Washington(MI)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Washington(MI) clear sky chart from 2005-11-06 to 2026-02-01.

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% 3 8% 5% 5% 5% 4 6% 7% 34%	126793
	Night	14% 10% 4 8% 5% 4 5% 4 5% 7% 35%	125324
Transparency	Day	48% 4 12% 22% 13% 2	130363
	Night	48% 4 12% 22% 13% 1	129811
Seeing	Day	18% 10% 29% 24% 14% 6%	16942
	Night	19% 9% 28% 30% 12% 1	26686

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	11% 15% 5% 15% 6% 5% 4 4 4 6% 26%	3697
	11th to 20th	Day	14% 15% 6% 16% 8% 10% 6% 3 5% 5% 12%	3700
	21st to end	Day	21% 16% 6% 11% 7% 5% 6% 3 4 5% 17%	4547
February	1st to 10th	Day	15% 14% 5% 13% 7% 6% 5% 4 5% 6% 21%	1800
	11th to 20th	Day	13% 14% 5% 11% 8% 5% 5% 3 5% 5% 25%	1866
	21st to end	Day	13% 16% 6% 10% 6% 5% 4 3 5% 6% 26%	1650
March	1st to 10th	Day	15% 13% 5% 10% 5% 4 3 3 4 6% 31%	4618
	11th to 20th	Day	12% 11% 3 9% 6% 5% 4 3 5% 8% 33%	4980
	21st to end	Day	19% 13% 4 9% 5% 5% 4 3 4 6% 29%	5465
April	1st to 10th	Day	16% 12% 3 8% 5% 4 4 5% 5% 6% 31%	2303
	11th to 20th	Day	16% 10% 3 8% 6% 4 4 4 6% 7% 34%	2557
	21st to end	Day	17% 9% 3 8% 5% 5% 4 3 5% 6% 35%	2600
May	1st to 10th	Day	18% 9% 3 7% 5% 4 4 4 5% 6% 34%	5862
	11th to 20th	Day	16% 9% 3 7% 5% 4 5% 4 6% 8% 33%	5861
	21st to end	Day	13% 6% 2 8% 5% 4 4 4 5% 7% 41%	6433
June	1st to 10th	Day	9% 6% 3 7% 5% 5% 5% 4 6% 9% 41%	2942
	11th to 20th	Day	9% 5% 2 7% 4 5% 5% 4 7% 9% 41%	3000
	21st to end	Day	8% 7% 3 6% 6% 5% 6% 5% 7% 10% 37%	2940
July	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 10% 39%	6360
	11th to 20th	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 9% 45%	6360
	21st to end	Day	6% 5% 3 6% 5% 5% 6% 4 7% 9% 44%	6480
August	1st to 10th	Day	12% 5% 2 6% 4 5% 6% 4 7% 8% 41%	4234
	11th to 20th	Day	8% 5% 3 7% 5% 5% 6% 4 9% 9% 39%	4174
	21st to end	Day	8% 5% 3 8% 5% 5% 6% 5% 7% 9% 38%	4675
September	1st to 10th	Day	10% 6% 3 7% 6% 4 5% 4 6% 9% 41%	2251
	11th to 20th	Day	9% 6% 1 5% 4 4 5% 4 6% 10% 47%	2200
	21st to end	Day	14% 7% 3 8% 6% 4 5% 4 6% 8% 36%	2200
October	1st to 10th	Day	11% 8% 1 6% 4 4 5% 4 6% 6% 44%	2125
	11th to 20th	Day	16% 9% 3 7% 5% 5% 6% 3 5% 6% 36%	2000
	21st to end	Day	18% 11% 3 8% 5% 4 5% 4 5% 7% 30%	2055
November	1st to 10th	Day	11% 10% 3 8% 5% 4 4 4 6% 7% 38%	1852
	11th to 20th	Day	14% 11% 3 8% 6% 5% 5% 4 5% 6% 31%	1890
	21st to end	Day	16% 13% 5% 10% 5% 4 5% 3 4 6% 28%	1711
December	1st to 10th	Day	12% 14% 6% 13% 6% 4 5% 3 6% 7% 24%	2680
	11th to 20th	Day	19% 19% 4 9% 5% 3 5% 3 5% 5% 21%	2872
	21st to end	Day	25% 21% 6% 11% 5% 4 4 3 3 5% 14%	3853
January	1st to 10th	Night	13% 13% 5% 11% 6% 5% 5% 3 4 6% 29%	6488
	11th to 20th	Night	11% 15% 6% 14% 8% 6% 6% 4 5% 6% 19%	6500
	21st to end	Night	16% 16% 7% 10% 5% 5% 5% 3 4 4 23%	6636
February	1st to 10th	Night	14% 15% 5% 11% 7% 5% 5% 4 5% 5% 23%	2601
	11th to 20th	Night	13% 13% 4 10% 7% 5% 6% 4 6% 6% 27%	2418
	21st to end	Night	18% 12% 3 9% 5% 5% 4 3 5% 6% 29%	1980
March	1st to 10th	Night	15% 11% 3 9% 4 4 4 3 5% 6% 35%	5235
	11th to 20th	Night	9% 8% 3 7% 5% 5% 5% 4 5% 8% 41%	4980
	21st to end	Night	15% 9% 3 9% 5% 4 4 3 4 5% 38%	5467
April	1st to 10th	Night	17% 11% 3 6% 5% 4 4 4 6% 7% 34%	2115
	11th to 20th	Night	17% 9% 3 6% 4 4 3 4 5% 7% 38%	1792
	21st to end	Night	16% 8% 2 6% 4 4 5% 3 6% 8% 39%	1800
May	1st to 10th	Night	19% 9% 3 8% 5% 4 4 3 5% 6% 34%	4033
	11th to 20th	Night	16% 7% 3 7% 4 5% 4 3 5% 6% 39%	4032
	21st to end	Night	13% 5% 2 6% 4 4 4 4 5% 8% 45%	4421
June	1st to 10th	Night	10% 5% 2 7% 4 4 4 4 5% 9% 47%	1449
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 5% 6% 8% 45%	1400
	21st to end	Night	8% 6% 2 6% 4 4 4 3 7% 8% 49%	1452
July	1st to 10th	Night	7% 5% 2 5% 4 4 5% 4 7% 10% 47%	3618
	11th to 20th	Night	8% 4 2 5% 4 4 5% 4 7% 9% 49%	3617
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 49%	4373
August	1st to 10th	Night	10% 6% 2 6% 4 3 5% 3 6% 9% 47%	2915
	11th to 20th	Night	8% 5% 3 7% 4 4 5% 4 6% 8% 47%	2875
	21st to end	Night	8% 5% 2 6% 4 4 5% 3 6% 8% 48%	3223
September	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 5% 7% 48%	2124
	11th to 20th	Night	8% 5% 2 5% 3 3 3 3 5% 8% 56%	2200
	21st to end	Night	14% 6% 2 6% 4 4 5% 3 5% 7% 44%	2200
October	1st to 10th	Night	13% 6% 3 5% 4 3 3 4 5% 7% 48%	2274
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 4 5% 5% 38%	2400
	21st to end	Night	20% 8% 3 8% 4 4 5% 4 6% 6% 33%	2780
November	1st to 10th	Night	12% 8% 3 6% 4 4 4 4 4 7% 43%	2666
	11th to 20th	Night	14% 10% 3 8% 6% 5% 6% 5% 6% 7% 31%	2730
	21st to end	Night	18% 13% 4 8% 6% 4 5% 4 6% 6% 27%	2905
December	1st to 10th	Night	12% 13% 5% 12% 6% 6% 6% 4 6% 6% 24%	4720
	11th to 20th	Night	14% 18% 6% 10% 7% 5% 5% 3 5% 5% 22%	5544
	21st to end	Night	25% 20% 6% 10% 5% 4 4 3 4 4 17%	7361

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	60% 4 11% 17% 7% 1	3698
	11th to 20th	Day	72% 4 9% 8% 6% 1	3700
	21st to end	Day	70% 3 12% 8% 6% 1	4547
February	1st to 10th	Day	63% 5% 9% 15% 8%	1800
	11th to 20th	Day	61% 3 8% 18% 9% 1	1875
	21st to end	Day	59% 3 12% 17% 8% 2	1650
March	1st to 10th	Day	55% 3 14% 17% 8% 2	4618
	11th to 20th	Day	49% 4 14% 23% 8% 2	4980
	21st to end	Day	58% 3 12% 15% 11% 2	5465
April	1st to 10th	Day	52% 4 11% 21% 11% 1	2303
	11th to 20th	Day	49% 4 10% 21% 14% 2	2557
	21st to end	Day	49% 4 13% 19% 14% 2	2600
May	1st to 10th	Day	49% 4 10% 20% 12% 4	5897
	11th to 20th	Day	48% 5% 12% 22% 12% 1	5865
	21st to end	Day	42% 4 10% 21% 19% 4	6447
June	1st to 10th	Day	39% 4 12% 27% 15% 2	2942
	11th to 20th	Day	38% 5% 14% 25% 16% 3	3000
	21st to end	Day	39% 6% 13% 24% 16% 2	2940
July	1st to 10th	Day	38% 6% 13% 26% 16% 2	6291
	11th to 20th	Day	32% 6% 14% 29% 18% 1	6285
	21st to end	Day	34% 6% 14% 22% 23% 1	6295
August	1st to 10th	Day	38% 6% 13% 26% 16% 1	4221
	11th to 20th	Day	37% 6% 12% 33% 11% 1	4213
	21st to end	Day	39% 6% 13% 28% 14% 1	4674
September	1st to 10th	Day	39% 6% 13% 27% 14% 2	2251
	11th to 20th	Day	32% 5% 12% 34% 16% 1	2200
	21st to end	Day	45% 4 12% 24% 13% 1	2200
October	1st to 10th	Day	30% 4 11% 33% 20% 2	3463
	11th to 20th	Day	40% 3 11% 27% 18%	3240
	21st to end	Day	45% 4 13% 23% 13% 1	3292
November	1st to 10th	Day	45% 5% 11% 26% 12% 1	1852
	11th to 20th	Day	53% 4 13% 20% 10% 1	1890
	21st to end	Day	58% 4 11% 19% 7% 1	1711
December	1st to 10th	Day	59% 4 16% 16% 5%	2680
	11th to 20th	Day	64% 3 12% 13% 7%	2868
	21st to end	Day	74% 3 9% 8% 6%	3853
January	1st to 10th	Night	55% 4 11% 21% 8% 2	6488
	11th to 20th	Night	64% 4 12% 12% 6% 1	6500
	21st to end	Night	64% 3 11% 15% 8%	6636
February	1st to 10th	Night	62% 5% 9% 15% 8% 1	2601
	11th to 20th	Night	56% 4 10% 19% 10% 1	2420
	21st to end	Night	55% 3 11% 20% 9% 1	1980
March	1st to 10th	Night	49% 4 14% 22% 10% 1	5235
	11th to 20th	Night	41% 5% 14% 24% 15% 1	4980
	21st to end	Night	48% 3 11% 21% 15% 2	5467
April	1st to 10th	Night	49% 4 10% 21% 13% 2	2115
	11th to 20th	Night	45% 4 11% 19% 18% 2	1792
	21st to end	Night	44% 4 11% 21% 17% 3	1800
May	1st to 10th	Night	51% 4 10% 17% 14% 5%	4060
	11th to 20th	Night	45% 5% 10% 26% 12% 2	4033
	21st to end	Night	38% 4 13% 24% 17% 5%	4429
June	1st to 10th	Night	35% 5% 10% 29% 19% 2	1449
	11th to 20th	Night	36% 5% 13% 26% 18% 2	1400
	21st to end	Night	32% 5% 13% 26% 22% 1	1452
July	1st to 10th	Night	31% 5% 15% 29% 16% 4	3580
	11th to 20th	Night	30% 5% 15% 31% 17% 2	3572
	21st to end	Night	31% 6% 15% 23% 23% 2	4245
August	1st to 10th	Night	34% 5% 15% 28% 17% 1	2904
	11th to 20th	Night	33% 6% 13% 35% 12% 2	2902
	21st to end	Night	33% 6% 12% 34% 14% 1	3223
September	1st to 10th	Night	34% 5% 13% 30% 16% 2	2124
	11th to 20th	Night	28% 4 12% 33% 21% 2	2200
	21st to end	Night	40% 4 12% 30% 13% 1	2200
October	1st to 10th	Night	26% 3 10% 32% 27% 1	3716
	11th to 20th	Night	43% 3 11% 24% 19%	3899
	21st to end	Night	41% 3 12% 28% 14% 1	4480
November	1st to 10th	Night	41% 4 12% 26% 16% 1	2666
	11th to 20th	Night	50% 4 14% 22% 10% 1	2730
	21st to end	Night	56% 4 14% 19% 7%	2905
December	1st to 10th	Night	58% 4 17% 16% 4	4720
	11th to 20th	Night	63% 4 12% 15% 6% 1	5547
	21st to end	Night	72% 3 10% 9% 6%	7361

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% 18% 39% 14% 7%	330
	11th to 20th	Day	24% 17% 41% 14% 3 1	330
	21st to end	Day	26% 13% 37% 18% 4 1	363
February	1st to 10th	Day	24% 19% 38% 14% 4 1	300
	11th to 20th	Day	24% 18% 39% 16% 2	300
	21st to end	Day	22% 22% 42% 12% 2	249
March	1st to 10th	Day	26% 17% 37% 17% 3 1	360
	11th to 20th	Day	23% 13% 31% 25% 6% 1	500
	21st to end	Day	29% 12% 32% 21% 5% 1	550
April	1st to 10th	Day	20% 13% 37% 20% 9% 1	500
	11th to 20th	Day	25% 15% 31% 15% 8% 5%	492
	21st to end	Day	24% 11% 29% 23% 11% 3	500
May	1st to 10th	Day	23% 10% 30% 23% 11% 3	503
	11th to 20th	Day	20% 9% 28% 23% 13% 7%	527
	21st to end	Day	14% 7% 24% 27% 19% 9%	573
June	1st to 10th	Day	11% 9% 32% 30% 15% 4	697
	11th to 20th	Day	11% 6% 33% 29% 17% 4	730
	21st to end	Day	13% 6% 29% 30% 17% 5%	730
July	1st to 10th	Day	9% 5% 22% 31% 21% 13%	721
	11th to 20th	Day	10% 6% 25% 31% 19% 9%	718
	21st to end	Day	8% 4 23% 30% 24% 11%	606
August	1st to 10th	Day	10% 2 20% 27% 25% 15%	526
	11th to 20th	Day	11% 3 17% 31% 23% 14%	519
	21st to end	Day	12% 3 19% 31% 22% 13%	583
September	1st to 10th	Day	12% 5% 25% 22% 22% 14%	530
	11th to 20th	Day	8% 3 18% 23% 30% 17%	530
	21st to end	Day	18% 7% 23% 23% 21% 8%	530
October	1st to 10th	Day	17% 7% 25% 23% 18% 10%	530
	11th to 20th	Day	21% 11% 34% 24% 8% 3	530
	21st to end	Day	24% 13% 37% 20% 5% 1	438
November	1st to 10th	Day	19% 17% 34% 22% 6% 2	330
	11th to 20th	Day	23% 20% 33% 16% 7% 1	330
	21st to end	Day	24% 17% 35% 20% 5%	236
December	1st to 10th	Day	25% 16% 37% 14% 8% 1	220
	11th to 20th	Day	30% 19% 34% 12% 4 1	220
	21st to end	Day	32% 15% 33% 15% 4	311
January	1st to 10th	Night	22% 14% 36% 22% 5% 1	1050
	11th to 20th	Night	24% 15% 33% 24% 3 1	1050
	21st to end	Night	19% 13% 33% 29% 6%	927
February	1st to 10th	Night	21% 13% 38% 25% 3	801
	11th to 20th	Night	21% 15% 33% 26% 5%	783
	21st to end	Night	24% 15% 38% 21% 2	660
March	1st to 10th	Night	21% 12% 35% 27% 6%	800
	11th to 20th	Night	17% 15% 36% 26% 6% 1	800
	21st to end	Night	23% 11% 31% 27% 8% 1	880
April	1st to 10th	Night	23% 12% 33% 27% 4 1	715
	11th to 20th	Night	23% 9% 31% 28% 8% 2	593
	21st to end	Night	20% 7% 31% 33% 10%	600
May	1st to 10th	Night	20% 5% 29% 36% 10% 1	600
	11th to 20th	Night	22% 5% 25% 30% 16% 1	591
	21st to end	Night	11% 3 22% 42% 20% 2	650
June	1st to 10th	Night	13% 5% 24% 45% 13%	420
	11th to 20th	Night	12% 4 22% 51% 12% 1	400
	21st to end	Night	10% 2 21% 47% 19%	452
July	1st to 10th	Night	8% 2 18% 41% 28% 4	585
	11th to 20th	Night	11% 3 16% 41% 26% 3	582
	21st to end	Night	7% 2 18% 48% 24% 2	657
August	1st to 10th	Night	8% 1 16% 38% 33% 3	597
	11th to 20th	Night	8% 2 17% 38% 31% 4	594
	21st to end	Night	10% 2 18% 36% 32% 3	660
September	1st to 10th	Night	11% 5% 18% 32% 28% 5%	734
	11th to 20th	Night	10% 3 15% 35% 31% 6%	800
	21st to end	Night	18% 4 20% 32% 21% 5%	800
October	1st to 10th	Night	16% 5% 25% 31% 19% 3	800
	11th to 20th	Night	22% 9% 29% 29% 9% 2	800
	21st to end	Night	24% 10% 33% 29% 5%	880
November	1st to 10th	Night	18% 10% 31% 27% 12% 1	820
	11th to 20th	Night	21% 13% 32% 25% 8% 1	840
	21st to end	Night	25% 12% 34% 22% 6%	840
December	1st to 10th	Night	24% 13% 34% 23% 6% 1	840
	11th to 20th	Night	22% 14% 35% 24% 3	930
	21st to end	Night	31% 9% 32% 25% 3	1155

Page generated at 2026-01-29 01:21:45. Version ac07

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