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 2026-09-14.

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% 4 9% 5% 5% 5% 4 6% 7% 34%	148773
	Night	14% 11% 4 9% 5% 5% 4 3 5% 6% 33%	142545
Transparency	Day	48% 6% 12% 21% 13% 1	152316
	Night	50% 5% 11% 20% 12% 1	147066
Seeing	Day	18% 12% 28% 23% 13% 5%	18332
	Night	19% 10% 30% 29% 11% 1	28095

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	13% 17% 7% 17% 7% 5% 4 4 4 4 17%	4691
	11th to 20th	Day	11% 16% 8% 19% 12% 11% 5% 3 3 3 9%	4710
	21st to end	Day	16% 17% 5% 13% 9% 6% 7% 3 4 4 16%	5357
February	1st to 10th	Day	13% 14% 5% 12% 9% 7% 6% 4 5% 5% 20%	1895
	11th to 20th	Day	13% 13% 6% 13% 9% 6% 4 3 3 5% 25%	2048
	21st to end	Day	14% 15% 6% 12% 6% 4 5% 3 5% 6% 24%	1730
March	1st to 10th	Day	14% 12% 4 10% 5% 4 4 4 5% 5% 32%	4580
	11th to 20th	Day	11% 11% 4 9% 6% 5% 4 3 5% 7% 34%	5078
	21st to end	Day	18% 15% 4 9% 5% 4 4 3 5% 6% 27%	5619
April	1st to 10th	Day	18% 13% 3 8% 6% 4 4 4 5% 5% 29%	2520
	11th to 20th	Day	16% 10% 3 8% 4 5% 5% 4 5% 5% 36%	2608
	21st to end	Day	16% 9% 3 8% 5% 5% 4 4 5% 7% 34%	2730
May	1st to 10th	Day	16% 9% 3 7% 5% 5% 5% 4 5% 7% 35%	7616
	11th to 20th	Day	13% 8% 3 8% 4 5% 5% 4 6% 8% 35%	7626
	21st to end	Day	15% 6% 2 6% 4 4 4 3 5% 7% 45%	8741
June	1st to 10th	Day	10% 4 2 6% 6% 5% 5% 4 7% 8% 43%	2940
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 5% 6% 9% 41%	2940
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 5% 8% 9% 40%	2940
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 10% 39%	8280
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 4 7% 10% 49%	8280
	21st to end	Day	7% 6% 2 5% 5% 4 5% 5% 7% 9% 45%	8798
August	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	6014
	11th to 20th	Day	11% 7% 3 7% 5% 5% 5% 4 7% 8% 39%	5951
	21st to end	Day	7% 5% 3 7% 6% 6% 6% 5% 7% 9% 40%	6337
September	1st to 10th	Day	11% 6% 2 7% 5% 5% 4 4 6% 9% 41%	2431
	11th to 20th	Day	10% 4 2 5% 4 3 4 4 6% 9% 48%	2233
	21st to end	Day	13% 8% 3 8% 4 5% 4 5% 6% 8% 38%	2200
October	1st to 10th	Day	13% 7% 2 6% 5% 4 5% 4 5% 7% 43%	2197
	11th to 20th	Day	18% 9% 4 7% 5% 4 5% 3 6% 6% 32%	1976
	21st to end	Day	20% 11% 3 8% 5% 5% 5% 4 5% 6% 28%	1980
November	1st to 10th	Day	11% 13% 3 7% 4 5% 4 3 5% 6% 39%	1852
	11th to 20th	Day	14% 15% 4 9% 6% 5% 5% 4 5% 6% 26%	1890
	21st to end	Day	18% 15% 6% 10% 6% 3 4 3 4 5% 26%	1890
December	1st to 10th	Day	10% 17% 10% 15% 7% 6% 5% 3 5% 6% 17%	2937
	11th to 20th	Day	16% 22% 8% 12% 6% 4 4 3 4 4 16%	3088
	21st to end	Day	23% 22% 7% 12% 4 4 4 3 4 4 12%	4070
January	1st to 10th	Night	13% 17% 7% 16% 6% 5% 4 3 4 5% 20%	8232
	11th to 20th	Night	10% 16% 8% 18% 9% 10% 5% 3 4 4 12%	8280
	21st to end	Night	14% 16% 7% 13% 8% 7% 6% 3 4 6% 17%	8843
February	1st to 10th	Night	14% 16% 5% 11% 8% 5% 5% 4 5% 4 22%	2719
	11th to 20th	Night	13% 13% 6% 12% 7% 6% 5% 4 5% 5% 25%	2458
	21st to end	Night	17% 12% 5% 10% 5% 5% 4 4 5% 6% 28%	2076
March	1st to 10th	Night	14% 10% 4 8% 4 4 4 3 5% 7% 37%	5493
	11th to 20th	Night	10% 10% 3 6% 4 4 4 4 5% 8% 42%	5101
	21st to end	Night	17% 11% 4 9% 5% 4 4 3 4 6% 34%	5588
April	1st to 10th	Night	16% 12% 3 7% 5% 3 4 4 5% 6% 35%	2108
	11th to 20th	Night	19% 9% 2 8% 4 4 4 3 5% 6% 36%	1960
	21st to end	Night	16% 8% 2 7% 4 5% 4 4 4 7% 38%	1890
May	1st to 10th	Night	15% 9% 3 8% 4 4 4 3 5% 8% 35%	5237
	11th to 20th	Night	15% 9% 3 6% 4 4 4 3 5% 7% 42%	5234
	21st to end	Night	14% 6% 2 6% 4 4 4 3 4 7% 45%	5425
June	1st to 10th	Night	12% 4 2 6% 4 3 4 4 6% 9% 46%	1680
	11th to 20th	Night	11% 5% 2 5% 5% 4 4 3 7% 8% 44%	1680
	21st to end	Night	9% 5% 2 5% 5% 3 4 4 6% 10% 46%	1680
July	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	4708
	11th to 20th	Night	7% 4 2 5% 3 4 4 4 6% 10% 53%	4707
	21st to end	Night	9% 6% 3 6% 4 4 3 3 5% 8% 47%	5286
August	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 8% 45%	4135
	11th to 20th	Night	13% 7% 3 7% 5% 4 4 4 6% 8% 40%	4095
	21st to end	Night	7% 7% 3 7% 5% 4 5% 4 6% 8% 45%	4785
September	1st to 10th	Night	9% 5% 2 5% 5% 5% 4 4 6% 7% 49%	2167
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 7% 57%	2234
	21st to end	Night	15% 6% 2 6% 4 5% 4 3 5% 7% 43%	2200
October	1st to 10th	Night	14% 7% 2 6% 4 3 3 3 5% 6% 47%	2201
	11th to 20th	Night	18% 11% 2 8% 5% 4 4 3 5% 5% 34%	2420
	21st to end	Night	20% 10% 3 8% 5% 4 4 3 5% 6% 32%	2860
November	1st to 10th	Night	14% 10% 3 7% 4 4 4 3 5% 6% 40%	2666
	11th to 20th	Night	13% 14% 4 10% 5% 5% 5% 4 6% 7% 27%	2730
	21st to end	Night	18% 16% 5% 9% 4 4 4 3 5% 6% 26%	2730
December	1st to 10th	Night	12% 18% 8% 14% 6% 5% 4 3 5% 5% 21%	4448
	11th to 20th	Night	15% 21% 6% 15% 8% 4 4 3 4 4 16%	5339
	21st to end	Night	25% 22% 6% 11% 5% 4 3 3 4 5% 13%	7150

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	68% 6% 11% 12% 2	4692
	11th to 20th	Day	79% 4 7% 5% 4	4710
	21st to end	Day	73% 3 11% 9% 4	5357
February	1st to 10th	Day	64% 6% 10% 14% 6%	1895
	11th to 20th	Day	64% 3 8% 15% 9% 1	2058
	21st to end	Day	61% 5% 11% 15% 6% 1	1730
March	1st to 10th	Day	52% 5% 13% 19% 10% 2	4580
	11th to 20th	Day	48% 5% 15% 22% 9% 1	5078
	21st to end	Day	58% 4 9% 16% 11% 1	5621
April	1st to 10th	Day	56% 5% 10% 18% 11% 1	2520
	11th to 20th	Day	48% 6% 10% 20% 14% 2	2608
	21st to end	Day	48% 5% 12% 19% 13% 2	2730
May	1st to 10th	Day	47% 5% 10% 22% 14% 1	7651
	11th to 20th	Day	45% 7% 12% 21% 13% 1	7630
	21st to end	Day	39% 5% 8% 22% 22% 4	8755
June	1st to 10th	Day	36% 7% 12% 27% 17% 2	2940
	11th to 20th	Day	37% 7% 13% 24% 18% 1	2940
	21st to end	Day	38% 8% 13% 24% 16% 2	2940
July	1st to 10th	Day	38% 7% 13% 25% 16% 2	8211
	11th to 20th	Day	29% 6% 12% 31% 21% 1	8205
	21st to end	Day	33% 6% 13% 24% 22% 1	8604
August	1st to 10th	Day	41% 6% 12% 21% 19% 1	6001
	11th to 20th	Day	40% 7% 14% 29% 9% 1	5990
	21st to end	Day	37% 7% 15% 30% 10% 1	6336
September	1st to 10th	Day	39% 7% 13% 25% 15% 1	2431
	11th to 20th	Day	32% 6% 13% 29% 19% 1	2233
	21st to end	Day	44% 5% 13% 22% 16%	2200
October	1st to 10th	Day	31% 4 9% 34% 21% 1	3574
	11th to 20th	Day	42% 4 11% 26% 17%	3192
	21st to end	Day	48% 4 12% 24% 10% 1	3180
November	1st to 10th	Day	46% 6% 12% 22% 13% 1	1852
	11th to 20th	Day	57% 5% 12% 18% 7% 1	1890
	21st to end	Day	60% 5% 13% 16% 6%	1890
December	1st to 10th	Day	66% 7% 15% 9% 2	2937
	11th to 20th	Day	72% 4 9% 12% 2	3085
	21st to end	Day	76% 4 7% 9% 4	4070
January	1st to 10th	Night	67% 5% 9% 13% 6% 1	8233
	11th to 20th	Night	74% 4 9% 7% 5%	8280
	21st to end	Night	68% 4 10% 13% 4	8843
February	1st to 10th	Night	63% 5% 10% 14% 6% 1	2719
	11th to 20th	Night	60% 4 9% 17% 8% 1	2459
	21st to end	Night	56% 4 13% 17% 8% 1	2076
March	1st to 10th	Night	47% 4 15% 24% 10% 1	5493
	11th to 20th	Night	39% 5% 15% 26% 15% 1	5101
	21st to end	Night	51% 5% 12% 19% 12% 2	5588
April	1st to 10th	Night	49% 6% 10% 19% 15% 1	2108
	11th to 20th	Night	47% 5% 11% 18% 17% 2	1960
	21st to end	Night	44% 6% 13% 20% 14% 3	1890
May	1st to 10th	Night	47% 5% 12% 18% 16% 2	5264
	11th to 20th	Night	42% 5% 9% 25% 15% 2	5235
	21st to end	Night	39% 5% 9% 22% 21% 5%	5435
June	1st to 10th	Night	34% 7% 10% 27% 20% 3	1680
	11th to 20th	Night	37% 6% 14% 24% 17% 2	1680
	21st to end	Night	32% 7% 14% 28% 18% 1	1680
July	1st to 10th	Night	33% 5% 13% 28% 16% 4	4670
	11th to 20th	Night	26% 5% 12% 31% 23% 1	4662
	21st to end	Night	35% 5% 12% 22% 24% 2	5168
August	1st to 10th	Night	38% 5% 11% 24% 21% 1	4124
	11th to 20th	Night	40% 7% 13% 28% 10% 1	4122
	21st to end	Night	36% 6% 14% 31% 12% 1	4785
September	1st to 10th	Night	33% 6% 12% 29% 19% 2	2167
	11th to 20th	Night	28% 5% 12% 32% 22% 2	2234
	21st to end	Night	40% 6% 12% 25% 15% 1	2200
October	1st to 10th	Night	26% 4 10% 36% 23% 1	3604
	11th to 20th	Night	45% 4 10% 21% 19% 1	3931
	21st to end	Night	41% 4 10% 30% 14% 1	4610
November	1st to 10th	Night	45% 5% 10% 24% 15% 1	2666
	11th to 20th	Night	54% 6% 12% 19% 8% 1	2730
	21st to end	Night	59% 5% 12% 18% 6%	2730
December	1st to 10th	Night	65% 5% 13% 13% 3	4448
	11th to 20th	Night	71% 4 9% 11% 4	5341
	21st to end	Night	75% 3 9% 8% 5%	7150

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% 15% 39% 17% 6% 2	330
	11th to 20th	Day	22% 19% 42% 12% 4 1	330
	21st to end	Day	28% 18% 31% 18% 5%	363
February	1st to 10th	Day	22% 25% 32% 16% 4 1	330
	11th to 20th	Day	24% 19% 39% 16% 2	330
	21st to end	Day	25% 27% 37% 9% 3	273
March	1st to 10th	Day	22% 22% 39% 13% 4	330
	11th to 20th	Day	24% 16% 32% 20% 7%	528
	21st to end	Day	27% 16% 31% 20% 5% 1	594
April	1st to 10th	Day	25% 15% 32% 21% 6% 1	540
	11th to 20th	Day	26% 18% 29% 16% 7% 4	532
	21st to end	Day	21% 14% 31% 22% 11% 2	540
May	1st to 10th	Day	24% 15% 28% 22% 9% 2	543
	11th to 20th	Day	19% 12% 28% 23% 13% 5%	567
	21st to end	Day	16% 9% 26% 25% 17% 7%	733
June	1st to 10th	Day	12% 8% 30% 30% 15% 5%	780
	11th to 20th	Day	15% 8% 31% 27% 16% 4	780
	21st to end	Day	11% 9% 27% 32% 15% 5%	780
July	1st to 10th	Day	10% 6% 21% 30% 21% 13%	771
	11th to 20th	Day	10% 6% 26% 29% 20% 9%	768
	21st to end	Day	7% 5% 26% 32% 22% 8%	784
August	1st to 10th	Day	9% 4 21% 29% 19% 18%	566
	11th to 20th	Day	13% 5% 20% 27% 25% 10%	559
	21st to end	Day	11% 5% 22% 25% 25% 12%	627
September	1st to 10th	Day	15% 7% 21% 25% 21% 11%	570
	11th to 20th	Day	10% 4 18% 24% 30% 15%	542
	21st to end	Day	18% 12% 18% 25% 17% 10%	530
October	1st to 10th	Day	17% 9% 27% 24% 16% 7%	530
	11th to 20th	Day	20% 14% 30% 27% 8% 1	506
	21st to end	Day	26% 15% 37% 17% 4 1	363
November	1st to 10th	Day	21% 18% 33% 20% 8% 1	330
	11th to 20th	Day	26% 22% 31% 16% 4	330
	21st to end	Day	27% 18% 37% 13% 5%	330
December	1st to 10th	Day	24% 24% 28% 17% 7% 1	330
	11th to 20th	Day	25% 21% 37% 13% 3	330
	21st to end	Day	26% 23% 35% 12% 3	363
January	1st to 10th	Night	21% 14% 37% 21% 5% 1	1050
	11th to 20th	Night	24% 16% 35% 21% 4	1050
	21st to end	Night	19% 13% 37% 27% 5%	1083
February	1st to 10th	Night	24% 13% 35% 26% 3	840
	11th to 20th	Night	22% 14% 36% 24% 4	823
	21st to end	Night	23% 15% 40% 18% 3	692
March	1st to 10th	Night	20% 13% 36% 24% 6%	840
	11th to 20th	Night	19% 15% 35% 25% 5% 1	840
	21st to end	Night	23% 11% 32% 27% 6%	924
April	1st to 10th	Night	21% 14% 36% 24% 5%	638
	11th to 20th	Night	24% 11% 34% 22% 8% 1	623
	21st to end	Night	22% 8% 34% 30% 6%	630
May	1st to 10th	Night	19% 8% 32% 33% 8% 1	630
	11th to 20th	Night	22% 6% 31% 29% 11% 1	621
	21st to end	Night	13% 4 29% 35% 19% 2	683
June	1st to 10th	Night	12% 4 26% 43% 14% 1	630
	11th to 20th	Night	14% 4 28% 39% 15%	630
	21st to end	Night	10% 4 24% 41% 19% 1	630
July	1st to 10th	Night	9% 2 18% 41% 27% 3	615
	11th to 20th	Night	10% 2 20% 41% 25% 2	612
	21st to end	Night	7% 3 19% 48% 23% 2	690
August	1st to 10th	Night	8% 2 16% 46% 26% 2	627
	11th to 20th	Night	10% 2 18% 40% 26% 4	624
	21st to end	Night	11% 2 19% 39% 26% 3	693
September	1st to 10th	Night	10% 4 21% 37% 24% 4	697
	11th to 20th	Night	11% 4 15% 37% 29% 4	813
	21st to end	Night	17% 7% 22% 30% 20% 5%	800
October	1st to 10th	Night	17% 6% 24% 34% 18% 2	800
	11th to 20th	Night	23% 12% 29% 28% 8% 1	800
	21st to end	Night	24% 11% 34% 25% 6%	880
November	1st to 10th	Night	19% 12% 30% 29% 9% 1	820
	11th to 20th	Night	20% 16% 36% 22% 6%	840
	21st to end	Night	26% 12% 33% 25% 4	840
December	1st to 10th	Night	25% 15% 34% 20% 6%	882
	11th to 20th	Night	24% 13% 37% 22% 3	1050
	21st to end	Night	33% 11% 35% 19% 2	1155

Page generated at 2026-09-11 04:11:55. Version ac07

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