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 2024-01-16.

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% 8% 3 6% 5% 3 4 5% 5% 7% 39%	74779
	Night	13% 8% 4 6% 5% 3 4 4 5% 7% 42%	75052
Transparency	Day	44% 4 12% 24% 13% 2	74483
	Night	43% 4 11% 24% 15% 3	74868
Seeing	Day	15% 10% 28% 26% 16% 5%	14590
	Night	16% 10% 31% 30% 12% 1	24563

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% 11% 5% 10% 7% 3 5% 6% 4 7% 29%	1517
	11th to 20th	Day	14% 15% 6% 10% 7% 4 5% 4 4 5% 24%	1536
	21st to end	Day	13% 16% 7% 10% 7% 2 4 4 4 5% 28%	1782
February	1st to 10th	Day	15% 13% 6% 9% 6% 3 5% 4 5% 5% 29%	1620
	11th to 20th	Day	14% 9% 4 6% 7% 4 5% 5% 5% 6% 34%	1677
	21st to end	Day	15% 12% 6% 8% 6% 3 2 4 5% 5% 33%	1480
March	1st to 10th	Day	15% 12% 5% 6% 5% 3 5% 4 4 5% 35%	1825
	11th to 20th	Day	14% 10% 3 7% 6% 3 5% 5% 5% 7% 35%	1980
	21st to end	Day	20% 12% 4 7% 8% 3 4 4 5% 7% 26%	2286
April	1st to 10th	Day	16% 8% 4 6% 6% 4 4 4 5% 7% 37%	2160
	11th to 20th	Day	15% 9% 3 6% 5% 3 4 5% 5% 7% 39%	2134
	21st to end	Day	19% 7% 3 7% 6% 4 4 5% 5% 6% 34%	2160
May	1st to 10th	Day	18% 8% 3 7% 6% 3 5% 5% 6% 7% 32%	2320
	11th to 20th	Day	18% 8% 3 5% 6% 4 4 5% 5% 7% 37%	2479
	21st to end	Day	14% 7% 3 7% 6% 4 6% 4 7% 8% 35%	2725
June	1st to 10th	Day	8% 5% 2 6% 6% 4 5% 5% 6% 9% 46%	2520
	11th to 20th	Day	8% 5% 2 6% 6% 3 5% 4 6% 8% 47%	2520
	21st to end	Day	8% 5% 2 5% 5% 4 6% 6% 7% 9% 42%	2520
July	1st to 10th	Day	8% 4 2 5% 6% 3 5% 5% 7% 11% 46%	2520
	11th to 20th	Day	7% 4 2 4 5% 4 6% 5% 7% 10% 45%	2520
	21st to end	Day	7% 5% 2 4 5% 4 6% 6% 7% 9% 45%	2685
August	1st to 10th	Day	8% 5% 2 5% 6% 4 5% 6% 8% 10% 41%	2328
	11th to 20th	Day	9% 5% 2 6% 5% 3 5% 6% 5% 9% 45%	2176
	21st to end	Day	8% 4 2 4 5% 3 4 4 6% 8% 51%	2376
September	1st to 10th	Day	13% 5% 2 5% 4 2 4 4 6% 8% 48%	2160
	11th to 20th	Day	10% 4 1 4 3 2 5% 4 5% 8% 54%	2151
	21st to end	Day	6% 5% 2 5% 5% 4 5% 6% 6% 9% 49%	1949
October	1st to 10th	Day	12% 6% 3 4 4 3 4 4 5% 5% 50%	1800
	11th to 20th	Day	17% 8% 3 6% 4 2 4 3 4 6% 44%	1800
	21st to end	Day	19% 8% 3 6% 5% 2 2 4 5% 6% 40%	1931
November	1st to 10th	Day	10% 7% 2 5% 4 2 4 4 5% 7% 49%	1672
	11th to 20th	Day	17% 8% 4 6% 4 3 3 3 5% 6% 41%	1710
	21st to end	Day	16% 11% 4 7% 6% 2 3 4 3 5% 38%	1539
December	1st to 10th	Day	13% 12% 5% 8% 5% 2 5% 4 5% 6% 36%	1520
	11th to 20th	Day	14% 12% 4 7% 5% 2 4 5% 6% 6% 35%	1918
	21st to end	Day	23% 18% 7% 11% 5% 3 3 4 4 5% 18%	2783
January	1st to 10th	Night	11% 10% 6% 7% 6% 4 5% 3 4 6% 38%	2648
	11th to 20th	Night	13% 13% 6% 8% 7% 3 5% 4 5% 6% 30%	2549
	21st to end	Night	13% 10% 5% 9% 7% 3 5% 4 5% 7% 31%	2574
February	1st to 10th	Night	16% 11% 6% 8% 6% 3 5% 4 4 6% 32%	2340
	11th to 20th	Night	14% 9% 4 6% 5% 3 4 4 5% 7% 37%	2168
	21st to end	Night	15% 10% 4 7% 5% 2 3 4 3 6% 40%	1776
March	1st to 10th	Night	13% 11% 3 6% 5% 3 4 4 4 6% 41%	2150
	11th to 20th	Night	16% 10% 3 5% 4 2 4 5% 5% 6% 39%	1980
	21st to end	Night	21% 11% 4 6% 5% 4 5% 4 5% 5% 29%	2070
April	1st to 10th	Night	13% 9% 3 5% 6% 2 5% 4 6% 6% 41%	1800
	11th to 20th	Night	15% 8% 3 5% 4 3 4 4 5% 7% 42%	1775
	21st to end	Night	19% 6% 3 6% 6% 3 4 4 5% 6% 39%	1800
May	1st to 10th	Night	14% 8% 3 6% 5% 4 5% 5% 6% 7% 38%	1635
	11th to 20th	Night	16% 5% 3 6% 5% 2 4 4 4 8% 42%	1416
	21st to end	Night	12% 5% 3 6% 6% 3 5% 6% 5% 8% 40%	1551
June	1st to 10th	Night	7% 4 3 5% 5% 3 4 4 5% 9% 53%	1440
	11th to 20th	Night	9% 4 2 4 5% 3 4 4 5% 9% 50%	1440
	21st to end	Night	6% 5% 3 5% 6% 3 4 5% 7% 8% 48%	1440
July	1st to 10th	Night	8% 4 3 4 5% 3 5% 4 6% 10% 50%	1440
	11th to 20th	Night	5% 3 1 4 5% 2 5% 6% 6% 9% 55%	1440
	21st to end	Night	5% 4 2 4 5% 2 5% 5% 5% 9% 53%	1629
August	1st to 10th	Night	5% 3 1 4 4 3 5% 5% 6% 11% 52%	1611
	11th to 20th	Night	7% 5% 2 5% 5% 4 4 4 5% 6% 54%	1724
	21st to end	Night	7% 3 1 3 4 2 4 4 5% 8% 59%	1980
September	1st to 10th	Night	11% 5% 2 5% 4 2 3 3 5% 6% 56%	1800
	11th to 20th	Night	9% 4 2 5% 5% 3 3 4 5% 8% 54%	1800
	21st to end	Night	7% 4 2 4 6% 3 5% 5% 6% 8% 51%	1997
October	1st to 10th	Night	10% 4 2 4 4 3 4 4 5% 6% 53%	2160
	11th to 20th	Night	14% 5% 2 5% 4 2 4 4 4 6% 51%	2160
	21st to end	Night	18% 7% 3 5% 4 2 4 4 5% 6% 42%	2424
November	1st to 10th	Night	11% 6% 3 4 4 2 4 3 5% 6% 53%	2406
	11th to 20th	Night	14% 7% 3 6% 4 2 4 4 5% 7% 44%	2470
	21st to end	Night	17% 10% 3 5% 5% 3 3 4 5% 6% 41%	2636
December	1st to 10th	Night	14% 11% 4 6% 5% 3 4 4 5% 7% 36%	2660
	11th to 20th	Night	15% 10% 4 8% 5% 3 3 3 4 6% 38%	3279
	21st to end	Night	22% 17% 9% 10% 7% 3 4 3 3 3 19%	4884

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	55% 4 11% 18% 12% 1	1518
	11th to 20th	Day	63% 3 10% 18% 6%	1536
	21st to end	Day	60% 3 13% 16% 8% 1	1782
February	1st to 10th	Day	58% 3 13% 18% 6% 2	1620
	11th to 20th	Day	51% 5% 12% 21% 11% 1	1686
	21st to end	Day	53% 4 10% 21% 10% 2	1480
March	1st to 10th	Day	52% 4 11% 23% 9% 1	1825
	11th to 20th	Day	49% 4 14% 23% 9% 1	1980
	21st to end	Day	58% 4 10% 20% 7% 1	2286
April	1st to 10th	Day	46% 4 12% 25% 12%	2160
	11th to 20th	Day	45% 4 10% 26% 13% 2	2134
	21st to end	Day	50% 4 10% 21% 13% 2	2160
May	1st to 10th	Day	50% 5% 13% 21% 11% 1	2320
	11th to 20th	Day	47% 5% 13% 23% 12% 1	2483
	21st to end	Day	46% 6% 12% 19% 15% 1	2725
June	1st to 10th	Day	35% 5% 13% 30% 15% 2	2520
	11th to 20th	Day	35% 6% 10% 24% 22% 2	2520
	21st to end	Day	35% 7% 16% 23% 17% 3	2520
July	1st to 10th	Day	33% 6% 14% 30% 14% 4	2451
	11th to 20th	Day	32% 7% 16% 27% 15% 3	2445
	21st to end	Day	33% 6% 15% 30% 15% 1	2536
August	1st to 10th	Day	36% 6% 16% 30% 11% 2	2314
	11th to 20th	Day	35% 6% 13% 30% 14% 2	2176
	21st to end	Day	31% 6% 11% 28% 20% 5%	2376
September	1st to 10th	Day	35% 5% 10% 27% 18% 5%	2160
	11th to 20th	Day	29% 4 10% 30% 22% 4	2151
	21st to end	Day	32% 5% 10% 30% 21% 2	1949
October	1st to 10th	Day	36% 3 10% 26% 21% 3	1800
	11th to 20th	Day	44% 3 7% 25% 19% 2	1800
	21st to end	Day	46% 2 11% 24% 14% 3	1931
November	1st to 10th	Day	35% 3 15% 26% 18% 3	1672
	11th to 20th	Day	46% 2 10% 26% 14% 2	1710
	21st to end	Day	50% 4 12% 22% 11%	1539
December	1st to 10th	Day	51% 4 14% 21% 10% 1	1520
	11th to 20th	Day	49% 3 9% 27% 9% 2	1915
	21st to end	Day	70% 3 8% 13% 6%	2783
January	1st to 10th	Night	50% 3 11% 22% 15% 1	2648
	11th to 20th	Night	56% 3 13% 20% 8% 1	2549
	21st to end	Night	54% 3 13% 19% 9% 1	2574
February	1st to 10th	Night	55% 4 11% 18% 11% 2	2340
	11th to 20th	Night	47% 3 11% 25% 11% 2	2169
	21st to end	Night	47% 3 9% 25% 13% 3	1776
March	1st to 10th	Night	47% 3 9% 26% 14% 1	2150
	11th to 20th	Night	47% 4 12% 22% 13% 3	1980
	21st to end	Night	57% 5% 11% 20% 7% 1	2070
April	1st to 10th	Night	43% 4 11% 25% 14% 3	1800
	11th to 20th	Night	42% 5% 8% 24% 16% 4	1775
	21st to end	Night	48% 3 10% 21% 14% 4	1800
May	1st to 10th	Night	45% 5% 14% 21% 14% 1	1635
	11th to 20th	Night	41% 6% 12% 22% 18% 1	1417
	21st to end	Night	41% 5% 14% 18% 19% 3	1552
June	1st to 10th	Night	29% 4 16% 28% 20% 4	1440
	11th to 20th	Night	32% 4 11% 26% 22% 5%	1440
	21st to end	Night	33% 8% 15% 21% 21% 3	1440
July	1st to 10th	Night	31% 6% 13% 32% 14% 4	1400
	11th to 20th	Night	24% 6% 13% 34% 20% 3	1392
	21st to end	Night	28% 5% 14% 29% 22% 3	1538
August	1st to 10th	Night	27% 5% 17% 35% 14% 2	1601
	11th to 20th	Night	31% 4 11% 32% 20% 2	1724
	21st to end	Night	24% 6% 13% 28% 22% 8%	1980
September	1st to 10th	Night	31% 3 10% 26% 23% 7%	1800
	11th to 20th	Night	31% 3 10% 27% 23% 6%	1800
	21st to end	Night	30% 5% 9% 27% 25% 3	1997
October	1st to 10th	Night	32% 4 11% 24% 25% 5%	2160
	11th to 20th	Night	36% 3 9% 27% 21% 4	2160
	21st to end	Night	44% 3 11% 21% 19% 2	2424
November	1st to 10th	Night	33% 4 11% 26% 21% 5%	2406
	11th to 20th	Night	41% 3 11% 24% 18% 2	2470
	21st to end	Night	46% 3 10% 26% 14% 1	2636
December	1st to 10th	Night	49% 3 12% 24% 10% 1	2660
	11th to 20th	Night	49% 3 11% 26% 10% 1	3281
	21st to end	Night	72% 2 8% 13% 5% 1	4884

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% 19% 30% 21% 9%	270
	11th to 20th	Day	23% 22% 38% 14% 3	257
	21st to end	Day	17% 24% 37% 16% 6%	264
February	1st to 10th	Day	24% 19% 40% 14% 3	240
	11th to 20th	Day	22% 23% 31% 18% 6% 1	240
	21st to end	Day	22% 21% 39% 16% 2	198
March	1st to 10th	Day	19% 25% 38% 16% 3	240
	11th to 20th	Day	28% 15% 35% 16% 7%	240
	21st to end	Day	33% 15% 32% 16% 4 1	372
April	1st to 10th	Day	20% 17% 32% 23% 7% 1	420
	11th to 20th	Day	18% 14% 36% 21% 10% 2	412
	21st to end	Day	20% 14% 34% 23% 8% 1	420
May	1st to 10th	Day	22% 12% 33% 24% 7% 2	486
	11th to 20th	Day	20% 13% 28% 25% 12% 2	625
	21st to end	Day	16% 6% 30% 26% 15% 7%	679
June	1st to 10th	Day	8% 4 23% 34% 24% 6%	630
	11th to 20th	Day	8% 5% 25% 36% 22% 4	630
	21st to end	Day	9% 10% 29% 30% 18% 4	630
July	1st to 10th	Day	10% 4 14% 30% 29% 14%	621
	11th to 20th	Day	8% 2 23% 36% 23% 7%	618
	21st to end	Day	9% 2 21% 34% 29% 5%	684
August	1st to 10th	Day	7% 3 18% 38% 24% 9%	626
	11th to 20th	Day	10% 3 18% 28% 29% 12%	490
	21st to end	Day	6% 2 18% 31% 32% 11%	495
September	1st to 10th	Day	13% 5% 19% 29% 27% 7%	450
	11th to 20th	Day	8% 3 18% 35% 28% 9%	450
	21st to end	Day	7% 11% 25% 27% 23% 8%	419
October	1st to 10th	Day	14% 9% 33% 26% 14% 4	270
	11th to 20th	Day	16% 22% 35% 19% 7%	270
	21st to end	Day	30% 12% 36% 17% 4	297
November	1st to 10th	Day	12% 11% 42% 20% 12% 3	270
	11th to 20th	Day	20% 19% 30% 23% 7% 2	270
	21st to end	Day	23% 14% 36% 22% 5%	270
December	1st to 10th	Day	12% 17% 42% 20% 7% 3	270
	11th to 20th	Day	20% 14% 39% 22% 5%	270
	21st to end	Day	25% 22% 37% 15% 2	297
January	1st to 10th	Night	16% 16% 41% 20% 7%	950
	11th to 20th	Night	18% 16% 39% 22% 5%	930
	21st to end	Night	18% 16% 36% 27% 3	990
February	1st to 10th	Night	22% 13% 39% 22% 4	900
	11th to 20th	Night	21% 14% 36% 26% 3	773
	21st to end	Night	22% 15% 39% 20% 3	592
March	1st to 10th	Night	19% 15% 40% 21% 5%	710
	11th to 20th	Night	20% 12% 34% 27% 7%	540
	21st to end	Night	24% 12% 35% 23% 5% 1	594
April	1st to 10th	Night	17% 15% 37% 26% 4	540
	11th to 20th	Night	18% 12% 32% 29% 8% 1	533
	21st to end	Night	22% 9% 33% 27% 8%	540
May	1st to 10th	Night	17% 6% 37% 31% 8% 1	540
	11th to 20th	Night	18% 5% 30% 34% 12% 1	531
	21st to end	Night	13% 5% 27% 33% 20% 2	584
June	1st to 10th	Night	9% 3 21% 45% 21% 1	540
	11th to 20th	Night	10% 4 23% 44% 19% 1	540
	21st to end	Night	7% 4 30% 39% 19% 1	540
July	1st to 10th	Night	9% 3 13% 40% 32% 3	525
	11th to 20th	Night	5% 2 17% 49% 25% 2	522
	21st to end	Night	7% 1 14% 46% 31% 2	591
August	1st to 10th	Night	7% 2 11% 49% 28% 3	537
	11th to 20th	Night	7% 3 13% 40% 33% 4	534
	21st to end	Night	8% 1 14% 37% 40% 2	594
September	1st to 10th	Night	14% 4 15% 39% 25% 4	540
	11th to 20th	Night	10% 3 18% 36% 28% 5%	540
	21st to end	Night	8% 7% 23% 36% 22% 4	710
October	1st to 10th	Night	11% 6% 28% 32% 21% 2	720
	11th to 20th	Night	16% 11% 33% 29% 11%	720
	21st to end	Night	21% 14% 32% 26% 7%	792
November	1st to 10th	Night	14% 10% 39% 27% 9% 1	740
	11th to 20th	Night	17% 14% 37% 25% 6% 1	760
	21st to end	Night	21% 12% 36% 25% 6%	926
December	1st to 10th	Night	19% 13% 38% 25% 5% 1	950
	11th to 20th	Night	22% 11% 34% 26% 6%	950
	21st to end	Night	25% 17% 33% 22% 2	1045

Page generated at 2024-01-13 18:28:27. Version ac07

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