Macomb
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Macomb clear sky chart from 2005-11-06 to 2026-04-17.

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	12% 8% 3 7% 5% 4 4 4 6% 7% 39%	131825
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 41%	130629
Transparency	Day	43% 4 12% 24% 15% 2	135375
	Night	43% 4 11% 24% 16% 2	135156
Seeing	Day	15% 11% 29% 26% 15% 4	17648
	Night	16% 11% 31% 30% 12% 1	27618

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% 10% 5% 13% 6% 5% 5% 4 5% 7% 28%	4691
	11th to 20th	Day	7% 10% 4 9% 8% 6% 7% 5% 6% 6% 32%	4887
	21st to end	Day	12% 15% 7% 10% 5% 4 4 3 5% 5% 31%	5812
February	1st to 10th	Day	14% 13% 5% 9% 5% 4 4 4 6% 6% 31%	1890
	11th to 20th	Day	13% 10% 4 8% 6% 5% 5% 4 5% 6% 35%	1965
	21st to end	Day	13% 13% 5% 9% 5% 3 2 3 5% 5% 37%	1730
March	1st to 10th	Day	18% 12% 3 6% 3 3 2 2 3 4 44%	4662
	11th to 20th	Day	8% 7% 2 6% 5% 4 5% 4 6% 9% 45%	5090
	21st to end	Day	17% 11% 3 9% 5% 4 4 4 5% 7% 30%	5864
April	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 6% 6% 36%	2520
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 4 5% 6% 38%	2446
	21st to end	Day	18% 7% 3 8% 5% 5% 5% 4 5% 6% 34%	2400
May	1st to 10th	Day	15% 8% 2 8% 5% 4 5% 4 6% 8% 34%	5845
	11th to 20th	Day	15% 7% 2 6% 4 3 4 3 5% 8% 43%	6319
	21st to end	Day	13% 8% 2 7% 5% 5% 5% 4 6% 7% 38%	6935
June	1st to 10th	Day	8% 5% 2 7% 5% 5% 4 4 6% 8% 46%	2800
	11th to 20th	Day	8% 5% 2 7% 5% 4 5% 3 6% 8% 47%	2800
	21st to end	Day	8% 6% 2 6% 5% 5% 6% 4 7% 9% 43%	2800
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	6360
	11th to 20th	Day	9% 7% 3 6% 5% 5% 5% 4 7% 9% 39%	6360
	21st to end	Day	11% 6% 3 7% 5% 4 6% 5% 7% 10% 37%	6771
August	1st to 10th	Day	6% 4 2 6% 5% 4 5% 5% 8% 11% 46%	4234
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 5% 6% 10% 41%	3942
	21st to end	Day	6% 5% 2 5% 4 4 4 4 6% 10% 50%	4312
September	1st to 10th	Day	11% 5% 2 5% 3 3 3 4 6% 7% 50%	2400
	11th to 20th	Day	9% 4 1 4 3 4 4 4 6% 8% 54%	2389
	21st to end	Day	8% 5% 2 5% 4 5% 4 4 6% 8% 49%	2165
October	1st to 10th	Day	12% 6% 3 4 4 4 4 3 5% 5% 51%	2000
	11th to 20th	Day	15% 8% 3 6% 4 3 3 2 4 5% 46%	2000
	21st to end	Day	18% 8% 3 7% 4 3 3 3 5% 6% 41%	2145
November	1st to 10th	Day	9% 8% 2 6% 3 3 4 3 5% 7% 49%	1852
	11th to 20th	Day	16% 10% 3 7% 3 4 3 2 5% 6% 41%	1890
	21st to end	Day	16% 12% 3 9% 5% 2 3 3 4 5% 37%	1701
December	1st to 10th	Day	7% 8% 3 8% 4 3 4 3 4 6% 49%	2690
	11th to 20th	Day	14% 12% 5% 12% 4 4 5% 4 6% 6% 29%	3088
	21st to end	Day	23% 22% 7% 11% 4 3 4 3 4 4 16%	4070
January	1st to 10th	Night	12% 12% 7% 11% 4 4 4 2 4 5% 34%	8232
	11th to 20th	Night	9% 11% 5% 11% 7% 6% 6% 4 6% 5% 30%	8100
	21st to end	Night	13% 12% 5% 11% 5% 5% 4 3 4 5% 34%	8402
February	1st to 10th	Night	14% 11% 5% 8% 5% 4 4 3 5% 6% 35%	2730
	11th to 20th	Night	14% 10% 3 7% 5% 3 4 3 5% 7% 38%	2540
	21st to end	Night	14% 10% 4 8% 4 3 2 3 4 5% 43%	2076
March	1st to 10th	Night	18% 11% 3 6% 4 3 3 2 3 5% 40%	5454
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 5% 6% 50%	5090
	21st to end	Night	16% 12% 4 8% 5% 5% 5% 3 5% 6% 31%	5293
April	1st to 10th	Night	14% 10% 3 6% 5% 4 4 3 6% 5% 41%	2100
	11th to 20th	Night	14% 8% 3 6% 4 4 4 3 5% 7% 42%	2035
	21st to end	Night	18% 6% 3 7% 5% 4 4 3 6% 6% 39%	2000
May	1st to 10th	Night	18% 8% 3 7% 4 4 4 4 5% 7% 36%	4053
	11th to 20th	Night	13% 5% 2 5% 4 4 4 4 6% 10% 43%	3596
	21st to end	Night	12% 7% 3 6% 4 4 5% 4 5% 7% 43%	3942
June	1st to 10th	Night	8% 4 2 5% 4 3 4 3 6% 9% 52%	1600
	11th to 20th	Night	9% 4 2 5% 4 4 3 3 5% 9% 51%	1600
	21st to end	Night	7% 6% 2 6% 5% 3 4 4 6% 8% 49%	1600
July	1st to 10th	Night	10% 5% 2 6% 5% 4 4 4 6% 11% 44%	3618
	11th to 20th	Night	5% 4 2 6% 5% 4 6% 5% 7% 8% 48%	3617
	21st to end	Night	10% 7% 2 6% 4 4 5% 4 6% 9% 43%	4096
August	1st to 10th	Night	4 3 1 4 3 4 4 4 6% 10% 56%	2926
	11th to 20th	Night	7% 5% 2 5% 4 4 4 3 6% 7% 53%	3109
	21st to end	Night	5% 3 2 5% 4 5% 4 3 6% 9% 55%	3586
September	1st to 10th	Night	10% 5% 1 5% 3 3 3 2 4 6% 58%	2000
	11th to 20th	Night	8% 4 2 6% 4 4 3 3 5% 8% 53%	2000
	21st to end	Night	8% 5% 2 5% 5% 4 4 3 6% 7% 50%	2221
October	1st to 10th	Night	9% 5% 2 5% 3 3 4 3 5% 6% 55%	2400
	11th to 20th	Night	13% 5% 2 6% 4 3 4 3 4 6% 52%	2400
	21st to end	Night	17% 7% 3 5% 4 4 4 3 5% 6% 42%	2694
November	1st to 10th	Night	12% 7% 2 5% 4 3 3 3 5% 6% 52%	2666
	11th to 20th	Night	14% 8% 3 7% 3 3 3 3 5% 7% 43%	2730
	21st to end	Night	16% 11% 4 6% 4 4 3 3 5% 6% 39%	2914
December	1st to 10th	Night	10% 10% 3 7% 4 4 4 3 5% 6% 46%	4720
	11th to 20th	Night	15% 11% 3 11% 5% 4 4 2 5% 6% 34%	5339
	21st to end	Night	24% 18% 7% 10% 5% 4 4 3 4 4 18%	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	56% 4 13% 19% 8% 1	4692
	11th to 20th	Day	51% 4 10% 19% 13% 3	4887
	21st to end	Day	58% 2 9% 23% 7% 1	5812
February	1st to 10th	Day	55% 3 14% 19% 7% 2	1890
	11th to 20th	Day	51% 4 11% 21% 11% 2	1974
	21st to end	Day	49% 3 10% 24% 11% 2	1730
March	1st to 10th	Day	47% 2 7% 23% 18% 2	4662
	11th to 20th	Day	35% 3 10% 32% 18% 1	5090
	21st to end	Day	54% 3 14% 23% 5% 1	5866
April	1st to 10th	Day	48% 4 12% 23% 12%	2520
	11th to 20th	Day	46% 4 10% 25% 13% 2	2446
	21st to end	Day	50% 4 10% 22% 13% 2	2400
May	1st to 10th	Day	47% 4 13% 21% 15% 1	5880
	11th to 20th	Day	42% 4 11% 28% 12% 4	6323
	21st to end	Day	45% 5% 10% 22% 18% 1	6949
June	1st to 10th	Day	35% 5% 13% 30% 15% 2	2800
	11th to 20th	Day	35% 6% 10% 26% 21% 2	2800
	21st to end	Day	34% 6% 16% 24% 17% 2	2800
July	1st to 10th	Day	36% 6% 13% 29% 15% 1	6291
	11th to 20th	Day	39% 7% 15% 23% 15% 1	6285
	21st to end	Day	39% 8% 19% 23% 11%	6578
August	1st to 10th	Day	31% 6% 17% 34% 11% 1	4220
	11th to 20th	Day	37% 6% 13% 30% 13% 1	3980
	21st to end	Day	30% 6% 15% 31% 15% 4	4311
September	1st to 10th	Day	33% 4 10% 28% 20% 5%	2400
	11th to 20th	Day	29% 4 11% 30% 22% 4	2389
	21st to end	Day	33% 4 10% 29% 21% 2	2165
October	1st to 10th	Day	24% 2 6% 18% 46% 3	3260
	11th to 20th	Day	28% 2 7% 23% 34% 6%	3240
	21st to end	Day	42% 3 8% 26% 20% 2	3447
November	1st to 10th	Day	36% 3 14% 26% 18% 3	1852
	11th to 20th	Day	46% 2 10% 25% 14% 3	1890
	21st to end	Day	50% 4 13% 22% 11%	1701
December	1st to 10th	Day	39% 3 16% 31% 11% 1	2690
	11th to 20th	Day	56% 4 9% 21% 8% 2	3085
	21st to end	Day	74% 3 9% 10% 4	4070
January	1st to 10th	Night	54% 3 15% 22% 7%	8233
	11th to 20th	Night	55% 4 9% 17% 14% 2	8100
	21st to end	Night	54% 2 11% 21% 11% 1	8402
February	1st to 10th	Night	52% 4 11% 21% 11% 1	2730
	11th to 20th	Night	47% 3 11% 26% 12% 2	2541
	21st to end	Night	45% 3 9% 25% 16% 3	2076
March	1st to 10th	Night	49% 2 6% 24% 17% 2	5454
	11th to 20th	Night	37% 3 8% 29% 18% 5%	5090
	21st to end	Night	54% 4 13% 21% 7% 2	5293
April	1st to 10th	Night	44% 4 10% 25% 14% 3	2100
	11th to 20th	Night	42% 5% 9% 24% 16% 4	2035
	21st to end	Night	47% 4 10% 22% 14% 3	2000
May	1st to 10th	Night	48% 4 11% 23% 12% 2	4083
	11th to 20th	Night	38% 4 15% 26% 13% 4	3597
	21st to end	Night	40% 5% 12% 22% 19% 2	3950
June	1st to 10th	Night	29% 4 16% 28% 19% 4	1600
	11th to 20th	Night	31% 4 11% 27% 23% 4	1600
	21st to end	Night	33% 8% 14% 22% 20% 3	1600
July	1st to 10th	Night	35% 6% 13% 29% 15% 2	3580
	11th to 20th	Night	31% 7% 12% 30% 18% 1	3572
	21st to end	Night	36% 7% 17% 23% 15% 2	3978
August	1st to 10th	Night	23% 6% 19% 33% 17% 2	2916
	11th to 20th	Night	30% 5% 14% 33% 16% 1	3137
	21st to end	Night	26% 6% 15% 31% 17% 4	3586
September	1st to 10th	Night	29% 3 10% 27% 25% 6%	2000
	11th to 20th	Night	30% 3 10% 27% 24% 6%	2000
	21st to end	Night	31% 5% 9% 26% 26% 4	2221
October	1st to 10th	Night	22% 3 6% 23% 42% 4	3920
	11th to 20th	Night	25% 2 9% 22% 36% 5%	3899
	21st to end	Night	39% 3 9% 21% 23% 4	4342
November	1st to 10th	Night	34% 4 11% 26% 20% 4	2666
	11th to 20th	Night	42% 3 11% 24% 18% 2	2730
	21st to end	Night	47% 3 10% 25% 13% 1	2914
December	1st to 10th	Night	40% 3 12% 33% 12% 1	4720
	11th to 20th	Night	53% 3 11% 22% 10% 1	5341
	21st to end	Night	71% 2 10% 12% 4	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	20% 19% 32% 22% 8%	330
	11th to 20th	Day	20% 23% 40% 14% 2	330
	21st to end	Day	18% 24% 37% 15% 6%	363
February	1st to 10th	Day	22% 17% 41% 15% 5%	330
	11th to 20th	Day	23% 23% 32% 17% 5% 1	330
	21st to end	Day	21% 21% 41% 15% 2	273
March	1st to 10th	Day	20% 25% 38% 15% 2	330
	11th to 20th	Day	25% 20% 33% 17% 5%	330
	21st to end	Day	29% 17% 35% 15% 3 1	489
April	1st to 10th	Day	24% 20% 30% 20% 6% 1	540
	11th to 20th	Day	20% 17% 34% 20% 8% 1	516
	21st to end	Day	21% 14% 35% 22% 7% 1	500
May	1st to 10th	Day	21% 12% 33% 25% 7% 2	574
	11th to 20th	Day	18% 13% 28% 25% 13% 2	725
	21st to end	Day	16% 7% 31% 26% 14% 6%	789
June	1st to 10th	Day	8% 6% 25% 33% 22% 6%	730
	11th to 20th	Day	8% 5% 26% 35% 21% 4	730
	21st to end	Day	8% 9% 31% 30% 17% 4	730
July	1st to 10th	Day	11% 4 16% 31% 26% 12%	721
	11th to 20th	Day	9% 3 23% 35% 23% 8%	718
	21st to end	Day	9% 3 20% 34% 28% 5%	794
August	1st to 10th	Day	7% 3 19% 39% 24% 8%	726
	11th to 20th	Day	10% 4 18% 29% 28% 11%	576
	21st to end	Day	6% 2 17% 32% 32% 10%	583
September	1st to 10th	Day	11% 5% 19% 30% 27% 7%	530
	11th to 20th	Day	7% 2 16% 34% 30% 10%	530
	21st to end	Day	9% 11% 23% 26% 21% 9%	495
October	1st to 10th	Day	13% 8% 31% 26% 16% 5%	330
	11th to 20th	Day	15% 21% 34% 22% 9%	330
	21st to end	Day	27% 15% 37% 18% 4	363
November	1st to 10th	Day	14% 13% 40% 20% 11% 3	330
	11th to 20th	Day	19% 19% 33% 21% 6% 2	330
	21st to end	Day	25% 15% 32% 22% 5%	330
December	1st to 10th	Day	13% 18% 42% 19% 6% 2	330
	11th to 20th	Day	21% 16% 38% 21% 4	330
	21st to end	Day	27% 21% 35% 15% 2	363
January	1st to 10th	Night	16% 16% 41% 20% 6%	1050
	11th to 20th	Night	18% 18% 39% 20% 5%	1050
	21st to end	Night	19% 17% 36% 26% 3	1155
February	1st to 10th	Night	20% 14% 39% 23% 4	1050
	11th to 20th	Night	21% 15% 35% 26% 3	905
	21st to end	Night	21% 16% 40% 21% 2	692
March	1st to 10th	Night	21% 15% 39% 21% 4	827
	11th to 20th	Night	20% 14% 34% 26% 6%	630
	21st to end	Night	23% 15% 35% 22% 4	693
April	1st to 10th	Night	19% 17% 36% 25% 4	630
	11th to 20th	Night	18% 14% 32% 28% 7%	611
	21st to end	Night	22% 11% 33% 28% 7%	600
May	1st to 10th	Night	16% 7% 38% 31% 8% 1	600
	11th to 20th	Night	17% 6% 30% 34% 12% 1	591
	21st to end	Night	12% 6% 28% 33% 19% 2	650
June	1st to 10th	Night	9% 3 23% 44% 21% 1	600
	11th to 20th	Night	10% 4 23% 45% 18% 1	600
	21st to end	Night	7% 4 31% 40% 18% 1	600
July	1st to 10th	Night	9% 3 13% 40% 32% 3	585
	11th to 20th	Night	5% 2 16% 48% 26% 2	582
	21st to end	Night	8% 1 14% 44% 31% 2	657
August	1st to 10th	Night	7% 2 12% 48% 28% 3	597
	11th to 20th	Night	8% 3 13% 40% 32% 4	594
	21st to end	Night	7% 1 13% 39% 38% 2	660
September	1st to 10th	Night	12% 4 16% 38% 27% 3	600
	11th to 20th	Night	9% 3 18% 37% 30% 4	600
	21st to end	Night	9% 7% 22% 35% 23% 4	790
October	1st to 10th	Night	10% 6% 27% 33% 21% 2	800
	11th to 20th	Night	16% 11% 32% 30% 11%	800
	21st to end	Night	20% 14% 33% 26% 6%	880
November	1st to 10th	Night	15% 11% 38% 27% 8% 1	820
	11th to 20th	Night	18% 15% 37% 24% 6%	840
	21st to end	Night	22% 13% 35% 24% 5%	1024
December	1st to 10th	Night	19% 13% 39% 24% 4 1	1050
	11th to 20th	Night	23% 13% 34% 25% 6%	1050
	21st to end	Night	26% 16% 34% 21% 2	1155

Page generated at 2026-04-14 01:44:24. Version ac07

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