Chanhassen
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chanhassen clear sky chart from 2005-11-06 to 2025-07-21.

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%	120752
	Night	12% 9% 4 8% 5% 4 4 4 5% 6% 39%	118576
Transparency	Day	44% 6% 13% 24% 11% 1	124374
	Night	45% 5% 12% 24% 13% 2	123097
Seeing	Day	18% 13% 33% 24% 10% 2	17000
	Night	16% 12% 34% 29% 9% 1	26883

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% 13% 5% 19% 7% 6% 5% 3 4 6% 23%	3617
	11th to 20th	Day	6% 11% 7% 13% 7% 6% 9% 8% 8% 5% 21%	3694
	21st to end	Day	6% 16% 7% 13% 5% 4 4 3 4 5% 32%	4488
February	1st to 10th	Day	9% 11% 5% 10% 7% 6% 5% 5% 6% 6% 31%	1800
	11th to 20th	Day	9% 11% 5% 11% 6% 4 5% 4 5% 6% 34%	1754
	21st to end	Day	10% 12% 4 9% 6% 4 6% 4 5% 5% 34%	1535
March	1st to 10th	Day	13% 9% 3 6% 3 3 4 3 5% 8% 45%	4878
	11th to 20th	Day	10% 11% 3 7% 4 4 4 3 5% 8% 41%	4980
	21st to end	Day	22% 12% 4 10% 5% 5% 4 3 4 6% 26%	5498
April	1st to 10th	Day	17% 10% 3 7% 5% 4 3 3 5% 7% 36%	2400
	11th to 20th	Day	19% 13% 3 8% 5% 4 5% 3 4 6% 32%	2398
	21st to end	Day	22% 11% 2 8% 5% 5% 3 3 5% 5% 31%	2600
May	1st to 10th	Day	13% 6% 2 6% 3 3 4 3 4 6% 50%	6081
	11th to 20th	Day	18% 7% 2 5% 3 3 3 3 5% 7% 44%	6319
	21st to end	Day	18% 7% 3 7% 4 4 4 3 5% 7% 37%	6935
June	1st to 10th	Day	12% 5% 2 4 4 4 4 4 7% 8% 46%	2800
	11th to 20th	Day	14% 7% 3 6% 6% 5% 4 4 7% 9% 35%	2800
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 8% 40%	2949
July	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 5% 7% 10% 39%	4590
	11th to 20th	Day	6% 3 1 4 3 3 4 4 5% 8% 60%	4580
	21st to end	Day	6% 4 2 6% 4 5% 4 4 7% 10% 48%	4725
August	1st to 10th	Day	12% 5% 2 6% 5% 4 6% 5% 6% 7% 42%	4104
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 43%	4041
	21st to end	Day	10% 6% 3 7% 4 4 5% 3 5% 7% 48%	4348
September	1st to 10th	Day	11% 5% 2 5% 4 4 3 4 5% 7% 49%	2280
	11th to 20th	Day	12% 6% 2 5% 4 3 4 4 6% 8% 46%	2235
	21st to end	Day	15% 6% 2 6% 4 4 4 3 5% 7% 44%	2009
October	1st to 10th	Day	17% 6% 2 7% 4 3 4 4 4 6% 43%	1900
	11th to 20th	Day	15% 9% 3 6% 4 5% 4 3 5% 7% 41%	1900
	21st to end	Day	18% 10% 4 7% 4 3 3 3 3 6% 37%	2083
November	1st to 10th	Day	13% 12% 5% 7% 4 4 4 3 6% 6% 38%	1631
	11th to 20th	Day	11% 15% 6% 11% 7% 4 4 3 4 6% 30%	1600
	21st to end	Day	14% 11% 4 8% 5% 4 5% 3 5% 8% 34%	1600
December	1st to 10th	Day	7% 11% 4 13% 12% 6% 6% 4 5% 7% 25%	2610
	11th to 20th	Day	10% 18% 6% 10% 6% 5% 5% 4 4 6% 27%	3008
	21st to end	Day	21% 18% 9% 19% 4 3 3 3 3 4 14%	3982
January	1st to 10th	Night	7% 12% 6% 16% 8% 5% 4 3 5% 5% 28%	6348
	11th to 20th	Night	7% 11% 5% 13% 7% 7% 10% 7% 6% 5% 22%	6268
	21st to end	Night	7% 18% 6% 10% 5% 5% 4 3 5% 4 33%	6490
February	1st to 10th	Night	8% 12% 5% 10% 6% 6% 5% 3 5% 7% 34%	2600
	11th to 20th	Night	6% 10% 3 8% 6% 7% 5% 4 5% 6% 39%	2533
	21st to end	Night	11% 10% 3 8% 6% 4 5% 4 6% 5% 38%	2095
March	1st to 10th	Night	10% 7% 2 6% 4 4 4 3 5% 7% 47%	5017
	11th to 20th	Night	10% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	4980
	21st to end	Night	24% 12% 3 10% 4 3 3 3 4 5% 29%	5430
April	1st to 10th	Night	15% 10% 3 7% 3 4 4 4 5% 6% 38%	2000
	11th to 20th	Night	19% 10% 3 8% 4 4 4 2 4 6% 36%	1946
	21st to end	Night	19% 9% 2 7% 4 5% 4 3 5% 6% 36%	1800
May	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 5% 51%	3833
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 5% 6% 50%	3596
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 6% 40%	3942
June	1st to 10th	Night	11% 5% 2 4 4 4 4 4 6% 9% 49%	1600
	11th to 20th	Night	9% 6% 3 6% 4 4 6% 3 8% 8% 44%	1600
	21st to end	Night	8% 3 2 5% 3 3 4 3 7% 8% 53%	1432
July	1st to 10th	Night	11% 4 1 5% 4 4 4 5% 7% 9% 45%	2568
	11th to 20th	Night	3 3 1 4 3 3 4 3 6% 8% 60%	2610
	21st to end	Night	6% 4 2 4 3 4 4 3 5% 8% 57%	2836
August	1st to 10th	Night	12% 6% 3 5% 3 3 5% 4 5% 6% 49%	2836
	11th to 20th	Night	14% 5% 2 3 3 3 3 3 5% 7% 52%	2798
	21st to end	Night	10% 5% 3 6% 5% 3 4 4 5% 7% 49%	3311
September	1st to 10th	Night	9% 4 1 5% 4 3 4 3 4 8% 55%	1900
	11th to 20th	Night	9% 4 2 4 4 4 3 4 5% 8% 53%	1943
	21st to end	Night	13% 5% 2 5% 3 3 4 3 4 5% 53%	2152
October	1st to 10th	Night	13% 7% 2 5% 3 3 3 2 4 7% 50%	2280
	11th to 20th	Night	14% 10% 2 6% 4 4 4 3 5% 6% 43%	2280
	21st to end	Night	17% 11% 3 7% 4 3 3 3 6% 5% 37%	2513
November	1st to 10th	Night	14% 8% 3 6% 5% 4 4 3 5% 6% 42%	2664
	11th to 20th	Night	13% 12% 5% 11% 5% 4 4 3 4 5% 35%	2800
	21st to end	Night	13% 10% 4 10% 5% 4 4 3 4 6% 37%	2800
December	1st to 10th	Night	6% 9% 4 14% 7% 7% 5% 4 6% 6% 31%	4580
	11th to 20th	Night	10% 17% 6% 13% 7% 5% 5% 4 5% 5% 24%	5199
	21st to end	Night	22% 15% 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	62% 5% 11% 17% 5%	3618
	11th to 20th	Day	60% 5% 9% 16% 10%	3694
	21st to end	Day	55% 6% 16% 16% 7%	4488
February	1st to 10th	Day	52% 6% 15% 18% 8% 1	1800
	11th to 20th	Day	50% 6% 12% 24% 8% 1	1763
	21st to end	Day	50% 7% 13% 19% 11%	1535
March	1st to 10th	Day	38% 5% 18% 27% 11% 2	4878
	11th to 20th	Day	41% 5% 14% 28% 10% 1	4980
	21st to end	Day	60% 6% 10% 17% 7%	5500
April	1st to 10th	Day	48% 6% 12% 21% 12% 1	2400
	11th to 20th	Day	54% 5% 11% 18% 11% 2	2398
	21st to end	Day	54% 6% 11% 20% 8% 1	2600
May	1st to 10th	Day	34% 6% 13% 28% 17% 2	6119
	11th to 20th	Day	40% 6% 10% 23% 16% 5%	6323
	21st to end	Day	45% 6% 10% 29% 9% 1	6949
June	1st to 10th	Day	33% 7% 16% 30% 13% 2	2800
	11th to 20th	Day	43% 7% 14% 21% 14% 1	2800
	21st to end	Day	37% 10% 16% 25% 10% 2	2949
July	1st to 10th	Day	37% 9% 20% 23% 11% 1	4521
	11th to 20th	Day	23% 5% 17% 35% 18% 2	4505
	21st to end	Day	29% 9% 15% 30% 17% 1	4576
August	1st to 10th	Day	40% 7% 12% 28% 12% 2	4090
	11th to 20th	Day	37% 7% 13% 33% 9%	4080
	21st to end	Day	35% 6% 16% 28% 14% 1	4347
September	1st to 10th	Day	35% 7% 14% 31% 14%	2280
	11th to 20th	Day	34% 6% 17% 33% 9%	2235
	21st to end	Day	39% 6% 12% 31% 11% 1	2009
October	1st to 10th	Day	31% 3 9% 34% 23%	3160
	11th to 20th	Day	39% 4 11% 27% 17% 1	3140
	21st to end	Day	44% 3 14% 29% 9%	3409
November	1st to 10th	Day	45% 7% 14% 19% 13% 2	1631
	11th to 20th	Day	55% 5% 14% 17% 9% 1	1600
	21st to end	Day	49% 6% 17% 21% 7% 1	1600
December	1st to 10th	Day	58% 6% 16% 13% 5% 1	2610
	11th to 20th	Day	59% 5% 15% 16% 5%	3005
	21st to end	Day	75% 5% 9% 8% 4	3982
January	1st to 10th	Night	57% 5% 12% 20% 7%	6348
	11th to 20th	Night	61% 5% 10% 14% 10%	6268
	21st to end	Night	54% 5% 12% 23% 7%	6490
February	1st to 10th	Night	50% 5% 13% 20% 10% 1	2600
	11th to 20th	Night	45% 6% 14% 25% 9% 1	2534
	21st to end	Night	46% 6% 13% 21% 12% 1	2095
March	1st to 10th	Night	36% 5% 13% 28% 16% 2	5017
	11th to 20th	Night	38% 6% 14% 28% 13% 1	4980
	21st to end	Night	59% 4 9% 18% 9% 1	5430
April	1st to 10th	Night	46% 5% 10% 24% 13% 1	2000
	11th to 20th	Night	49% 5% 9% 19% 15% 2	1946
	21st to end	Night	48% 7% 9% 20% 14% 2	1800
May	1st to 10th	Night	33% 6% 11% 27% 21% 2	3860
	11th to 20th	Night	34% 6% 10% 22% 20% 8%	3597
	21st to end	Night	43% 7% 10% 27% 12% 1	3950
June	1st to 10th	Night	31% 6% 15% 28% 18% 2	1600
	11th to 20th	Night	35% 8% 15% 21% 18% 2	1600
	21st to end	Night	27% 7% 17% 30% 17% 3	1432
July	1st to 10th	Night	32% 7% 20% 25% 14% 1	2528
	11th to 20th	Night	21% 6% 14% 39% 18% 2	2562
	21st to end	Night	25% 7% 16% 31% 18% 3	2746
August	1st to 10th	Night	36% 6% 12% 28% 14% 4	2826
	11th to 20th	Night	32% 6% 14% 32% 16% 1	2825
	21st to end	Night	34% 6% 17% 27% 13% 2	3311
September	1st to 10th	Night	28% 7% 14% 32% 18% 1	1900
	11th to 20th	Night	28% 7% 16% 31% 17%	1943
	21st to end	Night	33% 5% 13% 30% 17% 1	2152
October	1st to 10th	Night	23% 3 7% 35% 28% 4	3800
	11th to 20th	Night	32% 5% 13% 25% 22% 4	3779
	21st to end	Night	43% 4 12% 28% 12% 1	4137
November	1st to 10th	Night	42% 6% 14% 23% 13% 2	2664
	11th to 20th	Night	52% 6% 12% 19% 11% 1	2800
	21st to end	Night	49% 5% 16% 22% 7% 1	2800
December	1st to 10th	Night	52% 6% 18% 19% 5%	4580
	11th to 20th	Night	61% 6% 11% 17% 4 1	5201
	21st to end	Night	71% 5% 9% 12% 3	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	15% 12% 33% 29% 10% 2	300
	11th to 20th	Day	19% 14% 37% 26% 3 1	300
	21st to end	Day	16% 15% 38% 20% 10% 2	330
February	1st to 10th	Day	17% 16% 44% 18% 4	300
	11th to 20th	Day	13% 23% 35% 23% 5% 1	300
	21st to end	Day	18% 17% 42% 21% 3	249
March	1st to 10th	Day	19% 15% 42% 17% 6%	300
	11th to 20th	Day	20% 15% 38% 20% 6% 1	300
	21st to end	Day	27% 19% 28% 18% 6% 2	341
April	1st to 10th	Day	25% 17% 34% 20% 5%	500
	11th to 20th	Day	31% 18% 24% 18% 8%	516
	21st to end	Day	28% 16% 30% 18% 7% 1	700
May	1st to 10th	Day	19% 17% 34% 22% 7% 1	703
	11th to 20th	Day	22% 14% 28% 22% 12% 2	725
	21st to end	Day	20% 11% 30% 26% 12% 2	789
June	1st to 10th	Day	11% 10% 31% 32% 14% 2	730
	11th to 20th	Day	18% 11% 39% 23% 8% 1	730
	21st to end	Day	14% 13% 34% 24% 13% 2	730
July	1st to 10th	Day	9% 5% 27% 34% 17% 7%	721
	11th to 20th	Day	10% 10% 31% 31% 15% 3	718
	21st to end	Day	6% 8% 31% 34% 18% 4	740
August	1st to 10th	Day	10% 6% 31% 31% 18% 3	676
	11th to 20th	Day	16% 6% 23% 30% 19% 5%	665
	21st to end	Day	11% 9% 31% 31% 15% 3	642
September	1st to 10th	Day	14% 12% 30% 27% 15% 2	490
	11th to 20th	Day	15% 9% 31% 28% 15% 2	445
	21st to end	Day	18% 17% 29% 20% 14% 2	300
October	1st to 10th	Day	20% 14% 29% 23% 11% 3	300
	11th to 20th	Day	18% 25% 36% 18% 3	300
	21st to end	Day	29% 18% 36% 11% 5%	330
November	1st to 10th	Day	23% 17% 37% 16% 6% 1	300
	11th to 20th	Day	20% 21% 40% 16% 3	300
	21st to end	Day	24% 18% 43% 12% 3	300
December	1st to 10th	Day	15% 17% 39% 22% 7%	300
	11th to 20th	Day	21% 21% 34% 21% 3	300
	21st to end	Day	32% 12% 36% 17% 3	330
January	1st to 10th	Night	11% 14% 39% 28% 7% 1	1000
	11th to 20th	Night	15% 15% 37% 27% 5% 1	1000
	21st to end	Night	18% 13% 38% 26% 5%	1100
February	1st to 10th	Night	15% 15% 39% 25% 6%	1000
	11th to 20th	Night	11% 15% 42% 25% 6% 1	979
	21st to end	Night	16% 15% 36% 25% 7% 1	775
March	1st to 10th	Night	16% 13% 37% 26% 7% 1	650
	11th to 20th	Night	18% 14% 37% 25% 6%	600
	21st to end	Night	23% 12% 30% 23% 10% 2	660
April	1st to 10th	Night	21% 15% 33% 26% 6%	600
	11th to 20th	Night	25% 12% 29% 26% 6% 1	593
	21st to end	Night	24% 11% 34% 23% 8% 1	600
May	1st to 10th	Night	20% 12% 32% 30% 5% 1	600
	11th to 20th	Night	17% 8% 37% 28% 10% 1	591
	21st to end	Night	16% 9% 28% 34% 12%	650
June	1st to 10th	Night	12% 7% 32% 40% 9%	600
	11th to 20th	Night	11% 6% 38% 38% 8%	600
	21st to end	Night	11% 6% 28% 40% 15% 1	600
July	1st to 10th	Night	6% 4 28% 36% 25% 1	585
	11th to 20th	Night	6% 6% 31% 40% 16% 1	582
	21st to end	Night	5% 4 31% 40% 19% 2	624
August	1st to 10th	Night	7% 5% 23% 45% 19% 1	567
	11th to 20th	Night	12% 5% 22% 38% 21% 3	564
	21st to end	Night	7% 6% 31% 34% 21% 1	627
September	1st to 10th	Night	10% 7% 27% 38% 14% 3	570
	11th to 20th	Night	12% 6% 36% 28% 15% 2	570
	21st to end	Night	13% 12% 33% 26% 15% 1	632
October	1st to 10th	Night	18% 12% 31% 26% 13%	760
	11th to 20th	Night	21% 14% 34% 23% 7% 1	760
	21st to end	Night	25% 14% 30% 26% 6%	836
November	1st to 10th	Night	19% 14% 34% 25% 7% 1	908
	11th to 20th	Night	19% 17% 35% 23% 6%	1000
	21st to end	Night	18% 18% 35% 24% 5%	1000
December	1st to 10th	Night	16% 12% 38% 27% 7% 1	1000
	11th to 20th	Night	20% 14% 36% 25% 5% 1	1000
	21st to end	Night	25% 13% 33% 24% 4	1100

Page generated at 2025-07-18 00:09:58. Version ac07

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