	1st to 10th	Night	32% 6% 13% 28% 18% 2	2000
	11th to 20th	Night	29% 4 12% 35% 19% 1	2183
	21st to end	Night	42% 5% 12% 27% 13% 1	2200
October	1st to 10th	Night	31% 4 9% 34% 21% 1	3590
	11th to 20th	Night	41% 4 14% 25% 15% 1	4031
	21st to end	Night	45% 4 12% 27% 13%	4610
November	1st to 10th	Night	50% 5% 12% 20% 12% 1	2666
	11th to 20th	Night	63% 4 12% 14% 5% 1	2730
	21st to end	Night	67% 3 14% 13% 2	2735
December	1st to 10th	Night	72% 7% 12% 7% 2	4720
	11th to 20th	Night	79% 4 9% 6% 1	5341
	21st to end	Night	73% 5% 10% 9% 3	7150

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	21% 19% 38% 17% 3 2	330
	11th to 20th	Day	26% 20% 36% 12% 4 1	318
	21st to end	Day	26% 20% 35% 15% 4	330
February	1st to 10th	Day	24% 27% 31% 13% 3 2	300
	11th to 20th	Day	23% 29% 34% 12% 2	300
	21st to end	Day	31% 27% 33% 8% 1	249
March	1st to 10th	Day	22% 29% 39% 7% 2	300
	11th to 20th	Day	24% 18% 33% 17% 7%	410
	21st to end	Day	29% 15% 32% 18% 5% 1	550
April	1st to 10th	Day	28% 18% 31% 18% 5%	500
	11th to 20th	Day	27% 26% 24% 15% 6% 2	492
	21st to end	Day	25% 16% 32% 19% 8% 1	500
May	1st to 10th	Day	19% 19% 34% 20% 6% 2	503
	11th to 20th	Day	19% 13% 30% 24% 11% 4	588
	21st to end	Day	16% 12% 32% 25% 12% 3	789
June	1st to 10th	Day	11% 11% 39% 27% 9% 3	730
	11th to 20th	Day	14% 10% 34% 29% 10% 3	730
	21st to end	Day	15% 9% 37% 26% 10% 4	730
July	1st to 10th	Day	7% 6% 30% 34% 17% 6%	721
	11th to 20th	Day	8% 9% 30% 33% 15% 5%	718
	21st to end	Day	8% 6% 32% 32% 17% 5%	794
August	1st to 10th	Day	9% 6% 25% 30% 23% 8%	606
	11th to 20th	Day	11% 5% 22% 31% 22% 9%	519
	21st to end	Day	12% 7% 25% 31% 18% 7%	583
September	1st to 10th	Day	13% 9% 25% 28% 18% 7%	530
	11th to 20th	Day	8% 6% 22% 27% 28% 8%	530
	21st to end	Day	15% 12% 25% 26% 15% 6%	530
October	1st to 10th	Day	18% 13% 25% 26% 16% 2	530
	11th to 20th	Day	24% 18% 32% 22% 4	385
	21st to end	Day	33% 16% 32% 16% 2 1	363
November	1st to 10th	Day	28% 18% 34% 15% 4 2	330
	11th to 20th	Day	28% 23% 36% 10% 3	330
	21st to end	Day	29% 21% 38% 10% 2	330
December	1st to 10th	Day	29% 23% 26% 17% 5%	330
	11th to 20th	Day	27% 27% 30% 13% 2 1	330
	21st to end	Day	30% 23% 33% 11% 2 1	363
January	1st to 10th	Night	22% 17% 33% 22% 6%	1050
	11th to 20th	Night	26% 18% 31% 20% 5% 1	1031
	21st to end	Night	23% 12% 32% 26% 6%	1100
February	1st to 10th	Night	20% 17% 34% 25% 3 1	880
	11th to 20th	Night	21% 15% 34% 24% 5%	783
	21st to end	Night	23% 18% 35% 21% 3	660
March	1st to 10th	Night	21% 14% 32% 24% 9% 1	800
	11th to 20th	Night	18% 13% 35% 25% 8% 1	800
	21st to end	Night	21% 11% 29% 30% 9%	767
April	1st to 10th	Night	21% 11% 33% 29% 6% 1	600
	11th to 20th	Night	27% 11% 29% 24% 8% 1	593
	21st to end	Night	21% 11% 31% 26% 9% 1	600
May	1st to 10th	Night	19% 6% 34% 32% 8% 1	600
	11th to 20th	Night	18% 8% 30% 30% 13% 1	591
	21st to end	Night	15% 6% 26% 33% 18% 2	650
June	1st to 10th	Night	11% 6% 27% 41% 14% 1	600
	11th to 20th	Night	13% 5% 30% 34% 17% 1	600
	21st to end	Night	11% 6% 24% 39% 19% 2	600
July	1st to 10th	Night	9% 2 19% 39% 28% 3	585
	11th to 20th	Night	7% 4 21% 38% 29% 2	582
	21st to end	Night	9% 3 19% 40% 28% 1	657
August	1st to 10th	Night	8% 2 18% 42% 27% 3	597
	11th to 20th	Night	11% 2 15% 40% 27% 5%	594
	21st to end	Night	10% 3 18% 41% 25% 3	660
September	1st to 10th	Night	10% 6% 18% 37% 24% 4	600
	11th to 20th	Night	11% 5% 19% 33% 27% 5%	783
	21st to end	Night	15% 9% 22% 30% 19% 5%	800
October	1st to 10th	Night	19% 6% 24% 32% 18% 1	800
	11th to 20th	Night	27% 12% 27% 23% 10% 1	800
	21st to end	Night	29% 11% 29% 23% 7%	880
November	1st to 10th	Night	23% 13% 31% 23% 9% 1	820
	11th to 20th	Night	27% 17% 30% 20% 5%	840
	21st to end	Night	29% 14% 31% 22% 4	845
December	1st to 10th	Night	26% 18% 32% 20% 4	1050
	11th to 20th	Night	29% 16% 31% 19% 3 1	1050
	21st to end	Night	32% 14% 33% 18% 2	1155

Page generated at 2026-01-14 01:14:28. Version ac07

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