Minneapolis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Minneapolis 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% 9% 3 8% 5% 4 4 4 5% 7% 38%	126665
	Night	12% 10% 4 9% 5% 4 4 4 5% 6% 38%	122353
Transparency	Day	45% 3 13% 27% 11% 1	130229
	Night	46% 3 12% 25% 13% 1	126865
Seeing	Day	18% 13% 32% 24% 11% 2	17222
	Night	17% 12% 33% 28% 9% 1	27025

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	9% 14% 5% 20% 7% 6% 5% 2 5% 6% 22%	3617
	11th to 20th	Day	5% 11% 6% 14% 8% 6% 8% 9% 9% 4 19%	3648
	21st to end	Day	6% 16% 7% 12% 6% 5% 5% 3 5% 5% 30%	4488
February	1st to 10th	Day	9% 11% 6% 10% 7% 6% 6% 5% 5% 6% 29%	1800
	11th to 20th	Day	8% 12% 5% 10% 6% 5% 5% 4 6% 7% 33%	1754
	21st to end	Day	10% 12% 5% 10% 6% 5% 5% 4 6% 7% 31%	1545
March	1st to 10th	Day	12% 10% 3 6% 4 3 3 3 5% 8% 44%	4837
	11th to 20th	Day	9% 11% 3 8% 4 4 4 4 5% 8% 41%	4980
	21st to end	Day	22% 11% 4 10% 5% 4 5% 4 4 6% 26%	5525
April	1st to 10th	Day	16% 10% 3 8% 5% 4 4 3 5% 7% 35%	2400
	11th to 20th	Day	19% 11% 4 8% 4 5% 4 3 5% 5% 31%	2385
	21st to end	Day	21% 12% 4 6% 5% 4 4 4 5% 5% 31%	2600
May	1st to 10th	Day	14% 6% 2 5% 3 3 4 3 4 7% 49%	6127
	11th to 20th	Day	17% 8% 2 5% 3 3 4 3 5% 7% 43%	6319
	21st to end	Day	17% 8% 2 7% 4 4 4 4 5% 8% 38%	6935
June	1st to 10th	Day	11% 5% 2 5% 3 4 4 4 6% 8% 46%	2800
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 8% 8% 35%	2800
	21st to end	Day	12% 4 2 6% 5% 5% 6% 5% 7% 10% 38%	2800
July	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 44%	6360
	11th to 20th	Day	9% 3 1 4 3 3 3 3 5% 8% 57%	6360
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 7% 9% 46%	6844
August	1st to 10th	Day	12% 6% 2 6% 4 4 4 5% 6% 8% 43%	4234
	11th to 20th	Day	13% 5% 2 6% 3 4 5% 4 6% 9% 43%	4171
	21st to end	Day	10% 6% 2 6% 5% 5% 4 3 6% 7% 46%	4461
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 6% 8% 47%	2316
	11th to 20th	Day	13% 5% 1 4 4 4 4 4 7% 8% 45%	2252
	21st to end	Day	15% 6% 2 5% 4 4 4 4 5% 6% 44%	1998
October	1st to 10th	Day	17% 7% 3 6% 4 5% 3 4 4 6% 43%	1900
	11th to 20th	Day	15% 10% 3 7% 4 4 4 3 5% 7% 38%	1900
	21st to end	Day	17% 11% 3 7% 4 3 4 3 4 6% 37%	2066
November	1st to 10th	Day	13% 11% 4 8% 5% 4 4 4 5% 5% 37%	1643
	11th to 20th	Day	11% 14% 7% 12% 6% 4 4 3 5% 6% 28%	1600
	21st to end	Day	12% 13% 4 9% 5% 5% 3 4 5% 7% 33%	1600
December	1st to 10th	Day	7% 11% 4 15% 12% 7% 5% 4 5% 6% 23%	2610
	11th to 20th	Day	11% 17% 6% 11% 6% 5% 5% 3 4 5% 27%	3008
	21st to end	Day	20% 19% 9% 19% 4 4 3 2 3 4 13%	3982
January	1st to 10th	Night	7% 12% 5% 15% 8% 6% 4 3 5% 6% 29%	6348
	11th to 20th	Night	7% 11% 6% 13% 7% 7% 10% 9% 7% 5% 20%	6318
	21st to end	Night	8% 18% 6% 10% 6% 5% 4 3 5% 4 32%	6490
February	1st to 10th	Night	7% 12% 5% 10% 7% 6% 5% 3 4 6% 34%	2600
	11th to 20th	Night	6% 10% 3 9% 7% 6% 5% 4 5% 7% 38%	2533
	21st to end	Night	11% 11% 3 9% 6% 5% 4 3 5% 6% 37%	2085
March	1st to 10th	Night	9% 8% 3 7% 4 3 4 3 6% 7% 47%	5061
	11th to 20th	Night	9% 7% 3 7% 5% 5% 5% 4 7% 9% 39%	4980
	21st to end	Night	24% 12% 4 10% 4 3 3 3 4 4 28%	5404
April	1st to 10th	Night	15% 12% 3 6% 4 3 5% 3 6% 7% 37%	2000
	11th to 20th	Night	20% 11% 3 7% 4 4 3 3 5% 6% 34%	1961
	21st to end	Night	19% 10% 2 7% 4 4 4 4 4 6% 35%	1800
May	1st to 10th	Night	12% 7% 2 6% 4 3 4 3 5% 5% 51%	3787
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 4 7% 50%	3596
	21st to end	Night	16% 8% 3 6% 4 4 4 4 5% 7% 39%	3942
June	1st to 10th	Night	10% 6% 2 5% 4 3 4 3 6% 8% 49%	1600
	11th to 20th	Night	8% 7% 2 5% 5% 5% 5% 4 6% 8% 45%	1600
	21st to end	Night	8% 5% 2 5% 3 4 4 3 7% 9% 50%	1600
July	1st to 10th	Night	8% 4 2 4 4 4 5% 4 6% 9% 50%	3618
	11th to 20th	Night	6% 4 1 4 3 3 5% 4 6% 9% 54%	3617
	21st to end	Night	8% 5% 2 5% 5% 4 4 4 6% 8% 49%	4025
August	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 7% 47%	2926
	11th to 20th	Night	14% 4 1 4 3 3 4 4 5% 9% 50%	2888
	21st to end	Night	9% 6% 2 7% 4 4 4 4 5% 6% 48%	3439
September	1st to 10th	Night	8% 4 2 5% 4 3 5% 4 4 8% 53%	1930
	11th to 20th	Night	10% 5% 1 5% 3 3 4 3 6% 7% 53%	1924
	21st to end	Night	13% 6% 2 5% 3 3 3 3 5% 5% 52%	2161
October	1st to 10th	Night	14% 6% 2 6% 3 4 3 3 4 6% 49%	2280
	11th to 20th	Night	15% 11% 2 5% 4 4 4 4 5% 6% 41%	2280
	21st to end	Night	18% 11% 4 6% 3 4 4 3 5% 6% 38%	2532
November	1st to 10th	Night	14% 9% 3 6% 4 4 4 4 5% 6% 41%	2653
	11th to 20th	Night	13% 13% 5% 11% 5% 4 4 3 4 5% 33%	2800
	21st to end	Night	14% 11% 3 9% 6% 5% 4 3 4 6% 36%	2800
December	1st to 10th	Night	6% 9% 5% 14% 7% 8% 5% 4 6% 7% 29%	4580
	11th to 20th	Night	10% 17% 7% 14% 6% 5% 4 4 4 5% 24%	5199
	21st to end	Night	22% 16% 8% 15% 5% 4 3 3 3 4 17%	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	65% 2 9% 19% 5%	3618
	11th to 20th	Day	63% 2 8% 17% 9%	3648
	21st to end	Day	57% 3 16% 18% 7%	4488
February	1st to 10th	Day	54% 4 13% 20% 8% 1	1800
	11th to 20th	Day	51% 3 10% 27% 8% 1	1763
	21st to end	Day	52% 4 12% 21% 11%	1545
March	1st to 10th	Day	40% 1 18% 27% 11% 2	4837
	11th to 20th	Day	44% 2 14% 29% 10% 1	4980
	21st to end	Day	60% 2 10% 20% 7%	5527
April	1st to 10th	Day	49% 3 12% 22% 13% 1	2400
	11th to 20th	Day	55% 3 9% 19% 12% 1	2385
	21st to end	Day	55% 3 11% 22% 8% 1	2600
May	1st to 10th	Day	37% 2 10% 30% 18% 2	6165
	11th to 20th	Day	43% 2 9% 25% 16% 5%	6323
	21st to end	Day	47% 2 8% 32% 10% 1	6949
June	1st to 10th	Day	34% 4 15% 33% 13% 2	2800
	11th to 20th	Day	45% 5% 13% 23% 14% 1	2800
	21st to end	Day	39% 4 16% 29% 10% 2	2800
July	1st to 10th	Day	34% 6% 17% 33% 10%	6291
	11th to 20th	Day	27% 3 15% 39% 15% 1	6285
	21st to end	Day	33% 6% 14% 31% 16% 1	6649
August	1st to 10th	Day	39% 4 12% 29% 13% 2	4220
	11th to 20th	Day	37% 5% 13% 34% 11%	4210
	21st to end	Day	36% 4 16% 30% 13% 1	4460
September	1st to 10th	Day	35% 4 13% 34% 13%	2316
	11th to 20th	Day	37% 3 16% 35% 9%	2252
	21st to end	Day	40% 3 11% 35% 11% 1	1998
October	1st to 10th	Day	32% 1 8% 36% 23%	3160
	11th to 20th	Day	40% 3 10% 28% 17% 1	3140
	21st to end	Day	44% 2 14% 30% 9%	3380
November	1st to 10th	Day	49% 3 13% 20% 13% 2	1643
	11th to 20th	Day	57% 3 13% 17% 9% 1	1600
	21st to end	Day	51% 3 16% 22% 7% 1	1600
December	1st to 10th	Day	61% 4 17% 13% 5% 1	2610
	11th to 20th	Day	60% 2 15% 17% 5%	3005
	21st to end	Day	78% 2 7% 8% 4	3982
January	1st to 10th	Night	58% 2 11% 22% 7%	6348
	11th to 20th	Night	63% 2 11% 15% 10%	6318
	21st to end	Night	56% 3 11% 23% 7%	6490
February	1st to 10th	Night	53% 2 12% 22% 10% 1	2600
	11th to 20th	Night	46% 3 14% 27% 9% 1	2534
	21st to end	Night	49% 2 12% 23% 12% 1	2085
March	1st to 10th	Night	38% 2 13% 28% 16% 2	5061
	11th to 20th	Night	42% 1 13% 28% 15% 1	4980
	21st to end	Night	61% 2 9% 18% 9% 1	5404
April	1st to 10th	Night	48% 3 8% 26% 14% 1	2000
	11th to 20th	Night	52% 2 8% 21% 16% 2	1961
	21st to end	Night	51% 3 8% 23% 14% 2	1800
May	1st to 10th	Night	37% 2 9% 28% 21% 2	3814
	11th to 20th	Night	35% 3 10% 25% 20% 8%	3597
	21st to end	Night	46% 2 9% 29% 13% 1	3950
June	1st to 10th	Night	34% 3 12% 30% 19% 2	1600
	11th to 20th	Night	37% 4 15% 23% 18% 2	1600
	21st to end	Night	30% 2 16% 32% 17% 3	1600
July	1st to 10th	Night	30% 5% 19% 31% 14% 1	3580
	11th to 20th	Night	27% 4 14% 39% 15% 2	3572
	21st to end	Night	33% 6% 14% 29% 16% 2	3909
August	1st to 10th	Night	38% 3 11% 29% 14% 4	2916
	11th to 20th	Night	32% 4 15% 32% 16% 1	2915
	21st to end	Night	36% 5% 16% 29% 13% 2	3439
September	1st to 10th	Night	30% 4 12% 36% 18% 1	1930
	11th to 20th	Night	31% 3 16% 32% 17%	1924
	21st to end	Night	35% 2 12% 33% 17% 1	2161
October	1st to 10th	Night	25% 2 5% 36% 28% 4	3800
	11th to 20th	Night	35% 3 12% 25% 22% 3	3779
	21st to end	Night	45% 2 12% 29% 13%	4168
November	1st to 10th	Night	44% 3 12% 26% 13% 2	2653
	11th to 20th	Night	53% 3 12% 20% 11% 1	2800
	21st to end	Night	51% 3 15% 23% 7% 1	2800
December	1st to 10th	Night	54% 4 18% 19% 5%	4580
	11th to 20th	Night	64% 3 10% 17% 5% 1	5201
	21st to end	Night	73% 2 8% 13% 4	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	14% 13% 31% 27% 12% 3	300
	11th to 20th	Day	17% 15% 36% 27% 4 1	300
	21st to end	Day	16% 12% 40% 21% 9% 2	330
February	1st to 10th	Day	18% 16% 41% 21% 4	300
	11th to 20th	Day	14% 21% 34% 24% 5% 1	300
	21st to end	Day	19% 14% 40% 22% 4	249
March	1st to 10th	Day	16% 17% 40% 20% 6%	300
	11th to 20th	Day	22% 12% 37% 21% 6% 2	300
	21st to end	Day	26% 19% 26% 19% 7% 2	355
April	1st to 10th	Day	24% 17% 34% 20% 5%	500
	11th to 20th	Day	33% 15% 26% 17% 8%	503
	21st to end	Day	30% 16% 28% 18% 7% 1	700
May	1st to 10th	Day	21% 17% 32% 20% 8% 1	703
	11th to 20th	Day	23% 13% 28% 24% 11% 2	725
	21st to end	Day	19% 11% 30% 26% 12% 2	789
June	1st to 10th	Day	11% 10% 33% 30% 13% 2	730
	11th to 20th	Day	16% 15% 38% 23% 8% 1	730
	21st to end	Day	15% 12% 33% 24% 13% 2	730
July	1st to 10th	Day	9% 7% 26% 34% 17% 7%	721
	11th to 20th	Day	11% 10% 31% 30% 15% 4	718
	21st to end	Day	6% 10% 31% 32% 16% 4	794
August	1st to 10th	Day	10% 7% 29% 31% 18% 3	726
	11th to 20th	Day	16% 7% 24% 31% 19% 4	715
	21st to end	Day	12% 8% 29% 33% 15% 4	680
September	1st to 10th	Day	16% 11% 30% 26% 15% 2	502
	11th to 20th	Day	15% 8% 32% 28% 16% 2	462
	21st to end	Day	17% 17% 30% 21% 12% 2	300
October	1st to 10th	Day	22% 14% 29% 22% 11% 3	300
	11th to 20th	Day	20% 24% 38% 14% 4	300
	21st to end	Day	27% 18% 38% 11% 5%	330
November	1st to 10th	Day	22% 21% 34% 17% 6% 1	300
	11th to 20th	Day	21% 23% 37% 16% 3	300
	21st to end	Day	23% 20% 41% 12% 4	300
December	1st to 10th	Day	16% 17% 37% 23% 7% 1	300
	11th to 20th	Day	20% 20% 33% 23% 4	300
	21st to end	Day	29% 15% 34% 19% 3	330
January	1st to 10th	Night	13% 14% 37% 28% 7% 1	1000
	11th to 20th	Night	17% 14% 36% 27% 5% 1	1000
	21st to end	Night	19% 14% 35% 26% 6%	1100
February	1st to 10th	Night	16% 15% 38% 24% 6%	1000
	11th to 20th	Night	12% 17% 40% 24% 7% 1	979
	21st to end	Night	18% 14% 36% 24% 8%	765
March	1st to 10th	Night	17% 12% 36% 26% 8% 1	669
	11th to 20th	Night	19% 14% 35% 25% 6%	600
	21st to end	Night	24% 11% 30% 23% 11% 2	660
April	1st to 10th	Night	23% 14% 32% 26% 6%	600
	11th to 20th	Night	26% 12% 30% 25% 6% 1	593
	21st to end	Night	25% 12% 32% 23% 8% 1	600
May	1st to 10th	Night	20% 12% 32% 29% 6% 1	600
	11th to 20th	Night	17% 10% 36% 28% 9% 1	591
	21st to end	Night	16% 10% 28% 34% 12%	650
June	1st to 10th	Night	14% 6% 31% 39% 10%	600
	11th to 20th	Night	12% 7% 35% 39% 7%	600
	21st to end	Night	12% 7% 29% 37% 14% 1	600
July	1st to 10th	Night	6% 3 27% 38% 25% 1	585
	11th to 20th	Night	7% 7% 30% 40% 15% 1	582
	21st to end	Night	7% 4 31% 39% 18% 2	657
August	1st to 10th	Night	7% 6% 22% 44% 19% 1	597
	11th to 20th	Night	13% 5% 22% 36% 22% 3	594
	21st to end	Night	9% 5% 30% 34% 21% 1	660
September	1st to 10th	Night	9% 8% 28% 36% 17% 3	579
	11th to 20th	Night	11% 8% 36% 28% 15% 3	570
	21st to end	Night	15% 12% 31% 27% 14% 1	641
October	1st to 10th	Night	19% 11% 31% 26% 12% 1	760
	11th to 20th	Night	24% 11% 34% 23% 7% 1	760
	21st to end	Night	26% 13% 29% 25% 7%	836
November	1st to 10th	Night	20% 13% 33% 27% 6% 1	897
	11th to 20th	Night	21% 17% 32% 23% 7% 1	1000
	21st to end	Night	20% 18% 34% 22% 6%	1000
December	1st to 10th	Night	17% 13% 36% 27% 6% 1	1000
	11th to 20th	Night	20% 15% 34% 24% 5% 1	1000
	21st to end	Night	26% 14% 32% 23% 5%	1100

Page generated at 2025-09-01 00:51:02. Version ac07

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