Traverse City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Traverse City clear sky chart from 2005-11-06 to 2025-09-04.

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% 11% 4 10% 5% 5% 4 3 5% 6% 33%	125389
	Night	14% 13% 5% 11% 6% 5% 4 3 4 5% 28%	123475
Transparency	Day	51% 6% 10% 21% 11% 1	128888
	Night	57% 6% 11% 17% 9% 1	128050
Seeing	Day	18% 12% 29% 25% 12% 4	16905
	Night	20% 10% 29% 29% 11% 1	26840

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	9% 21% 13% 28% 7% 4 3 2 3 3 6%	3617
	11th to 20th	Day	11% 16% 8% 25% 14% 10% 5% 3 3 2 4	3620
	21st to end	Day	13% 17% 9% 19% 9% 5% 7% 3 3 4 11%	3982
February	1st to 10th	Day	8% 19% 6% 17% 15% 7% 5% 2 4 3 13%	1713
	11th to 20th	Day	11% 15% 7% 17% 12% 7% 5% 3 4 3 14%	1948
	21st to end	Day	11% 18% 7% 13% 9% 6% 5% 4 5% 5% 19%	1650
March	1st to 10th	Day	12% 11% 4 12% 7% 4 4 4 5% 5% 32%	4480
	11th to 20th	Day	11% 11% 5% 13% 5% 5% 5% 4 6% 8% 28%	4833
	21st to end	Day	21% 12% 8% 14% 6% 4 3 3 3 4 21%	5688
April	1st to 10th	Day	17% 15% 4 8% 5% 4 5% 3 4 5% 30%	2400
	11th to 20th	Day	19% 12% 4 6% 4 4 4 3 4 5% 35%	2467
	21st to end	Day	15% 11% 4 8% 4 4 4 4 6% 7% 33%	2600
May	1st to 10th	Day	14% 9% 3 6% 4 3 3 3 4 6% 43%	5862
	11th to 20th	Day	12% 9% 2 6% 4 4 4 4 4 6% 43%	6086
	21st to end	Day	14% 8% 2 6% 4 4 4 3 4 6% 43%	6935
June	1st to 10th	Day	13% 6% 1 6% 4 4 4 4 6% 7% 44%	2800
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 4 6% 9% 42%	2800
	21st to end	Day	13% 6% 2 6% 4 4 4 5% 6% 8% 42%	2800
July	1st to 10th	Day	16% 5% 2 5% 3 3 4 3 6% 9% 45%	6360
	11th to 20th	Day	11% 4 2 5% 3 4 4 3 6% 8% 51%	6360
	21st to end	Day	9% 5% 2 5% 3 4 4 3 6% 10% 49%	6924
August	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	4398
	11th to 20th	Day	15% 5% 2 5% 3 4 4 3 5% 6% 48%	4174
	21st to end	Day	13% 6% 3 7% 4 4 4 3 5% 6% 45%	4454
September	1st to 10th	Day	15% 4 2 5% 4 5% 4 3 6% 7% 43%	2297
	11th to 20th	Day	14% 5% 2 5% 3 3 4 5% 5% 8% 46%	2090
	21st to end	Day	16% 7% 2 7% 3 4 5% 4 7% 8% 38%	2090
October	1st to 10th	Day	18% 8% 3 7% 4 4 3 4 5% 7% 37%	2090
	11th to 20th	Day	22% 16% 4 8% 6% 5% 6% 2 5% 6% 22%	1800
	21st to end	Day	23% 16% 4 10% 5% 6% 5% 4 6% 5% 17%	1881
November	1st to 10th	Day	16% 18% 5% 7% 5% 4 4 3 5% 7% 27%	1762
	11th to 20th	Day	13% 22% 6% 13% 5% 6% 5% 3 5% 6% 17%	1800
	21st to end	Day	16% 25% 8% 12% 5% 4 3 2 4 5% 14%	1718
December	1st to 10th	Day	13% 27% 12% 18% 7% 5% 5% 3 3 2 6%	2280
	11th to 20th	Day	11% 23% 9% 19% 9% 6% 5% 3 3 4 8%	2648
	21st to end	Day	18% 22% 10% 13% 7% 6% 4 3 3 3 8%	3982
January	1st to 10th	Night	10% 21% 9% 29% 8% 5% 3 2 2 2 8%	6348
	11th to 20th	Night	10% 17% 8% 21% 16% 9% 4 3 3 3 7%	6360
	21st to end	Night	11% 20% 10% 16% 8% 7% 6% 3 4 4 11%	6996
February	1st to 10th	Night	10% 19% 7% 16% 13% 8% 4 4 3 3 13%	2682
	11th to 20th	Night	11% 15% 8% 16% 10% 6% 4 3 5% 4 17%	2338
	21st to end	Night	14% 17% 6% 15% 7% 4 4 3 5% 6% 21%	1980
March	1st to 10th	Night	16% 10% 4 10% 5% 3 4 3 5% 6% 35%	5373
	11th to 20th	Night	11% 12% 5% 9% 5% 4 5% 3 5% 7% 33%	5126
	21st to end	Night	19% 13% 5% 10% 6% 4 4 3 4 5% 27%	5284
April	1st to 10th	Night	18% 14% 3 9% 4 4 4 4 5% 6% 31%	2000
	11th to 20th	Night	21% 10% 4 7% 4 3 3 3 4 6% 34%	1882
	21st to end	Night	16% 10% 3 6% 4 4 4 4 4 6% 38%	1800
May	1st to 10th	Night	14% 9% 3 6% 4 4 4 3 5% 7% 41%	4033
	11th to 20th	Night	14% 8% 2 7% 4 4 5% 4 6% 6% 40%	3816
	21st to end	Night	19% 8% 3 6% 3 3 3 3 4 6% 42%	3942
June	1st to 10th	Night	14% 5% 2 6% 5% 3 5% 4 5% 7% 43%	1600
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 5% 6% 9% 42%	1508
	21st to end	Night	12% 6% 2 6% 5% 3 4 3 5% 8% 45%	1600
July	1st to 10th	Night	12% 6% 2 6% 3 4 5% 4 5% 9% 44%	3618
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 5% 7% 52%	3617
	21st to end	Night	9% 5% 2 5% 4 4 4 3 5% 7% 51%	3947
August	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 3 6% 8% 42%	2756
	11th to 20th	Night	15% 4 2 5% 3 3 3 3 5% 7% 48%	2875
	21st to end	Night	12% 5% 2 6% 3 4 4 3 5% 7% 48%	3442
September	1st to 10th	Night	11% 7% 3 6% 4 3 4 3 5% 5% 50%	1930
	11th to 20th	Night	14% 5% 2 6% 4 3 3 3 6% 7% 47%	2090
	21st to end	Night	18% 6% 2 7% 5% 3 4 3 5% 7% 39%	2090
October	1st to 10th	Night	17% 9% 2 8% 5% 4 4 3 4 6% 39%	2090
	11th to 20th	Night	22% 12% 3 9% 5% 4 5% 3 5% 6% 26%	2379
	21st to end	Night	23% 15% 4 10% 6% 4 4 3 4 5% 23%	2717
November	1st to 10th	Night	14% 16% 3 9% 5% 5% 4 4 5% 6% 28%	2536
	11th to 20th	Night	14% 22% 6% 11% 6% 5% 5% 4 4 5% 18%	2600
	21st to end	Night	17% 21% 7% 13% 6% 5% 4 4 4 5% 14%	2675
December	1st to 10th	Night	12% 21% 12% 17% 7% 5% 5% 3 4 4 10%	4910
	11th to 20th	Night	12% 23% 9% 17% 9% 5% 5% 3 4 4 9%	5539
	21st to end	Night	21% 21% 9% 14% 6% 5% 4 3 4 4 11%	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	85% 3 6% 4 1	3618
	11th to 20th	Day	86% 5% 4 4 1	3620
	21st to end	Day	76% 6% 10% 7% 1	3982
February	1st to 10th	Day	77% 4 8% 9% 2	1713
	11th to 20th	Day	74% 5% 9% 9% 3	1958
	21st to end	Day	68% 5% 9% 15% 3 1	1650
March	1st to 10th	Day	53% 6% 14% 17% 9% 1	4480
	11th to 20th	Day	54% 6% 13% 18% 8% 1	4833
	21st to end	Day	66% 6% 7% 14% 6%	5690
April	1st to 10th	Day	58% 5% 9% 18% 10%	2400
	11th to 20th	Day	52% 5% 8% 21% 14% 1	2467
	21st to end	Day	48% 7% 10% 16% 16% 3	2600
May	1st to 10th	Day	42% 5% 9% 22% 19% 3	5897
	11th to 20th	Day	41% 6% 8% 25% 18% 2	6090
	21st to end	Day	41% 6% 8% 22% 20% 2	6949
June	1st to 10th	Day	38% 6% 10% 28% 17% 2	2800
	11th to 20th	Day	39% 6% 12% 23% 19% 2	2800
	21st to end	Day	39% 7% 12% 25% 15% 1	2800
July	1st to 10th	Day	36% 5% 13% 29% 15% 1	6291
	11th to 20th	Day	30% 6% 12% 36% 15% 1	6285
	21st to end	Day	30% 7% 13% 31% 18% 1	6728
August	1st to 10th	Day	36% 7% 14% 29% 14% 1	4383
	11th to 20th	Day	37% 6% 11% 33% 13% 1	4213
	21st to end	Day	40% 7% 11% 30% 12% 1	4453
September	1st to 10th	Day	39% 7% 13% 26% 15% 2	2297
	11th to 20th	Day	35% 7% 14% 29% 14% 1	2090
	21st to end	Day	43% 7% 14% 25% 10%	2090
October	1st to 10th	Day	33% 5% 8% 34% 19% 1	3480
	11th to 20th	Day	56% 4 9% 19% 11%	2964
	21st to end	Day	64% 5% 13% 15% 3	3081
November	1st to 10th	Day	58% 5% 10% 19% 8%	1762
	11th to 20th	Day	69% 5% 12% 11% 4	1800
	21st to end	Day	74% 5% 11% 8% 2	1718
December	1st to 10th	Day	84% 6% 5% 4 1	2280
	11th to 20th	Day	82% 5% 7% 5% 1	2644
	21st to end	Day	79% 7% 7% 6% 2	3982
January	1st to 10th	Night	83% 4 6% 6% 1	6348
	11th to 20th	Night	84% 5% 6% 4 1	6360
	21st to end	Night	77% 6% 7% 9% 1	6996
February	1st to 10th	Night	76% 3 8% 9% 4	2682
	11th to 20th	Night	69% 6% 9% 13% 3	2339
	21st to end	Night	64% 5% 11% 16% 4	1980
March	1st to 10th	Night	50% 5% 17% 19% 8%	5373
	11th to 20th	Night	49% 5% 18% 20% 7% 1	5126
	21st to end	Night	58% 5% 11% 17% 8%	5284
April	1st to 10th	Night	54% 5% 9% 21% 11% 1	2000
	11th to 20th	Night	52% 4 7% 20% 14% 2	1882
	21st to end	Night	48% 4 10% 21% 15% 3	1800
May	1st to 10th	Night	42% 6% 11% 20% 18% 4	4060
	11th to 20th	Night	43% 7% 7% 25% 17% 1	3817
	21st to end	Night	42% 6% 11% 22% 15% 4	3950
June	1st to 10th	Night	39% 6% 11% 28% 15% 1	1600
	11th to 20th	Night	37% 7% 13% 24% 16% 2	1508
	21st to end	Night	38% 6% 13% 25% 16% 2	1600
July	1st to 10th	Night	37% 5% 13% 26% 15% 3	3580
	11th to 20th	Night	31% 6% 12% 30% 19% 2	3572
	21st to end	Night	31% 7% 15% 29% 18% 1	3832
August	1st to 10th	Night	39% 7% 14% 25% 13% 1	2747
	11th to 20th	Night	35% 5% 16% 29% 15% 1	2902
	21st to end	Night	35% 6% 15% 25% 19% 1	3442
September	1st to 10th	Night	35% 7% 12% 24% 20% 1	1930
	11th to 20th	Night	36% 5% 14% 30% 14%	2090
	21st to end	Night	43% 6% 15% 25% 10% 1	2090
October	1st to 10th	Night	40% 6% 10% 31% 13% 1	3480
	11th to 20th	Night	50% 5% 10% 23% 12%	3954
	21st to end	Night	55% 5% 12% 22% 6%	4467
November	1st to 10th	Night	56% 6% 13% 18% 7% 1	2536
	11th to 20th	Night	68% 5% 12% 10% 5% 1	2600
	21st to end	Night	73% 5% 11% 9% 1	2675
December	1st to 10th	Night	76% 8% 9% 7% 1	4910
	11th to 20th	Night	78% 6% 8% 6% 1	5542
	21st to end	Night	76% 7% 9% 6% 3	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	18% 16% 38% 21% 6% 1	300
	11th to 20th	Day	21% 14% 41% 19% 5%	300
	21st to end	Day	23% 17% 31% 23% 5% 1	330
February	1st to 10th	Day	18% 26% 34% 16% 3 2	300
	11th to 20th	Day	20% 22% 38% 17% 4	300
	21st to end	Day	23% 23% 39% 13% 2	249
March	1st to 10th	Day	22% 22% 37% 16% 3	300
	11th to 20th	Day	24% 15% 29% 22% 8% 1	431
	21st to end	Day	29% 13% 28% 20% 9% 1	550
April	1st to 10th	Day	26% 14% 31% 22% 5% 1	500
	11th to 20th	Day	26% 20% 28% 16% 9% 3	492
	21st to end	Day	21% 15% 27% 24% 10% 3	500
May	1st to 10th	Day	20% 15% 32% 19% 10% 3	503
	11th to 20th	Day	15% 11% 29% 30% 11% 4	622
	21st to end	Day	15% 10% 28% 27% 15% 4	789
June	1st to 10th	Day	15% 10% 31% 28% 13% 3	730
	11th to 20th	Day	15% 11% 30% 29% 12% 4	730
	21st to end	Day	16% 8% 29% 29% 14% 4	730
July	1st to 10th	Day	9% 6% 27% 33% 18% 6%	721
	11th to 20th	Day	12% 8% 26% 31% 17% 7%	718
	21st to end	Day	8% 5% 29% 34% 19% 5%	794
August	1st to 10th	Day	9% 5% 22% 31% 23% 8%	626
	11th to 20th	Day	12% 5% 20% 29% 22% 11%	519
	21st to end	Day	16% 8% 22% 28% 20% 6%	583
September	1st to 10th	Day	17% 8% 22% 27% 18% 9%	502
	11th to 20th	Day	12% 6% 19% 30% 24% 9%	490
	21st to end	Day	19% 9% 19% 27% 20% 6%	490
October	1st to 10th	Day	22% 12% 26% 24% 14% 4	490
	11th to 20th	Day	27% 16% 29% 23% 5%	366
	21st to end	Day	31% 17% 32% 15% 5% 1	330
November	1st to 10th	Day	27% 18% 31% 15% 9%	300
	11th to 20th	Day	22% 19% 40% 16% 4	300
	21st to end	Day	26% 22% 34% 15% 2	285
December	1st to 10th	Day	30% 18% 31% 16% 6% 1	200
	11th to 20th	Day	21% 23% 37% 16% 3	205
	21st to end	Day	25% 19% 37% 14% 3 2	330
January	1st to 10th	Night	20% 14% 35% 24% 7% 1	1000
	11th to 20th	Night	23% 14% 34% 22% 7% 1	1000
	21st to end	Night	18% 11% 34% 28% 8% 1	1100
February	1st to 10th	Night	18% 12% 36% 27% 6% 1	895
	11th to 20th	Night	20% 15% 35% 24% 6%	783
	21st to end	Night	23% 16% 33% 24% 5%	660
March	1st to 10th	Night	17% 12% 34% 27% 10% 1	800
	11th to 20th	Night	17% 13% 34% 30% 5% 1	800
	21st to end	Night	21% 10% 29% 32% 7% 1	800
April	1st to 10th	Night	25% 9% 32% 29% 6% 1	600
	11th to 20th	Night	24% 14% 26% 27% 9% 1	593
	21st to end	Night	19% 9% 30% 32% 9% 1	600
May	1st to 10th	Night	17% 6% 31% 35% 11% 1	600
	11th to 20th	Night	19% 7% 25% 35% 14%	591
	21st to end	Night	16% 5% 25% 35% 18% 1	650
June	1st to 10th	Night	17% 5% 28% 36% 13% 1	600
	11th to 20th	Night	13% 6% 22% 44% 14% 1	508
	21st to end	Night	14% 4 26% 36% 19% 1	600
July	1st to 10th	Night	11% 3 17% 42% 25% 2	585
	11th to 20th	Night	11% 3 20% 39% 25% 2	582
	21st to end	Night	10% 4 19% 42% 24% 2	657
August	1st to 10th	Night	10% 2 16% 43% 28% 1	597
	11th to 20th	Night	10% 3 19% 38% 27% 4	594
	21st to end	Night	13% 4 18% 40% 22% 2	660
September	1st to 10th	Night	15% 5% 22% 32% 22% 4	579
	11th to 20th	Night	16% 3 20% 34% 23% 4	760
	21st to end	Night	21% 6% 20% 31% 18% 4	760
October	1st to 10th	Night	20% 8% 25% 29% 16% 1	760
	11th to 20th	Night	29% 10% 28% 27% 6% 1	760
	21st to end	Night	30% 12% 28% 24% 6%	836
November	1st to 10th	Night	25% 12% 30% 26% 6%	780
	11th to 20th	Night	25% 15% 35% 22% 4	800
	21st to end	Night	27% 12% 36% 22% 3	850
December	1st to 10th	Night	23% 15% 36% 22% 4	1000
	11th to 20th	Night	23% 15% 36% 20% 4 1	1000
	21st to end	Night	27% 13% 36% 21% 3	1100

Page generated at 2025-09-01 01:51:08. Version ac07

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