Lansing
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lansing clear sky chart from 2005-11-06 to 2025-05-11.

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% 5% 4 5% 7% 33%	113640
	Night	14% 12% 4 9% 5% 5% 4 3 5% 6% 32%	115445
Transparency	Day	49% 6% 12% 20% 12% 1	117230
	Night	51% 5% 11% 20% 12% 1	119985
Seeing	Day	18% 12% 28% 23% 13% 6%	16383
	Night	19% 9% 30% 29% 11% 1	26362

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% 17% 7% 17% 8% 5% 4 4 4 4 19%	3617
	11th to 20th	Day	12% 16% 7% 18% 11% 11% 6% 3 4 4 8%	3620
	21st to end	Day	20% 19% 6% 14% 6% 4 6% 2 3 4 15%	4131
February	1st to 10th	Day	13% 14% 5% 12% 9% 7% 6% 4 5% 5% 20%	1805
	11th to 20th	Day	14% 13% 6% 14% 9% 6% 4 3 3 4 24%	1948
	21st to end	Day	14% 16% 5% 12% 6% 4 5% 3 5% 6% 24%	1650
March	1st to 10th	Day	14% 12% 4 10% 5% 4 4 4 5% 6% 32%	4480
	11th to 20th	Day	11% 11% 4 9% 6% 5% 4 3 5% 7% 34%	4969
	21st to end	Day	18% 15% 4 9% 5% 4 4 3 5% 6% 28%	5498
April	1st to 10th	Day	18% 13% 3 8% 6% 4 4 4 5% 5% 30%	2400
	11th to 20th	Day	16% 9% 3 7% 4 5% 5% 4 5% 6% 36%	2482
	21st to end	Day	16% 9% 3 8% 5% 5% 4 4 5% 7% 35%	2600
May	1st to 10th	Day	17% 9% 2 7% 4 4 4 4 5% 7% 35%	4212
	11th to 20th	Day	15% 8% 2 7% 4 5% 4 4 6% 8% 38%	4081
	21st to end	Day	11% 7% 2 6% 5% 4 4 3 5% 8% 45%	4658
June	1st to 10th	Day	11% 4 2 6% 6% 5% 5% 4 6% 8% 43%	2660
	11th to 20th	Day	11% 5% 2 6% 5% 4 4 5% 6% 9% 43%	2660
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 8% 8% 40%	2660
July	1st to 10th	Day	11% 7% 2 7% 5% 5% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	7% 4 2 4 4 4 5% 4 7% 10% 49%	4440
	21st to end	Day	6% 5% 2 6% 6% 4 6% 5% 7% 9% 44%	4705
August	1st to 10th	Day	12% 5% 2 5% 5% 5% 5% 4 6% 8% 42%	4104
	11th to 20th	Day	11% 6% 2 6% 5% 4 5% 4 6% 8% 43%	4044
	21st to end	Day	7% 6% 3 7% 5% 5% 6% 4 7% 8% 41%	4351
September	1st to 10th	Day	11% 6% 3 7% 5% 5% 4 4 6% 8% 42%	2199
	11th to 20th	Day	11% 5% 2 5% 4 3 4 4 6% 9% 47%	2090
	21st to end	Day	13% 8% 3 8% 4 5% 4 5% 6% 8% 37%	2090
October	1st to 10th	Day	13% 7% 2 7% 5% 4 5% 4 5% 7% 41%	2087
	11th to 20th	Day	18% 10% 4 7% 5% 4 5% 3 6% 7% 31%	1877
	21st to end	Day	20% 12% 3 8% 4 5% 5% 4 5% 6% 27%	1881
November	1st to 10th	Day	11% 13% 3 7% 4 5% 4 3 5% 6% 39%	1762
	11th to 20th	Day	15% 15% 4 10% 6% 5% 4 4 5% 6% 26%	1800
	21st to end	Day	19% 15% 5% 10% 6% 3 4 3 4 5% 26%	1800
December	1st to 10th	Day	10% 17% 10% 14% 6% 6% 5% 3 5% 6% 18%	2849
	11th to 20th	Day	16% 22% 8% 12% 6% 4 4 3 4 4 16%	3008
	21st to end	Day	23% 22% 7% 12% 4 4 4 3 4 4 12%	3982
January	1st to 10th	Night	12% 17% 7% 16% 7% 5% 5% 3 4 5% 19%	6348
	11th to 20th	Night	13% 15% 7% 17% 9% 8% 5% 3 5% 5% 12%	6360
	21st to end	Night	17% 18% 8% 12% 6% 6% 5% 3 4 5% 17%	6837
February	1st to 10th	Night	15% 16% 5% 12% 9% 5% 5% 4 5% 4 22%	2590
	11th to 20th	Night	13% 13% 6% 12% 7% 6% 5% 4 5% 5% 25%	2338
	21st to end	Night	17% 11% 5% 10% 5% 5% 4 4 5% 6% 28%	1980
March	1st to 10th	Night	14% 10% 4 8% 4 4 3 3 5% 7% 37%	5373
	11th to 20th	Night	9% 10% 3 6% 4 4 4 4 5% 8% 43%	4990
	21st to end	Night	17% 11% 4 9% 4 4 4 3 4 6% 34%	5467
April	1st to 10th	Night	16% 11% 3 7% 5% 3 4 4 5% 6% 35%	2008
	11th to 20th	Night	19% 9% 2 7% 4 4 4 3 5% 6% 37%	1866
	21st to end	Night	16% 8% 2 7% 4 5% 4 4 4 7% 38%	1800
May	1st to 10th	Night	14% 9% 3 7% 4 4 5% 4 6% 9% 35%	2903
	11th to 20th	Night	17% 8% 2 6% 4 4 3 3 4 6% 43%	2818
	21st to end	Night	11% 6% 3 6% 3 5% 5% 4 5% 9% 45%	2899
June	1st to 10th	Night	12% 4 2 6% 4 3 4 4 6% 8% 46%	1520
	11th to 20th	Night	11% 5% 2 5% 5% 4 4 3 7% 8% 45%	1520
	21st to end	Night	9% 5% 2 5% 5% 3 4 4 6% 10% 46%	1520
July	1st to 10th	Night	8% 5% 2 5% 5% 4 5% 4 7% 10% 44%	2530
	11th to 20th	Night	9% 4 2 5% 3 4 4 4 5% 7% 55%	2530
	21st to end	Night	5% 5% 3 7% 5% 5% 4 5% 6% 9% 46%	2841
August	1st to 10th	Night	9% 5% 2 6% 4 4 4 3 5% 9% 48%	2825
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 5% 7% 47%	2785
	21st to end	Night	9% 7% 3 7% 5% 4 5% 4 6% 7% 45%	3302
September	1st to 10th	Night	9% 6% 2 5% 4 5% 4 4 6% 7% 49%	1961
	11th to 20th	Night	10% 5% 2 4 4 3 3 3 4 7% 55%	2090
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 7% 42%	2090
October	1st to 10th	Night	15% 7% 2 6% 4 3 3 3 5% 6% 46%	2091
	11th to 20th	Night	18% 12% 2 8% 4 4 4 3 5% 5% 33%	2299
	21st to end	Night	20% 10% 3 8% 5% 4 4 3 5% 6% 31%	2717
November	1st to 10th	Night	14% 10% 3 7% 4 4 4 3 4 6% 41%	2536
	11th to 20th	Night	14% 14% 4 10% 5% 5% 5% 4 5% 7% 27%	2600
	21st to end	Night	18% 15% 5% 9% 4 4 5% 3 5% 6% 27%	2600
December	1st to 10th	Night	12% 18% 8% 15% 6% 5% 4 3 5% 5% 21%	4316
	11th to 20th	Night	15% 21% 6% 15% 8% 4 4 3 4 4 16%	5199
	21st to end	Night	25% 22% 6% 10% 5% 4 3 3 4 5% 13%	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	67% 6% 11% 13% 3	3618
	11th to 20th	Day	78% 5% 9% 5% 3	3620
	21st to end	Day	74% 3 11% 8% 3	4131
February	1st to 10th	Day	63% 6% 10% 13% 6%	1805
	11th to 20th	Day	65% 3 7% 16% 8% 1	1958
	21st to end	Day	61% 5% 11% 15% 7% 1	1650
March	1st to 10th	Day	53% 5% 13% 18% 10% 2	4480
	11th to 20th	Day	47% 5% 15% 22% 10% 1	4969
	21st to end	Day	58% 4 9% 16% 11% 1	5500
April	1st to 10th	Day	56% 5% 10% 18% 11% 1	2400
	11th to 20th	Day	48% 6% 10% 20% 13% 2	2482
	21st to end	Day	48% 5% 12% 19% 14% 2	2600
May	1st to 10th	Day	47% 7% 12% 20% 14% 1	4250
	11th to 20th	Day	42% 8% 14% 24% 10% 1	4085
	21st to end	Day	36% 7% 11% 21% 23% 3	4671
June	1st to 10th	Day	37% 7% 12% 27% 15% 2	2660
	11th to 20th	Day	37% 7% 12% 24% 18% 1	2660
	21st to end	Day	38% 8% 13% 22% 16% 2	2660
July	1st to 10th	Day	42% 7% 12% 20% 15% 3	4371
	11th to 20th	Day	28% 7% 14% 32% 18% 2	4365
	21st to end	Day	34% 8% 15% 20% 22% 2	4556
August	1st to 10th	Day	37% 7% 12% 26% 16% 1	4091
	11th to 20th	Day	37% 6% 11% 31% 13% 1	4083
	21st to end	Day	37% 7% 12% 29% 13% 2	4350
September	1st to 10th	Day	39% 7% 13% 25% 15% 2	2199
	11th to 20th	Day	34% 6% 12% 30% 18% 1	2090
	21st to end	Day	44% 6% 13% 22% 15%	2090
October	1st to 10th	Day	31% 5% 9% 34% 20% 1	3464
	11th to 20th	Day	42% 4 11% 26% 17%	3093
	21st to end	Day	49% 4 12% 24% 10% 1	3081
November	1st to 10th	Day	46% 6% 12% 22% 13% 1	1762
	11th to 20th	Day	58% 5% 12% 17% 7% 1	1800
	21st to end	Day	60% 5% 13% 16% 6% 1	1800
December	1st to 10th	Day	66% 7% 16% 9% 2	2849
	11th to 20th	Day	72% 5% 9% 12% 2	3005
	21st to end	Day	76% 4 7% 9% 4	3982
January	1st to 10th	Night	66% 5% 9% 14% 5% 1	6348
	11th to 20th	Night	72% 5% 9% 8% 6%	6360
	21st to end	Night	69% 4 11% 11% 4	6837
February	1st to 10th	Night	64% 5% 10% 13% 6% 1	2590
	11th to 20th	Night	60% 5% 9% 17% 8% 1	2339
	21st to end	Night	56% 5% 13% 16% 8% 2	1980
March	1st to 10th	Night	47% 4 15% 23% 10% 1	5373
	11th to 20th	Night	38% 5% 15% 26% 15% 1	4990
	21st to end	Night	51% 5% 11% 19% 12% 2	5467
April	1st to 10th	Night	48% 6% 11% 19% 15% 1	2008
	11th to 20th	Night	46% 5% 11% 18% 17% 2	1866
	21st to end	Night	45% 6% 13% 19% 15% 3	1800
May	1st to 10th	Night	45% 6% 13% 20% 14% 2	2930
	11th to 20th	Night	41% 7% 8% 25% 17% 2	2819
	21st to end	Night	36% 7% 11% 22% 20% 4	2907
June	1st to 10th	Night	34% 7% 11% 28% 18% 3	1520
	11th to 20th	Night	36% 6% 14% 24% 18% 2	1520
	21st to end	Night	33% 7% 13% 27% 18% 2	1520
July	1st to 10th	Night	34% 5% 13% 27% 14% 7%	2490
	11th to 20th	Night	28% 5% 12% 31% 22% 1	2482
	21st to end	Night	33% 7% 17% 17% 24% 2	2750
August	1st to 10th	Night	33% 6% 14% 28% 19% 1	2814
	11th to 20th	Night	35% 7% 9% 33% 14% 1	2812
	21st to end	Night	37% 6% 11% 30% 15% 2	3302
September	1st to 10th	Night	33% 7% 11% 28% 19% 2	1961
	11th to 20th	Night	29% 5% 11% 31% 22% 2	2090
	21st to end	Night	40% 6% 12% 26% 15% 1	2090
October	1st to 10th	Night	27% 4 10% 36% 23% 1	3494
	11th to 20th	Night	45% 4 10% 21% 19% 1	3810
	21st to end	Night	41% 4 10% 30% 14% 1	4467
November	1st to 10th	Night	45% 5% 10% 24% 14% 1	2536
	11th to 20th	Night	55% 6% 12% 18% 8% 1	2600
	21st to end	Night	58% 5% 13% 18% 6%	2600
December	1st to 10th	Night	65% 5% 13% 13% 3	4316
	11th to 20th	Night	71% 4 9% 11% 4	5201
	21st to end	Night	75% 3 9% 8% 5%	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% 15% 40% 18% 6% 2	300
	11th to 20th	Day	20% 17% 44% 13% 5% 1	300
	21st to end	Day	28% 18% 32% 18% 5%	330
February	1st to 10th	Day	23% 25% 31% 16% 3 1	300
	11th to 20th	Day	24% 18% 39% 17% 2	300
	21st to end	Day	25% 26% 37% 10% 3	249
March	1st to 10th	Day	21% 21% 41% 13% 4	300
	11th to 20th	Day	23% 15% 33% 21% 8%	489
	21st to end	Day	27% 14% 31% 21% 5% 1	550
April	1st to 10th	Day	24% 14% 32% 22% 6% 1	500
	11th to 20th	Day	26% 17% 29% 16% 7% 5%	492
	21st to end	Day	21% 13% 31% 22% 12% 2	500
May	1st to 10th	Day	25% 14% 27% 23% 10% 2	503
	11th to 20th	Day	18% 10% 26% 25% 15% 6%	487
	21st to end	Day	15% 7% 24% 27% 19% 9%	633
June	1st to 10th	Day	12% 8% 28% 31% 16% 5%	680
	11th to 20th	Day	14% 6% 30% 29% 18% 4	680
	21st to end	Day	12% 9% 26% 30% 17% 6%	680
July	1st to 10th	Day	9% 6% 19% 30% 22% 14%	671
	11th to 20th	Day	10% 6% 24% 29% 21% 10%	668
	21st to end	Day	7% 4 25% 33% 23% 9%	680
August	1st to 10th	Day	9% 3 21% 28% 19% 20%	486
	11th to 20th	Day	14% 4 17% 27% 26% 12%	479
	21st to end	Day	11% 4 21% 26% 26% 13%	539
September	1st to 10th	Day	14% 7% 21% 24% 22% 11%	490
	11th to 20th	Day	11% 4 18% 24% 29% 13%	490
	21st to end	Day	18% 12% 19% 24% 18% 10%	490
October	1st to 10th	Day	18% 10% 27% 23% 15% 7%	490
	11th to 20th	Day	20% 15% 29% 26% 9% 1	467
	21st to end	Day	28% 15% 35% 16% 4 1	330
November	1st to 10th	Day	19% 18% 33% 21% 8% 1	300
	11th to 20th	Day	25% 22% 32% 17% 4	300
	21st to end	Day	26% 16% 39% 14% 5%	300
December	1st to 10th	Day	23% 25% 27% 17% 6% 1	300
	11th to 20th	Day	24% 20% 38% 14% 4	300
	21st to end	Day	25% 22% 35% 13% 3	330
January	1st to 10th	Night	21% 14% 37% 21% 6% 1	1000
	11th to 20th	Night	24% 15% 35% 22% 4 1	1000
	21st to end	Night	19% 12% 37% 27% 5%	1032
February	1st to 10th	Night	24% 13% 35% 25% 3	800
	11th to 20th	Night	22% 14% 36% 25% 4	783
	21st to end	Night	23% 15% 40% 19% 3	660
March	1st to 10th	Night	20% 13% 36% 25% 6% 1	800
	11th to 20th	Night	17% 15% 36% 25% 6% 1	800
	21st to end	Night	23% 10% 32% 28% 7%	880
April	1st to 10th	Night	20% 13% 36% 25% 5%	608
	11th to 20th	Night	24% 10% 34% 23% 8% 1	593
	21st to end	Night	22% 8% 34% 30% 6% 1	600
May	1st to 10th	Night	20% 8% 31% 33% 8% 1	600
	11th to 20th	Night	23% 4 31% 30% 12% 1	563
	21st to end	Night	13% 3 27% 35% 20% 2	617
June	1st to 10th	Night	12% 4 25% 43% 15% 1	570
	11th to 20th	Night	13% 4 26% 40% 16% 1	570
	21st to end	Night	10% 4 23% 41% 20% 1	570
July	1st to 10th	Night	8% 2 17% 41% 28% 3	555
	11th to 20th	Night	11% 1 20% 40% 26% 3	552
	21st to end	Night	6% 3 19% 47% 23% 2	624
August	1st to 10th	Night	8% 1 16% 46% 27% 2	567
	11th to 20th	Night	9% 2 17% 39% 28% 5%	564
	21st to end	Night	12% 2 18% 38% 27% 3	627
September	1st to 10th	Night	11% 3 20% 37% 25% 4	631
	11th to 20th	Night	12% 4 16% 37% 27% 4	760
	21st to end	Night	17% 7% 23% 29% 19% 5%	760
October	1st to 10th	Night	18% 6% 24% 33% 17% 2	760
	11th to 20th	Night	23% 12% 28% 28% 8% 1	760
	21st to end	Night	24% 11% 34% 24% 7%	836
November	1st to 10th	Night	20% 11% 29% 29% 9% 1	780
	11th to 20th	Night	21% 15% 36% 21% 7%	800
	21st to end	Night	25% 11% 34% 26% 4	800
December	1st to 10th	Night	25% 14% 35% 20% 6%	840
	11th to 20th	Night	25% 12% 37% 22% 3	1000
	21st to end	Night	33% 11% 35% 20% 2	1100

Page generated at 2025-05-08 09:34:00. Version ac07

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