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 2024-01-12.

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 7% 6% 3 5% 5% 5% 7% 34%	74830
	Night	15% 11% 5% 8% 6% 3 5% 4 5% 6% 32%	74910
Transparency	Day	50% 4 12% 22% 11% 1	74531
	Night	54% 4 11% 20% 10% 1	74730
Seeing	Day	19% 14% 30% 22% 11% 4	14677
	Night	20% 10% 28% 29% 12% 1	24659

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% 15% 9% 13% 11% 5% 5% 4 4 4 14%	1517
	11th to 20th	Day	16% 17% 8% 13% 10% 5% 6% 5% 5% 6% 11%	1453
	21st to end	Day	14% 20% 11% 15% 9% 5% 5% 3 3 3 11%	1584
February	1st to 10th	Day	12% 16% 7% 12% 13% 6% 6% 4 5% 4 15%	1628
	11th to 20th	Day	13% 14% 7% 13% 10% 5% 5% 4 5% 5% 19%	1748
	21st to end	Day	14% 16% 7% 12% 7% 4 6% 5% 4 5% 19%	1480
March	1st to 10th	Day	14% 11% 6% 8% 7% 4 5% 5% 5% 7% 28%	1800
	11th to 20th	Day	12% 10% 4 8% 7% 3 4 5% 5% 7% 36%	1907
	21st to end	Day	18% 11% 3 7% 6% 3 5% 6% 5% 6% 30%	2281
April	1st to 10th	Day	19% 12% 4 7% 5% 2 4 5% 5% 7% 30%	2160
	11th to 20th	Day	19% 10% 3 6% 5% 3 4 5% 4 6% 35%	2175
	21st to end	Day	17% 8% 4 7% 6% 3 5% 4 4 7% 35%	2340
May	1st to 10th	Day	17% 7% 3 5% 5% 3 4 4 6% 9% 37%	2340
	11th to 20th	Day	18% 6% 3 5% 5% 3 4 4 5% 7% 39%	2341
	21st to end	Day	12% 6% 2 5% 4 3 5% 5% 6% 8% 44%	2725
June	1st to 10th	Day	11% 5% 2 5% 5% 3 5% 5% 5% 9% 45%	2520
	11th to 20th	Day	11% 4 2 5% 5% 3 5% 4 5% 9% 47%	2520
	21st to end	Day	12% 5% 2 5% 5% 3 6% 4 5% 10% 44%	2520
July	1st to 10th	Day	6% 4 2 4 4 3 4 5% 5% 9% 55%	2520
	11th to 20th	Day	9% 4 2 4 4 2 5% 5% 6% 8% 50%	2520
	21st to end	Day	8% 4 2 5% 5% 3 5% 5% 7% 9% 49%	2743
August	1st to 10th	Day	9% 4 2 5% 4 3 6% 6% 6% 9% 45%	2386
	11th to 20th	Day	11% 3 2 5% 6% 3 5% 5% 6% 9% 46%	2303
	21st to end	Day	10% 6% 2 5% 4 3 4 5% 5% 9% 47%	2393
September	1st to 10th	Day	11% 6% 2 6% 6% 4 5% 4 5% 7% 44%	2148
	11th to 20th	Day	13% 4 2 5% 5% 3 4 4 6% 8% 46%	1980
	21st to end	Day	13% 7% 3 5% 6% 3 5% 5% 5% 8% 41%	1980
October	1st to 10th	Day	17% 6% 2 6% 6% 3 4 4 4 7% 41%	1980
	11th to 20th	Day	22% 11% 4 7% 7% 4 5% 6% 5% 6% 24%	1738
	21st to end	Day	23% 12% 4 7% 8% 4 5% 4 3 7% 23%	1782
November	1st to 10th	Day	14% 11% 4 7% 6% 3 5% 4 5% 6% 35%	1672
	11th to 20th	Day	15% 20% 6% 9% 7% 3 5% 4 5% 6% 21%	1710
	21st to end	Day	21% 19% 5% 8% 5% 3 4 3 4 6% 21%	1710
December	1st to 10th	Day	14% 20% 11% 14% 8% 3 4 3 4 5% 13%	1525
	11th to 20th	Day	14% 19% 11% 13% 9% 3 5% 5% 5% 5% 12%	1918
	21st to end	Day	22% 24% 8% 11% 8% 4 3 4 4 4 9%	2783
January	1st to 10th	Night	15% 16% 9% 13% 10% 5% 5% 4 4 4 16%	2648
	11th to 20th	Night	16% 18% 9% 12% 8% 5% 5% 4 4 4 15%	2547
	21st to end	Night	12% 17% 10% 15% 10% 4 5% 5% 4 4 13%	2772
February	1st to 10th	Night	12% 16% 8% 13% 13% 4 6% 4 4 5% 16%	2328
	11th to 20th	Night	14% 13% 7% 11% 9% 4 6% 4 5% 6% 21%	2098
	21st to end	Night	17% 13% 5% 10% 8% 4 5% 4 5% 5% 24%	1776
March	1st to 10th	Night	16% 9% 4 7% 7% 4 4 5% 5% 7% 33%	2160
	11th to 20th	Night	13% 9% 3 6% 6% 2 4 3 6% 7% 41%	2052
	21st to end	Night	18% 9% 4 6% 6% 3 5% 4 5% 7% 33%	2090
April	1st to 10th	Night	16% 10% 4 6% 5% 3 5% 4 5% 8% 34%	1800
	11th to 20th	Night	20% 8% 4 5% 4 3 5% 4 5% 6% 36%	1732
	21st to end	Night	16% 9% 3 6% 5% 2 5% 4 4 7% 39%	1620
May	1st to 10th	Night	15% 8% 3 7% 6% 3 5% 4 5% 8% 36%	1620
	11th to 20th	Night	17% 5% 2 6% 6% 3 5% 5% 5% 8% 39%	1549
	21st to end	Night	13% 6% 3 6% 4 4 5% 5% 5% 7% 42%	1551
June	1st to 10th	Night	11% 5% 3 5% 4 3 4 5% 7% 9% 45%	1440
	11th to 20th	Night	10% 5% 2 5% 5% 2 4 5% 6% 9% 46%	1440
	21st to end	Night	10% 5% 2 5% 4 3 5% 4 6% 9% 47%	1440
July	1st to 10th	Night	7% 4 1 4 5% 3 4 5% 6% 10% 52%	1440
	11th to 20th	Night	6% 4 2 4 5% 3 5% 5% 6% 9% 52%	1440
	21st to end	Night	7% 5% 2 4 5% 3 4 4 6% 7% 53%	1575
August	1st to 10th	Night	8% 3 2 5% 4 3 4 6% 5% 9% 50%	1550
	11th to 20th	Night	8% 3 2 5% 4 2 5% 5% 7% 8% 51%	1598
	21st to end	Night	9% 5% 3 5% 4 2 4 5% 5% 8% 51%	1960
September	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 5% 5% 7% 50%	1800
	11th to 20th	Night	10% 5% 2 4 3 2 4 4 5% 6% 55%	1972
	21st to end	Night	14% 6% 2 6% 5% 3 4 4 5% 8% 43%	1980
October	1st to 10th	Night	17% 6% 2 5% 4 2 3 3 5% 6% 46%	1980
	11th to 20th	Night	22% 10% 4 7% 4 3 4 3 4 5% 33%	2219
	21st to end	Night	24% 9% 3 7% 5% 3 4 4 4 7% 30%	2574
November	1st to 10th	Night	15% 9% 4 6% 6% 3 5% 4 5% 6% 37%	2406
	11th to 20th	Night	17% 14% 6% 8% 7% 4 5% 5% 6% 7% 22%	2470
	21st to end	Night	19% 17% 5% 8% 6% 3 4 4 4 6% 23%	2470
December	1st to 10th	Night	16% 16% 10% 14% 8% 4 4 5% 4 5% 14%	2650
	11th to 20th	Night	16% 20% 8% 11% 8% 4 5% 4 5% 4 15%	3279
	21st to end	Night	25% 21% 7% 10% 6% 3 4 4 4 4 13%	4884

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	75% 4 8% 10% 2	1518
	11th to 20th	Day	75% 5% 9% 8% 3	1453
	21st to end	Day	81% 3 5% 8% 3	1584
February	1st to 10th	Day	73% 5% 7% 14% 1	1628
	11th to 20th	Day	68% 4 8% 13% 6%	1758
	21st to end	Day	66% 4 10% 14% 5%	1480
March	1st to 10th	Day	56% 4 14% 18% 7% 1	1800
	11th to 20th	Day	49% 4 13% 20% 12% 2	1907
	21st to end	Day	54% 4 12% 21% 9% 1	2281
April	1st to 10th	Day	55% 3 9% 21% 11%	2160
	11th to 20th	Day	50% 4 10% 20% 14% 3	2175
	21st to end	Day	49% 3 12% 20% 13% 2	2340
May	1st to 10th	Day	45% 4 11% 27% 13% 1	2340
	11th to 20th	Day	44% 4 13% 22% 15% 2	2345
	21st to end	Day	37% 5% 14% 27% 16% 1	2725
June	1st to 10th	Day	36% 4 11% 29% 18% 2	2520
	11th to 20th	Day	35% 4 14% 24% 22% 1	2520
	21st to end	Day	37% 4 15% 25% 17% 2	2520
July	1st to 10th	Day	27% 3 14% 34% 17% 4	2451
	11th to 20th	Day	31% 4 13% 30% 19% 3	2445
	21st to end	Day	32% 5% 12% 29% 19% 3	2591
August	1st to 10th	Day	34% 4 14% 34% 13% 2	2371
	11th to 20th	Day	34% 5% 15% 30% 15% 2	2303
	21st to end	Day	34% 4 14% 28% 17% 3	2393
September	1st to 10th	Day	39% 4 13% 27% 15% 2	2148
	11th to 20th	Day	36% 4 13% 32% 13% 2	1980
	21st to end	Day	41% 5% 12% 27% 14%	1980
October	1st to 10th	Day	45% 4 9% 28% 13% 1	1980
	11th to 20th	Day	60% 4 13% 16% 7%	1738
	21st to end	Day	64% 3 11% 15% 6%	1782
November	1st to 10th	Day	51% 5% 12% 21% 11%	1672
	11th to 20th	Day	66% 3 12% 14% 5%	1710
	21st to end	Day	66% 4 13% 13% 4	1710
December	1st to 10th	Day	76% 4 8% 10% 2	1525
	11th to 20th	Day	77% 3 11% 8% 1	1915
	21st to end	Day	81% 2 7% 7% 2	2783
January	1st to 10th	Night	73% 4 8% 11% 3	2648
	11th to 20th	Night	74% 4 9% 8% 4	2547
	21st to end	Night	76% 4 9% 7% 3	2772
February	1st to 10th	Night	72% 3 7% 13% 4	2328
	11th to 20th	Night	66% 4 8% 16% 7%	2099
	21st to end	Night	63% 4 11% 15% 7%	1776
March	1st to 10th	Night	51% 4 13% 23% 8% 1	2160
	11th to 20th	Night	43% 4 13% 24% 13% 3	2052
	21st to end	Night	52% 2 10% 23% 11% 2	2090
April	1st to 10th	Night	51% 3 10% 22% 13% 1	1800
	11th to 20th	Night	50% 3 6% 19% 18% 3	1732
	21st to end	Night	47% 3 11% 21% 13% 4	1620
May	1st to 10th	Night	49% 3 12% 22% 13% 2	1620
	11th to 20th	Night	43% 5% 10% 21% 17% 4	1550
	21st to end	Night	42% 5% 10% 25% 15% 3	1552
June	1st to 10th	Night	35% 4 11% 31% 15% 3	1440
	11th to 20th	Night	35% 4 14% 26% 20% 2	1440
	21st to end	Night	35% 4 15% 27% 16% 3	1440
July	1st to 10th	Night	28% 5% 13% 30% 20% 4	1400
	11th to 20th	Night	29% 5% 14% 29% 20% 3	1392
	21st to end	Night	31% 5% 13% 28% 20% 4	1487
August	1st to 10th	Night	31% 4 16% 31% 16% 2	1541
	11th to 20th	Night	30% 5% 13% 33% 18% 2	1598
	21st to end	Night	33% 5% 10% 28% 21% 3	1960
September	1st to 10th	Night	34% 5% 10% 30% 18% 2	1800
	11th to 20th	Night	31% 3 10% 38% 17% 1	1972
	21st to end	Night	42% 3 12% 30% 12% 1	1980
October	1st to 10th	Night	41% 3 8% 30% 16% 2	1980
	11th to 20th	Night	55% 3 12% 21% 9% 1	2219
	21st to end	Night	55% 4 13% 18% 9%	2574
November	1st to 10th	Night	49% 5% 10% 23% 12% 1	2406
	11th to 20th	Night	62% 4 11% 16% 6% 1	2470
	21st to end	Night	64% 3 14% 14% 3	2470
December	1st to 10th	Night	74% 4 9% 10% 3	2650
	11th to 20th	Night	73% 4 10% 9% 3	3281
	21st to end	Night	77% 3 10% 7% 2	4884

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	22% 17% 34% 19% 5% 1	270
	11th to 20th	Day	27% 14% 38% 16% 4 1	245
	21st to end	Day	27% 20% 32% 18% 3	264
February	1st to 10th	Day	23% 30% 30% 15% 3	240
	11th to 20th	Day	23% 29% 34% 13% 2	240
	21st to end	Day	28% 31% 33% 6% 2 1	198
March	1st to 10th	Day	24% 35% 30% 9% 2	240
	11th to 20th	Day	22% 19% 31% 20% 9%	347
	21st to end	Day	29% 15% 29% 20% 6% 2	462
April	1st to 10th	Day	27% 16% 32% 18% 6% 1	420
	11th to 20th	Day	29% 23% 23% 16% 7% 2	412
	21st to end	Day	24% 17% 30% 19% 9% 1	420
May	1st to 10th	Day	23% 16% 32% 19% 7% 3	423
	11th to 20th	Day	20% 14% 30% 21% 11% 3	487
	21st to end	Day	16% 13% 29% 26% 12% 4	679
June	1st to 10th	Day	11% 11% 39% 25% 10% 4	630
	11th to 20th	Day	16% 9% 33% 27% 10% 4	630
	21st to end	Day	15% 9% 38% 25% 10% 4	630
July	1st to 10th	Day	7% 6% 29% 31% 19% 7%	621
	11th to 20th	Day	7% 9% 31% 33% 14% 6%	618
	21st to end	Day	9% 7% 32% 30% 16% 6%	684
August	1st to 10th	Day	11% 5% 26% 27% 21% 10%	505
	11th to 20th	Day	12% 4 21% 31% 21% 12%	439
	21st to end	Day	13% 7% 23% 29% 19% 8%	495
September	1st to 10th	Day	15% 8% 26% 27% 18% 6%	450
	11th to 20th	Day	10% 6% 24% 26% 26% 7%	450
	21st to end	Day	16% 13% 24% 25% 16% 6%	450
October	1st to 10th	Day	19% 13% 25% 24% 17% 3	450
	11th to 20th	Day	28% 19% 28% 20% 4	334
	21st to end	Day	35% 19% 32% 10% 3 2	297
November	1st to 10th	Day	24% 22% 32% 15% 5% 2	270
	11th to 20th	Day	23% 27% 37% 9% 4	270
	21st to end	Day	29% 20% 37% 12% 2	270
December	1st to 10th	Day	28% 25% 28% 14% 6%	270
	11th to 20th	Day	24% 29% 31% 12% 3 1	270
	21st to end	Day	29% 23% 35% 10% 3	297
January	1st to 10th	Night	22% 15% 31% 25% 6% 1	950
	11th to 20th	Night	26% 13% 31% 24% 6% 1	910
	21st to end	Night	21% 10% 34% 28% 7%	990
February	1st to 10th	Night	19% 16% 35% 26% 4 1	780
	11th to 20th	Night	21% 16% 32% 25% 6% 1	703
	21st to end	Night	26% 16% 34% 21% 4	592
March	1st to 10th	Night	20% 13% 31% 27% 9% 1	720
	11th to 20th	Night	19% 12% 34% 27% 8% 1	720
	21st to end	Night	22% 10% 29% 30% 9% 1	704
April	1st to 10th	Night	19% 10% 34% 29% 7% 1	540
	11th to 20th	Night	26% 10% 30% 26% 7% 1	533
	21st to end	Night	22% 9% 32% 26% 10% 1	540
May	1st to 10th	Night	19% 8% 32% 32% 8% 1	540
	11th to 20th	Night	18% 8% 31% 30% 12% 1	531
	21st to end	Night	16% 5% 26% 34% 18% 2	584
June	1st to 10th	Night	12% 5% 28% 41% 14% 1	540
	11th to 20th	Night	14% 4 29% 35% 17% 1	540
	21st to end	Night	11% 6% 22% 41% 19% 1	540
July	1st to 10th	Night	8% 2 18% 40% 29% 3	525
	11th to 20th	Night	6% 4 22% 40% 26% 2	522
	21st to end	Night	9% 3 20% 41% 26% 2	591
August	1st to 10th	Night	8% 2 17% 44% 27% 2	537
	11th to 20th	Night	9% 3 14% 43% 27% 5%	534
	21st to end	Night	11% 2 20% 40% 25% 2	594
September	1st to 10th	Night	10% 6% 19% 39% 22% 5%	540
	11th to 20th	Night	12% 5% 21% 32% 26% 4	712
	21st to end	Night	16% 8% 23% 30% 20% 4	720
October	1st to 10th	Night	19% 6% 23% 33% 17% 1	720
	11th to 20th	Night	27% 11% 27% 25% 9% 1	720
	21st to end	Night	28% 11% 29% 24% 8%	792
November	1st to 10th	Night	21% 11% 32% 26% 9% 1	740
	11th to 20th	Night	25% 17% 31% 21% 5% 1	760
	21st to end	Night	26% 13% 29% 27% 4	760
December	1st to 10th	Night	24% 15% 33% 22% 5%	940
	11th to 20th	Night	25% 15% 33% 21% 4 1	950
	21st to end	Night	30% 14% 33% 20% 3	1045

Page generated at 2024-01-09 16:24:22. Version ac07

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