Muskegon Astronomical Society
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Muskegon Astronomical Society clear sky chart from 2005-11-06 to 2025-11-18.

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% 10% 4 9% 5% 4 4 3 5% 7% 34%	126737
	Night	14% 12% 5% 10% 6% 5% 4 3 5% 6% 31%	123861
Transparency	Day	49% 4 11% 22% 13% 1	130263
	Night	54% 3 10% 20% 11% 1	128409
Seeing	Day	19% 15% 31% 22% 11% 4	17285
	Night	19% 10% 29% 29% 12% 1	27112

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% 21% 12% 23% 7% 4 3 2 3 3 10%	3617
	11th to 20th	Day	11% 15% 8% 21% 16% 10% 5% 3 3 3 5%	3620
	21st to end	Day	15% 20% 9% 21% 6% 4 6% 2 3 3 12%	3982
February	1st to 10th	Day	11% 18% 5% 14% 11% 7% 5% 4 4 4 17%	1809
	11th to 20th	Day	12% 16% 7% 15% 9% 6% 5% 3 4 5% 18%	1948
	21st to end	Day	13% 17% 6% 12% 6% 6% 5% 4 5% 5% 20%	1650
March	1st to 10th	Day	14% 11% 5% 11% 5% 4 4 3 5% 6% 32%	4480
	11th to 20th	Day	11% 7% 5% 9% 6% 5% 4 4 5% 7% 37%	4795
	21st to end	Day	21% 13% 6% 8% 5% 4 4 3 4 5% 28%	5732
April	1st to 10th	Day	18% 13% 4 8% 5% 4 4 4 4 7% 30%	2400
	11th to 20th	Day	18% 10% 3 7% 4 5% 4 4 4 6% 35%	2421
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 5% 7% 35%	2600
May	1st to 10th	Day	17% 7% 2 5% 3 3 4 3 6% 8% 40%	5862
	11th to 20th	Day	14% 7% 2 7% 4 4 4 3 6% 8% 41%	5985
	21st to end	Day	14% 6% 2 5% 4 4 4 4 5% 8% 44%	6935
June	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 4 6% 9% 44%	2800
	11th to 20th	Day	11% 5% 2 6% 4 5% 4 4 5% 9% 46%	2800
	21st to end	Day	13% 5% 2 5% 4 4 5% 3 6% 9% 44%	2800
July	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 5% 9% 44%	6360
	11th to 20th	Day	8% 5% 2 5% 3 4 4 4 6% 9% 51%	6360
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	6924
August	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	4337
	11th to 20th	Day	12% 5% 1 5% 4 4 4 3 6% 7% 48%	4174
	21st to end	Day	8% 6% 2 6% 4 5% 5% 4 6% 9% 46%	4330
September	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 3 5% 7% 46%	2386
	11th to 20th	Day	12% 4 1 6% 4 4 4 3 6% 8% 48%	2200
	21st to end	Day	13% 7% 2 6% 5% 4 5% 4 5% 7% 42%	2200
October	1st to 10th	Day	16% 6% 2 6% 4 4 4 3 5% 7% 43%	2200
	11th to 20th	Day	20% 11% 4 8% 5% 5% 5% 5% 5% 7% 26%	1930
	21st to end	Day	21% 11% 3 8% 6% 6% 5% 3 4 7% 25%	1980
November	1st to 10th	Day	14% 11% 4 8% 4 4 5% 4 5% 6% 35%	1852
	11th to 20th	Day	15% 20% 6% 10% 6% 4 4 3 5% 5% 21%	1863
	21st to end	Day	20% 20% 5% 10% 5% 4 4 2 4 6% 20%	1800
December	1st to 10th	Day	10% 24% 9% 16% 7% 5% 4 3 5% 4 13%	2615
	11th to 20th	Day	16% 22% 13% 12% 9% 4 4 3 4 4 10%	3008
	21st to end	Day	24% 24% 7% 11% 6% 4 2 2 4 4 12%	3982
January	1st to 10th	Night	10% 22% 10% 20% 6% 4 3 2 4 4 14%	6348
	11th to 20th	Night	12% 18% 9% 22% 12% 9% 4 2 3 2 7%	6360
	21st to end	Night	15% 21% 9% 17% 7% 6% 5% 3 3 3 12%	6996
February	1st to 10th	Night	12% 17% 6% 14% 11% 5% 5% 3 4 5% 18%	2587
	11th to 20th	Night	13% 15% 7% 12% 8% 6% 5% 4 5% 5% 21%	2338
	21st to end	Night	15% 14% 4 12% 6% 6% 4 4 5% 5% 24%	1980
March	1st to 10th	Night	16% 9% 3 9% 5% 4 4 3 5% 6% 35%	5373
	11th to 20th	Night	10% 8% 3 7% 5% 4 4 3 6% 8% 41%	5164
	21st to end	Night	17% 12% 4 8% 5% 4 5% 3 5% 6% 30%	5240
April	1st to 10th	Night	17% 11% 3 7% 4 5% 4 3 5% 7% 34%	2000
	11th to 20th	Night	19% 10% 4 6% 4 4 5% 3 5% 6% 36%	1926
	21st to end	Night	16% 9% 3 8% 4 4 4 3 5% 7% 38%	1800
May	1st to 10th	Night	16% 8% 3 7% 5% 5% 4 3 5% 7% 36%	4033
	11th to 20th	Night	14% 6% 3 7% 5% 4 5% 3 5% 7% 40%	3911
	21st to end	Night	19% 7% 2 6% 3 4 3 4 4 5% 43%	3942
June	1st to 10th	Night	11% 5% 2 5% 5% 4 5% 5% 7% 8% 44%	1600
	11th to 20th	Night	10% 5% 2 7% 4 4 4 4 6% 9% 45%	1600
	21st to end	Night	10% 6% 2 6% 4 5% 4 4 6% 9% 46%	1600
July	1st to 10th	Night	10% 7% 2 6% 5% 4 5% 4 7% 9% 41%	3618
	11th to 20th	Night	7% 5% 1 6% 4 4 4 4 5% 8% 52%	3617
	21st to end	Night	8% 7% 3 6% 4 4 3 3 5% 7% 50%	3947
August	1st to 10th	Night	9% 5% 2 6% 3 3 4 3 5% 9% 50%	2813
	11th to 20th	Night	11% 4 2 5% 3 3 5% 3 5% 7% 51%	2875
	21st to end	Night	8% 6% 3 6% 4 4 5% 4 6% 8% 47%	3551
September	1st to 10th	Night	8% 5% 2 6% 3 4 4 4 5% 7% 51%	2000
	11th to 20th	Night	9% 5% 2 4 3 3 4 3 5% 6% 56%	2192
	21st to end	Night	13% 6% 3 7% 4 4 4 3 5% 8% 42%	2200
October	1st to 10th	Night	16% 6% 2 6% 3 3 3 3 5% 6% 48%	2200
	11th to 20th	Night	21% 10% 4 8% 4 4 4 3 4 6% 34%	2467
	21st to end	Night	22% 9% 3 7% 4 4 4 3 4 8% 32%	2860
November	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 5% 6% 36%	2666
	11th to 20th	Night	16% 15% 5% 9% 6% 5% 5% 4 7% 7% 22%	2692
	21st to end	Night	18% 19% 5% 9% 6% 4 3 3 5% 6% 22%	2600
December	1st to 10th	Night	12% 20% 8% 17% 6% 5% 5% 4 4 6% 15%	4570
	11th to 20th	Night	16% 25% 8% 13% 9% 5% 3 2 4 3 11%	5199
	21st to end	Night	24% 20% 6% 10% 5% 4 4 3 5% 5% 14%	6996

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	83% 2 6% 9% 1	3618
	11th to 20th	Day	86% 3 5% 5% 1	3620
	21st to end	Day	80% 2 8% 8% 1	3982
February	1st to 10th	Day	71% 4 7% 15% 3	1809
	11th to 20th	Day	69% 4 7% 14% 6%	1958
	21st to end	Day	65% 4 11% 14% 6%	1650
March	1st to 10th	Day	54% 2 15% 19% 9% 1	4480
	11th to 20th	Day	47% 3 16% 22% 11% 1	4795
	21st to end	Day	60% 2 10% 16% 11% 1	5734
April	1st to 10th	Day	55% 3 9% 21% 11% 1	2400
	11th to 20th	Day	50% 4 9% 22% 13% 2	2421
	21st to end	Day	49% 3 12% 21% 13% 2	2600
May	1st to 10th	Day	43% 3 9% 25% 18% 2	5897
	11th to 20th	Day	42% 3 12% 23% 18% 3	5989
	21st to end	Day	39% 3 10% 28% 20% 2	6949
June	1st to 10th	Day	36% 4 11% 29% 18% 2	2800
	11th to 20th	Day	35% 5% 14% 25% 21% 1	2800
	21st to end	Day	37% 4 15% 25% 17% 2	2800
July	1st to 10th	Day	38% 4 12% 29% 16% 2	6291
	11th to 20th	Day	30% 4 13% 32% 19% 2	6285
	21st to end	Day	32% 5% 14% 28% 19% 2	6728
August	1st to 10th	Day	38% 4 11% 31% 15% 1	4322
	11th to 20th	Day	33% 5% 12% 32% 17% 1	4213
	21st to end	Day	35% 5% 15% 27% 17% 2	4329
September	1st to 10th	Day	38% 4 12% 30% 14% 2	2386
	11th to 20th	Day	34% 4 13% 31% 17% 2	2200
	21st to end	Day	41% 5% 11% 27% 16%	2200
October	1st to 10th	Day	29% 3 8% 39% 19% 2	3590
	11th to 20th	Day	45% 4 13% 25% 13%	3120
	21st to end	Day	53% 3 14% 21% 8%	3180
November	1st to 10th	Day	51% 5% 12% 21% 11%	1852
	11th to 20th	Day	65% 3 11% 14% 5%	1863
	21st to end	Day	67% 4 13% 13% 4	1800
December	1st to 10th	Day	74% 7% 9% 9% 1	2615
	11th to 20th	Day	81% 2 8% 8% 1	3005
	21st to end	Day	78% 2 6% 10% 4	3982
January	1st to 10th	Night	76% 3 6% 10% 4	6348
	11th to 20th	Night	86% 3 5% 4 2	6360
	21st to end	Night	80% 2 8% 8% 2	6996
February	1st to 10th	Night	70% 3 8% 13% 6%	2587
	11th to 20th	Night	65% 4 7% 17% 6%	2339
	21st to end	Night	61% 4 12% 15% 7% 1	1980
March	1st to 10th	Night	50% 3 14% 24% 8% 1	5373
	11th to 20th	Night	41% 3 15% 27% 12% 2	5164
	21st to end	Night	57% 2 9% 19% 12% 1	5240
April	1st to 10th	Night	51% 3 10% 22% 14% 1	2000
	11th to 20th	Night	50% 3 7% 20% 17% 3	1926
	21st to end	Night	47% 3 11% 22% 14% 4	1800
May	1st to 10th	Night	49% 3 12% 18% 15% 3	4060
	11th to 20th	Night	44% 4 9% 24% 15% 3	3912
	21st to end	Night	45% 3 7% 23% 19% 3	3950
June	1st to 10th	Night	36% 4 11% 31% 15% 3	1600
	11th to 20th	Night	36% 4 14% 26% 19% 2	1600
	21st to end	Night	36% 4 15% 26% 16% 3	1600
July	1st to 10th	Night	39% 4 12% 27% 13% 5%	3580
	11th to 20th	Night	31% 4 12% 27% 24% 2	3572
	21st to end	Night	35% 4 13% 24% 22% 2	3832
August	1st to 10th	Night	32% 4 13% 30% 20% 1	2804
	11th to 20th	Night	33% 4 10% 35% 17% 1	2902
	21st to end	Night	35% 5% 9% 28% 21% 2	3551
September	1st to 10th	Night	33% 5% 10% 32% 18% 2	2000
	11th to 20th	Night	29% 3 10% 36% 20% 1	2192
	21st to end	Night	42% 4 11% 29% 14% 1	2200
October	1st to 10th	Night	31% 2 8% 36% 20% 2	3590
	11th to 20th	Night	41% 3 12% 27% 16%	4016
	21st to end	Night	44% 3 11% 29% 13%	4610
November	1st to 10th	Night	50% 4 10% 23% 12% 1	2666
	11th to 20th	Night	61% 4 11% 16% 6% 1	2692
	21st to end	Night	65% 3 14% 14% 3	2600
December	1st to 10th	Night	71% 5% 13% 9% 2	4570
	11th to 20th	Night	78% 3 8% 8% 2	5201
	21st to end	Night	73% 3 9% 10% 4	6996

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	20% 17% 38% 19% 5% 1	300
	11th to 20th	Day	25% 18% 38% 14% 4 1	300
	21st to end	Day	27% 20% 33% 17% 3	330
February	1st to 10th	Day	22% 29% 29% 15% 3 1	300
	11th to 20th	Day	23% 29% 32% 14% 2	300
	21st to end	Day	28% 29% 34% 6% 2 1	249
March	1st to 10th	Day	23% 32% 35% 8% 2	300
	11th to 20th	Day	25% 18% 32% 18% 8%	419
	21st to end	Day	29% 16% 29% 19% 5% 1	550
April	1st to 10th	Day	29% 18% 32% 16% 5% 1	500
	11th to 20th	Day	29% 23% 24% 15% 6% 2	492
	21st to end	Day	24% 16% 31% 18% 9% 1	500
May	1st to 10th	Day	23% 15% 34% 19% 7% 2	503
	11th to 20th	Day	20% 13% 31% 21% 12% 4	573
	21st to end	Day	16% 15% 30% 24% 11% 4	789
June	1st to 10th	Day	12% 12% 39% 24% 9% 4	730
	11th to 20th	Day	16% 10% 35% 26% 10% 3	730
	21st to end	Day	15% 9% 37% 25% 10% 4	730
July	1st to 10th	Day	8% 7% 31% 31% 17% 6%	721
	11th to 20th	Day	8% 9% 30% 34% 13% 6%	718
	21st to end	Day	9% 6% 32% 30% 16% 6%	794
August	1st to 10th	Day	10% 5% 25% 28% 21% 10%	591
	11th to 20th	Day	12% 5% 21% 31% 21% 11%	519
	21st to end	Day	12% 7% 24% 31% 18% 8%	583
September	1st to 10th	Day	14% 8% 26% 26% 19% 7%	530
	11th to 20th	Day	9% 6% 22% 25% 27% 10%	530
	21st to end	Day	15% 12% 24% 26% 16% 6%	530
October	1st to 10th	Day	17% 13% 25% 26% 17% 2	530
	11th to 20th	Day	25% 18% 30% 23% 5%	400
	21st to end	Day	31% 19% 32% 14% 3 1	363
November	1st to 10th	Day	25% 21% 33% 15% 4 2	330
	11th to 20th	Day	26% 25% 35% 10% 3	321
	21st to end	Day	27% 21% 37% 12% 2	300
December	1st to 10th	Day	27% 25% 27% 14% 6%	300
	11th to 20th	Day	24% 28% 32% 12% 3 1	300
	21st to end	Day	32% 22% 32% 10% 4 1	330
January	1st to 10th	Night	21% 15% 32% 25% 6% 1	1000
	11th to 20th	Night	25% 15% 32% 22% 5% 1	1000
	21st to end	Night	21% 11% 34% 27% 6%	1100
February	1st to 10th	Night	18% 16% 35% 26% 4 1	867
	11th to 20th	Night	21% 16% 33% 25% 5% 1	783
	21st to end	Night	24% 16% 36% 21% 3	660
March	1st to 10th	Night	20% 13% 33% 26% 8% 1	800
	11th to 20th	Night	19% 13% 34% 26% 7% 1	800
	21st to end	Night	22% 10% 29% 30% 8% 1	782
April	1st to 10th	Night	20% 10% 34% 28% 6% 1	600
	11th to 20th	Night	26% 11% 30% 24% 7% 1	593
	21st to end	Night	22% 10% 33% 26% 9% 1	600
May	1st to 10th	Night	18% 8% 33% 32% 8% 1	600
	11th to 20th	Night	18% 8% 31% 30% 12% 1	591
	21st to end	Night	16% 5% 28% 33% 16% 2	650
June	1st to 10th	Night	12% 5% 29% 40% 13% 1	600
	11th to 20th	Night	13% 4 30% 37% 15% 1	600
	21st to end	Night	12% 6% 24% 40% 18% 1	600
July	1st to 10th	Night	8% 2 19% 40% 28% 3	585
	11th to 20th	Night	7% 4 21% 40% 26% 2	582
	21st to end	Night	9% 2 20% 41% 26% 2	657
August	1st to 10th	Night	8% 2 17% 46% 26% 2	597
	11th to 20th	Night	10% 3 13% 44% 25% 4	594
	21st to end	Night	11% 2 19% 40% 26% 2	660
September	1st to 10th	Night	9% 5% 19% 39% 24% 5%	600
	11th to 20th	Night	11% 5% 19% 33% 28% 4	792
	21st to end	Night	15% 9% 22% 31% 20% 3	800
October	1st to 10th	Night	18% 6% 23% 36% 17% 1	800
	11th to 20th	Night	25% 11% 27% 26% 10% 1	800
	21st to end	Night	26% 11% 29% 26% 8%	880
November	1st to 10th	Night	22% 11% 33% 25% 8% 1	820
	11th to 20th	Night	25% 17% 31% 21% 5%	829
	21st to end	Night	27% 13% 29% 27% 4	800
December	1st to 10th	Night	24% 15% 32% 23% 6%	990
	11th to 20th	Night	26% 16% 33% 21% 4 1	1000
	21st to end	Night	31% 14% 32% 20% 3 1	1100

Page generated at 2025-11-15 00:56:00. Version ac07

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