Decorah
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Decorah clear sky chart from 2005-11-06 to 2025-11-18.

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 8% 5% 4 4 4 5% 7% 38%	127371
	Night	12% 9% 4 8% 5% 4 4 3 5% 6% 39%	123269
Transparency	Day	43% 6% 13% 24% 12% 1	130911
	Night	44% 6% 12% 23% 14% 2	127805
Seeing	Day	17% 12% 31% 25% 12% 4	17364
	Night	16% 10% 32% 30% 10% 1	27197

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	6% 11% 6% 21% 8% 7% 6% 3 4 6% 23%	3617
	11th to 20th	Day	7% 9% 7% 12% 7% 5% 7% 8% 9% 6% 23%	3620
	21st to end	Day	11% 14% 8% 11% 4 3 4 3 5% 6% 31%	4488
February	1st to 10th	Day	8% 13% 4 11% 6% 6% 4 5% 6% 7% 28%	1800
	11th to 20th	Day	12% 11% 4 8% 5% 5% 4 5% 6% 7% 33%	1754
	21st to end	Day	13% 10% 4 10% 5% 5% 4 2 5% 6% 35%	1645
March	1st to 10th	Day	15% 8% 3 5% 3 3 3 3 4 6% 49%	4662
	11th to 20th	Day	11% 7% 2 6% 4 4 4 4 5% 9% 44%	4980
	21st to end	Day	24% 12% 4 9% 4 4 4 3 4 5% 29%	5645
April	1st to 10th	Day	19% 13% 3 8% 5% 3 4 3 5% 7% 31%	2400
	11th to 20th	Day	18% 12% 4 7% 4 5% 4 3 5% 6% 31%	2374
	21st to end	Day	22% 10% 3 7% 5% 5% 4 4 5% 6% 31%	2463
May	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 5% 6% 42%	6179
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 5% 7% 43%	6319
	21st to end	Day	18% 6% 2 6% 4 4 5% 4 5% 7% 38%	6935
June	1st to 10th	Day	11% 5% 3 6% 4 4 4 4 6% 8% 45%	2800
	11th to 20th	Day	13% 6% 2 7% 5% 4 5% 4 6% 8% 40%	2800
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 6% 9% 38%	2800
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 5% 7% 10% 40%	6360
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 49%	6360
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 39%	6892
August	1st to 10th	Day	9% 6% 2 7% 5% 6% 5% 5% 7% 8% 41%	4234
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 9% 43%	4150
	21st to end	Day	8% 6% 2 5% 4 4 4 4 7% 8% 47%	4312
September	1st to 10th	Day	13% 5% 3 5% 3 3 4 4 5% 7% 47%	2400
	11th to 20th	Day	12% 5% 2 7% 4 4 5% 3 6% 7% 46%	2400
	21st to end	Day	13% 7% 2 5% 4 4 4 3 5% 8% 44%	2110
October	1st to 10th	Day	15% 7% 1 5% 3 4 4 3 5% 6% 47%	2000
	11th to 20th	Day	17% 9% 3 7% 4 4 3 3 4 7% 39%	2000
	21st to end	Day	16% 12% 3 6% 4 4 3 3 4 6% 40%	2136
November	1st to 10th	Day	11% 8% 3 7% 4 5% 4 4 6% 7% 42%	1852
	11th to 20th	Day	13% 11% 5% 10% 6% 4 5% 3 5% 6% 33%	1684
	21st to end	Day	12% 13% 4 7% 5% 3 4 3 5% 7% 37%	1600
December	1st to 10th	Day	8% 9% 4 11% 7% 6% 6% 4 5% 6% 35%	2610
	11th to 20th	Day	14% 14% 5% 14% 8% 5% 4 4 5% 6% 21%	3008
	21st to end	Day	19% 21% 10% 15% 4 3 3 2 3 4 15%	3982
January	1st to 10th	Night	7% 10% 6% 18% 8% 6% 4 3 5% 5% 27%	6348
	11th to 20th	Night	8% 14% 5% 13% 7% 5% 6% 7% 9% 6% 21%	6343
	21st to end	Night	11% 13% 6% 10% 5% 5% 4 4 5% 5% 31%	6490
February	1st to 10th	Night	9% 11% 5% 11% 7% 6% 5% 4 5% 6% 32%	2600
	11th to 20th	Night	9% 11% 4 8% 6% 5% 4 4 5% 7% 38%	2533
	21st to end	Night	14% 9% 3 8% 6% 4 5% 3 5% 5% 37%	1985
March	1st to 10th	Night	14% 8% 4 7% 4 3 3 3 4 5% 45%	5235
	11th to 20th	Night	9% 8% 3 7% 3 4 4 4 6% 7% 46%	4980
	21st to end	Night	24% 12% 4 10% 4 4 3 3 4 4 28%	5284
April	1st to 10th	Night	15% 12% 3 6% 5% 3 3 3 4 6% 39%	2000
	11th to 20th	Night	18% 10% 2 5% 5% 4 4 4 5% 6% 37%	1975
	21st to end	Night	19% 9% 2 7% 5% 3 4 4 5% 6% 37%	1934
May	1st to 10th	Night	16% 7% 2 5% 4 3 3 3 5% 6% 46%	3734
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 7% 49%	3596
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 7% 41%	3942
June	1st to 10th	Night	9% 5% 3 6% 4 4 4 4 7% 7% 47%	1600
	11th to 20th	Night	10% 5% 2 8% 5% 4 4 5% 6% 9% 42%	1600
	21st to end	Night	11% 5% 2 6% 4 3 4 3 5% 7% 51%	1600
July	1st to 10th	Night	9% 5% 2 5% 3 4 4 4 6% 9% 47%	3618
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 6% 9% 52%	3617
	21st to end	Night	7% 4 2 6% 4 4 5% 4 7% 9% 49%	3962
August	1st to 10th	Night	10% 4 2 5% 4 4 5% 4 6% 7% 50%	2926
	11th to 20th	Night	11% 5% 2 4 4 3 3 3 4 7% 53%	2906
	21st to end	Night	9% 5% 2 5% 4 3 4 3 5% 7% 52%	3586
September	1st to 10th	Night	10% 5% 1 6% 4 3 3 4 4 5% 56%	2000
	11th to 20th	Night	11% 5% 2 5% 3 4 3 3 4 6% 54%	2000
	21st to end	Night	10% 6% 1 5% 3 3 3 2 5% 6% 56%	2264
October	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 5% 7% 52%	2400
	11th to 20th	Night	16% 7% 2 5% 4 4 3 3 5% 6% 45%	2400
	21st to end	Night	16% 9% 3 7% 4 4 3 3 5% 6% 40%	2702
November	1st to 10th	Night	12% 9% 3 6% 4 3 3 3 5% 6% 47%	2666
	11th to 20th	Night	12% 12% 5% 9% 5% 3 4 3 4 5% 37%	2868
	21st to end	Night	14% 11% 3 8% 5% 4 3 3 5% 6% 37%	2800
December	1st to 10th	Night	7% 8% 3 10% 6% 7% 5% 4 6% 8% 37%	4580
	11th to 20th	Night	14% 15% 6% 12% 5% 5% 5% 3 5% 6% 26%	5199
	21st to end	Night	19% 18% 8% 16% 5% 4 4 3 4 4 16%	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	64% 5% 10% 15% 5%	3618
	11th to 20th	Day	54% 6% 11% 11% 17%	3620
	21st to end	Day	55% 5% 14% 16% 10%	4488
February	1st to 10th	Day	52% 7% 14% 17% 10% 1	1800
	11th to 20th	Day	48% 7% 12% 23% 9% 1	1763
	21st to end	Day	49% 6% 13% 20% 9% 2	1645
March	1st to 10th	Day	38% 4 14% 27% 13% 4	4662
	11th to 20th	Day	34% 6% 14% 32% 12% 1	4980
	21st to end	Day	58% 6% 12% 16% 8% 1	5647
April	1st to 10th	Day	52% 6% 13% 19% 9% 1	2400
	11th to 20th	Day	52% 6% 11% 19% 10% 1	2374
	21st to end	Day	52% 7% 12% 16% 11% 1	2463
May	1st to 10th	Day	40% 6% 10% 24% 19%	6218
	11th to 20th	Day	39% 7% 13% 27% 13% 2	6323
	21st to end	Day	43% 7% 11% 27% 11% 1	6949
June	1st to 10th	Day	34% 9% 14% 28% 14% 1	2800
	11th to 20th	Day	40% 8% 13% 22% 16% 1	2800
	21st to end	Day	41% 8% 15% 22% 13% 2	2800
July	1st to 10th	Day	36% 8% 16% 31% 8% 1	6291
	11th to 20th	Day	32% 7% 14% 31% 16% 1	6285
	21st to end	Day	39% 8% 15% 22% 15% 1	6696
August	1st to 10th	Day	39% 7% 13% 26% 13% 2	4220
	11th to 20th	Day	37% 7% 13% 29% 12% 1	4189
	21st to end	Day	33% 7% 15% 29% 16% 1	4311
September	1st to 10th	Day	35% 6% 14% 27% 17% 1	2400
	11th to 20th	Day	36% 7% 15% 29% 12%	2400
	21st to end	Day	38% 7% 11% 28% 14% 1	2110
October	1st to 10th	Day	25% 4 7% 41% 23% 1	3260
	11th to 20th	Day	34% 4 11% 28% 20% 3	3240
	21st to end	Day	41% 3 11% 30% 13% 1	3426
November	1st to 10th	Day	40% 6% 14% 24% 14% 2	1852
	11th to 20th	Day	52% 5% 12% 20% 10% 1	1684
	21st to end	Day	48% 4 17% 22% 8% 1	1600
December	1st to 10th	Day	49% 7% 15% 22% 7% 1	2610
	11th to 20th	Day	63% 6% 13% 11% 6% 1	3005
	21st to end	Day	74% 4 8% 11% 3	3982
January	1st to 10th	Night	58% 6% 11% 17% 7%	6348
	11th to 20th	Night	57% 5% 12% 12% 13%	6343
	21st to end	Night	52% 5% 13% 18% 11% 1	6490
February	1st to 10th	Night	52% 6% 12% 17% 12% 1	2600
	11th to 20th	Night	45% 6% 13% 23% 12% 2	2534
	21st to end	Night	47% 7% 11% 20% 13% 2	1985
March	1st to 10th	Night	41% 5% 10% 27% 14% 4	5235
	11th to 20th	Night	35% 5% 12% 29% 17% 2	4980
	21st to end	Night	60% 5% 11% 14% 10% 1	5284
April	1st to 10th	Night	46% 5% 11% 21% 15% 2	2000
	11th to 20th	Night	46% 7% 11% 20% 14% 3	1975
	21st to end	Night	46% 7% 10% 22% 13% 2	1934
May	1st to 10th	Night	38% 6% 10% 22% 23% 1	3760
	11th to 20th	Night	33% 7% 12% 23% 17% 6%	3597
	21st to end	Night	41% 8% 10% 29% 12% 1	3950
June	1st to 10th	Night	33% 9% 14% 26% 17% 2	1600
	11th to 20th	Night	36% 8% 12% 21% 20% 2	1600
	21st to end	Night	33% 7% 16% 25% 16% 4	1600
July	1st to 10th	Night	32% 7% 17% 30% 14% 1	3580
	11th to 20th	Night	28% 7% 15% 34% 15% 1	3572
	21st to end	Night	30% 8% 19% 23% 18% 1	3847
August	1st to 10th	Night	33% 6% 13% 29% 17% 1	2916
	11th to 20th	Night	31% 6% 15% 32% 15% 1	2933
	21st to end	Night	32% 6% 14% 27% 18% 3	3586
September	1st to 10th	Night	30% 7% 10% 30% 22% 1	2000
	11th to 20th	Night	32% 5% 14% 32% 16% 1	2000
	21st to end	Night	30% 6% 10% 31% 22% 2	2264
October	1st to 10th	Night	24% 4 7% 34% 29% 2	3920
	11th to 20th	Night	29% 4 12% 24% 26% 4	3899
	21st to end	Night	44% 4 10% 24% 16% 1	4362
November	1st to 10th	Night	38% 5% 14% 24% 17% 2	2666
	11th to 20th	Night	49% 5% 11% 21% 11% 2	2868
	21st to end	Night	48% 4 14% 25% 8% 1	2800
December	1st to 10th	Night	44% 5% 20% 23% 7% 1	4580
	11th to 20th	Night	59% 6% 13% 16% 6% 1	5201
	21st to end	Night	72% 5% 8% 10% 5%	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% 17% 38% 21% 7% 2	300
	11th to 20th	Day	20% 17% 39% 20% 4 1	300
	21st to end	Day	18% 18% 40% 18% 5% 1	330
February	1st to 10th	Day	16% 21% 42% 17% 2 1	300
	11th to 20th	Day	20% 25% 34% 17% 3 1	300
	21st to end	Day	20% 19% 41% 16% 3	249
March	1st to 10th	Day	15% 20% 43% 15% 6% 1	300
	11th to 20th	Day	24% 17% 35% 17% 7% 1	300
	21st to end	Day	28% 18% 30% 17% 6% 1	410
April	1st to 10th	Day	27% 15% 37% 16% 5%	500
	11th to 20th	Day	24% 20% 27% 20% 9%	492
	21st to end	Day	26% 15% 30% 20% 6% 2	563
May	1st to 10th	Day	21% 12% 31% 26% 8% 1	703
	11th to 20th	Day	21% 14% 26% 24% 12% 3	725
	21st to end	Day	19% 11% 29% 24% 14% 4	789
June	1st to 10th	Day	12% 8% 29% 31% 16% 3	730
	11th to 20th	Day	16% 10% 32% 28% 12% 2	730
	21st to end	Day	15% 8% 32% 28% 12% 5%	730
July	1st to 10th	Day	9% 5% 21% 33% 22% 11%	721
	11th to 20th	Day	8% 5% 29% 31% 21% 6%	718
	21st to end	Day	7% 4 27% 37% 19% 7%	794
August	1st to 10th	Day	7% 3 23% 36% 21% 9%	726
	11th to 20th	Day	13% 6% 21% 31% 20% 9%	707
	21st to end	Day	9% 7% 26% 31% 20% 7%	583
September	1st to 10th	Day	14% 8% 25% 28% 19% 6%	530
	11th to 20th	Day	10% 6% 26% 33% 20% 5%	530
	21st to end	Day	16% 13% 27% 24% 15% 4	400
October	1st to 10th	Day	17% 9% 32% 26% 13% 2	330
	11th to 20th	Day	22% 22% 32% 18% 6%	330
	21st to end	Day	22% 16% 37% 17% 6% 2	363
November	1st to 10th	Day	17% 16% 38% 21% 5% 2	330
	11th to 20th	Day	19% 22% 34% 17% 7% 1	321
	21st to end	Day	22% 16% 40% 18% 5%	300
December	1st to 10th	Day	13% 18% 40% 21% 8%	300
	11th to 20th	Day	22% 12% 40% 19% 7%	300
	21st to end	Day	29% 12% 40% 15% 2 1	330
January	1st to 10th	Night	13% 14% 40% 26% 6% 1	1000
	11th to 20th	Night	17% 15% 37% 26% 5% 1	1000
	21st to end	Night	20% 13% 36% 26% 5%	1100
February	1st to 10th	Night	16% 15% 37% 26% 6%	1000
	11th to 20th	Night	15% 16% 40% 22% 5% 1	979
	21st to end	Night	19% 14% 38% 24% 5%	665
March	1st to 10th	Night	19% 13% 38% 25% 5% 1	740
	11th to 20th	Night	17% 13% 36% 26% 7% 1	600
	21st to end	Night	24% 11% 33% 25% 6% 1	660
April	1st to 10th	Night	21% 14% 36% 26% 3	600
	11th to 20th	Night	22% 14% 32% 26% 5% 1	593
	21st to end	Night	21% 8% 36% 27% 7% 1	600
May	1st to 10th	Night	20% 9% 32% 32% 7% 1	600
	11th to 20th	Night	18% 9% 31% 31% 10% 1	591
	21st to end	Night	17% 6% 27% 37% 12% 1	650
June	1st to 10th	Night	11% 6% 28% 42% 12% 1	600
	11th to 20th	Night	12% 6% 30% 41% 11%	600
	21st to end	Night	13% 4 28% 41% 14% 1	600
July	1st to 10th	Night	7% 2 19% 43% 27% 3	585
	11th to 20th	Night	7% 2 23% 41% 24% 3	582
	21st to end	Night	7% 2 19% 48% 21% 3	657
August	1st to 10th	Night	6% 2 19% 48% 24% 2	597
	11th to 20th	Night	10% 3 17% 40% 25% 5%	594
	21st to end	Night	9% 3 21% 41% 24% 2	660
September	1st to 10th	Night	11% 5% 25% 36% 20% 4	600
	11th to 20th	Night	12% 3 25% 36% 22% 3	600
	21st to end	Night	11% 8% 26% 37% 17% 1	739
October	1st to 10th	Night	14% 7% 30% 32% 15% 1	800
	11th to 20th	Night	20% 12% 34% 27% 8%	800
	21st to end	Night	21% 11% 32% 30% 6%	880
November	1st to 10th	Night	15% 13% 38% 26% 7% 1	820
	11th to 20th	Night	18% 16% 39% 21% 6%	1005
	21st to end	Night	19% 15% 37% 22% 7%	1000
December	1st to 10th	Night	17% 13% 40% 24% 5% 1	1000
	11th to 20th	Night	20% 13% 38% 23% 6%	1000
	21st to end	Night	25% 15% 33% 22% 4	1100

Page generated at 2025-11-14 23:56:00. Version ac07

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