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 2024-03-28.

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% 4 7% 6% 3 5% 5% 5% 7% 36%	78718
	Night	12% 10% 4 7% 6% 3 5% 5% 5% 6% 38%	81327
Transparency	Day	48% 3 13% 25% 10% 1	78420
	Night	48% 3 12% 24% 12% 1	81145
Seeing	Day	17% 13% 32% 25% 11% 2	15062
	Night	17% 11% 33% 28% 10% 1	25179

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% 15% 7% 16% 8% 4 4 3 5% 5% 20%	2527
	11th to 20th	Day	6% 11% 6% 13% 11% 6% 8% 9% 6% 5% 20%	2544
	21st to end	Day	8% 20% 8% 11% 7% 3 5% 4 5% 6% 23%	3135
February	1st to 10th	Day	9% 10% 7% 9% 8% 5% 6% 6% 6% 6% 30%	1710
	11th to 20th	Day	8% 10% 6% 9% 7% 4 5% 5% 5% 7% 33%	1664
	21st to end	Day	11% 11% 5% 9% 7% 3 5% 5% 5% 7% 30%	1470
March	1st to 10th	Day	13% 13% 5% 8% 6% 3 4 4 5% 8% 32%	2042
	11th to 20th	Day	13% 9% 4 7% 6% 3 4 5% 4 7% 37%	2090
	21st to end	Day	21% 11% 4 6% 5% 3 4 5% 4 6% 30%	2277
April	1st to 10th	Day	16% 9% 4 7% 6% 3 5% 4 4 7% 35%	2160
	11th to 20th	Day	20% 10% 4 6% 5% 4 4 5% 5% 6% 32%	2143
	21st to end	Day	21% 11% 4 5% 5% 3 5% 5% 5% 5% 31%	2340
May	1st to 10th	Day	17% 8% 3 6% 6% 3 5% 5% 5% 8% 34%	2437
	11th to 20th	Day	17% 9% 3 5% 5% 3 4 4 5% 8% 38%	2479
	21st to end	Day	15% 6% 3 6% 6% 4 5% 5% 5% 8% 37%	2725
June	1st to 10th	Day	12% 5% 2 4 4 3 4 5% 6% 9% 46%	2520
	11th to 20th	Day	12% 6% 3 6% 6% 4 5% 5% 7% 9% 38%	2520
	21st to end	Day	10% 4 2 5% 5% 4 6% 6% 7% 11% 40%	2520
July	1st to 10th	Day	7% 4 1 4 5% 3 6% 5% 7% 10% 48%	2520
	11th to 20th	Day	9% 3 2 5% 4 2 5% 5% 5% 9% 51%	2520
	21st to end	Day	6% 3 2 5% 5% 3 6% 6% 7% 10% 47%	2717
August	1st to 10th	Day	9% 5% 3 6% 6% 3 6% 7% 7% 8% 40%	2328
	11th to 20th	Day	14% 6% 1 5% 4 3 4 5% 5% 7% 45%	2301
	21st to end	Day	9% 5% 2 4 5% 3 3 5% 6% 7% 52%	2464
September	1st to 10th	Day	12% 5% 2 4 5% 3 5% 4 6% 8% 46%	2160
	11th to 20th	Day	13% 5% 2 3 5% 3 5% 5% 6% 8% 45%	2134
	21st to end	Day	16% 6% 2 5% 5% 3 5% 4 5% 7% 42%	1893
October	1st to 10th	Day	18% 7% 3 6% 5% 4 3 4 4 6% 41%	1800
	11th to 20th	Day	16% 9% 3 6% 5% 3 4 4 5% 7% 38%	1800
	21st to end	Day	18% 11% 4 7% 5% 2 4 4 4 6% 36%	1958
November	1st to 10th	Day	12% 10% 5% 8% 5% 3 4 5% 5% 5% 38%	1559
	11th to 20th	Day	12% 12% 8% 11% 8% 3 5% 4 4 6% 28%	1520
	21st to end	Day	13% 11% 4 7% 6% 3 4 4 6% 7% 34%	1520
December	1st to 10th	Day	11% 12% 5% 11% 9% 4 6% 4 4 6% 26%	1520
	11th to 20th	Day	11% 13% 7% 10% 9% 4 4 5% 4 6% 28%	1918
	21st to end	Day	22% 15% 8% 15% 6% 3 3 3 3 4 17%	2783
January	1st to 10th	Night	10% 15% 8% 13% 7% 4 4 4 4 4 27%	4428
	11th to 20th	Night	7% 10% 7% 12% 9% 5% 9% 9% 6% 5% 21%	4412
	21st to end	Night	10% 21% 8% 11% 5% 3 4 4 3 4 26%	4532
February	1st to 10th	Night	7% 11% 6% 9% 8% 4 6% 4 4 6% 35%	2470
	11th to 20th	Night	7% 9% 4 7% 8% 4 6% 4 5% 7% 39%	2403
	21st to end	Night	12% 10% 4 7% 7% 4 5% 4 5% 6% 37%	1984
March	1st to 10th	Night	12% 11% 4 7% 6% 3 4 4 5% 6% 38%	2156
	11th to 20th	Night	13% 10% 4 7% 5% 3 5% 4 5% 6% 39%	2090
	21st to end	Night	19% 10% 4 7% 5% 3 3 5% 4 6% 35%	2233
April	1st to 10th	Night	15% 11% 3 6% 4 2 5% 4 6% 7% 37%	1800
	11th to 20th	Night	21% 10% 4 7% 5% 3 3 4 4 6% 33%	1763
	21st to end	Night	19% 9% 3 7% 5% 3 4 5% 4 6% 35%	1620
May	1st to 10th	Night	18% 7% 3 6% 5% 2 4 5% 5% 6% 40%	1522
	11th to 20th	Night	15% 5% 2 5% 5% 3 5% 5% 5% 8% 43%	1416
	21st to end	Night	12% 5% 3 5% 5% 4 6% 6% 5% 7% 42%	1551
June	1st to 10th	Night	10% 5% 2 4 5% 2 4 4 6% 8% 49%	1440
	11th to 20th	Night	8% 6% 2 4 6% 3 5% 6% 6% 8% 47%	1440
	21st to end	Night	7% 4 2 5% 4 3 5% 4 6% 9% 52%	1440
July	1st to 10th	Night	3 4 3 3 4 2 4 5% 6% 10% 56%	1440
	11th to 20th	Night	6% 3 1 4 4 3 4 5% 7% 10% 54%	1440
	21st to end	Night	5% 3 1 3 4 2 4 5% 6% 9% 58%	1599
August	1st to 10th	Night	6% 3 2 5% 6% 3 5% 5% 6% 8% 50%	1611
	11th to 20th	Night	12% 3 1 3 3 2 4 5% 5% 8% 52%	1600
	21st to end	Night	7% 4 2 5% 4 2 4 5% 5% 5% 57%	1890
September	1st to 10th	Night	9% 4 2 4 5% 3 5% 5% 4 8% 52%	1800
	11th to 20th	Night	10% 4 1 4 4 3 4 4 6% 7% 53%	1822
	21st to end	Night	14% 5% 2 4 4 3 3 4 5% 6% 50%	2047
October	1st to 10th	Night	15% 6% 3 6% 3 3 4 4 4 6% 47%	2160
	11th to 20th	Night	16% 10% 3 4 4 3 4 5% 5% 6% 40%	2160
	21st to end	Night	18% 10% 4 5% 4 3 4 3 4 6% 38%	2398
November	1st to 10th	Night	14% 9% 3 6% 5% 3 4 5% 4 6% 42%	2517
	11th to 20th	Night	13% 12% 5% 11% 6% 3 5% 4 4 5% 33%	2660
	21st to end	Night	14% 9% 3 7% 7% 4 5% 4 4 6% 37%	2660
December	1st to 10th	Night	10% 11% 5% 10% 9% 3 5% 4 5% 7% 31%	2660
	11th to 20th	Night	11% 14% 6% 10% 8% 4 4 5% 5% 6% 27%	3279
	21st to end	Night	22% 14% 6% 10% 6% 3 4 4 4 4 22%	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	67% 2 11% 16% 4	2528
	11th to 20th	Day	66% 2 10% 17% 5%	2544
	21st to end	Day	62% 3 13% 17% 4	3135
February	1st to 10th	Day	53% 4 13% 21% 8% 1	1710
	11th to 20th	Day	51% 4 11% 26% 8% 1	1673
	21st to end	Day	53% 4 11% 21% 11%	1470
March	1st to 10th	Day	53% 2 15% 22% 8% 1	2042
	11th to 20th	Day	48% 3 15% 26% 8% 1	2090
	21st to end	Day	56% 3 11% 23% 7% 1	2277
April	1st to 10th	Day	49% 3 12% 22% 12% 1	2160
	11th to 20th	Day	55% 2 9% 20% 12% 2	2143
	21st to end	Day	56% 3 11% 22% 8% 1	2340
May	1st to 10th	Day	49% 4 11% 24% 10% 2	2437
	11th to 20th	Day	46% 3 12% 26% 12% 1	2483
	21st to end	Day	47% 4 11% 25% 12% 1	2725
June	1st to 10th	Day	35% 4 15% 33% 12% 2	2520
	11th to 20th	Day	42% 4 13% 24% 15% 1	2520
	21st to end	Day	37% 4 17% 30% 10% 2	2520
July	1st to 10th	Day	32% 4 16% 33% 14% 1	2451
	11th to 20th	Day	32% 4 14% 29% 18% 3	2445
	21st to end	Day	31% 5% 15% 31% 17% 2	2566
August	1st to 10th	Day	39% 4 14% 30% 10% 3	2314
	11th to 20th	Day	37% 4 15% 32% 11% 1	2301
	21st to end	Day	31% 3 14% 33% 18% 1	2464
September	1st to 10th	Day	37% 4 13% 32% 14%	2160
	11th to 20th	Day	37% 3 16% 35% 8%	2134
	21st to end	Day	42% 3 11% 35% 9%	1893
October	1st to 10th	Day	44% 2 11% 30% 12% 1	1800
	11th to 20th	Day	46% 3 12% 26% 12% 1	1800
	21st to end	Day	51% 2 12% 24% 10%	1958
November	1st to 10th	Day	48% 3 13% 20% 13% 2	1559
	11th to 20th	Day	58% 3 13% 17% 9%	1520
	21st to end	Day	50% 3 17% 22% 7% 1	1520
December	1st to 10th	Day	60% 4 16% 15% 5%	1520
	11th to 20th	Day	59% 2 19% 16% 4	1915
	21st to end	Day	73% 2 8% 11% 5%	2783
January	1st to 10th	Night	62% 2 11% 19% 6%	4428
	11th to 20th	Night	63% 2 12% 16% 6%	4412
	21st to end	Night	64% 2 9% 19% 5% 1	4532
February	1st to 10th	Night	52% 3 11% 23% 10% 1	2470
	11th to 20th	Night	46% 3 14% 27% 9% 1	2404
	21st to end	Night	49% 2 11% 24% 12% 1	1984
March	1st to 10th	Night	48% 3 15% 24% 10%	2156
	11th to 20th	Night	48% 2 11% 24% 14% 1	2090
	21st to end	Night	52% 3 10% 25% 9% 1	2233
April	1st to 10th	Night	48% 3 9% 25% 14% 1	1800
	11th to 20th	Night	53% 2 8% 20% 15% 3	1763
	21st to end	Night	50% 3 8% 23% 14% 2	1620
May	1st to 10th	Night	45% 3 13% 22% 16% 1	1522
	11th to 20th	Night	40% 5% 13% 25% 15% 3	1417
	21st to end	Night	43% 3 11% 23% 17% 2	1552
June	1st to 10th	Night	34% 2 13% 30% 19% 1	1440
	11th to 20th	Night	35% 5% 15% 24% 18% 3	1440
	21st to end	Night	29% 2 16% 33% 16% 3	1440
July	1st to 10th	Night	24% 3 14% 37% 20% 2	1400
	11th to 20th	Night	26% 4 14% 34% 18% 4	1392
	21st to end	Night	22% 4 15% 35% 18% 5%	1510
August	1st to 10th	Night	31% 3 14% 32% 15% 4	1601
	11th to 20th	Night	30% 4 17% 30% 17% 2	1600
	21st to end	Night	29% 3 14% 32% 19% 3	1890
September	1st to 10th	Night	31% 4 11% 36% 18% 1	1800
	11th to 20th	Night	31% 3 16% 32% 17%	1822
	21st to end	Night	37% 2 13% 32% 15% 1	2047
October	1st to 10th	Night	39% 2 8% 32% 16% 2	2160
	11th to 20th	Night	46% 2 12% 24% 14% 2	2160
	21st to end	Night	49% 2 12% 24% 12% 1	2398
November	1st to 10th	Night	44% 3 12% 26% 14% 2	2517
	11th to 20th	Night	53% 3 12% 20% 11% 1	2660
	21st to end	Night	50% 3 16% 24% 7% 1	2660
December	1st to 10th	Night	53% 3 15% 22% 6%	2660
	11th to 20th	Night	58% 3 13% 18% 6% 2	3281
	21st to end	Night	68% 1 10% 16% 4	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	15% 12% 30% 28% 11% 3	270
	11th to 20th	Day	16% 15% 36% 27% 4 1	270
	21st to end	Day	17% 10% 41% 20% 10% 2	297
February	1st to 10th	Day	17% 15% 42% 20% 5%	270
	11th to 20th	Day	15% 22% 33% 23% 6% 1	270
	21st to end	Day	20% 15% 39% 23% 4	225
March	1st to 10th	Day	16% 19% 39% 19% 7%	270
	11th to 20th	Day	20% 12% 36% 23% 7% 2	270
	21st to end	Day	29% 19% 24% 18% 8% 2	307
April	1st to 10th	Day	23% 16% 35% 21% 5%	420
	11th to 20th	Day	32% 12% 26% 20% 10%	421
	21st to end	Day	29% 15% 27% 20% 8% 2	600
May	1st to 10th	Day	22% 17% 33% 20% 7% 1	603
	11th to 20th	Day	23% 13% 28% 23% 11% 3	625
	21st to end	Day	18% 10% 29% 27% 13% 3	679
June	1st to 10th	Day	10% 9% 33% 32% 14% 2	630
	11th to 20th	Day	13% 14% 38% 25% 8% 1	630
	21st to end	Day	12% 12% 33% 25% 15% 3	630
July	1st to 10th	Day	8% 7% 26% 35% 19% 6%	621
	11th to 20th	Day	10% 10% 31% 31% 14% 4	618
	21st to end	Day	6% 11% 30% 32% 16% 5%	684
August	1st to 10th	Day	9% 7% 29% 32% 19% 3	626
	11th to 20th	Day	16% 7% 22% 31% 19% 5%	615
	21st to end	Day	11% 8% 29% 33% 15% 4	583
September	1st to 10th	Day	16% 11% 29% 27% 15% 2	450
	11th to 20th	Day	15% 8% 32% 28% 16% 2	424
	21st to end	Day	19% 17% 31% 20% 10% 2	270
October	1st to 10th	Day	23% 12% 30% 20% 12% 3	270
	11th to 20th	Day	19% 25% 36% 15% 4	270
	21st to end	Day	28% 18% 37% 11% 5%	297
November	1st to 10th	Day	20% 21% 34% 17% 6% 1	270
	11th to 20th	Day	19% 23% 38% 17% 3	270
	21st to end	Day	23% 18% 42% 12% 4	270
December	1st to 10th	Day	16% 17% 35% 24% 7% 1	270
	11th to 20th	Day	20% 19% 32% 24% 4	270
	21st to end	Day	30% 14% 34% 19% 2	297
January	1st to 10th	Night	13% 14% 37% 28% 7% 1	950
	11th to 20th	Night	17% 14% 35% 27% 5% 1	950
	21st to end	Night	19% 14% 34% 26% 6%	1045
February	1st to 10th	Night	15% 15% 38% 25% 7%	950
	11th to 20th	Night	12% 16% 40% 24% 7% 1	929
	21st to end	Night	19% 13% 35% 25% 8%	728
March	1st to 10th	Night	17% 12% 35% 26% 9% 1	636
	11th to 20th	Night	19% 13% 36% 26% 7%	570
	21st to end	Night	24% 11% 29% 23% 11% 2	615
April	1st to 10th	Night	22% 13% 33% 26% 6%	540
	11th to 20th	Night	27% 11% 29% 26% 7% 1	533
	21st to end	Night	24% 11% 32% 23% 9% 1	540
May	1st to 10th	Night	21% 12% 32% 29% 5% 1	540
	11th to 20th	Night	18% 9% 36% 27% 10% 1	531
	21st to end	Night	16% 10% 27% 34% 13%	584
June	1st to 10th	Night	13% 4 32% 40% 11%	540
	11th to 20th	Night	11% 6% 36% 39% 7%	540
	21st to end	Night	10% 6% 27% 40% 16% 1	540
July	1st to 10th	Night	5% 3 27% 37% 26% 1	525
	11th to 20th	Night	7% 7% 30% 41% 15% 1	522
	21st to end	Night	6% 4 31% 40% 18% 2	591
August	1st to 10th	Night	6% 5% 22% 45% 20% 1	537
	11th to 20th	Night	13% 5% 22% 34% 23% 3	534
	21st to end	Night	9% 4 31% 32% 22% 2	594
September	1st to 10th	Night	10% 8% 28% 36% 16% 3	540
	11th to 20th	Night	11% 8% 35% 28% 15% 3	540
	21st to end	Night	16% 12% 32% 26% 13% 1	607
October	1st to 10th	Night	19% 11% 31% 26% 13% 1	720
	11th to 20th	Night	25% 10% 33% 23% 7% 1	720
	21st to end	Night	26% 13% 28% 26% 7%	792
November	1st to 10th	Night	20% 13% 33% 27% 6% 1	851
	11th to 20th	Night	20% 17% 32% 23% 7% 1	950
	21st to end	Night	20% 17% 34% 22% 7%	950
December	1st to 10th	Night	17% 13% 35% 27% 6% 1	950
	11th to 20th	Night	20% 14% 35% 25% 5% 1	950
	21st to end	Night	26% 14% 33% 22% 4	1045

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