Kalamazoo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kalamazoo 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	13% 11% 4 9% 5% 5% 4 4 5% 7% 33%	125868
	Night	15% 12% 5% 10% 5% 4 4 3 5% 6% 31%	123050
Transparency	Day	49% 6% 12% 20% 12% 1	129409
	Night	52% 6% 11% 19% 11% 1	127570
Seeing	Day	18% 16% 30% 22% 11% 4	16924
	Night	19% 12% 30% 27% 10% 1	26716

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% 19% 9% 21% 6% 4 4 3 4 5% 14%	3617
	11th to 20th	Day	11% 17% 7% 20% 12% 12% 7% 2 2 3 6%	3620
	21st to end	Day	19% 18% 8% 17% 6% 5% 6% 2 4 4 14%	3999
February	1st to 10th	Day	14% 15% 7% 15% 10% 7% 4 2 4 5% 17%	1881
	11th to 20th	Day	14% 14% 7% 16% 9% 5% 4 3 4 4 20%	1948
	21st to end	Day	15% 16% 6% 14% 6% 4 4 3 5% 4 21%	1650
March	1st to 10th	Day	14% 13% 5% 13% 5% 5% 4 3 4 6% 29%	4480
	11th to 20th	Day	10% 9% 4 9% 6% 4 5% 4 6% 8% 34%	4857
	21st to end	Day	18% 16% 7% 9% 5% 5% 4 3 5% 5% 23%	5643
April	1st to 10th	Day	17% 15% 4 7% 6% 4 4 4 6% 6% 29%	2400
	11th to 20th	Day	16% 11% 3 7% 4 4 4 4 4 7% 36%	2423
	21st to end	Day	17% 10% 3 7% 5% 5% 4 3 5% 7% 35%	2600
May	1st to 10th	Day	19% 9% 3 6% 4 4 4 4 5% 7% 34%	5862
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 4 6% 8% 37%	5861
	21st to end	Day	15% 7% 2 6% 4 4 4 3 5% 8% 42%	6838
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 4 6% 9% 44%	2800
	11th to 20th	Day	10% 5% 2 7% 4 5% 4 4 6% 10% 43%	2800
	21st to end	Day	10% 6% 3 6% 5% 4 6% 4 7% 9% 40%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 10% 40%	6360
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 7% 10% 45%	6360
	21st to end	Day	8% 5% 2 6% 4 4 5% 5% 7% 10% 44%	6893
August	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 9% 44%	4234
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 4 5% 7% 46%	4174
	21st to end	Day	8% 5% 2 6% 5% 4 5% 4 6% 9% 46%	4347
September	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 4 5% 7% 45%	2278
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 8% 48%	2090
	21st to end	Day	12% 8% 3 7% 4 5% 4 4 6% 8% 39%	2090
October	1st to 10th	Day	14% 7% 3 7% 4 4 5% 3 5% 6% 42%	2090
	11th to 20th	Day	19% 10% 3 8% 5% 5% 5% 4 5% 7% 29%	1870
	21st to end	Day	22% 12% 3 10% 5% 4 5% 3 5% 6% 25%	1881
November	1st to 10th	Day	13% 12% 4 7% 4 4 5% 3 5% 6% 36%	1762
	11th to 20th	Day	16% 18% 5% 11% 6% 4 4 4 5% 5% 23%	1800
	21st to end	Day	20% 17% 7% 11% 5% 4 3 3 5% 5% 20%	1800
December	1st to 10th	Day	10% 21% 10% 16% 6% 5% 4 3 4 4 16%	2770
	11th to 20th	Day	16% 23% 12% 14% 8% 3 3 2 3 3 13%	3008
	21st to end	Day	24% 24% 7% 13% 6% 3 3 2 3 5% 10%	3982
January	1st to 10th	Night	13% 19% 10% 21% 6% 4 4 3 3 4 14%	6348
	11th to 20th	Night	12% 18% 8% 22% 9% 9% 5% 3 4 3 8%	6360
	21st to end	Night	20% 16% 7% 16% 6% 6% 5% 3 4 4 15%	6978
February	1st to 10th	Night	13% 18% 6% 13% 10% 5% 4 3 4 5% 21%	2515
	11th to 20th	Night	14% 14% 6% 14% 8% 5% 3 3 4 4 23%	2338
	21st to end	Night	17% 12% 5% 11% 7% 4 4 3 5% 5% 27%	1980
March	1st to 10th	Night	15% 9% 5% 10% 5% 4 4 3 4 6% 34%	5373
	11th to 20th	Night	11% 8% 3 7% 5% 4 4 3 5% 7% 43%	5102
	21st to end	Night	18% 12% 5% 10% 4 4 4 3 4 6% 30%	5316
April	1st to 10th	Night	15% 10% 4 7% 4 5% 4 3 5% 7% 35%	2000
	11th to 20th	Night	18% 10% 3 6% 5% 3 4 3 5% 6% 36%	1925
	21st to end	Night	17% 9% 3 6% 5% 4 3 4 5% 7% 38%	1800
May	1st to 10th	Night	19% 10% 3 8% 5% 4 4 3 5% 6% 34%	4033
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 6% 42%	4032
	21st to end	Night	16% 6% 2 7% 4 4 4 3 5% 7% 42%	4031
June	1st to 10th	Night	11% 6% 1 5% 3 3 4 3 7% 11% 46%	1600
	11th to 20th	Night	11% 5% 2 5% 4 5% 5% 5% 7% 10% 42%	1600
	21st to end	Night	9% 5% 1 6% 5% 4 5% 4 7% 9% 45%	1600
July	1st to 10th	Night	8% 5% 2 5% 4 5% 5% 4 6% 10% 45%	3618
	11th to 20th	Night	8% 5% 2 6% 4 4 3 3 6% 8% 51%	3617
	21st to end	Night	9% 6% 2 6% 3 4 4 3 6% 9% 47%	3963
August	1st to 10th	Night	9% 5% 2 5% 3 4 5% 4 6% 10% 47%	2915
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 5% 7% 47%	2875
	21st to end	Night	8% 6% 2 7% 4 4 5% 4 6% 7% 47%	3548
September	1st to 10th	Night	9% 6% 2 6% 4 3 4 3 6% 8% 50%	1949
	11th to 20th	Night	10% 6% 1 5% 3 4 3 3 4 7% 54%	2090
	21st to end	Night	13% 8% 3 7% 3 4 4 3 5% 6% 43%	2090
October	1st to 10th	Night	15% 7% 2 6% 4 3 4 3 4 6% 46%	2090
	11th to 20th	Night	17% 11% 3 8% 5% 4 3 3 4 6% 36%	2305
	21st to end	Night	24% 10% 2 6% 4 4 4 3 4 6% 32%	2717
November	1st to 10th	Night	15% 12% 3 7% 5% 4 4 3 4 5% 39%	2536
	11th to 20th	Night	15% 17% 4 10% 5% 4 5% 3 5% 7% 24%	2600
	21st to end	Night	18% 17% 5% 10% 6% 4 4 3 5% 6% 24%	2600
December	1st to 10th	Night	13% 19% 10% 17% 5% 5% 4 3 4 4 16%	4411
	11th to 20th	Night	16% 24% 10% 16% 6% 4 3 3 3 3 12%	5199
	21st to end	Night	25% 22% 6% 11% 5% 4 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	72% 6% 10% 10% 2	3618
	11th to 20th	Day	83% 7% 6% 3 1	3620
	21st to end	Day	74% 5% 10% 8% 3	3999
February	1st to 10th	Day	70% 5% 9% 10% 5% 1	1881
	11th to 20th	Day	67% 5% 8% 12% 7%	1958
	21st to end	Day	64% 6% 12% 11% 6% 1	1650
March	1st to 10th	Day	56% 6% 13% 18% 7%	4480
	11th to 20th	Day	45% 7% 16% 23% 8% 1	4857
	21st to end	Day	62% 5% 9% 14% 9%	5645
April	1st to 10th	Day	55% 6% 9% 19% 11%	2400
	11th to 20th	Day	47% 6% 11% 21% 13% 2	2423
	21st to end	Day	47% 7% 13% 18% 14% 2	2600
May	1st to 10th	Day	47% 7% 11% 19% 14% 1	5897
	11th to 20th	Day	41% 8% 15% 22% 13% 1	5865
	21st to end	Day	39% 6% 10% 24% 19% 1	6852
June	1st to 10th	Day	36% 7% 12% 26% 17% 2	2800
	11th to 20th	Day	36% 7% 14% 24% 18% 2	2800
	21st to end	Day	38% 9% 14% 20% 17% 2	2800
July	1st to 10th	Day	38% 6% 13% 25% 16% 2	6291
	11th to 20th	Day	33% 7% 14% 28% 17% 1	6285
	21st to end	Day	33% 8% 15% 24% 18% 1	6697
August	1st to 10th	Day	35% 7% 15% 26% 16% 1	4221
	11th to 20th	Day	35% 7% 13% 29% 15% 1	4213
	21st to end	Day	33% 7% 13% 29% 16% 2	4346
September	1st to 10th	Day	38% 6% 14% 24% 15% 3	2278
	11th to 20th	Day	33% 6% 12% 30% 18% 1	2090
	21st to end	Day	41% 7% 12% 23% 16% 1	2090
October	1st to 10th	Day	30% 4 9% 38% 18% 1	3480
	11th to 20th	Day	41% 5% 11% 24% 18%	3073
	21st to end	Day	49% 4 11% 24% 10% 1	3081
November	1st to 10th	Day	47% 6% 12% 21% 12% 1	1762
	11th to 20th	Day	62% 6% 10% 15% 6% 1	1800
	21st to end	Day	65% 5% 12% 13% 3	1800
December	1st to 10th	Day	70% 7% 13% 8% 2	2770
	11th to 20th	Day	77% 5% 8% 8% 1	3005
	21st to end	Day	78% 5% 7% 9% 2	3982
January	1st to 10th	Night	73% 5% 7% 10% 3 1	6348
	11th to 20th	Night	80% 6% 7% 5% 2	6360
	21st to end	Night	73% 5% 12% 7% 3	6978
February	1st to 10th	Night	66% 6% 10% 12% 6% 1	2515
	11th to 20th	Night	63% 5% 9% 15% 7%	2339
	21st to end	Night	59% 4 14% 15% 6% 2	1980
March	1st to 10th	Night	50% 5% 13% 24% 7% 1	5373
	11th to 20th	Night	39% 7% 13% 29% 12% 2	5102
	21st to end	Night	54% 6% 10% 16% 12% 1	5316
April	1st to 10th	Night	48% 7% 11% 21% 13% 1	2000
	11th to 20th	Night	48% 5% 9% 18% 17% 3	1925
	21st to end	Night	44% 7% 11% 20% 15% 2	1800
May	1st to 10th	Night	50% 6% 11% 18% 12% 3	4060
	11th to 20th	Night	42% 6% 11% 23% 16% 2	4033
	21st to end	Night	41% 7% 9% 22% 19% 2	4039
June	1st to 10th	Night	31% 6% 12% 30% 17% 3	1600
	11th to 20th	Night	34% 9% 13% 24% 18% 2	1600
	21st to end	Night	33% 9% 16% 24% 17% 2	1600
July	1st to 10th	Night	34% 6% 13% 27% 15% 5%	3580
	11th to 20th	Night	31% 6% 14% 26% 22% 1	3572
	21st to end	Night	33% 6% 14% 21% 23% 2	3848
August	1st to 10th	Night	32% 7% 15% 30% 16% 1	2904
	11th to 20th	Night	34% 6% 12% 31% 16% 1	2902
	21st to end	Night	35% 6% 10% 29% 17% 2	3548
September	1st to 10th	Night	31% 7% 13% 28% 19% 3	1949
	11th to 20th	Night	30% 5% 9% 32% 22% 1	2090
	21st to end	Night	41% 6% 10% 25% 16% 1	2090
October	1st to 10th	Night	27% 4 10% 34% 24% 1	3480
	11th to 20th	Night	41% 4 10% 23% 21%	3828
	21st to end	Night	42% 4 9% 28% 16% 1	4467
November	1st to 10th	Night	47% 6% 10% 23% 13% 1	2536
	11th to 20th	Night	59% 6% 12% 15% 7% 1	2600
	21st to end	Night	61% 6% 13% 17% 3	2600
December	1st to 10th	Night	71% 6% 11% 9% 3	4411
	11th to 20th	Night	77% 4 8% 8% 2	5201
	21st to end	Night	76% 5% 9% 8% 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	21% 21% 35% 17% 5% 1	300
	11th to 20th	Day	24% 23% 41% 9% 3	300
	21st to end	Day	24% 22% 35% 16% 2	330
February	1st to 10th	Day	27% 25% 30% 14% 2 1	300
	11th to 20th	Day	27% 23% 36% 13% 1	300
	21st to end	Day	26% 34% 30% 8% 1	249
March	1st to 10th	Day	21% 29% 38% 10% 3	300
	11th to 20th	Day	22% 21% 33% 18% 5%	442
	21st to end	Day	29% 20% 31% 15% 4 1	550
April	1st to 10th	Day	28% 19% 31% 18% 4	500
	11th to 20th	Day	27% 24% 26% 14% 7% 2	492
	21st to end	Day	25% 18% 31% 18% 7% 1	500
May	1st to 10th	Day	22% 20% 30% 19% 7% 2	503
	11th to 20th	Day	20% 13% 31% 23% 10% 4	527
	21st to end	Day	14% 14% 29% 25% 14% 4	744
June	1st to 10th	Day	12% 13% 34% 26% 11% 4	730
	11th to 20th	Day	13% 10% 33% 29% 13% 2	730
	21st to end	Day	11% 13% 33% 28% 11% 3	730
July	1st to 10th	Day	8% 7% 27% 31% 19% 8%	721
	11th to 20th	Day	11% 7% 31% 27% 17% 7%	718
	21st to end	Day	8% 5% 29% 31% 21% 6%	788
August	1st to 10th	Day	9% 6% 21% 28% 24% 13%	526
	11th to 20th	Day	11% 5% 26% 27% 24% 8%	519
	21st to end	Day	11% 6% 24% 29% 23% 7%	583
September	1st to 10th	Day	13% 8% 25% 26% 20% 8%	502
	11th to 20th	Day	8% 7% 21% 26% 30% 8%	490
	21st to end	Day	16% 15% 22% 25% 16% 6%	490
October	1st to 10th	Day	18% 12% 27% 24% 14% 4	490
	11th to 20th	Day	23% 19% 28% 24% 6%	410
	21st to end	Day	29% 21% 34% 13% 3	330
November	1st to 10th	Day	19% 20% 34% 21% 5% 1	300
	11th to 20th	Day	26% 27% 28% 15% 4	300
	21st to end	Day	29% 20% 38% 11% 2	300
December	1st to 10th	Day	24% 34% 22% 14% 4	300
	11th to 20th	Day	22% 28% 35% 13% 2	300
	21st to end	Day	24% 30% 32% 12% 2	330
January	1st to 10th	Night	23% 18% 33% 21% 5%	1000
	11th to 20th	Night	24% 17% 36% 20% 3 1	1000
	21st to end	Night	22% 14% 37% 25% 3	1095
February	1st to 10th	Night	24% 16% 37% 20% 4	800
	11th to 20th	Night	21% 19% 33% 23% 4	783
	21st to end	Night	23% 19% 37% 17% 3	660
March	1st to 10th	Night	21% 16% 34% 23% 6%	800
	11th to 20th	Night	17% 16% 39% 23% 6%	800
	21st to end	Night	24% 14% 31% 25% 6%	819
April	1st to 10th	Night	18% 17% 33% 26% 5% 1	600
	11th to 20th	Night	24% 13% 34% 23% 5% 1	593
	21st to end	Night	21% 12% 36% 25% 6% 1	600
May	1st to 10th	Night	20% 10% 34% 28% 7% 1	600
	11th to 20th	Night	22% 8% 28% 32% 10%	591
	21st to end	Night	15% 5% 32% 31% 15% 1	650
June	1st to 10th	Night	11% 6% 30% 39% 14%	600
	11th to 20th	Night	14% 5% 27% 40% 14% 1	600
	21st to end	Night	10% 5% 25% 40% 19% 2	600
July	1st to 10th	Night	8% 3 21% 37% 26% 4	585
	11th to 20th	Night	9% 3 21% 41% 22% 4	582
	21st to end	Night	8% 3 18% 44% 26% 1	657
August	1st to 10th	Night	9% 3 15% 44% 26% 3	597
	11th to 20th	Night	9% 3 17% 42% 26% 4	594
	21st to end	Night	9% 3 19% 36% 30% 3	660
September	1st to 10th	Night	10% 4 21% 36% 24% 4	598
	11th to 20th	Night	11% 4 19% 36% 27% 4	760
	21st to end	Night	17% 9% 23% 29% 18% 4	760
October	1st to 10th	Night	17% 8% 25% 30% 18% 1	760
	11th to 20th	Night	22% 14% 30% 26% 7% 1	760
	21st to end	Night	28% 14% 31% 20% 6%	836
November	1st to 10th	Night	22% 14% 30% 24% 9%	780
	11th to 20th	Night	24% 19% 33% 19% 5% 1	800
	21st to end	Night	26% 14% 36% 22% 3	800
December	1st to 10th	Night	27% 17% 34% 18% 4	896
	11th to 20th	Night	26% 16% 37% 18% 3	1000
	21st to end	Night	32% 17% 33% 15% 2	1100

Page generated at 2025-09-01 01:51:06. Version ac07

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